Diffraction-free propagation of collimated SAW around a quartz ball

Principle and application of ball SAW devices

“…For [9,19,20], and a method to form a piezoelectric thin film on a non-piezoelectric material ball [8]. Multiple roundtrip characteristics on the crystal ball have been discovered experimentally.…”

“…Here, the numbers in parentheses represent the Euler angle designating the roundtrip route. In contrast, in a quartz or a langasite, the roundtrip characteristics for the route along the equator perpendicular to the Z axis (Z cylinder) are best [9]. Calculating roundtrip routes theoretically and predicting new routes has yet to be performed.…”

“…(9) ing IDT; ∆V: magnitude of the velocity dispersion as a result of the sensitive film; V p (k) = ω / k: phase velocity; α = ω/(2QV R ): attenuation constant. Equation (9) has its origin in the possibility of SAW on a ball to omit the effects of diffraction and reflection by using the fact that the wave front is preserved even after roundtrips. The waveform obtained as a result of using frequency dispersion by creating a PdNi selective film on the two-frequency ball SAW device [30] using a double electrode IDT that can generate harmonics at three times the fundamental frequency and reduce the reflection loss can be measured very precisely, as shown in Fig.…”

“…Moreover, the temperature effect compensation on the delay time was performed based on the measured temperature and a temperature coefficient of 12.5 ns/°C, which had been separately evaluated [9]. shows the results of the delay time change (∆t) when changing the hydrogen concentration.…”

“…In this situation, the authors' group discovered during research on defect inspection on ball bearings using SAW a phenomenon in which a SAW on a sphere naturally forms a collimate beam and can make over 100 roundtrips without loss due to reflection or diffraction [4][5][6][7][8] of this phenomenon the authors developed a ball SAW sensor [8][9][10][11] forming an electrode on a single crystal ball. Because high-precision measurements are possible based on the SAW velocity and attenuation, a hydrogen gas sensor with the widest sensing range of 10 ppm-100% concentration was created.…”