L. Reindl

University of Freiburg, Freiburg, Baden-Württemberg, Germany

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Publications (296)108.97 Total impact

  • Tobias Volk · Sebastian Stöcklin · Adnan Yousaf · Leonhard M. Reindl ·
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    ABSTRACT: A precise measurement of two relative distances requires more sophisticated measurement schemes, which often demand two channels and consequently additional technical effort. Based on our current research on multi-resonator systems, we can demonstrate a novel method using two passive structures and a single transceiver. This presented method does not require an optical connection and is therefore robust against dust or other iron-free surroundings.
    Procedia Engineering 12/2015; 120:180-184. DOI:10.1016/j.proeng.2015.08.604
  • S. Stoecklin · T. Volk · A. Yousaf · L. Reindl ·
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    ABSTRACT: Inductive power transfer systems are widely used to supply the current generation of biomedical implants. However, the power transfer efficiency is highly dependent on both the mutual coupling of the coils and the load impedance of the implant side. To overcome the challenge of time-dependent coil orientation and load impedance changes due to different power consumption levels, a maximum efficiency point tracking (MEPT) system for inductive links is presented within this work. After characterizing the momentary mutual inductance of the transmission channel, the designed system calculates the optimum load impedance and performs a dynamic impedance matching by emulating this optimum load with an input voltage-controlled switching regulator. Therefore, the presented system is capable of extracting energy at the best case efficiency for a wide range of real loads. The implemented system features a small system size (14 x 14 mm2) and a low self-consumption of only 250 μW, while providing up to 100 mW to the load.
    Procedia Engineering 12/2015; 120:451-454. DOI:10.1016/j.proeng.2015.08.666
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    ABSTRACT: Wireless powering allows the implementation of active implanted medical devices (AIMD) without batteries being inserted. The power is commonly transferred by an inductive link, which exhibits a strong relation between efficiency and coil configuration. For example, the electro-magnetic coupling and consequently the transferable power rapidly decreases when the distance is larger than the biggest coil radius. To overcome this obstacle, we investigate an array of multiple equal small-sized electro-magnetic resonators, which not only provides wireless power to a distant position with higher efficiencies, but also allows reducing the dimensions of the terminal coils.
    Procedia Engineering 12/2015; 120:511-515. DOI:10.1016/j.proeng.2015.08.687
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    ABSTRACT: Unsynchronized localization systems based on the measurement of time (difference) of arrival require reliable time stamps of the received signal. Noise, frequency shifts, and echoes disturb the signal and induce measurement errors of the time stamp, which leads to localization errors. Furthermore, the line of sight (LOS) signal has to be distinguished from the echoes to avoid false signal tracking. The proposed method combines the information of an ultrasound transmission with the measured time stamp and estimates the identifier. In our approach, the ultrasound transmission system uses phase-shift keying to modulate the signal. The received symbols and the time stamps are tracked and fused by the Kalman filter to increase the signal-to-noise ratio of the fused symbols and improve the validity of the decoding. Hence, the bias of the received symbols is tracked and the tracking allows to distinguish between the LOS signal and the echoes. As a result, the data fusion reduces the packet error rate from 70% at a distance of 21 m to 4.5%. Moreover, the median error of the localization is reduced from 7 to 4.6 cm.
    IEEE Sensors Journal 10/2015; 15(10):5946-5953. DOI:10.1109/JSEN.2015.2452227 · 1.76 Impact Factor
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    ABSTRACT: In this paper we present two new motion capture sensors to monitor motoric dysfunction in laboratory animals. The parameters that are recorded by our system correspond to neurological deficits that are typical for multiple sclerosis (MS)-like symptoms in animals. Normally, quantification of motor impairment requires neurological examination and complex behavioral testing. However, to perform these tests is an error-prone and time consuming process. Therefore, a strong interest exists in the automation and objective analysis of motoric behavior. Our presented small, accurate, and lightweight motion sensors provides an optimal solution for this problem. The developed motion sensors have the smallest volume and weight requirements available at the moment to monitor motoric dysfunction of animals. The collected data from the sensor is more representative since the subjective human factor is minimized and the animal can stay in its usual environment rather than being placed in a separate observation cage. We present two wireless motion sensors. An active sensor is powered with battery and saving the data on a SD-Card. The second sensor works completely passive and is powered via electromagnetic field. The sensors provide full control over the data of a three-axis accelerometer, a three-axis gyroscope, and a three-axis magnetometer. The two principles were successfully tested in an initial animal experiment.
  • Timo Kumberg · R. Tannhaeuser · L. M. Reindl ·
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    ABSTRACT: In this article we present polarization diversity in the wake-up path of a low-power wireless sensor node. Due to antenna diversity, the node shows an improved wake-up signal strength and optimized sensitivity in a multipath propagation environment. We verify the design using simulations and di®erent measurement setups. The resulting combined antenna signal has a gain of +3 dB when both diversity antennas receive the same signal strength. In this case, the wake-up receiver has an improved sensitivity around ¡53:7 dBm. Furthermore, we introduce a smart antenna for the communication link by using just one extra antenna switch. The proposed design can be used for any wake-up receiver of this kind.
    PIERS Proceedings, Prague; 07/2015
  • Source
    Fabian Hoflinger · Jorg Muller · M. Tork · Leonhard M. Reindl · Wolfram Burgard ·

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    ABSTRACT: In this paper we present a novel indoor localization approach based on 868MHz radio landmarks and inertial sensor data as a guidance system for emergency responders. For the first time we use low-power wake-up technology to develop real-time capable landmarks that overcome the problem of limited landmark lifetime. While in sleep mode our landmarks have an overall power consumption of 5.6μW making them ready-to-use in case of an emergency for up to 8 years. The landmarks are small and cost-efficient and may be integrated into the building infrastructure, e.g. into smoke detectors. Additionally, we have developed a handheld device for firefighters which communicates with our landmarks by an initial radio wake-up call and subsequent measuring of the received signal strength (RSSI) of the response. The measurements are used as an input to estimate and display the positions of the firefighter and the landmarks using local optimization algorithms. Furthermore, our handheld device communicates with a body-mounted wireless micro-inertial measurement unit (μIMU) to receive the angular rate, acceleration and magnetic field information in all three dimensions improving the accuracy of positioning. With this easy-to-setup guidance system emergency forces can be more effective, and the duration of rescue operations is reduced, hereby improving both the safety of rescue forces and increasing the chances of disaster victims.
    Conference Record - IEEE Instrumentation and Measurement Technology Conference 07/2015; 2015:309-314. DOI:10.1109/I2MTC.2015.7151285
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    ABSTRACT: This paper investigates the use of emitter windows with varying passivation layers in an intensity range between 1 and 10−3 suns. The results are compared with a cleaved sample without emitter windows. It is found that the passivation of the nondiffused region outside the emitter windows is very important to reduce recombination. The surface passivation schemes investigated are the three most commonly used for solar cells: aluminum oxide, silicon dioxide, and silicon nitride. The aluminum oxide and silicon dioxide resulted in a reduction in edge recombination of 8 and 4.56 times, respectively. The silicon nitride passivation resulted in worse performance than the unpassivated sample, as a result of increased recombination. The impact of the thickness of the region outside of the emitter was investigated by reducing the outside area from a 2-mm border to a 200-μm border. The aluminum oxide sample was hardly influenced, while the silicon dioxide passivated sample suffered as the carrier was now able to travel to the edge and recombine. The performance of the silicon nitride passivated sample was improved with a reduction of the outside region. However, the performance is still reduced compared with the control sample with unpassivated emitter edges.
    IEEE Journal of Photovoltaics 07/2015; 5(4):1067-1073. DOI:10.1109/JPHOTOV.2015.2434597 · 3.17 Impact Factor
  • T. Aftab · A. Yousaf · J. Hoppe · S. Stoecklin · T. Ostertag · L. Reindl ·
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    ABSTRACT: This paper presents a wireless passive strain sensing concept that functions by detuning a dielectric resonator. It is shown how a high Q resonator functions as a wireless passive sensor when correctly matched with an antenna. Finite element and analytical models are compared with experimental data and the sensor cross sensitivity with respect to temperature and humidity are also explored. The sensitivity of the resonance frequency to the strain, temperature and humidity is measured to be 51.6 ppm/μm, 10.09 ppm/K and -0.65 ppm/% respectively.
  • S. Stocklin · T. Volk · A. Yousaf · J. Albesa · L. Reindl ·
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    ABSTRACT: This paper describes a size and tissue absorption based comprehensive approach to optimize a pair of coils for the purpose of wireless powering of brain implanted sensors. In the first step, the optimum transmission frequency is determined by considering tolerable coil size, power transmission efficiency and tissue absorption effects. After modeling the important quantities at the frequency of interest, a numerical analysis is performed, revealing a set of coils suitable for efficient inductive powering. This numerical analysis was verified by both FEM simulation and concluding measurements. All simulations account for the layered structure of the human head, modeling the dielectric properties with Cole-Cole dispersion effects. Furthermore, a strategy of boosting power transmission efficiency is covered in simulation and measurement, particularly the application of a ferrite shielding to the transmission coil. In consequence, a link efficiency of 80% at a coil separation distance of 5mm and 20% at 20 mm using a 10mm planar receiving coil can be achieved, contributing to a higher integration density of multi-channel brain implanted sensors.
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    ABSTRACT: Implants like brain pacemakers or brain computer interfaces (BCI) fundamentally requires an improved and efficient wireless power distribution system. This work therefore presents a novel concept based on an intermediate resonator, which provides the opportunity to power multiple implants and to minimize furthermore the dimensions of the external power transmitter. Numerical computations specify requirements to the antenna configuration and a model show the electrical behavior. Finally, a prototype system presents an initial implementation, allowing the evaluation of the concept.
    Instrumentation and Measurement Technology Conference (I2MTC), 2015 IEEE International, Pisa, Italy; 05/2015
  • Alexander Ens · Leonhard M Reindl ·
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    ABSTRACT: In decentralized localization systems, the received signal has to be assigned to the sender. Therefore, longrange airborne ultrasound communication enables the transmission of an identifier of the sender within the ultrasound signal to the receiver. Further, in areas with high electromagnetic noise or electromagnetic free areas, ultrasound communication is an alternative. Using code division multiple access (CDMA) to transmit data is ineffective in rooms due to high echo amplitudes. Further, piezoelectric transducers generate a narrow-band ultrasound signal, which limits the data rate. This work shows the use of multiple carrier frequencies in orthogonal frequency division multiplex (OFDM) and differential quadrature phase shift keying modulation with narrowband piezoelectric devices to achieve a packet length of 2.1 ms. Moreover, the adapted channel coding increases data rate by correcting transmission errors. As a result, a 2-carrier ultrasound transmission system on an embedded system achieves a data rate of approximately 5.7 kBaud. Within the presented work, a transmission range up to 18 m with a packet error rate (PER) of 13% at 10-V supply voltage is reported. In addition, the transmission works up to 22 m with a PER of 85%. Moreover, this paper shows the accuracy of the frame synchronization over the distance. Consequently, the system achieves a standard deviation of 14 μs for ranges up to 10 m.
    IEEE transactions on ultrasonics, ferroelectrics, and frequency control 05/2015; 62(5):905-914. DOI:10.1109/TUFFC.2014.006803 · 1.51 Impact Factor
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    Antwi Nimo · Tobias Beckedahl · Thomas Ostertag · Leonhard Reindl ·
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    ABSTRACT: In this paper, analytical modeling of passive rectifying circuits and the harvesting of electromagnetic (EM) power from intentionally generated as well as from ubiquitous sources are presented. The presented model is based on the linearization of rectifying circuits. The model provides an accurate method of determining the output characteristics of rectifying circuits. The model was verified with Advance Design System (ADS) Harmonic balance (HB) simulations and measurements. The results from the presented model were in agreement with simulations and measurements. Consequently design considerations and trade-off of radio frequency (RF) harvesters are discussed. To verify the exploitation of ambient RF power sources for operation of sensors, a dual-band antenna with a size of ~λ/4 at 900 MHz and a passive dual-band rectifier that is able to power a commercial Thermo-Hygrometer requiring ~1.3 V and 0.5 MΩ from a global system for mobile communications (GSM) base station is demonstrated. The RF power delivered by the receiving dual-band antenna at a distance of about 110 m from the GSM base station ranges from −27 dBm to −50 dBm from the various GSM frequency bands. Additionally, wireless range measurements of the RF harvesters in the industrial, scientific and medical (ISM) band 868 MHz is presented at indoor conditions.
    AIMS Journal 04/2015; 3(2):184-200. DOI:10.3934/energy.2015.2.184
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    ABSTRACT: A new RFID/NFC (ISO 15693 standard) based inductively powered passive SoC (System on chip) for biomedical applications is presented here. The proposed SOC consists of an integrated 32 bit microcontroller, RFID/NFC frontend, sensor interface circuit, analog to digital converter and some peripherals such as timer, SPI interface and memory devices. An energy harvesting unit supplies the power required for the entire system for complete passive operation. The complete chip is realized on CMOS 0.18 μm technology with a chip area of 1.5 mm × 3.0 mm.
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    ABSTRACT: We have investigated the acoustic properties of silicon dioxide thin films. Therefore, we determined the phase velocity dispersion of LiNbO3 substrate covered with SiO2 deposited by a plasma enhanced chemical vapor deposition and a physical vapor deposition (PVD) process using differential delay lines and laser ultrasonic method. The density p and the elastic constants (c11 and c44) can be extracted by fitting corresponding finite element simulations to the phase velocities within an accuracy of at least +4%. Additionally, we propose two methods to improve the accuracy of the phase velocity determination by dealing with film thickness variation of the PVD process.
    IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 04/2015; 62(4):736-743. DOI:10.1109/TUFFC.2014.006921 · 1.51 Impact Factor
  • Alexander Ens · Leonhard M. Reindl ·
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    ABSTRACT: Zusammenfassung Unsynchronisierte Ultraschall-Lokalisierungssysteme ermöglichen dezentrale Positionsbestimmungen, unabhängig von Steuerleitungen oder -signalen. Somit benötigt das gesendete Signal zusätzliche Informationen über den Sender. Auf diese Weise ist eine kostengünstige Messung der Verschiebung mehrerer Objekte in zwei Dimensionen möglich. Störungen durch Echos werden durch die Aufteilung der Daten im orthogonalen Frequenz-Multiplex (OFDM) auf das Ultraschall-Signal reduziert. Bei der Verwendung zweier Trägerfrequenzen zur Entfernungsmessung wird eine Standardabweichung von 0,4 mm erreicht. Die Kommunikation mit 5,7 kBaud ist bis zu einer Reichweite von 18 m möglich.
    tm - Technisches Messen 01/2015; 82(3). DOI:10.1515/teme-2014-0021 · 0.12 Impact Factor
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    ABSTRACT: Since 2011, an annual award system was instituted to recognize outstanding Sensors papers that are related to sensing technologies and applications and meet the aims, scope and high standards of this journal [1-4]. This year, the winners were chosen by the Section Editor-in-Chiefs of Sensors from among all the papers published in 2011 to track citations. Reviews and full research articles were considered separately. We gladly announce that the following eight papers were awarded the Sensors Best Paper Award in 2015.[...].
    Sensors 01/2015; 15(1):2228-2231. DOI:10.3390/s150102228 · 2.25 Impact Factor

  • IEEE Sensors Journal 01/2015; DOI:10.1109/JSEN.2015.2487606 · 1.76 Impact Factor
  • Sebastian Stoecklin · Adnan Yousaf · Tobias Volk · Leonhard Reindl ·

    IEEE Transactions on Instrumentation and Measurement 01/2015; DOI:10.1109/TIM.2015.2482278 · 1.79 Impact Factor

Publication Stats

2k Citations
108.97 Total Impact Points


  • 2004-2015
    • University of Freiburg
      • Department of Microsystems Engineering (IMTEK)
      Freiburg, Baden-Württemberg, Germany
  • 2012-2014
    • Evangelische Hochschule Freiburg, Germany
      Freiburg, Baden-Württemberg, Germany
    • Instrumentation Laboratory
      Lexington, Massachusetts, United States
  • 2000-2008
    • Technische Universität Clausthal
      • Department of Electrical Information Technology
      Bergstadt-Clausthal-Zellerfeld, Lower Saxony, Germany
  • 1998-2000
    • Johannes Kepler University Linz
      • Institut für Nachrichtentechnik und Hochfrequenzsysteme
      Linz, Upper Austria, Austria
  • 1995-1999
    • Vienna University of Technology
      • Institute of Sensor and Actuator Systems
      Wien, Vienna, Austria
  • 1988-1994
    • Siemens
      München, Bavaria, Germany