What is a piezoelectric sensor

Piezoelectric sensors are based on the piezoelectric effect of certain dielectrics. Under the action of an external force, a charge is generated on the surface of the dielectric, thereby enabling non-electricity measurement.

The piezoelectric sensing element is a force-sensitive element, so it can measure those physical quantities that can eventually be converted into force, such as force, pressure, acceleration, and the like.

Piezoelectric sensors have the advantages of wide frequency response, high sensitivity, high signal-to-noise ratio, simple structure, reliable operation, and light weight. In recent years, due to the rapid development of electronic technology, with the advent of secondary instrumentation and the appearance of low noise, small capacitance, and high insulation resistance cables, the use of piezoelectric sensors has become more convenient. Therefore, it has been widely used in many fields such as engineering mechanics, biomedicine, petroleum exploration, sonic logging, and electroacoustics.

1. Piezoelectric Effect Positive Piezoelectric Effect (Pliable Piezoelectric Effect): When some dielectric material is deformed by applying force along a certain direction, polarization occurs inside, and it is generated on a certain surface thereof. When the external force is removed, the charge is restored to the uncharged state. As the direction of the force changes, so does the polarity of the charge.

Inverse piezoelectric effect (electrostrictive effect): When an electric field is applied in the direction of polarization of the dielectric, these dielectrics produce mechanical deformation or mechanical pressure in a certain direction. When the applied electric field is removed, these distortions or stresses also disappear. phenomenon.

Sensor based on piezoelectric effect. It is a self-generating and electromechanical transducer. Its sensitive element is made of piezoelectric material. Piezoelectric materials are charged on the surface after they are stressed. This charge is amplified and transformed by the charge amplifier and measurement circuit and becomes proportional to the power output of the external force. Piezoelectric sensors are used to measure forces and non-electrical quantities that can be converted to force, such as pressure, acceleration, etc. (see Piezoelectric Pressure Sensors, Accelerometers). Its advantages are frequency bandwidth, high sensitivity, high signal-to-noise ratio, simple structure, reliable work, and light weight. The disadvantage is that some piezoelectric materials require moisture protection measures, and the output has a poor dc response, requiring the use of high input impedance circuits or charge amplifiers to overcome this drawback. The appearance of supporting instruments and low noise, small capacitance and high insulation resistance cables make the use of piezoelectric sensors more convenient. It is widely used in engineering mechanics, biomedicine, electroacoustics and other technical fields.

Piezoelectric effects Piezoelectric effects can be divided into positive piezoelectric effects and inverse piezoelectric effects. The positive piezoelectric effect means that when the crystal is subjected to an external force in a certain fixed direction, an electrical phenomenon occurs inside, and at the same time, opposite charges are generated on a certain surface; when the external force is removed, the crystal is restored to an uncharged state. State; When the direction of the external force changes, the polarity of the charge also changes; the amount of charge generated by the force of the crystal is proportional to the magnitude of the external force. Piezoelectric sensors are mostly made using positive piezoelectric effects. The inverse piezoelectric effect refers to the phenomenon that the crystal is mechanically deformed by applying an alternating electric field to the crystal. It is also called the electrostrictive effect. Transducers manufactured with inverse piezoelectric effects can be used for electro-acoustic and ultrasonic engineering. Piezoelectric elements are deformed in the following five basic forms: thickness deformation, length deformation, volume deformation, thickness shear, and plane shear (see figure). Piezoelectric crystals are anisotropic and not all crystals can produce piezoelectric effects in these five states. For example, quartz crystals have no volumetric deformation piezoelectric effect, but have good thickness deformation and length deformation piezoelectric effect.

Piezoelectric materials can be classified into piezoelectric single crystals, piezoelectric polycrystals, and organic piezoelectric materials. Piezoelectric sensors are most commonly used in piezoelectric ceramics and piezoelectric crystals in various types of piezoelectric crystals. Other piezoelectric single crystals include lithium niobate and lithium niobate, lithium niobate, and bismuth niobate, which are suitable for high-temperature radiation environments. Piezoelectric ceramics include barium titanate ceramics, lead zirconate titanate ceramics, niobate series ceramics and lead magnesium niobate ceramics belonging to the binary system. The advantages of piezoelectric ceramics are easy firing, easy molding, moisture resistance, and high temperature resistance. The disadvantage is pyroelectricity, which can interfere with mechanical measurements. There are more than ten kinds of polymer materials such as polyvinyl difluoride, polyvinyl fluoride and nylon in organic piezoelectric materials. The organic piezoelectric material can be mass-produced and made into a large area. It has unique advantages in matching with the acoustic resistance of air, and it is a new electro-acoustic material with great development potential. Since the 1960s, crystals with both semiconductor and piezoelectric properties have been discovered, such as zinc sulfide, zinc oxide, and calcium sulfide. This kind of material can be used to make a new type of piezoelectric sensor that integrates the sensing element and the electronic circuit, which is promising for development.