| 摘要 |
<p>A piezoelectric crystal (12) has a concave active surface and a high acoustical impedance. A flat layer (15) of molded material having a low acoustical impedance faces the active surface of the crystal to form a space therebetween. An intermediate layer (16) of molded material having an intermediate acoustical impedance fills the space between the crystal and the flat layer. Preferably, the intermediate material has a sonic velocity near that of water, and the flat layer has a uniform thickness of approximately 1/4 of the average wavelength of the ultrasonic energy emitted by the crystal, A housing (10) supports the crystal, the flat layer, and the intermediate layer.</p> |
