Simulations Toward Design of Matching Layer in Acoustic Emission Sensor

Acoustic emission technique (AET) is widely accepted method for nondestructive testing (NDT), extending its use in some other applications like leak detection, corrosion detection, heath monitoring, etc. Basic structure of acoustic emission (AE) sensor consists of piezoelectric material as a transducer with matching layer (ML) on top. Matching layer acts as wear plate for the sensor element, thereby protecting the sensor from any damage. For different applications, designing and optimization of sensors are carried out analytically using different one- or two-dimensional models. Selection of matching layer plays a crucial part in designing a sensor as it also serves as a coupling for transferring acoustic energy from AE source to piezoelectric transducer. The sensitivity of AE sensor is highly dependent upon the optimization of matching layer. For maximum energy transfer, the layer dimensions and material of construction are required to be optimized. Software using finite element method (FEM) is widely used to study AE wave propagation. In this paper, the COMSOL Multiphysics software has been used for optimization of matching layer material and its dimensions for cylindrical piezoelectric acoustic sensor. Matching layer having alumina as the material and approximate thickness of λ/4 (λ corresponding to the resonant frequency) has given the optimized performance in the simulation results. This paper deals with basic structure of AE sensors, analytical models used for ML optimization, different modes of piezoelectric disk, simulations regarding ML material selection and optimization of ML dimensions.