Research Of Weak Signal Detection Principle Based On Chaos Theory And Its Application To Metal Detector

Metal detector is a kind of equipment for metal detection. It makes use of physical principles of electromagnetism and radial and gets induction signal for metal objects in mixture and body to effect an elimination and alarm. With the improvement of living standard, people are more concerned about the security of food, medication and dry-goods. Metal content is an important quality target over the above-mentioned products. So it is necessary that metal is detected for these products to examine the defective ones before delivery. At present high-precision metal detectors are mostly imported because of technical limitation which is powerful but expensive. With the development of modern industry towards high-precision and high-quality and customer's requirements on product quality, high-precision metal detectors will have a very broad market. Therefore, there are very considerable economic benefits to develop a high accuracy but relatively low cost metal detector. In addition, there are very considerable social benefits to make the core technology independent and get rid of dependence on foreign products.Chaos theory is a rapidly developing frontier. One of the basic features of chaotic systems is the initial value sensitivity. That is, each initial value corresponds to an unique movement track. Small changes in initial value will lead to tremendous changes in track of chaotic systems.Therefore,to use this feature.by detecting the tremendous changes in chaotic orbit.we can determine small changes in initial values. This is the theoretical basis on which chaotic detection of weak signal based.Duffing oscillator is a chaotic system that has been proved. Duffing equation describes the nonlinear dynamic system, including periodic oscillation, bifurcation, chaos and other complex states and has become an important model for study of chaos theory.In this paper, we choose the chaotic duffing oscillator as a model system to study.At first, we derive and analyze the mathematical equation and trajectory of duffing oscillator.establish the simulation model of duffing oscillator based on its mathematical model in Matlab/Simulink enviroment,and then analyze the method of weak signal detection by disturbing the driving force.When using this method,the frequency of weak signal is limited,so we propose a new method of detecting weak signals by disturbing the damping ratio of duffing oscillator.This method makes weak signals be no longer limited by frequency,and expand the applications of duffing oscillator.Everything has two sides.the method of disturbing damping ratio has no limit on the frequency.but also it loses its natural immunity to random noise.So we make further analysis on the questions of noise and stability of the duffing oscillator.Based on the full study of chaotic system and the pinciple of its weak signal detection, we propose a new idea that make the chaotic system be applied into the metal detectors.that is,make the chaotic systems and traditional metal detectors combined. We design a new chaotic metal detector prototype.