Pulse-echo Insertion Loss Research Articles

A modular FPGA-based ultrasonic array system for applications including non-destructive testing

This paper reports work aimed at the development of an ultrasonic imaging system comprising modular, reprogrammable building blocks, or 'tiles', which can be customised for multiple applications, including and within non-destructive testing (NDT), by the user. The key component is an autonomous module containing the ultrasonic array and all the electronics necessary to operate it. This contrasts with most previous research on system integration which has focused only on the transducer and front-end electronics. In the present work, a 4 x 4 element 2D piezoelectric array with a 16 mm x 16 mm aperture has been produced, with the entire transmission and reception electronics within the same footprint. The proximity of the transducer array and electronics removes the need for cabling, reducing signal degradation due to cross talk and interference. In addition, it avoids the problem of electrical impedance matching of cable between the array elements and the electronics. Pulse-echo insertion loss of 48 dB has been measured from back-wall reflections in 73 mm-thick aluminium without decoding, and results with decoded signals show adequate signal-to-noise ratio (SNR) with ±3.3 V excitation at an operating frequency of 1.2 MHz, within the range required for deep penetration in nuclear power plant. Crucially, the ability to construct 2D arrays of any size and shape from generic building blocks represents a departure from almost all previous work in ultrasound, which has traditionally been highly application specific. This may allow ultrasonic NDT to be used in applications for which the investment in customised devices could not previously be justified.

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

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.