“…Recently, Duffing chaotic oscillator has become a hotspot in the field of weak signal detection, because of its strong advantage of being immune to noise and irrelavant signals while highly sensitive to the signal whose frequency is close to the internal reference frequency [1,2,3] . To make the best use of Duffing oscillator, the determination of the critical threshold of reference amplitude and the indentification among chaotic state, intermittent chaotic state and large-scale periodic state are of great significance [4,5] . However, many researchers address these tasks by their experience, experiments and observing, instead of quantitative analysis, which limits the engineering application of their methods.…”