Research On Phased Array Ultrasonic Testing System And Its Key Technology

Ultrasonic phased array technique can help to achieve flexible, controllable synthesized ultrasound beam by exciting each element of an ultrasonic array transducer with independent phase delay. Phased array ultrasonic testing can accomplish dynamic focusing, obtain visual image, inspect component of complex geometry. Also it can improve detection sensitivity, resolution and SNR, so it has recently been highly recognized in NDT research domain. In this thesis, a 16-channel experimental phased array ultrasonic testing system is originally designed and developed, upon which several key technologies are thoroughly studied.In this thesis, firstly the history and current situation of ultrasonic testing especially the ultrasonic imaging is outlined. After that the merits of phased array ultrasonic testing are discussed, then the principles and realizations of several key technologies of phased array ultrasonic testing system are explicated in details.In the following chapters, a 16-channel experimental phased array ultrasonic testing system is thoroughly explained, including digital beam forming, low noise programmable amplification of received ultrasound signal, multi-channel hi-speed hi-precision data acquisition, hi-speed real-time processing of multi-channel ultrasound signal, and hi-speed data transfer based on PCI bus. In addition, the frame of software system is built.As concerning to the interference condition between different transmit/receive channels in the system, a detailed error analysis is given, and the clock and synchronization scheme is explicated. The measure adopted to enhance phase clock's precision is explained. Concerning the key technology of phase delay, the principles and its implementation of digital waveform phase delay based on waveform excitation is explained, which has achieved high transmission phase resolution in experimentation. As to phased array receiving, a scheme of separating the delay clock and sampling clock is explicated, which effectively enhance the phased receiving delay resolution.How to process the large amount of sampling data of ultrasonic phase array system is one of the difficulties in the system. On the basis of the architecture of DSP+FPGA, hi-speed real-time ultrasound signal processing is achieved. Digital filter accomplished in FPGA makes obvious effect on noise suppression, the speed performance is highly improved comparing to software program. In addition, the FPGA's static reconfiguration and real-time reconfiguration are studied and accomplished, which fully exert the performance advantages of reconfigurable computing.Finally a set of experimentations are done to verify this phased array ultrasonic testing system. The results show that the phase control effect is satisfactory, and the intensity of focused ultrasound beam can reach above 91% of the ideal value.