We can transform energy from one form to another, but we cannot destroy it. In some circumstances, we must use assistance from one type of energy to transform it into another. Therefore, “Transducers” may be used in the energy conversion process. There are several different kinds of transducers, including capacitive, piezoelectric, ultrasonic, temperature, and pressure transducers. This article will explain what a capacitive transducer is, how it functions, how it is used, what types there are, how it can be used, and what its benefits and drawbacks are.

What is a Capacitive Transducer?

Active and passive transducers are the two categories into which transducers fall. One type of transducer that doesn’t need any power to function is an active transducer. While passive transducers can operate without external power during the energy conversion process, they cannot. Passive transducers includes these transducers. These transducers are preferred because their definition of a capacitive transducer is to measure displacement (how much distance it covers), pressure, and other various physical quantities. The capacitance between the plates in these transducers varies due to differences in the dielectric medium, plate overlap, and distance between the plates.

Capacitive Transducer Working Principle

The capacitive transducer is depicted in the above diagram. Variable capacitance is the basis for a capacitive transducer’s operation. According to their structure, these have two parallel metal plates that keep a certain distance between them. You can fill a dielectric medium, like air, in the space between them. Therefore, the capacitance can vary depending on the distance between these two metal plates and the positioning of the plates. Therefore, these transducers operate on the principle of variable capacitance. Normal capacitors have constant capacitor plates, whereas capacitive transducers’ capacitor plates are movable. This is the main distinction between the two types of capacitors.

The capacitance of the variable capacitor can be measured by this formula.

In this formula:

C indicates the capacitance of the variable capacitance
εo indicates the permittivity of free space
εr indicates the relative permittivity
A indicates the area of the plates
D indicates the distance between the plates

The variable capacitance value is thus dependent on four significant parameters, per the formula. They are the variable capacitor’s variable plate spacing, variable plate area, variable plate permittivity, relative permittivity, and variable plate dielectric material. The variable capacitor’s capacitance value can be changed depending on these factors.

• Change in dielectric constant can vary the capacitance of this transducer.
• The area of the plates of these transducers can vary its capacitance value.
• Distance between the plates can vary the transducers’ capacitance value. This method is mostly used. In this method, the dielectric medium and area of the plates are kept constant. When the plates are moving then the distance is varied and this results in the changing of the capacitance of the capacitive transducer.

This transducer’s capacitance value can be changed using the three methods mentioned above.

Capacitive Circuit Diagram

The circuit diagram shown above is a capacitive transducer’s equivalent circuit diagram. The variable capacitor differs from a standard capacitor in that its capacitance can be adjusted, whereas a standard capacitor’s capacitance value is fixed and cannot be altered.

Types of Capacitive Transducer

There are four different types of capacitive transducers, which are discussed below. Those are

• Parallel plate capacitance with rectangular plates.
• Cylindrical capacitor transducer.
• Semi circular parallel plates.
• Change in dielectric between parallel plates.

Parallel Plate Capacitance with Rectangular Plates

This type of capacitive transducer is also known as a flat transducer. One plate in this kind of transducer is fixed, while the other plate is movable. The area A or the distance d can be changed through this variation. This has an impact on the transducer’s capacitance value.

If area A varies and the capacitance value C would be when the plates are having the distance of x, then

C= ε(A-wx)/d

Cylindrical Capacitive Transducer

Considering the length of the cylinder is to be L, then the capacitance

Semi Circular Capacitive Transducer

When the two capacitive plates are stacked on top of one another, this type will offer the highest capacitance value. When the circuit needs the most capacitance, these are preferred.

In this type capacitive transducer, area A = πr²/2  and the capacitance C=ε πr²/2d

Change in Dielectric Medium between Parallel Plates

This transducer has two parallel plates, and as the dielectric medium changes, so does the capacitance of the transducer.

Therefore capacitance C= εo (ε1*L1*w + ε2*L2*w)/d

Here – L1 and L2 are indicating the length of the 1st and 2nd plates length.

W indicates the width of the plate

D indicates the distance between the plates

Advantages

The capacitive transducer advantages are discussed below. They are

• These transducers have a very strong frequency response.
• These transducers offer high input impedance. So the loading effects value will be too low.
• Low power is needed to operate these. These transducers are therefore referred to as low power consuming devices.
• These transducers are highly sensitive.
• Using these transducers can enable high resolution.

Disadvantages

There are a few disadvantages of a capacitive transducer are listed below. They are

• These transducers exhibit non-linear behaviors due to edge effects.
• Its output impedance is very high. The output must be measured using a complex circuit due to the high output impedance value. Additionally, a strong output circuit is required to maintain this high output immense value.
• These are influenced by temperature. So This transducer capacitance value may be influenced by the outside temperature.

Applications

The Applications of the capacitive transducer are

• These transducers can be used to measure angular and linear displacement with sensitivity.
• This transducer can be used to measure a variety of quantities, including pressure, temperature, and displacement. Below is a list of applications for capacitive transducers.
• The application of the variable capacitance pressure transducer is to determine the variations in pressure.
• Finding the humidity level is one of the best uses for this transducer. So The capacitance value of this transducer changes along with the humidity value. This number allows us to calculate the change in humidity.

Thus, by measuring the change in capacitance value, capacitive transducers are useful for converting one form of energy into another. These are passive transducers because they need an external source of power to function. So And we can measure the pressure, temperature, displacement, and other things with the aid of these transducers.