Multi-frequency excitation of Rayleigh waves using an elliptical reflector focusing structure and its application for measurement of the acoustic properties of liquids

This study describes multi-frequency Rayleigh wave excitation below 10 MHz, which is impossible with a conventional piezoelectric-single-crystal surface acoustic wave (SAW) device. To overcome this limitation, we utilized a SAW device with an elliptical reflector focusing structure (ELIPS). The prototype ELIPS SAW device excited a Rayleigh wave on a duralumin surface at 1.1 MHz, 3.4 MHz, 5.6 MHz, and 7.9 MHz in the single device. The maximum vibration velocities were 0.38 m s−1, 0.21 m s−1, 0.070 m s−1, and 0.034 m s−1, respectively, which suggests the possibility of high-power mechatronics applications. To demonstrate the usefulness of the multi-frequency SAW below 10 MHz in a single device, we measured the frequency dependence of leaky SAW attenuation with a liquid droplet. The result showed that the acoustic properties of the liquid could be successfully estimated.