Wirelessly sensing resonant frequency of passive resonators with different Q factors

This paper presents a method of wirelessly sensing the resonant frequency of passive resonators using modulated waveforms. A pulse signal with a relatively wide frequency spectrum is transmitted towards a passive resonator, which in turn, reflects energy back to the interrogator. After time-domain gating and processing, the resonant frequency of the passive resonator can be wireless detected. This technique can be used for developing high-temperature sensors within harsh environments where only passive devices, made of high-temperature-stable materials, can survive. Resonators with different Q factors are studied herein on the effect of wireless sensing distance. A wireless sensing system up to 20 cm sensing distance has been demonstrated.