The Suppression Of Grating Lobes Generated By Random Phased Array HIFU Transducer

The suppression of grating lobes is of great significance in research and application for the safe treatment of high intensity focused ultrasound(HIFU).Random phased array technique is used to suppress grating lobes of the ultrasonic sound field and three random strategies are used to produce the position of the linear phased array.For the first and second random strategies,elements move randomly based on the element position of regular phased array.However,for the third one,elements move randomly within the range of the phased array.For the three random strategies,the element movable range of the array elements is ranked as follows: first<second<third.Based on the Rayleigh-Sommerfeld integral and nonlinear Westervelt equation,the linear and nonlinear ultrasonic sound field generated from regular and random phased arrays are calculated.The results of suppressing grating lobes are discussed using three evaluation parameters,i.e.the normalized maximum sound pressure peak of grating lobes,normalized averaged sound intensity of the grating lobes and normalized averaged sound intensity of side lobes.The results show that the increase in element movable range is beneficial for the suppression of grating lobes in the linear sound field.When the best parameters to suppress grating lobes are used,the normalized maximum sound pressure peak of the grating lobes for three random strategies is 30.7%,53.8%,and 55.8% lower than that of the regular phased array respectively.In the nonlinear field,with the increase of the random degree,the effect of suppressing grating lobes generated by the same random strategies is enhanced.For the random array produced by the third random strategy,when the random degree is 0.9,the peak positive and negative sound pressure peaks of the grating lobes decrease by 55.6% and 54.8% compared to that of the regular array.Furthermore,when the focus shifts,the performance of suppressing grating lobes in nonlinear sound field is studied.The results reveal that the focus of the ultrasonic sound generated by second and the third random strategy can steer ±6mm and ±10mm transversely,when the level of the grating lobe intensity in the field is 8d B lower than the maximum intensity of the focal region.This study provides an attractive approach to suppress grating lobes and is helpful for the optimization and design of the HIFU phased array transducer.