Development of a high-precision nano millimeter-wave radar system for non-contact bridge displacement monitoring

Precise displacement monitoring is essential for evaluating the safety and dynamic response of bridge structures under service loads. Conventional techniques, such as displacement gauges and GPS, are often constrained by installation complexity, limited accuracy, and sensitivity to environmental factors. To overcome these limitations, this study introduces a novel non-contact monitoring system based on a 60.25 GHz millimeter-wave radar chip. The system achieves high measurement precision and rapid deployment without direct attachment to the structure. Target indication using mean cancellation and hamming windowing, combined with advanced displacement identification algorithms based on ap-FFT, further enhances measurement precision. Additionally, a customized MATLAB graphical user interface (GUI) was further developed to facilitate real-time data collection and analysis. Rigorous testing commenced with controlled laboratory experiments, followed by validation against measurements from a fixed-action camera for displacement. The system's practicality was validated through field experiments on the Phoenix bridge subjected to live loading, emphasizing its efficacy in real-world scenarios. In field applications, the system demonstrated reliable accuracy, achieving a root mean square error (RMSE) of just 0.02 mm compared to validated measurements. In conclusion, this innovative radar-based system effectively addresses the need for accurate, non-intrusive, and easily deployable methods for evaluating bridge structural behavior. By seamlessly integrating modified radar technology with sophisticated displacement identification algorithms, this system proves its effectiveness across controlled environments and practical field applications.