【摘要】 <正>一、引 言 近年来,声表面波卷积器因其高速信号处理能力而引人注意。其中利用材料非线性效应作成的弹性卷积器,因其结构简单、造价低廉而尤其受人重视。然而,由于弹性非线性系数比较小,因而通常要用大孔径叉指换能器来激励宽的声束,而后设法压缩束宽,使得互作用区内有高的声强。从弹性卷积器的要求来看,考虑压缩效果的指标主要是:在尽量小的距离内达更多还原

【Abstract】 In this letter, the foaused surface acoustic wave field which is excited by an IDT fabricated in the shape of a circular arc and propagating on the metallized surface rather than on the free surface of the TZ-LiNbO3 is visualized hy means of the Schlie-ren method. Prom the photographs of the wavefronts taken by using a pulse laser as the light source and of the intensity distribution taken by using He-Ne laser, the total focusing procedure, the wavefronts and the intensity distribution in the focal region, and the rapid change of the phase near the first pair of the minima are demonstrated. These informations are important for the investigators who devote to study the focusing phenomena.Two parameters, i.e., the focal length and the focus width are measured. It is shown that the foical length formed on the metallized surface is smaller than that formed on. free surface by a factor of 0.7, and the focus width is the same. It means that the focusing performance on the metallized surface is more efficient. In addition, the feature of being a plane wave in the focal region (more than 30 wavelengths) is quite good, and it is impor-tant for the SAW elastic convolvers.更多还原