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Micromachines 2016, 7(1), 12; doi:10.3390/mi7010012

Dynamic Electromechanical Coupling of Piezoelectric Bending Actuators

School of Mechanical, Aerospace and Civil Engineering, The University of Manchester, Manchester M13 9PL, UK
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Academic Editors: Nathan Jackson and Joost Lötters
Received: 28 September 2015 / Revised: 9 January 2016 / Accepted: 12 January 2016 / Published: 20 January 2016
(This article belongs to the Special Issue Piezoelectric MEMS)
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Abstract

Electromechanical coupling defines the ratio of electrical and mechanical energy exchanged during a flexure cycle of a piezoelectric actuator. This paper presents an analysis of the dynamic electromechanical coupling factor (dynamic EMCF) for cantilever based piezoelectric actuators and provides for the first time explicit expressions for calculation of dynamic EMCF based on arrangement of passive and active layers, layer geometry, and active and passive materials selection. Three main cantilever layer configurations are considered: unimorph, dual layer bimorph and triple layer bimorph. The actuator is modeled using standard constitutive dynamic equations that relate deflection and charge to force and voltage. A mode shape formulation is used for the cantilever dynamics that allows the generalized mass to be the actual mass at the first resonant frequency, removing the need for numerical integration in the design process. Results are presented in the form of physical insight from the model structure and also numerical evaluations of the model to provide trends in dynamic EMCF with actuator design parameters. For given material properties of the active and passive layers and given system overall damping ratio, the triple layer bimorph topology is the best in terms of theoretically achievable dynamic EMCF, followed by the dual layer bimorph. For a damping ratio of 0.035, the dynamic EMCF for an example dual layer bimorph configuration is 9% better than for a unimorph configuration. For configurations with a passive layer, the ratio of thicknesses for the passive and active layers is the primary geometric design variable. Choice of passive layer stiffness (Young’s modulus) relative to the stiffness of the material in the active layer is an important materials related design choice. For unimorph configurations, it is beneficial to use the highest stiffness possible passive material, whereas for triple layer bimorph configurations, the passive material should have a low stiffness. In all cases, increasing the transverse electromechanical coupling coefficient of the active material improves the dynamic EMCF. View Full-Text
Keywords: piezoelectric; MEMS; actuators; electromechanical coupling; dynamics; resonance; actuation efficiency piezoelectric; MEMS; actuators; electromechanical coupling; dynamics; resonance; actuation efficiency
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Nabawy, M.R.A.; Crowther, W.J. Dynamic Electromechanical Coupling of Piezoelectric Bending Actuators. Micromachines 2016, 7, 12.

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