Comparison of different frequency detector algorithms for a generic adjustable notch filter

Notch filters are used in many industrial applications to attenuate undesired frequencies within signals. Such undesirable frequencies are common in flexible dynamic systems, power plants, medical monitoring systems, etc. In many aerospace flexible dynamic systems the desired center frequency shifts due to the nonlinearities and coupling of the system. The conventional approach in aerospace is to generate a large database filled with filter coefficients. This requires a significant verification and validation activity, as well as a large storage capacity for the filter coefficients. In this paper the problem is approached in two parts: 1) adjustable notch filter and 2) desired filter center frequency (fc). A routine that generates Butterworth filter coefficients from the input fc is introduced. Methods based on Hilbert transforms are compared for their capability to detect cyclic signals.