Tip-tapered All-silica Fiber-optic Fabry-perot Interferometer And Measurement Method For SSFU Acoustic Fields

High intensity focused ultrasound(HIFU),as a new non-invasive technology in the field of medicine,has attracted attention in the international community because its treatment method is different from the traditional treatment method,and is developing rapidly.Spherical Standing Wave Focused Ultrasound(SSFU)is a new generation of Spherical Standing Wave Focused Ultrasound(SSFU),which can achieve more accurate therapeutic effects in the field of biomedical engineering by further reducing the focal size to the level of subwavelength and increasing the focal acoustic pressure to the level of gigapascal,breaking through the traditional traveling wave focusing approach.This enables the SSFU transducer to focus the ultrasonic waves on the diseased tissue in the organism more accurately,achieving the best non-invasive therapeutic effect.In addition,the extreme and complex acoustical environment created by the SSUF transducer can also provides a new research environment for a number of disciplines,such as physics and materials science,to further promote the development of related disciplines.However,in order to further develop the SSFU technology and its application comprehensively,it is necessary to accurately and comprehensively characterize the characteristics of the acoustic field generated by SSFU transducers.Therefore,it is imperative to study a measurement method for characteristicing the SSFU acoustic field(such as focal pressure,focal size,sound field distribution).In order to achieve accurate measurement of the SSFU acoustic field to promote the development of this technology,the main research work and achievements of this thesis include:(1)A Tip-Tapered All-Silica Fiber-optic Fabry-Perot interferometer(TTAS-FOFPI)with high acoustic pressure resistance,high spatial resolution,high temperature resistance,immunity the effects of cavitation and with sufficient bandwidth is proposed.The structure and basic principle of TTAS-FOFPI were analyzed in detail.The preparation method of TTAS-FOFPI and several commonly used demodulation methods of cavity length variation were discussed.(2)In order to obtain the relationship between the cavity length change of TTAS-FOFPI and the focal region acoustic pressure of the SSFU sound field,a coupling model of TTAS-FOFPI and the SSFU sound field was established.The numerical simulation analysis of the final formula of the coupling model between TTAS-FOFPI and the SSFU acoustic field is carried out,and the influence of TTAS-FOFPI structure,material and other factors on the response bandwidth is analyzed,which plays a guiding role for the design of TTAS-FOFPI.(3)At present,the intensity-based linear demodulation method is used to demodulate the acoustic pressure of the SSFU acoustic field.The demodulation range is limited.An intensity-phase based hybrid nonlinear demodulation method for fiber-optic Fabry-Perot interferometric sensors with arbitrary setting of bias point for the SSFU acoustic field is proposed.Based on this method,TTAS-FOFPI instrument system is designed and developed.The results illustrate that the demodulation method is correct.(4)A SSFU acoustic field measurement experimental system was built.The experimental results showed that the proposed measurement method for SSFU acoustic field is more accurate.The research work in this paper provides a new method for the accurate measurement of SSFU acoustic field,and provides an effective guarantee for its safety,accuracy and high efficiency in non-invasive medical treatment,and further promotes the application of SSFU technology.