Diffraction-free propagation of collimated SAW around a quartz ball

A ball SAW (surface acoustic wave) device was fabricated on a single crystal quartz ball of 10 mm diameter. There were four specific routes on the surface of the ball along which the SAW was excited effectively showing round trips with low attenuation factors. One route was called the "Z-axis cylinder", and the other three routes were trisymmetric meridians to the Z-axis of single crystal quartz ball. Their averaged velocities on "Z-axis cylinder" and other routes were 3.21*10³ m/s and 3.57 - 3.61*10³ m/s, respectively. On the "Z-axis cylinder", we could detect a signal in the 300th turn, and observed changes of delay time of the signals due to the temperature variation.