Study Of Chaotic Oscillator For Metal Detection

The metal detector is a metal detection equipment, which uses physical principles such as electromagnetic induction, to detect the induced signal from mixed goods or human-carrying metal material, and thus alarm. The detector on the assembly line can detect metal substance mixed in the raw materials, to protect production equipment or control quality of food, medicine and other products. This paper discusses the detectors for industrial production and product quality control. In order to improve the sensitivity of the detector, this paper will design a chaotic detection system for the metal detector which is high accuracy with reasonable structure and easy to operate to detect weak signals emitted by the metal detector probe.There is no chaotic detection technology for metal detector reported, so the topic is the first of application and basic research. The chaotic detection system for the metal detector is not a system which is simply combined with the probe. According to the characteristics of the metal detector, an innovative chaotic detection system should be designed. Especially problems should be solved such as the higher frequency detection, the threshold determination, high frequency chaotic detection circuit and elimination of blind spot. This innovative technology can provide theories and ideas to other fields such as pipeline inspection, power system harmonic analysis and fault alarmWith the increasing requirements of the users to the product quality, and the national strict supervision on the safety of products, high sensitivity metal detector market will be very broad. Therefore, to develop a high sensitivity and low cost metal detector has considerable economic benefits. In addition, the core technology of autonomy to get rid of dependence on foreign products has considerable social benefits. The main work of this paper is summarized as follows:(1) According to current conclusions and methods, this paper makes a computer software program by Matlab. The software can calculate the weak voltage signal from the probe, when different material metal particles (metal impurities) with different diameters, is passing through the balanced coil of the metal detector. Analysis of the characteristics of the signal can help to determine the accuracy and frequency of chaotic detection system. It provides the theoretical basis to design chaotic detection system for metal detection.(2) Based on the principle of weak signal detection of L-Y chaotic system, a high frequency chaotic detection system for metal detection has been built. The Lyapunov characteristic exponents of the system have been obtained through the RHR algorithm. It can help to determine the state of the system accurately, and provides quantitative means to accurate discrimination of the system state. On this basis, this paper proposes an improved numerical simulation model. The model has been built by the simulation toolbox Simulink of Matlab. The model can output the L-Y system numerical solution, phase diagram and Lyapunov characteristic exponents simultaneously. The available Lyapunov characteristic exponents can judge the state of the system, and overcome the disadvantage of observing phase diagram to determine system state. This model is used to analyze the dynamic behavior, sensitivity to weak signals and detection performance to weak signals. Simulations show that L-Y is a chaotic system, which is very sensitive to the initial value. A slight increase of the amplitude of the sinusoidal signal can make the system change into to the large-scale periodic state from chaotic state. And then the signal-to-noise ratio is obtained. The feasibility and effectiveness are verified.(3) In order to solve the problem that present Duffing chaotic circuit is only applicable to the low-frequency signal detection, this paper proposes an improved L-Y chaotic detection circuit. This circuit can solve the problem that the high magnification can cause instant saturation. If appropriate adjustments to the parameters of the circuit, it can detect the weak signal from low to high frequency. The detailed designs of each unit circuit have been finished.(4) The L-Y chaotic circuit is built by the Electronic Work Platform software (Multisim). The dynamic behavior and the detection performance of weak signals of the circuit in the higher frequency have been analyzed. Simulation results show that:The circuit is a chaotic circuit, and it is very sensitive to the initial value. If slightly increase in the amplitude of the sinusoidal signal, the circuit will change into the large-scale periodic state from the chaotic state. If the thermal noise is added to the circuit, simulation results show that:with the increase of the accuracy of the critical threshold, the signal-to-noise ratio is becoming less and less. Additionally, from the analysis of L-Y circuit structure, it can be seen that the circuit is composed by two low pass filters in series, so it can filter out high frequency noise. This is verified by the amplitude-frequency characteristic curve which is outputted by the simulation. This phenomenon is hard to be discovered by the pure numerical simulation of the Matlab.(5) This paper proposes dual chaotic system detection method to eliminate the blind spot. The causes why there is the blind spot have been discussed. In order to solve this problem, two chaotic systems are involved in the detection. The two systems can complement each other to eliminate the blind spot. Numerical simulation is used to verify the feasibility of the method. Another method to eliminate the blind spot detection-autocorrelation method, is discussed. The method can both eliminate the blind spot and filter noise. The autocorrelation method can be used together with chaotic detection technology.