Stochastic Resonance in Time-delayed Bistable Systems Driven by Weak   Periodic Signal
  We study theoretically a bistable systems with time-delayed feedback driven by weak periodic force. The effective potential function and the steady-state probability density are derived. The delay time and the strength of its feedback can change the shapes of the potential wells. In the adiabatic approximation, the signal-to-noise ratio (SNR) of the system with a weak periodic force is obtained. The time-delayed feedback modulates the magnitude of SNR by changing the shape of the potential and the effective strength of signal. The maximum of SNR decreases with increasing the feedback intensity $\epsilon$. When $\epsilon$ is negative (or positive), the time delay can suppress (or promote) the stochastic resonance phenomenon. 
Rui-Hua Shao and Yong Chen