The formula of the resonance frequency of this link is that the square of S plus 2ζωn times the square of S plus ωn equals 0.

The resonant frequency of the second-order oscillation link can be obtained by calculating the undamped natural frequency of the system, which is the natural frequency attribute of the second-order oscillation system, and the system will oscillate freely at this frequency without external damping.

For the general second-order oscillation link, its characteristic equation can be written as a standard: the square of S plus 2ζωn times the square of S plus ωn equals 0.