Optimization of wireless sensors based on intermodulation communication

Intermodulation communication principle has been recently developed to wirelessly read-out passive sensors. Intermodulation communication sensors reply the sensor information at an intermodulation frequency when interrogated by a reader device with two tones. This paper derives an analytical expression for optimizing the electrical circuitry of such a sensor. The derived equations are verified by harmonic balance simulations. An optimized sensor is designed and fabricated and experimentally characterized. Results show that 1% change in the sensor capacitance can still be detected at a 13 m-distance and the read-out principle could enable an extreme resolution at shorter distances (less than per mille below 5 m). A wireless electrocardiography measurement is demonstrated.