The effect of 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 the 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 acoustic absorber are calculated based on layered model with same output parameters of transducer and different physical parameters.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,like intensity on axis and-6 dB beam width,are calculated by the method that based on hydrophone and infrared thermal imaging.The sound distribution in the water which is calculated in theoretical are treated baseline.The sound field characteristics calculated by theoretical calculation and method are compared and 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 less than 15%.Due to the changing of sound speed in the absorber,the distribution thermal field in absorber is changed,which lead 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 appropriated choosing of this parameter play 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.