Edge-bonded surface-acoustic-wave transducer array

A new type of transducer array has been designed and built for imaging surface defects in metals such as aluminum. The array is formed by edge bonding a piece of piezoelectric material to a substrate of the same material as the sample to be tested. The individual elements in the array are formed by photolithography, and each element acts as an edge-bonded surface wave transducer. The array has 32 elements resonant at a center frequency of 3.1 MHz with a round trip 6-dB bandwidth of 65%. Each element has a two-way insertion loss of 14 dB and a ± ° 3-dB acceptance angle. Because of the good acoustic impedance match between the piezoelectric material and the substrate material, the array does not need to be slotted. Electrical isolation between individual elements is achieved by depositing ground strips between the elements.