Multiple access SAW sensors using orthogonal frequency coding

Orthogonal frequency coding (OFC) provides a novel method of coding SAW sensors for use in multi-sensor environments. The OFC approach is general and should be applicable to physical, chemical, and biological measurands. OFC sensors offer increased range due to enhanced processing gain and reduced power spectral density. In addition, a reduction in compressed pulse time ambiguity results in increased sensitivity when compared with single frequency signals of similar duration. Successful implementation of an OFC SAW sensor system requires optimization of parameters related to sensitivity and range for the measurand and environment of interest. Several device embodiments are shown, and a discussion of design parameters such as SAW coupling, strip reflectivity, attenuation, and temperature coefficient, and optimal materials for various applications are given. Experimental sensor data are shown and compared with coupling-of-modes (COM) model predictions