Lamb waves are a growing method for the Non-Destructive Testing and Evaluation (NDT&E) and structural health monitoring (SHM) of aerospace vehicles. These guided waves can propagate over large distances and have a strong tendency to interact with damage. Whilst several methods exist for the modelling of Lamb wave propagation, this paper is the first to introduce a first principles numerical model that can efficiently and accurately predict the behaviour of Lamb waves. The numerical model is easier to understand and implement compared with analytical solutions and significantly faster than discretised numerical methods. The numerical model is presented in detail for an isotropic and homogenous plate, along with validation against the industry accepted, WaveForm Revealer 3 (WFR3) software. The results show a mean correlation across all assessed parameters of 90.4% and 96.6% for the symmetric and antisymmetric modes, respectively. Further discussion is provided on future developments to the model, including on the topic of high temperature effects, anisotropic materials and edge reflections.

In this study 22 patients (44 ears) with noise-induced permanent hearing loss were audiologically evaluated using transient-evoked otoacoustic emissions (TEOAE) and auditory brain-stem response (ABR). Twenty-one normal subjects (42 ears) without exposure to occupational noise were used as controls. Based upon the hearing loss at 4, 3, 2 and 1 kHz on the pure-tone audiogram, they were classified into four groups. In group 1 (eight ears), emissions were present in all ears but their TEOAE-noise level and their reproducibility (percentage) proved to be weak. The auditory brain-stem response (ABR) indicated that the I/V amplitude ratio, the latency values of wave V and the I–V intervals fell within the normal range in all ears. In Group 2 (14 ears), 40 per cent had no emissions, whereas the remaining ears showed weak emissions. The ABR revealed that in all ears the I/V amplitude ratio became small while wave V peak latency as well as I–V intervals were within the normal range. In Group 3 (10 ears), emissions were absent in 50 per cent, while in the other ears the emissions were very weak. The ABR revealed that the I/V amplitude ratio, which could be calculated in the 60 per cent in which wave I was present, was smaller than in Group 2. Wave V latency as well as I–V intervals were within the normal range. In Group 4 (12 ears), none of the ears showed emissions. The ABR indicated that the I/V amplitude ratio was much smaller when wave I was present (27 per cent) as well as I–V interval values being within the normal range. Wave V absolute latency value (δV index) indicated a positive index in 17 per cent of this group (two ears) when wave I was absent. In the present study a dynamic process from cochlear outer hair cells to cochlear neurons was seen, correlating with an increasing hearing loss.