Eddy current detection is the basic principle of the magnetic effect of the application of current, ultrasonic flaw detector quotation will be a sinusoidal wave current to encourage the probe coil, when the probe is close to the metal surface, the alternating magnetic field around the coil causes an induced electromotive force on the metal surface. For the metal material of tablet computer, the inflow of induced electromotive force is a ring of coils in the same boat, shaped near the vortex, which is called the eddy current. In addition, the eddy creates a magnetic field of the same frequency, which is in the opposite direction of the coil's magnetic field.
The dissipation resistor of the eddy current safety channel and the anti-magnetic flux caused by the eddy current reflect the surface to the probe coil, which changes the current size and phase difference of the coil, that is, changes the characteristic impedance of ultrasonic flaw detection. Therefore, when the probe moves on the metal surface, the eddy current flaw detector encounters defects or material, specifications and other changes, the reaction force of the eddy current magnetic field on the coil is different, resulting in the transformation of the coil characteristic impedance. According to the measurement of such changes by the eddy current detection instrument, it can distinguish whether the metal surface is defective or other chemical properties change. There are many factors that harm the eddy current field, such as the coupling level of the probe coil and the raw material to be measured, the appearance and specification of the raw material, the electrical conductivity, magnetic permeability, and its shortcomings. Therefore, the basic principle of eddy current can be used to deal with the problems of flaw detection, thickness measurement and screening of metal composite materials.