CHEN Zhenglin1, XIAO Renxian2, WANG Xingguo3, WU Nanxing4
(School of Mechanical and Electronic Engineering, Jingdezhen Ceramic Institute, Jingdezhen 333403, Jiangxi, China)
Abstract: Air-coupled ultrasonic is a non-contact technique which can be used in non-destructive testing. The acoustic propagation of aircoupled ultrasound in Si3N4 ceramics at vertical incidence and different frequencies has been investigated. A mathematical model for the ultrasonic testing of Si3N4 ceramics based on the propagation mechanism of the wave in the material is established using wave equations,transfer matrices and boundary conditions for acoustic wave transmission between gas and solid. Simulation results show the acoustic transmission coefficient is the maximum when the plate thickness is an integer times of half of the wavelength or when the frequency thickness product is an integer times of half of the product of sound velocity in Si3N4 ceramics and its plate thickness. The experimental results by ultrasonic testing of Si3N4 ceramics are consistent with those from simulation.
Key words: air coupled; wave equation; transmission coefficient; Si3N4 ceramics