Numerical modelling for the optimization of multi-element, capacitive, ultrasonic, air-coupled transducer

This paper presents an analytical method to predict the acoustic pressure field produced in the air by concentric, annular sources. The sources correspond to a multi-element, ultrasonic, air-coupled array, which should be used further for non-destructive testing (NDT) purposes. After validation of the model based on the comparison of the predicted acoustic pressure with experimental results, a numerical study of the consequence of the annular sources arrangement on the acoustic field is realized. This helps in optimizing the design of the array, so that the intended ultrasonic field is produced. For high spatial resolution to be obtained in further NDT process this field should be focused and, ideally, the frequency used for inspecting the tested piece should be tuned so that wavelengths in the inspected material take suitable values in regards of piece thickness and defect sizes. Numerical simulations show that the multi-element array allows dynamic focussing to be made by judiciously adjusting delay laws of the excitation signals applied to each individual element.