L. Reindl

University of Freiburg, Freiburg, Baden-Württemberg, Germany

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Publications (286)105.42 Total impact

  • [Show abstract] [Hide abstract]
    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
  • 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
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    Fabian Hoflinger · Jorg Muller · M. Tork · Leonhard M. Reindl · Wolfram Burgard
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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
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    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: 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
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    ABSTRACT: Mice and rats make up 95 percent of all animals used in medical research and drug discovery and development. Monitoring of physiological functions such as ECG, blood pressure, and body temperature over the entire period of an experiment is often required. Restraining of the animals in order to obtain this data can cause great inconvenience. The use of telemetric systems solves this problem and provides more reliable results. However, these devices are mostly equipped with batteries, which limit the time of operation or they use passive power supplies, which affects the operating range. The semi-passive telemetric implant being presented is based on RFID technology and overcomes these obstacles. The device is inductively powered using the magnetic field of a common RFID reader device underneath the cage, but is also able to operate for several hours autonomously. Being independent from the battery capacity, it is possible to use the implant over a long period of time or to re-use the device several times in different animals, thus avoiding the disadvantages of existing systems and reducing the costs of purchase and refurbishment.
    Sensors and Actuators A Physical 11/2014; 221. DOI:10.1016/j.sna.2014.10.021 · 1.90 Impact Factor
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    ABSTRACT: Telemetry systems enable researchers to continuously monitor physiological signals in unrestrained, freely moving small rodents. Drawbacks of common systems are limited operation time, the need to house the animals separately, and the necessity of a stable communication link. Furthermore, the costs of the typically proprietary telemetry systems reduce the acceptance. The aim of this paper is to introduce a low-cost telemetry system based on common radio frequency identification (RFID) technology optimized for battery independent operational time, good reusability, and flexibility. The presented implant is equipped with sensors to measure electrocardiogram (ECG), arterial blood pressure, and body temperature. The biological signals are transmitted as digital data streams. The device is able to monitor several freely moving animals housed in groups with a single reader station. The modular concept of the system significantly reduces the costs to monitor multiple physiological functions and refining procedures in preclinical research.
    IEEE transactions on bio-medical engineering 10/2014; 62(2). DOI:10.1109/TBME.2014.2361856 · 2.35 Impact Factor
  • Matthias Knapp · Philipp Jäger · Werner Ruile · Ingo Bleyl · Leonhard M. Reindl
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    ABSTRACT: We use differential delay lines to extract the phase velocity of a SAW on a LiNbO3 substrate covered with thin SiO2 films which have been deposited by a plasma enhanced chemical vapour deposition (PECVD) and a physical vapour deposition (PVD) process. The variation in film thickness of the PVD process between the differential delay lines has to be corrected to a reference thickness which is done by signal processing. The accuracy of the results allows the determination of the elastic constants (c11 and c44) and the density ρ of the PECVD thin film within an accuracy of ±2.4% and of the PVD SiO2 process within an accuracy of ±4.1% by fitting corresponding simulations.
    IEEE International Ultrasonics Symposium; 09/2014
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    ABSTRACT: We propose an ultrasound communication system designed for time difference of arrival (TDOA) based indoor loca-lization. The concept involves an infrastructure of stationary and independent senders tracking mobile receivers. The main goal is pure line-of-sight (LOS) communication for correct localization. When ignoring the reception energy of multi-paths the transmission range is reduced to 20 meters and we need more devices to cover the same area (0.03 devices/m 2). Thus, for cost-effectiveness and easy installation, we focus in the sender design on low power consumption for long battery or even energy independent operation. Moreover, we use the energy efficient π/4-DQPSK modulation technique to send 8 data bits in 3.5 ms. An identifier in each message along with the reception time can be used for TDOA localization. The frame synchronization error for a distance of 20 m at 3 dB SNR is 11.2 ns. Thus, for speed of sound the distance measurement error is 3.7 µm.
    22nd European Signal Processing Conference (EUSIPCO 2014), Lisbon, Portugal; 09/2014
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    ABSTRACT: Today, the vast majority of personal communication devices, such as laptops, smartphones, and logically wireless fidelity (Wi-Fi) access points feature IEEE 802.11 chipsets. In turn, wake-up radio (WuR) systems are used to reduce the significant energy waste that wireless devices cause during their idle communication mode. A novel WuR system is introduced that enables any IEEE 802.11-enabled device to be used as a WuR transmitter without requiring any hardware modification. The corresponding developed WuR receiver achieves a remarkably low power consumption of 10.8 -W and operates in the Wi-Fi 2.4 GHz band. By means of thorough physical tests, it is shown that the proposed IEEE 802.11-based WuR system enables important energy savings.
    Electronics Letters 09/2014; 50(20-20):1484-1486. DOI:10.1049/el.2014.2468 · 0.93 Impact Factor
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    ABSTRACT: Time of arrival (TOA) based localization extracts the positions from the signal delay between senders and receivers in a network and puts high requirements on synchronization, in particular synchronization on the line-of-sight (LOS) signal. We propose an ultrasound based system with pure LOS synchronization and data transmission for sender identification. We use two carriers with 38 respectively 40 kHz in a baseband OFDM scheme and by comparison of the phase shift of both carriers we estimate with the Cramér-Rao lower bound a distance error between sender and receiver of 0.047 mm for a transmission range of 20 m. We transmit 8 bit in 1.5 ms where no inter-symbol interferences are expected in most practical scenarios for robust localization. When transmitting data in a communication system, the properties transmission delay and signal attenuation available as RSSI values can additionally be used for distance measurements between sender and receiver, which is the input for a localization system. However, the measured distance can be imprecise due to multipath propagation, since the signal strength has strong local fluctuations due to the wave characteristics and the reception time of the multipath signal is a mixture of all paths. In contrast, the line-of-sight (LOS) signal only represents the shortest path between sender and receiver where the signal attenuation and signal delay can be uniquely mapped onto the distance between sender and receiver. Thus, separating the LOS signal from the remaining signal paths can drastically improve the localization accuracy. We present a novel data transmission system for localization which transmits a short message in such a short time (1.5 ms) that the LOS path and the other paths do not overlap in time in practical scenarios. Thus, we can process the pure LOS signal at the receiver and ignore the signal of the remaining paths giving false information. Our ultrasound system uses two carriers in a baseband OFDM scheme to increase the data rate and keep the transmission time short. We focus additionally in this paper on precise frame synchronization at the receiver not only for a low bit error rate (BER) at low signal-to-noise ratio (SNR) and long transmission ranges but also to measure a precise signal delay
    18th International OFDM Workshop 2014 (InOWo’14), Essen, Germany; 08/2014
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    ABSTRACT: We have investigated the temperature dependent elastic constants of SiO2 and GeO2. For this purpose, the phase velocity of the layered system has to be calculated using surface acoustic wave (SAW) differential delay lines on LiNbO3 substrates. Both SiO2 and GeO2 have a positive temperature coefficient of velocity. The GeO2 layer shows a significant reduction of the phase velocity compared to SiO2 which yields to an improved energy trapping of the surface acoustic wave in the overlay. However, severe stability issues arise using the GeO2 layer.
    European Frequency and Time Forum; 06/2014
  • Timo Kumberg · R. Tannhaeuser · G.U. Gamm · L.M. Reindl
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    ABSTRACT: The available energy of wireless sensor nodes is limited due to the fact that they often operate on batteries and due to their small size. One approach to reduce power consumption of wireless sensor nodes, is to reduce their active time. This can be done by duty cycling or by using a wake-up strategy as presented by Gamm et al. 2012. In this approach, a node is inactive until it gets awaken by another node or an external event. The energy efficiency of the wake-up strategy depends on the energy consumed per wake-up message. In this paper we investigate the wake-up messages introduced by Gamm et al. 2012 to develop a method to reduce their duration from 13.2 ms to 2.26 ms, which corresponds to an energy saving of around 83 %. To examine sensitivity and wake-up range of the wake-up receiver for messages of different durations four message types of different lengths are tested. For three types, the receiver reaches a sensitivity of -50 dBm and a range of 45 meters. Using the shortest type of message, the wake-up range is around 30 meters.
    Sensors and Measuring Systems 2014; 17. ITG/GMA Symposium; Proceedings of, Nuremberg, Germany; 06/2014
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    ABSTRACT: With the development of new integrated circuits to interface radio frequency identification protocols, inductive air interfaces have become more and more important. Near field communication is not only able to communicate, but also possible to transfer power wirelessly and to build up passive devices for logistical and medical applications. In this way, the power management on the transponder becomes more and more relevant. A designer has to optimize power consumption as well as energy harvesting from the magnetic field. This paper discusses a model with simple equations to improve transponder antenna matching. Furthermore, a new numerical analysis technique is presented to calculate the coupling factors, inductions, and magnetic fields of multiantenna systems.
    IEEE Transactions on Magnetics 06/2014; 50(6):1-9. DOI:10.1109/TMAG.2014.2300042 · 1.39 Impact Factor
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    Fabian Hoflinger · Gerd Ulrich Gamm · Joan Albesa · Leonhard M. Reindl
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    ABSTRACT: In most home automation scenarios electronic devices like shutters or entertainment products (Hifi, TV) are constantly in a standby mode that consumes a considerable amount of energy. The standby mode is necessary to react to commands triggered by the user. To reduce the standby current we present a node that can be attached to the plug of electronic devices and that can turn them on and off. The node contains a wake-up receiver module that reacts to an acoustic 18 kHz tone and that switches the node from active to passive mode. In active mode the node can turn on or off the respectively power source for the device under control. The acoustic wake-up signal can be sent out by any kind of speaker which enables a commercial smartphone to act as an universal acoustic remote control without line-of-sight requirement. Our wake-up receiver consists of an 18 kHz LF receiver and an MEMs-Microphone. A wake-up range of 7.5 m using a smartphone as a sender was achieved. The overall power consumption was measured to 56 μW in standby mode. Using a 230 mAh coin cell as the energy supply a theoretical lifetime of 500 days is possible.
    2014 IEEE International Instrumentation and Measurement Technology Conference (I2MTC); 05/2014

Publication Stats

2k Citations
105.42 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
  • 2006
    • Max Planck Institute for Solar System Research
      Göttingen, Lower Saxony, Germany
    • Tohoku University
      • Department of Nanomechanics
      Sendai-shi, Miyagi-ken, Japan
  • 2003–2005
    • Paul Drude Institute for Solid State Electronics
      Berlín, Berlin, Germany
  • 2000–2003
    • Technische Universität Clausthal
      • Department of Electrical Information Technology
      Bergstadt-Clausthal-Zellerfeld, Lower Saxony, Germany
  • 2002
    • Electronic Components, Modules and Systems (EPCOS)
      München, Bavaria, 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