Research On Positioning Method Of Non-magnetic Metal Conductor Based On Eddy Current Magnetic Effect

The target detection technology based on magnetic anomaly plays an important role in geological exploration,underwater monitoring,military defense and other fields due to its wide detection range,high positioning accuracy and all-weather monitoring.The traditional method of ferromagnetic target location is that the metal target is regarded as a magnetic dipole,which can be detected and located by solving the position coordinates and magnetic moment vector of the magnetic dipole.However,some metals or alloys themselves are non-magnetic,such as copper,aluminum alloy,non-magnetic steel and so on.The main work of this paper is to study the localization of non-magnetic metal targets based on the magnetic effect of eddy current.According to the principle of electromagnetic induction: when the magnetic flux through the metal conductor changes,the induced electromotive force is generated on the conductor,and then eddy current is generated on the conductor surface.The magnitude of eddy current is related to the conductivity,permeability,shape of conductor and the change speed of magnetic field around the conductor.There are three ways to change the magnetic flux:(1)the metal conductor moves in the non-uniform magnetic field;(2)the metal conductor rotates in the magnetic field;(3)the variable magnetic field passes through the metal conductor.The eddy current caused by the first two ways is called dynamic eddy current,and the eddy current caused by the third way is called induced eddy current.In this paper,through the transmitting system composed of power supply module and drive module,AC signal is applied to the coil to generate alternating excitation magnetic field in the space where the non-magnetic metal target is located,and then induced eddy current is generated on the metal surface,which will produce eddy current magnetic field in space.In view of the fact that the eddy current magnetic field is always mixed with exciting magnetic field and complex background noise,a signal extraction algorithm is designed to separate the eddy current magnetic field from the mixed magnetic field and take it as the measurement value of eddy current magnetic field.The theoretical formula of eddy current magnetic field produced by non-magnetic metal target is derived,and the estimated value of eddy current magnetic field at the observation point is calculated by the formula.Finally,the particle swarm optimization algorithm is used to locate the non-magnetic metal target,and the aluminum alloy shell with the maximum size of 0.2m is located in the plane of 1.2m × 1.2m.The results show that the positioning error in each axis is less than 2%.