P3M-4 Phase Shift of Traveling Rayleigh Wave by a Surface Acoustic Wave Motor Slider

Surface acoustic wave motor has already shown a superior potential. However, the efficiency from the electrical input to mechanical output is still low. To improve the efficiency, an energy circulation driving method has been proposed and demonstrated. In this method, the traveling SAW is initially excited by two phases power source of IDTs. The excited traveling wave propagates the stator. Then the wave is received by one unidirectional IDT, to convert into electric energy; the energy is circulated to the front of the stator and transduced to traveling wave again. It is very important that the circulated wave and the initially excited wave are added in phase to efficiently excite the Rayleigh wave. On the other hand, it has been found that Rayleigh wave beneath the slider is scattered, so that the phase of the wave shifts from the designed value. This phase shift affects on the addition of the waves. Phase shift decreases the efficiency of the motor. So we need to know the characteristics of the phase shift in order to design the motor with high efficiency. From several experimental results, it has been found that the phase shift is related to the projections parameter of the slider. The relationship between the slider projections contact, friction phenomenon and the phase shift was investigated by numerical simulation using the finite element method. Two dimensional FEM analysis in time domain was carried out to simulate the wave propagation from driving points through a preloaded silicon slider. Contact and friction simulation was applied to the boundary condition between the stator and the slider projections. As the result, we obtained values of phase shift down to -5 degrees up to 100 degrees. Large preload and large contact areas caused large phase shift. These results were close to the experimental results