Touch is one of the less exploited sensory channels in human machine interactions. While the introduction of the tactile feedback would improve the user experience in several fields, such as training for medical operators, teleoperation, computer aided design and 3D model exploration, no interfaces able to mimic accurately and realistically the tactile feeling produced by the contact with a real soft object are currently available. Devices able to simulate the contact with soft bodies, such as the human organs, might improve the experience. The existing commercially available tactile displays consist of complex mechanisms that limit their portability. Moreover, no devices are able to provide tactile stimuli via a soft interface that can also modulate the contact area with the finger pad, which is required to realistically mimic the contact with soft bodies, as needed for example in systems aimed at simulating interactions with virtual biological tissues or in robot-assisted minimally invasive surgery. The aim of this thesis is to develop such a wearable tactile display based on the dielectric elastomer actuators (DEAs). DEAs are a class of materials that respond to an electric field producing a deformation. In particular, in this thesis, the tactile element consists of a so-called hydrostatically coupled dielectric elastomer actuator (HC-DEAs). HC-DEAs rely on an incompressible fluid that hydrostatically couples a DEA-based active part to a passive part interfaced to the user. The display was also tested within a closed-loop configuration consisting of a hand tracking system and a custom made virtual environment. This proof of concept system allowed for a validation of the abilities of the display. Mechanical and psychophysical tests were performed in order to assess the ability of the system to provide tactile stimuli that can be distinguished by the users. Also, the miniaturisation of the HC-DEA was investigated for applications in refreshable Braille displays or arrays of tactile elements for tactile maps.

<div>Hydrogels are soft polymers comprising of a three-dimensional network capable of absorbing significant amount of water or other aqueous bio-fluids. A group of hydrogels, commonly referred to as “environmentally-sensitive hydrogels” are designed such that they can undergo reversible volume change in response to a variety of physical and chemical stimuli. Although mechanically soft, embedding organic and inorganic micro and nanoparticles into the hydrogel network increases their mechanical strength. Hydrogels have been extensively explored as scaffolding for tissue engineering or smart materials for biomedical transducers. Hydrogels in the mm-scale are typically associated with a slow response time. At micro-scale, however, they can be fast and useful as smart sensors and actuators. Several micromachining techniques have been employed to pattern thin films of hydrogel. Micro-patterning methods are based on traditional fabrication techniques such as lithography, etching, and micro-molding. These methods are time consuming, expensive, and do not scale well to large production. In addition, they have limitations as related to processing composite gels (e.g., UV light cannot penetrate through the gel and particles can mask dry etch). In this work, we outline a doctoral research aimed at alternative solution based on direct laser patterning, allowing low cost, fast, and scalable fabrication for mass production.</div><div><br></div><div><div>We characterized and analyzed a series of transient features of the laser-engineered patterns, including the ablated width, sidewall quality and resolution, as a function of laser beam parameters and hydrogel thermal & optical properties by laser-machining the hydrogels at different moisture level of hydrogels till fully dry at an interval of one hour. All the optimal patterns appear at 1-2 hours of drying (hydrogel losing 35%-65% weight), thus identifying an optimal window for a rapid end-to-end fabrication. Then, two types of composite gels were created and laser engineered, consisting of nano-iron particles embedded hydrogel (“ferrogel”) and micro-silica beads loaded hydrogel (“silicagel”); the results show comparable features similar to the bare hydrogel, confirming the processability of laser micro-machining on the composite gels. Next, we studiedthe swelling kinetics of the laser-machined hydrogels and identified tradeoffs between swelling speed and mechanical force. At the final, we used the laser patterning method to design and fabricate two pH-regulated autonomous drug delivery devices, a 3D printed smart capsule for targeted drug delivery in small intestine and a flexible patch for delivering antibiotics to infected chronic wounds. In both cases, their delivery capabilities can be tuned by either controlling the spatial resolution of the hydrogel actuator (the former) or using an n × n array (the latter).</div></div>

Atuadores Piezelétricos Flextensionais consistem de uma estrutura flexível atuada por cerâmicas piezelétricas (ou &#8220;pilhas&#8221; de cerâmicas). A estrutura flexível conectada a piezocerâmica deve gerar deslocamentos e forças em diferentes pontos específicos do domínio, para uma direção especificada. Estes atuadores são usados em aplicações de mecânica de precisão, tal como, sistemas microeletromecânicos (MEMS), manipulador de células, interferometria laser, equipamentos de nanotecnologia, equipamentos de microcirurgias, nanoposicionadores, sonda de varredura microscópica, e etc. Porém, devido ao fato destes atuadores consistirem principalmente de um mecanismo flexível, seu projeto é complexo. A estrutura flexível comporta-se como um transformador mecânico pela amplificação para converter, direcionar e amplificar os pequenos deslocamentos gerados pela piezocerâmica (ordem de nanômetros). A estrutura flexível é projetada distribuindo-se flexibilidade e rigidez no domínio de projeto, o que pode ser obtido usando a otimização topológica. Portanto, o objetivo deste trabalho é implementar um método sistemático baseado no método de otimização topológica para projetar atuadores piezelétricos flextensionais. Essencialmente, o método de otimização topológica consiste em encontrar a distribuição ótima de material perfurando o domínio de projeto com infinitos microfuros. O material em cada ponto pode alterar de vazio a total presença de material, também assumindo material intermediário (ou compósito). A implementação do método de otimização topológica é baseado no modelo de material SIMP (Simple Isotropic Material with Penalization). O problema de otimização é posto como a maximização dos deslocamentos gerados (ou força de blocagem) em diferentes pontos e direções especificadas do domínio. Considerando o comportamento linear da piezocerâmica. Alterando a flexibilidade e a rigidez da estrutura flexível conectada a piezocerâmica obtém-se diferentes tipos de atuadores piezelétricos flextensionais, que podem ser projetados para determinadas aplicações. Para ilustrar o método, os exemplos mostrados são modelos bidimensionais (2D), uma vez que a maior parte das aplicações envolve dispositivos planos. Estes atuadores são fabricados usando corrosão química em chapas de cobre abaixo de 200 &#956;m de espessura através do método de litografia. Técnica de corrosão química tem um baixo custo e permite-nos fabricar diversos protótipos para testes. Esta técnica pode ser facilmente utilizada no LNLS (Laboratório Nacional de Luz Síncrotron &#8211; Campinas). Análise experimental destes protótipos são procedidas para medição de deslocamentos usando uma Probe Station. Como trabalho futuro, estes protótipos serão construídos em escala de MEMS. / Flextensional Piezoelectric Actuators consist of a flexible structure actuated by piezoelectric ceramics (or a stack of piezoceramics). The flexible structure connected to the piezoceramic must generate displacements and forces in different specified points of the domain, according to a specific direction. These actuators are applied to precision mechanic applications such as microelectromechanical systems (MEMS), cell manipulators, laser interferometers, nanotechnology equipment, microsurgery equipment, nanopositioners, scanning probe microscopy, etc. However, due to the fact these actuators essentially consist of a compliant mechanism their design is complex. The compliant structure behaves as a mechanical transform by amplifying and changing the direction of small output displacements generated by piezoceramics (order of nanometer). The flexible structure is designed by distributing flexibility and stiffness in the design domain, which can be archieved by using topology optimization. Therefore, the objective of this work is to implement a systematic method based on topology optimization method to design flextensional piezoelectric actuators. Essentially, the topology optimization method consists of finding the optimal material distribution in a perforated design domain with infinite microvoids. The material in each point can change from void to full material, also assuming intermediate (or composite) material. The implemented topology optimization method is based on the SIMP (Simple Isotropic Material with Penalization) material model. The optimization problem is posed as maximization of output displacements (or grabbing forces) in different specified directions and points of the domain. A linear behavior of piezoceramic is considered. By changing the flexibility and stiffness of flexible structure connected to the piezoceramics different types of flextensional piezoelectric actuators can be designed for a desired application. To illustrate the method, examples presented herein are limited to two-dimensional (2D) models once in most part of applications of these actuators they are planar devices. These actuators are manufactured by using chemical corrosion on a 200 um thickness copper plate through lithography method. Chemical corrosion technique has a low cost and it allow us to manufacture several prototypes for testing. For this technique, facilities of the micromachining laboratory of National Sincroton Light Laboratory (LNLS - Campinas) are used. Experimental analysis of these prototypes are conducted by measuring displacements using a probe station. As a future work, these prototypes will be built in a MEMS scale.

Para se obter alto desempenho em máquinas-ferramenta de ultraprecisão, são necessários o desenvolvimento de sistemas de posicionamento e o controle de movimento, os quais não raramente devem operar com resolução e repetibilidade na faixa submicrométrica. A utilização das modernas técnicas de metodologia de projeto auxiliam no desenvolvimento deste tipo de sistema. Neste trabalho são discutidas e analisadas as diversas alternativas disponíveis para os elementos constituintes do sistema de posicionamento. Aspectos críticos como cinemática, acionamento, guias e apoios são estudados e confrontados usando o método de análise de valor. E baseados no resultado do estudo prévio, obtém-se um sistema híbrido para microposicionamento angular de alta rigidez e ampla largura de banda, capaz de posicionar uma superfície com resolução angular inferior a 4.\'10 POT.-5\' graus. Através das técnicas de modelagem, pode-se verificar a funcionalidade desse sistema projetado, quanto ao seu comportamento estático e dinâmico. Uma modelagem cinemática é apresentada com o objetivo de auxiliar na veracidade do projeto do posicionador angular, através da qual pretende-se observar a influência de cada ponto de apoio no posicionamento final. São apresentados os resultados obtidos em simulações numéricas, as quais constatam não só o próprio desempenho do posicionador, como também, a validade da técnica utilizada. / In order to achieve high performance in ultra-precision machine tools, appropriate capability is required of motion control and positioning systems which have to operate at resolutions and repeatability in the sub-micrometre range. Machining may reach high levels of precision through the use of suitable sensors, actuators and controllers so that the development of micro-positioner with low backlash, high bandwidth and accuracy is a crucial aspect of high precision machining technology. Modern design techniques can greatly assist in the development and design of such systems. In this work, several design options for the elements of a positioning system are discussed and analysed. Critical aspects such as kinematics, driving and bearings are studied and compared using the value analysis method. A hybrid system based upon the results of this study is proposed which combines the best characteristics of each design option. The system possesses the capability of positioning a workpiece and/or tool angularly and/or linearly (micro-tilt stage) with a resolution better than 4 \'10 POT.-5\' arc degree and high stiffness and bandwidth. Through modelling techniques, it is possible to verify the static and dynamic behaviour of the system. A kinematics model of the micro-tilt stage is presented in order to establish a relationship between the displacement of the actuators and the final position of the stage. It is anticipated that such an approach will be required in respect of interferometric feedback control. Simulations of the model are performed showing that the technique applied is valid and the system fulfils the requirements for ultra-precision design.

Methods for comprehensive structural dynamic analysis generally employ input-output modal analysis with a mathematical model of structural vibration using excitation and response data. Recently operational modal analysis methods using only vibration response data have been developed. In this thesis, both input-output and operational modal analysis, in the presence of significant unmeasured excitations, is considered. This situation arises when a test structure cannot be effectively isolated from ambient excitations or where the operating environment imposes dynamically-important boundary conditions. The limitations of existing deterministic frequency-domain methods are assessed. A novel time-domain estimation algorithm, based on the estimation of a discrete-time autoregressive moving average with exogenous excitation (ARMAX) model, is proposed. It includes a stochastic component to explicitly account for unmeasured excitations and measurement noise. A criterion, based on the sign of modal damping, is incorporated to distinguish vibration modes from spurious modes due to unmeasured excitations and measurement noise, and to identify the most complete set of modal parameters from a group of estimated models. Numerical tests demonstrate that the proposed algorithm effectively identifies vibration modes even with significant unmeasured random and periodic excitations. Random noise is superimposed on response measurements in all tests. Simulated systems with low modal damping, closely spaced modes and high modal damping are considered independently. The accuracy of estimated modal parameters is good except for degreesof- freedom with a low response level but this could be overcome by appropriate placement of excitation and response measurement points. These observations are reflected in experimental tests that include unmeasured periodic excitations over 200% the level of measured excitations, unmeasured random excitations at 90% the level of measured excitations, and the superposition of periodic and random unmeasured excitations. Results indicate advantages of the proposed algorithm over a deterministic frequency domain algorithm. Piezoceramic plates are used for structural excitation in one experimental case and the limitations of distributed excitation for broadband analysis are observed and characterised in terms of actuator geometry and modal deformation. The ARMAX algorithm is extended for use with response measurements exclusively. Numerical and experimental tests demonstrate its performance using time series data and correlation functions calculated from response measurements.

In this thesis, the development of a novel electro-thermally actuated bi-stable out-of-plane two way actuated buckled micro-bridge for a potential application in optical switching is presented. The actuator consists of a bridge supported by 'legs' and springs at its four corners. The springs and the bridge are made of a tri-layer structure comprising of 2.5??m thick low-stress PECVD oxide, 1??m thick high-stress PECVD oxide and 2??m thick heavily phosphorus doped silicon. The legs, on the other hand, are 2??m thick single layer heavily phosphorus doped silicon. Both legs and springs provide elastically constrained boundary conditions at the supporting ends, without of which important features of the micro-bridge actuator could not have been achieved. This microbridge actuator is designed, simulated using ANSYS, fabricated and tested. The results from the testing have shown a good agreement with analytical prediction and ANSYS simulation. The actuator demonstrated bi-stability, two-way actuation and 31??m out-of-plane movement between the two-states using low voltage drive. Buckled shape model, design method for bi-stability and thermo-mechanical model are developed and employed in the design of the micro-bridge. These models are compared with Finite Element (FE) based ANSYS simulation and measurements from the fabricated micro-bridge and have shown a good agreement. In order to demonstrate the potential application of this actuator to optical switching, ANSYS simulation studies have been performed on a micro-mirror integrated with the micro-bridge actuator. From these studies, the optimum micro-mirror size that is appropriate for the integration has been obtained. This optimal mirror size ensures the important features of the actuator. Mirror fabrication experiments in (110) wafer have been carried out to find out the appropriate compensation mask size for a given etch depth and the suitable wafer thickness that can be used to fabricate the integrated system.

Shape control of a structure with distributed piezoelectric actuators can be achieved through optimally selecting the loci, shapes and sizes of the piezoelectric actuators and choosing the electric fields applied to the actuators. Shape control can be categorised as either static or dynamic shape control. Whether it is a transient or gradual change, static or dynamic shape control, both aim to determine the loci, sizes, and shapes of piezoelectric actuators, and the applied voltages such that a desired structural shape is achieved effectively. This thesis is primarily concerned with establishing a finite element formulation for the general smart laminated composite plate structure, which is capable to analyse static and dynamic deformation using non-rectangular elements. The mechanical deformation of the smart composite plate is modelled using a third order plate theory, while the electric field is simulated based on a layer-wise theory. The finite element formulation for static and dynamics analysis is verified by comparing with available numerical results. Selected experiments have also been conducted to measure structural deformation and the experimental results are used to correlate with those of the finite element formulation for static analysis. In addition, the Linear Least Square (LLS) method is employed to study the effect of different piezoelectric actuator patch pattern on the results of error function, which is the least square error between the calculated and desired structural shapes in static structural shape control. The second issue of this thesis deals with piezoelectric actuator design optimisation (PADO) for quasi-static shape control by finding the applied voltage and the configuration of piezoelectric actuator patch to minimise error function, whereas the piezoelectric actuator configuration is defined based on the optimisation technique of altering nodal coordinates (size/shape optimisation) or eliminating inefficient elements in a structural mesh (topology optimisation). Several shape control algorithms are developed to improve the structural shape control by reducing the error function. Further development of the GA-based voltage and piezoelectric actuator design optimisation method includes the constraint handling, where the error function can be optimised subjected to energy consumption or other way around. The numerical examples are presented in order to verify that the proposed algorithms are applicable to quasi-static shape control based on voltage and piezoelectric actuator design optimisation (PADO) in terms of minimising the error function. The third issue is to use the present finite element formulation for a modal shape control and for controlling resonant vibration of smart composite plate structures. The controlled resonant vibration formulation is developed. Modal analysis and LLS methods are also employed to optimise the applied voltage to piezoelectric actuators for achieving the modal shapes. The Newmark direct time integration method is used to study harmonic excitation of smart structures. Numerical results are presented to induce harmonic vibration of structure with controlled magnitude via adjusting the damping and to verify the controlled resonant vibration formulation.

A new dynamic model is presented for piezoelectric tube actuators commonly used in high-precision instruments. The model captures coupling between motions in all three axes such as bending motion due to a supposedly pure extension of the actuator. Both hysteresis and creep phenomena are included in the overall actuator model permitting modeling nonlinear sensitivity in the voltage to displacement response. Experimental data on hysteresis and creep are presented to support the modeling. Experiments and model predictions show that due to coupling a voltage Vz corresponding to vertical displacement will produce lateral displacement that acts as a disturbance to the main lateral response. The resonance frequency for the lateral dynamics is inherently lower than that of the longitudinal dynamics. Therefore, Vz is expected to contain frequencies that may excite the lateral resonance. Accordingly, this out of bandwidth disturbance will not be well compensated for either in open or closed loop control of the actuator. In order to preserve performance in open loop actuator control and stability and performance in closed loop control, a large reduction in the bandwidth of vertical motion would be required to avoid exciting the first bending mode. / Singapore-MIT Alliance (SMA)

The objective of this research is to present a theoretical study of the compressibility effects on the performance of an electric D/C motor driven synthetic jet actuator for flow separation control. Hot wire anemometer experiments were conducted to validate the jet exit velocities predicted by the theoretical model. The optimal jet exit velocity required to achieve maximum flow reattachment at reasonable blowing momentum coefficients is predicted. A dynamic electro-acoustic model of the D/C motor driven actuator is developed to accurately predict its performance and efficiency. This model should help formulate a feedback optimal control strategy for real-time flow control using an array of actuators. This model is validated by comparing with hot wire anemometer experiments conducted under similar conditions. The effects of geometric parameters like the slot width, slot geometry, and cavity volume on the performance of the actuator are also tested using this model.

A reflective type Fresnel lens using an array of micromirrors is designed and fabricated using the MUMPs?? surface micromachining process. The focal length of the lens can be rapidly changed by controlling both the rotation and translation of electrostatically actuated micromirrors. The suspension spring, pedestal and electrodes are located under the mirror to maximize the optical efficiency. The micromirror translation and rotation are plotted versus the applied voltage. Relations are provided for the fill-factor and the numerical aperture as functions of the lens diameter, the mirror size, and the tolerances specified by the MUMPs?? design rules. Linnik interferometry is used to measure the translation, rotation, and flatness of a fabricated micromirror. The reflective type Fresnel lens is controlled by independent DC voltages of 16 channels with a 0 to 50V range, and translational and torsional stiffness are calibrated with measured data. The spot diameter of the point source by the fabricated and electrostatically controlled reflective type Fresnel lens is measured to test focusing quality of the lens.