The effect of acoustic absorber’s physical parameters on estimating acoustic intensity in high intensity focused ultrasound field using infrared thermometry

The physical parameters of acoustic absorber play an important role in estimating acoustic intensity in high intensity focused ultrasound(HIFU)using infrared thermometry.In order to analyze the rule of the influence of different physical parameters(density,sound speed,attenuation,thermal diffusivity,specific heat capacity)on the measurement results,the theoretical simulation was applied.The sound and thermal field in the absorber with different physical parameters and same power output are calculated based on layered model.The finite difference method is used to calculate the temperature change at interface during the irradiation.The character value of sound field in the focal region,e.g.intensity on axis and—6 dB beam width,are calculated by the method based on hydrophone and infrared thermal imaging.The result is compared with the theoretical characteristics of sound field in water.The influence of different physical parameters on the result is analyzed.The acoustic and thermal parameters of absorbers have no significant influence on the measurement results except the sound speed,and the maximum relative difference is<15%.Due to the changing of sound speed in the absorber,the distribution of thermal field in absorber is changed,which leads to a great deviation,and the maximum relative difference in-6 dB beam width and axis intensity are 95.37%and 69.97%,respectively.Therefore,the appropriate choosing of this parameter plays an important role.When the acoustic parameters of absorber are similar to that of water,the measurement results based on hydrophone and infrared thermal imaging have satisfactory accuracy within the focal region.