Fraunhofer Institute for High Frequency Physics and Radar Techniques FHREnergy-efficient high-frequency sensor for production
The microcontroller-based radar sensor µRADAS allows for micrometer-precise and non-destructive measurement of distances, contours, and surfaces in real-time and under challenging conditions. The system enables spot investigations as well as tomographic imaging, facilitating resource-efficient quality monitoring during production.
Are there plastic or glass fragments in the chocolate running off the production line? Have production-related defects such as air inclusions occurred in the plastic pipe? To answer such questions, X-ray methods like computed tomography are currently employed. However, these require strict safety measures and X-rays struggle to distinguish materials with similar attenuation coefficients. In other words, inclusions like glass or plastic fragments in chocolate are hardly detectable in an X-ray image.
µRADAS: Resource- and energy-efficient, sensitive, and non-ionizing
Researchers at Fraunhofer FHR have addressed these challenges with the µRADAS technology. "Terahertz technology can penetrate non-conductive materials, allowing it to be used similarly to X-rays for imaging and tomographic quality assurance," says Sabine Gütgemann, head of the department at Fraunhofer FHR. "Protective measures are unnecessary, as radar waves do not ionize." Another advantage over X-rays is that the terahertz radar can differentiate materials with similar attenuation coefficients, such as glass and chocolate. The system captures not only the amplitude of the signal but also the phase information, making the edges between materials clearly visible. The frequency range can be realized through various front-ends either at 60 to 90 gigahertz or 120 to 160 gigahertz, depending on the desired resolution. Ultimately, the higher the frequency of the radar waves, the more precise the measurement. To generate three-dimensional images, the sample is rotated during measurement, and the sensor is moved up and down. "We have already developed a feasibility demonstrator: even a small, cost-effective sensor can achieve tomographic imaging," explains Gütgemann.
However, µRADAS is by no means limited to imaging methods. The system can also secure production with single-channel micrometer-precise distance measurements at rates of up to four kilohertz. For example, in steel processing: mounted on both sides of the steel strip, it accurately measures the width of slabs or steel sheets, and fixed above and below the conveyor belt, it measures their thickness. Is the steel sheet too wide or too thin? With a compact size of 130 mm x 70 mm x 50 mm, the sensor can be used in places that were previously too tight for sensors. For such distance and thickness measurements, the sensor is already ready for industrial use, unlike in tomographic applications.