L. Reindl

University of Freiburg, Freiburg, Baden-Württemberg, Germany

Are you L. Reindl?

Claim your profile

Publications (318)112.55 Total impact

  • Metin Erd · Frank Schaeffer · Milos Kostic · Leonhard M. Reindl
    [Show abstract] [Hide abstract]
    ABSTRACT: Information gathering in tunnels, buildings, bridges, etc. during disasters is of vital importance in speeding up rescue efforts and for protecting the fire fighters. The collected data can be used by the emergency services in the planning of rescue operations and allocation of human resources at a local level. In this article we present design and implementation of a wireless sensor network, which consists of energy-efficient wireless sensor nodes with an integrated ultrasonic sensor, which establish a collision free data transmission in an emergency scenario. The developed network was tested in a field experiment in an explosion within a building to confirm its functionality and reliability. The wireless sensor network was able to pass critical data to the emergency units to initiate the rescue procedures during this disaster scenario.
    No preview · Article · Feb 2016 · International Journal of Disaster Risk Reduction
  • Source

    Full-text · Article · Jan 2016
  • Tobias Volk · Sebastian Stöcklin · Adnan Yousaf · Leonhard M. Reindl
    [Show abstract] [Hide abstract]
    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.
    No preview · Article · Dec 2015 · Procedia Engineering
  • Source
    S. Stoecklin · T. Volk · A. Yousaf · L. Reindl
    [Show abstract] [Hide abstract]
    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.
    Preview · Article · Dec 2015 · Procedia Engineering
  • Source
    [Show abstract] [Hide abstract]
    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.
    Preview · Article · Dec 2015 · Procedia Engineering
  • Source
    M. Schulz · E. Mayer · I. Shrena · D. Eisele · M. Schmitt · L. M. Reindl · H. Fritze
    [Show abstract] [Hide abstract]
    ABSTRACT: The full set of electromechanical data of langasite (La3Ga5SiO14) is determined in the temperature range from 20 to 900 °C using differently oriented bulk acoustic wave resonators. For data evaluation a physical model of vibration is developed and applied. Thereby, special emphasis is taken on mechanical and electrical losses at high temperatures. The resulting data set is used to calculate the properties of surface acoustic waves. Direct comparison with experimental data such as velocity, coupling coefficients and propagation loss measured using surface acoustic wave devices with two different crystal orientations shows good agreement.
    Preview · Article · Dec 2015
  • [Show abstract] [Hide abstract]
    ABSTRACT: To realize in-situ structural health monitoring of critical infrastructure such as bridges, we present a powerful, but also low power and flexible, wireless sensor node utilizing a wake-up transceiver. The sensor node is equipped with several kinds of sensors, such as temperature, pressure and acceleration for in-situ monitoring of critical infrastructure. In addition to these commonly used sensors in wireless sensor networks, some nodes are equipped with global navigation satellite system receivers (GNSS) and others with tilt and acceleration sensors of very high accuracy that were developed by Nothrop Grumman LITEF GmbH. We present a low power wakeup multi-hop routing protocol that is able to transmit data with little overhead by supporting the use of wake-up receivers in combination with long-range communication radios. The wireless sensor nodes and the routing protocol are tested at a large-scale highway bridge in south-west Germany, where a prototype network was installed in June 2015 following a first test installation earlier in June at the same bridge. A gateway node equipped with a Global System for Mobile Communications (GSM) modem transfers the network data to a remote server located at the University of Freiburg.
    No preview · Conference Paper · Dec 2015
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present a novel system which measures the respiration rate using two three-axis accelerometers strapped to the chest and the back of a person. Respiration and heart rate are used as a measurement to determine an athlete's fitness level during the exercise phase. Common respiration rate measurement methods require devices which are mostly stationary or at least clunky and uncomfortable to wear for an extended period of time. By using techniques such as differential measurement, pre-measurement optimization, adaptive filtering and peak detection we are able to obtain respiration rate even when the athlete is running fast. Our system is low-cost, small, and, by using a digital signal processor, fully capable of processing the data in an online way. Results are compared with a reference spirometer and have shown a very low normalized root mean square error (NRMSE) down to 1.42 %. Additionally, the heart rate of an athlete can be measured with the same sensor setup and similar methods.
    Full-text · Conference Paper · Nov 2015
  • Sebastian Stoecklin · Adnan Yousaf · Tobias Volk · Leonhard Reindl
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper describes the complete mathematical optimization process of an inductive powering system suitable for the application within implanted biomedical systems. The optimization objectives are thereby size, energy efficiency, and tissue absorption. Within the first step, the influence of the operational frequency on the given quantities is computed by means of finite element simulations, yielding a compromise of power transfer efficiency of the wireless link and acceptable tissue heating in terms of the specific absorption rate. All simulations account for the layered structure of the human head, modeling the dielectric properties with Cole-Cole dispersion effects. In the second step, the relevant coupling and loss effects of the transmission coils are modeled as a function of the geometrical design parameters, enabling a noniterative and comprehensible mathematical derivation of the optimum coil geometry given an external size constraint. Further investigations of the optimum link design also consider high-permeability structures being applied to the primary coil, enhancing the efficiency by means of an increased mutual inductance. Thereby, a final link efficiency of 80% at a coil separation distance of 5 mm and 20% at 20 mm using a 10-mm planar receiving coil can be achieved, contributing to a higher integration density of multichannel brain implanted sensors. Moreover, the given procedure does not only give insight into the optimization of the coil design, but also provides a minimized set of mathematical expressions for designing a highly efficient primary side coil driver and for selecting the components of the secondary side impedance matching. All mathematical models and descriptions have been verified by simulation and concluding measurements.
    No preview · Article · Nov 2015 · IEEE Transactions on Instrumentation and Measurement

  • No preview · Article · Oct 2015
  • [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.
    No preview · Article · Oct 2015 · IEEE Sensors Journal
  • Source
    [Show abstract] [Hide abstract]
    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.
    Full-text · Article · Sep 2015
  • [Show abstract] [Hide abstract]
    ABSTRACT: We present a powerful, but nevertheless low power and flexible, wireless sensor node utilizing a wake-up transceiver. The sensor node is equipped with several kinds of sensors, such as temperature, pressure and acceleration to monitor critical infrastructure. In sleep state, the node consumes only around 9 µW. We present a wake-up multi-hop routing protocol that supports the use of wake-up receivers in combination with long-range communication radios. The wireless sensor nodes and the routing protocol are tested at a large-scale highway bridge in south-west Germany, where a prototype network was installed in June 2015. A gateway node equipped with a Global System for Mobile Communications (GSM) modem transferred the network data to a remote server located at the University of Freiburg.
    No preview · Conference Paper · Sep 2015
  • Timo Kumberg · R. Tannhaeuser · L. M. Reindl
    [Show abstract] [Hide abstract]
    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.
    No preview · Conference Paper · Jul 2015
  • Source
    Fabian Hoflinger · Jorg Muller · M. Tork · Leonhard M. Reindl · Wolfram Burgard

    Full-text · Dataset · Jul 2015
  • [Show abstract] [Hide abstract]
    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.
    No preview · Article · Jul 2015 · Conference Record - IEEE Instrumentation and Measurement Technology Conference
  • [Show abstract] [Hide abstract]
    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.
    No preview · Article · Jul 2015 · IEEE Journal of Photovoltaics
  • [Show abstract] [Hide abstract]
    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.
    No preview · Article · Jun 2015
  • S. Stocklin · T. Volk · A. Yousaf · J. Albesa · L. Reindl
    [Show abstract] [Hide abstract]
    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.
    No preview · Article · Jun 2015
  • Source
    [Show abstract] [Hide abstract]
    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.
    Full-text · Conference Paper · May 2015

Publication Stats

3k Citations
112.55 Total Impact Points

Institutions

  • 2003-2015
    • 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
  • 1996
    • University of Vienna
      Wien, Vienna, Austria
  • 1988-1994
    • Siemens
      München, Bavaria, Germany