Technology And System Based On Time - Frequency Analysis For Ultrasonic Testing Of Coarse Grain Materials

Because of the strong scattering, the coarse grain materials make seriousnoises and attenuation to ultrasound signals. This results to low sensitivityand signal to noise ratio (SNR) in ultrasonic testing of coarse grain materials.Now it is still a difficult problem to test coarse grain materials. Signalprocessing is an important way to improve the testing capability and SNR.The split spectrum processing (SSP) is a main technology with goodperformance of enhancing SNR in ultrasound signal processing. But SSP issensitive to its parameters and its capability is lacking to find small defects.So SSP is not popularized up-to-dately in industry. The time-frequencyanalysis is a new signal processing technology. Different to pute time domainor frequency domain analysis, time-frequency analysis translate time domainsignals into 2D time-frequency images. So time-frequency analysis canexhibit more information in ultrasonic signals, and it is more potential inultrasound applications. This thesis carrys in-depth study to the ultrasound applications oftime-frequency analysis. A time-frequency analysis "three-step method" forultrasonic testing is put forward. And This thesis develops the correspondingtime-frequency analysis ultrasonic testing system. The "three-step method" has optimized parameters without the sensitivityto parameters like SSP. It has powerful capability to find small defects andenhance SNR in testing coarse grain materials. It is very applied forindustries.The time-frequency analysis ultrasonic testing system has full differentialhardware structure and digital signal processing power. Many performanceparameters are comparative with international advanced instruments. Theexperience shows the system can testing typical coarse grain materials withhigh sensitivity. The system can detect φ 0.8mm flat-bottom hole (at a depth of65mm ) and φ 0.5mm horizontal hole (at a depth of 70mm ) in stainless steel sampleof average grain size 0.6mm. This is an importance evolvement in ultrasonic testing.