Wireless pulse echo interrogation of an AC electric potential resonator sensor

In this paper, a wireless interrogation method based on pulse-echo technique is demonstrated for passive resonator based sensors. This technique can be employed for the measurement of time varying measurands. The measurand studied in this paper is a 60 Hz AC electric potential that varies the resonance frequency of a passive, resonator sensor. The resonance frequency shifts in response to applied potentials due to a varactor that is coupled to the cavity. The interrogator sends radio frequency pulses to the resonator and records the ringback received from the resonator. The wireless interrogation system is designed for the frequency range of 2400-2500 MHz in the ISM band. The pulses that contain the RF signal have a repetition frequency of 1.5 MHz for a resonator with a quality factor of 500. The maximum interrogation distance is then theoretically calculated as 15.75 m for a maximum resolution of 20 kHz corresponding to a potential shift of 100 mV.