Fiber Vibration Sensing Method Of HIFU Transducer Surface And HIFU Acoustic Field Measurement

High intensity focused ultrasound(HIFU)has been widely used in the field of medical ultrasound engineering in recent years,such as tumor therapy,neurosurgery,targeted drug delivery and so on.A key to the use of HIFU acoustic field for treatment is to achieve accurate localization of high-energy acoustic focus regions to avoid causing incomplete treatment or damage to normal tissues.Meanwhile,the detection of sound pressure of the acoustic focus area has certain guiding significance for the development and application of HIFU transducers.HIFU acoustic field has unique characteristics,it is required that the method used for sound pressure measurement can avoid the interference to the acoustic field,while avoiding the impact caused by high temperature,high sound pressure and cavitation response.However,some of the methods reported at present have some defects in the application range,measurement upper limit,anti-jamming ability and accuracy.In the previous works of our team,an acoustic field calculation model based on Rayleigh integral has proposed.According to the calculation principle,the normal vibration velocity distribution function of all particles on the radiation surface of HIFU transducer can be obtained to describe the field distribution.On this basis,the method of measuring the surface vibration velocity of the HIFU transducer,and the sound pressure measurement as well as the distribution of HIFU acoustic field are studied in this paper.The main research work and achievements of this thesis include:1.Based on Rayleigh integral model,the method of reconstruction and description of HIFU acoustic field is studied.Finite element simulation of concave spherical focused ultrasonic transducer is carried out to obtain the characteristics of vibration velocity distribution on transducer surface.The method of measuring normal vibration velocity on transducer surface is established,which provides a reference for the experimental measurement.2.The optical interference principle and structure of a Fabry-Perot interference type optical fiber vibration sensor are analyzed,and the sensor output characteristics and influencing factors are simulated.The relationship between reflectivity at both ends of sensor interference cavity and output intensity is obtained.The influence of air gap size as interference cavity on output intensity is further analyzed,which lays a foundation for the design of HIFU acoustic field measurement system based on optical fiber vibration sensor.3.A method of detecting the absolute amount of Doppler frequency shift using the frequency-selective characteristics of the Fabry-Perot optical resonant cavity is proposed,and the optical feedback signal modulation process and the interference output signal are theoretically analyzed.An all-fiber Doppler vibration measurement experimental system based on optical fiber vibration sensor is designed,and the selected experimental instruments are introduced.4.According to the all-fiber Doppler vibration measurement system scheme,a corresponding vibration measurement experimental platform is built to realize a non-contact measurement of the piezoelectric ceramic surface vibration velocity.The experimental results show that the proposed system can accurately demodulate the vibration velocity of the piezoelectric ceramic surface,which provides experimental verification for the vibration velocity measurement method.5.All-fiber Doppler vibration measurement system based on optical fiber vibration sensor is built to experimentally verify the vibration velocity distribution of HIFU transducer and the sound pressure of HIFU acoustic field.Experimental results show that the proposed system can accurately demodulate the vibration velocity of HIFU transducer surface and the distribution of HIFU sound field can be obtained by using the measured vibration velocity distribution and Rayleigh integral model.The research work in this thesis provides a theoretical basis for non-contact measurement of transducer surface vibration velocity,accurate characterization of HIFU acoustic field and non-invasive detection of sound pressure,and provides a new method for measuring acoustic field with high sound pressure and small focus area.