| Metal detector is an equipment be used to detect metals. There are many types of metaldetectors, including conveying metal detectors, walk-through metal detectors, handheld metaldetectors and subterranean metal detectors and so on. The metal detector we researched in thispaper is a kind of subterranean metal detector. It has two detection modes: the discriminationmode and the pin-point mode. In the discrimination mode, the detector can discriminate seventypes of metals, and In the pin-point mode, it can estimate the depth of the seven types ofmetals.On the basis of reviewed the technology of subterranean metal detector in and out ofabroad, we selected the induction balance metal detection technology as a foundation for thesystem in this paper. The system is divided into two parts, the signal detection part and thesignal processing part. The signal detection part consists of a number of analog circuit,including the transmission circuit, the receiving and coupling circuit, the amplifier and filtercircuit, and the orthogonal demodulation circuit. The signal processing part is used to processthe received signal, including the algorithm for filtering, the algorithm for discrimination andthe algorithm for ground-canceling in the pin-point mode.In the first place, we introduced two mainly theoretical foundation of the inductionbalanced subterranean metal detector, the electromagnetic induction theory and the eddycurrent theory. By them we explained the form of the metal signal. Then, the paper analyzedthe received signals induced by ferromagnetic metal non-ferromagnetic metal respectively.Next, the article introduced the main circuit and the formation of metal signal of the detector,and processed the original signal which sampled by ADC with digital filter preliminary. Then,we introduced and analyzed the influence of background noise on the subterranean metaldetector, and we designed some algorithms to eliminate the influence of this noise. We testedthe system we designed in the last. |
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