Low voltage operation of 2D ultrasonic arrays for NDT

The use of ultrasonic array transducers for nondestructive testing is presently growing rapidly, supported by the introduction of several new commercial array controllers. However, practical problems with the flexibility of 1D arrays have been realized. For example, it is impossible to skew the beam on curved surfaces without losing acoustic coupling. As 2D ultrasonic arrays allow 3D beam steering, including skewing, they are therefore of major interest for NDT. However, using conventional excitation voltages of the order of 200 V with the many elements in 2D arrays is inconvenient. In contrast, low voltage operation allows direct interfacing with electronics and low power consumption for portable systems. In the work reported here, a 2D ultrasonic array has been produced, with 16 elements in a 4 x 4 matrix, using PZT 5A ceramic and epoxy resin for the piezocomposite plate, with an operating frequency of 1.46 MHz. The element size is 1.2 mm x 1.2 mm, and the edge-to-edge separation 0.4 mm. This array has been tested at excitation voltages of 3.3V. This evaluation over the arrays includes electro-acoustical characterizations (pitch-catch and displacement measurements) and electrical cross-coupling measurements. The results indicate that arrays made with monolithic piezocomposite material have much better performance for NDT than previous similar arrays made with monolithic ceramic and that low voltage excitation is viable, with low noise amplification and appropriate data analysis.