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## Abstract

This paper reviews recent achievements in the technology and design of fluxgate sensors and magnetometers. The major recent trends were decreasing of the sensor size, power consumption and price, and, on the other hand, increasing of the precision in the large range of the measured fields. The potential frequency range was increased up to units of kHz. Present fluxgate sensors have a resolution comparable with high-temperature superconducting quantum interference devices (SQUIDs), while their precision is the best of vectorial field sensors.

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... For the magnetic anomaly to be detected, the objects forming this anomaly must be made of ferromagnetic materials and positioned perpendicular to the earth's magnetic field. However, today's sensors can detect objects in different positions [31]. In the presence of magnetic material, the decrease in flux density in the area where the sensor is located causes an electrical charge in the sensor and changes the output voltage. ...
... Analog fluxgate magnetometer[31] ...
Article
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Buried mines pose great dangers to humans and animals around the world, which means thousands of people die each year fromburied mines. Detecting and destroying these mines without harming people is an important issue. Today, these landmines aredetected using different methods such as Ground Effect Radar, Electromagnetic induction, Infrared and Nuclear QuadrupoleResonance and active sensors are generally used in most of these methods. Although active sensor-based landmine detectors areoften used for performance reasons, they can cause unintentional landmine explosions because they operate with transmitted andreflected signals. On the other hand, there is no such obstacle that can perform better in passive sensor-based landmine detectorsdepending on the design criteria. Therefore, in this study, a prototype design including passive sensor with magnetic anomalymethod has been developed and shown. For the performance analysis of this detector, real landmines are used and the designedsystem is tested with different distance values in different soil types. The results show that the prototype produced successfullydetects different types of landmines, is assertive in its lightness and only 1750 grams with its battery, providing sensitivity as wellas advantages such as ease of use and low cost. It also shows the feature of being the first handheld landmine detector based onmagnetic anomaly.
... For the magnetic anomaly to be detected, the objects forming this anomaly must be made of ferromagnetic materials and positioned perpendicular to the earth's magnetic field. However, today's sensors can detect objects in different positions [31]. In the presence of magnetic material, the decrease in flux density in the area where the sensor is located causes an electrical charge in the sensor and changes the output voltage. ...
... Analog fluxgate magnetometer[31] ...
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Gömülü mayınlar, dünyanın her yerindeki insanlar ve hayvanlar için büyük tehlikeler oluşturuyor, bu da her yıl binlerce insanın gömülü mayınlardan ölmesi anlamına geliyor. Bu mayınların insanlara zarar vermeden tespit edilip imha edilmesi önemli bir konudur. Günümüzde bu kara mayınları Yer Etkili Radar, Elektromanyetik indüksiyon, Kızılötesi ve Nükleer Dört Kutuplu Rezonans gibi farklı yöntemlerle tespit edilmekte ve bu yöntemlerin çoğunda genellikle aktif sensörler kullanılmaktadır. Aktif sensör tabanlı kara mayını dedektörleri genellikle performans nedenleriyle kullanılsa da, iletilen ve yansıyan sinyallerle çalıştıkları için kasıtsız kara mayını patlamalarına neden olabilirler. Öte yandan, tasarım kriterlerine bağlı olarak pasif sensör tabanlı kara mayını dedektörlerinde daha iyi performans gösterebilecek böyle bir engel yoktur. Bu nedenle bu çalışmada manyetik anomali yöntemi ile pasif sensör içeren bir prototip tasarımı geliştirilmiş ve gösterilmiştir. Bu dedektörün performans analizi için gerçek mayınlar kullanılmış ve tasarlanan sistem farklı toprak tiplerinde farklı mesafe değerleri ile test edilmiştir. Elde edilen sonuçlar, üretilen prototipin farklı tipteki mayınları başarıyla tespit ettiğini, hafifliğiyle iddialı olduğunu ve piliyle sadece 1750 gramlık hassasiyet sağladığını, kullanım kolaylığı ve düşük maliyet gibi avantajların yanında hassasiyet sağladığını gösteriyor. Ayrıca manyetik anomaliye dayalı ilk el mayın dedektörü olma özelliğini de göstermektedir.
... Higher accuracy demands a higher CT ratio and therefore higher costs [4,5]. As a result, digital CTs are a new alternative for researchers and industries [6][7][8][9][10]. In modern smart grids, compact and noninvasive current measurement sensors have proven to be beneficial for operation and cost efficiency. ...
... Recently, digital sensors that are based on advanced electronics such as Rogowski coils, Hall sensors, and digital fiber CTs have been researched in order to determine their application in current measurement processes [6][7][8][9][10][11][12]. These sensors are a good replacement for conventional CTs, but they cannot be applied to a wide frequency range or higher magnitude AC currents. ...
Article
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A large increase in distributed generation integrated within power system networks has resulted in power quality challenges and in the need to resolve complex system faults. The monitoring of the real-time state of the power parameters of the transmission and distribution grid helps to control the stability and reliability of the grid. In such a scenario, having current monitoring equipment that is flexible and easy to install can always be of great help to reduce the price of energy monitoring and to increase the dependability of a smart grid. Advances in magnetic sensor research offer measurement system accuracy that is less complex to install and that can be obtained at a lower less cost. Tunneling magnetoresistive (TMR) sensors can be used to measure the AC current by sensing the magnetic field that is generated by the current-carrying conductor in a contactless manner. This paper illustrates the results of a thorough investigation of factors that can influence the performance of the TMR sensors that are used for the current phasor measurements of a single-phase AC current application, such as the effects of distance, harmonics, and conductor insulation.
... Magnetic field sensors have attracted increasing interests due to its plenty of applications in navigation, vehicle, current detections, and information storage [1]. Various solutions including anisotropic magnetoresistive sensors [2], fluxgate magnetometer [3], superconducting quantum interference device (SQUID) magnetometers [4] and optically pumped magnetometers [5], have been proposed to implement the magnetic measurement. Although the SQUID magnetometer has demonstrated the highest magnetic field sensitivity at the 17 10 − T level, the detectors must be operated at strict laboratory conditions, such as cryogenic temperature environment, perfect conducting (zero resistance) material, limiting it practical application. ...
... The low temperature sensitivity measured by the wavelength drift difference of 0.389 pm/℃ is obtained shown in Fig. 13, illustrating a potential way to implement the temperature-independent magnetic field sensing. By analyzing the slopes of the wavelengths of the two FBGs and wavelength drift difference, the change of magnetic field can be calculated by (3). The change of temperature also can be obtained simultaneously by (4). ...
Article
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A magnetic field sensor with temperature insensitivity implemented by two fiber Bragg gratings (FBGs) structure is presented and experimentally demonstrated. In the proposed sensing probe, a Terfenol-D piece is bonded with the same type of two FBGs in different direction relative to magnetic field. Two center wavelengths of the notches of FBG filters are mainly determined by the magnetic field, and the two FBGs experience different magnetic-field-induced strain and the same thermal expansion, leading to the linear relationship between the wavelength drift difference and the magnetic field and temperature insensitivity. By monitoring the shift of the wavelength drift difference, the magnetic field measurement for thermal-insensitive interrogation of the magnetic field sensor can be realized. Owing to its compact and temperature independent advantages, the proposed sensor has potential application especially in the unstable direction of magnetic field. Moreover, the sensor can also serve the purpose of temperature measurement by monitoring one of the center wavelengths. The measured sensitivity of the magnetic field intensity of the proposed sensor is 8.77 pm/mT.
... One of the first sensors exploiting the nonlinear saturation between the magnetic field strength and the flux density was the fluxgate magnetometer invented by Friedrich Förster in 1937 [8]. The saturation effect allows to measure magnetic fields very precisely. ...
... The calibration factor can be determined by a sample with a known magnetic moment. For a uniformly magnetized sample, we finally obtain the magnetic flux density within a sample of volume (8) The field strength is measured by a small hall sensor placed between the pickup coils. Figure 7 shows the highly anisotropic behavior of the Sensorvac material. ...
... The frequency divider stage is a voltage-to-current converter stage that produces a weak analog output current, which is insufficient to drive the magnetic core to saturation directly. Hence, the need for current amplification by use of complementary emitter-follower [15]. Following the work of Karthik [16], a low-noise class-AB power amplifier is employed in this study using NPN and PNP transistors Q1 and Q2, respectively, as complementary emitter-follower, as shown in Figure 4. Resistor 4 and diode 1 biased the NPN transistor 1 while 2 and 3 biased the transistor ...
Article
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The importance of magnetic sensors in their use to explain some of the complex phenomena relating to geomagnetic storms and solar-terrestrial systems, most of them still have problems of sensitivity, noise level and linearity due to the magnetic material used in designing them. This study developed a ferrite-based, highly sensitive Fluxgate Sensor (FS) for earth's magnetic field explorations using Manganese Zinc (MnZn) ferrite alloy ring core material. The characteristic of the fluxgate sensor was modeled using a trans-impedance operational amplifier and high-quality band-pass filter using multiple feedback band-pass filter MFB-BPF. The result shows that with an optimum core diameter of 12.82mm and excitation current of 25mA, the core was saturated at an excitation frequency of 2kHz with the maximum magnetic field of ±49.44μT (i.e. 4.34V towards the North Pole with corresponding field 49.44μT(49,440nT) and 0.187V towards South Pole with the corresponding field-49.44μT(-49,440nT)) and sensitivity of 87.78mV/μT was realized. The developed FS has reduced sensor dimension, less power consumption, enhanced sensitivity, less noise level and lower fabrication cost, thus meeting the earth's magnetic field studies requirements.
... They are also used by some airport security systems to identify firearms. [10,11]. ...
Article
In an Intelligent Transportation System (ITS), vehicle identification and categorization (VIC) from a moving platform is critical (ITS). VIC is input into traffic control and management systems. Due to a variety of circumstances such as different types of cars, vehicles with nearly identical qualities having unique classes, and so on, in congested traffic, vehicle identification and classification is still a challenge. When compared to different sensors, the magnetic sensor has great implementation potential in the vehicle detection sector Because of its high sensitivities and lightweight. This paper aims to discuss how the magnetic characteristics of Vehicles can be used to detect and classify vehicles. First, a brief operating principle and properties of the most commonly used magnetic sensors are reviewed. This paper also reviewed the most recent applications, implementations, and research in using the magnetic sensor to detect and identify vehicles, as well as classify and determine Vehicle speeds.
... If we transform Faraday's law of induction into an equation for the fluxgate circuit, the electrical signal generated in a measuring coil with a ferromagnetic core in a changing magnetic field is represented by the equation (Ripka, 2003). ...
Conference Paper
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Bu çalışmada, düşük termal genleşme katsayısına sahip, uzay, havacılık, elektronik ve yüksek sıcaklık uygulamalarında tercih edilen silindirik Invar (FeNi36) alaşımının WEDM ile kesilmesi çalışılmıştır. Çinko bakımından zengin pirinç kaplı bakır tel elektrot kullanılarak kesilen Invar36 alaşımının yüzeyinde, termal işlemeden kaynaklı ergimiş iş parçası ve elektrot kalıntılarından meydana gelen yeniden döküm tabakası olarak adlandırılan beyaz tabaka (white layer) oluşmuştur. Genellikle oluşan beyaz tabakalar giderilerek iş parçaları nihai kullanıma sunulur. Bu durumu simüle etmek için WEDM ile kesilen yüzeydeki beyaz tabaka 800’lük zımpara ile giderilmiş ve ortalama yüzey pürüzlülüğü (Ra), 3.12µm değerinden 0.32µm değerine düşerek % 89.74 iyileşme sağlanmıştır. WEDM ile işlenen yüzeylerin zımparalama öncesi ve sonrası SEM görüntüleri ve EDX analizleri yapılarak, zımparalama öncesi işlenmiş yüzeylerde O, Fe, Ni, Cu ve Zn gibi oksit, iş parçası ve elektrot kalıntılarının olduğu, zımparalama sonrası white layer tabakasının işlenmiş yüzeyden giderilmesiyle Cu, Zn gibi elektrot kalıntılarının temizlendiği tespit edilmiştir. WEDM ile işlenen yüzeyin sertlik dağılımı ve işlemsiz numuneyle sertlik karşılaştırması yapılabilmesi için numunelerden 50, 200, 500 ve 1000 gram ağırlık kullanılarak vikers yöntemiyle sertlik değerleri ölçülmüştür. WEDM ile işlenen yüzeyin kenar kısmının sertlik değerleri işlemsiz numuneden yüksek çıkarken orta kısımların ise işlemsiz numuneye göre daha az sertliğe sahip olduğu tespit edilmiştir. WEDM işleminde kullanılan dielektrik sıvısın kenar kesmelerde, kesme sürecinde yüzeyde oluşan ısıyı kısa sürede ortamdan uzaklaştırması sonrası, yüzeyde sertlik artışı olurken iş parçasının orta kısımları kesilirken ilgili sıvının ortama ulaşması ve oradaki ısıyı uzaklaştırması zaman aldığından dolayı orta kısımların yüzeyinde sertlik değerlerinin ana malzemenin sertlik değerlerinden daha düşük değerlere düştüğü görülmüştür.
... (3) The decrease in iron core volume leads to a sharp decline in the performance of the micro-fluxgate, (4) particularly a significant increase in noise. (5) At present, the noise level of a micro-fluxgate is greater than that of a traditional fluxgate. ...
... Sensors for measuring weak magnetic fields must have detectivities in the range of pT to a few mT and detect the vector fields simultaneously to be suitable for navigation applications. Fluxgate sensors are one of the most common sensor technologies owing to their outstanding advantages of high sensitivity, low noise, and non-offset (Ripka, 2003). If sensor size is not considered, fluxgate sensors can be constructed using standard technologies such as cutting machines and wire wrapping that help reduce costs and increase reliability. ...
Article
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An anti-serial fluxgate sensor configuration is proposed in this report. The design comprises two identical bilayer-rod fluxgate sensors connected anti-serially in a straight line. Each bilayer-rod sensor is constructed of an excitation coil and a pick-up coil wrapped around a core. The core material consists of Metglas ribbon, an amorphous alloy with high permeability, negligible hysteresis, and a high saturated magnetic field. The core is cut into a bar shape and uses double layers to enhance modulated flux density. A high sensitivity of 10 mV/Oe (with excitation of 45 kHz and 250 mA) is obtained experimentally with low noise of 1´10-5 Oe/Ö Hz at 1 Hz. In measurements of weak magnetic fields, the azimuth response indicates its vector feature. The proposed design is suitable for electronic compass and displacement applications.
... Traditional magnetic field sensors are usually of the electrical signal type (Ripka 2003;Hauser et al. 2000), but such sensors as large and inability to be miniaturized. Although optical sensors based on ferrofluid are more challenging to fill and package, these sensors have outstanding advantages such as small size, corrosion resistance, no mechanical wear and tear, high immunity to electromagnetic interference. ...
Article
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With the broader use of ferrofluid in industry and the sciences, ferrofluid research has produced many new branches. To obtain systematic analytical results and to help researchers gain insight into the dynamics of ferrofluid research, in this review, we first track and summarize the ferrofluid research over the past 15 years to assay how ferrofluid can contribute to modern technology. We have got several important research directions (basic physics research, medical applications, and engineering applications) using keywords as an entry point by visualizing the cluster analysis. Visualization to highlight important schools and organizations. By analyzing the number of papers and citations at a given institution, we obtained a list of influential institutions and schools and indicated the current research directions of these institutions. This list greatly helps researchers to understand the authoritative papers as well as the latest results. In particular, we draw connections between publication year and novel engineering applications and show how they impact future development—the increasing use of ferrofluids in microfluidic environments and the increasing study of their soft and reshapable properties. Next, we focus on ferrofluid applications in six engineering fields and summarize the development history and research status. Finally, by analyzing the current status of each application, we summarize two challenges, that is to strengthen the research on the micromechanism of ferrofluid and to prepare a ferrofluid with better performance. The originality of this study is that it uses visualization to describe the current state of research and development patterns instead of thousands of papers, providing valuable reference information for existing researchers and practitioners.
... In recent years, magnetic materials have been adopted in different fields of science and technology, such as information storage (8), catalysis (9), magnetic imaging (10), drug delivery (11), separation (12), anti-corrosion (13), and so on (14). In addition, abundant fabrication and research is carried out by scientists on the different types of magnetic sensors including fluxgate-sensors (15), Hall-effect magnetic sensing devices (16), magneto-optical (17), giant magneto-resistive (GMR) modules (18), resonance magnetometers (19), and superconducting quantum interference device (SQUID) gradiometers (20). ...
Article
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Parasitic helminths, despite their known negative impact (biomaterial) on human health and animal production, have fascinating features. In this study, we find fantastic magnetic properties in several forms: inductor [between 20.10 and 58.85 (±2.50) H], source of detectable electrical voltage [from +0.5 to 7.3 (±0.1) V, vs. the ground, GND, measured by an AVO meter] and different inductor magnitude [between 3.33 and 41.23 (±0.76)] μH, detected by electrochemical impedance spectroscopy as well as frequency scannable electromagnetic wave horn) in several frequencies (including 100, 120, Hz, and 1, 10, 100 kHz) in “Fasciola hepatica”, “ Parascaris equorum ” (with and without larvae), “ Dicrocoelium dendriticum,” “ Taenia multiceps ”, and “ Moniezia expansa” eggs. This claim is attributed to some surprising characteristics, including superior inductance and intrinsic magnetic susceptibility. This feature along with a close relationship to helminth egg structure, is a novel probe with acceptable reproducibility (RSD > 8.0%) and high enough trustworthiness for adequate differentiation in their magnitudes, relatively. These traits were measured by the “ Single Cell Rrecording ” methodology using a three-microelectrode system, implanted to each egg at the Giga ohm sealed condition (6.08 ± 0.22 GΩ cm ⁻¹ , n = 5). The reliability of these results was further confirmed using multiple calibrated instruments such as a high-resolution inductance analyzer, LCR meter, impedance spectrometer, potentiometer, and an anomalous Hall effect (Magnetic field density) sensor. In addition, the critical role played (Synergistic Effect) by water-like molecules as the intermediate medium, besides the partial influence of other compounds such as dissolved oxygen, are investigated qualitatively, and specific relation between these molecules and magnetic field creation in helminth eggs was proved. These intrinsic characteristics would provide novel facilitators for efficient arriving at the researchable bio-based magnetic biomaterials, besides innovative and real-time identification probes in the “ Parasitology” fields.
... A broad selection of magnetic sensors exploiting different physical principles have been developed, which differ in sensitivity, measurement range, cost, etc. Magnetic sensors based on the Hall and magnetoresistance effect are the most widespread, together with the so-called Fluxgate Sensors (FS), which are exceeded only by SQUIDs in terms of resolution. Their high sensitivity, high accuracy, temperature stability, and robustness [1][2][3][4][5] make them one of the best candidate to be applied in many fields such as astrophysics and satellite attitude control [6][7][8][9], geophysics [10], electronic compasses [11][12][13], current sensors [14,15], nondestructive testing [16,17], bio-medical diagnostics [18,19], etc. In recent years, particular efforts have been spent in miniaturizing and integrating FSs in digital chip-sets, paying particular attention at minimizing the power consumption, with the aim of developing light, portable, and flexible devices. ...
Article
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Miniaturization and on-chip integration are major lines of research in many branches of science and technology developments, undoubtedly in sensor technology. Fluxgate magnetometers are very sensitive, and accurate magnetic sensors able to detect weak fields both AC and DC, which in recent years saw a great effort in minimizing their dimensions, weight, and power consumption. The physics behind the fluxgate principle is rather complex and makes simulations difficult and only partially used in the literature. The limited physical access to micro sensors for measurements and the need to optimize the entire integrated system, including the sensor geometry and the excitation and readout circuits, make numerical analyses particularly useful in the design of miniaturized sensors. After a thorough review of the miniaturized solutions proposed so far, the present paper examines in detail the possibility of adopting a model based approach for designing miniaturized fluxgate sensors. The model of the fluxgate effect of two different technologies proposed in the literature has been implemented to benchmark simulation results with real data. In addition to the advantages for an optimized design, the implementation and computational challenges of the numerical analyses are precisely outlined.
... To achieve these goals of flexible siting, convenience in monitoring and intensive deployment, the traditional fluxgate sensor needs to be improved. Current developments in fluxgate sensors are directed toward miniaturization, low power consumption, low cost and improved accuracy over a large measurement range [17][18][19][20]. Three main types of microfluxgate magnetic sensor are available: (1) CMOS-based devices with flat coils, (2) sensors with thin-film or microfabricated solenoids and (3) PCB-based devices with solenoids made from tracks and vias [21,22]. ...
Article
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Traditional fluxgate sensors used in geomagnetic field observations are large, costly, power-consuming and often limited in their use. Although the size of the micro-fluxgate sensors has been significantly reduced, their performance, including indicators such as accuracy and signal-to-noise, does not meet observational requirements. To address these problems, a new race-track type probe is designed based on a magnetic core made of a Co-based amorphous ribbon. The size of this single-component probe is only Φ10 mm × 30 mm. The signal processing circuit is also optimized. The whole size of the sensor integrated with probes and data acquisition module is Φ70 mm × 100 mm. Compared with traditional fluxgate and micro-fluxgate sensors, the designed sensor is compact and provides excellent performance equal to traditional fluxgate sensors with good linearity and RMS noise of less than 0.1 nT. From operational tests, the results are in good agreement with those from a standard fluxgate magnetometer. Being more suitable for modern dense deployment of geomagnetic observations, this small-size fluxgate sensor offers promising research applications at lower costs.
... Newer developments on FGMs are discussed by new developments of fluxgate sensors to e.g. Ripka (1992), Ripka (2003), and Grosz et al. (2017). ...
... Currently, the LOD of SAW magnetic field sensors is most comparable with magnetoresistive sensors with values around 100 pT/ √ Hz at 10 Hz [31,32]. However, giant magnetoimpedance [33] and fluxgate sensors [34], for example, still achieve significantly better low-frequency values around or even below 10 pT/ √ Hz. Apart from the fact that even values on measured limits of detection are rarely given, no detailed results on the noise behavior of magnetoelastic SAW delay line sensors have been reported so far. ...
Article
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Surface acoustic wave (SAW) sensors for the detection of magnetic fields are currently being studied scientifically in many ways, especially since both their sensitivity as well as their detectivity could be significantly improved by the utilization of shear horizontal surface acoustic waves, i.e., Love waves, instead of Rayleigh waves. By now, low-frequency limits of detection (LOD) below 100 pT/sqrt(Hz) can be achieved. However, the LOD can only be further improved by gaining a deep understanding of the existing sensor-intrinsic noise sources and their impact on the sensor’s overall performance. This paper reports on a comprehensive study of the inherent noise of SAW delay line magnetic field sensors. In addition to the noise, however, the sensitivity is of importance, since both quantities are equally important for the LOD. Following the necessary explanations of the electrical and magnetic sensor properties, a further focus is on the losses within the sensor, since these are closely linked to the noise. The considered parameters are in particular the ambient magnetic bias field and the input power of the sensor. Depending on the sensor’s operating point, various noise mechanisms contribute to f^(0) white phase noise, f^(−1) flicker phase noise, and f^(−2) random walk of phase. Flicker phase noise due to magnetic hysteresis losses, i.e. random fluctuations of the magnetization, is usually dominant under typical operating conditions. Noise characteristics are related to the overall magnetic and magnetic domain behavior. Both calculations and measurements show that the LOD cannot be further improved by increasing the sensitivity. Instead, the losses occurring in the magnetic material need to be decreased.
... [51,[57][58][59] The fluxgate magnetometers used to measure weak magnetic fields around 0.1 nT -100 µT. [51,[60][61][62] Superconducting quantum magnetometer utilizing the Josephson effect to measure ultralow magnetic fields around 1 fT -1 nT. [51,59] An induction coil sensor is used to measure AC fields in the range of 10 fT -1mT. ...
Article
BiFeO3-CoFe2O4 (BFO-CFO) vertically aligned nanocomposite (VAN) thin-film promises great potentials for next-generation electronic devices. Its strong magnetoelectric, antiferromagnetic-ferrimagnetic, and structural couplings occur via large interface area interactions across the vertical surface between BFO and CFO phases; this leads to emergent exotic fundamental physics rendering its potential applications for various electronics, such as magnetic sensor, data storages or memory devices, and energy harvesting devices. The distinctive photoactivity of both BFO and CFO phases in the BFO-CFO VAN system also can generate advanced applications as photovoltaic and photocatalytic devices. Furthermore, owing to small overpotential and excellent stability in alkaline media, BFO-CFO nanocomposites becomes the next electrode in electrocatalysis devices. The BFO-CFO VAN also have been exponentially developed having various type of thin-film architectures grown on various substrates. In this present article, we review the current status of the BFO-CFO VAN thin-film and discuss the fundamental understanding as well as the technology involved in developing this material. We also address the challenges that hinder the commercialization of this material and propose some plausible solutions to encourage BFO-CFO VAN-based electronic devices to reach their maturity level. Furthermore, the potential marketability of the BFO-CFO VAN materials and devices for future consumer products is also discussed.
... The alternative changes in the external magnetic field are detected by the sense coil. Usually, the results of these changes are recorded in the form of voltage-output, but some of the fluxgate sensors operate in current-output mode [15,20]. ...
Chapter
Due to their superparamagnetism property as well as the high surface-to-volume ratios, magnetic nanomaterials (MNMs) have been utilized as both sorbents and sensors in analytical chemistry. Different aspects of the application of MNMs in analytical chemistry have widely been reviewed. However, the application of MNMs in the magnetic field sensors has been less investigated. Magnetic field sensors can be generally divided into two categories: magnetoresistive sensors and nonmagnetoresistive sensors. Magnetoresistive sensors rely on the dependence of material resistance to its magnetization state. The nonmagnetoresistive sensors can be utilized under high magnetic fields without being bothered by magnetic saturation. This chapter provides an overview of the application of MNMs in magnetic field sensors along with fundamental principles.
... The core often made of permalloy with high permeability and low coercivity. The excitation coil generates an alternating excitation magnetic field and the induction coil senses an induced voltage in relation to the measured magnetic field according to Faraday's law of electromagnetic induction [6]. Fluxgate sensor structure of dual core as shown in figure 1. ...
Article
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The fluxgate sensor uses the nonlinear characteristics of soft magnetic materials to measure the geostationary magnetic field, which has the characteristics of high sensitivity, wide magnetic measurement range and easy portability, and is widely used in geological exploration, navigation, space technology and other fields. In this paper, the research is based on the second harmonic method of the development of fluxgate sensor, since the second harmonic contains static magnetic field direction and amplitude information, so the second harmonic signal to noise ratio enhancement can effectively improve the resolution of the fluxgate sensor. In this paper, the induction signal is first resonated to the second harmonic frequency using a resonant circuit, and then filtered after an amplification circuit, the second harmonic signal-to-noise ratio is significantly enhanced by 13 times.
Article
We report on the magnetic and structural characterization of Co75.4Fe2.3Mn2.3Nb4Si2B14 (nominal) nanocomposite thin films and compositional derivatives formed by the co-sputtering of additional cobalt and boron followed by ex-situ vacuum annealing at 520 °C for different annealing times. The structural and compositional analyses of these samples were performed using transmission electron microscopy and atom probe tomography (APT). For the quasi-static magnetic measurements, vibrating sample magnetometry (VSM) was used and the magnetization dynamics was studied using a custom-built broadband ferromagnetic resonance (FMR) instrument with a frequency range of 1–65 GHz and fields up to 1.6 T. Two strong resonances were observed for the annealed nominal and B-added samples whereas a dominant single resonance was observed for all as-deposited and all annealed Co-added samples. This observation correlates with APT results where Mn-rich columnar structures were observed in the as-deposited nominal and Co-added annealed films. Whereas, a nearly equiaxed morphology of the crystalline phase was observed for annealed nominal and B-added films. Hence, FMR spectroscopy was found to be sensitive to the different phases present in the samples and differences in morphology. The quasi-static magnetic properties measured using VSM were not able to distinguish between the individual contributions. However, they provide important information regarding the overall magnetization. The VSM results suggested that short time annealing of the nominal composition results in better soft magnetic properties compared to the derivative compositions that were investigated in this study.
Chapter
This chapter examines phenomena that change continuously, primarily in time. Examples are drawn from life sciences and engineering, including yeast populations, predator-prey interactions, laser beams, oscillations of a quartz crystal, sensors of magnetic fields, and pharmokinetic systems.
Article
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Accurate high-precision magnetic field measurements are a significant challenge for many applications, including constellation missions studying space plasmas. Instrument stability and orthogonality are essential to enable meaningful comparison between disparate satellites in a constellation without extensive cross-calibration efforts. Here we describe the design and characterization of Tesseract – a fluxgate magnetometer sensor designed for low-noise, high-stability constellation applications. Tesseract's design takes advantage of recent developments in the manufacturing of custom low-noise fluxgate cores. Six of these custom racetrack fluxgate cores are securely and compactly mounted within a single solid three-axis symmetric base. Tesseract's feedback windings are configured as a four-square Merritt coil to create a large homogenous magnetic null inside the sensor where the fluxgate cores are held in a near-zero field, regardless of the ambient magnetic field, to improve the reliability of the core magnetization cycle. A Biot–Savart simulation is used to optimize the homogeneity of the field generated by the feedback Merritt coils and was verified experimentally to be homogeneous within 0.42 % along the racetrack cores' axes. The thermal stability of the sensor's feedback windings is measured using an insulated container filled with dry ice inside a coil system. The sensitivity over temperature of the feedback windings is found to be between 13 and 17 ppm ∘C−1. The sensor's three axes maintain orthogonality to within at most 0.015∘ over a temperature range of −45 to 20 ∘C. Tesseract's cores achieve a magnetic noise floor of 5 pT √Hz−1 at 1 Hz. Tesseract will be flight demonstrated on the ACES-II sounding rockets, currently scheduled to launch in late 2022 and again aboard the TRACERS satellite mission as part of the MAGIC technology demonstration which is currently scheduled to launch in 2023.
Article
In recent years, magnetic sensors based on the magnetoelectric (ME) coupling effect have made remarkable progress in the detection of an ac magnetic field, but the detection of the dc magnetic field is still a challenging issue. Therefore, our work aims to develop a highly sensitive device for measuring the dc magnetic field. The designed ME device is based on a pair of highly consistent ME sensors and an intelligent differential configuration. By applying a strong driving ac magnetic field, the even-order harmonic components of the output voltage can be eliminated, and the odd-order harmonic components are superimposed concurrently. Due to the high responsivity (149 mV/ $\mu \text{T}$ ) of the first harmonic component to the dc magnetic field, we obtained a low detection limit of 0.8 nT for the dc magnetic field. These results further advance the research of ME composites used in dc field detection. This ME device may play an important role in many fields of magnetic field detection, such as magnetic localization, magnetic navigation, and so on.
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Zusammenfassung In diesem Beitrag wird ein magneto-optischer Sensor auf Basis des Faraday-Effekts vorgestellt. Hiermit können anhand der Messung einer Komponente der magnetischen Flussdichte zerstörungsfrei und sogar kontaktlos elektrische Stromdichten und Permanentmagnetisierungen bestimmt werden. Aufgrund seiner Bauweise kann der Sensor bis zu $$6\,\upmu\text{m}$$ 6 μ m an das Messobjekt angenähert werden. In der vorgestellten Anwendung sollen magnetische Muster mit Strukturgrößen von $$50\,\upmu\text{m}$$ 50 μ m mit Remanenzen im Bereich 0 mT bis 500 mT auf $$1\,\text{m}\text{T}$$ 1 mT aufgelöst werden. Der Aufbau wird bezüglich seiner Messunsicherheit hinsichtlich dieser Anforderung untersucht. Es soll aber darüber hinaus herausgestellt werden, was allgemein bei der Umsetzung eines Faraday-Magnetometers beachtet werden muss. Dies ermöglicht das Abschätzen des Potenzials für eine große Bandbreite möglicher Anwendungen.
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Article
Compact atomic magnetometer has become an important approach for noise measurement of magnetic shielding systems as well as biomagnetic measurement. In this study, we propose a novel method that enables time-shard triaxial magnetic field measurements in near-zero magnetic field through a compact high-performance atomic magnetometer with femtotesla sensitivity. With pump–probe orthogonal configuration, the magnetometer can be operated without optical and magnetic modulation. The y -axis magnetic field measurement was realized in zero field, whereas the x - and z - axes magnetic fields were measured by the cross-application of the bias magnetic fields operating in near-zero field. The maximum response amplitude and sensitivity with bandwidths of 46.8 Hz ( x - axis), 10.5 Hz ( y -axis), and 10.9 Hz ( z -axis) are achieved under bias magnetic fields of $B_{z-\mathrm {offset}}= 8$ nT and $B_{x-\mathrm {offset}} = 2$ nT. The bandwidth along x - axis was extended to 232 Hz under $B_{z-\mathrm {offset}} = 32$ nT, which can further be improved by increasing $B_{z-\mathrm {offset}}$ . The linear interval of measurable magnetic field are between −11.7 to +11.7 nT ( x - axis), −0.8 to +0.8 nT ( y -axis), and −28.2 to +28.2 nT ( z -axis). For x - and z -axes, the measurable interval can further be improved by increasing $B_{z-\mathrm {offset}}$ and $B_{x-\mathrm {offset}}$ , respectively. The triaxial sensitivities achieved through our method reached 3.1 ± 0.3 fT/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> ( x - axis), 2.0 ± 0.1 fT/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> ( y - axis), and 6.0 ± 0.5 fT/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> ( z - axis). This system is measured in a low-noise ferrite magnetic shield to ensure extra-low magnetic noise condition. Furthermore, the non-modulation triaxial vector operation demonstrated in this study is advantageous for reducing interference and spin-exchange relaxation caused by magnetic field modulation.
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Chapter
Magnetometers provide high-fidelity observations of the Earth's magnetic field from single- and multipoint in-situ vantage points within the magnetosphere and from distributed arrays of ground-based instruments. These magnetometers can be used to diagnose wave processes and both large- and small-scale current systems throughout the coupled magnetosphere–ionosphere system. In this chapter we review the basic concepts of search coil and fluxgate magnetometers and discuss emerging magnetometer technologies. Following this we discuss the utility of ground-based and in-situ magnetometers in diagnosing magnetosphere and ionosphere phenomena and describe the analysis and signal processing techniques used to study magnetometer data. This includes a discussion of field-aligned and ionospheric current systems, wave power and imaging the magnetospheric system with waves which play a crucial role in energetic particle dynamics, field-line resonances and diagnosing magnetospheric plasma density, and finally substorm dynamics and characterizing the substorm current wedge and substorm expansion phase onset.
Article
Magnetoelectric heterostructures have been one of the hottest topics for the research community in the material science field. The interaction between piezoelectric and ferromagnetic orders leads to magnetoelectric coupling. The magnetic sensors based on magnetoelectric coupling have gained attention for futuristic device applications due to their low cost, easy fabrication, high sensitivity, and room temperature working. A series of milestones have been achieved in increasing the sensing performance of magnetoelectric-based magnetic sensors. This review compiles the recent research related to magnetoelectric sensors. The output noises and self-bias effects of these magnetoelectric sensors in different designs are summarized by compiling the recent research. Firstly, the magnetoelectric sensor based on the induced voltage mechanism has been explored in bulk, thin-film, and cantilever configurations. The magnetoelectric coupling improves at the electromechanical resonant frequency of the cantilever due to the reduction in noise level. However, these cantilever-based sensors suffer from the narrow bandwidth in resonance mode and exhibit decrement in sensitivity below their resonant frequency. Recently emerged signal modulation and delta-E (∆E) effect-based magnetoelectric sensors are thoroughly reviewed to measure low frequency or DC magnetic fields. In modulated signal-based magnetoelectric sensors, the electrical, magnetic, rotation, and amplitude modulation techniques are explored. However, an external carrier field requirement generates additional magnetic noises and degrades the sensitivity. On the other hand, the magnetic field-induced alteration in the resonant frequency is measured in the ∆E-based magnetic sensor. The ∆E-based sensors are discussed in cantilever and acoustic resonator configurations. The hybrid magnetoelectric configurations are also explored with fluxgate and magnetoresistive technology. The real-time application of a magnetoelectric sensor can be examined to detect the spatial orientation of the earth's magnetic field, magnetic signals from the brain and heart of the human body. These magnetoelectric sensors are the futuristic candidate for next-generation practical applications in bio-medical, geomagnetic, and magnetic anomaly detections.
Article
Large working range is of vital importance for magnetic sensors when exposed to complicated magnetic field profile, especially in automation and power industry where large field variation is frequently encountered. The design for traditional magnetic sensors, e.g., magnetoresistive and fluxgate magnetometers, utilizes ferromagnetic materials with ultrahigh permeability to maximize the field sensitivity, resulting in strictly confined dynamic range due to limited saturation field. Here, an integratable ferromagnetic resonance (FMR) prototype magnetic sensor with high sensitivity and theoretically unlimited working range is reported. An ultrawide working range (>450 mT) which is more than two orders larger than that of commercial sensors with similar field resolution is experimentally verified. Moreover, the FMR magnetometer is a vector sensor in contrast to the traditional scalar sensors based on magnetic resonance. With a navigating magnetic field of 50 μT (ca. the Earth's magnetic field), the resolution for azimuth angle is 0.006°. Compared with traditional nuclear magnetic resonance and electron paramagnetic resonance sensors with large size and high power consumption, the compact FMR sensor with large dynamic range and high sensitivity has much broader application prospects, especially in magnetically harsh environments. Magnetic field sensor based on ferromagnetic resonance is developed based on yttrium iron garnet films on a coplanar waveguide. An ultrawide working range which is more than two orders larger than that of commercial sensors with similar field resolution has been experimentally verified. With a navigating magnetic field of 50 μT (Earth's magnetic field), the resolution for azimuth angle is 0.006°.
Article
Magnetic sensing platform techniques have been used in many years in an attempt to better evaluate the likelihood of recoverable hydrocarbon reservoirs by determining the depth and pattern of sedimentary rock formations containing magnetic minerals, such as magnetite. Utilizing airplanes, large-area magnetic surveys have been conducted to estimate, for example, the depth of igneous rock and the thickness of sedimentary rock formations. In this case, the vector magnetic survey method can simultaneously obtain the modulus and direction information of the Earth's magnetic field, which can effectively reduce the multiplicity on data inversion, contribute to the quantitative interpretation of the magnetic body and obtain more precise information and characteristics of magnetic field resource, so as to improve the detection resolution and positioning accuracy of the underground target body. This paper presents a state-of-the-art review of the application situations, the technical features, and the development of the vector magnetic sensing platform-technical aspects for different application scenarios, i.e., ground, wells, marine, airborne, and satellites, respectively. The potential of multi-survey sensing platform technique fusion for magnetic field detection is also discussed.
Thesis
Les travaux de cette thèse portent sur la mesure de champ électrique continu et à basse fréquence. Si la façon la plus simple de mesurer, de façon directionnelle un champ électrique, est au moyen de paire d'électrodes de capture métalliques répondant à l'influence du champ électrique, ce dispositif, à l'instar de la bobine de capture pour le champ magnétique, ne peut pas fonctionner au continu. Il existe depuis des décennies, des capteurs de champ électrique continu exploitant un dispositif mobile pour créer un pseudo champ alternatif détectable par une ou plusieurs électrodes de capture. Cette approche s'accompagne d'usure mécanique des pièces mobiles et de dégradation de la directionnalité tout en restant avec une limitation sévère de la bande passante. Pour s'affranchir de la partie mécanique mobile, cette thèse se penche en premier sur la conception d'un capteur de champ électrique innovant sans hacheur mécanique de type fluxgate électrique (FGE) en suivant le principe de la dualité entre paires de grandeurs physiques des domaines électriques et magnétiques, notamment celles intervenant dans le principe de mesure des fluxgates magnétiques (FGM). Or, l'analyse de la faisabilité technique du FGE est difficilement réalisable. Cette thèse propose une seconde possibilité d’approche, s’appuyant sur un dispositif voisin du FGM : le capteur de champ électrique à réluctance diélectrique variable. Ce capteur dérive de son dual magnétique, le capteur de champ magnétique à réluctance magnétique variable. La caractérisation du capteur magnétique à réluctance variable dans gamme de fréquence de 0,1 Hz à 1 kHz, présente une sensibilité de l'ordre de 22 mV/μT avec un niveau de bruit magnétique de l'ordre de 15 nTrms/√Hz . La caractérisation au continue du capteur de champ électrique à réluctance variable, ne permet pas de juger sur le bon fonctionnement du capteur car, les résultats obtenus sont trop parcellaires pour pouvoir juger d’une bonne adéquation au modèle de fonctionnement. Néanmoins, un modèle simplifié du capteur de champ électrique à réluctance variable avec deux électrodes supplémentaires sur sa structure annulaire donne de bon signe de fonctionnement avec une sensibilité de l’ordre de 25 μV/(V.m-1) .
Article
Design, fabrication, characterisation and calibration of a three-axis, ring-core, second harmonic fluxgate magnetometer is described in detail. Owing to the good material selection, precise structural fabrication, and high-performance processing unit, in addition to implementation of a novel and effective calibration algorithm, the sensor features good characteristics such as $$0.1^{\circ }$$ non-orthogonality, 0.03% accuracy and 0.08% linearity. The power consumption of the fabricated sensor is 0.7 W. We have also compared the noise level of two types of commercial ring cores and shown that the experimental findings confirm our expectation about the noise level of the cores. In addition, a novel calibration method using the neural network was used to reduce errors of the fluxgate sensor.
Chapter
Sample preparation is necessary for the determination of analytes in biological matrices. The presence of endogenous compounds makes biological matrices complex to be analyzed. In recent years, different extraction techniques have been proposed in this area. An innovative approach is solid-phase extraction based on magnetic nanomaterials that can be manipulated using magnetic fields. These materials have been used in extraction fields due to their exclusive features, including extremely large surface area, selective adsorption ability, easy separation only by applying an external magnet, and possibilities for surface modification/functionalization. These materials have been used for the determination of various analytes in biological fluids. In this chapter, various magnetic nanomaterials are classified based on their compositions and the recent applications of these materials in the field of bioanalysis under solid-phase (micro) extraction format are reviewed. Also, the analytical performance of the methods is addressed from a preventative and critical point of view.
Article
Traditional coreless current sensors have multiple magnetic sensors, the same number of operational amplifier and analog-to-digital converter (ADC). This requires more components and basically cannot meet the practical use because of area-effective and cost-effective requirements. In this paper a novel coreless tunnel magnetoresistance (TMR) array current sensor has the characteristics of simple N-1-1 topology, light weight, and low power consumption. Three TMRs are directly connected in parallel and unified only by one programmable amplifier to directly output to meet the current measurement. A relatively simple circuit structure is adopted and a good result is obtained. Finally, the applicability of the scheme is verified by theoretical analysis and actual measurement.
Chapter
In this paper, a magnetostrictive-based optical fiber micro-cantilever resonant magnetic field sensor is proposed. The magnetic field sensor is based on the optical fiber end face design of the optical fiber micro-cantilever beam. The surface of the optical fiber micro-cantilever beam is plated with a magnetostrictive film, and the two form a double layer micro-cantilever beam structure. The magnetostrictive film generates a magnetostrictive effect under a magnetic field, which causes the double-layer cantilever structure to deflect and change its resonant frequency. The magnetic field can be determined by detecting the change in resonant frequency. Then use ANSYS simulation software to simulate the resonance frequency of the double-layer micro-cantilever structure under the magnetic field, and obtain the relationship between the magnetic field and the resonance frequency, in order to optimize the size of the double-layer cantilever structure, and then obtain the best sensitivity of the magnetic field sensor. The simulation results show that: when the double-layer micro-cantilever structure is 90 μm long, the thickness of the fiber-optic micro-cantilever is 2 μm, and the thickness of the magnetostrictive film is 3⁄5 of the thickness of the fiber-micro-cantilever, the magnetic field sensor can reach the maximum sensitivity of 40,760 Hz/Gs.
Article
In this paper, an open-loop self-oscillating fluxgate-based current measurement method is presented. The proposed sensor does not require the low-pass filter necessary in traditional measurement technologies and does not require an analog-to-digital converter when connected to digital systems. More importantly, although the proposed measurement method is based on the open-loop configuration, its measurement accuracy is close to that of the traditional self-oscillating fluxgate measurement technology based on the closed-loop configuration. Accurate mathematical models are established to describe the basic characteristics of the measurement method, and design criteria of the sensor are proposed. The test results show that the proposed measurement method has good linearity; for example, in the full scale of 100 A, its linearity is about 0.4% and can be improved to below 0.2% when the first-order polynomial fitting method is used.
Article
This work presents a simple structure of a fluxgate sensor with superior characteristics, using an excitation-bridge coil without the need of a conventional pick-up coil. The proposed device is characterized by the dual role of the excitation coil, which serves both to magnetize the soft magnetic core periodically and to pick-up the external magnetic fields simultaneously. In fulfilling such roles, the excitation coil is designed in two-rod cores and configured into two branches of an anti-serial circuit. Each branch is combined with an external resistance to forming an excitation-bridge circuit that induces a differential signal proportional to the external magnetic fields. The experimental results demonstrate a significant sensitivity of 629 mV/mT and a noise level of 320 pT/√[email protected] The proposal has many merits without the pick-up coil, including simplified integration, miniature size, and high sensitivity.
Article
With the rapid development of sensing technology, it has attracted tremendous interests in the field of biomedicine because of its good biocompatibility, reliability, and safety. In comparison to other sensors, magnetic sensor has a broad application prospect in biomedical field due to its high sensitivity, small size, and intriguing non‐invasive detection property. The purpose of this review is to discuss the applications of magnetic sensors in the biomedical field. First, some widely used magnetic sensors are reviewed based on their working principle and characteristics. Then, the applications of magnetic sensors in biomedical field are introduced from the aspects of magnetic label‐based bioassays, detection of biological movement, and biology magnetism. Finally, the future development direction and prospect of magnetic sensors in biomedical field are prospected. This review will provide a general outlook for the applications of magnetic sensors in biomedicine.
Article
Flexible magnetic sensors are attracting more and more attention because of their application in wearable devices. In this paper, Metglas/polyvinylidene fluoride (PVDF) bilayer composite with good flexibility was fabricated to evaluate its applicability as a flexible in-plane magnetic sensor. The magnetoelectric (ME) coupling characteristics and sensing performance of the sample were investigated under different test conditions, including different AC and DC magnetic field, and changing the direction of the magnetic field and the bending degree of the sample. The sample shows a large ME coefficient with a value of 176.41 V cm⁻¹ Oe. The sensitivity, linearity and deviation of the sample are 892.96 mV Oe⁻¹, 0.99965 and ±2% for the AC magnetic field, and 157.6 mV Oe⁻¹, 0.99444 and ±5% for the DC magnetic field, respectively, and it shows excellent stability over repetitions. Moreover, the sample was gradually rotated anticlockwise in the magnetic fields. The output voltage of the sample varies with the rotation angle and has a good symmetry in plane, which is described well by a sine function. In addition, the clamping effect of the sample was studied. Even when bent, the sample still maintains an excellent and stable performance. The sensitivity and linearity of the sample with a bent angle of 23.5◦ are 254.37 mV Oe⁻¹ and 0.99975 for the AC magnetic field, and 28.07 mV Oe⁻¹ and 0.99309 for the DC magnetic field, respectively. The deviation of measurements is small for both the AC and DC magnetic sensors. In summary, the present study shows that the Metglas/PVDF bilayer composite has a good sensing performance and is suitable for = flexible in-plane resonant magnetic sensors.
Article
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Fluxgate voltage output contains information about the measured DC magnetic field in amplitude of even harmonic components. Tuning the sensor output causes the concentration of output energy to specific harmonics (usually 2f) and parametric amplification. A short-circuited output current fluxgate cannot be tuned, but it in principle requires less turns of the pick-up coil. The noise measurements performed on amorphous ring-core sensors show no significant difference between current-output and tuned voltage-output, and higher noise level for untuned voltage-output
Article
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Miniature fluxgate sensors with symmetrical closed core elements on both sides of the planar coils were manufactured using standard microtechnology. The new sensors have shown substantial improvement over the standard single-sided micro.-fluxgate sensors: for the same field range the sensor noise was reduced 10-times to 20 nT rms (20 mHz … 10 Hz) and the perming suppressed below 5 μT, for field shocks of 6 mT. The maximum sensitivity for sinewave excitation was 32 V/μT for 1 MHz frequency and 200 mA p-p excitation current amplitude. Pulse shape of the excitation current allows use of high current peaks to suppress perming, while the rms value is low. Using a 20% duty factor squarewave excitation with 180 mA p-p amplitude, the sensitivity was twice that of the sinewave excitation, while the chip temperature dropped from 80°C to 40°C
Article
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We discuss the performances of highly sensitive magnetometers using flux gates, as well as magnetotransport effects (magnetoresistance - AMR/GMR and magnetoimpedance - GMI). Soft magnetic materials operating at room temperature or cryogenic temperatures are involved in these effects. We report on their performances (sensitivity, bandwidth, etc.) with emphasis on their noise properties. The latter often fall to 1-10 pT/√Hz even for active areas as low as 1-2 mm<sup>2</sup>. Amorphous magnetic flux guides are often used to enhance the field sensitivity of micro-devices. Their replacement by superconducting concentrators, which could lead to much larger gain factors, is discussed. This review, together with new results, confirms a new research field which could lead to highly sensitive, low noise, superconducting-magnetic hybrid magnetometers
Article
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This paper presents a CMOS two-dimensional (2-D) vector magnetic sensor system integrating two planar microfluxgate sensors and the complete electronics for sensor excitation and signal readout. The system is based on an industrial 0.8-μm double-poly, double-metal CMOS technology with ferromagnetic NiFeMo cores added in a simple postprocessing sequence. The fluxgate sensors are embedded in a ΣΔ analog-to-digital converter for a stable and precise digital detection of weak magnetic fields. A cascaded ΣΔ modulator topology is utilized to obtain second-order noise shaping and to suppress pattern noise. Within the range of ±50 μT, the system nonlinearity is less than 1.5 μT. The angular resolution as a 2D vector sensor is less than 4° for a measured magnetic induction of 50 μT. This makes the 2-D microfluxgate magnetometer suitable for use as fully integrated electronic compass
Article
In NDE, the most appropriate sensor for any situation is usually a compromise between signal sensitivity, potential spatial resolution and simplicity of operation. In eddy current NDE, the range of sensors encompasses the simple (induction coils) to the esoteric (SQUIDs). Lying somewhere in the middle ground, fluxgate magnetometers possess attributes which make them suitable for the detection of flaws in such samples as aluminium and steel plates and reinforcing steel bars contained in concrete samples. Here, we describe the performance of commercially available fluxgate magnetometers and present results obtained with the above samples. Wherever applicable, reference is made to the other sensors available.
Article
In physical, technical and biological systems measurements of weak magnetic fields are of great importance. A highly sensitive magnetic sensor with a frequency output signal for robust information transmission is presented. It consists of a tuned r.f. oscillator the frequency of which is determined by a weak external magnetic field in the magnetic range of picotesla to microtesla (a magnetically controlled oscillator, MCO). This low-noise magnetic-field-to-frequency converter with a large bandwidth ( > 200 kHz at −3 dB) is very simple in construction, relatively cheap in production and shows a sensitivity of more than 200 GHz T−1. It is suitable for a magnetic readout system or an integrated magnetic sensor array, especially for high-frequency magnetic heads, navigation applications and for geomagnetic measurements.
Article
The usability of tensile stress-annealed Romanian Co68.25Fe4.5Si12.25B15 ribbons as the sensing element in Vacquier–Foerster type sensor was studied. Using the ribbons exposed to a 1/2 h pre-annealing at 300°C followed by 1/2 h stress-annealing at 300°C with applied longitudinal tensile stress of 418 MPa, good results were obtained with regard to the offset stability and noise of the sensors. The possibility of using the sensor for measuring low frequency magnetic fields was studied using Fourier analysis. The external a.c. field generates sidebands at the even harmonics in the output signal, which increase with the amplitude of the external field. The transfer characteristics of the sensor are linear for field amplitudes up to 240 μTpp and in a frequency range from 0 to 10 kHz. The measurements demonstrate the usability of the sensor in a magnetometer for both continuous and alternating magnetic field measurements.
Article
The single axis magnetic gradiometer based on two compact detector compensation (CDC) fluxgate ringcore sensors separated 20cm is described. Despite its high stability and precision better than 1nT, the calibration procedures are not straightforward. Firstly, the mono-axial measurement does not provide vector information about the magnetic field. Secondly, one of the sensors measures the ambient magnetic field and is used to compensate for the main field at both sensors. Several methods have been developed for characterization of the gradiometer, and the calibration of the gradient measurements is achieved by using a magnetic dipole of strength 2mAm2. In a coil facility, the gradient can be determined with an accuracy of 0.3nT/mRMS.
Article
In this paper, harmonics content of sinusoidal excited fluxgate sensors response is analyzed by means of a simple electrical model developed for SPICE. The model construction is detailed and it is applied to the simplest fluxgate sensor. Well known characteristics of these sensors are confirmed through the simulations, while new useful outcomes are discussed. In particular it is found that the 4th harmonic response has, in analogy to that of the 2nd one, a linear range which is of greater sensitivity independent of the shape of the BH curve. Second and 4th harmonic responses present a negative slope region. Using a previously developed 2nd harmonic fluxgate magnetometer, some preliminary experimental results are obtained confirming the appearance of the negative slope region at its output.
Article
A race-track single-core fluxgate magnetic gradient sensor has achieved a noise level of 30 pT cm−1 r.m.s. (50 mHz–10 Hz) with a gradiometric base of only 3.75 cm. Such a sensor has sensitivity high enough to replace SQUIDs in the detection of ferromagnetic particles deposited in human lungs. Measurements on tissue samples, dust from respiration filters and experiments with phantoms have proved that the total amount and spatial distribution of dust in the lungs may be measured in the case of welders, grinders and other metal workers. Measurements on coal miners and asbestos workers are less specific. The construction of the magnetization device for in vivo experiments is in the progress.
Article
A model of a fluxgate magnetometer based on the field interactions in the fluxgate core has been derived. The non-linearity of the ringcore sensors due to large uncompensated fields transverse to the measuring axis are calculated and compared with measurements. Measurements of the non-linearity are made with a spectrum analyzer measuring the higher harmonics of an applied sinusoidal field. For a sensor with a permalloy ringcore of 1 in. in diameter the deviation from linearity is measured to about 15 nTp-p in the earth's field and the measurements are shown to fit well the calculations. Further, the measurements and the calculations are also compared with a calibration model of the fluxgate sensor onboard the ‘MAGSAT’ satellite. The later has a deviation from linearity of about 50 nTp-p but shows basically the same form of non-linearity as the measurements.
Article
The construction of a triaxial fluxgate sensor with very high axis stability and low temperature coefficients is described. The axis orthogonalities change less than 2.1 s of are in the whole testing temperature range +20 to -10 degrees C. The temperature coefficients for the sensitivities of the three axes are 6.7, 10.1 and 13.3 ppm K-1, respectively. This high stability is achieved by using a newly developed ceramic, C-SiC, as the supporting construction material. (C) 1997 Elsevier Science S.A.
Article
The processing of the sensor core material was investigated on the operation of the Fluxset magnetic field sensor. Static and dynamic magnetic properties were measured, and the signal of the pick-up coil was investigated as a function of processing. The sensitivity and signal/noise ratio of the sensor can be improved significantly by polishing of the ribbon and heat annealing.
Article
A simple fluxgate magnetometer is developed using low magnetostrictive ferromagnetic amorphous alloy acting as a sensing element. It uses the fact that the magnetization of sensing element symmetrically magnetized by a sinusoidal field contains even harmonic components in presence of dc signal field H and the amplitude of the second harmonic component of magnetization is proportional to H. The sensitivity and linearity of the magnetometer with signal field are studied for parallel configuration and the field ranging from 10 nT to 10 muT can be measured. The functioning of the magnetometer is demonstrated by studying the shielding and flux-trapping phenomena in high-Tc superconductor.
Article
Making use of the inverse Wiedemann effect in non-magnetostrictive hairpin shaped metallic glass ribbons we have made flux-gate sensors with small dimensions (d × l = 3 × 8 mm2) and RMS noise levels of 2 nT (0.02-1 Hz). The inverse Wiedemann effect arises from a helical anisotropy induced by torsional stress annealing. Danish Space Research Institute, Lundtoftevej 7, DK-28OO Lyngby, Denmark.
Article
We have fabricated ring-core and single-domain rod-core flux-gate magnetic field sensors with 1/f noise levels at 1 Hz of 1.4 pT/ and 3.5 pT/, respectively. These noise sensitivities were achieved by applying an electrical current through the core of the flux gate to magnetically bias the magnetic rotation of the core perpendicular to the easy-axis direction. We also found that in the rod-core sensor, the spatial correlation lengths of the magnetic fluctuations were 25 and 40 mm with and without the biasing current. The cross-power spectrum magnitude at 1 Hz was less than 200 fT/. © 2001 American Institute of Physics.
Article
Magnetic fluxgates provide very good noise properties together with a large dynamic range in small, solid-state sensors used in many applications. We investigate racetrack shaped fluxgate sensors with a core of (CoFe)70(MoSiB)30 amorphous metal. We investigate the influence of the excitation current in the drive coil of our fluxgates on the sensor noise properties. The output signal is obtained by a modulation technique with demodulation from the second harmonics of the excitation. To achieve a large dynamic range with good linearity the fluxgates are operated in a feedback loop. The linearity is characterized by measurements of the total harmonic distortion in dependence on the signal amplitude. The noise properties are investigated in shielded and unshielded environment. In both cases the obtained noise level is (2 kHz)=960 fT/. We compare our noise properties to recent data on superconducting quantum interference devices from high temperature superconductors operated in unshielded environment. © 2000 American Institute of Physics.
Article
The general characteristics and system level concepts for space-based magnetometers are presented to illustrate the instruments, principles, and tools involved in making accurate magnetic field measurements in space. Special consideration is given to the most important practical problems that need to be solved to ensure the accuracy of the measurements and their overall impact on system design and mission costs. Several types of instruments used to measure magnetic fields aboard spacecraft and their capabilities and limitations are described according to whether they measure scalar or vector fields. The very large dynamic range associated with magnetic fields of natural origin generally dictates the use of optimized designs for each particular space mission although some wide-range, multimission magnetometers have been developed and used. Earth-field magnetic mapping missions are the most demanding in terms of absolute accuracy and resolution, approaching <1 part in 100 000 in magnitude and a few arcsec in direction. The difficulties of performing sensitive measurements aboard spacecraft, which may not be magnetically clean, represent a fundamental problem which must be addressed immediately at the planning stages of any space mission that includes these measurements. The use of long, deployable booms to separate the sensors from the sources of magnetic contamination, and their impact on system design are discussed. The dual magnetometer technique, which allows the separation of fields of external and spacecraft origin, represents an important space magnetometry tool which can result in significant savings in complex contemporary spacecraft built with minimum magnetic constraints. Techniques for in-flight estimation of magnetometer biases and sensor alignment are discussed briefly, and highlight some basic considerations within the scope and complexity of magnetic field data processing and reduction. The emerging field of space weather is also discussed, including the essential role that space-based magnetic field measurements play in this complex science, which is just in its infancy. Finally, some considerations for the future of space-based magnetometers are presented. Miniature, mass produced sensors based on magnetoresistance effects and micromachined structures have made significant advances in sensitivity but have yet to reach the performance level required for accurate space measurements. The miniaturization of spacecraft and instruments to reduce launch costs usually results in significantly increased magnetic contamination problems and degraded instrument performance parameters, a challenge that has yet to be solved satisfactorily for “world-class” science missions. The rapidly disappearing manufacturing capabilities for high-grade, low noise, soft magnetic materials of the Permalloy family is a cause of concern for the development of high performance fluxgate magnetometers for future space missions.
Article
In this paper, we present a planar fluxgate magnetic sensor for on-chip integration using silicon process technology. The fabrication process is simplified by using a newly developed sensing element which is composed of thin-film ferromagnetic cores at the top layer, and excitation and differential pick-up coils. The sensor core used is permalloy film deposited by sputtering. The coils are fabricated using a two-layer metallization process. The fabrication process for the sensing element is suitable for integrating the on-chip interface circuits. In order to achieve the optimum excitation condition, the sensing element structure is investigated by means of computation analysis. The sensing element is fabricated with 2-μm-thick, 1400-μm-long cores and excitation and pick-up coils (25 turns each). The sensing element fabricated using planar technology has a magnetic sensitivity of about 73 V/T at an excitation frequency of 1 MHz and a driver current of 150 mAp-p.
Article
Although fluxgates may have a resolution of 50 pT and an absolute precision of 1 nT, their accuracy is often degraded by crossfield response, non-linearities, hysteresis and perming effects. The trends are miniaturization, lower power consumption and production cost, non-linear tuning and digital processing. New core shapes and signal-processing methods have been suggested.
Article
The output current impulses of the short-circuited fluxgate depend on the input magnetic field, and on a number of core parameters such as the demagnetization factor, the cross sectional area, the time spent in saturation, etc. Following a theoretical treatment, experimental tests of the parameter dependences are reported, and additional experimental evidence of the noise performance is presented.
Article
A novel design of a magnetic field feedback compensation coil system for triaxial fluxgate magnetometers is presented. The coils are wound on three concentric spherical shells of slightly different diameters with the fluxgate sensors placed in the 60 mm diameter internal field-free space. Measurements of the temperature coefficient and of the internal field homogeneity are given, and the noise performance is evaluated for a magnetometer incorporating the coil. The total outer diameter of the system is 90 mm and the weight is 350 g including the sensors. The main advantage of a vector feedback system is the exact definition of the magnetic axes. These are determined exclusively by the coil axes, and they are independent of even large angular displacements of the individual magnetic axes of the fluxgate elements.
Article
The experiments and theoretical considerations leading to the construction of a high-performance three-axis fluxgate magnetometer are described. The magnetometer will be used (1996) in the Earth's field mapping satellite named 'OErsted'. The fluxgate sensors are based on stress-annealed metallic glass ribbons as core materials. It is shown that very simple physical models can be used to explain the fluxgate mode of operation, thereby making it easy to calculate the overall sensor performance from first principles. Special attention is drawn to the core excitation current which is analysed on the basis of nonlinear electrical circuitry. It is furthermore shown that the ring-core demagnetizing field obeys a simple cosine law which permits the calculation of the sensor sensitivity with high accuracy. The sensitivity, that is the signal-to-noise ratio, is ultimately determined by the sensor noise which is about 15 pT RMS (0.06-10 Hz), corresponding to a noise power density (1/f noise) of 6.2 pT Hz-1/2 at 1 Hz. The actual magnetometer operating range and sensitivity is determined by the 1 bit resolution of the Earth's field represented by the output from the 18 bit AD converted used in the instrument (+or-65536 nT with 0.5 nT resolution). The maximum attainable bandwidth is half the sensor excitation frequency (1/2*15 kHz) but the OErsted magnetometer bandwidth is limited to 250 Hz. The thermal stability of the sensor has been measured to be better than 1 nT in the temperature range -20 to +60 degrees C.
Article
Fluxgate sensors are mostly used in closed-loop d.c. magnetometer systems; they can also measure alternating fields up to several kilohertz, either in open-loop mode or from an error signal in the slow-feedback loop as in the Thunderstorm rocket magnetometer, which has 0.1 nT resolution up to 3 kHz. The alternative is to use the direct induction effect in the pick-up or feedback coil. While the low L/R constant of the pick-up coil causes a high −3 dB frequency corner, the spherical feedback coil has narrow frequency characteristics and low noise up to 10 kHz when used as a search coil. The noise level achieved is 56 pT r.m.s. from 123 Hz to 10 kHz.
Article
The magnetic field transverse to the sensing axis may affect the performance of magnetic sensors. In the case of fluxgates, this effect is not as dramatic as it is for AMR sensors, but it still may cause errors up to 40 nT in the Earth's field. We performed measurements on voltage output fluxgate sensors of various constructions. Ring-cores are the most susceptible, showing around 10 nT error for 50 μT perpendicular field, while Vacquier-type (bar-core) sensors suppress the crossfield by their shape anisotropy. Racetrack fluxgates are the best candidates for crossfield resistant low-noise sensors.
Article
A method is proposed by which a magnetometer with symmetric response and zero offset can be realized with an orthogonal fluxgate. The sign of the sensitivity is changed by changing the sign of the dc bias current to the wire core of the magnetometer, whereas offset is unchanged. Symmetrical response is obtained by taking the difference of outputs obtained with a positive dc bias and with a negative dc bias, which also leads to zero offset. A prototype is examined with an as-cast amorphous Co-based wire as a core. Good performance is obtained with small excitation current (ac component 5 mA, dc component 7 mA).
Article
A magnetometer for digital analysis of a magnetic field is presented. The method of measuring is based on the detection of the coil relaxation time, after its excitation up to saturation by means of short current pulses. The time detection uses a voltage limiter, before an active comparation. An external magnetic field causes a width modulation of the relax-pulses, due to the total consumption of the supplied energy. The width of the relax-pulses is evaluated by counters and, after buffering, picked up to IBM/PC parallel I/O. The sensitivity of the present magnetometer is 10 nT from DC up to 500 Hz and 100 pT up to 5 Hz, in real time. Data analysis could be utilized for autonomical navigation systems, as well as for an industrial, environmental and medical use
Conference Paper
The first microfluxgate based on a standard CMOS process is presented. The ferromagnetic sensor cores are electrodeposited at room temperature on top of the chip passivation. The post-processing is fully compatible with all standard IC technologies. The second harmonic of the sensor output voltage exhibits a linear response to small magnetic fields below 50 μT. The linearity error including hysteresis is smaller than 1.2% full scale. The angular field response deviates less than 1.6% from a sine function. The sensor has a maximum sensitivity of 2.7 V/T at 2 MHz at a power consumption of 60 mW. The equivalent signal noise is 6 nT/√Hz at 10 Hz
Article
Small, racetrack shaped fluxgate-sensors with a core of (CoFe)<sub>70</sub>(MoSiB)<sub>30</sub> amorphous metal tape are optimized in geometry to achieve a high sensitivity to external magnetic fields and low intrinsic white noise. For optimization we employed statistical methods of experimental design. We varied the length, the width and the number of tape layers in the core keeping constant the peak magnetization during the magnetic field modulation. Numerical simulations help us to understand the interaction of sensor core geometry and the observed sensitivity and noise. The best white noise level is below √(S<sub>B</sub>)(1 kHz)=400 fT/√(Hz). This noise level has so far been achieved with small sensors only by SQUIDs. We discuss the consequences of the geometry influence on the miniaturization of fluxgate sensors
Article
The relationship existing between the open circuit terminal voltage of a dipole antenna and the intensity of the surrounding field is well known. A magnetic structure whose properties are similar is obtained by replacing the pair of the dipole conducting arms by a pair of highly permeable ferromagnetic arms. As a result, an MMF whose features are similar to those of the open circuit voltage appears across the gap between the arms. Our experiments demonstrate that this MMF is related to the magnetic structure length and surrounding field in the same way that the electric open circuit voltage is related to the dipole length and surrounding field. Furthermore, a relatively long fluxgate magnetometer was developed. It assisted in demonstrating that the measured field related flux and the magnetometer output signal are directly proportional to a gap MMF related value. In addition, a new approach has been discovered for relating the fluxgate magnetometer output signal to the surrounding field intensity in cases where the measured field is non-uniform.
Article
This paper presents a new micro-fluxgate magnetic sensor based on micromachined 3-dimensional toroidal type planar coils used as excitation and sensing elements. A rectangular-ring shaped magnetic core and the second harmonic' operation principle are adopted in this fluxgate sensor. With the use of a newly developed UV-LIGA thick photoresist process and electroplating techniques, excitation and sensing coils as well as permalloy magnetic cores were fabricated to realize a planar three-dimensional magnetic fluxgate sensor on silicon wafers. Excellent linear response over the range of −500 μT to +500 μT, with a system sensitivity of 8360 V T−1 and a resolution of 60 nT was achieved from the sensor realized in this work. The total response range of the sensor is −1.3 to +1.3 mT. The electroplated thick, Cu coil windings result in low coil resistance and a low power consumption of ∼100 mW for an operational frequency range of 1–100 kHz. The small size, the high sensitivity and resolution, and lower power consumption, make this integratable magnetic fluxgate sensor suitable for various applications such as: portable navigation systems, space research, and proximity sensors and detectors.
Article
We report on a miniaturized magnetic-field sensor system consisting of a fluxgate sensor fabricated in CMOS-compatible planar technology and a CMOS-ASIC for sensor supply, readout and signal processing using the second-harmonic principle with a feedback loop for zero-field operation. The system exhibits a sensitivity of 9.2±0.1 mV μT−1 for a magnetic field range of ±90 μT and a temperature range of 0 to 70 °C. The 3 dB bandwith is 300 Hz and a noise value of 30 nT Hz has been estimated. Using 5 V supply voltage, the power consumption of the system is measured to be 160 mW.
Article
This paper describes high-resolution micro-fluxgate magnetic sensing elements using magnetic thin films and closely coupled excitation and pick-up coils based on a solenoid-shaped coil structure. In order to improve the sensitivity of the sensing element, the optimal coupling structure between excitation and pick-up coils, and the formation method of permalloy magnetic films are investigated. The closely coupled coil structure allows the magnetic core to be excited in an optimal condition with reduced excitation current. The addition of indium to the permalloy plating bath greatly reduces the degradation of the magnetic core due to the thermal treatment process. The sensitivity of the fabricated sensing element is measured to be 2700 VT−1 at an excitation frequency of 3 MHz. The noise level, or resolution in d.c. to 10 Hz bandwidth is measured to be about 40 nTp−p.
Article
A high sensitivity sensor has been developed recently, suitable for measuring DC and/or middle frequency AC magnetic field. The device has a sensitivity better than 100 pT, it operates in a wide temperature range, it is simple and cheap. Good stability and linearity of the device have been measured. The sensor can be applied for different purposes. High sensitivity and high frequency versions of the sensor are shown in the paper with the most important technical parameters, and some application possibilities in the industry are also indicated. Results, achieved by the sensor in eddy current testing (ECT), are shown more detailed.
Article
Simple anisotropic magnetoresistance magnetometer with improved parameters was developed. New flipping circuits deliver optimized current pulse with 2.8 A amplitude. New type of signal processing uses switched integrator to avoid the most noisy time intervals. The achieved linearity is 0.2% in the ±200 μT range without feedback and 0.04% using integrated feedback coil. The magnetometer noise at 1 Hz is 2 nT/Hz1/2, uncompensated temperature coefficient of sensitivity is −0.25%/K without the feedback and 0.01%/K with feedback. Temperature offset drift is typically 10 nT/K.
Article
We have fabricated two-dimensional inductive devices by integrating micropatterned magnetic foils of high permeability (μr=100 000) with winding patterns realised in printed circuit boards (PCBs) and flex-foil technology. We realise relatively high inductances of 1–10 μH for transformer type devices and a sensitivity of 60 V/T at 30 kHz for fluxgate magnetic induction sensing devices. The same type of device is also used as a current sensor; here we typically find sensitivities of 10 mV/A for excitation currents of a few 100 mA. We think our technology opens the way to a new class of functional and economic sensing devices.
Article
New micro-fluxgate sensor with flat excitation and sensing coils and double-sided symmetrical core has significantly improved parameters over the original asymmetric single-sided core design. The main advantage of the new design is that the demagnetization with respect to the excitation field is much lower than demagnetization with respect to the external measured field. The magnetic circuit of the new sensor is almost closed with respect to the excitation field and so the core is deeper saturated. Comparing the new double sided core with the single-sided design, the sensor hysteresis was decreased from 30 to 2.5 μT (for full range of 1200 μT). Noise level was decreased from 242 to 27 nT rms (0.1–10 Hz.). The sensor linear range was extended from 600 μT to 1 mT. Perming was reduced from 50 to 5 μT after the field shock of 6 mT.
Article
The vector magnetometer sensor onboard the Astrid-2 satellite is made as a compact ringcore fluxgate sensor with single axis compensation. The ringcores used in the sensor are identical to the cores used in the fluxgate (CSC-) sensor in the high quality magnetometer onboard the field mapping satellite called Ørsted'. To obtain good axial stability special attention is drawn to the mechanical construction of the tri-axial sensor configuration. Almost all parts of the sensor are machined from the glassy material MACOR® that has approximately the same thermal expansion coefficient as the core ribbon. The single axis compensated ringcore sensors are known to have some linearity problems with large uncompensated fields perpendicular to the measuring axis. This phenomenon is also seen for the Astrid-2 sensor, and from a coil-calibration of the flight-spare sensor we observe non-linearities in the order of 2.1 to 4.3 nTp. From the results of the calibration, an unfortunate magnetic coupling between two of the axes was discovered. This coupling is also associated with the ringcore geometry and large uncompensated transverse field.
Article
A new compact 2D planar fluxgate sensor using a ferromagnetic amorphous metal core is described. The fluxgate sensor consists of two orthogonal planar metallic coils and a ring shaped amorphous magnetic ribbon mounted on a PCB substrate. Each planar coil is used alternatively as excitation or as pick-up coil. An electronic interface drives alternatively the two coils and performs a feedback on each sensing coil in order to compensate for the two measured magnetic field components. The sensing element has a magnetic sensitivity of 55 V/mT at an excitation frequency of 8.4 kHz with a 160 mApeak driving current. Used as an electronic compass, the reached precision angle is better than 1°.
Article
The design, construction and performance of a novel micro-fluxgate sensor is presented in this work. The sensor is based on the large Matteucci effect that is observed in amorphous fibers of typical stoicheiometry Fe77.5Si7.5B15 after proper annealing. The sensor requires a single planar coil to function, which was constructed with conventional printed-circuit techniques along with the sensor signal conditioning circuitry. A new signal extraction technique was applied that is superior to the conventional second-order-harmonic concept, as far as sensitivity and signal-to-noise ratio are concerned. A conventional fiber, with diameter 125 μm and a glass-covered fiber, with core diameter 20 μm and glass-cover thickness 20 μm, were used as magnetic cores in the fluxgate sensor. The amorphous fibers were mounted, subsequently, above a planar coil by soldering each two ends without any further mechanical treatment, like bending or twisting. Current annealing was performed before mounting, for both magnetic core types in order to optimize the inductive response of the fibers. The sensor sensitivity, before amplification, was measured to be 74000 V/T. The low magnetic noise observed allows for a relatively high overall precision, which in the case of glass-covered fiber has been verified to be 60 nT; this figure may easily improve by known signal conditioning techniques. The overall sensor head dimensions are mm. Further scaling down may be achieved by means of advanced lithographic techniques in the case of glass-covered amorphous fibers only, which exhibit significant Matteucci effect in lengths down to 5 mm.
Article
Micro-fluxgate sensor with symmetrical core on both sides of the planar rectangular excitation and pick-up coils has substantially improved parameters compared to its single-core predecessor. Almost closed magnetic path for the excitation field allows much deeper saturation of the sensor core, which reduces the perming effect, hysteresis and noise. Perming of maximum 5 μT for 6 mT field shock, 28 V/T sensitivity and 24 nT rms noise were achieved for 2 mm long sensor excited by 1 MHz, 180 mA rms sinewave current, without magnetic feedback.
Article
Since the 1930s, fluxgate sensors have been used for measuring d.c. magnetic fields up to 1 mT with a maximum resolution of 10 pT. In the sensor core the flux is gated by the excitation field. The preferable sensor geometry is a ring-core; both crystalline and amorphous ferromagnetic materials can be used for the core. Although a lot of fluxgate magnetometer types have appeared, the classical type with detection of the second harmonics by a phase-sensitive detector is the most popular. Fluxgate sensors are reliable and rugged and their applications range from space research to submarine detection.
Article
We have developed a cheap and simple trilayer printed circuit board (PCB)-based technology, adapted for the fabrication of fluxgate magnetic sensors. The two outer layers of the PCB stack comprise the electrical windings of the fluxgate, while the inner layer is made of patterned amorphous magnetic core with extremely high relative magnetic permeability (μr≈100,000). The output voltage and the sensitivity of the fluxgate devices have been studied as a function of the external field and of the geometry of the magnetic core. We have found a relatively high sensitivity of 18 V/T at an excitation current frequency of 10 kHz. The results obtained clearly show the potential of this miniaturised fluxgate device for application as a magnetic field sensor.
Article
A miniature fluxgate magnetic sensor has been demonstrated with microtesla resolution, a dynamic range of four orders of magnitude and a frequency response extending from DC to 1 MHz. The sensor comprises a millimetre long solenoid winding with a thin amorphous metal core, excited by an RF source. The system is illustrated reading magnetic card data across a 0.25 mm air gap and non-contact monitoring of milliampere currents flowing in PCB tracks
Article
The expression for the demagnetization of ringcores has evolved from the equation for the magnetic field inside simple-shaped objects whose magnetization is uniform. A modified expression that allows for the angular distribution of the magnetic field in the ringcore is developed from calculations for a infinite length tube. The modified expression is shown to provide a good fit to measured data. This modified equation is important when the product of the relative permeability and the demagnetization constant has a value around one or less
Article
This work treats two dc field sensors. The first sensor is the “covering fieldmill” that is employed to measure dc electric fields. The second sensor is the “fluxgate magnetometer” that is utilized to measure dc magnetic fields. An unusual approach is suggested to deal with the devices evaluation. It is shown that both devices can be associated with related ac field sensors-electric and magnetic. This association leads to modeling the dc sensors by Thevenin circuit models. It is then shown that in both cases the coupling between the sensors output circuitry and the measured field sources is due to series time-varied reactances. This enables a similar analytical treatment to both devices. Furthermore, it is also suggested that both sensors are related to the large family of antennas. As a result, an unusual way is found to relate the sensors output signal to the measured field. It is well known that the signal in electric antennas is related to the measured field times the effective antenna length. It is therefore relatively easily acceptable that also in the dc electric sensor case a similar relationship holds. The work, however, suggests that this relationship (that non relates the output signal to the measured dc magnetic field times the effective magnetic structure length) also holds in the fluxgate magnetometer case. An extension of this result is useful when attempting to measure nonuniform dc magnetic fields and is treated toward the end of the paper
Article
This paper presents a weak magnetic field measurement system using micro-fluxgate (FG) sensors and a sensor signal processing technique using the delta-sigma modulation in the negative feedback loop. The feedback of the lowpass filtered bitstream output of a delta-sigma modulator to the magnetic field improves system linearity, hysteresis, and stability. In spite of the fact that the second-order delta-sigma modulator is used, the third-order noise shaping can be obtained in the digital output bit-stream by the use of an integrator in the loop. This improves the SNR of the digital output. The measured noise of the implemented system meets the measured noise of the FG sensing element itself. The weak magnetic field in the range of the Earth's magnetic field is successfully measured. The nonlinearity error is less than 0.4% in the range of ±100 μT.
Article
. The calibration parameters of a vector magnetometer are estimated only by the use of a scalar reference magnetometer. The method presented in this paper differs from those previously reported in its linearized parametrization. This allows the determination of three offsets or signals in the absence of a magnetic field, three scale factors for normalization of the axes and three non-orthogonality angles which build up an orthogonal system intrinsically in the sensor. The advantage of this method compared with others lies in its linear least squares estimator, which finds independently and uniquely the parameters for a given data set. Therefore, a magnetometer may be characterized inexpensively in the Earth's magnetic-field environment. This procedure has been used successfully in the pre-flight calibration of the state-of-the-art magnetometers on board the magnetic mapping satellites rsted, Astrid-2, CHAMP and SAC-C. By using this method, full-Earth-field-range magnetometers (65536.0 ...
Article
The current-output fluxgate may be tuned by using a serial capacitor. Such tuning increases the sensor sensitivity in the situation when the pick-up coil has a low number of turns. We achieved a signal/feedthrough ratio improvement by a factor of 5. The measured parameters fit the simplified theoretical model within 20% deviation Keywords: magnetic sensors, magnetometer, fluxgate INTRODUCTION Fluxgate sensors serve for the measurement of DC and low-frequency AC magnetic fields. Their principle is based on modulation of the flux in the pick-up coil by changing the permeability of the ferromagnetic core by means of the AC excitation field [1]. In order to erase all the remanent magnetization of the sensor core and thus suppress memory effects, the core should be deeply saturated. High narrow peaks of the excitation current may be achieved by using a tuning capacitor either parallel to the excitation winding (for higher source resistance) or connected serially (for voltage-mode excitation...