Electrically Tunable Lenses: A Review

Optical lenses with electrically controllable focal length are of growing interest, in order to reduce the complexity, size, weight, response time and power consumption of conventional focusing/zooming systems, based on glass lenses displaced by motors. They might become especially relevant for diverse robotic and machine vision-based devices, including cameras not only for portable consumer electronics (e.g. smart phones) and advanced optical instrumentation (e.g. microscopes, endoscopes, etc.), but also for emerging applications like small/micro-payload drones and wearable virtual/augmented-reality systems. This paper reviews the most widely studied strategies to obtain such varifocal “smart lenses”, which can electrically be tuned, either directly or via electro-mechanical or electro-thermal coupling. Only technologies that ensure controllable focusing of multi-chromatic light, with spatial continuity (i.e. continuous tunability) in wavefronts and focal lengths, as required for visible-range imaging, are considered. Both encapsulated fluid-based lenses and fully elastomeric lenses are reviewed, ranging from proof-of-concept prototypes to commercially available products. They are classified according to the focus-changing principles of operation, and they are described and compared in terms of advantages and drawbacks. This systematic overview should help to stimulate further developments in the field

Optical Fiber Interferometric Sensors

The contributions presented in this book series portray the advances of the research in the field of interferometric photonic technology and its novel applications. The wide scope explored by the range of different contributions intends to provide a synopsis of the current research trends and the state of the art in this field, covering recent technological improvements, new production methodologies and emerging applications, for researchers coming from different fields of science and industry. The manuscripts published in the Special issue, and re-printed in this book series, report on topics that range from interferometric sensors for thickness and dynamic displacement measurement, up to pulse wave and spirometry applications

MICROFLUIDIC APPROACHES FOR DISEASED CELL SEPARATION FROM BLOOD

Ph.DDOCTOR OF PHILOSOPH

Trapped between two beams – higher order laser mode manipulation for cell rotation

Laser light is an exceptionally powerful tool which has been utilised across all natural sciences and engineering. The very high intensities of extremely controllable light have allowed for a diverse range of studies to be carried out. When the intensities are large enough, the act of redirecting the light can create a force which can be sufficient to move small transparent objects. In biology one application of this phenomenon forms a tool for trapping and handling microscopic cellular samples in a contactless way using two laser beams. Such a laser-based tool is the Optical Stretcher, it was invented for measuring the mechanical properties of single cellular biological samples. The work presented in this thesis built upon the Optical Stretcher and to gain expertise in the field, several different biological samples were tested using it, gaining insights into the impact of particular proteins to cell mechanics. The Optical Stretcher, along with the vast majority of cell trapping experiments utilises a rotationally symmetric laser beam, which allows the cells to be moved and held in place, but their orientation is random and subject to large fluctuations. Controlled orientation of cellular specimen can lead to improved 3D imaging of the sample and is an important field of study. Previous work has shown that it is possible to orient a cell using a specially shaped laser beam, however the experimental setups were not well suited to use in biological labs. Henceforth, this thesis investigated and engineered a Dual Beam Laser Trapping device called the Higher Order Mode Cell Rotator, in short HOMCR, in order to build a powerful all-in-fibre tool for tomographic cell rotation. The major component giving rise to the HOMCR was a polarisation controlling device that alters the state of light by squeezing on the laser fibre and inducing local changes in the polarisation profile of the laser light. By characterising this device, its capability has been shown for the first time to manipulate the two lobe higher order modes travelling in optical fibres, leading to an all-in-fibre dynamic cell rotator which was used successfully to trap and orient individual cells and larger biological samples

Design and synthesis of microcapsules using microfluidics for autonomic self-healing in cementitious materials

A capsule-based self-healing cementitious material, capable of autonomically repairing its own cracks, can extend the service life of concrete structures and decrease the costs associate with repair and maintenance actions. However, the size, shell thickness, shell material and mechanical properties of the capsules still need to be optimised to ensure self-healing performance. Thus, the objective of this research was to explore the controlled microfluidic encapsulation to investigate the production of microcapsules for physically triggered self-healing in cementitious materials. A flow-focusing microfluidic device was used to produce double emulsions to be selectively photopolymerised to generate a core-shell structure. Subsequently, the physical triggering was assessed by embedding the produced microcapsules in cement paste, fracturing it and observing the cracked surface in the SEM. The results showed the production of microcapsules with 80-140 μm of diameter with excellent control over size and shell thickness. Using water-in-oil-in-water (w/o/w) double emulsion, microcapsules were synthesised containing water, colloidal silica solution and sodium silicate solution as core material. In addition, an oil-in-oil-in-water (o/o/w) double emulsion was used to encapsulate mineral oil and emulsified healing agents. The formation of the core-shell structure with aqueous and organic cores was characterised using optical microscopy and SEM. It was demonstrated that the water is not retained inside of the capsule, resulting in the formation of dimples and buckled capsules, particularly for shells thickness ~7 μm. On the other hand, TGA confirmed the retention of mineral oil for shells thickness of ~2 μm and the encapsulation efficiency was demonstrated to be 66%. When the capsules were added to the cement paste, four key factors were observed to prevent physical triggering: (i) thick shells, (ii) buckling of thinner shells due to the loss of water core, (iii) mechanical properties and (iv) poor interfacial bonding. As a result, a mechanical characterisation of the shell material was performed, indicating brittle fracture at room temperature, reduced Young’s modulus when compared with cementitious matrix and stress at rupture of 15-36 MPa. In addition, an innovative methodology was proposed to functionalise the surface of the microcapsules with hydrophilic groups in order to increase the interfacial bonding between the cement paste and the microcapsules. Thus, microcapsules with low tensile strength, low shell thickness, organic core and good interfacial bonding were successfully synthesised and demonstrated to rupture upon crack formation. These results experimentally demonstrate the importance of reduced shell thickness, core retention and interfacial bonding as valuable guides during the design of microcapsules for physically triggered self-healing in cementitious materials.Science without Borders/Brazil (BEX 9185/13-5