Question: Explain transduction pertaining to capacitive measurement, Piezo-resistive for MEMS. Also state different parameters on which this transduction depend

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- 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.

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