The Research Of Weak Signal With Unknown Frequency Detection Based On The Chaos Theory

The weak signal detection has been widely used in the areas of radar, sonar, vibration measurement, fault diagnosis, and so on. Internationally, with the development of the micro-electronics technology and the theory of nonlinear detection, fault diagnosis technology has also developed rapidly, however, it still need a lot of investment on the detection of weak signal in China, to strengthen the technological innovation of intellectual property rights and transformation of scientific research has become a pressing issue. Aiming at the problem of micro-chemical fluid pipeline leak detection, mechanical vibration fatigue failure prediction and so on, a sub-frequency measurement test method and a weak signal detection method based on the compound system for weak signal with unknown frequency is proposed, which implements the detection of weak signal submerged in strong noise and provides for the basic theory and technical support for the protection of industrial processes to efficient and stable operation, using the sensitivity of the state transitions of the phase trajectories of the system (from the chaotic state to the large-scale periodic state) to the weak signal input. The research is done as follow:Firstly, the detection theory of the single Duffing system and the double coupled Duffing system is researched in detail, and the SNR threshold of the two systems under different noise levels is analyzed. The simulation results show that the double coupled Duffing system has stronger antinoise performance than the single Duffing system.Secondly, aiming at the difficult problems of weak signal detection, a sub-frequency measurement test method of weak signal with unknown frequency based on the double coupled Duffing system is proposed, through the study of the intermittent chaotic motion characteristics of Duffing system, and the definition and the detection theory of this method are expounded in detail. The simulation results show that the frequency of any period signal can be detected accurately under different noise levels.Finally, the advantages and the disadvantages of the correlation method and the double coupled Duffing system in the aspects of weak signal detection are investigated in detail. Combining this two methods, a composite system for the weak signal detection with unknown frequency is proposed, which combines the the cross-correlation method and the sub-frequency measurement test method of weak signal based on the double coupled Duffing system, and gives full play to their strengths. The simulation results show that the weak signal can be picked up from the strong noise by this method, and the SNR threshold can be reduced greatly.