Feasibility study on ultrasonic lateral displacement measurement for structural health monitoring

In structural health monitoring, measuring the relative lateral displacement of the structure is essential for direct damage detection. Although large numbers of studies have been made on the development of the range finder utilizing an optical sensor, little attention has been given to the measuring method for lateral displacement. We propose a novel measurement method for directly measuring the lateral displacement of the structures by means of the air-coupled ultrasound. The measurement system is composed of two flat-type air-coupled ultrasound transducers and a steel wire as a target. The ultrasound transducers are immobilized on a fixed point, whereas a steel wire is separately arranged on the opposite side. When the steel wire is displaced laterally to the ultrasound detectors, the lateral displacement is calculated by taking advantage of the intensity ratio of the reflected ultrasound waves. The accuracy of the lateral displacement measurement is experimentally assessed by conducting a laboratory test. The estimated displacement value in the far field region of the transducer agrees well with the reference. The result shows that the developed displacement measurement method will be useful for the health diagnosis of structures.