Multiple apodized self-correlating tapped delay line for ID-tag and sensor applications

A special SAW device design, derived from conventional tapped delay lines and optimized for wireless interrogation as a two-terminal ID-tag and sensor, is presented. The working principle is based on superposition of the correlation signals of multiple apodized transducer pairs that are connected in parallel. In the device, every transducer (tap) works as both, receiver and transmitter. Design rules for calculating the apodization of multiple transducers for a given PSK-code sequence are discussed under consideration of second order effects. Optimization criteria for low-loss design of diffraction-compensated devices are addressed. Measurement results for designs with and without diffraction compensation are shown and device characteristics are derived from the results. The measured ID-tag samples were fabricated on a 128°-YX-LiNbO₃ substrate to operate at 433.92 MHz