High-Performance SAWR Strain Sensor With Piston-Mode Operation

Compared with apodization, the piston-mode technique is a preferable solution to suppress the spurious transverse modes in surface acoustic wave (SAW) devices. This paper extends the technique to the SAW resonator (SAWR) strain sensors to achieve a high performance, that is, conquer some negative influence in the wireless strain sensing system caused by the spurious modes, such as low signal to noise ratio (SNR), high misreading rate and demodulation difficulty. The principle of piston-mode operation was presented and a modified expression was given for primary design of the piston-mode waveguide, which takes into account the anisotropy difference in different electrode regions. SAWRs based on the Al/ST-quartz with the conventional and two common piston-mode configurations were designed, simulated, fabricated and measured. The experiments to evaluate the wireless performance and strain sensitivity of the SAWR strain sensors with different electrode configurations were performed.