It is useful to remember that large d ij constants relate to large mechanical displacements which are usually sought in motional transducer devices. Conversely, the coefficient may be viewed as relating the charge collected on the electrodes, to the applied mechanical stress. The subscripts in d 15 indicate that the charge is collected on electrodes which are at right angles to the original poling electrodes and that the applied mechanical stress is shear. To view the d ij coefficients in this manner is useful when charge generators are contemplated, e.g., accelerometers. Output voltage is obtained by multiplying the calculated electric field by the thickness of ceramic between electrodes.
High g ij constants favor large voltage output, and are sought after for sensors.
Although the g coefficient are called voltage coefficients, it is also correct to say the g ij is the ratio of strain developed over the applied charge density with units of meters per meter over coulombs per square meter. Whereas the relative dielectric constant is strictly a material property, the capacitance is a quantity dependent on the type of material and its dimensions. Units are expressed in farads. K 3 is related to the capacitance between the original poling electrodes. K 1 is related to the capacitance between the second pair of electrodes applied after removal of the poling electrodes for the purposes of shear excitation.