L. Reindl

University of Freiburg, Freiburg, Baden-Württemberg, Germany

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Publications (275)105.47 Total impact

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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 · 1.50 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 · 2.05 Impact Factor
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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 01/2015; 5(4):1067-1073. DOI:10.1109/JPHOTOV.2015.2434597 · 3.00 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 · 1.94 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 · 2.23 Impact Factor
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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: 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 · 1.07 Impact Factor
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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
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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, 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 · 1.21 Impact Factor
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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
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    ABSTRACT: This paper presents investigations of thermo-mechanical stress generated due to the integration process of Surface Acoustic Wave (SAW) strain sensors. A 3D finite element (FE) model, based on visco-elastic material measurements, is developed for thermo-mechanical stress computation. The simulation results are compared with experiments. Therefore, SAW strain sensors were mounted, the sensor response and the sensor deformation measured. The deviation between the simulated and measured sensor chip deflection is ≤ 14.4% for the full measurement range. Simulated thermo-mechanical stresses were used for the frequency shift computation of the SAW sensor device. The calculated frequency shift and the performed deformation measurement verified the correctness of the FE model.
    2014 15th International Conference on Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Microsystems (EuroSimE); 04/2014
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    Antwi Nimo, Joan Albesa, Leonhard M. Reindl
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    ABSTRACT: This work presents the effect of parasitic components on the performance of wireless RF energy harvesters. Since ambient RF power density is low, only optimal wireless RF energy harvesters will be able to power remote microwatt sensors. By knowing the effect of each parasitic component on the performance of wireless RF harvesters, components may be realized or selected that increases the overall efficacy of the harvester. The analytical and experimental investigation of the component parastics on the harvester output performance is compared at various operating frequencies; both at HF and UHF.
    Multi-Conference on Systems, Signals & Devices (SSD), 2014 11th International, Barcelona; 02/2014
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    ABSTRACT: This paper presents a novel torque sensing concept, based on resonant perturbation of an open parallel plate dielectric resonator. When torque is applied to the shaft, the air gap between the parallel plates fixed on a clamp system is changed, which in turn shifts the frequency of the dielectric resonator. Finite Element Method (FEM) simulations using HFSS (ANSYS®) and experimental results regarding the effects of air gap variation on the TE01δ mode in the 2-3 GHz range are presented to prove the sensing concept.
    2014 11th International Multi-Conference on Systems, Signals & Devices (SSD); 02/2014
  • Gerd Ulrich Gamm, Sebastian Stoecklin, Leonhard Michael Reindl
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    ABSTRACT: Sensor nodes often have to work for a long time with a single battery. A change of the power source is sometimes not possible or involves effort and costs. If the node needs to be accessible for communication at any point of time it must have a radio in permanent receive state. This depletes the battery in a few days. The contradiction between long lifetime and permanent accessibility can be solved by using a separate wake-up receiver on the node. In this work we present a sensor node with included wake-up receiver working in the 433MHz ISM band. Our solution consumes 2.8 μA of current in sleep state while still maintaining a realtime behaviour. The low current consumption is achieved by modulating a 125 kHz wake-up signal on the 433MHz carrier in the sender. In the receiving node a passive demodulation circuit extracts the wake-up signal and feeds it to an 125 kHz low frequency receiver IC. An additional 16 bit address coding is used for an selective wake-up of nodes.
    2014 11th International Multi-Conference on Systems, Signals & Devices (SSD); 02/2014
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    ABSTRACT: This paper presents the results of a German research project aiming at improving Urban Search And Rescue (USAR). It comprises two wireless search technologies for the detection and localization of trapped or buried unconscious victims and auxiliary assisting technologies. Victims can be localized through their cellular phone (GSM) if it is active, but it might be out of order. Results detecting inactive phones are presented. However, with this technology a victim without cellular phone cannot be detected. In this case, a ground-penetrating, continuous wave radar can be used that is as well presented. A channel model for estimating signal disturbances in debris between victim and receiving antenna is proposed that aims at improving the accuracy of these technologies. Furthermore, the I-LOV system assists decision-makers by a mobile IT-system called FRIEDAA that allows gathering, processing, and representation of relevant information such as search results and personnel locations in real time. Therefore, infrastructure and inertial sensor based personal localization systems are presented.
    Ad Hoc Networks 02/2014; 13:69–82. DOI:10.1016/j.adhoc.2012.06.005 · 1.94 Impact Factor
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    ABSTRACT: The power conversion efficiency of photovoltaic devices depends strongly on the light spectrum and light intensity. Both parameters vary significantly between different environments and locations - indoors as well as outdoors. Since placement of energy harvesting devices is governed more by the intended functionality of the system than by optimizing with respect to light conditions, the knowledge of light conditions in different environments is necessary for the design and dimensioning of photovoltaic energy converters. With this paper we want to present a simple approach to systematically measure and analyze light conditions and energy availability in different environments and to provide the basis for the development of a database of 'typical' light conditions. This will help to understand the energy availability and the dimensioning and design of photovoltaic devices in energy harvesting systems.
    2014 11th International Multi-Conference on Systems, Signals & Devices (SSD); 02/2014
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    ABSTRACT: In this paper we present our acoustic indoor-localization system ASSIST (Acoustic Self-calibrating System for Indoor Smart phone Tracking) running on embedded ARM CPUs. The developed system uses acoustic signals beyond the audible range to localize COTS (commercial off-the-shelf) smart phones. The sound receivers installed with the infrastructure are connected using a Wi-Fi network. Furthermore, the sound receivers synchronize the clocks and exchange the time differences of arrival of the received sound signals from the Wi-Fi network. In this way, using an iterative multilateration algorithm, the locations of smart phones are calculated. We present our developed novel receiver hardware. The integrated single-board computer based on ARM replaces the external computer units to synchronize the receivers with the network and calculates the position via a TDoA (Time Difference of Arrival) algorithm. By powering the receivers via power-over-Ethernet the installation effort is minimized. The integrated inertial sensors of the smart phone can be used to calculate the position in a non-line of sight condition. Therefore different methods are available to support the position calculation for ASSIST.
    2014 11th International Multi-Conference on Systems, Signals & Devices (SSD); 02/2014
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    ABSTRACT: Recently developed wake-up receivers pose a viable alternative for duty-cycling in wireless sensor networks. Here, a special radio signal can wake up close-by nodes. We model the wake-up range by the unit-disk graph. Such wake-up radio signals are very energy expensive and limited in range. Therefore, their number must be minimized.
    Algorithms for Sensor Systems, Edited by Flocchini, Paola and Gao, Jie and Kranakis, Evangelos and Meyer auf der Heide, Friedhelm, 01/2014: pages 35-50; Springer Berlin Heidelberg., ISBN: 9783642453458

Publication Stats

2k Citations
105.47 Total Impact Points

Institutions

  • 2004–2015
    • University of Freiburg
      • Department of Microsystems Engineering (IMTEK)
      Freiburg, Baden-Württemberg, Germany
    • Carinthian Tech Research AG
      Villach, Carinthia, Austria
  • 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
  • 1988–1998
    • Siemens
      München, Bavaria, Germany