Research On Magnetoelastic Coupled Torsional Wave Displacement Sensor Based On Magnetostrictive Material

The magnetostrictive material will deform and generate magnetostriction phenomenon when the externalmagnetic field acts,which forms the torsion guide wave in the material.The magnetoelastic coupled torsional wave displacement sensor utilizes the propagation delay of the vertical torsional guided wave for displacement(or level)measurement.There are many advantages of the sensor,like high precision,strong anti-interference,strong environment adaptability.It has also become an important branch of today's sensor field with important research value and a wide range of applications.This thesis briefly describes the correlational research and application background of the magnetostrictive displacement sensor,and introduces the advantages and development status of it.The basic principle of the magnetoelastic coupled torsional wave displacement sensor is elaborated in detail.Coupled theory,magneto-elastic coupled torsional wave generation mechanism and magneto-elastic coupled torsional wave detection principle are in-depth studied and analyzed.Then,according to the pressure-magnetic equation of ferromagnetic materials,the electromagnetic force generated in the waveguide wire is leaded into the elastic mechanical equation to determine the deformation of the material,thereby constructing the wave equation of the torsional wave.Using the wave equation and getting the specific solutions of boundary conditions,the strain of the waveguide wire of the torsional wave propagation is obtained.Analyzing various magnetic field energies present in the waveguide wire,and combined with Maxwell's equations and the Gilbert magnetization precession equation with a damping term,which obtain the relative magnetic permeability of the waveguide wire at the coupling magnetic field,the expression of the output voltage of the induction coil is constructed by using the electromagnetic induction theorem.Moreover,according to the design requirements of the measurement scheme,the signal conditioning circuit of the magnetoelastic coupled torsional wave displacement sensor system is given to implement the power amplification of the excitation signal,amplification of the output inductive signal,voltage comparison and shaping.In order to reduce the measurement error caused by the influence of the temperature on the propagation speed of torsional waves,a temperature compensation measurement scheme using the ratio of the time difference between two magnets with a fixed relative position was proposed.The principle and advantages of the proposed scheme were elaborated in detail.Finally,a hardware test platform was designed based on the sensor system design.It was used to verify the measurement circuit of the system.The experimental waveform shows that the circuit design scheme meets the actual needs.Both analog and digital measurement schemes were measured and verified respectively.The static characteristics of the related measurements were given: the theoretical linearity was ± 0.555%,±0.836%,and the sensitivity was 823.83mV/m and 0.352ms/m respectively.The hysteresis was 0.585% and 1.071%,respectively;the repeatability was ±1.0462% and ±0.1942%;the total system accuracy was 1.312% and 1.372%,respectively.This platform is used to verify the temperature compensation scheme.The experimental data shows that the maximum relative error is 0.366% with the temperature compensation scheme and 2.27% without the temperature compensation.This shows that the scheme reduces the measurement relative error.At the same time,the pulse width and frequency of the excitation source and the number of turns of the induction coil that affect the output voltage are verified.The experimental results are in accordance with the output voltage model,which shows that the model has certain rationality and practicality.The output voltage theoretical calculation model established in this dissertation has certain engineering application value for the theoretical research of iron-nickel alloy magnetostrictive displacement sensor.The proposed temperature compensation strategy for the ratio of the time difference between two magnets is innovative.