Locally passive hybrid sensing tags based on flexible substrates and surface acoustic wave devices

This paper describes the integration of surface acoustic wave (SAW) filters, microfabricated transmission lines, and sensors onto polymer substrates to enable a passive wireless sensor platform. Incident microwave pulses on the integrated antenna are converted to an acoustic wave via the SAW filter and transmitted to a notional impedance-based sensor, which for this work is a photodiode. Changes in sensor state induce a corresponding change in impedance resulting in a reflectance profile. Data collected at a calibrated receiver can be used to infer the state of the sensor. Based on this principle, light flux intensity is wirelessly sensed at distances up to 3.6 m.