Mumbai University > Electronics Engineering > Sem 8 > MEMS Technology

Marks: 10M

• The capacitive transducer or sensors is nothing but the capacitor with variable capacitance.
• The capacitive transducer comprises of two parallel metal plates separated by air/ mica.
• In the instruments using capacitive transducers the value of capacitance changes due to change in the value of input quantity to be measured.

• This change can be measured easily and calibrated against input quantity

  

• Where $ε_0$ is the absolute permittivity, $ε_r$ is the relative permittivity, A is the area between the plates and d is the distance between the plates.

• It is clear from the above formula that capacitance of capacitive transducer changes with respect to area, distance and dielectric constant.

Piezoresistivity:

• It is the change in material resistance resulting from a change in stress in material.
• When deciding if piezoresistance can be used as a transduction measurand, for a particular measurand oe has to determine if the sensor can be designed such that the measurand can produce a stress on a portion of the device where piezo-resistor can be located.
• Examples of measurand are pressure, vibration, acceleration and magnetic field.
• Piezoresistive transduction depends on change in resistance, strain and temperature.