Piezoelectric Sensor

Pressure is a quantity that plays a vital role in all kinds of industries and power plants. Thus, it becomes mandatory to monitor and control the pressure flow and other parameters that are related to the pressure to maintain a smooth process. There are a lot of sensors that are used for this purpose. The following article explains how a piezoelectric crystal is used in pressure measurement.

Contents:

  1. What is a Piezoelectric Material?
  2. What are Piezoelectric Sensors?
  3. Working Principle of a Piezoelectric Sensor
  4. Properties of a Piezoelectric Sensor
  5. Sensitivity of a Piezoelectric Sensor
  6. Applications of Piezoelectric Sensors
  7. Piezoelectric Pressure Sensor
  8. Advantages and Disadvantages of a Piezoelectric Sensor

What is a Piezoelectric Material?

Some natural crystals and some man-made crystals tend to create an electric current when they are subjected to pressure. Such materials are known as piezoelectric materials. Other major properties and examples of piezoelectric material are as follows.

  • Every element in nature has atoms that are arranged together for that element to be complete.
  • Non-Piezoelectric elements have a structure in which its atoms are arranged while a piezoelectric material does not have an order or a structure.
  • Instead, the atoms in a piezoelectric crystal are put up together in the form of lumps or heaps, making it easier for the free electrons to move.
  • When pressurized, the free electrons start to move which produces a current inside the crystal.
  • Quartz crystal is one of the well-known piezoelectric materials which is even used in mechanical clocks.
  • Other such piezoelectric materials are topaz, Barium titanate, tourmaline, polyvinylidene fluoride etc.

What are Piezoelectric Sensors?

Some devices use piezoelectricity to measure some other physical parameters like pressure temperature, strain etc. Such devices are known as piezoelectric sensors. The concept of piezoelectric sensors is explained below.

  • Though piezoelectricity can be used to measure various parameters, pressure measurement is one of the important applications of piezoelectric sensors.
  • Pressure measurement using piezoelectric is done using a piezoelectric material which is in the form of a thin sheet.
  • While the measurement of other parameters uses tiny blocks of piezoelectric crystals.
  • Though the sensors use different forms of piezoelectric materials, they work based on the same principle i.e., conversion of mechanical energy to electrical energy.

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Working Principle of a Piezoelectric Sensor

The working principle of a piezoelectric sensor is pretty much simple. It works on the principle that when a piezoelectric crystal is subjected to external mechanical stress like force or pressure, it tends to produce electricity inside the crystal. When a piezoelectric crystal is subjected to pressure, there are three ways in which they develop an electric current inside them. The below table explains this variation in tabular form.

Mode of operation The direction in which the force is applied Expression for the current produced Explanation of terms in the expression
Transverse Effect Force is applied along the y axis of the crystal Q = F*P*H/L Q – Current produced
F – Force applied
P – Piezoelectric coefficient
H – Height of the crystal
L – Length of the crystal
Longitudinal Effect When many crystals are stacked together in series while force is applied Q = P*F*N Q – Current produced
F – Force applied
P – Piezoelectric coefficient
N – Number of crystals
Shear Effect When many crystals are stacked together in parallel while force is applied Q = 2*P*F*N Q – Current produced
F – Force applied
P – Piezoelectric coefficient
N – Number of crystals

Properties of a Piezoelectric Sensor

Piezoelectric sensors are devices that can be used in various fields of technology. Below are some important characteristics of piezoelectric sensors which make them a highly accurate and versatile device.

  • Piezoelectric sensors give a high voltage output which is easier to measure and the power loss during the transmission will be low.
  • The stability of the piezoelectric sensors is very high.
  • The impact resistance of piezoelectric sensors is high.
  • The frequency range of a piezoelectric sensor is wide.
  • The DC output impedance of a piezoelectric sensor is very high.
  • Most of the time, piezoelectric sensors are smaller in size when compared to other pressure measurement devices.

Sensitivity of a Piezoelectric Sensor

The sensitivity of a sensor is defined as a minimum amount of input to which the sensor provides an output. In other words, it can be defined as a scale to measure the efficiency of the instrument. A sensor is said to be effective if the sensitivity of the sensor is high and vice versa. The method in which the sensitivity of a piezoelectric sensor is measured and how does it impact the efficiency is explained below.

  • Just like the other sensors, the sensitivity of the piezoelectric sensor is measured in two ways, voltage sensitivity and current sensitivity.
  • The voltage sensitivity of the crystal is defined as the output produced when a static force of 10 N is applied.
  • The current sensitivity of the sensor is defined as the slope of the characteristic curve when the force applied is used as the X-axis and the output voltage is used as the Y-axis.
  • The sensitivity of the sensor is increased by connecting a capacitor with high capacitance in parallel to the sensor.

Applications of Piezoelectric Sensors

Piezoelectric sensors are used in various fields. Some of the main applications of piezoelectric sensors are listed below.

  • Piezoelectric sensors are used in automation. They are used to design burglar alarms which can be used to automatically sense human presence.
  • They are used in fire alarms. Fire alarms are widely used in public places like malls, arcades etc. to detect fire and to extinguish it at the beginning itself.
  • Piezoelectric sensors are used in electronic devices such as PIN pads, alarm clocks, microphones, etc.
  • They are also used in medical instruments like stethoscopes, pacemakers etc.
  • Piezoelectric sensors are used in industries in pressure monitoring, temperature control, etc.
  • They are also used in speakers as they can produce high-quality audio.

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Piezoelectric Pressure Sensor

Though piezoelectricity can be used to measure various parameters, pressure measurement is one of the main applications of piezoelectricity. The construction and working of a piezoelectric pressure sensor are explained below.

  • Just like the other piezoelectric sensors, a piezoelectric pressure sensor works under the principle that a piezoelectric material conducts electricity when pressurized.
  • The sensor consists of a piezoelectric material, whose two ends are externally connected to a voltmeter.
  • A diaphragm is connected on the top of the crystal and the pressure applied is transferred to the diaphragm first.
  • When pressure is applied, the diaphragm moves and it creates pressure on the crustal.
  • Due to the pressure, a voltage is induced across the crystal.
  • By measuring the amount of voltage produced, the amount of pressure applied can be calculated as both the voltage and pressure is directly proportional to each other.
  • Due to their strong construction, these pressure sensors are versatile and is used in a wide range of applications.

Advantages and Disadvantages of a Piezoelectric Sensor

Just like any other device, the piezoelectric sensor also has its pros and cons. The main advantages and disadvantages of the piezoelectric sensor are tabulated below. The below table just states the pros and cons separately and is not a comparison between the columns.

Parameter Advantages Disadvantages
Environmental Durability Piezoelectric sensors are rugged, making them a suitable measurement device in a harsh atmosphere Certain piezoelectric materials are prone to moisture and need strong maintenance
Temperature Range They can also work in an atmosphere with extremely high temperatures with greater accuracy The output response of the piezoelectric sensor can be very low sometimes
Cost Piezoelectric materials are inexpensive when compared to other materials used for pressure measurement Sometimes the high input impedance of the sensor may cause trouble in the circuits.
Electromagnetic Interference Resistance The sensor is not easily affected by external electromagnetic radiations In the case of pressure measurement, these sensors cannot be used to measure static pressure
Power Consumption They are low-power devices that do not require a lot of external power supply to energize In the case of temperature measurement, the sensitivity of the sensor may decrease sometimes

Key Points to Remember

Here are the key points we need to remember about “Piezoelectric sensors”

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  • A piezoelectric material is a substance that can produce electric current when pressurized.
  • A sensor that is manufactured using piezoelectric material is known as a piezoelectric sensor.
  • This sensor works on the principle that as the amount of stress exerted on the piezoelectric crystal changes, the current produced by the crystal also changes.
  • Though they are smaller in size, piezoelectric sensors are effective pressure measurement devices.
  • The sensitivity of the piezoelectric sensor will always be a higher value.
  • Piezoelectric sensors are versatile and is used in various fields of technology.
  • All the disadvantages of piezoeletric sensors are negligible when compared to the advantages of the sensor.

If you find any mistake above, kindly email to [email protected]

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Manish Bhojasia - Founder & CTO at Sanfoundry
Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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