| With the continuous progress of science and technology and the continuous improvement of computer computing performance,electromagnetic ultrasonic detection technology has become a hot spot in the field of ultrasonic detection.Electromagnetic ultrasonic nondestructive testing(EMUS)technology plays an important role in nondestructive testing because of its high efficiency and no coupling agent.With the development of electromagnetic ultrasonic transducer and the development of electromagnetic ultrasonic technology,electromagnetic ultrasonic nondestructive testing has been widely used in all aspects of manufacturing,such as the detection of aircraft wings and train tracks.Electromagnetic ultrasonic transducer is the core of ultrasonic excitation and reception in electromagnetic ultrasonic nondestructive testing technology One piece.Because of its unique advantages and characteristics,electromagnetic ultrasonic transducer has a very important research value and a wide range of application scenarios in the field of nondestructive testing.in order to analyze the factors affecting the impedance of the electromagnetic ultrasonic transducer and the distribution of lorentz force in the tested block,the impedance of the electromagnetic ultrasonic transducer and the lorentz force excited in the non-ferromagnetic plate are studied in this paper.Based on the neglect of proximity effect and displacement current,a theoretical model of electromagnetic ultrasonic transducer EMAT established by electromagnetic field theory.Based on the analysis and calculation of the electromagnetic ultrasonic model,the calculation formulas of the impedance of the double-layer spiral coil and the eddy current density of the measured point in the tested block are derived.The applicability and reliability of the double-layer spiral coil electromagnetic ultrasonic transducer model can be proved by analyzing the measured value of coil impedance and the calculated value of coil impedance.To improve electromagnetism The energy exchange efficiency and signal-to-noise ratio ofthe transducer can match the impedance of the excitation coil of the electromagnetic ultrasonic transducer.The theoretical calculation of the Lorentz force on the measured points in the tested blocks can be used as the theoretical basis of the electromagnetic ultrasonic transducer spiral coil electromagnetic ultrasonic transducer.Firstly,the energy transfer mechanism and detection principle of double-layer spiral coil electromagnetic ultrasonic transducer are expounded,and the core components of electromagnetic ultrasonic transducer are explained.for the tested members with different materials or structures,different types of ultrasonic can be used to detect them,and the factors related to the energy exchange efficiency of the electromagnetic ultrasonic transducer are analyzed.the design of the excitation coil of the electromagnetic ultrasonic transducer is guided.the spiral coil used in the impedance measurement experiment is introduced.Then,based on the assumption,the theory model of the double-layer spiral coil electromagnetic ultrasonic transducer is presented,and the theoretical calculation method is put forward to solve the impedance problem of the electromagnetic ultrasonic transducer.According to the theory model of electromagnetic ultrasonic transducer and electromagnetic field theory,the impedance integral expression of double helix coil is derived.On the basis of this,the eddy current integral expression of the double-layer coil electromagnetic ultrasonic transducer in the tested block is derived,and the Lorentz force in the tested block is further obtained.In order to calculate the static Lorentz force generated in the test block under the action of excitation current,the static permanent magnet is analyzed and calculated.Forever in the analytical model of the magnet,the vector magnetic position generated by the permanent magnet in the space region can be equivalent treated by passing a constant current into the coil.To obtain the static Lorentz force,the Br and Bz,generated by the static permanent magnet in space are first obtained and transformed into series by the method of truncation region characteristic function expansion.and then the time domain solution is transformed by fourier transform.Finally,the static Lorentz force on the measured point in the test block is obtained.After that,the expression of the coil impedance is transformed into a series form whichis convenient to calculate and solve by using the method of truncation region characteristic function expansion,and the Mathematic software is used to program it to calculate the impedance value of the double helix coil.Based on the validation of the model,the integral expressions of eddy current and vector magnetic positions in the test blocks are transformed into series expressions which are easier to solve.After obtaining the eddy current density and magnetic induction intensity of the measured points in the tested blocks,the results are obtained The Lorentz force is calculated by the formula of Lorentz force.In order to test the reliability of electromagnetic ultrasonic transducer model,Agilent impedance analyzer was used to measure the impedance values of coils with different inner diameters at different frequencies,and compared with the theoretical calculation results,and analyzed and displayed in the form of charts.Based on the verification of the model reliability,the influence of different coil lift-off distance and coil width on the excitation coil impedance is studied,which provides theoretical guidance for the optimization of electromagnetic ultrasonic transducer.Finally,in order to solve the Lorentz force,the permanent magnet is modeled.The influence of different coil lifting distance,coil turn number and coil inner diameter on Lorentz force is studied by calculating the eddy current density and Lorentz force. |
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