Wireless SAW Sensor Temperature Extraction Precision

Surface acoustic wave (SAW) devices are suitable for use in harsh environments because of their ruggedness under radiation and extreme temperatures and ability to be configured as passive wireless sensors. This orthogonal frequency coded (OFC) sensor system consists of a transceiver that wirelessly interrogates the passive SAW sensor, which can be used in several types of environments. A modified radar equation is presented that can be used to estimate the signal power from the returned sensor signal as a function of practical parameters. The precision performance of the OFC passive wireless sensor, not previously investigated, is shown to be a function of signal-to-noise ratio as expected from an analog sensor; extracted temperature precision better than 0.001 °C is reported. Signal integration is an effective means to increase the precision and/or range of the wireless temperature extraction scheme when deciding if the OFC passive wireless sensing scheme will fit a particular application.