Preparation And Performance Study Of 8.5 MHz Non-destructive Testing Ultrasonic Transducer

Due to the advantages of high specific strength and stiffness,as well as strong designability,the amount of carbon fiber composite materials used in aircraft structures is increasing year by year.With the passage of time,various forms of defects are inevitable in the structural forming and use of aircraft composite materials.If defects are not detected in a timely manner,it will increase the probability of accidents occurring.The ultrasonic probe is the core part of the phased array ultrasonic testing system,and the sensitivity and bandwidth of the probe determine the performance of the entire system.This article has developed two types of probes by selecting suitable piezoelectric materials and designing new backing materials.The main research content and results of this article are as follows:1.In the theoretical basis section,the law of ultrasonic propagation in the medium was studied,and the acoustic impedance and thickness requirements required for the matching layer were obtained.The sound field expressions corresponding to the deflection and focusing of the linear phased array sound beam were derived,and the effects of the number of array elements,array element width,and array element spacing on the probe directivity function and effective detection area were obtained.Furthermore,the design rules related to the linear phased array,including resonance frequency,number of array elements,array element width,and array element spacing,were obtained.2.The influence of thickness on the resonant and anti-resonant frequencies of piezoelectric components was simulated using COMSOL 5.6 finite element software.The effects of the number and spacing of array elements on the directionality of linear phased arrays,as well as the effects of the type and thickness of the backing on sensitivity and bandwidth,were analyzed.The geometric design of the linear array transducer,as well as the type and thickness of the backing used and processed,were determined.3.In the production of backing,this article uses epoxy resin and curing agent as the matrix,and tungsten powder,aluminum nitride,and mica powder as fillers to prepare two types of backing.The relationship between backing performance and tungsten powder mass fraction was obtained in the first type of backing,and the relationship between backing performance and mica powder mass fraction was obtained in the second type of backing.It was found that the addition of an appropriate amount of mica powder in the backing can significantly increase the sound attenuation coefficient while maintaining a relatively stable sound impedance of the backing.4.Two types of backing were selected for the preparation of the probe,and the performance of the probe was tested using the pulse echo method.The experimental results showed that the acoustic impedance of the backing would affect the center frequency of the probe,and the acoustic attenuation coefficient of the backing would affect the sensitivity and bandwidth.Therefore,using a suitable backing can significantly improve the performance of the probe.The center frequency,sensitivity,and bandwidth of the probe a developed in this paper are 9.31 MHz,-41.77 d B,respectively 61.66%,the center frequency,sensitivity,and bandwidth of probe b are9.5 MHz,-42.91 d B,and 63.27%,respectively.