New design of differential metal detector for long distance metal detection

This paper presents a new metal detector design structure based on the traditional pulse induction (PI) metal detector (MD). The new design is able to restrain interference to the receiving coil resulted from the magnetic field of the transmitter coil and the ambient noise. The new metal detector is composed of transmitter coil, compensation coil and differential receiver coil, with all modules arranged in the same plane. This paper determines the relationship between the whole structure and each module based on theoretic analysis, and assures the signal-to-noise ratio of the whole design by use of the constrained relationship between radius and number of windings of each module, and builds a new detector. Upon the experimental verification, it is found that the output voltage of the receiving coil is only a few microvolts when not approaching metal, which is 100 times lower than that of the traditional differential metal detector. The metal can be detected clearly based on changes of the output voltage when approaching metal. Therefore, the new design has the potential for the long distance metal detection.