| With the accelerated pace of life, A modern commercial business changes from the traditional of counter sales to the open. Open business model has brought new problem. One of them is Commodity Security. In recent years, the theft problem of goods becomes more and more prominent. EAS (short for Electronic Article Surveillance )change the way of closely attention to use technological. Based on the high-tech knowledge can prevent some stolen of the books and goods. And therefore, the research of developing Electronic Article Surveillance (EAS) is up to us.Now there are about four kinds of systems based on different principle. They are Electromagnetic system(ES), Acoustic Magnetic system(AM),Microwave Frequency system(MF) and Radio Frequency Identification(RFID).Among these, Electromagnetic system, which we will study and achieve, is the most high security.Misinforming, which is an important index requires the picking-up of resonant frequency to be accurate and the interim band to be less than 1%. But nowadays it's too hard to make a filter in traditional ways, whose band is narrow like that.After analyzing some designing problems, a scheme of the Electronic Article Surveillance system has been proposed, especially the processing of the signals received, the core of which is synchronous detector and narrow-band filter. Also clock-signal generators are shortly introduced in order to running and testing the circuits. We will give EAS detector's principle and way of realization.In the designing process, and on the basis of US Patent Application No.4384281, Theft detection apparatus using saturable magnetic targets, we break the traditional approaches. At last we realize the detecting circuits using a few chips with high stability, whose band width is about 100Hz in processing the116.508 KHz and 117.762 KHz signals.Now there has been no EAS systems which transmit frequency is 58 KHz and is based on amorphous magnetic materials. They can reduce consumption of copper and transmitter power. |
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