Research On The Key Technology Of Ultrasonic Phased Array Testing

Ultrasonic phased array detection as a commonly used non-destructive testing means,can be performed on the workpiece with complex geometric shape.Phase delay is one of the key technologies of ultrasonic phased array,the time delay accuracy affects beam deflection and focusing as well as ultrasound imaging.In this paper,the time delay accuracy of ultrasonic phased array was discussed,including the calculation of time delay and how to obtain high accuracy time delay.The basic principle of ultrasonic phased array detection technology was introduced,including the focusing and deflection of the beam,also ultrasonic phased array of common scanning methods.Then,the ultrasonic phased array transmitting and receiving focusing model was analyzed,and the expression of delay quantity of phased array element is deduced.And the delay precision is analyzed.The delay expression of phased array elements was deduced and the time delay accuracy of ultrasonic phased array was analyzed.Given that the characteristics of Field Programming Gate Array(FPGA)parallelly computing,this paper has presented a floating point focusing algorithm based on FPGA,the calculations of time delay are transferred to the FPGA.Different from PC calculating time delay,this algorithm calculates each channel time delay parallelly,which greatly improves the operation speed.The modules of the algorithm are designed independently,including floating point addition,floating point subtraction,floating point multiplication,floating point division,floating point sine/cosine.The floating point sine/cosine module is based on CORDIC algorithm.By improving the traditional CORDIC algorithm,the delay time of the focusing algorithm can reach 1ns in the case of iteration is 13 times.In addition,this paper also used a time-sharing method to calculate time delay of each channel,ensuring the speed of calculation while saving hardware resources.Moreover,this paper also presented a model of automatic scanning defects based on this algorithm.In order to improve the accuracy of ultrasonic phased array focusing time delay,analyzing the original interpolation Cascade-Integrator-Comb(CIC)filter,an 8x interpolation CIC filter parallel algorithm was proposed,so that interpolation and multichannel decomposition can simultaneously process.Moreover,we summarized the general formula of arbitrary multiple interpolation CIC filter parallel algorithm and established an ultrasonic phased array focusing time delay system based on 8x interpolation CIC filter parallel algorithm.Improving the algorithmic structure,12.5% of addition and 29.2% of multiplication was reduced,meanwhile the speed of computation is still very fast.Considering the existing problems of CIC filter,we compensated CIC filter,the compensated CIC filter's pass band is more flat,transition band becomes steep,and stop band attenuation increases.Finally,we verified the feasibility of this algorithm on FPGA.In the case of system clock is 125 MHz,after 8x interpolation filtering and decomposition,time delay accuracy of the defect echo becomes 1ns.Simulation and experimental results both show that the algorithm we proposed has strong feasibility.Because of the fast calculation,small computational amount and high resolution,this algorithm is especially suitable for applications with high time delay accuracy and fast detection.