To ensure the availability and operational safety of wind turbine blades, regular inspections are required according to specified maintenance intervals. As with all periodic inspections, damage that develops between two inspection dates remains undetected until the next inspection. In recent years, monitoring systems have therefore been developed that enable independent structural health monitoring (SHM) with permanently installed sensors. The most important representatives here include vibration analysis, acoustic emission testing and ultrasonic methods. In addition, it is necessary for an SHM system to distinguish between signal changes resulting from damage or changing environmental and operating conditions. The present work presents a new approach for the in-situ assessment of wind turbine blades via embedding radar networks in the frequency band from 58 to 63.5 GHz. Therefore, 40 FMCW (frequency-modulated continuous wave) radar sensors have been embedded into a wind turbine blade during manufacturing. This contribution provides additional information related to the hardware design of the sensor nodes, its preliminary testing and the specific implementation of the radar network during a fullscale fatigue test of a 31m long wind turbine blade [1]. Damage indicators can be formulated relative to baseline conditions to see the development of fatigue damage over time. Reference: [1] Simon, J.; Kurin, T.; Moll, J.; Bagemiel, O.; Wedel, R.; Krause, S.; Lurz, F.; Nuber, A.; Issakov, V. & Krozer, V., Embedded Radar Networks for Damage Detection in Wind Turbine Blades: Validation in a Full-scale Fatigue Test, Structural Health Monitoring, 2023, https://doi.org/10.1177/14759217231152815

This paper presents a direct sampling receiver with an adjustable bandpass filter for passive radar with FM radio. The adjustable bandpass filter allows the advantages of a direct sampling receiver, such as its good linearity properties, to be exploited without the use of additional attenuators at high signal levels, which leads to an increased noise figure, or narrowband filters with a fixed centre frequency, which limits the flexibility in the selection of the useful signal.

This paper presents a novel concept for achieving angular estimation and target separation using a bistatic single input single output mmWave radar system operating at 60 GHz. A simulation framework was designed to investigate the antenna configuration required for angle estimation using beam squinting. With this concept, two targets at the same distance and velocity can be separated in angle using power evaluation of range-Doppler plots with constant false alarm rate detection. The simulations were verified with measurements. This proof of concept paves the way to an affordable mmWave single input single output radar system with the capability of angle estimation complementing such systems usually limited to range-Doppler monitoring without angular separation.

This paper presents a 60 GHz MIMO radar system on a moving robot for person presence detection. Due to the movement of the robot, many environmental influences are added. For this purpose, various scenarios were created and 8,000 data frames were recorded and processed. A convolutional neural network (CNN) was trained and evaluated using this data. Ultimately this low-cost system achieves 97% accuracy in classifying whether a person is present or absent.

This work aims at a structural health monitoring (SHM) system using radar sensors at 60 GHz embedded in a wind turbine blade. For a reliable operation of the system, the influences of changes in the ambient climate on the embedded sensors has to be taken into account and shall thus be studied and analyzed. Three sensors are embedded for experiments and are exposed to a defined environmental state in a climate chamber. The signals for different target states are measured, processed and discussed. An evaluation of the dependencies shows how critical these influences are on radar signals and baseline-based SHM methods working with them. These results motivate the development and classification of compensation methods. The considered methods are a baseline selection method and a polynomial fitting approach. Both methods are exemplarily applied to the measured data. Finally the sensors are used to measure ice formation. Conclusions on the detectability of ice are made, as well as on its influence to other measurements.

This paper presents the design and experimental realization of a cooperative radar network for structural health monitoring (SHM) of wind turbine blades. For this purpose, 40 FMCW (frequency-modulated continuous wave) radar sensors operating from 58 to 63.5 GHz have been installed in a 31-m-long blade during manufacturing. A subset of 10 sensors is material-embedded in the core material of the blade, and the remaining thirty sensors are placed inside the blade on an inner rotor blade surface. The sensors are distributed over the entire blade based on previous high-frequency electromagnetic simulations. A full-scale fatigue test has been performed under controlled laboratory conditions. In addition, holes have been drilled into the blade by hand to represent a well-defined and relatively small damage. During the experimental campaign, measurements from the complete radar network have been transferred to a base station through a wireless communication link. Finally, it was demonstrated that fatigue as well as artificial damage could be detected accurately using the proposed damage indicator (DI) approach.

Mobile phone localization of buried victims in quick response search-and-rescue (SAR) operations require control over the radio network. To gain control via emergency fallback procedures, jamming the valid base stations in range is necessary. This publication introduces the concept and realization of a LTE jamming system, that can mask specific base stations by jamming the cell-specific reference signal. The selected jamming method allows low-power operation of the jammer for portable use.

This paper demonstrates a new noninvasive sensor system to acquire information about a beehives’ health using the micro-Doppler of a FMCW radar at 60 GHz. The possibility to track the presence of the queen bee as well as the general hive activity is demonstrated.

A new transceiver setup for joint communication and sensing (JCAS) application in V-band with a 3 dB bandwidth of 2.57 GHz is presented in this work. With new communication standards like 6G and a rising amount of wireless transmitted data, new transceiver setups for higher carrier frequencies and larger bandwidth need to be developed. The new transceiver setup has differential IQ input ports and a carrier frequency ranging from 57 GHz to 64 GHz. For the proof of radar and communication applications, the reflected IQ signal was detected, and the usability confirmed. This setup can be used for JCAS applications in meter range with high resolution and data rates.

Clock drift is a major challenge for most RF systems in the field. There are many different solutions to obviate or compensate clock drift in these applications, though most are very complex and expensive. In this publication we present an arbitrary clock source, that uses a hybrid phase-locked loop concept to compensate drift of an oven-controlled oscillator by using an integrated clock synthesizer circuit. This allows for a cost effective design, that can use global satellite navigation systems, internal and external temperature sources, an aging model and automatic frequency control information from RF transceivers as an error correction source for the clock drift.

This paper discusses a novel ultra low power sensor system for monitoring a beehives' health condition, which can be determined by measuring internal temperature and humidity variations. It comprises an autonomous battery powered sensor node which transmits the measured data over a 868 MHz wireless radio link. Expected runtime is greater than 2.1 years.

In this paper a frequency selective super heterodyne receiver with double conversion for passive radar with FM radio is presented. Multiple receiver channels allow the processing of eight useful signals. In addition, to minimize signal crosstalk, a low cost shielding cover is made of aluminum plates to avoid expensive milled work.

Joint communication and sensing (JCAS) combines radar and data transmission into one system. Applying this, a frequency modulated continuous wave (FMCW) radar is chosen for sensing and gets modulated by frequency shift keying (FSK) to transmit data. The transmission takes place at 60 GHz with a bandwidth of 5 GHz which leads to a high sensing resolution of 0.03 m. For comparison, the FMCW radar is evaluated without modulation, with an additional frequency offset and with FSK. The results show that FMCW radar with an additional frequency offset does not substantially impact the sensing functionality. The received FSK data were demodulated and could be reconstructed completely at a measuring distance of 1.9 m and with a bit error rate of 3.6 % at a measuring distance of 2.5 m. A JCAS system in V-band was developed and its functionality proven.

In this publication a miniaturized low-power radar system is introduced that allows detection, tracking and measurement of motorized vehicles passing a bicycle rider. The main focus of this paper is to show a system that is responding with a situation adapted modulation to different measurement requirements while keeping power consumption and BOM cost to a minimum. This is achieved with using an integrated 60 GHz radar and a STM32 ultra-low-power microcontroller for the required signal processing.

The present work describes the simulation procedure to determine an optimal sensor placement for RadCom (radar and communication) sensors operating in the frequency band from 57-63 GHz inside a wind turbine blade. Optimal placement means a full penetration and coverage of the blade as well as a communication path from every node to the blade’s root can be achieved. Furthermore, triple coverage is necessary to allow the localization of structural changes in the blade and its surface, such as ice aggretion. The sensors are partly applied to the surface and partly embedded in the core material of the rotor blade. In this way the blade can be monitored during the entire operation for structural health monitoring (SHM) purposes. The simulations take into account the transmission of waves, refraction, dispersion in the material and are based on material data obtained from measurements of rotor blade materials, as well as antenna data. The resulting sensor distribution is the basis for a prototype design of a 30 m long blade with embedded sensors for full-scale SHM testing. Since embedded sensors are not accessible after completion of the manufacturing process, the simulation results are key to the experiments success.

This work aims at radar sensors in the frequency band from 57 to 64 GHz that can be embedded in wind turbine blades during manufacturing, enabling non-destructive quality inspection directly after production and structural health monitoring (SHM) during the complete service life of the blade. In this paper, we show the fundamental damage detection capability of this sensor technology during fatigue testing of typical rotor blade materials. Therefore, a frequency modulated continuous wave (FMCW) radar sensor is used for damage diagnostics, and the results are validated by simultaneous camera recordings. Here, we focus on the failure modes delamination, fiber waviness (ondulation), and inter-fiber failure. For each failure mode, three samples have been designed and experimentally investigated during fatigue testing. A damage index has been proposed based on residual, that is, differential, signals exploiting measurements from pristine structural conditions. This study shows that the proposed innovative radar approach is able to detect continuous structural degradation for all failure modes by means of gradual signal changes.

This paper presents an embedded mm-wave FMCW-radar based sensor system designed to monitor the structural health of a wind turbine rotor blade. Special consideration is given to the evaluation of thermal performance and the possibility of correlating measurements with the current rotor blade orientation. The sensitivity of the sensor in its embedded state is analyzed and evaluated for system performance.

This paper presents a low power sensor node that is embedded into glass fiber composite material of rotor blades during production. The structural condition of the rotor blade is monitored by an integrated FMCW radar. The sensor can achieve a lifetime of 20+ years due to the longevity of a supercapacitor based energy supply. As the available power is low, special consideration must be given to energy saving and system uptime optimization. The concept was proven by embedding the sensor in epoxy resin and consecutively in test sheets produced like rotor blade material.

This paper presents a numerical study on the application of radar and communication (RadCom) sensor nodes operating in the frequency band from 57-64 GHz. The sensor nodes are embedded in the laminate of wind turbine blades, enable a quality inspection directly after rotor blade manufacturing as well as a structural health monitoring (SHM) throughout the service life of the blade. Given by a lack of dielectric properties for typical rotor blade materials, we have performed experimental studies on material characterization including glass fibre composites, balsa wood, infusion glue, etc. This material database serves as input for wave propagation simulations in a full scale 3D rotor blade model. The analysis also includes a parametric study on path losses as well as an optimal sensor placement strategy.

Most modern digital speech codecs are proprietary and do not give insights into their implementations. "Codec 2" is an open-source codec and opens up the possibility of application-tailored adaptations. In this publication a new 450 bit/s mode is introduced. It includes a pseudo-wideband mode that can be optionally enabled at the receiver without resulting in a higher bit rate. By sorting the codebook vectors a bit error rate of 10(-1) is still intelligible. An encoded audio transmission was tested with two low-power Sub-GHz transceivers in the 70 cm amateur radio band achieving a sensitivity of -130 dBm. For proofing the concept, a field test was conducted and compared to a propagation simulation.