| Giant magnetization materials—Iron-gallium?Galfenol?alloy has the advantages of low saturation magnetic field,small hysteresis and large strain value.The use of Galfenol alloy in the guided wave detection device can improve the detection efficiency and output voltage amplitude of the detection device.The Galfenol-based waveguide sensor operates under the common excitation of static magnetic field and dynamic high-frequency magnetic field,and there is a complex electro-magnetic-force-acoustic coupling.By considering the nonlinearity of the magneto-magnetic coupling relation,a complete theoretical model of guided wave excitation,propagation and reception is established by using the finite element method,makes up the deficiency that the existing model only contains the excitation but lacks of the reception,and guides the design and optimization of the guided wave sensor.First,the low and high frequency characteristics of the Galfenol alloy were tested.When the frequency is lower than 100Hz,the hysteresis curve and magnetostrictive curve of Galfenol alloy were tested and analyzed.When the frequency is higher than 20kHz,the hysteresis curve of the ring Galfenol alloy was tested,and the electromagnetic loss and magnetic energy storage of the Galfenol alloy were analyzed.The experimental results show that,under static magnetic field,the application of appropriate compressive stress can improve the saturation strain of the material;under high frequency magnetic field,the electromagnetic loss of Galfenol material increases with the increase of frequency.Therefore,in the Galfenol-based waveguide sensor optimization design,the appropriate compressive stress to the material and a lower excitation frequency which meets the operating frequency?>20kHz?requirements are required to be applied.Secondly,the structure and detection principle of Galfenol-based waveguide sensor are introduced.The conduction wave transmission in the plate structure is analyzed.The dispersion curve of the Lamb wave is drawn by using the Matlab software,determining that A0 mode is used in the detection process.This paper focuses on the multi-field coupling characteristics of the Galfenol-based waveguide sensor,including the electro-magnetic-mechanical-acoustic coupling of the excitation,propagation and reception processes,and deduces the weak solution form of the coupled equation.The model is analyzed by COMSOL finite element software.By analyzing the magnetic field distribution of the sensor and the strain and stress of the observing point,comparing the velocity of the guided wave and the velocity in the dispersion curve,the effectiveness of the simulation model is proved.Finally,the nonlinear force-magnetic coupling model is analyzed,which plays a major role in the Galfenol alloy waveguide sensor.The influence of the bias magnetic field and the stress on the output strain and the magnetization coefficient is studied.Magnetic field strength of 4.8kA/m,the magnetic flux coefficient reached a maximum of 1.56×10-8m/A under the magnetic field strength of 4.8kA/m,at this time,the conversion efficiency reached the maximum;appropriate compressive stress?<60MPa?will increase the value of magnetostriction.The parameters of the static magnetic field and the dynamic magnetic field are optimized by the above theory.It is concluded that when the remanence of the permanent magnet is 1.0T,the separation distance is 2.5mm and the excitation current frequency is 40kHz,the amplitude is 1A,the performance of the sensor can achieve the best.And the optimized parameters are provided for the sensor.The influence of the defect on the output voltage is analyzed.It is proved that the Galfenol-based waveguide sensor can be used for the detection of defects. |
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