Radar-based Mechanical Vibration Sensing for Structural Health Monitoring Applications: A Comparison of Radar Transceiver Measurements at 24GHz and 100GHz

Conventional strategies to measure mechanical vibrations from remote distance are based on Laser-Doppler-vibrometry (LDV). This technique is only rarely used in practical structural health monitoring (SHM) applications, due to the high costs of these devices. Radar technology represents a promising new approach towards in-situ SHM-scenarios with permanently installed sensors, because of the low costs of the radar-modules (only few Euros), the ability to measure mechanical vibrations behind barrier materials and the low attenuation which enables long distance measurements. In this paper, we report on an experimental study with two radar transceivers at 24 GHz and 94.3 GHz for mechanical vibration sensing in SHM-applications. Interesting here is that the radar transceiver at 24 GHz has low costs and shows similar performance compared to a laboratory radar-transceiver system at 94.3 GHz. The low costs makes this kind of radar sensor extremely interesting for a variety of SHM-applications. Results will be demonstrated here for mechanical vibration sensing behind a barrier material, i.e. a polystyrol foam. This measurement could not be performed with an LDV-approach, because the laser beam is not able to penetrate the barrier material. Additional results are shown for damage detection and for harmonic oscillation measurements with a shaker system. This approach demonstrates the principle to sense mechanical vibrations at microwaveand millimeter-wave frequencies behind a barrier material.