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Current effects in magnetostrictive piezoelectric sensors
Abstract
Some important improvements in magnetostrictive piezoelectric sensors have been obtained by applying an alternating current to the ferromagnetic amorphous ribbon. First, we present a way to minimize the hysteresis in these devices using a demagnetizing current through the magnetic sample. Second, the current, at a frequency half that of the longitudinal piezoelectric resonance, is used to induce size changes in the high-magnetostriction amorphous ribbon, and these changes, which depend on the external magnetic field, can be read by the piezoelectric support. Then, with this configuration, it is not necessary to have a coil for the detection of a magnetic field.
... In order to avoid this limit, field modulation methods can be applied for magnetic field sensing. The principle of operation is based on the field-dependent couplings between the magnetization, strain and electric polarizations[3],[4],[5]. A ME composite can be driven at a given excitation frequency by using a sine wave magnetic field signal. ...
The mechanical noise limit of a strain-coupled magneto(elasto)electric composite has been investigated when a magnetic or an electric field modulation is applied to sense a low-frequency magnetic field and access dc field measurement capabilities. The sensitivity and noise of such a composite sensor were derived from constitutive equations based on the piezoelectric and ferromagnetic material properties. The analysis was used to evaluate the equivalent noise floor of the composite sensor and to explain the origin of noise by constituting a mechanically coupled electromagnetic model. Experimental measurements revealed a good fit with the proposed model. For example, an equivalent magnetic noise level of ~60 pT/Hz at 1 Hz with dc capability was achieved using an appropriate field modulation.
... Then, for low H/(2K) values, H can be easily determined by measuring the magnetization changes. This effect or the inverse one has been used to develop very sensitive magnetic sensors [18,19] that show high sensitivity and low noise. Recently, a commercial device based in this principle has appeared [20]. ...
A new generation of hybrid magnetic sensors is presented. These sensors inherit the principles of the piezoelectric–magnetostrictive sensors improving some of their deficiencies by using a stripe actuator instead of a single piezo ceramic. The hysteresis of these sensors has almost been reduced to zero in magnetic sensors using amorphous ribbons and is widely diminished when the amorphous material is directly grown over the stripe actuator. Therefore, the viscous interface between the magnetic and the piezoelectric material is avoided. In this work, we describe the characterization of both stripe actuators and amorphous materials and the performances of their magnetic sensors.
... In both superlattices, the strain effect plays an important role in deterring their ferroelectromagnetic properties. J.L. PRIETO et al. [30] presented a new working configuration for magnetostrictive – piezoelectric magnetic sensors. Magnetostrictive – piezoelectric sensors are very interesting because of their good characteristics such as their high sensitivity, great frequency response, easy construction, law cost etc. ...
Chemical compositions and basic properties of smart materials (ferroics, biferroics, multiferroics) are introduced in this paper. Single phase and composite ferroelectromagnetics are characterized in detail. Multiferroic ferroelectromagnetics are materials which are both ferromagnetic/ferrimagnetic/ antiferromagnetic and ferroelectric/ferrielectric, antiferrolectric in the same phase. As a result they have a spontaneous magnetization which can be switched by an applied magnetic field, a spontaneous polarization which can be switched by an applied electric field, and often there is some coupling between those fields. The physical mechanisms of the coupling process were analyzed. In the case of the ferroelectromagnetics in general the transitions method d electrons, which are essential for magnetism, reduce the tendency for off-center ferroelectric distortion. Such materials have all the potential applications of both their parent ferroelectric and ferromagnetic materials.
... The quasi-linear range covers AE5 Oe and it is magni®ed in the inset of the ®gure; the sensitivity is approximately 25 mV/Oe. The curve shows a small coercivity that can be easily removed using an ac technique [8]. ...
A new integrated magnetic sensor, which is based on a micro-patterned spin valve bridge design, is described in this paper. The main advantage of the design is that an adjacent soft magnetic layer guides the magnetic flux, allowing a balanced bridge sensor to be sensitive to the direction of the external magnetic field. This new design avoids some of the additional circuitry and processing steps required in previous spin valve-based field sensors. We report a significant increase in the device sensitivity (∼15 mV/(VxOe)), even in non-optimised prototype devices compared to other commercially available lake NVE (15 mV/(V·Oe)).
This paper presents the results obtained with a prototype of a magnetostrictive-piezoelectric magnetic sensor where the ferromagnetic material has been grown by sputtering over the piezoelectric support where a copper layer has been previously deposited and electrolitically polished. In this way, the coupling between the piezoelectric and the ferromagnetic materials is stronger than that obtained by using a viscous fluid between both materials, as it is used to be. The most significant advances are the good sensitivity of 0.5 mV/μT for a 1.5-μm-thick ferromagnetic layer and the important reduction of the magnetic hysteresis due to the piezoelectric vibration.
A review of the engineering theory and the sensing element applications of the magnetostrictive delay line (MDL) technique is presented. The state of the art of magnetic materials and effects used in sensor design is overviewed and the operation of MDLs and their basic engineering properties are discussed. The resulting position, stress and field sensors based on this technique as well as their most significant applications are demonstrated. Finally, the industrialization process and the integration of the sensors with electronic circuitry as well as their evaluation with respect to the state of the art are discussed.
An amorphous bimetal ribbon consisting of magnetostrictive (Fe 40 Ni 40 B 20 ) and nonmagnetostrictive (Co 67 Fe 4 Cr 7 Si 8 B 12 ) layers was prepared by planar flow casting from a double‐chamber crucible. The effect of applied tensile stress on hysteresis loops and the surface domain structures of the stress‐relieved bimetal was investigated at room temperature. The hysteresis loops can be well explained by superpositions of hysteresis loops of the individual layers. Only the magnetostrictive layer is responsible for the influence of applied stress on magnetic behavior. At a certain stress, the magnetic anisotropy of the magnetostrictive layer abruptly changes from a hard‐ribbon‐axis to an easy‐ribbon‐axis type. This transition is accompanied by a change of domain structure and a sharp maximum of the coercive field. A simple model taking into account an interplay of the applied tensile stress with the compressive stress produced by thermal contraction after stress relief and/or by bending of the ribbon has been developed. The observed behavior can be well explained by the model. © 1995 American Institute of Physics.
A low‐frequency magnetometer has been constructed by interfacing a transversely field‐annealed amorphous metal ribbon to a resonating piezoelectric ceramic plate. Power spectrum measurements from 20 mHz to 1.0 Hz demonstrate a minimum detectable field of 8.7 pT/√Hz at 1.0 Hz with an approximate 1/f rise in the noise floor.
A new simple two-axis magnetometer has been developed. based on
the superposition of an amorphous ferromagnetic disc over a disc-shaped
piezoelectric support. At low frequencies, this device exhibits a
sensitivity of ~1.7 μV/μT when the external magnetic field is
orthogonal to one of the pick-up coils
Magnetic field measurements are very important for magnetic and
superconducting material research. Hall sensors have many advantages for
these measurements. They can also be used for magnetic field profile
measurements, which provide information about material homogeneity. We
have developed a three-axis Hall system which consists of three
perpendicular InSb Hall sensors for operation at room as well as
cryogenic temperatures. The active area of each sensor is 50 × 50
μm2. It is located at the corner edge of the substrate and
is suitable for detecting the spatial field profile within a cube of 225
× 225 × 225 μm3. The sensitivity of the sensor
is of the order of 20 mV/T and the offset voltage is < 50 μV for a
nominal control current of 10 mA. The problems of detecting the 3D field
components using planar Hall sensors and the oscillatory signal
behaviour due to quantum effects are discussed.
Soft magnetic fibers, 20 to 50 μm in diameter, have been cast by melt extraction. A giant magnetoimpedance effect (GMI) of about 60% was observed in a (NiCo)70FeSiBMn fiber driven by a rf current. The magnetic field and frequency responses of fibers depend on the density and the frequency of the drive current. The GMI effect at saturation decreases from 70% at 3 μA/μm2 to 55% at 30 μA/μm2. The saturation field increases with an increase in frequency, and is larger for lower current densities. These fibers can be used as sensing elements for a new generation of magnetic field sensors.
In this work we present a system to measure weak magnetic field, based on measurements of anhysteretic states of a ferromagnetic nucleus. In order to improve this magnetometric sensor, cores of amorphous ribbons with different characteristics have been tested. An electronic set-up has been built to perform the measurements and to avoid the sensor noise. The sensitivity of this device exhibits a large dependence on the magnetic anisotropy distribution of the core. A theoretical model has been deduced to explain the obtained results.
A fluxgate-like magnetometer using planar technology has been
developed. The performance is comparable to conventional fluxgates. Due
to minor inductive and capacitive effects of the planar coils, higher
exciting frequencies can be used
We discuss the magnetization processes in sensors based on the superposition of a magneto‐ restrictive amorphous ribbon over a piezoelectric plate. These devices show an unusual behavior of the null condition in the response curves, which we have related theoretically and experimentally to the coercive force of the magnetic sample and to changes in the magnetic domain pattern for frequencies near the longitudinal piezoelectric resonance frequency. © 1996 American Institute of Physics.
A novel magnetometer based on a classical xylophone resonator is described. The device consists of an aluminum bar supported by two wires placed at the nodal points of the fundamental resonance frequency. The wires also supply current of this frequency to the bar. In the presence of a magnetic field, the Lorentz force causes the resonator to vibrate. The amplitude of this vibration is proportional to a vector component of the magnetic field. The device is intrinsically linear, and by altering the drive current the sensitivity can range from nanoteslas to teslas. © 1996 American Institute of Physics.
An analysis of the sensitivity of a pnp lateral magnetotransistor (LMT) fabricated in bipolar technology is presented. In addition, the role of the n+‐buried layer is studied. The devices were designed as differential LMTs. It has been found that the change in sensitivity of pnp LMT increases by one order of magnitude if the n+‐buried layer is not omitted. The obtained sensitivity is the highest ever reported for a pnp LMT.
A study about the influence of an electric current flowing through an amorphous ribbon Fe40Ni40P14B6 has been done. It has been found that the magnetization curves are strongly influenced by such a current (from 0 up to 5000 Hz). Bitter patterns under the action of the current have been observed in order to gain a better knowledge of these effects. The wall energy has been evaluated from a simple model.
Sensors are devices that convert one form of energy into another. Magnetics sensors are a sub-group of the above which make use of one of the magnetic principles for conversion, namely: the galvanomagnetic effect, the electromagnetic effect, the magnetoelastic effect, movement of domain boundaries, and the superconductive effect. Amorphous materials have been commercially available in ribbon (1973), in wire (1981) or in powder form (1983). The combination of good magnetic properties in the absence of magnetocrystalline anisotropy, and the mechanical strength of these alloys make them suitable for sensor applications. Amorphous materials are broadly classified into two categories, highly magnetostrictive and near-zero magnetostrictive types, both of which are extensively used in sensor applications. In this paper the uses of amorphous materials as a sensor material in the detection of force, displacement (angular or linear), vibration, acceleration, pressure, rotational speed, torque and temperature are reviewed, showing operating characteristics with typical results.
A simple and inexpensive magnetometer is presented which uses a piezomagnetic primary sensor together with a piezoelectric transducer to convert a magnetic field into an electrical signal. A linear operating range is achieved by employing a negative feedback configuration. The detection sensitivity is 1.5 x 10-4 A/m per Hz1/2at low frequencies.
A fluxgate magnetometer is presented which exploits the magnetic field dependence to the stress-driven magnetisation fluctuations in magnetostrictive metallic glass ribbons. A magnetometer constructed with an unannealed ribbon, a piezoelectric ceramic driving element and a 100-turn pick-up coil exhibits a minimum detectable magnetic field of 15 nT/¿Hz in the DC to 1 Hz bandwidth.
We present a new linear magnetic field sensor (MFS) made in standard CMOS technology with a sensitivity of 1.26 percent/mT (1 percent/T ≡ 0.01 T-1). The device is a dual-collector lateral magneto-transistor (LMT) with suppressed injection of the emitter sidewalls, confinement of the injection to the center bottom of the emitter-base junction, and double deflection of carriers. Desirable collector current levels can be set without major loss of sensitivity by choosing from a wide range of operating points.
This paper presents results on magneto-impedance (MI) in a
NiFe/Co/NiFe sandwich film of 0.2 μm thickness, which exhibits the
impedance change up to 8% for a field of 4 Oe at a frequency of 400 MHz.
The effect of voltage change with the field can be especially large
(~200% for 5 Oe) if the sandwich film is incorporated in a self
oscillation circuit which can be directly used for magnetic sensor head
applications. The comparative analysis of MI in a sandwich film and a
single magnetic layer is given, demonstrating that the sandwich
structure can show an increase in MI of about a factor of 6 over a
single magnetic layer and the maximum MI effect occurs at frequencies of
an order of magnitude lower
A complete theoretical analysis is presented of the operation of a
magnetoelastic amorphous metal low-frequency magnetic field sensor. This
directional magnetometer is a hybrid device consisting of a
piezoelectric plate, a field-annealed amorphous metal ribbon, and a
viscous fluid, and it exhibits a low-frequency magnetic field detection
level of 8.0 pT/√Hz at 1.0 Hz. The sensor may also be configured
as a first- and second-order gradiometer. The device analysis focuses on
the influence of the constituent materials on the magnetometer
performance, identifying potential noise sources and optimal design
parameters. This analysis may be applied to a variety of magnetoelastic
amorphous metal sensors, e.g. stress, strain, and torque sensors, and is
also useful in research concerning fundamental aspects of
magnetoelasticity. Experimental data are presented demonstrating the
performance of magnetometers constructed with amorphous metal ribbons
exhibiting striped and closure domain structures