| 摘要 |
PURPOSE:To improve both the one-way property and the converging property of the ultrasonic beam, by securing a special relation between the space among the fingers of the roller screen type electrode and the phase of the application voltage and the space among the electrode fingers. CONSTITUTION:A pair of roller screen type electrodes 3 and 4 of the inter-digital structure are provided on the upper surface of the piezoelectric substrate 1 having a thickness less than the length of the ultrasonic wave, and the plane electrode 4 is provided at the side touching the liquid surface 5. The electrodes 3 and 4 are asymmetric at the space between the adjacent electrode fingers. Then the electric signal, which has a sum of 180 deg. of the phase difference between the electric signals applied to the electrodes 3 and 4 and the phase distance of the lower space among the electrode fingers, is applied to the electrodes 3 and 4. Thus the sound wave of sintheta= Vw/VL (theta: direction of sound wave to be radiated; Vw: sound speed in liquid; VL: rhm wave speed in piezoelectric substance) is radiated in a single direction. Furthermore, the theta is varied by changing the narrow space between the electrode fingers. In this connection, the ultrasonic beams can be converged by securing a proper relation among the spaces mentioned above. |
