Enhancement of SAW multi-sensor systems using a combination of time and frequency diversity techniques

Passive wireless sensors such as surface acoustic wave (SAW) devices are advantageous for applications such as heavy equipment monitoring and process control where harsh environments, moving parts, or limited battery lifetime preclude the use of wired or battery powered wireless sensors. In this work, Barker coded SAW delay lines with desirable autocorrelation properties were developed using time and frequency diversity to enhance the number of devices that may be accessed simultaneously. SAW device responses were modeled in MatLab and response correlations were simulated. Design parameters were selected to allow 100 sensors to be simultaneously operable in a single wireless system, and simulated and experimental results are presented. Results indicate that the combination of time diversity and frequency diversity techniques can significantly increase the number of individually identifiable passive sensors achievable over currently available systems.