In 1880 Curie brothers invented the direct piezoelectric effect in a certain solid crystalline and dielectric substance such as quartz. The piezo word originates from the Greek word piezein, which means to press. The Piezoelectric sensor is a sensor used to measure the change in the pressure, force, temperature and acceleration. The general benefits of the piezoelectric accelerometer are it has a wide frequency range, the output noise is very low, there is no external power supply is required & it has self-power generating.
What is a Piezoelectric Sensor?
The piezoelectric sensor is a device used to the piezoelectric effect. This sensor is used to measure the change of pressure, force, temperature, strain and acceleration. They are converted into an electrical charge. The following circuit shows the schematic symbol of the piezoelectric sensor.
Principle & Operation of Piezoelectric Sensor
There are three main operations in the piezoelectric sensor which are transverse effective, transducer effect, and shear effect.
The transverse effect is said to be a force applied to the y-axis and changes along the x-axis direction. They are perpendicular to the line of force. The Cx is the amount of the charge which depends on the geometrical dimensions of the respective piezoelectric element. The dimensions of the a, b, c can be applied as
Cx = dxyFyb/a
a is represented as a dimension of a line
b is a line with the charge generating axis
d is the corresponding piezoelectric effect
The produced charge is directly proportional to the applied force and it is independent of the elements of piezoelectric like size & shape. Mechanically several elements are gathering in series and electrically in parallel to increase the charge output. The following equation shows the charge output.
Cx= dxx Fx n
Fx is said to be as an applied force in the x direction
dxx is the piezoelectric coefficient for a charge in the x-axis.
n is the corresponding to the number of stacked elements
In the shear effect, the produced charge is directly proportional to the applied force and independent elements like size and shape. For n number of elements mechanically they are in series and electrically in parallel. The charge equation is given as
Cx = 2dxx Fx n
Circuit Diagram of Piezoelectric Sensor
The following circuit shows the piezoelectric sensor circuit diagram. The components required for this circuit are four resistors, speaker, two NPN transistor, capacitor, and piezo diaphragm. The generation of the electrical signal in the piezo diaphragm is when it is subjected to the pressure variation due to the sound in the vicinity. The output of the piezo-diaphragm is supplied to the two transistors of T1 & T2 (BC548) and the two transistors are known as a Darlington pair, it has a very high current.
If piezo diaphragm receives any audio signals, in the opposite faces it produces the voltage difference. By using the capacitors C1 of 0.1µF the signal is filtered or a DC component. The first transistor T1 of the Darlington pair amplifiers of the input signal and the output appears at the resistor R2. For the transistor T1, base-collector bias is given by the resistor R1 of 470k. The output of the first transistor T1 is given to the base of the T2 transistor after it is filtered by another capacitor C2.
In further the output of the transistor T1 is amplified by the transistor T2 and at the resistor R4, the amplified signal is produced. The R3 resistor is used for the necessary bias for the transistor T2. The output of the second transistor T2 is filtered with the capacitor C3 and it is connected to the speakers.
Piezoelectric Pressure Sensor
When we use the piezoelectric effect in the pressure sensor, then the sensor uses the diaphragm, when the pressure is applied it deflects slightly. The pressure on the crystal causes a small voltage to be produced that is proportional to the pressure. The applied voltage to the traditional voltage signal is from the 0-10 volts. The following figure shows the example of the piezoelectric sensor.
Applications of the Piezoelectric Sensor
Some important applications of the piezoelectric sensor are following
Manufacturing equipment in transportation system, machine tools, engines, rockets, The first application of the piezoelectric materials is applied during the world war 1
Advantages of Piezoelectric Sensor
- This sensor is a pollution free sensor.
- The maintenance of piezoelectric sensor is very low.
- The replacement of this equipment is very easy.
- This sensor is unaffected by the external electromagnetic field.
Disadvantage of the Piezoelectric Senor
- If we use the high temperature, it may get affected.
- Crystal is prone to cracking if it is overstressed.
In this article, we will discuss the working of the piezoelectric sensor and its applications. I hope by reading this article you have gained some basic information about the working of the piezoelectric sensor. If you have any queries about this article or about the final year electrical projects for engineering students, please feel free to comment in the below section. Here is the question for you, what are the function of the piezoelectric sensor.