Study of metal detection based on chaotic theory

The detection system of a metal detector is proposed using a chaotic system-Duffing oscillator. The Duffing equation is improved on its expression suitable for high frequency weak signal detection of a metal detector through a time scale conversion. By calculating the two Lyapunov exponents of the duffing oscillator, the threshold value in critical state has been obtained accurately and it will be as the amplitude of the internal reference signal in the simulation model. And the quick convergent time of the two Lyapunov exponents shows that the duffing oscillator is suitable for immediate alarm of a detector. Meanwhile, Based on the phase transforms of Duffing oscillator, a corresponding simulation model is made by the Simulink of Matlab7. Simulation results indicate that Duffing oscillator is very sensitive to sinusoidal signal and immune to noise in high frequency cases. Thus it can improve the signal-noise ratio greatly, correspondingly raise the sensitivity of a metal detector.