Guided ultrasonic wave measurement in plates using low-cost equipment

Guided waves can propagate along thin-walled structures, such as pipes and plates, with limited energy loss, thus enabling the efficient inspection and monitoring of large structures from a limited number of sensor locations. This allows Structural Health Monitoring (SHM) using permanently installed monitoring systems with limited access and sensor requirements. However, guided wave propagation is complicated due to multiple propagating wave modes and dispersion, potentially causing the signals to become distorted. Both analytical and numerical analysis and experimental measurements are essential for guided wave research. Specialized laboratory equipment such as non-contact laser vibrometers can be expensive and unaffordable. This contribution presents a preliminary investigation on what can be achieved experimentally using low-cost sensors, suitable for research and teaching in circumstances with limited budgets. For low frequency guided wave propagation in an isotropic plate (A0 Lamb wave mode), the influence of different measurement configurations on the accuracy of group velocity quantification was investigated. Results from experimental setups employing different receive transducers were evaluated and quantified. Accuracy of sensor placement and coupling as well as measurement repeatability and Signal-to-Noise Ratio (SNR) were investigated. Accurate experimental quantification of the group velocity, using the different movable sensors, was demonstrated by comparison to theoretical predictions based on the nominal aluminum material properties.