Research On Optimal Parameters Design Of Array Probe Based On Ultrasonic Phased Array

Ultrasonic phased array testing technique is gaining great attention in the intemationalnon-destructive testing field due to its unique excellences recently.Two characteristics areutilized in the application of the new technique to industry,i.e.,maneuverable steering beamand dynamic focusing beam.In comparison with the conventional ultrasonic testingtechnique,the phased array testing technique provides a method of rapid beam steering andsequential addressing of a large area of interest without requiring mechanical or manualscanning,and a method of dynamic focusing on which the focal length of the ultrasonic beamvaries as the pulse propagates through the material,thus the whole area of interest can bedetected with only a few probes and several scanning actions.Meanwhile combining thephased array technique with the imaging technique,the testing system is capable of providingimages of the inside of all examined specimen in a real-time fashion.Ultrasonic imagescontain intuitional and abuadant information about material characteristics,in virtue of theseimages,position,size and type of defections within specimen can be determined accurately.The image formation in phased array technique results from rapid steering of radiationbeam from a phased array probe,the array probe plays a very important role in obtaining thehigh quailty images.Phased array probe is a sensor to implement the conversion betweensound wave and electric signal,whose characteristics of acoustic field are the most importantfactors to determine whether the echoed information of the inspected area in a specimen canbe obtained and utilized effectively,which is the main basis of designing the array parameters.On the basis of introducing the principles of ultrasonic phased array,the time delayregulations of steering beam and focusing beam were studied thoroughly in thisdissertation.With the basic principles of linear acoustics,which is Rayleigh integral formulaand Huygens principle,a set of expressions of radiating acoustic pressure field wereestablished,i.e.,single rectangular element,simple point sources linear array and rectangularelement Iinear phased array,and their spatial distribution were calculated and analyzed.Based on studying the beam directivity function of ultrasonic phased array,thecharacteristics of the radiation beam field from a linear phased array were analyzed in asystematic way.Effects of the designed array parameters on capability of beam steering andbeam focusing were investigated emphatically by simulation and comparison,includingoperating frequency,array mode,array aperture,size of elements,number of elements,etc.Summed up its regularity, providing theoretical basis and guidance to the optimum designarithmetic of array parameters in this dissertation. In virtue of the criteria of orientational parameters for spatial beam,such as orientational acuteangle,half power angle,side lobe amplitudes and traits of grating lobes,etc.,the optimum array parametersfor linear phased array probe were designed.Based on simple point sources linear array,the values of upperlimit and lower limit for inter-element spacing,and the optimum inter-element spacing of eliminatinggrating lobes were calculated.Using the methods of mathematical analysis,the influence of element widthon spatial distribution characteristics of the sound field were analyzed in detail，the critical inter-clementspacing of rectangular element linear phased arrey was deduced，and the upper limit value of element widthwas calculated.The one-dimensional ultrasound phased array probe parameters to optimize the designprinciples were summed up. Beam directionality of sound field space was simulated and analyzed withoptimized parameters. By contrast,confirmed that the optimized array probe has the better beam steeringand focusing performance,the correctness of parameter optimization design principles of one-dimensionalultrasonic phased array were verified.