Modal Analysis of Structures Using a Millimeter-Wave Sensor

Millimeter-wave (mmWave) sensors are being actively researched and developed for sensing vibrations in construction, infrastructure, and machinery. Moreover, vibration modal analysis, including mode shape identification, is used to detect structural deterioration. This study examines the feasibility of vibration modal analysis using mmWave sensors. The laser Doppler vibrometer (LDV) and camera-based methods are often used as a noncontact vibration sensor for vibration modal analysis. Compared to these methods, mmWave sensors are less expensive and easier to miniaturize; however, they have a low spatial resolution. This study experimentally verifies the potential to use mmWave sensors for modal analysis, including mode shape identification, under the condition that the reflection response can be narrowed down to a single point by considering the surface reflectivity of the object. An aluminum alloy plate was excited sinusoidally at specific frequencies. A mmWave sensor and an LDV, as a reference, were used to measure the vibrations of the specimen at multiple points by changing their positions. The root mean square error for all points was at most 2.2 µm against a maximum displacement of 67.5 µm, confirming that vibration modes were measured accurately using mmWave sensors under appropriate conditions.