Fourier analysis
Any periodical signal can be built of an infinite series of sinusoidal frequency components
v(t) = a0 + S an cosnw0t + S an sinnw0t
where v(t) is the signal in time and w0 is the fundamental frequency in radians per second.
The fundamental frequency is determined by the period (T=2p /w0 ) of the signal, the other components are multiples of this frequency