Research On Key Technologies To Improve The Ultrasonic Phased Array System Measurement Accuracy And Real-time Performance

Ultrasonic phased array is one of important instruments that have characteristics of complete coverage of space sound field?without moving the probe?,high accuracy,strong anti-interference ability,omni-directional real-time ultrasound imaging,and may replace industrial computed tomography?CT?,which is usually used to evaluate material characteristic parameter,analyze failure mechanism of material and predict life and so on.Firstly,the paper accord to the function frame of the ultrasonic phased array,focused research theory and implementation skills include coding incentives,precision of time delay and beamform,transformation of data quantity,and large data storage and transmission,and so on,then are used in the instrument,to speed up the nondestructive testing technology and equipment level of our country,to promote the modern testing technology of high precision,high speed,high efficiency,has the important academic value and practical significance.The Research is funded by the national major scientific instruments and equipment development?2013YQ230575?and the Guangzhou science and technology plan projects?201509010008?.The paper based on the principle of ultrasonic phased array instrument,from coding incentive,delay focusing of receiving,signal processing,large data storage and transmission and other key parts,discusses the advances at home and abroad,and determines the research content of the paper as follow:According to excitation condition of ideal coding and excitation characteristics of orthogonal complementary Golay?A,B?,to solve the problem that one ideal decoding needs two excitations by traditional way,this paper put forward the quasi-single incentive technology:After only A or B coding excitation,produce a ultrasonic echo by excitation factor transformation relying on an algorithm,then obtain two incentives in order to decode.Secondly,it put forward two kinds of effective methods of constructing long orthogonal complementary Golay code which could be easy to implement by FPGA.At last,complete the simulation of orthogonal complementary Golay code with quasi-single code incentive technology through Field II and Matlab.The Golay code?L_c=8?excitation test was carried out on the scattered spots.As a result,RF signal amplitude increase about 16?2?L_c?times.Scan multiple spots scattered into the imaging by phased array technology,making image of the focus spots clearer.The precision of time delay focusing is the core and difficulty of the various focusing algorithms affiliated to ultrasonic phased array instruments.To overcome some disadvantages such as poor commonality,high cost and controllability created by traditional time-delay method,the precise time delay of the multi-phase interpolation filter algorithm is proposed as a flexible digital signal processing technogy.Refer to the classical FIR interpolation filter,a multi-phase interpolation time-delay algorithm model based on the CIC filter is established.Its special feedback structure is converted into polyphase interpolation,and the mathematical expression of polyphase interpolation is derived,and given a FPGA circuit implemented 1ns time-delay precision.The experiment compares FIR,multistage HB,and CIC interpolation filtering time-delay algorithm.CIC interpolation time-delay has a smaller error with excellent versatility and portability,and the lowest Peak Sidelobe Noise Level of the focusing beamline.Otherwise,the algorithm has the highest SNR and focusing ability.To get the higher digital resolution and realize the sampling rate being arbitrarily converted under a condition of fixed sampling rate based on the ultrasonic phased array system,and to relieve the unicity of upsampling and compression algorithm leading to overly dependent on the processor performance,this paper puts up the coarse and fine interpolation technology combining multiphase interpolation and polynomial interpolatio.Firstly,a piecewise sliding cubic Spline-Hermite fine interpolation method of upsampling with small multiple is studied,which replace the large points N node with a small number of N'nodes for interpolation,deducing a suitable value N_suit to meet certain accuracy.The integer interpolation is implemented by the CIC polyphase interpolation to obtain any optimal times of upsampling.Secondly,CIC polyphase interpolation presents multiphase low rate signals that can be compressed in parallel by time-division so that the data processing clock frequency is constant.It not only improves the stability,but also implements upsampling and rate conversion.The experimental results show that the seven points cubic Spline-Hermite interpolation produce the maximum relative error of 0.35%when the sampling rate is100MHz and the echo frequency is 15MHz.Through the method of the CIC polynomial interpolation unsampling and peak holding parallel compression,the 4.75MHz echo envelope was simulated,when four times upsampling and seven times compression.The peak holding compression error was 0.496%,which effectively implements the technology of upsampling and real-time dynamic compressing about high speed signal.The paper carries out research on improving the SNR and real-time of ultrasonic phased array instrument.Aiming at the non-real-time problems of the traditional offline large data processing,the large data processing and high-speed data interaction problems brought by the multi-group scanning mode of ultrasonic phased array instrument,a control algorithm about DDR3 caching based on large data,and a scheduling algorithm about sharing bandwidth utilization maximization base on Multi-group scanning mode data transmission by PCIe are proposed.Firstly,a method of controlling caching of large data with multichip DDR3 based on a finite state machine is proposed,which can solve noise threshold in real-time by pipeline way,and improve the efficiency of noise reduction algorithm.Secondly,the formula of maximizing utilization of data transmission bandwidth about N groups scanning modes of ultrasonic phased array is derived,and multi-fifo variable length scheduling algorithm is designed,improving PCIe bandwidth utilization.Experimental analysis of real-time control to four DDR3 effectively implement denoising algorithm of moving average and lifting wavelet.Meanwhile,the bandwidth utilization ratio of multi FIFO scheduling algorithm is one time higher than that of the common blind scheduling algorithm.Research on the application of key technologies in a novel ultrasonic phased array developed by ourselves.To test the crack grooves?2mm wide and 2mm deep?of the wind generated rotor bearing with thickness of 5cm²0cm provided by the cooperator,with better performance tested,all the indexes meet the expected requirements,which shows the effectiveness and feasibility of the basic theory researchs of key technologies used to improve the measurement accuracy and real-time performance of ultrasonic phased array system.