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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.