Field-induced shaping of sessile paramagnetic drops

We use the electromagnetic stress tensor to describe the elongation of paramagnetic drops in uniform magnetic fields. This approach implies a linear relationship between the shape of the drops and the square of the applied field, which we confirm experimentally. We show that this effect scales with the volume and susceptibility of the drops. By using this unified electromagnetic approach, we highlight the potential applications of combining electric and magnetic techniques for controlled shaping of drops in liquid displays, liquid lenses, and chemical mixing of drops in microfluidics

Color tunable pressure sensors based on polymer nanostructured membranes for optofluidic applications

We demonstrate an integrated optical pressure sensing platform for multiplexed optofluidics applications. The sensing platform consists in an array of elastomeric on-side nanostructured membranes -effectively 2D photonic crystal- which present colour shifts in response to mechanical stress that alter their nanostructure characteristical dimensions, pitch or orientation. The photonic membranes are prepared by a simple and cost-effective method based on the infiltration of a 2D colloidal photonic crystal (CPC) with PDMS and their integration with a microfluidic system. We explore the changes in the white light diffraction produced by the nanostructured membranes when varying the pneumatic pressure in the microfluidics channels as a way to achieve a power-free array of pressure sensors that change their reflective colour depending on the bending produced on each sensor. The structural characterization of these membranes was performed by SEM, while the optical properties and the pressure-colour relation were evaluated via UV-Vis reflection spectrometry. Maximum sensitivities of 0.17 kPa is obtained when measuring at Littrow configuration (θ = −θ ), and close to the border of the membranes. The reflected colour change with pressure is as well monitorized by using a smartphone camera

Variable optical elements for fast focus control

In this Review, we survey recent developments in the emerging field of high-speed variable-z-focus optical elements, which are driving important innovations in advanced imaging and materials processing applications. Three-dimensional biomedical imaging, high-throughput industrial inspection, advanced spectroscopies, and other optical characterization and materials modification methods have made great strides forward in recent years due to precise and rapid axial control of light. Three state-of-the-art key optical technologies that enable fast z-focus modulation are reviewed, along with a discussion of the implications of the new developments in variable optical elements and their impact on technologically relevant applications

Electrically controlled localized charge trapping at amorphous fluoropolymer-electrolyte interfaces

Charge trapping is a long-standing problem in electrowetting-on-dielectric (EWOD), causing reliability reduction and restricting its practical applications. Although this phenomenon has been investigated macroscopically, the microscopic investigations are still lacking. In this work, the trapped charges are proven to be localized at three-phase contact line region by using three detecting methods -- local contact angle measurements, electrowetting (EW) probe, and Kelvin Probe Force Microscopy (KPFM). Moreover, we demonstrate that this EW-induced charge trapping phenomenon can be utilized as a simple and low-cost method to deposit charges on fluoropolymer surfaces. Charge density near the three-phase contact line up to 0.46 mC/m2 and the line width with deposited charges ranging from 20 to 300 micrometer are achieved by the proposed method. Particularly, negative charge densities do not degrade even after harsh testing with a water droplet on top of the sample surfaces for 12 hours, as well as after being treated by water vapor for 3 hours. These findings provide an approach for applications which desire stable and controllable surface charges

Numerical analysis of wavefront aberration correction using multielectrode electrowetting-based devices.

We present numerical simulations of multielectrode electrowetting devices used in a novel optical design to correct wavefront aberration. Our optical system consists of two multielectrode devices, preceded by a single fixed lens. The multielectrode elements function as adaptive optical devices that can be used to correct aberrations inherent in many imaging setups, biological samples, and the atmosphere. We are able to accurately simulate the liquid-liquid interface shape using computational fluid dynamics. Ray tracing analysis of these surfaces shows clear evidence of aberration correction. To demonstrate the strength of our design, we studied three different input aberrations mixtures that include astigmatism, coma, trefoil, and additional higher order aberration terms, with amplitudes as large as one wave at 633 nm

High extinction ratio, low insertion loss, optical switch based on an electrowetting prism

An optical switch based on an electrowetting prism coupled to a multimode fiber has demonstrated a large extinction ratio with speeds up to 300 Hz. Electrowetting prisms provide a transmissive, low power, and compact alternative to conventional free-space optical switches, with no moving parts. The electrowetting prism performs beam steering of &plusmn;3&deg; with an extinction ratio of 47 dB between the ON and OFF states and has been experimentally demonstrated at scanning frequencies of 100&ndash;300 Hz. The optical design is modeled in Zemax to account for secondary rays created at each surface interface (without scattering). Simulations predict 50 dB of extinction, in good agreement with experiment.</p

Electrowetting y lentes líquidas

El electrowetting, es una tecnología que consiste en la variación del ángulo de contacto de una gota mediante la aplicación de un voltaje. Con ello se puede modificar la curva- tura de la gota, y así variar su poder dióptrico. El objetivo del trabajo, es hacer una revisión de las lentes liquidas y de todas las posibles aplicaciones que presenta. Las primeras referencias que se tienen acerca del electrowetting, se remontan a finales del siglo XIX con los primeros estudios de Lippmann, posteriormente de Frounkine y ya en el siglo XX con Berni y Hackwood, que fue lo que propició que actualmente cada vez se utilice más en distintos campos. Esta técnica, se ha ido desarrollando y perfeccionando hasta conseguir aplicarlo tanto en el mundo de la óptica, como en la biomedicina. Se han estudiado diferentes utilidades de las cuales algunas no se han continuado inves- tigando por falta de resultados y otras se han seguido desarrollando hasta su fabricación y comercialización. Debido a las múltiples características que ofrece, las demandas de mercado en la actualidad han hecho que en los últimos años se numerosas empresas muestren su interés por esta tecnología. Hay cierta controversia con lo que puede ofrecer el electrowetting, ya que tiene ciertas limitaciones, pero se continúa investigando para tratar de mejorarlo.Grado en Óptica y Optometrí

Estudos numéricos em eletrohidrodinâmica

Orientador: Marcos Akira D'ÁvilaTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia MecânicaResumo: A eletrohidrodinâmica (EHD) descreve o movimento do fluido induzido por tensões elétricas. Sob o efeito de um campo elétrico, as moléculas de fluido podem polarizar e uma migração de íons carregados ou cargas livres através do fluido é induzida. Estes fenômenos dão origem a forças elétricas que atuam sobre a superfície do fluido colocando-a em movimento até que a tensão superficial e as tensões viscosas proporcionem o equilíbrio necessário. Aplicações como atomização de líquidos, transferência de calor e massa, dispersão de polímeros e tecnologias microfluídicas fizeram com que a eletrohidrodinâmica fosse extensivamente estudada ao longo dos anos no intuito de compreender as respostas de sistemas de fluidos submetidos a campos elétricos e de desenvolver novos processos. No entanto, a natureza complexa dos processos EHD limita as explorações tanto experimentais como de desenvolvimento. Portanto, para obter resultados mais rápidos e com custos menores, são frequentemente utilizados estudos envolvendo modelagem e simulações numéricas. Neste trabalho, utilizando um solver eletrohidrodinâmico baseado no modelo leaky dielectric, analisamos dois problemas diferentes relacionados à EHD. O primeiro consiste em investigar o efeito da viscoelasticidade na deformação e quebra de gotículas inseridas em um campo elétrico uniforme. Este é um dos primeiros e mais fundamentais problemas em EHD, porém nunca foi avaliado através de simulações numéricas utilizando fluidos não-Newtonianos. Assim, com os resultados aqui apresentados, pretendemos elucidar alguns dos principais aspectos da deformação viscoelástica em problemas de EHD. O segundo caso é um problema aplicado tem atraído um crescente interesse nos últimos anos. Consiste na deformação de lentes líquidas pela aplicação de um campo elétrico. Por meio de simulações numéricas, investigamos a influência do formato do eletrodo na deformação da lente e analisamos seu desempenho usando uma plataforma de design óptico. Esta abordagem nunca foi feita antes e sugere uma nova visão sobre os sistemas micro-ópticos adaptáveisAbstract: Electrohydrodynamics (EHD) describes the fluid motion induced by electric stresses. Under the effect of an electric field the fluid molecules may get polarized and a migration of charged ions or free charges through the fluid is induced. These phenomena give rise to electric forces that act on the fluid surface putting it into motion until the surface tension and viscous stresses provide the necessary balance. Applications such as liquid atomization, heat and mass transfer, polymer dispersion and microfluidic technologies have made electrohydrodynamics to be extensively studied over the years in order to understand the responses of fluids systems subjected to electric fields and to develop new processes. However, the complex nature of EHD processes limits both experimental and development explorations. Therefore, in order to obtain faster results and at lower costs, studies involving modeling and numerical simulations are frequently used. In this work, using an EHD solver based on the leaky dielectric model, we analyze two different problems related to electrohydrodynamics. The first one consists on the investigation of the effect of viscoelasticity on the deformation and breakup of droplets inserted in a uniform electric field. This is one of the first and most fundamental problems in EHD. However it has never been evaluated through numerical simulations using non-Newtonian fluids. Thus, with the results presented here we aim to elucidate some of the main aspects of the viscoelastic deformation in EHD problems. The second case is an applied problem that has drawn increasing interest in the past few years. It consists in the deformation of liquid lenses by the application of an electric field. By means of numerical simulations we investigate the influence of the electrode shape on the lens deformation and we analyze its performance using an optical design platform. This approach has never been done before and it suggests a new insight into the adaptive micro-optical systemsDoutoradoMateriais e Processos de FabricaçãoDoutor em Engenharia Mecânica233361/2014-6CNP

Advances in Optofluidics

Optofluidics a niche research field that integrates optics with microfluidics. It started with elegant demonstrations of the passive interaction of light and liquid media such as liquid waveguides and liquid tunable lenses. Recently, the optofluidics continues the advance in liquid-based optical devices/systems. In addition, it has expanded rapidly into many other fields that involve lightwave (or photon) and liquid media. This Special Issue invites review articles (only review articles) that update the latest progress of the optofluidics in various aspects, such as new functional devices, new integrated systems, new fabrication techniques, new applications, etc. It covers, but is not limited to, topics such as micro-optics in liquid media, optofluidic sensors, integrated micro-optical systems, displays, optofluidics-on-fibers, optofluidic manipulation, energy and environmental applciations, and so on

Recent Developments in Optofluidic Lens Technology

Optofluidics is a rapidly growing versatile branch of adaptive optics including a wide variety of applications such as tunable beam shaping tools, mirrors, apertures, and lenses. In this review, we focus on recent developments in optofluidic lenses, which arguably forms the most important part of optofluidics devices. We report first on a number of general characteristics and characterization methods for optofluidics lenses and their optical performance, including aberrations and their description in terms of Zernike polynomials. Subsequently, we discuss examples of actuation methods separately for spherical optofluidic lenses and for more recent tunable aspherical lenses. Advantages and disadvantages of various actuation schemes are presented, focusing in particular on electrowetting-driven lenses and pressure-driven liquid lenses that are covered by elastomeric sheets. We discuss in particular the opportunities for detailed aberration control by using either finely controlled electric fields or specifically designed elastomeric lenses