High-Precision Interferometric Radar for Sheet Thickness Monitoring

Contactless sensing plays an important role in today's highly automated industrial environment, as modern sensors allow for an increased product quality in high-speed manufacturing lines. Hereby, a measurement system for sheet thickness monitoring in aluminum and steel rolling mills is presented. The presented concept is based on a differential measurement principle using two cooperating six-port radar systems. The radio-frequency front ends are designed in a high-density substrate-integrated waveguide technology at a frequency of 61 GHz. Furthermore, a detailed analysis of nonideal behavior of monostatic six-port radar front ends is presented. Moreover, the measurement principle is evaluated in a simplified measurement setup and the results are compared with the previously presented theory. Finally, an overview of modern sensing technology for steel rolling mills is presented and compared with the proposed measurement system considering the important aspects, i.e., update rate, precision, and thickness limit.