Technique Research On Multiple Frequency Induction Material Recognition

The rapid development of modern society, In the meantime, security issue and terrorism are becoming a matter of concern for more and more people. Safety check for people is mainly by the security gates and hand-held metal detectors at important places such as international conferences, sports venues and airports.though a combination of these two approaches meets the requirements on many occasions,the shoe is a blind area for detection.Therefore,developing a shoe security detector has a huge market with wide prospect.At the beginning, this paper summarizes the development process of metal detection technology, introduced the current research status of metal detection technology and the technological index of the security detector, analyzes the theoretical basis of metal detection - Electromagnetic induction and the Implementation Principle of Security detector, through analysis of the phase characteristics of various metals in a magnetic field by experiment, obtaines important experimental results to identify the materials. Then the overall design is briefly intruduced. the various parts of the hardware and software is started later, to prevent interference takes some anti-interference measures. The debug request and modulation process of the machine is detailed. The pictrue of transmitting and receiving waveforms in practice is showed.In signal processing aspect, the paper discusses of the functions of the digital down-conversion, details of the principle and design of the DDS and NCO technology in the heterodyne modulator, the principle of decimation and interpolation in multi-rate signal processing ,and the capability of the cascade integrator comb filter and half-band filter. According the index of performance of security detector, the narrow-band filter is designed and taken a variety of simulation. Then the paper makes the various modules to establish the necessary down-conversion system,and carries out simulation of down-conversion and filtering to verify the feasibility of the scheme. Finally two methods used to programming the TMS320C2407A , one is use of the eXpressDSP toolbox of matlab / simulink that the program of DSPchip is directly generated by graphics file, another is use of C language and Assembly language to write the program of DSP chip. The paper discusses in detail the two Implementation Schemes, both having efficiency and applicability, the paper chooses the second method to realize Digital Down Converter.