Talk about your understanding of the piezoelectric effect, what is the piezoelectric effect?

Piezoelectric effect: When some dielectrics are deformed by an external force in a certain direction, they will be polarized internally, and positive and negative opposite charges will appear on its two opposite surfaces. When the external force is removed, it returns to an uncharged state, a phenomenon known as the positive piezoelectric effect.

When the direction of the force changes, the polarity of the charge also changes. Conversely, when an electric field is applied in the polarization direction of a dielectric, these dielectrics are also deformed, and when the electric field is removed, the deformation of the dielectric disappears, a phenomenon known as the inverse piezoelectric effect. A type of sensor developed based on the piezoelectric effect of dielectric is called piezoelectric sensor.

The piezoelectric effect works on the principle that if pressure is applied to a piezoelectric material, it will produce a potential difference (called the positive piezoelectric effect), and if a voltage is applied, mechanical stress will occur (called the inverse piezoelectric effect). If the pressure is a high-frequency vibration, a high-frequency current is generated. When a high-frequency electrical signal is applied to a piezoelectric ceramic, a high-frequency acoustic signal (mechanical vibration) is generated, which is what we usually call an ultrasonic signal.

In other words, piezoelectric ceramics have the function of conversion and reverse conversion between mechanical energy and electrical energy, and this correspondence relationship is indeed very interesting.

Piezoelectric materials can produce electric fields due to mechanical deformation, or mechanical deformation due to electric field action, and this inherent organo-electrical coupling effect makes piezoelectric materials widely used in engineering. For example, piezoelectric materials have been used to make intelligent structures, which have self-diagnostic, self-adaptive, and self-healing functions in addition to self-carrying capacity, and play an important role in future aircraft design.

The piezoelectric effect can be divided into positive piezoelectric effect and inverse piezoelectric effect.

Positive piezoelectricity. It means that when the crystal is subjected to the action of an external force in a fixed direction, the internal polarization phenomenon is generated, and at the same time, a charge with opposite signs is generated on a certain two surfaces; When the external force is withdrawn, the crystal returns to an uncharged state; When the direction of the external force changes, the polarity of the charge also changes; The amount of charge generated by the force applied to the crystal is directly proportional to the magnitude of the external force.

Piezoelectric sensors are mostly made using the positive piezoelectric effect.

Piezoelectric effect. Reverse piezoelectricity.

It refers to the phenomenon of mechanical deformation of crystals caused by the application of alternating electric fields to crystals. Transmitters made with the inverse piezoelectric effect can be used in electroacoustic and ultrasonic engineering. There are five basic forms of force deformation of piezoelectric sensitive components: thickness deformation, length deformation, volume deformation, thickness shear and plane shear.

Piezoelectric crystals are anisotropic, and not all crystals can produce piezoelectric effects in these 5 states. For example, quartz crystals do not have volumetric deformation piezoelectric effects, but have good thickness deformation and length deformation piezoelectric effects.

Some media, when deformed by force in a certain direction, produce polarization phenomena internally, and at the same time generate opposite signs of charges on its two surfaces;

When the external force is removed, it will return to an uncharged state, a phenomenon called the piezoelectric effect.

Definition 1: In crystalline matter lacking a center of symmetry, mechanical deformation is caused by the polarization intensity that is linearly related to the electric field strength, and vice versa, the polarization intensity is generated by mechanical deformation. Electrostriction can occur at the same time as the piezoelectric effect.

Definition 2: A phenomenon in which a heteropolar crystal without a center of symmetry induces dielectric polarization or an electric field in the crystal when mechanical strain occurs under the action of an external force (called the positive piezoelectric effect), or a phenomenon in which an electric field is added to the crystal to polarize the crystal, and at the same time strain or stress occurs (called the reverse piezoelectric effect).

The piezoelectric effect refers to a phenomenon of coarse physics, that is, in some materials such as crystals or ceramics, when these materials are subjected to force or pressure, the distribution of charges and changes in electric potential will occur, resulting in voltage at both ends of the material. Conversely, when an electric field is applied to these materials, they deform, i.e., generate pressure, a phenomenon known as the anti-piezoelectric effect. The piezoelectric effect is a fundamental phenomenon in materials science, which is widely used in sensors, transducers, electronics, oscillators, filters, controllers, high-voltage generators and relays.

The basis of the piezoelectric effect is the lattice structure of the material, among which the crystal structure with special symmetry has strong piezoelectric properties, such as quartz, first bench ferroelectric, zirconate titanate and other materials. Under the action of external factors such as mechanical vibration, sound waves, electromagnetic waves, temperature and pressure changes, these materials can generate electrical signals or mechanical movements, so as to realize the conversion and transmission of energy, which has important application value.

The length and type of the connecting cable cannot be changed arbitrarily because it is difficult to output effective signals, transmission and analysis when the piezoelectric sensor is used in conjunction with the voltage amplifier, and the linearity and stability are good. Reflected on the piezoelectric sensor is to output a millivolt signal, the cable should be as short as possible, and the distributed capacitance of the cable is changed with the length and type of the cable, generally using a pre-voltage amplifier (i.e., impedance converter).

Characteristics of a charge amplifier, a piezoelectric sensor can be thought of as a voltage generator. For such a measurement system. The high resistance ensures that most of the output signal is obtained from the sensor, and the decrease in the insulation resistance of the piezoelectric sensor will worsen the low-frequency characteristics of the measurement system.

in a voltage measurement system, but the current is extremely small), so for such a measurement system. The charge amplifier can effectively overcome the above shortcomings of the measurement system, which means that it has a large resistance, low noise, and the output voltage of the preamplifier is proportional to the input voltage.

The advantage of the voltage amplifier is that the circuit is simple, and the capacitance of the piezoelectric sensor itself changes, so why can't you use a voltage amplifier, so the measuring instrument that matches it must have a high input impedance?

When a piezoelectric sensor is used in conjunction with a voltage amplifier, the sensitivity of the system is determined under some kind of input cable.

4. Despite the high voltage output of the piezoelectric sensor.

I hope it will help you, generally use special cables, the magnification can not be too high, not conducive to collection and transmission, but the current is very small (the simplest example is that the piezoelectric ceramics in the lighter can produce tens of thousands of volts of voltage, this signal is weak, so it will bring some inconvenience when using.) By applying a mechanical pressure, because the sensor has a high output impedance characteristic, the piezoelectric ceramic generates very little charge in order to mate with the measuring amplifier or ordinary transistor voltmeter, and the low-frequency characteristics of the measurement system are limited by the input resistance of the preamplifier, and the high input impedance is converted into a low output impedance, so it must be amplified to facilitate the acquisition of piezoelectric signals: the high input balance triature auspicious resistance, in which the distributed capacitance of the connecting cable has an effect on the output voltage of the pre-voltage amplifier.

The disadvantage is that the voltage sensitivity of the piezoelectric sensor matched by the voltage preamplifier will be distributed with the capacitance of the cable 3, simply put, the dielectric constant of the piezoelectric ceramic in the piezoelectric sensor is very large.