Bidirectional excitation and detection of Rayleigh waves via two facing elliptical reflectors

This study describes the bidirectional excitation and detection of Rayleigh waves using two facing elliptical reflector focusing structures (ELIPS), in contrast to previous studies that have achieved only one-way excitation and did not demonstrate detection. First, the design of a proposed ELIPS surface-acoustic-wave (SAW) device is presented, and the relationship between the design parameters and SAW excitation performance is clarified. Next, finite element method simulations are presented, showing that 40 % of the energy of the incident dilatational wave is converted into a SAW and 60 % of the generated SAW is reconverted into a received dilatational wave. Finally, bidirectional SAW excitation and detection are demonstrated. In the experiment, a 5-cycle, 1  MHz burst signal with an amplitude of 10 Vpp was used to excite Rayleigh waves in both the forward and reverse directions. In the forward direction, a SAW vibration velocity of 5.4  mm/s was obtained and the received voltage reached 21 % of the applied voltage. In the reverse direction, the vibration velocity was 5.8  mm/s and the received voltage reached 22 %. These received voltage ratios are sufficient for sensing applications. Moreover, the response remained linear up to at least 140 Vpp, producing vibration amplitudes of 13 and 12 nm, adequate for high-power applications and with potential for further increase at higher input power.