Micro-Electro-Mechanical-Systems work with a capacitive sensing principle.
The sensor shown on following picture consists of a seismic mass, several fingers and isolators. If acceleration is applyed to the sensor, the seismic mass moves. The isolated mounts of the seismic mass acts as springs. The position of the fingers mounted on the mass change their position relative to the fingers of the housing.
Due to this, the electrical capacity between these fingers change. This change of capacity can be measured and an appropriate acceleration value can be calculated.
MEMS acceleration sensor. An applied acceleration deflects the seismic mass. The position change of the mass’s fingers and the fingers of the housing leads to a measurable change of capacity.
This type of sensor can be built very small with photo lithographic processes. The sensing element made out of electronis has the dimension of a few mm or less.
MEMS sensors are able to survive very shock loads due to their small size. They provide high Eigen-frequencies and therefore a high measurement bandwidth.
The MEMS fabrication processes are fully developed and the costs per sensor element are very low priced.