Designing a Passive Retrodirective Wireless Sensor

This letter presents a wireless sensing approach implemented using a fully passive sensor element and a retrodirective antenna array. The utilized sensor is based on frequency modulation, and the proposed concept is investigated both theoretically and experimentally. Results of the study show that the designed sensor platform can be used to detect a change in sensor capacitance across a distance of up to 12 m. Furthermore, the retrodirective sensor can cover an angular range of almost –90<inline-formula><tex-math notation="LaTeX">$^\circ$</tex-math> </inline-formula> to +90<inline-formula><tex-math notation="LaTeX">$^\circ$</tex-math></inline-formula>, which is considerably broader than what can be obtained with a simpler passive RFID sensor.