A passive wireless displacement sensor for structural health monitoring of civil structures

摘要

A passive wireless displacement sensor suitable for use in civil structural health monitoring applications is presented. The sensor is based on a resonant electromagnetic cavity with one end of the cavity formed by a flexible membrane. A rod attached to the membrane causes the dimensions of the cavity to change when the rod is displaced. The change in dimensions causes a shift the resonant frequency of the cavity that is directly related to the displacement of the rod. In the example shown the shift is 7 MHz per mm for a cavity with a resonant frequency of 2450 MHz. Using a pulse echo interrogation technique resonant shifts of 100 kHz are resolvable. In the laboratory, displacements of 0.014 mm were measurable, with the distance between the interrogator and the sensor of up to 4.5 m.