Research On Photoacoustic Phased Array Technology In Metal

With the continuous development of modern industry,the requirements for non-destructive testing technology are also increasing.Based on conventional ultrasonic testing technology,while facing with the high-pressure and high-temperature industrial operating environment and the complexity of the industrial structure,therefore,ultrasonic phased array technology and laser ultrasonic technology have emerged.which also become popular research directions in current non-destructive testing technology.This paper studies the photoacoustic phased array technology that combines these two technologies.The intensity-modulated laser excites photoacoustic signals on the metal surface,and how to focus the photoacoustic signals excited by multiple such laser array elements at a specified position.The above is the key research content of this article.The main content of this thesis are as follows: Firstly,it explains the background and significance of the research on the subject photoacoustic phased array technology,investigates the research content involved in the subject,checks and sorts out the current research status at home and abroad including laser ultrasound technology,ultrasound phased array technology,and laser ultrasound array technology,as well as determines the research direction of this article.Secondly,the photoacoustic effect and the theory of the phase-conjugation-based acoustic focusing method used in this paper are described.The sound field simulation of this method is carried out using COMSOL software,the basic principle of acousto-optic modulator which is the key device to realize intensity modulated in this thesis is introduced.Thirdly,an experimental system with fiber laser as excitation source was designed through Solid Works software,including rack design and laser array fixed structure design.The system uses an acousto-optic modulator to modulate the continuous laser with a square wave,which greatly reduces the complexity of the experimental system,at last the experimental system was built according to the design.Fourthly,based on the Xilinx platform,a ten-channel signal generator is designed as the modulation signal source of the laser array,including the physical design and digital logic design of the signal generator.And finally the time response of the key component of the experimental system,the acousto-optic modulator gets tested and establishes a sound distribution test system.Fifthly,it carries out experimental research to analyze the influence of different parameters such as frequency,phase difference,number of array elements,focus point position,etc.on photoacoustic focusing.The experimental results show that:(1)The higher the laser modulation frequency,the smaller the focus point width,and the better the focus effect;(2)The focusing effect of the linear array on the two-dimensional plane is better than that of the area array,and the increase in the number of array elements can greatly improve the acoustic focusing effect;(3)The farther the focus point is from the array,the weaker the focusing effect.This paper verifies the acoustic focusing ability of the photoacoustic phased array,analyzes the influencing factors of focusing,and lays the foundation for the application of this technology in the field of non-destructive testing.