Capacitive sensors are based on changes in capacitance in response to physical variations. Capacitive displacement sensors are noncontact devices yielding high-resolution measurements of the position and/or change of position. œey are used in a wide variety of applications such as assembly of equipment, disk drives, thickness measurements, machine tools, semiconductor devices, machining, and in some cases in density measurements. In some cases, the basic operational and sensing principles are common in dissimilar applications, and in other cases, di¥erent principles can be used for the same applications. For example, capacitive microphones are based on variations of spacing between plates in response to acoustical pressure, thus turning audio signals to variations in capacitance. On the other hand, a capacitive level indicator makes use of the changes in the relative permittivity between the plates.