Numerical Analysis of Dynamic Effects of a Nonlinear Vibro-Impact Process for Enhancing the Reliability of Contact-Type MEMS Devices

This paper reports on numerical modeling and simulation of a generalized contact-type MEMS device having large potential in various micro-sensor/actuator applications, which are currently limited because of detrimental effects of the contact bounce phenomenon that is still not fully explained and requires comprehensive treatment. The proposed 2-D finite element model encompasses cantilever microstructures operating in a vacuum and impacting on a viscoelastic support. The presented numerical analysis focuses on the first three flexural vibration modes and their influence on dynamic characteristics. Simulation results demonstrate the possibility to use higher modes and their particular points for enhancing MEMS performance and reliability through reduction of vibro-impact process duration

Study of natural frequency shifting in a MEMS actuator due to viscous air damping modeled by nonlinear reynolds equation

We report on finite element (FE) modeling and simulation of effect of squeeze-film damping on flexible microstructure operating in ambient air in close proximity to a fixed surface, which is a common case in many MEMS devices. A coupled fluidic-structural problem is solved by applying a nonlinear compressible Reynolds equation, which is derived from the Navier-Stokes equations, transformed into weak form and added to commercial FE modeling software. The proposed model enables investigation of influence of surrounding air on dynamics of different microstructures taking into account air rarefaction and air compressibility effects. The paper presents results of numerical analysis, which aim was to study the phenomenon of natural frequency shifting in the case of free and forced vibrations of the cantilever microstructure. Simulations demonstrate that squeeze-film damping may result in the increase of natural frequency of the microstructure due to system stiffening caused by air compression. The magnitude of this effect is determined by such parameters as ambient air pressure, air-film thickness, vibration frequency and lateral dimensions of the microstructur

Research of nonlinear electromechanical and vibro-impact interactions in electrostatically driven microactuator

This paper provides results of dynamic numerical analysis of nonlinear electromechanical and vibro-impact interactions in electrically-actuated contact-type microactuator, which is a common component in such devices as microswitches. Mathematical modeling was performed by means of finite element method, representing microactuator as a 3D cantilever microstructure and taking into account influence of bending forces generated by electrostatic field, damping forces due to squeezed air-film in the gap as well as bouncing of the microactuator tip upon its contact with substrate. Electrostatic-structural simulations were performed in order to predict actuation (pull-in) voltages of fabricated microswitches as well as to study influence of various system parameters on the value of the voltage. Results of these simulations were compared with experimental findings obtained by using electrical probe measurements of fabricated microswitches. Numerical analysis of free impact vibrations was carried out and allowed determination of effect of ambient air pressure and intermolecular adhesive interactions on the phenomenon of contact bouncin

Parametrization-based shape optimization of shell structures in the case of free vibrations

A finite-element-based shape optimization methodology has been developed for three-dimensional shell structures and shape optimization of shell structures has been performed. The shape optimization program is implemented by a job control language and commercial finite element analysis software ANSYS is used for structural analysis. Principles of structural analysis and automatic mesh generation are applied for achieving shape optimization. The objective is to minimize the weight of the shell structure under frequency constrains and the move limit for each design variable. In this paper several optimization examples are provide

Multi-dimensional Data Analysis in Electron Microscopy

This thesis discusses various large multi-dimensional dataset analysis methods and their applications. Particular attention is paid to non-linear optimization analyses and general processing algorithms and frameworks when the datasets are significantly larger than the available computer memory. All new presented algorithms and frameworks were implemented in the HyperSpy analysis toolbox. A novel Smart Adaptive Multi-dimensional Fitting (SAMFire) algorithm is presented and applied across a range of scanning transmission electron microscope (STEM) experiments. As a result, the Stark effect in quantum disks was mapped in a cathodoluminescence STEM experiment, and fully quantifiable 3D atomic distributions of a complex boron nitride core-shell nanoparticle were reconstructed from an electron energy loss spectrum (EELS) tilt-series. The EELS analysis also led to the development of two new algorithms to extract EELS near-edge structure fingerprints from the original dataset. Both approaches do not rely on standards, are not limited to thin or constant thickness particles and do not require atomic resolution. A combination of the aforementioned fingerprinting techniques and SAMFire allows robust quantifiable EELS analysis of very large regions of interest. A very large dataset loading and processing framework, “LazySignal”, was developed and tested on scanning precession electron diffraction (SPED) data. A combination of SAMFire and LazySignal allowed efficient analysis of large diffraction datasets, successfully mapping strain across an extended (ca. 1 μm × 1 μm) region and classifying the strain fields around precipitate needles in an aluminium alloy

Vibroacoustic handling and levitation of microparticles in air

The levitation and controlled movement of substances in the air has many potential applications, from materials handling to biochemistry and pharmacy. In this work, the handling of microparticles by sound field in vibrating cylinder was investigated by simulation and experimental measurement. A standing wave field created between the piezotransducer and the reflector created the conditions for levitating microparticles, which were concentrated at nodes of the vibrating cylinder surface. The acoustic wave and the cylinder walls were excited by the same disk-shaped piezotransducer fixed to the bottom of the cylinde

Efficiency improvement of energy harvester at higher frequencies

This research suggests employing electrode segmentation in order to avoid charge cancellation in the piezoelectric layers of harvester, which occurs, if strain nodes of vibrating harvester are covered by continuous electrodes. Two types of piezoelectric energy harvester prototypes were produced from piezoelectric plate, epoxy bonded to stainless steel substrate for experimental investigations. The first (reference) harvester prototype posses no electrode segmentation, while electrodes covering piezoelectric material of second harvester were segmented. Segmentation of the second harvester was configured for its operation at the second resonant frequency – i.e., performed so, that the electrodes of piezoelectric layer are not covering strain node of the second vibration mode. Experimental results revealed that segmented harvester prototype posses efficiency advantage as compared to the non-segmented counterpart – adding voltages, generated at each segment would result from 16 % to 60 % increase of maximum generated voltage. Also conception, that using stopper, placed at appropriate position, energy harvesting process could be stabilized, i.e. bandwidth of operating frequency could be increased

Excitation dependent Fano-like interference effects in plasmonic silver nanorods

Surface plasmon resonances in metal nanoparticles are an emerging technology platform for nano-optics applications from sensing to solar energy conversion. The electromagnetic near field associated with these resonances arises from modes determined by the shape, size, and composition of the metal nanoparticle. When coupled in the near field, multiple resonant modes can interact to give rise to interference effects offering fine control of both the spectral response and spatial distribution of fields near the particle. Here, we present an examination of experimental electron energy loss spectroscopy (EELS) of silver nanorod monomer surface plasmon modes and present an explanation of observed spatial amplitude modulation of the Fabry-Pérot resonance modes of these silver nanorods using electrodynamics simulations. For these simulations, we identify differences in spectral peak symmetry in light scattering and electron spectroscopies (EELS and cathodoluminescence) and analyze the distinct near-field responses of silver nanorods to plane-wave light and electron beam excitation in terms of a coupled oscillator model. Effects of properties of the material and the incident field are evaluated, and the spatially resolved EELS signals are shown to provide a signature for assessing Fano-like interference effects in silver nanorods. These findings outline key considerations and challenges for interpreting electron microscopy data on plasmonic nanoparticles for understanding nanoscale optics and for characterization and design of photonic devices.S.M.C. acknowledges support of a Gates Cambridge Scholarship. D.R. acknowledges support from the Royal Society's Newton International Fellowship scheme. We acknowledge the use of computing facilities provided by CamGrid. Parts of this work were also performed using the Darwin Supercomputer of the University of Cambridge High Performance Computing Service (http://www.hpc.cam.ac.uk/), provided by Dell Inc. using Strategic Research Infrastructure Funding from the Higher Education Funding Council for England and funding from the Science and Technology Facilities Council. We thank F.J. de la Peña for helpful discussions on the use of hyperspy. The research leading to these results has received funding from the European Research Council under the European Union's Seventh Framework Program (Grant No. FP7/2007-2013)/ERC Grant Agreement No. 291522-3DIMAGE. Data on rod “B” were acquired by one of us (D. Rossouw) with support of a NSERC Discovery Grant (G. A. Botton) at the Canadian Centre for Electron Microscopy, a national facility supported by NSERC and McMaster University. We thank G. A. Botton for access to data on rod “B” and for helpful comments on this manuscript. P.A.M. also acknowledges funding from the European Union's Seventh Framework Program under a contract for an Integrated Infrastructure Initiative (Reference No. 312483-ESTEEM2)

Development and experimental analysis of piezoelectric optical scanner with implemented periodical microstructure

Piezoelectric optical scanner is developed for multi-coordinate control of optical laser beam by excitation of microstructures. The manufactured microstructure is the periodical structure which was implemented in piezoelectric optical scanner design. Such type of opto-micro-mechanical systems can be used for accurate angular or linear deflection of optical elements in various optomechanical and optoelectronic systems. The operating principle of these devices is based on piezoelectric effect and on conversion of high-frequency multi-dimensional mechanical oscillations of piezoelectric vibration transducers into directional multi-coordinate motion of the optical elements in the measurement chain. The main distinctive feature of such optical piezoelectric scanners is the combination of high micrometer range resolution with a wide range of angular deflections of the scanning elements. The manufacturing process and visualization of the microstructure were presented. The device consists of piezoelectric cylinder and a scanning element with three degrees of freedom. The control model of this device was derived using simulation results of optical scanner by COMSOL Multiphysics software. ESPI digital holographic PRISMA system was used to validate the result of simulation of piezoelectric optical scanner and to test the functionality of piezoelectric optical scanner with implemented microstructure

Output Power Optimization of Energy Harvester, Employing Segmentation of Its Electrodes

This research suggests employing electrode segmentation in order to avoid charge cancellation in the piezoelectric layers of harvester, which occurs, if strain nodes of vibrating harvester are covered by continuous electrodes. For the experimental investigations two types of piezoelectric energy harvester prototypes were produced from piezoelectric T107 H4E 602 plate, epoxy bonded to stainless steel substrate. The first (reference) harvester prototype posses no electrode segmentation, while electrodes covering piezoelectric material of second harvester were segmented. Segmentation of the second harvester was configured for its operation at the second resonant frequency – i. e., performed so, that the electrodes of piezoelectric material are not covering strain node of the second vibration mode. Experimental results revealed that segmented harvester prototype posses efficiency advantage as compared to the non-segmented counterpart – adding voltages, generated at each segment would result from 8% to 52% increase of maximum generated voltage