Measurement Of Physical Parameters Of Multi-layer Elastic Medium Based On Air-coupled Ultrasound

Multi-layer elastic medium material has been widely used in the field of scientific research and engineering application.The measurements of their key parameters including density are essential for many practical applications such as in new energy and aerospace industries.This project aims to study the wave propagation of air-coupled ultrasound in sub-wavelength thin multi-layered media.The study is intended to develop an alternative rapid,noncontact,and non-destructive approach based on air-coupled ultrasound to measure key parameters of thin elastic multi-layered media.The main contents are as follows:To study the air coupled ultrasound propagation in a multi-layer elastic media,this paper first discussed the influence of wave velocity,thickness and density on the reflection and transmission coefficient based on the classical Brekhovskikh's formula.Then new simplified equation was proposed and was compared to Brekhovskikh's formula using MATLAB.A method of attenuation measurement is proposed to calculate transmission attenuation in multilayer media.Surface density of multilayered medium was obtained from the calculated attenuation date.An air coupled ultrasonic system was built based on the graphical programming development platform LabVIEW.The system is capable of measuring date.Based on the above,surface density of the typical multilayer elastic lithium battery film was measured.The error between the measured surface density value and the standard formula is within 0.1%.The error between the measured surface density value and the measured value of the physical standard is within 3%.Using sinusoidal signal and sinusoidal pulse signal as the excitation signal,surface density is more accurate.The above work has a certain guide for real-time online application of ultrasonic nondestructive testing technology.