Abstract
Suppose one wants to look at a weak periodic signal within a random noise: a way to improve the Signal to Noise Ratio (SNR) is to use a lock-in amplifier, but the frequency of the periodic component must be known to achieve a high amplification. A different method is offered by the mechanism of Stochastic Resonance (SR)1, 2. SR is a mechanism which uses a nonlinear device (a bistable system could be an example, but other possibilities are known3) to enhance the SNR even if the frequency of the periodic modulation is not exactly known. Most intriguing and counterintuitive, there exists a range of noise intensities for which the SNR increases as the noise intensity is increased. The effect is shown in Fig. 1 where (left hand side) we send a periodic signal plus a random term to a nonlinear filtering device (middle, a bistable electronic circuit) and we obtain a strong filtered signal (right hand side, jagged line) at the driving frequency; by comparison, on the right hand side we report with a dashed line the periodic component buried in the noisy input signal, amplified by a factor 10.
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