| Laser ultrasound imaging technology,as an emerging imaging tool,combines optical imaging with ultrasound imaging,which has very wide applications in biological therapy,oil and gas exploration,non-destructive testing and other fields.With the continuous improvement of residents’income,the quality of life and the happiness index also showed a linear upward trend.An increasing number of people is becoming aware of the importance of health testing and the resulting demand for medical treatments.Photoacoustic imaging provides a new way for medical treatment,which can image the internal tissues of the human body,and is a very important technology for the diagnosis and detection of diseases.As fossil energy sources such as oil and natural gas are currently in short supply,it is also particularly important to study the surface energy structure and explore more oil and gas resources.Photoacoustic imaging has played an important role in the field of oil and gas exploration.Laser ultrasonic excitation technology is used to image seismic physical models,to provide basic data for in-well seismic surveys,to simulate in-well seismic wave field surveys from actual data,and to identify and analyze the propagation characteristics of seismic waves in complex wells.In this thesis,based on laser ultrasonic excitation technology,both excitation and reception ports of the imaging system are optimized,and a multifunctional nanomaterial SiO2/C/Fe3O4 and a highly sensitive Fabry-Perot interferometric ultrasonic sensor are developed.Details are as follows:At the laser excitation port,the multifunctional nanomaterial SiO2/C/Fe3O4 is designed and prepared not only to improve the conversion efficiency of laser-excited ultrasound and provide high-quality laser excitation signal;but also to improve the thermal threshold of biological tissues and model surfaces.The multifunctional nanomaterial SiO2/C/Fe3O4 was synthesized by ultrasound-assisted Stober method,which is low cost,can be prepared in batch,has high success rate and is easy to operate.The material morphology and structure are analyzed using various characterization tools such as scanning electron microscopy,transmission electron microscopy,X-ray diffraction,and UV-Vis absorption spectroscopy.On the theoretical side,the finite element analysis method is used to build models to analyze the photoacoustic signals of different materials.On the experimental side,a laser ultrasonic excitation system is built to characterize the photoacoustic properties of materials.A high-sensitivity fiber optic Fabry-Perot interferometric ultrasonic transducer was designed and fabricated at the ultrasonic receiver port to improve the response to ultrasonic signals.The ultrasonic sensor is made based on the high sensitivity of the tapered fiber and the focusing effect of the curved end face.First,the tapered optical fiber was made using a flame-drawn taper system.Then,the end face of the tapered optical fiber was processed using a manual discharge from an optical fiber fusion machine,resulting in a curved end face.Finally,the Fabry-Perot ultrasonic sensor with high sensitivity was made using a gold film as the reflective surface.An ultrasonic test system was built to characterize the response of the transducer to ultrasonic waves of different center frequencies.The experiments showed that the ultrasonic transducer responded well to ultrasonic signals with a center frequency of 1 MHz.The novel composite nanomaterial SiO2/C/Fe3O4 and the highly sensitive Fabry-Perot interferometric ultrasonic sensor investigated in this thesis are of great significance for laser ultrasonic excitation technology.In the subsequent research,new photoacoustic functional materials and fiber optic ultrasonic sensors were combined to work on a complete system of all-optical imaging with improved imaging quality.We continue to innovate and optimize the laser ultrasonic excitation system in two areas:photoacoustic functional materials and the design of fiber optic ultrasonic sensors. |
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