CDMA for wireless SAW sensor applications

A well known spread spectrum technique is used to get the sensor information from an individually addressed SAW sensor. Coded ID tag type and BPSK type SAW sensors are picked out of a number of sensors by correlating the received signal with the known code of a particular sensor. The ID-tag type and BPSK-coded SAW sensor's function is observed as a scaling of time and shape respectively. The time scaling factor is equal to the mechanical extension of the substrate of a sensor due to temperature, etc. This scaling factor is evaluated by use of correlative signal processing techniques. The principal concept, mathematical simulations, numerical estimations and finally an overview of the implemented SAW sensor system are shown. Preliminary results for readout of OOK and BPSK coded passive remote SAW sensors using the Wavelet Transform processed within a SAW convolver are presented.