Design And Implementation Of High SNR Ultrasonic Nondestructive Testing System

Ultrasonic non-destructive testing technology is widely used in many industrial field while the electronic information technology developed.This paper investigated the principles of ultrasonic nondestructive testing and digital signal processing method for ultrasonic signal,and designed a ultrasonic non-destructive testing system with real-time digital signal processing.According to the industry standards,the implementation plan and performance expectations of this system were established.The system consists of several parts: ultrasonic function circuit,FPGA control circuit,embedded system etc.The design of an ultrasonic signal amplifying circuit with low equivalent input noise and 120 dB adjustable gain range was completed,which can be controlled by DAC to achieve a gain step of 0.1 dB,and the output signal will be converted into a digital signal by a 100 MSPS high-speed sampling circuit;A transmitting circuit based on Boost circuit and charge pump circuit was also realized,and can generate a negative square wave pulse excitation signal with an amplitude of up to 400 V with setting a feedback network.This paper implements a fourth-order ⅡR digital filter and a 5-level wavelet threshold denoising module that can run at a clock frequency of 100 MHz in FPGA,to suppress white noise and scattered noise in ultrasonic echo signals,and discuss the influence of parameters on the effect of ultrasonic signal processing.such as ⅡR filter order,wavelet base type,wavelet decomposition series.In the embedded module,a variety of peripheral circuits such as camera,GPS,WiFi,etc.are designed to ensure that the system has rich scalability.At the end of the paper,the system is tested according to industry standards for ultrasonic nondestructive testing equipment.The results show that the transmission and reception performance of the system are better than the requirements of the standards.The equivalent input noise is up to19.71nV/√Hz,and the net gain can reach 73.3dB,and the wavelet processing module used in the system can improve the signal-to-noise ratio of ultrasonic echo signals up to 6 dB.