Design Method of Antenna Sensor for Displacement Monitoring by Encoding Notch Frequency in Cross-Polarized Signal

In this paper, a passive and wireless displacement sensor, which comprise spiral resonator, microstrip line, receiving and transmitting antenna, is proposed. The sensor utilizes internally coupled resonators to encode deformation information in the echo signal. The spiral resonator, coupled to the microstripe line, acts as a stopband filter, introducing amplitude attenuation and the phase ripple at its resonant frequency. The spiral resonator is set up as two separate components, and the relative motion between the two components changes the size of the resonator and thus the resonant frequency. Furthermore, the receiving and transmitting antennas are set to cross polarization to avoid interference from the reflected signal in the wireless inquiry. And the wireless measurement accuracy of the sensor can be improved by identifying multi-dimensional electromagnetic characteristic parameters of the received echo signal. The equivalent circuit model of the sensor is established to demonstrate the sensing principle. The finite element analysis of the sensor was performed in High Frequency Structure Simulator (HFSS). The simulation results show that the change of the resonant frequency of the sensor is approximately linear with the deformation of the spiral resonator, and the sensor has high sensitivity up to 300 MHz/mm.