Study On Physical Properties Of PDMS-based Composite Photo-induced Ultrasound Transducer And Applications

Scientific research should insist to the"four facing",among which the guiding ideology for facing people's life and health shows that the health of the whole people should be placed in the strategic position of priority development.Therefore,related research on"Healthy China"is of great significance.Ultrasound plays an important role in the treatment and diagnosis of diseases.The most core of ultrasonic medical treatment is the ultrasound transducer which generally adopts an electric drive device based on the piezoelectric effect.The piezoelectric ultrasound transducer has complex electric connections and electromagnetic interference,etc.Recently,based on the photoacoustic effect optoacoustic transducer has been widely concerned,which have the characteristics of no electrical connections and anti-electromagnetic interference.The optoacoustic transducer is mainly composited of inorganic materials(light-absorption materials)and polydimethylsiloxane(PDMS).When the composite is irradiated by a pulsed-laser,local heating occurs,and periodic thermal expansion happens,resulting in the generation of acoustic wave.The optoacoustic transducer has these potential applications,such as drug delivery,nerve stimulation,tissue imaging,and others.However,there are still challenges in improving the energy conversion efficiency and frequency of optoacoustic transducer.The intensity of ultrasound affects the effect of ultrasonic treatment;the frequency of ultrasound determines the resolution of ultrasonic diagnosis.In view of this,based on theoretical analyses and experiments,the selection of light absorption materials,thermoacoustic theory,structural design,improvement of energy conversion efficiency,frequency regulation,and applications of ultrasonic therapy and diagnosis for the optoacoustic transducer were studied in this paper.Firstly,in order to explore the influence of the thermal performance of the light-absorption materials on the acoustic pressure characteristics of the optoacoustic transducer.The effect of the size of the light absorption materials carbon nanotubes(CNTs)on its thermal performance and the acoustic pressure characteristics of the optoacoustic transducer were studied.The length of CNTs influence the thermal conductivity by affecting the mean free path of phonons.It causes the thermal conductivity of CNTs to increase with the length and finally converge to a fixed value.The phonon group velocity of CNTs is affected by diameter,resulting in an approximate inverse ratio of thermal conductivity to diameter.According to experimental and theoretical analysis,the CNTs with long length(20-30?m)and short diameter(?5 nm)were selected for the preparation of the optoacoustic transducer with high energy conversion efficiency.Because they have better thermal properties and can effectively improve the thermal transmission efficiency between CNTs and PDMS.Secondly,for the sake of solving the problem that high-intensity ultrasound transducers are easily damaged in therapeutic applications,the acoustic self-healing performance of the focused self-healing optoacoustic transducer and the application of ultrasound therapy were studied.The transducer produced a high acoustic pressure of more than 50 MPa and realized the dissolution of an animal thrombus in vitro.The ultrasound transducer can self-healing after being damaged.The experiments found that after 10 times of damage and repair,the peak acoustic pressure of the transducer can be self-healed to 92.3%of its initial value,and the center frequency basically remains at 2.5 MHz.The performance of self-healing is of great significance for enhancing the life time and anti-fatigue characteristics of the device.Then,on behalf of modulation the frequency of the optoacoustic transducer,the CNTs array-PDMS composite optoacoustic transducer of the thermal conductivity anisotropic was designed.Theoretical analysis showed that the frequency of the transducer is approximately inversely proportional to its thickness.In this paper,inductively coupled plasma etching(ICPE)technology was proposed to etched the transducer's thickness from 200?m to 18?m,and the central frequency was increased from 3 MHz to 20.2 MHz,thus the frequency of the transducer was modulated.The ultrasound imaging of the phantom was performed.Finally,on behalf of further improve the energy conversion efficiency of high-frequency optoacoustic transducer,we use perovskite MAPb I₃ with high light absorption,low specific heat capacity and thermal diffusion coefficient as the light absorption material.The frequency characteristic,energy conversion efficiency,and the application of ultrasonic imaging of PDMS/MAPb I₃/PDMS/Glass layered structure optoacoustic transducer were studied.The central frequency of this transducer is as high as 29.2 MHz,and the energy conversion efficiency is 2.97×10^-2 which is the highest value reported.The results showed that:MAPb I₃ high light absorption,low specific heat capacity,and low heat diffusion coefficient can improve the energy conversion efficiency of the transducer;the MAPb I₃layer is as thin as 323 nm under the condition of ensuring light absorption,which can improve the heat transfer and frequency characteristics of the transducer;the layered structure of the transducer improves the output acoustic pressure.Finally,MAPb I₃/PDMS composite optoacoustic transducer was prepared on multi-mode fiber,and an all-optical ultrasonic imaging system was built to realize high-resolution ultrasonic imaging of fish-eye section.