Yasuhiko Nakagawa

Material constants of new piezoelectric Ta2O5 thin films

The first measurement of the material constants of Ta2O5 thin films is described. x‐axis‐oriented Ta2O5 thin films were deposited on fused quartz using the dc diode sputtering method. The material constants were determined from the phase velocity and the electromechanical coupling constant of the bulk waves and the surface acoustic waves propagating on the layered substrate.

Deposition of new piezoelectric Ta2O5 thin films and their surface acoustic-wave properties

A new technique for the deposition of the crystallized Ta2O5 thin films is described. Crystallized Ta2O5 thin films have been deposited on fused quartz substrates by reactive dc‐diode sputtering. Crystalline structure and piezoelectric properties of the Ta2O5 thin film were investigated. Surface acoustic‐wave properties, including a phase velocity, coupling coefficient, temperature coefficient of delay, and propagation loss, were measured.

New piezoelectric Ta2O5 thin films

Crystallized Ta2O5 thin films have been deposited on fused quartz substrates by reactive dc diode sputtering. Crystalline structures and piezoelectric properties of the films were investigated. The electromechanical coupling coefficient K2 of the surface acoustic waves was 0.5% for hk=1.0. This value is comparable to that for ZnO thin films.

Elastic‐surface‐wave temperature coefficients of delay line with ZnO thin film

The elastic‐surface‐wave device with a zero first‐order temperature coefficient has been fabricated on Pyrex glass by use of a ZnO thin‐film overlay. The second‐order temperature coefficient of ZnO/Pyrex glass was about 1.24 times as much as that of ST‐cut quartz and was similar in sign. It is shown theoretically that the dispersion is very low at a ZnO film thickness of hK∼1.7, which gives a zero first‐order temperature coefficient.

Suppression of bulk wave radiation from leaky surface acoustic waves by loading with thin dielectric films

The bulk wave, which is radiated into the substrate from the leaky surface acoustic wave (LSAW), can be suppressed by loading the substrate with a thin film of dielectric such as tantalum pentoxide (Ta2O5) and silicon dioxide (SiO2). Rotated Y-cut X-propagating lithium niobate (LiNbO3) is used for the substrate. For a certain range of the rotation angle, the attenuation of the LSAW can be suppressed by choosing the appropriate material and thickness for the film. For the free surface of 64° Y−X LiNbO3 with Ta2O5 film, and the metallized surface of 41° Y−X LiNbO3 with SiO2 film, the measured propagation losses decreased approximately to one-fourth to half of that of the sample without the thin film. It is shown that, even if the propagation path is a free surface, the particle displacement distribution in the LSAW is concentrated near the substrate surface by the loading with the thin film, as for the metallized surface. This result suggests that the bulk wave radiation in the LSAW excitation can be suppre...

Ultrasonic Motor Using Flexural Standing Wave

A flexural standing wave excited in elastic board has vertical and horizontal components of oscillation. By causing a collision between the two components the standing wave can drive a slider.

New excitation method of surface polaritons

We propose a new excitation method for surface polaritons of an evanescent mode which cannot be excited by the attenuated total reflection method. We designed and produced a thin‐film waveguide to excite surface polaritons of evanescent modes at a Ag‐SiO2 interface. If the wave number of the optical guided waves propagating in the dielectric thin‐film waveguide (SiO2/Ta2O5/SiO2) is equal to the wave number of the surface polaritons, then a coupling between the two modes occurs. We can confirm the excitation of the surface polaritons by an attenuation of the optical guided waves.

Rotary Ultrasonic Motor Using Symmetric Contour Vibration of Rectangular Plate

By restraining the center point in the side of a rectangular plate, symmetrical contour vibration can be excited which has nodal points at the centers of the sides. If this contour mode is used instead of the longitudinal mode in an ultrasonic motor, the vibrator can be fixed at the center of the side and will withstand high rotor pressure.

Reversible Ultrasonic Flat Motor Drived by Single Phase Driver

By using the coupled modes between longitudinal and flexural mode of flat vibrator, the possibility of a reversible ultrasonic flat motor drived by a single phase driver is assured. The single phase motor has simpler structure and driver than dual-phase motor.

Enhancement of photoelastic constant of optical thin film waveguide assisted by surface acoustic wave

In the present research, we proposed a method of controlling the photoelastic constant using surface acoustic waves, which had not previously been reported, and carried out experimental studies thereof. A Bragg diffraction was carried out to determine the photoelastic constants of Ta2O5. As a result, it is confirmed that the photoelastic constant of a Ta2O5 thin film undergoing a sputtering process, during which surface acoustic waves were excited on the substrate, was about 2.19-2.27 times larger than those of thin films on which surface acoustic waves were not excited.