Study On Acoustic Power Measurement Of High Intensity Focused Ultrasonic Transducer

High intensity focused ultrasound technology has made great progress in the field of medical ultrasound,especially in the field of therapeutic ultrasound,The main parameters of radiation dose are ultrasonic power and sound field.However,in the international standard for ultrasonic power measurement,the upper limit of ultrasonic power measurement by radiative force balance method is 20 W,which is far less than the working power of high intensity focused ultrasonic transducer.In view of the problem that traditional measurement methods cannot accurately measure the ultrasonic power of transducers in the field of high intensity focusing,this paper extends and innovates two methods of ultrasonic power measurement.Based on the radiative force balance method,the effect of sudden pulse as signal input and new brush as absorption target on the upper limit of ultrasonic power measurement was studied.A radiative force balance ultrasonic power measurement system is designed and constructed,and a thermal voltage converter and a attenuator are combined to reduce the measurement error of the steady-state excitation voltage.The effective duty ratio determined by power and sound pressure waveform is compared and studied,and the calculation of effective duty ratio determined by power is more accurate.The experimental results show that the upper limit of ultrasonic power measurement can be raised to 350 W by the method of ultrasonic power measurement of high-intensity focused transducer using burst pulse combined with new brush absorption target.Based on the near field cross-spectrum method,a method of correcting the measurement error of near field cross-spectrum ultrasonic power by amplitude and frequency response compensation of unilateral cross-power spectrum hydrophone is studied.The near field cross spectral sound intensity measurement system was built,and the sound intensity distribution of each harmonic wave of the transducer under different voltages was studied,it is found that the proportion of harmonic component increases with the increase of voltage,which leads to the inaccuracy of sound pressure measurement.Based on this,the harmonic component of the electroacoustic intensity is compensated and corrected by the amplitude frequency response of the hydrophone,and the accurate sound intensity distribution is obtained.The ultrasonic power value can be obtained by integrating the sound intensity distribution.The ultrasonic power values before and after compensation and correction were compared,and the maximum deviation was found to be up to 5.4 %.The experimental results show that the upper limit of near-field cross-spectrum ultrasonic power measurement can be raised to 100 W after the amplitude and frequency response of the unilateral crosspower spectrum hydrophone is modified.Using burst pulse radiation balance method,near-field cross-spectrum method and based on the buoyancy of calorimetry has carried on the contrast ultrasound power measurement(10 W to 100 W),the experimental results show that the maximum deviation of not more than 10%,to verify the near-field cross-spectrum method and burst pulse radiation method in the consistency of high intensity focused ultrasound power measurement,improving the power of the high intensity focused ultrasound measurement limit.