High frequency guided wave ultrasound measurements using low-cost equipment

Abstract

Guided wave ultrasound can be applied to inspect large volumes of structures from a single transducer location and is particularly effective in one-dimensional structures such as rods, pipes and rail. An application, which is of interest in South Africa, is the inspection rock bolts in the mining industry. The difficulty in inspecting embedded rods is that there is rapid attenuation of the signals with distance. While guided wave systems generally operate at low frequencies (20 kHz to 200 kHz), high frequency operation (1 MHz to 10 MHz) can offer some advantages when inspecting rock bolts. Guided wave ultrasound testing is complicated by multi-modal propagation and dispersion, which require the use of sophisticated excitation signals, which are not available in equipment designed for conventional ultrasonic testing. It was therefore necessary to develop a measurement setup and the approach taken was to use standard lab instruments wherever possible and to only purchase the items that are unique to this measurement, using the very limited budget available. The measurement setup was used to perform measurements on a rod and confirmed theoretical predictions. These measurements identified the frequencies where modes propagate with low attenuation and allow the attenuation to be quantified.