L. Reindl

University of Freiburg, Freiburg, Baden-Württemberg, Germany

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Publications (200)62.37 Total impact

  • [Show abstract] [Hide abstract]
    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):1484-1486. · 1.04 Impact Factor
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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 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. 01/2014; 13:69–82.
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    Quirin Hamp, Leonhard Reindl, Denise Güthlin
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    ABSTRACT: The objective of assisting with tasks and decisions during incident response is to reduce the risks to victims and rescue personnel while increasing the efficiency of the rescue operation. Handling uncertain information during urban search and rescue (USAR) missions represents additional stress to the decision-maker. The aim of this study is to identify the decision-making behaviour of rescuers during USAR missions to pinpoint trapped or buried victims in debris in order to design assistance technologies and decision-support systems that meet their needs. In 2010, a survey was conducted among 10-15 per cent of all German rescue personnel specialised in search tasks. One of the major results of this survey is that a subjective assessment of the reliability of information available from heterogeneous sources influences the rescuers' actions and that there is no methodology for decision-making involving uncertain information. In addition, the study found that compliance with procedures does not require assistance.
    Disasters 01/2014; 38(1):84-107. · 0.69 Impact Factor
  • 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
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    ABSTRACT: The use of duty-cycling in Medium Access Control (MAC) protocols effectively helps improving the energy efficiency of wireless networks. However, while the benefits of these protocols are unquestionable, most of them still suffer from overhearing and idle listening, two issues that prevent duty-cycled systems from achieving optimum energy usage, which is a crucial aspect in specific types of wireless networks such as Wireless Sensor Networks (WSN).Wake-up Radio (WuR) systems have been employed recently to overcome these issues. Under this approach, the nodes' MicroController Unit (MCU) and main radio transceiver are completely switched off and only activated when a secondary, extremely low-power receiver in the node is triggered by a particular wireless transmission. Wake-up Radio systems allow for drastic energy savings since receiver nodes are only activated on-demand, maximizing their battery lifetimes. In this paper, we have modeled and simulated a real, recent and promising WuR hardware platform based on its time and energy consumption characterization. By comparing such WuR approach to B-MAC and IEEE 802.15.4, two well-known and widely employed MAC protocols, we show it effectively out-performs the conventional WSN MAC approaches in terms of energy efficiency. To the best of authors' knowledge, this is the first study to include a comparative analysis for multi-hop networks based on a real WuR platform, which shows WuR systems represent an energy-efficient solution that also provides a good tradeoff between latency, packet delivery ratio and applicability..
    Proceedings of the 16th ACM international conference on Modeling, analysis & simulation of wireless and mobile systems; 11/2013
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    Antwi Nimo, Dario Grgić, Tolgay Ungan, Leonhard M Reindl
    Microwave Conference (EuMC), 2013 43nd European; 10/2013
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    ABSTRACT: This paper presents a strain transfer investigation for Surface Acoustic Wave (SAW) strain sensors. For evaluation, a SAW strain sensor is assembled with a pre-tested bond material for potentially high strain transfer on a test holder. The setup is stressed with an axially homogeneous strain up to 500 ppm. The strain transfer ratio is computed from the applied load, the reference measurements with foil strain gauge, and the measured SAW strain sensor signal. The strain transfer performance of the bond material is also investigated with respect to the temperature dependency in the range between 22 °C and 85 °C. At this elevated temperatures an average strain transfer ratio of 0.606 ± 0.7% was measured. Mechanical load cycling tests up to 1000 cycles are used for the evaluation of the elastic fatigue of the bond material. The effects of mechanical load cycling and aging of the bond layer are analyzed with the SAW strain sensor response. After 1000 mechanical load cycles the transferred strain into the SAW strain sensor is 0.582 ± 0.153%. Finally, the experimental results are compared with the results of a 3D FEM simulation which are deviating less than 10%.
    ASME 2013 International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems; 07/2013
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    ABSTRACT: The main idea behind this project is to provide a unified platform which will cover a complete process for embedded systems learning. A modular approach is considered for skills practice through supporting individualization in learning. This platform shall facilitate a novel development of universal approach in creative learning environment and knowledge management that encourage use of ICT. New learning model is challenging the education of engineers in embedded systems design through real-time experiments that stimulate curiosity with ultimate goal to support students to understand and construct their personal conceptual knowledge based on experiments. In addition to the technological approach, the use of cognitive theories on how people learn will help students to achieve a stronger and smarter adaptation of the subject. Applied methodology will be evaluated from the scientific point of view in parallel with the implementation in order to feedback results to the R&D.
    16th Euromicro Conference on Digital System Design DSD 2013, Santander, Spain; 06/2013
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    ABSTRACT: We present an approach for the localisation of passive receiver nodes in a communication network. The only source of information is the time when environmental sound or ultrasound signals are received. The discrete signals occur at unknown positions and times, but they can be distinguished. The clocks of the receivers are synchronised, so the time differences of arrival TDOA of the signals can be computed. The goal is to determine the relative positions of all receiver nodes and implicitly the positions and times of the environmental signals. Our proposed approach, the Cone Alignment algorithm, solves iteratively a nonlinear optimisation problem of TDOA using a physical spring–mass simulation. We present a geometrical representation of the error function, which is modelled by physical springs. By iterative relaxation of the springs, the error function is minimised. The approach is tested in numerous simulations, whereby our algorithm shows a smaller tendency to get stuck in local minima than a nonlinear least-squares approach using gradient descent. In experiments in a real-world setting, we demonstrate and evaluate a tracking system for a moving ultrasound beacon without the need to initially calibrate the positions of the receivers. Using our algorithm, we estimate the trajectory of a moving model train and of an RC car with a precision in the range of few centimetres.
    Journal of Location Based Services 06/2013; 7(2):121-144.
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    ABSTRACT: This paper presents a signal processing algorithm which accurately evaluates the SAW properties of a substrate as functions of temperature. The investigated acoustic properties are group velocity, phase velocity, propagation loss, and coupling coefficient. With several measurements carried out at different temperatures, we obtain the temperature dependency of the SAW properties. The analysis algorithm starts by reading the transfer functions of short and long delay lines. The analysis algorithm determines the center frequency of the delay lines and obtains the delay time difference between the short and long delay lines. The extracted parameters are then used to calculate the acoustic properties of the SAW material. To validate the algorithm, its accuracy is studied by determining the error in the calculating delay time difference, center frequency, and group velocity.
    IEEE transactions on ultrasonics, ferroelectrics, and frequency control 04/2013; 60(4):805-13. · 1.80 Impact Factor
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    ABSTRACT: Passive high-temperature sensors are a most promising area of use for SAW devices. Langasite (La3Ga5SiO14; LGS) has been identified as promising piezoelectric material to meet high-temperature SAW challenges. Because it is necessary to know the material behavior for an accurate device design, the frequency¿temperature behavior of Rayleigh SAW (R-SAW) and shear-horizontal SAW (SH-SAW) LGS cuts is investigated on delay line and resonator test structures up to 700°C by RF characterization. In the range of the 434-MHz ISM band, the (0°, 22°, 90°) SH-SAW cut shows thermal behavior similar to the (0°, 138.5°, 26.7°) R-SAW cut. Associated with the (0°, 22°, 31°) cut, in which SAWs present mixed types of polarization, the (0°, 22°, 90°) SH-SAW orientation might allow differential measurements on a single substrate. In the temperature range of 400 to 500°C, delay line test devices using the SH-SAW cut show a considerable drop of signal. Theoretical analysis indicates that this newly described behavior might be a result of anisotropy effects in this cut, occurring in case of any slight misorientation of electrode alignment.
    IEEE transactions on ultrasonics, ferroelectrics, and frequency control 04/2013; 60(4):814-23. · 1.80 Impact Factor
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    ABSTRACT: This paper presents a study on efficiency of Urban Search and Rescue (USAR) missions that has been carried out within the framework of the German research project I-LOV. After three years of development, first field tests have been carried out in 2011 by professionals such as the Rapid Deployment Unit for Salvage Operations Abroad (SEEBA). We present results from evaluating search teams in simulated USAR scenarios equipped with newly developed technical search means and digital data input terminals developed in the I-LOV project. In particular, USAR missions assisted by the ‘bioradar’, a radar system for the detection of humanoid movements, a semi-active video probe of more than 10m length for rubble pile exploration, a snake-like rescue robot, and the decision support system FRIEDAA were evaluated and compared with conventional USAR missions. Results of this evaluation indicate that the developed technologies represent an advantage for USAR missions, which are discussed in this paper.
    Advanced Robotics 02/2013; 27(5):337-350. · 0.51 Impact Factor
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    ABSTRACT: Recently, an acoustic waveguide sensor based on multiple mode conversion of surface acoustic waves at the solid-liquid interfaces has been introduced for the concentration measurement of binary and ternary mixtures, liquid level sensing, investigation of spatial inhomogenities or bubble detection. In this contribution the sound wave propagation within this acoustic waveguide sensor is visualized by Schlieren imaging for continuous and burst operation the first time. In the acoustic waveguide the antisymmetrical zero order Lamb wave mode is excited by a single phase transducer of 1 MHz on thin glass plates of 1 mm thickness. By contact to the investigated liquid Lamb waves propagating on the first plate emit pressure waves into the adjacent liquid, which excites Lamb waves on the second plate, what again causes pressure waves traveling inside the liquid back to the first plate and so on. The Schlieren images prove this multi reflection within the acoustic waveguide, which confirms former considerations and calculations based on the receiver signal. With this knowledge the sensor concepts with the acoustic waveguide sensor can be interpreted in a better manner.
    Sensors 01/2013; 13(3):2777-85. · 2.05 Impact Factor
  • M. Freunek, L.M. Reindl
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    ABSTRACT: In the above paper (ibid., vol 3, no. 1, pp. 59-64, Jan. 2013), there is an error in the scale of Fig. 1. The corrected figure should appear as presented here. The correct maximum efficiency following the detailed balance model is close to 30% for a halogen lamp and for an incandescent bulb, respectively, and a bandgap close to the one of Germanium. The fluorescent tube reaches 50%, and the white RGB LED and the Phosphor LED achieve 64% and 57%, respectively. The maximum photovoltaic efficiency is 72% when irradiated by a sodium discharge lamp.
    IEEE Journal of Photovoltaics 01/2013; 3(4):1464-1464. · 3.00 Impact Factor
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    A. Nimo, D. Grgic, T. Ungan, L.M. Reindl
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    ABSTRACT: This work presents Resistor-Capacitor-Crystal (RC-Quartz) oscillators for use as passive amplification in RF energy harvesters. Quartz crystals can provide inductive reactance with extremely high quality factor (Q). This high Q inductive reactance coupled to a capacitor can provide the needed resonance for voltage amplification with minimal in-circuit losses. Detailed theoretical analyses of the condition precedents necessarily for voltage amplification of the R-C-Quartz foscillators are presented. RF harvesters based on this approach are realized and characterized for voltage sensitivity and efficiency. The circuits were realized on FR4 substrates with commercially available components. By using this approach, DC voltage sensitivity of 1.9 V and efficiency of 55% is measured for 1 μW (-30 dBm) RF input power at a frequency of ~13.56 MHz.
    Microwave Conference (EuMC), 2013 European; 01/2013
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    ABSTRACT: This paper presents a novel indoor localization solution using a smart phone. Instead of building the inertial measurement unit (IMU), the integrated calibrated sensors inside the smart phone provide all the sensor information needed. Meanwhile, we avoid the complicated calibration process, when the calibration machines or workstations are not available. Since smart phones are meant to be held in hand, algorithms and methods based on walking speed reset can not be utilized. Therefore, correct orientation and step length information are indispensable. In this study, a modified Kalman filter based sensor data fusion was used to achieve accurate orientation data by detecting and minimizing the effect of magnetic field disturbance. Three methods are presented and compared to calculate each step length based on vertical acceleration using biomechanic model or empirical relation. The experimental results show that the proposed solution is capable of tracking the person indoors and to achieve a tracking accuracy of less than 0.3m.
    Sensors Applications Symposium (SAS), 2013 IEEE; 01/2013
  • Journal of Sensors and Sensor Systems. 01/2013; 2:73-84.
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    Martin Kasemann, L M Reindl, K Rühle
    Proceedings SENSOR 2013, Nürnberg; 01/2013
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    ABSTRACT: Energy-efficient communication is one of the main concerns of wireless sensor networks nowadays. A commonly employed approach for achieving energy efficiency has been the use of duty-cycled operation of the radio, where the node's transceiver is turned off and on regularly, listening to the radio channel for possible incoming communication during its on-state. Nonetheless, such a paradigm performs poorly for scenarios of low or bursty traffic because of unnecessary activations of the radio transceiver. As an alternative technology, Wake-up Radio (WuR) systems present a promising energy-efficient network operation, where target devices are only activated in an on-demand fashion by means of a special radio signal and a WuR receiver. In this paper, we analyze a novel wake-up radio approach that integrates both data communication and wake-up functionalities into one platform, providing a reconfigurable radio operation. Through physical experiments, we characterize the delay, current consumption and overall operational range performance of this approach under different transmit power levels. We also present an actual single-hop WuR application scenario, as well as demonstrate the first true multi-hop capabilities of a WuR platform and simulate its performance in a multi-hop scenario. Finally, by thorough qualitative comparisons to the most relevant WuR proposals in the literature, we state that the proposed WuR system stands out as a strong candidate for any application requiring energy-efficient wireless sensor node communications.
    Sensors 01/2013; 14(1):22-51. · 2.05 Impact Factor

Publication Stats

1k Citations
62.37 Total Impact Points


  • 2004–2014
    • University of Freiburg
      • Department of Microsystems Engineering (IMTEK)
      Freiburg, Baden-Württemberg, Germany
  • 2013
    • University of Applied Sciences Coburg
      • Institute of Sensor and Actuator Technology (ISAT)
      Landkreis Coburg, Bavaria, Germany
  • 2012
    • Evangelische Hochschule Freiburg, Germany
      Freiburg, Baden-Württemberg, Germany
  • 2006
    • Max Planck Institute for Solar System Research
      Göttingen, Lower Saxony, Germany
    • Tohoku University
      • Department of Nanomechanics
      Sendai-shi, Miyagi-ken, Japan
  • 2004–2006
    • Carinthian Tech Research AG
      Villach, Carinthia, Austria
  • 1988–2006
    • Siemens
      München, Bavaria, Germany
  • 2003
    • Paul Drude Institute for Solid State Electronics
      Berlín, Berlin, Germany
  • 1999–2003
    • Technische Universität Clausthal
      Bergstadt-Clausthal-Zellerfeld, Lower Saxony, Germany
    • University of Vienna
      Wien, Vienna, Austria
  • 1998–2000
    • Johannes Kepler University Linz
      • Institut für Nachrichtentechnik und Hochfrequenzsysteme
      Linz, Upper Austria, Austria
  • 1995–2000
    • Vienna University of Technology
      Wien, Vienna, Austria
  • 1996
    • University of Oulu
      • Electronics Laboratory
      Oulu, Oulu, Finland