Inbar Hotzen Grinberg

Reversing the action of thermoelastic bimorphs using selective directional stiffeners

We present for the first time ever, a method for reversing the response of thermoelastic bimorph actuators, without changing the order of their layers. Our device is constructed from a flat stage that is suspended on three thermoelastic bimorph spiral arms. We demonstrate that the thermoelastic response of the spiral bimorphs can be affected by using directional stiffeners. We show that with no stiffeners, the thermoelastic response naturally displaces the stage downwards by 7μm. Stiffeners that are angled at 45° relative to the spiral tangent, enhance this response by a factor of 3, and increase the downward displacement to 23μm. Surprisingly, stiffeners which are angled at -45°, completely reverse the direction of the response, and result in an enhanced upward displacement of 23μm.

Selective Stiffening for Producing a Mass-Fabrication Compatible Motion Conversion Mechanism

We present a mechanism that converts in-plane to out-of-plane motions, which is fully compatible with mass-fabrication processes. By using selective stiffening, we induce coupling between in-plane and out-of-plane responses of the mechanism. The conversion ratio is constant (i.e., linear response), and it can be easily tailored by the number of stiffeners used in an otherwise unchanged design planform. The linearity of the motion conversion and the possibility to tailor it, are demonstrated experimentally using dedicated test devices. As a specific example of application, we use the motion conversion mechanism to achieve a parallel out-of-plane motion of a flat stage, which is driven by in-plane comb-drives.

A MEMS Implementation of a Classic Parametric Resonator

We present a microelectromechanical systems realization of a classic parametric resonator. This parametric resonator is ideal in the sense that the electrostatic stiffness, which may be time modulated, is not affected by motion. We also present a simple, efficient, and intuitive model of parametric excitation. This model predicts the minimal modulation amplitude required to obtain an unbounded response in a parametric system with linear damping. We show experimental results in which the system is operated as a Meissner resonator.

A Piezoelectric Twisting Beam Actuator

We present a novel piezoelectric bulk-unimorph beam actuator that can be directly driven in twisting. The bulk-unimorph beam is driven by interdigitated electrodes (IDEs), deposited over its top and bottom surfaces. These IDEs are oriented at 45° relative to the beam axis, and they are used for both poling and actuation. When subjected to a driving voltage, the IDEs induce both axial and shear stresses in the vicinity of the surface over which they are deposited. These stresses give rise to both internal bending and internal torsion moments. When one set of electrodes, either on the top or the bottom surface, is used to drive the lead zirconate titanate beam, a coupled bending/twisting response is induced. However, when both the top and bottom electrodes are used, we can achieve either a pure torsion mode or a pure bending mode, with no cross coupling, depending on the driving scheme. [2016-0313]

On the Notion of a Mechanical Battery

We present an electrostatic transducer in which voltage remains constant while charge is stored or extracted from the device. We achieve this by designing a nonlinear mechanical spring, which exactly counteracts the nonlinearity associated with electrostatic attraction forces. In essence, the new device responds like a rechargeable battery, only that here we store electric energy in elastic deformation, whereas in common batteries, electric energy is stored as chemical potential. The capacitance of the presented test devices is currently too small to be practical, and we are not, by any means, suggesting that this transducer can replace chemical rechargeable batteries. Nevertheless, some necessary steps toward constructing a more viable device with larger energy density are discussed.

A bulk-unimorph PZT actuator for large piston motions with 2-axis small angle adjustments

We present a bulk-unimorph PZT actuator that can achieve large piston motions, and small angle adjustments. The actuator is constructed from four spiral arms supporting a central stage, and each arm can be actuated separately. The spiral arms are driven by both internal bending moments and torsion moments. We experimentally show that the torsional deformation in the arms dominates the response, and that the internal bending moments have a negligible effect. The presented device achieves a piston motion of up to 75μm, and small tilting angles around two perpendicular in-plane axes.

Two axes actuators (x-z or x-θ) driven by in-line electrostatic comb-drives

We present a two axis actuator which can be controlled both in-plane, and out-of-plane. Previously we demonstrated a conversion mechanism in which in-plane motion was translated to out-of-plane motion. That mechanism harnesses comb-drive actuation and converts the in-plane motion of the comb-drive shuttle to a parallel out-of-plane motion of a rigid stage. In the present work we show a two axis control of the actuator, one axis inplane and one out-of-plane. We also show a new test device that converts in-plane motion to a tilting motion, in which both axes may be separately controlled. Presented experimental data is in good agreement with model predictions. Specifically, we demonstrate a linear relation between in-plane electrostatic force, and the tilt angle.

Selective Stiffening for Enhancing and/or Reversing the Action of Thermoelastic Actuators

We present a thermoelastic micromotor for driving a rigid plate in an out-of-plane motion. The plate is suspended on spiral thermoelastic bimorph arms, made of a nitride layer coated by gold. Heating of the thermoelastic arms is achieved by driving electric current, either through polysilicon resistors that are embedded in the nitride layer, or through the gold layer itself. Heating generates isotropic internal bending moments in the bimorphs. We show that this bending produces only small deflections of the plate. To improve the performance of the actuator, we use selective stiffeners to convert bending into torsional deformation of the spiral arms. In one orientation of the stiffeners, this conversion may be used to achieve a seven-fold increase of the thermoelastic response of the actuator. In a different orientation of the stiffeners, a complete reversal of the enhanced thermoelastic response is achieved.