SAW Multi-Sensor System with Temperature and Range

This paper explores the effect of time overlapping multiple Bragg reflectors on the waveform of a coded, passive SAW sensor. Typical SAW sensors utilize serial reflectors, or chips, with a constant waveform shape; however, by using a multi-track SAW configuration the overlap of chips can be optimized for a desired waveform independent of bandwidth. Theoretical results for common signal envelopes are discussed and fabricated results on YZ-LiNbO3 are presented. By properly designing the chip overlap an arbitrary envelope and weight can be achieved. These techniques are used to design a new type of orthogonal frequency coded (OFC) SAW sensor. The updated coding technique decreases device response length while preserving code diversity and bandwidth as compared to a traditional, serial OFC layout. Results of these devices in a multi-sensor system show the ability to simultaneously track temperature and range, with 4 concurrent devices tracked at distances between 5-14 meters. Single sensor operation at a range of 14 meters is highlighted with a range determination accuracy of 0.25 meters (at +/-3 degrees C).