Ultra wide band surface acoustic wave (SAW) RF ID tag and sensor

A new and novel spread spectrum approach employing orthogonal frequency coding (OFC) for a SAW sensor/tag is presented. This approach provides ultra wide band operation, multi-device interrogation, and reduced loss as compared to conventional SAW CDMA approaches. A traditional SAW CDMA tag consists of an input transducer that launches a surface wave on the substrate towards an array of single frequency collinear reflectors that reflect the wave back to the input after providing ID coding within the reflections. The OFC embodiment uses an appropriate wideband input transducer that launches a SAW towards a collinear multi-frequency reflector bank which encodes the ID information. The sensor information is encoded by interaction of the SAW with delay path changes due to temperature and other measurands. This novel OFC SAW approach enables multiple coded chips to have high reflectivity since the orthogonal frequency chips appear nearly transparent to others; yielding low reflector loss, minimal inter-chip distortion and both phase and frequency encoding.

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