Design And Implementation Of Portable Ultrasonic Flaw Detector Hardware System Based On FPGA

Portable ultrasonic flaw detector(PUFD)is a versatile handheld device that can be used in a wide range of materials testing,such as internal flaws detection/evaluation,thickness measurement,material characterization,etc.In this thesis,a separated PUFD is designed,including a pulser/receiver system and an Android device.Moreover,Noise is encountered in the process of ultrasonic testing,and the detection capability of existing PUFDs is limited due to lack of denoising ability,therefore,this thesis proposes an A-scan signal denoising method for PUFDs,the two parts of the method are implemented on the FPGA and the Android device respectively for the designed PUFD.This thesis mainly works as follows: The main noise sources in the ultrasonic testing process are introduced and relative denoising methods are analyzed firstly,then a finite impulse response(FIR)filter and wavelet thresholding algorithm co-design denoising method is proposed to promote the detection capability of the designed PUFD.The PUFD is divided into two parts,the pulser/receiver system and the Android device,these two parts can be separated or conneted via universal serial bus(USB),which reinforces the maintainability of the PUFD.The pulser/receiver system mainly consists of peripheral circuits and a FPGA-based controller.The design of each subcircit module of peripheral circuits is presented in detail,i.e.,pulser generation module,echo pulse reception module,front-end analog signal processing module and etc,which implements the fuctions of ultrasonic transmission with adjustable pulse amplitude and width,multi-channel echo pulse reception and variable gain amplification,etc.The FPGA-based data read and wirte control,parameter decoder,baseline calibration,digital demodulation,data compression,peak detection and other modules are designed to satisifiy the system control and digital signal processing requirements.Finally,the experimental environment is set up for the system and the denosing method testing,experimental results prove that system functions and performances satisfy design specification,meanwhile,noise can be suppressed significantly while valid echo pulse is retained by the denoising method.The main performaces are as follows: Combined with a 2.5P20 longtudinal wave straight probe,the horizontal linearity and vertical linearity of the instrument are 0.24% and 0.7% respectively,the sensitivity margin,dynamic range and resolution are 57.9dB,30.8dB and 40 dB respectively,the sampleing frequency can reach up to 100 MHz.Compared with two commercial PUFDs of CTS-1010 and HS620,vertical linearity,sensitivity margin and resolution are 0.14%,2.1dB and 9.2dB lower than reference PUFDs,but horizontal linearity and dynamic range are 2.3% and 8dB higher than reference PUFDs,indicating that the PUFD in this thesis has high gain accuracy and wide detection range.Compraring with a PUFD without the denoising method or with a FIR filter only,the maximum signal to noise ratio enhancement can reach up to 57.91 dB or 51.66 dB respectively,and practical test proves that the signal-to-noise ratio was obviously enhanced by the denoising method when a flat-bottom hole in a test-piece(CSK-1-5)was detected.