VI. CONCLUSIONFour error estimation techniques are investigated for use with adaptive -refinement procedures, and the LCN method, for electromagnetic integral equations. For a test suite of targets, the estimators were successful at correctly locating high-error regions.Of particular interest is the successful performance of the "discontinuity in " estimator on the smooth targets under consideration. This estimator only imposes a computational cost of . Since it is unbounded at edges where the charge density is unbounded, some regularization must be applied for it to be used in that case. Residual estimators also work well and can handle general situations, but impose a cost of at least . This study suggests that adaptive refinement procedures can be efficient for integral equation formulations and that future efforts are warranted to extend these ideas to general three-dimensional problems. Abstract-A continuously tunable, circularly polarized X-band microfluidic transmitarray unit cell employing the element rotation method is designed and fabricated. The unit cell comprises a double layer nested ringsplit ring structure realized as microfluidic channels embedded in Polydimethylsiloxane (PDMS) using soft lithography techniques. Conductive regions of the rings are formed by injecting a liquid metal (an alloy of Ga, In, and Sn), whereas the split region is air. Movement of the liquid metal together with the split around the ring provides 360 linear phase shift range in the transmitted field through the unit cell. A circularly polarized unit cell is designed to operate at 8.8 GHz, satisfying the necessary phase shifting conditions provided by the element rotation method. Unit cell prototypes are fabricated and the proposed concept is verified by the measurements using waveguide simulator method, within the frequency range of 8-10 GHz. The agreement between the simulation and measurement results is satisfactory, illustrating the viability of the approach to be used in reconfigurable antennas and antenna arrays.
REFERENCES
Dielectric colloidal nanospheres (NSs) are promising candidates for light management in photonic devices such as solar cells (SCs). NS arrays can direct the broad incident solar radiation into a set of tighter foci, at which light intensity becomes considerably concentrated, enabling higher photovoltaic conversion efficiency. Furthermore, the NS arrays acting as an effective medium on the SC surface can reduce reflectance and facilitate improved forward scattering. Therefore, uniform arrays of NSs located on top of the SC can behave as antireflection coatings or as microlenses, which can be regarded as a surface distributed light concentrator within the framework of concentrated photovoltaics. Fabrication of NS‐based light‐trapping structures is low‐cost and less complicated than common alternatives such as vacuum evaporated multilayer antireflection coatings. In this work, experimental demonstration and computational confirmation on the shape adjustment of such NS structures for improved light harvesting and efficiency enhancement in Si SCs are studied. The light conversion efficiency of Si solar cells is shown to improve by more than 27% with shape adjustment of NS arrays.
Thin metallic films on dielectric nanospheres are demonstrated to have a high potential for the fabrication of cost-effective SERS substrates. In addition to the morphological advantages that nanospheres offer for attaining a high density of hot spots, possessing shape adjustability by uncomplicated thermal treatment makes them an attractive platform for tuneable SERS substrates. Furthermore, when combined with the oblique angle metal deposition technique, adjustable gaps at a high density and adjustable shape of metal films, such as Ag films, can be achieved on nanospheres. Applying small changes in deposition angle can provide means for fine adjustment of the Raman enhancement factor (EF), resulting in EF up to 10 8 measured using crystal violet dye molecule as a Raman analyte. This practice paves the way for the fabrication of high EF SERS substrates at a reasonable cost using a monolayer of self-organized nanosphere patterns. An ultra-thin Ag film coated at 5°tilt is shown to be an excellent substitute for a film deposited at 0°with double the thickness. There is a strong agreement between the experimental results and finite-elements-method-based Maxwell simulations exhibiting expected field enhancements up to 10 9 at a tilt angle of 5°.
SERS has become a highly preferred method with the effect of advances in instrument technology and potential for application to many areas from medicine to art conservation for the detection of trace-level environmental and biological analytes. However, the effects of substrate variation 1 and the details of the enhancement mechanism 2 still of concern even much progress has been achieved in recent years. Therefore, it is important to control the size and shape of the materials for maximize the enhancement factor and ensure the reproducibility of the substrates by considering SERS uncertainty principle 3 . In this study, we present novel SERS substrate preparation methods that are highly promising in terms of both signal enhancement and reproducibility with high benefit-cost ratio.
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