Improving the probability of detection for a 2D ultrasonic array using digital signal processing techniques.

An experiment was conducted to investigate the potential of using a linear array of probes consisting of a single transmitter (Tx) and multi-passive receivers (Rx) to improve defect detection. The array consisted of three 5 MHz straight-beam probes were located at distances of 22.5 mm and 45 mm from the transmitter. A V1 calibration block was used to ensure repeatability, and the 2 mm notch was utilised as substitute defect. The probes were used in a single transmission with dual-receiver formation in alternate positions. This experimental set-up was used to reveal the clearest interpretation of the received signal. The readings were taken from the area before the first echo to eliminate confusion due to the sidewall reflections. Ultrasonic theory suggests that the reflected beam intensity would have insufficient signal-to-noise ratio (SNR) to be of practicable use with this probe array geometry. Work presented in this paper shows that the pre-processed SNR (in the order of 1.5 dB for a distance of 22.5 mm and less than zero at 45 mm), can be improved to around 20 dB by DSP techniques