Definitions & Terminology: Introduction
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In piezoelectric ceramics, material characteristics depend on the direction of the applied electric field, displacement, stress, and strain. Hence superscripts and subscripts indicating the direction are added to the symbols. The direction of polarization is generally designated as the z-axis of an orthogonal crystallographic system. The axes x,y and z are respectively represented as 1, 2 and 3 directions and the shear about these axes are represented as 4, 5 and 6. This is shown schematically in Figure-1. The various piezoelectric material constants are generally expressed with subscripts using this notation. For example, planar modes are expressed with a subscript 'p'. Other examples are also shown in Figure-1. The first subscript gives the direction of the electrical field associated with the voltage applied or the charge produced. The second subscript gives the direction of mechanical stress or strain. Superscripts indicate a constant mechanical or electrical boundary condition. A general description of the superscripts is given in Table-1 below. See also the Table of Symbols. Table-1: Superscript General Description
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