2D ultrasonic arrays with low-voltage operation for high density electronics

Abstract

The use of ultrasonic array transducers for NDT is growing rapidly, as commercial array controllers become more widely available. However, conventional 1D array designs limit the flexibility of such systems, for example, making it impossible to skew the beam on curved surfaces. As 2D arrays allow 3D beam steering, they are thus of major interest. However, the use of conventional excitation voltages, typically 200 V, with the many elements in 2D arrays may be inconvenient, making investigation of low-voltage operation worthwhile. The work reported here relates to array design for low-voltage operation for NDT. A 1D array was first produced, operating at approximately 1.5 MHz. This was based on a piezocomposite plate made with PZT 5A ceramic and epoxy resin. The plate was bonded to a PCB whose copper tracks defined the array elements, 10 mm long, 0.28 mm wide, and with edge-to-edge separation of 0.4 mm. The device was excited with a standard logic voltage of 3.3 V on a 75 mm-thick aluminium block. The pulse-echo insertion loss, using a signal reflected from the back wall of the aluminium, was found to be 59 dB. A 2D ultrasonic array has also been produced, with 16 elements in a 4 x 4 matrix, using the same piezocomposite material. In this case, the element size is 1.2 mm x 1.2 mm, and the edge-to-edge separation is 0.4 mm. In tests with 3.3 V peak-to-peak excitation voltage, the insertion loss was found to be 73 dB. The results suggest that arrays made with monolithic piezocomposite material have better performance for NDT than previous arrays made with monolithic ceramic and that low-voltage excitation will be viable in practice, with low noise amplification and appropriate signal processing.