Lowering the centre frequency of thick film PZT devices using acoustically matched backing layers

Our current research effort is directed towards fabricating PZT thick-films on a supporting substrate for use within industrial process monitoring equipment. The use of thick films in this application confers a number of important benefits. These include more straightforward device fabrication and the ability to fabricate transducers in more complex non-rectangular geometries. However, an important drawback of our current techniques is the low thickness (25-40¿m) of the deposited PZT film. The centre frequency of such a layer when used as a transducer is expected to be greater than 10MHz. Such high frequencies often make such transducers impractical for conventional B-scan imaging since overall beam penetration depth is severely curtailed. Ideally, to make such devices more practical a technique is required that allows the device centre frequency to be reduced without changing the thickness of the active PZT layer. In this paper we describe one such technique that uses multiple impedance matched ¿/2 backing layers to achieve the frequency reduction required.