Piezoelectric Drop-on-demand Piezoelectric Drop-on-demand Piezoelectric Ink Jet Piezoelectric Materials for Microfluidics

Abstract

a material. Requires a polarization that remains within a material in the absence of the application of an external field, in turn requiring a non-enantiomorphic polar symmetry in the composition of the material. Definition Piezoelectricity means squeeze or pressure electricity, from the Greek pieze which means to press or squeeze. The casual definition of piezoelectric materials is that they develop an electric charge differential along an axis of piezoelectric polarization if placed under appropriate mechanical strain, called the direct piezoelectric effect, and deform if an electric field is applied along the same axis of polarization, the converse piezoelectric effect. The electric field to mechanical strain coupling occurs when the positive and negative charge of the individual ions within the material do not displace symmetrically upon the application of an external strain. Strictly speaking, piezoelectric materials exhibit electric polarization upon the application of a stress and vice versa. Often the casual and strict definitions are the same, though confusion may arise with the casual definition. All piezoelectric materials are anisotropic, and there are useful examples of piezo-electric materials that are single crystals, polycrystalline ceramics, and polymers. Many of the known piezoelectric materials have at one time or another been used as sensors or actuators in microfluidics, for which their rapid response and large force transmission have been beneficial , though researchers have had to learn to overcome small strains, thermal losses, aging, and difficulties in fabrication , especially in process compatibility. Overview Piezoelectric materials offer the ability to directly transform (transduct) from electrical to mechanical energy and vice versa, convenient for microtechnology in sensing and actuation; a material is said to be piezoelec-tric if an applied stress generates an electric field within, and vice versa. They may be used to provide static and dynamic deformation at frequencies up to several giga-hertz, depending on the motion to be induced, the scale of the device, and the material used. Compared to other methods of power transduction, including electrostatic, elec-trostrictive, magnetostrictive, and electromagnetic means, piezoelectric transduction typically provides large forces at small strain rates (< 1% strain typically) for actu-ation, and relatively large voltages and small currents for sensing. Piezoelectricity is usually treated as a linear interaction between mechanical and electrical phenomena , though this assumption is generally invalid for high-power applications or in materials with either large losses or large deformations (polymers). The hystere-sis in such conditions is the deviation from linear trans-duction. …