Intermodulation Read-Out Principle for Passive Wireless Sensors

This paper presents a general intermodulation read-out principle for passive wireless sensors. A sensor utilizes a mixing element, such as a varactor, and it can be equipped with a capacitive, inductive, or resistive sensor element. When the sensor is illuminated with signals with two frequencies, it replies the sensor data at an intermodulation frequency. An analytical expression for the intermodulation response of the sensor is derived and verified by simulations. The concept is demonstrated at 1.2 GHz.