The units may then be expressed as meters per meter, per volts per meter (meters per volt). The piezoelectric constants relating the mechanical strain produced by an applied electric field are termed the strain constants, or the "d" coefficients. S = constant strain = mechanically clampedĪs an example, K T 3 expresses the relative dielectric constant (K), measured in the polar direction ( 3) with no mechanical clamping applied. The superscripts are T, E, D, and S, signifying:Į = constant electric field = short circuitĭ = constant electrical displacement = open circuit Several piezoceramic material constants may be written with a "superscript" which specifies either a mechanical or electrical boundary condition. The second subscript gives the direction of the mechanical stress or strain. The first subscript gives the direction of the electric field associated with the voltage applied, or the charge produced. Piezoelectric coefficients with double subscripts link electrical and mechanical quantities. When the mechanical stress or strain is shear, the subscript 5 is used in the second place. In this event, the 3 axis is not altered, but is then parallel to the electroded faces found on the finished element. In shear operations, these poling electrodes are later removed and replaced by electrodes deposited on a second pair of faces. This direction is established during manufacturing by a high DC voltage that is applied between a pair of electroded faces to activate the material. The polar, or 3 axis, is taken parallel to the direction of polarization within the ceramic. These axes, termed 1, 2, and 3, are analogous to X, Y, and Z of the classical three dimensional orthogonal set of axes. To identify directions in a piezoceramic element, three axes are used. Relationships between applied forces and the resultant responses depend upon: the piezoelectric properties of the ceramic the size and shape of the piece and the direction of the electrical and mechanical excitation. The following text describes the terminology of piezoceramics and the relationship among variables for functional applications. Since piezoceramic elements are capable of generating very high voltages, they are compatible with today's generation of solid-state devices - rugged, compact, reliable, and efficient. If the electrodes are not short-circuited, a voltage associated with the charge appears.Ī piezoceramic is therefore capable of acting as either a sensing or transmitting element, or both.
When it is stressed mechanically by a force, it generates an electric charge. When a piezoceramic element is stressed electrically by a voltage, its dimensions change.
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