What Is Electrostriction?

Electrostriction Some polycrystalline materials, such as lead zirconate titanate ceramics, have spontaneously formed molecular groups, so-called electrical domains, which have a certain polarization, and the length along the polarization direction is often different from other directions. When an external electric field is applied, this electric domain will rotate to make its polarization direction as much as possible consistent with the direction of the external electric field. Therefore, the length of this material along the direction of the external electric field will change. This phenomenon is called electrical Caused by the telescopic effect. ^[1]

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The current research direction of electrostrictive materials is to obtain deformation comparable to that of piezoelectric ceramics. Progress has been made in two areas: materials with considerable electrostrictive effects and small electrical hysteresis effects and aging phenomena have been made, and the use of monolithic capacitor structure processes has considerably reduced the voltage required to generate sufficient strain . Among them, the most preferable is a relaxation type ferroelectric ceramic based on lead niobium magnesium magnesiumate, which is being used to make an electrostrictive transducer.

The electrostrictive effect refers to a phenomenon in which an elastic deformation of a dielectric occurs in an electric field. It is the inverse effect of the piezoelectric phenomenon. This phenomenon can be explained as follows: When a dielectric is placed in an electric field, its molecules are polarized, and along the direction of the electric field, the positive electrode of one molecule is connected to the negative electrode of another molecule. Because the positive and negative electrodes attract each other, the entire dielectric shrinks in this direction until the internal elastic force and electrical attraction are balanced. If an alternating voltage is applied between the two surfaces of a dielectric object, and its frequency is the same as the natural frequency of the object, mechanical resonance will occur. Electrostriction has many applications in engineering technology, such as using piezoelectric quartz to make quartz clocks, generating ultrasonic waves, and so on.

Under the action of an external electric field E ( = x, y, z), a dielectric strain will appear proportional to the second term EE of the electric field. This effect is called electrostriction. The independent variable describing the electrostriction can be an electric field or a polarization intensity P; the response can be a strain or a stress. When the polarization intensity is used as the independent variable, the response is proportional to the quadratic term PP. For non-ferroelectric dielectrics, P and E have a linear relationship, and the relationship between this independent variable description method is very simple. For ferroelectric dielectrics, due to the hysteresis loop relationship between P and E, the response is proportional only to the quadratic term of the polarization intensity, and a butterfly loop relationship occurs with the electric field strength.

The electrostrictive effect is different from the inverse piezoelectric effect; the latter is a linear response effect of the first-order term and can only occur in solid dielectrics with no symmetrical center. The piezoelectric constant is a third-order tensor; the physical parameter describing the electrostrictive effect of anisotropic dielectric is a fourth-order tensor. Only electrostrictive effects occur in non-piezoelectric dielectrics; piezoelectric effects and electrostrictive effects occur simultaneously in piezoelectric bodies. [1]

Any dielectric has an electrostrictive effect. Since the electrostrictive effect is generally weak, it has not been used for a long time. In the late 1970s, it was found that high-dielectric constant materials and ferroelectric materials have a particularly large electrostrictive strain near the Curie point. They all belong to the dispersed phase change ferroelectrics of perovskite type structure, such as lead niobium magnesium magnesium oxide and lead titanate solid solution. When the external electric field is 10 kV / cm, the electrostrictive strain can reach 10-5, which is the same as the piezoelectric strain provided by a good piezoelectric body. Due to the good repeatability of electrostrictive materials, fast response time, good temperature stability and stability over time, it is particularly suitable for making precise micro-displacement modulators.

In engineering technology, the electrostrictive effect of piezoelectric crystals can be made: quartz clock, high-frequency variable-frequency oscillator and good selective filter. Telephone earphone and piezoelectric tuning fork (reducing electrical vibration to mechanical vibration of crystal and making sound through metal foil). Ultrasonic generator. The piezoelectric crystal sheet is placed between the parallel plate electrodes, and an exchange voltage with the same frequency as the natural frequency of the crystal is applied between the electrodes to cause the wafer to vibrate strongly and emit ultrasonic waves. Piezoelectric thickness gauge and piezoelectric flowmeter. The ultrasonic wave generated by the piezoelectric crystal is used to measure the thickness of the object and the flow rate of the fluid. The principle structure of the piezoelectric flowmeter is shown in the figure. Two ultrasonic transducers with a certain interval are set along the liquid flow direction, one sends a signal and the other receives a signal, and the transmission and reception of the two are interchanged every 1/100 second. Because the ultrasonic wave sends and receives under the conditions of forward and reverse current, there will be a phase difference proportional to the flow velocity, so as long as the phase difference is indicated, the flow velocity and the corresponding flow rate can be measured. [2]

Ceramics that undergo a small shape or size change due to the effect of expansion and contraction under the action of an electric field. The main products are lead niobium magnesium magnate (PMN), lead niobium magnesium magnate-lead titanate (PMN-PT), lead lanthanum zirconate titanate (PLZT), and lead barium zirconate titanate (Ba-PZT). It has the advantages of high resolution, good stability, high precision, and fast speed. The electrical strain is proportional to the square of the electrode strengthening, and the electrostrictive frequency is twice the frequency of the applied alternating electric field. Electro-induced strains can be on the order of 10-3. No aging caused by depolarization of electrical domains. It is used to make micro-displacement actuators, positioners, and micro-movement and positioning precision driving and conversion elements. It is widely used in high-tech fields ^[2] .