Daniel E. Glumac

High-displacement piezoelectric actuator utilizing a meander-line geometry I. Experimental characterization

The compact linear-motion piezoelectric actuator developed has relatively large displacement capabilities. It is composed of a number of parallel bars of lead zirconium titanate (PZT) connected together in a meander-line configuration so that they are mechanically in series and electrically in parallel. The polarity of the adjacent bars is arranged so that if a given bar expands under the applied voltage, the adjacent bars contract. An electromechanical model of the actuator predicted and measurements verified that stiffeners added to the basic meander line geometry significantly increased the force output without affecting the displacement versus applied voltage relationship.<<ETX>>

Design of linear-motion microactuators using piezoelectric thin films

Three types of microactuator for linear displacement are presented which use piezoelectric thin films for the electrical-to-mechanical energy conversion process. One actuator uses a folded-path or meander-line geometry to produce horizontal tethered linear displacements. The second geometry uses a number of unimorph bars arranged in a planar format and mechanically connected in series to produce a tethered displacement perpendicular to the plane containing the unimorphs. The third actuator uses an inertial recoil mechanism in conjunction with an electrostatic clamp to produce incremental stepping motion. Sufficient repetition of the stepping sequence produces virtually unlimited travel range, being limited by practical considerations such as electrical connections. Electromechanical models for all three actuators are developed and are used to quantitatively estimate the performance of microactuators designed to a particular set of dimensions. Fabrication procedures for the microactuators have been developed and the status of the fabrication efforts is presented.

Compact, high-displacement piezoelectric actuator with potential micromechanical applications

An actuator was developed that, in a macroscale version, is composed of a number of parallel bars of lead zirconate titanate (PZT) connected together in a meander line configuration so that they are mechanically in series and electrically in parallel. The polarity of the adjacent bars is arranged so that if a given bar expands under the applied voltage, the adjacent bars contract. Experimental measurements are in agreement with the predictions of an electromechanical model of the actuator. The design and fabrication of a micromechanical version of the actuator is also described.<<ETX>>

A planar unimorph-based actuator with large vertical displacement capability. II. Theory

A piezoelectric actuator utilizing a planar trellis-like arrangement of multiple unimorph elements is described which produces displacements perpendicular to the plane of the actuator. The unimorph elements are connected in series mechanically so that the vertical displacement of each unimorph element in the structure adds to the vertical displacements of the other elements, resulting in a large overall vertical displacement at the output of the actuator. A simple electromechanical model of the actuator is developed. The model consists of a voltage-actuated force source, which is the result of the piezoelectric properties of the unimorph bars that make up the actuator, in parallel mechanically with a stiff spring that models the elastic response, both bending and twisting, of the unimorph elements. The long moment arms inherent in the geometry of the actuator make a substantial contribution to the overall compliance of the actuator. The addition of stiffeners to the actuator can significantly reduce the effect of these moment arms, and thus substantially increase the stiffness of the actuator. As a result, the force generation capability of the actuator is significantly increased without affecting its displacement capability.

Field emission diodes using sharp vertical edge structure

Field emission diodes with sharp vertical edges have been fabricated for possible future cathodoluminescence and high frequency device applications. These devices are formed using self-aligned planar processing methods based on conformal thin film deposition techniques thereby eliminating many of the fabrication difficulty and performance variation associated with other previously used fabrication methods. Recessed sealed vacuum cavities have been formed as part thereby eliminating the need for external vacuum pumping.<<ETX>>

Characterization of Mems Actuators Via Nanoindentation

Nanoindentation has been used to characterize polycrystalline silicon serpentine structures which will become the “framework” for piezoelectric meander line microactuators. These structures are fabricated using silicon wafer surface micromachining processing techniques, and they are suspended about 1 micron above the wafer surface. Normally, nanoindentation equipment is used for materials scratch-testing; however, this equipment was modified so that a probe tip could make contact to the sides of the meander lines, thus enabling known forces to be applied parallel to the wafer surface. For one type of device, the nanoindentaion technique yielded a spring constant of 400 N/m, while simple beam theory gave 1300 N/m and the finite element analysis software ANSYS gave 1200 N/m. This measurement technique holds the promise of being able to apply a known force and then countering that force with piezoelectric actuation to determine the forces that future piezoelectric microactuators will be able to provide.