These actuators are usually cylindrical in shape and, for standard applications, much larger than the low voltage variant. The stacked structures are created by gluing together individual, finished PZT disks and electrodes. Unlike their low voltage cousins, these actuators are not monolithic. High voltage actuators have operating voltages that are typically above 500 V. Due to their smaller size, however, they are limited in the force that can be produced. These actuators are cheap, available in large quantities, and great for precision articulation. They have an electrical capacitance on the order of a few ♟ and tend to have a high elastic modulus. While they can vary in size, these actuators tend to stay on the small-to-medium size and are usually rectangular. These devices are monolithic stacks devices, meaning that the stacked structure is produced through sintering rather than gluing individual layers (see Figure 3). Low voltage actuators tend to have operating voltages below 200 V. This concept is discussed in more detail later in this tutorial.įigure 3: Three-Dimensional Cross Section of Multilayer Piezo with Interdigitated Electrodes These modes of deformation that act orthogonally to the pointing axis create real world limitations in the actual use of PZT actuators. While we consider the case where the actuation of the piezo is restricted to 1D movement, in general a piezo can be deformed through other modes as well (see Figure 2). This will be a concept we'll return to later when we discuss blocking force. The interesting consequence of this is that for any given mechanical strain upon a piezo, the force it can generate is proportional to the cross-sectional area of the piezo. The stress for such a configuration is given as F/A. These devices are normally constructed such that they are restricted to 1D operation with force and displacement occurring along the pointing axis (as defined by the electric field). The specific matrix elements are used to calculate the useful measures of PZT functionality, though the full derivation of these equations is beyond the scope of this tutorial.įigure 1 represents a simplified PZT device. Here D is the electric displacement vector, ε is the strain vector, E is the applied electric field vector, σ m is the stress vector, e σ ij is the dielectric permittivity, d d im & d c jk are the piezoelectric coefficients, and s E km is the elastic compliance (the inverse of stiffness). PZT devices are capable of driving precision articulation of mechanical devices (such as a mirror mount or translating stage) due to the piezoelectric effect, which can be described through a set of coupled equations known as strain-charge (essentially coupling the electric field equations with the strain tensor of Hooke’s law): It is not only piezoelectric but also pyroelectric and ferroelectric. Consequently, PZT is the ceramic material that makes up the bulk of piezoelectric actuator devices available on the market. One material in particular, lead-zirconate-titanate (PZT), has found prolific use for piezoelectric devices. Due to these modes, piezoelectric materials have found considerable use in both sensors and actuators and are often called “smart” or “intelligent” materials. Piezoelectrics either produce a voltage in response to mechanical stress (known as direct mode) or a physical displacement as a result of an applied electrical field (known as indirect mode). These devices utilize piezoelectricity, a phenomenon in which electricity is created from pressure on the device. In this tutorial we will look at some of the basics of piezoelectronic device structure and operation.
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