压电陶瓷的原理与应用

Piezoceramics：Principles and Applications

1.Types of Piezoceramics

●Piezoelectric Ceramic Ring

●Piezoelectric Ceramic Disc

●Piezoelectric Ceramic Tube

●Piezoelectric Ceramic Cylinder

●Piezoelectric Ceramic Ball/Hemisphere

●Piezoelectric Ceramic Square/Rectangular

2.Piezoelectric Ceramics:Piezoelectric Material PZT8

PZT8 piezoelectric ceramic has high mechanical quality factor , high electromechanical coupling factors , high stability , low dissipation factor, compatible with high voltages and high mechanical loads, so widely used in ultrasonic cleaner, ultrasonic welding, ultrasonic detector, ultrasonic motor, ultrasonic transformer and other high-power emanant transducers and so on.

3.Piezoelectric Ceramics:Piezoelectric Material PZT4

PZT4 piezoelectric ceramic has characteristics similar to P8 , but PZT4 is the middle power transmitting and receiving matrial,. It’s widely used in ultrasonic cleaners, ultrasonic welding, vibratory motors. high frequency transducers and stress pressure sensors and so on.

4.Piezoelectric Ceramics:Piezoelectric Material PZT5

PZT5 piezoelectric ceramic has the function of large displacements and high sensitivity, which is the soft material, so widely used in flow meters, medical ultrasound, level sensors, microphones and so on

5.Technical Piezo Ceramics description

Piezoelectricity is the property of nearly all materials that have a non-centrosymmetric crystal structure.

Some naturally occuring crystalline materials that possess these properties are quartz and

tourmaline.Some aritficially produced piezoelectric crystals are Rochelle salt, ammonium dihydrogen phosphate and lithium sulphate. Another class of materials possessing these properties is polarized piezoelectric ceramic. In contrast to the naturally occurring piezo-electric crystals, piezoelectric ceramics have a polycrystalline structure.

The most commonly produced piezoelectric ceramics are lead zirconate titanate (PZT), barium titanate and lead titan-ate. Ceramic materials have several advantages over single crystals, especially the ease of fabrication into a variety of shapes and sizes. In contrast, single crystals must be cut along certain crystallographic directions, limiting the possible

geometric shapes.

The Perovskite crystal structure

PZT (and many other piezoelectric materials) have crystal structures belonging to the perovskite family with the general formula AB03-tric) structure are shown.

A piezoelectric ceramic material consists of small grains (crystallites), each containing domains in which the polar direction of the unit cells are aligned. Before poling, these grains and domains are randomly oriented; hence the net polarization of the material is zero, i.e. the ceramic does not exhibit piezoelectric proper-ties.The application of a sufficiently high DC field(called poling process) will orient the domains in the field direction and lead to a rem-anent polarization of the material.

The perovskite structure is very tolerant to element substitution (doping) by formation of solid solutions. The possibilities of doping in these materials lead to an unlimited number of possible perovskite--type oxides.

Even small amounts of a dopant may cause huge changes in the properties of a material.

The coupling of electrical and mechanical energy makes piezoelectric materials useful in a wide range of applications.

Electric dipoles in piezoelectric materials before, during and after poling

Constitutive equations

The piezoelectric effect depends on directions. The reference axis, called axis 3, is taken parallel to the direction of poling. Axes 1 and 2 coordinate system with axis 3. 4, 5 and 6 represent shear movements around axes 1, 2 and 3 respectively.

Piezoelectric coefficients

Based on this coordinate system,the piezoelectric effect can be described in a simplified way by matrix coefficients. The coefficients “d” and “sE” are commonly used.

Basic piezoelectric equations

These coefficients are used to relate the strain “S”(6-components tensor) to the stress “T” and electrical field “E”(3-components vector).

S = sE.T + d.E

Designation of axes in piezoelectric materials

In this equation, the “sE.T” term describes the mechanical compliance of the component, simi-larly to any mechanical component. The “d.E” term describes the piezoelectric effect, i.e. strain generated by electrical field.

The above equations are useful for designing a piezoelectric application. However, it must be kept in mind that they represent an approximation.