1.Simple harmonics signal is simplest and the most important cyclicalsignal.Wilfully a cyclical signal may use simple harmonics signal toexpress,two between relates the bridge is the fourier's series,therefore the fourier's series is the cycle signal analysingrationale.
2.Appears the very complex signal in the time domain,or maps itstransformation the frequency range (including s and the z territory),can decompose into the extremely simple elementary signal form,carries on the analysis and the solution
3.The frequency spectrum is composed by not the continual spectral line,each spectral line represents a harmonic component.This kind offrequency spectrum is called the separate frequency spectrum.Betweenthe spectral line gap is equal to base frequency w the integralmultiple.Namely in the frequency spectrum each spectral line only canappear in the base frequency w integral multiple,various overtonesfrequency nw all is the base frequency integral multiple.