We tested two kinds of piezoelectric ceramics for small focusing ultrasonic generators. The radius of curvature of the ceramics are 8mm and 5.77mm. We measured acoustic pressure near the focus and visualized the ultrasonic field with the schlieren method. We investigated the effect of the radius of curvature on the focusing of ultrasonic wave. The result showed that better focusing is accomplished in the generator with the large radius of curvature. The experiments were simulated numerically using the finite difference method. The simulations showed the oscillating state of the edge of the ceramics affects the focusing of the ultrasonic wave.
