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Arnold, P.; Moll, J. & Krozer, V. "Cognitive Radar for Microwave Breast Cancer Detection – A Simulation Study." In Microwave Conference (GeMIC), Aachen, Germany, 2014, pp. 1-4, Link
Abstract: Microwave imaging is a promising technology for breast cancer detection since it provides independent information about malignant tissue compared to ultrasound or X-ray mammography. Since the tumour can occur close to the surface or deep within the tissue it can be advantageous to alter the excitation signal adaptively for higher detection probability. The contribution of this paper is to investigate on a simulation basis how the adaptation of the excitation waveform in a cognitive radar (CR) framework can improve the detection of breast cancer in the sense of an automatic self-learning frequency adjustment.
Key words: Cognitive radar, microwave breast cancer detection, wave propagation, FDTD
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Scholz, M.; Rediske, S.; Nuber, A.; Friedmann, H.; Moll, J.; Arnold, P.; Krozer, V.; Kraemer, P.; Salman, R. & Pozdniakov, D. "Structural Health Monitoring of Wind Turbine Blades using Radar Technology: First Experiments from a Laboratory Study." In 8th European Workshop on Structural Health Monitoring (EWSHM), Bilbao, Spain, 2016, pp. 1-10, Link
Abstract: Millimeter-wave and terahertz technology have been used successfully in non-destructive testing (NDT) applications. While being safe for human beings and animals, a high resolution imaging in a non-contact and non-destructive way is possible due to the short underlying wavelength. The contribution of this paper is to demonstrate, for the first time, that imaging radar systems can be used effectively for structural health monitoring (SHM) purposes. For validation reasons, we have developed a laboratory demonstrator of a wind turbine structure for millimeter-wave measurements of rotating samples, with which we investigated glass-fiber samples. Hereby we can adjust the rotor speed, pitch and vertical incline angle. The radar sensor is attached to a nearby platform and mounted on a linear motor stage. This allows us to scan a rotating sample in vertical direction. The focus of our contribution is to demonstrate the feasibility of the radar-based SHM-concept with experimental measurements in order to investigate typical defects in rotating glass-fiber materials in the frequency band of 24-25.6 GHz. With our setup, we are able to identify typical defects of rotor blades.
Key words: Radar-based structural health monitoring, wind turbine blades, experimental validation
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Moll, J.; Krozer, V.; Arnold, P.; Dürr, M.; Zimmermann, R.; Salman, R.; Hübsch, D.; Friedmann, H.; Nuber, A.; Scholz, M. & Kraemer, P. "Radar-based Structural Health Monitoring of Wind Turbine Blades." In 19th World Conference on Non-Destructive Testing (WCNDT), Munich, Germany, 2016, pp. 1-8, Link
Abstract: Millimeter-wave and terahertz technology have been used successfully in non-destructive testing (NDT) applications in order to identify material defects such as delamination, heat damages and inclusions. The contribution of this paper is to extend the millimeter-wave and terahertz technology from a classical NDT methodology towards a continuous structural health monitoring (SHM) approach. For the first time, we will propose a scalable radar-based SHM-concept for operating wind turbine blades, where the transmitting and receiving antennas are placed at the tower and the antennas radiate the electromagnetic waves towards the rotor blades. Exploiting the rotation of the wind turbine and therewith a synthetic aperture with regard to the ISAR (inverse synthetic aperture) principle, all blades can be inspected with a sensor array in a non-contact and highly automated way. This approach has economic relevance not only for new but also for ageing wind turbine structures. Additionally, the same radar sensor can be applied for the detection of bat and bird activities close to the wind turbine which is highly relevant for the permission to operate existing and newly installed turbines. Based on the evaluation of the condition status of the turbine and the knowledge of the instantaneous bat and bird activity, new and harmonizing concepts for the operation of wind turbines can be established that account for the demands of the wind turbine operator (and hence public energy supply) as well as the protection of nature. This paper focuses on the frequency bands 24 GHz to 24.25 GHz and 24 GHz to 25.6 GHz which allow a high penetration depth in glass-fiber reinforced materials. Simulation results will be presented that illustrate the concept of differential radar imaging of material defects. Moreover, an experimental proof of principle study is presented from transmission measurements of a rotor blade tip sample of a real wind turbine structure.
Key words: Radar-based structural health monitoring (SHM), inverse synthetic aperture (ISAR), detection of bat and bird activities, millimeter-wave
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Arnold, P.; Moll, J. & Krozer, V. "Design of a Sparse Antenna Array for Radar-based Structural Health Monitoring of Wind Turbine Blades." In IET Radar, Sonar & Navigation, Volume 11, Issue 8, August 2017, pp. 1259-1265, DOI 10.1049/iet-rsn.2016.0355, Link
Abstract: The imaging performance of a sparse antenna array depends on the arrangement of the transmitting and receiving elements. In this paper, we systematically extend the work presented by Caba et al. [1] by a constraint optimization of the Y-shaped antenna arrangement. This will lead to an improved point spread function (PSF) with reduced sidelobes. It was found that a 30% improvement of the imaging performance using backprojection techniques could be achieved compared to conventional array designs. The optimized sparse antenna array has been used in a simulation study to evaluate its performance for radar-based structural health monitoring of wind turbine blades. Depending on the damage position, either close to the front or back side of the rotor blade, the localization error has been quantified as a function of its generally unknown effective relative permittivity.
Key words: Planar antenna arrays, condition monitoring, radar antennas, structural engineering, transmitting antennas, wind turbines, sparse array design, ISAR, point spread function
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Moll, J.; Arnold, P.; Mälzer M.; Krozer, V.; Pozdniakov, D.; Salman, R.; Rediske S.; Scholz M.; Friedmann H. & Nuber A. "Radar-based structural health monitoring of wind turbine blades: The case of damage detection." In Structural Health Monitoring, August 2017, pp. 1-8, DOI 10.1177/1475921717721447, Link
Abstract: Structural health monitoring of wind turbine blades is challenging due to its large dimensions, as well as the complex and heterogeneous material system. In this article, we will introduce a radically new structural health monitoring approach that uses permanently installed radar sensors in the microwave and millimetre-wave frequency range for remote and in-service inspection of wind turbine blades. The radar sensor is placed at the tower of the wind turbine and irradiates the electromagnetic waves in the direction of the rotating blades. Experimental results for damage detection of complex structures will be presented in a laboratory environment for the case of a 10-mm-thick glass-fibre-reinforced plastic plate, as well as a real blade-tip sample.
Key words: Radar-based structural health monitoring, radar sensing, wind energy, composite materials, damage detection
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Arnold, P.; Moll, J.; Mälzer M.; Krozer, V.; Pozdniakov, D.; Salman, R.; Rediske S.; Scholz M.; Friedmann H. & Nuber A. "Radar-based structural health monitoring of wind turbine blades: The case of damage localization." In Wind Energy (Wiley), Volume 21, Issue 8, August 2018, pp. 676-680, DOI 10.1002/we.2184, Link
Abstract: This short communication reports on a radar approach for structural health monitoring of wind turbine blades. Therefore, a bistatic frequency‐modulated continuous wave (FMCW) radar in the frequency range from 33.4 to 36.0 GHz has been developed and tested experimentally using a laboratory wind turbine demonstrator. A differential damage localization framework is presented here that exploits signal differences between measurements from the intact and the damaged structure for 3D imaging of the defect. We have achieved the localization of a 30‐mm cut in a glass fiber composite structure as well as the localization of a water pack at the backside of the specimen with a localization error of several centimeters.
Key words: radar-based damage localization, structural health monitoring, volumetric inspection, wind turbine blades
