Ultrasonic Linear Array Transducer Geometry Error Analysis And Genetic Algorithm Optimization

The advancement of ultrasonic phased array technology is based on Huygens principle, this technology could adjust the ultrasonic scanning beam shape, focal position and scanning deflection angle by exciting each element of array transducer according to a certain rules and scheduling. In recent years, ultrasonic phased array technology is widely used in many fields, such as medical diagnosis and treatment, industrial non-destructive testing, development and exploration of marine, communications, aerospace, defense, radar, and antenna.The performance of the transducer array which is a key components in ultrasonic phased array system is greatly influenced by the transducer's geometric parameters. This paper mainly discussed the beam directivity that affected by the geometric error of array transducer element size and spacing, and then put forward the improvement measure to adjust the geometric error through incentive method, and finally optimized the transducer beam directivity to insure the linear array transducer with geometric error can reach the design indices or reach expected parameters indexes through excitation optimization.This paper research contains the following aspects:(1)According to the Huygens principle, the sound field distribution expression and directivity function of various array were studied. These arrays include single array element, uniform linear array composed of discrete single array and linear phased array. The influence of transducer geometry parameters on the beam direction indicators which consist of main beam width, the amplitude of side lobe and the occurrence of grating-lobes was further analyzed. The parameters include the frequency array, the number of array element, array element width and spacing and deflection angle.(2)The problem that correct the deviation of between beam direction actual indicators and design indicators was studied. The deviation is caused by the error of between the practical array element size and spacing of transducer and the design parameters. The paper simulated the directional pattern of linear array which includes a part of changed element size and spacing by means of MATLAB, and proposed improvement measure for error correction by element incentive way based on adaptive algorithm.(3)While geometric parameters optimization of uniform linear array transducer sometimes could not meet the needs of practical engineering, it proposed weighted methods to optimize the directivity of linear array. Based on two different optimization criteria for minimizing side-lobe amplitude and the total side lobe energy,this paper optimized beam directivity of linear array transducer by using genetic algorithm. Through the research, some conclusions are drawn as follows:(1) Transducer parameters have influence on the beam directivity as following:(a) The main beam width can be reduced by increasing the number of array elements and broadening the array element spacing, while it increased with the rising of deflection angle.In the case of actual technology and reasonable cost, more array elements should be selected.(b)The greater the array element spacing,the better the beam directivity. But if the array element spacing exceeds_the critical value(that is dmax=(N-1)λ/(N(1+sinθs)max),a strong gating lobe will be generated. If the scanning range is required to reach 180°, the array element spacing would not exceedλ/2;(c) The side-lobe amplitude is in inverse proportion to the number of array elements, element width and the deflection angle, but it increases with increasing the array elements spacing. When the number of array elements tends to the infinite, the side lobe amplitude will be close to-13.5dB(2/3π).(2) Element size and spacing errors of linear array transducer have influence on the beam directivity as following:The acoustic pressure amplitude of main beam increases with array element width increasing, but array element width has no effect on the main beam width; the changes of array element spacing result in time delay changes between neighboring elements, so there will be incoherent area, which lead to irregular side-lobe and the increase of side-lobe amplitude, Theoretical Analysis is basically same as simulation results. The geometric error of linear array transducer is corrected by using adaptive algorithm from incentive method. If array element size and spacing are reasonably arranged in certain law, beam directivity will be improved and greatly reduce the side-lobe amplitude.(3) On the basis of two different optimization criteria for minimizing side-lobe amplitude and the total side-lobe energy, the weighted coefficient of several different line arrays has been optimized by using genetic algorithm, the optimization result is very good.