Optimal Design Of Acoustic Field Of Focusing Transducer With Spiral Phased Array Of Archimedes

In the past 10 years,High Intensity Focused Ultrasound(HIFU)technology has been used as a new method for the treatment of tumors(uterus,breast,intracranial,liver,prostate,etc.)due to its non-invasive and non-invasive characteristics.The transducer is a key component of the focused ultrasound equipment,and its performance directly affects the treatment effect.Since its development,the focusing mode of the focused ultrasound transducer has undergone several morphological changes from lens focusing,mirror focusing,shell-type self-focusing to the current phased array focusing.Phased array ultrasound focusing does not require mechanical movement,has fast scanning speed and high accuracy,and can select the most appropriate beam control method according to the position and size of the tumor,so as to achieve the purpose of improving the efficiency of HIFU treatment.The main factors that affect the sound field characteristics of a phased array focused ultrasound transducer include the working frequency of the transducer,the structure of the array element,the arrangement of the array elements,the coupling between the elements,the geometric characteristics of a single element,and the characteristics of the transducer material.Much research has been conducted on the effect of array element arrangement on the performance of phased focused ultrasound transducers.At present,the array element arrangement can be roughly divided into three categories: periodic array,random array and spiral array.The spiral array is In recent years,a new array method has emerged.Studies have shown that compared with periodic arrays,spiral arrays have lower levels of grating lobes and side lobes;compared with random arrays,spiral arrays have focal points regardless of whether they are circular arrays or mosaic arrays.Higher energy;so this article uses the Archimedes spiral method to study the array element arrangement.First,use COMSOL modeling and simulation to study the influence of Archimedes’ spiral arrays with different filling coefficients on the focus sound pressure gain and side lobe grating lobes;then conduct focus deflection research in the acoustic axis direction and the horizontal axis direction,and pass experiments Study the acoustic field of the transducer,test the acoustic field characteristics and deflection ability of the transducer,study its deflection range and the influencing factors of focus energy,lay a good foundation for the development of ultrasonic focusing transducers,and use simulation research to explore phase control The changing law of the side and grating valves during the deflection of the transducer can provide a reliable method for the treatment of the deep abdomen and the ablation of the diseased tissue between the ribs.In this project,the main work done are:(1)A shell phased focusing transducer is designed,and the finite element simulation tool COMSOL is used to realize the modeling and simulation of Archimedes spiral arrays with different filling coefficients.It is found that the number of turns of the transducer N has little influence on the side lobe,but has influence on the gate lobe.The smaller the number of turns of the transducer,the larger the gate lobe is.At the same time,the sound pressure at the focus is proportional to the filling coefficient of the phased transducer,and the sound pressure at the focus gradually increases with the increasing of the filling coefficient.(2)Based on the simulation parameters,the design and fabrication of the spiral phased transducer are carried out,including the selection of piezoelectric materials,the selection of array elements,the wiring of array elements and the packaging of transducer.Here,each array element is embedded in the outer shell of the shell type transducer in the Mosaic mode,and the coordinate of the hole of the transducer is realized by using 5D technology to achieve the Archimedean spiral arrangement.After the production of the phased transducer,the sound field test of pure physical field and data analysis were carried out to obtain the actual focus and deflection of the Archimedean spiral phased transducer.According to literature investigation,the deflected range of the phased transducer is defined as the sidelobe or gate lobe is no more than 30% of the maximum sound pressure value of the focus.The experimental results are in good agreement with the simulation data.(3)The deflection ability of the focus in the direction of the acoustic axis is greater than that in the horizontal axis.When the focus is in the lateral deflection of 8mm,the focus sound pressure decreases by 33.38%,which is more accurate than the 29.75% decrease in the previous simulation.When the direction of sound axis is deflected by 15 mm,the focus sound pressure is reduced by 29.7%,and the simulated sound pressure is reduced by 23.25%.(4)By comparing the ratio of sidelobe and gate lobe of the experiment and simulation,the measured deflection range of the Archimedes spiral phased transducer is 16mm*16mm*20mm,and the transverse deflection range is in good agreement with the simulation results.