| 摘要 |
A broadband ultrasonic transducer has a layer of piezoelectric material sandwiched between respective layers of backing and matching material. The piezoelectric element is coupled to a pair of electrical terminals, across which a varying voltage is produced. The piezoelectric layer has a structure such that in response to the varying voltage, a forward-propagating wave emanating from its back surface does not destructively interfere with a forward-propagating wave emanating from its front surface when the frequency of the waves is an even multiple of the half-wave frequency of the particular piezoelectric layer. This effect can be attained by roughening the back surface of the piezoelectric layer or by spatially varying the piezoelectric coupling in the thickness direction in a portion of the piezoelectric layer which is proximate to the back surface. <IMAGE> |
