A Review of Smart Materials in Tactile Actuators for Information Delivery

As the largest organ in the human body, the skin provides the important sensory channel for humans to receive external stimulations based on touch. By the information perceived through touch, people can feel and guess the properties of objects, like weight, temperature, textures, and motion, etc. In fact, those properties are nerve stimuli to our brain received by different kinds of receptors in the skin. Mechanical, electrical, and thermal stimuli can stimulate these receptors and cause different information to be conveyed through the nerves. Technologies for actuators to provide mechanical, electrical or thermal stimuli have been developed. These include static or vibrational actuation, electrostatic stimulation, focused ultrasound, and more. Smart materials, such as piezoelectric materials, carbon nanotubes, and shape memory alloys, play important roles in providing actuation for tactile sensation. This paper aims to review the background biological knowledge of human tactile sensing, to give an understanding of how we sense and interact with the world through the sense of touch, as well as the conventional and state-of-the-art technologies of tactile actuators for tactile feedback delivery

Design of thermo-piezoelectric microstructured bending actuators via multi-field asymptotic homogenization

The use of integrated MicroElectroMechanical systems (MEMS) is recently spread thanks to their improved sensitivity, accuracy and reliability. Accurate preliminary computations born from the need of high precision in the manufacturing process of such devices. Piezoelectric materials are broadly employed in this field as direct converters between mechanical and electrical signals and some of these piezoelectric materials show pyroelectric features, which involve thermo-electrical interactions. Pyroelectric bending actuators are analyzed in the present study in plane conditions. They consists of active PZT layers with in-plane polarization and a microstructured composite layer characterized by a periodic microstructure where PZT fibers with an out of plane polarization are immersed in a polymeric matrix. The constitutive law of the composite layer at the macroscale has been determined by means of a multi-field asymptotic homogenization technique, recently developed for thermo-piezoelectric materials. Overall constitutive equations characterizing the behavior of the microstructured layer at the macroscale have been derived and the closed form of the overall constitutive tensors has been provided for the equivalent first-order (Cauchy) homogenized continuum. Deflection of unimorph and bimorph bender actuators has been investigated in relation to their geometrical features, exploiting the out of plane piezoelectric properties of the composite layer, which modify the stiffness of the entire bender. An accurate description of benders behavior at the structural length scale is of fundamental importance in order to design devices with high performances. In this regard, the influence of the microstructure on the global response of the actuator is investigated in the present study in order to understand how the composite material can be tailored to meet specific design requirements

Piezo-Polymer-Composite Unimorph Actuators for Active Cancellation of Flow Instabilities Across Airfoils

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.This article presents a smart device for active cancellation of flow instabilities. An array of two piezo unimorph actuators fabricated in piezo-polymer-composite technology is combined with a thin silicone membrane to mimic a movable wall with a closed surface. By locally displacing the thin membrane, a surface wave is generated that interferes with naturally occurring flow instabilities within the boundary layer of an airfoil. Using flow sensors and an intelligent control enables a destructive interference and therefore, an attenuation of natural flow instabilities. This leads to a delay of transition. The boundary layer remains laminar which means drag is reduced. Within the next pages, the setup of the device with actuators, membrane, sensors, and control is introduced. The main focus of this article is on actuator design, modeling, and implementation for wind tunnel experiments. Results of actuator characterization are presented. The non-linear behavior of the piezoactuator (harmonic distortions and impact of high electric fields) is investigated in detail. This study concludes with the results obtained in wind tunnel experiments which prove the functionality of the presented approach. A maximal attenuation of natural occurring flow instabilities of 80% is achieved.DFG, SPP 1207, Strömungsbeeinflussung in der Natur und Techni

Design of Unimorph Out-of-Plane Piezoelectric Actuator

Electromechanical transduction is an important component of microelectromechanical systems (MEMS), a technology with wide-ranging applications, including mobile computing, sensors, energy harvesting, and displays. These disparate applications have varying performance requirements, but generally transduction efficiency, mechanical precision, response time, cost, compatibility with photolithography and other fabrication processes, and operability at micro-scale are all desired metrics for MEMS devices. Piezoelectric transduction provides substantial advantages, including precise displacements, quick response times, and high transduction efficiency. These strengths make piezoelectric transduction particularly well-suited for use in resonators, sensors, and energy harvesters. However, piezoelectric transduction also produces much smaller magnitudes of movements than other electromechanical transduction mechanisms, such as thermal or capacitive. This limits the utility of piezoelectricity in designing MEMS actuators. Currently, MEMS designers compensate for this limitation by using sophisticated structures to amplify the small strains produced through the reverse piezoelectric effect. One of the oldest and simplest such designs is the bimorph cantilever beam. Comprised of two distinct, but mechanically connected, piezoelectric layers, the beam uses piezoelectricity to cause longitudinal strain in both layers. As one layer expands, the other contracts—this opposing motion creates a bending moment, causing the beam to deflect out-of-plane, often at substantially higher displacements than the expansion or contraction of either piezoelectric layer. This thesis presents a design and simulation results for a unimorph beam comprised of only one piezoelectric layer. Through use of a novel electrode pattern that applies a non-uniform electric field, this beam acts as a quasi-bimorph, creating a bending moment without the need for two distinct piezoelectric layers

Smart Material Wing Morphing for Unmanned Aerial Vehicles.

Morphing, or geometric adaptation to off-design conditions, has been considered in aircraft design since the Wright Brothers’ first powered flight. Decades later, smooth, bio-mimetic shape variation for control over aerodynamic forces still remains elusive. Unmanned Aerial Vehicles are prime targets for morphing implementation as they must adapt to large changes in flight conditions associated with locally varying wind or large changes in mass associated with payload delivery. The Spanwise Morphing Trailing Edge (SMTE) concept is developed to locally vary the trailing edge camber of a wing or control surface, functioning as a modular replacement for conventional ailerons without altering the wing’s spar box. The SMTE design was realized utilizing alternating active sections of Macro Fiber Composites (MFCs) driving internal elastomeric compliant mechanisms and passive sections of anisotropic, elastomeric skin with tailorable stiffness, produced by additive manufacturing. Experimental investigations of the modular design via a new scaling methodology for reduced-span test articles revealed that increased use of more MFCs within the active section did not increase aerodynamic performance due to asymmetric voltage constraints. The comparative mass and aerodynamic gains for the SMTE concept are evaluated for a representative finite wing as compared with a conventional, articulated flap wing. Informed by a simplistic system model and measured control derivatives, experimental investigations identified a reduction in the adaptive drag penalty up to 20% at off-design conditions. To investigate the potential for augmented aeroelastic performance and actuation range, a hybrid multiple-smart material morphing concept, the Synergistic Smart Morphing Aileron (SSMA), is introduced. The SSMA leverages the properties of two different smart material actuators to achieve performance exceeding that of the constituent materials. Utilizing the relatively higher work density and phase transformation of Shape-Memory Alloys combined with the larger bandwidth and conformal bending of MFCs, the resultant design is demonstrated to achieve the desired goals while providing additional control authority at stall and for unsteady conditions through synergistic use of reflex actuation. These advances highlight and motivate new morphing structures for the growing field of UAVs in which adaptation involves advanced compliance tailoring of complex geometry with synergistic actuation of embedded, smart materials.PhDAerospace EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/111533/1/alexmp_1.pd

Dual-Beam Actuation of Piezoelectric AlN RF MEMS Switches Monolithically Integrated with AlN Contour-Mode Resonators

This work reports on piezoelectric Aluminum Nitride (AlN) based dual-beam RF MEMS switches that have been monolithically integrated with AlN contour-mode resonators. The dual-beam switch design presented in this paper intrinsically compensates for the residual stress in the deposited films, requires low actuation voltage (5 to 20 V), facilitates active pull-off to open the switch and exhibits fast switching times (1 to 2 μs). This work also presents the combined response (cascaded S parameters) of a resonator and a switch that were co-fabricated on the same substrate. The response shows that the resonator can be effectively turned on and off by the switch. A post-CMOS compatible process was used for the co-fabrication of both the switches and the resonators. The single-chip RF solution presented herein constitutes an unprecedented step forward towards the realization of compact, low loss and integrated multi-frequency RF front-ends