Mechanical vibrations include crystal oscillators that oscillate due to the piezoelectric effect, SAW, and MEMS that resonate due to changes in capacitance caused by applying voltage to electrodes.

An equivalent circuit for a crystal oscillator is shown. Ignoring R in the equivalent circuit, the point where the impedance is minimum is the frequency where the impedance of the upper L and C is "0", and this frequency is the resonance frequency.

A crystal can only have a resonance frequency of about 100MHz, and cannot have a high frequency, so a crystal oscillator of about 200MHz can be configured by extracting and amplifying the third harmonic using a bandpass filter. Because the crystal has a high quality factor, it can oscillate a highly stable frequency.