High-displacement piezoelectric actuator utilizing a meander-line geometry II. Theory.

For pt.I see ibid., vol.38, no.5, p.454-60 (1991). A simple electromechanical model of the meander-line actuator is developed. The model consists of a voltage-actuated force source, which is the result of the piezoelectric properties of the bars that make up the actuator, in parallel mechanically with a stiff spring that models the compression-expansion response of the piezoelectric bars. This parallel combination is in series mechanically with a second spring. This series connection is subjected to large bending moments that cause the stiffness of this second spring to be much less than the stiffness of the spring in parallel with the force source. The addition of stiffeners to the actuator can significantly reduce these bending moments and thus increase the stiffness of this second spring. As a result, the force generation capability of the actuator is significantly increased without affecting its displacement capability.

A simple phenomenological model of tunable SAW devices using magnetostrictive thin films.

A simple phenomenological model has been developed that is useful for the approximate design of tunable SAW (surface acoustic wave) devices using magnetostrictive thin films. The model formulation, based on perturbation theory, relates the maximum magnetic-field-dependent velocity change or tunability range to the frequency of operation, film thickness, elastic properties of the film and substrate, and magnetic properties of the film. Iron-terbium-boron films deposited on quartz and lithium niobate substrates were used to verify the formula. A significant variability in the magnetic properties of the films was obtained by varying the amount of terbium (0-5 at.%) in the film (80% Fe and 15-20% B). A simple figure of merit for comparing various film-substrate combinations, independent of device dimensions, was derived and experimentally checked.

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.

A planar unimorph-based actuator with large vertical displacement capability. I. Experiment.

A piezoelectric actuator utilizing a planar arrangement of unimorph elements that produces displacements perpendicular to the plane of the actuator is described. The elements are connected in series mechanically so that the vertical displacement of each element adds to the vertical displacements of the other elements. Two prototype actuators were built and tested. One was stick-built from individual bars of PZT and aluminum, which were epoxied together and connected to each other with short aluminum connector bars. The other was fabricated monolithically from a single plate of PZT by bead-blasting the PZT plate through a steel shadowmask to mill out the desired actuator shape. Copper bars epoxied to the milled-out PZT bars then formed the unimorph elements. The unloaded output displacement of each actuator versus applied voltage was measured as well as the displacement versus applied force with no applied voltage. These measurements were in agreement with the predictions of an electromechanical model of the actuator that has been developed. The model predicted and measurements verified that stiffeners can be added to the basic geometry that will significantly increase the force output without affecting the displacement versus applied voltage characteristic.

Thin-film characterization using a scanning laser acoustic microscope with surface acoustic waves.

The use of surface acoustic waves in a scanning laser acoustic microscope for the characterization of the mechanical or acoustic properties of thin films deposited on piezoelectric substrates is demonstrated. Quantitative measurements of mass loading effects of 5000-A-thick tungsten films deposited on lithium niobate substrates were obtained using 100-MHz surface acoustic waves. No information about the tungsten film could be obtained using 100-MHz compressional waves. Methods of generating surface waves on nonpiezoelectric materials so that this technique could be used on arbitrary substrates are discussed.

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.

A linear piezoelectric stepper motor with submicrometer step size and centimeter travel range.

A linear stepper motor capable of submicrometer controlled movement has been constructed using the piezoelectric material lead zirconate titanate (PZT). This motor consists of a 25.4-mmx12.7-mmx1.6-mm piezoelectric driving element connected between a glider base and an attached load. The device is inset in a trench to constrain motion to one dimension. An electrode on the bottom of the glider is used with an electrode on the top of the trench to implement an electrostatic clamp. This clamp enables the stepper motor to climb slopes of up to 12 degrees , whereas without the clamp only slopes of 6 degrees or less are tolerated. A linear inertial sliding motion can be achieved by expanding and contracting the piezoelectric bar, but the addition of the electrostatic clamp enhances the movement capabilities of the glider by the periodic clamping and unclamping of the glider. Glider velocities of 5.7-476 mum/s are measured by timing the movement of the glider over a 1.0-mm portion of the track through an optical microscope. Displacement steps of 0.07-1.1 mum are calculated by dividing the measured glider velocity by the frequency of the applied voltage pulses. Displacement step size and glider velocity are controlled by the application of PZT extension voltages ranging from +/-(60-340) V.

Microdevices in medicine.

The application of microelectromechanical systems (MEMS) to medicine is described. Three types of biomedical devices are considered, including diagnostic microsystems, surgical microsystems, and therapeutic microsystems. The opportunities of MEMS miniaturization in these emerging disciplines are considered, with emphasis placed on the importance of the technology in providing a better outcome for the patient and a lower overall health care cost. Several case examples in each of these areas are described. Key aspects of MEMS technology as it is applied to these three areas are described, along with some of the fabrication challenges.