Explain the working principle of a resonant frequency accelerometer.

A resonant frequency accelerometer functions by employing a mass-spring system that oscillates at its natural resonant frequency when subjected to acceleration. This system consists of a mass suspended by a spring, where the acceleration causes the mass to move relative to the housing, thereby stretching or compressing the spring. The accelerometer detects the resonant frequency by measuring the electrical signal generated by the oscillating proof mass, typically using piezoelectric or capacitive transduction methods. By detecting the amplitude of oscillation at this resonant frequency, the accelerometer can determine the magnitude and direction of the applied acceleration. Resonant frequency accelerometers are designed to be sensitive only at their resonant frequency, allowing them to filter out unwanted vibrations or noise at other frequencies, thereby providing accurate measurements of acceleration.