Introduction to the basic principle of square resistance detection

According to Faraday's law of electromagnetic induction, a changing current can produce a magnetic field, and a changing magnetic field will cause the magnetic flux in the conductive material to change, resulting in an electric current. According to this principle, when an alternating current is attached to a metal coil, the coil will generate a magnetic field under the action of current transformation, and the magnetic field generated must also be alternating corresponding to the changing form of the current. At this time, if the coil is close to a conductive material, the alternating magnetic field generated by the alternating current in the coil will come into contact with the conductive material, and the magnetic flux on the surface of the material will also change accordingly under the action of the alternating magnetic field, and then generate a current on the surface of the conductive material. As shown in Figure 1, a sinusoidal alternating current is fed into the conductive coil, and an alternating magnetic field H is induced inside the coil under the action of a sinusoidal current, which excites eddy currents in the conductive material. In the same way, the alternating eddy current will also generate an induced magnetic field, and this magnetic field will be opposite to the direction of the magnetic field H, and the figure of merit and impedance values of the conductive coil will change under the action of the magnetic field. In eddy current testing, the conductive coil is the sensor as the probe, and the conductive material is the detected workpiece, and other material types, sizes, permittivity, permeability, surface finish and other parameters can change the density of the eddy current distribution, and then affect the size and density of the induced magnetic field. When the surface of the conductive material sample is uniform, the induced magnetic field is a stable alternating magnetic field in the detection, the use of control variables, when other elements have not changed, and the different resistivity of the sample material can be calculated by the change of coil impedance to calculate the AC impedance, and at the same time, the distortion and impedance values can be quantitatively calculated, and the functional relationship of the change can be quantitatively calculated, therefore, by measuring the output voltage of the conductive coil, and analyzing and collecting the voltage data, the calculation of the resistivity of the material can be completed.