Friction drive of an SAW motor. part V: Design criteria

Design criteria for the stable and durable operation of a surface acoustic wave (SAW) motor are discussed. The low electric conductivity and pyroelectricity of the lithium niobate (LN) stator used in the motor hindered the motor´s stability. We demonstrated that the use of LN whose conductivity had been enhanced by chemical reduction counteracted the instability caused by contact electrification and meniscus adhesion. The severe failure of the stator surface limits the durability of the SAW motor. Owing to the chemical inertness of LN, the surface failure of the stator was caused by mechanical stresses resulting from the indentation and sliding of the projections placed at the slider surface. The as-fabricated sharp edges of the projections are the obvious cause of failure. Thus, if the projections are necessary, a procedure in which the edges are worn off before operation is the only feasible method to correct this problem. Nevertheless, the optimum geometry to prevent surface failure was deduced as flat plane. The flat plane geometry was useful if the contact pressure is sufficiently large to diminish the effect of the layer of squeezed air between the surfaces.