Basic Design Rules Research Articles

Design of highly efficient far-field beam shapers with irregular maskless microlens arrays

Regular tandem microlens arrays are well described and widely used for beam shaping and homogenization. Applying absorbing slides between the entrance and exit lenslets and channel-wise variation of the slides’ shape and size allows flexible control of the beam’s intensity profile and silhouette. The downside of absorbing slides is a significant transmission loss, limiting the achievable level of system efficiency. This work describes a more efficient method for micro-optical beam shaping with maskless irregular microlens arrays (iMLA). The iMLAs are completely absorption-free elements, enhancing the overall efficiency of the optical system. We describe basic design rules for iMLAs, including stray-light suppression, tolerancing, and modeling under consideration of manufacturing imperfections.

Unraveling Mechanisms of Highly Efficient Yet Stable Electrochemiluminescence from Quantum Dots.

With CdSe/CdS/ZnS core/shell/shell quantum dots (QDs) as the model system, time- and potential-resolved spectroelectrochemical measurements are successfully applied for studying the general mechanisms and kinetics of electrochemiluminescence (ECL) generation. The rate constant of electron injection from the cathode into a QD to form a negatively charged QD (QD-) increases monotonically from -0.88 V to -1.2 V (vs Ag/AgCl). Mainly due to the deep LUMO of the QDs, the resulting QD- as the key intermediate for ECL generation is structurally stable and possesses very slow spontaneous deionization channels. The latter (the main non-ECL channels) are usually 3-4 orders of magnitude slower than the rate constant of the successive hole injection from an active co-reactant into a QD-. The kinetic studies quantify the internal ECL quantum yield of ideal QD ECL emitters to be nearly identical to that of photoluminescence, which is near unity for the current system. Identification of the key intermediate, discovery of the related elementary steps, and determination of all rate constants not only establish a general framework for understanding ECL generation but also offer basic design rules for ECL emitters.

Engineering angle selectivity of extraordinary optical transmission and nonlocal spatial filtering

Plasmonic metasurfaces can provide rich opportunities for miniaturized analog optical computing, such as ultrathin spatial filtering and free-space wavefront differentiation. In this work, the extraordinary optical transmission (EOT), one of the most fascinating phenomena of plasmonics, is revisited and rigorously studied in terms of the angle selectivity of the transmission resonance. In particular, the fundamental mechanisms of angle-selective transmission in 1D plasmonic nanoslit metasurfaces are investigated. Based on temporal coupled mode theory and Fano resonances, it is elucidated that the angle selectivity is due to strong coupling between multiple resonance channels. Using the theory that explains the origin of angle selectivity, the basic design rules for nonlocal lowpass and bandpass spatial filters based on infinite periodic metasurface structures were determined and verified numerically. Furthermore, the effect of the finite size of the metasurface structures on the nonlocality of the EOT was investigated and formulated by both a full numerical calculation and an analytical scalar wave approximation based on the convolution theorem together with the optical transfer function obtained for the infinite periodic structures. It is expected that the formulation of angle-selective EOT will be fruitfully exploited for the development of ultrathin designer spatial filters required for coherent imaging processes in compact Fourier optics applications.

Order-of-magnitude enhancement in boron removal by membrane-free capacitive deionization

Increasing global water stress motivates a growing interest in seawater desalination by reverse osmosis. Boron is typically weakly removed by reverse osmosis membranes at seawater pH, necessitating expensive post-processes such as caustic agent dosing of the permeate followed by additional filtration steps. It has been previously demonstrated that membraneless capacitive deionization can enable chemical-free boron removal from reverse osmosis permeate, with basic design rules established. However, the level of boron electrosorption per cell charge was limited to ∼0.5 µmol/g, a level too low for practical applications. We here explore, both theoretically and experimentally, methods to enhance boron removal by capacitive deionization. We found that reversing the polarity of the applied voltage during the discharge step resulted in an order of magnitude increase in boron electrosorption to nearly 4 µmol/g with promising energy consumption of 0.2 kW⋅h/m3. The promise of these results is highlighted when compared with recently-developed boron electrosorption cells requiring bipolar membranes, which demonstrate similar boron removal of 4.35 µmol/g but with much higher energy consumption of 18.3 kW⋅h/m3 while incurring significant membrane costs. Overall, we demonstrate for the first time that membrane- and chemical-free electrochemical technologies can remove sufficient boron from RO permeate in a single pass, significantly enhancing its potential to provide energy- and cost-efficient boron removal.

Analytical Bit-Error Model of NAND Flash Memories for Dosimetry Application

In this article, we provide an analytical model for the total ionizing dose (TID) effects on the bit error statistics of commercial flash memory chips. We have validated the model with experimental data collected by irradiating several commercial NAND flash memory chips from different technology nodes. We find that our analytical model can project bit errors at higher TID values [~20 krad (Si)] from measured data at lower TID values [<1 krad (Si)]. Based on our model and the measured data, we have formulated basic design rules for using a commercial flash memory chip as a dosimeter. We discuss the impact of NAND chip-to-chip variability, noise margin, and the intrinsic errors on the dosimeter design using detailed experimentation.

Structural DNA Nanotechnology: Immobile Holliday Junctions to Artifi.

DNA nanotechnology marvels the scientific world with its capabilities to design, engineer, and demonstrate nanoscale shapes. This review is a condensed version walking the reader through the structural developments in the field over the past 40 years starting from the basic design rules of the double-stranded building block to the most recent advancements in self-assembled hierarchically achieved structures to date. It builds from the fundamental motivation of building 3-dimensional (3D) lattice structures of tunable cavities going all the way up to artificial nanorobots fighting cancer. The review starts by covering the most important developments from the fundamental bottom-up approach of building structures, which is the 'tile' based approach covering 1D, 2D, and 3D building blocks, after which the top-down approach using DNA origami and DNA bricks is also covered. Thereafter, DNA nanostructures assembled using not so commonly used (yet promising) techniques like i-motifs, quadruplexes, and kissing loops are covered. Highlights from the field of dynamic DNA nanostructures have been covered as well, walking the reader through various approaches used within the field to achieve movement. The article finally concludes by giving the authors a view of what the future of the field might look like while suggesting in parallel new directions that fellow/future DNA nanotechnologists could think about.

Long-range exciton diffusion in molecular non-fullerene acceptors

The short exciton diffusion length associated with most classical organic semiconductors used in organic photovoltaics (5-20 nm) imposes severe limits on the maximum size of the donor and acceptor domains within the photoactive layer of the cell. Identifying materials that are able to transport excitons over longer distances can help advancing our understanding and lead to solar cells with higher efficiency. Here, we measure the exciton diffusion length in a wide range of nonfullerene acceptor molecules using two different experimental techniques based on photocurrent and ultrafast spectroscopy measurements. The acceptors exhibit balanced ambipolar charge transport and surprisingly long exciton diffusion lengths in the range of 20 to 47 nm. With the aid of quantum-chemical calculations, we are able to rationalize the exciton dynamics and draw basic chemical design rules, particularly on the importance of the end-group substituent on the crystal packing of nonfullerene acceptors.

Automatic spatial attribute and travel pattern generation for simulating living spaces for elderly individuals living alone

Simulators that generate records of virtual sensors are necessary for verifying and testing smart-home systems. However, their users usually need to build home models and body models of residents manually. They also have to define resident activity schedules and movement routes manually. This study proposes a framework for building a virtual database and using it to make diverse home and body models, activity schedules, and travel patterns for multiple simulation tools. We show that this framework is feasible by making two generators and two interfaces as a demonstration. The spatial attribute generator generates indoor spatial data on studio apartments by following basic design principles and rules for designing homes for elderly individuals. The travel pattern generator generates travel patterns of elderly individuals with dementia on the basis of a realistic-path model. Two interfaces are used to convert the generated spatial data into the home models of a simulator and convert travel patterns into the records of virtual sensors.

Synthesis and Properties of Benzoxazine Monomers Bearing Both 3-Methyltetrahydrophtalimide and Nitrile Groups: Para-Para vs. Ortho-Ortho

Two 3-methytetrahydrophtalimide-functional benzoxazine monomers containing nitrile group have been prepared in order to achieve the basic design rules for developing high-performance thermosets via multifunctional benzoxazines. The chemical structures of the two new synthesized benzoxazine monomers have been confirmed by 1H NMR, 13C NMR and FT-IR. Besides, the polymerization behavior has been studied by using DSC and in situ FT-IR. In addition, the thermal stability and flame retardant properties of the resulting polybenzoxazines have also been investigated using TGA and MCC. The polybenzoxazine based on ortho-3-methytetrahydrophtalimide functional benzoxazine containing ortho-nitrile group exhibits excellent thermal stability and low flammability, with a Td10 of 378 °C and a HRC value of 180 J/(g K).

Efficient coupling to a waveguide by combined gratings in a holographic waveguide display system.

Gratings are widely used as coupling parts in a waveguide display system for achieving a much lighter and more compact system, but their diffraction efficiency needs to be improved. Two combined gratings for integrating a subwavelength binary grating and volume holographic grating (VHG) are applied as incoupler and outcoupler of a holographic waveguide display system. Two basic design rules are put forward to guarantee the maximum diffraction energy guided into the waveguide and finally coupled out to enter into the user's eyes: one is the grating vector matching rule, the other is the refractive index matching rule on the interface of the binary grating and the VHG. The finite element method is used to simulate the couple-in parts and the whole waveguide display system. The combined grating with the metal binary grating is different from that with a dielectric binary grating for achieving higher diffraction efficiency and an additional second peak in the diffraction efficiency curve varied with the relative position between the binary grating and the VHG. The simulation results indicate that a VHG+Ag combined grating can obtain much higher diffraction efficiency compared to gold, aluminum, and other dielectric materials. In addition, several factors such as the Bragg wavelength, the index modulation of VHG, binary grating thickness, and the filling factor of the binary grating are discussed for the VHG+Ag combined grating. Moreover, a higher diffraction efficiency in the holographic waveguide system can be obtained by using VHG+Ag-VHG+Ag combined gratings as the incoupler and outcoupler.

Design of fire safety equivalence of building open arcades to exterior spaces

An arcade is a succession of arches, each counter-thrusting the next, supported by columns, piers, or a covered walkway enclosed by a line of such arches on one or both sides. In warm or wet climates regions, exterior arcades provide shelter for pedestrians. A building open arcade is sometimes called a porch. Arcades usually border a covered section of a building and sometimes they support roofs. They are very old architectural elements that date back thousands of years.Building open arcades (“Portici”) are traditionally employed in cities to provide shelter for pedestrians along public and private streets. Along the closed side of the arcades, commercial activities of all sort often offer their main entrance and exhibition spaces. Other activities as private dwellings or any other kind of civil activity may communicate directly through doors or other openings towards the covered space under the arcade.According to current prescriptive fire safety regulations, open arcades cannot be considered equivalent to exterior open spaces, and all the activities that have openings towards these covered spaces should be presumed in mutual communication from a fire safety design point of view. In fact, it is hypothesized that closed enclosures allow for the faster spread of fire effluents between the communicating spaces. Nevertheless, according to experiences and engineering judgments, under certain conditions and constraints, the open arcades allow for evacuation of smoke and heat towards the exterior spaces through the open side. When these conditions are met, all the activities that have openings towards these covered spaces could be assumed mutually independent from a fire safety design perspective, because, in case of fire, the fire effluents do not spread easily towards the adjoining activities.In this paper a fire safety engineering calculation is performed to assess in which circumstances an open arcade can be considered as equivalent to an exterior space for deemed-to-satisfy solutions of the Italian Fire Code (IFC 2015).The study proposes an arcade parametric fire model, whose pre-processor has been developed in Python, for assessing conditions, safety measures and geometric constraints that allow to recognize building open arcades as exterior safety places. The open arcade can be considered equivalent to exterior space for deemed-to-satisfy solutions when occupants can safely escape from the open arcade towards a safe place, occupants of other activities abutting in the same open arcade are not harmed by the fire effluents coming from the activity involved in the fire, and when fire and its effluents do not spread to other abutting activities. Furthermore, the paper assumes a simplified equivalent model structure of the building arcade where the parametric study conducted with FDS is aimed at setting some basic rules for the fire safety design of building open arcades. The results of the parametric study show that under certain conditions and constraints, the open arcades allow for evacuation of smoke and heat towards the exterior spaces through the open side. Therefore, when these conditions are met, all the activities that have openings towards these covered spaces could be assumed mutually independent from a fire safety design perspective, since in case of an outbreak of a fire the fire effluents do not spread easily towards the adjoining activities.

Preliminary design of advanced flight control system architectures for commercial transport aircraft

The functional enhancement of flight control systems (FCS) show potential benefits for commercial transport aircraft. Furthermore, the consideration of new technologies and more-electric concepts lead to a significant increase of the design space for FCS architectures. The objective of this contribution is to enable the preliminary design of advanced FCS architectures for a given FCS configuration. Based on a comprehensive literature research, the main subsystems are identified and simplified models of the architecture are developed. Additionally, technological constraints as well as design rules for actuator distribution, and power redundancy are defined. The design rules for advanced FCS architectures are derived from the basic design rules of existing FCS architectures of commercial transport aircraft. Finally, the presented method is implemented into a design tool. The resulting tool enables the preliminary design of multifunctional FCS architectures.

Plant-inspired pipettes.

The female sex organ of the liverwort (Marchantia polymorpha) has a characteristic parasol-like form highly suitable for collecting water droplets containing sperm for fertilization. Motivated by this observation and using three-dimensional printing techniques, we develop a parasol-like rigid object that can grab, transport and release water droplets of a maximum size of about 1 cm. By combining experiments and scaling theory, we quantify the object's fundamental wetting and fluid dynamical properties. We construct a stability phase diagram and suggest that it is largely insensitive to properties of liquids such as surface tension and viscosity. A simple scaling argument is developed to explain the phase boundary. Our study provides basic design rules of a simple pipette-like device with bubble-free capture and drop of liquids, which can be used in laboratory settings and has applications within soft robotics. Through systematic experimental investigations, we suggest the optimal design criteria of the liverwort-inspired object to achieve maximal pipetting performance. We also provide, based on our scalable model experiments, a biological implication for the mechanistic advantage of this structure in liverwort reproduction.

Contrasting underlying mechanisms of different barrier coating types

Barrier coatings are used in applications including food packaging, dry goods, and consumer products to prevent transport of different compounds either through or into paper and paperboard substrates. These coatings are useful in packaging to contain active ingredients, such as fragrances, or to protect contents from detrimental substances, such as oxygen, water, grease, or other chemicals of concern. They also are used to prevent visual changes or mechanical degradation that might occur if the paper becomes saturated. The performance and underlying mechanism depends on the barrier coating type and, in particular, on whether the barrier coating is designed to prevent diffusive or capillary transport. Estimates on the basis of fundamental transport phenomena and data from a broad screening of different barrier materials can be used to understand the limits of various approaches to construct barrier coatings. These estimates also can be used to create basic design rules for general classes of barrier coatings.

Self-propagating miniature device based on shape memory alloy

The development of novel locomotion mechanisms is beneficial for advancing the field of self-propagating devices, which are implemented in various civilian and military applications. In this work, we present a purely mechanic, mm-sized autonomous device capable of linear propagation on a smooth, relatively flat surface. The locomotion mechanism is driven by a shape memory alloy (SMA) wire that is connected to a metallic, ring-shaped, bias spring. Periodic changes in the temperature in the vicinity of the device activate the SMA wire, and result in alternating contraction-elongation deformations of the SMA-bias spring assembly. These deformations are transferred to a linear back and forth motion of small legs that are attached at the bottom of the ring. To generate locomotion, the general conditions for obtaining asymmetric friction between needle shaped legs and a smooth surface were formulated and validated experimentally. The structure and performance of the device are modeled analytically leading to basic design rules that are validated experimentally by real-time optical tracking of the device’s displacements and propagation. In addition, the potential of miniaturization of the presented locomotion concept down to the micro-meter scale is demonstrated.

Tip-to-tip variation mitigation in extreme ultraviolet lithography for 7 nm and beyond metallization layers and design rule analysis

The authors develop and present computational lithography solutions to mitigate the tip-to-tip variations in 7 nm and beyond metallization layers. An array of patterns that represent lithography challenges are generated from basic design rules. The lithography process is optimized by source mask co-optimization to achieve high image qualities and maximum overlapping process windows for all patterns. By analyzing the role of diffraction orders in forming images with tight tip-to-tip, the authors identify the diffraction orders that should be admitted or rejected in the projection imaging system. This leads to analytically derived source profiles that match and explain numerical results. The authors have also found optimal minimum pitches that can achieve robust lithography process as well as design flexibility without losing throughput. Our work provides design for manufacturability guidance to metallization layers in advanced technology nodes so that patterning failures can be avoided before time-consuming optical rule check and expensive wafer validation.

Optical Evaluation of the Rear Contacts of Crystalline Silicon Solar Cells by Coupled Electromagnetic and Statistical Ray-Optics Modeling

High-efficiency crystalline silicon (c-Si) solar cells increasingly feature sophisticated electron and hole contacts aimed at minimizing electronic losses. At the rear of photovoltaic devices, such contacts - usually consisting of stacks of functional layers - offer opportunities to enhance the infrared response of the solar cells. Here, we propose an accurate and simple modeling procedure to evaluate the infrared performance of rear contacts in c-Si solar cells. Our method combines full-wave electromagnetic modeling of the rear contact with a statistical ray optics model to obtain the fraction of optical energy dissipated from the rear contact relative to that absorbed by the Si wafer. Using this technique, we study the impact of the refractive index, extinction coefficient, and thickness of the rear-passivating layer and establish basic design rules. In addition, we evaluate novel optical structures, including stratified thin films, nanoparticle composites, and conductive nanowires embedded in a low-index dielectric matrix, for integration into advanced rear contacts in c-Si photovoltaic devices. From an optical perspective, nanowire structures preserving low contact resistance appear to be the most effective approach to mitigating dissipation losses from the rear contact.

In Vivo Fate of Carbon Nanotubes with Different Physicochemical Properties for Gene Delivery Applications.

Gene therapy has arisen as a pioneering technique to treat diseases by direct employment of nucleic acids as medicine. The major historical problem is to develop efficient and safe systems for the delivery of therapeutic genes into the target cells. Carbon nanotubes (CNTs) have demonstrated considerable promise as delivery vectors due to their (i) high aspect ratio and (ii) capacity to translocate through plasma membranes, known as the nanoneedle effect. To leverage these advantages, close attention needs to be paid to the physicochemical characteristics of the CNTs used. CNTs with different diameters (thinner and thicker) were treated by chemical oxidation to produce shorter fragments. Rigid (thick) and flexible (thin) CNTs, and their shortened versions, were coated with polyallylamine (ppAA) by plasma-enhanced chemical vapor deposition. The ppAA coating leads to a positively charged CNT surface that is able to electrostatically bind the green fluorescent protein plasmid reporter. This study shows how rigidity and length can affect their (i) behavior in biological media, (ii) ability to transfect in vitro, and (iii) biodistribution in vivo. This study also generates a set of basic design rules for the development of more efficient CNT-based gene-delivery vectors.

Basic design rules of unit cells for additive manufactured lattice structures

Additive Manufacturing is a cutting-edge technology for the production of complex, functional, filigree and topology-optimized components. The growing demand for high-tech light-weight structures increasingly requires support in the design process of fine lattice structures. However, due to the high information density regarding lattice structures, which is based on many scientific research studies, the effective design of a specifically product-oriented lattice structure is made more difficult. The focus of this work is to provide a user-friendly information basis for the user or constructor. Therefore, this scientific work serves to show the first basic rules for the design of simple unit cells for additive lattice structures. The approach is based on the evaluation of the limiting manufacturing factors, which can be reduced both to the minimum and maximum angle and length, as well as to the cross-sectional geometry. The analysis reveals a considerable extent to the cross-sectional geometries and their welding pattern in various quality forms. The results obtained form the basis for the development of complex functional unit cells. However, the construction of a unit cell is only a part of a lattice structure, so additional factors must be added to the unit cell assembly.

High-reflectivity high-contrast grating focusing reflector on silicon-on-insulator wafer**Project supported by the National Natural Science Foundation of China (Grant Nos. 61274044, 61574019 and 61020106007), the National Basic Research Program of China (Grant No. 2010CB327600), the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20130005130001), the Natural Science Foundation of Beijing, China (Grant No. 4132069), the

A high-contrast grating (HCG) focusing reflector providing phase front control of reflected light and high reflectivity is proposed and fabricated. Basic design rules to engineer this category of structures are given in detail. A 1550 nm TM polarized incident light of 11.86 mm in focal length and 0.8320 in reflectivity is obtained in experiment. The wavelength dependence of the fabricated HCGs from 1530 nm to 1580 nm is also tested. The test results show that the focal length is in the range of 11.81–12 mm, which is close to the designed focal length of 15 mm. The reflectivity is almost above 0.56 within a bandwidth of 50 nm. At a distance of 11.86 mm, the light is focused to a round spot with the highest concentration, which is much smaller than the size of the incident beam. The FWHM of the reflected light beam decreases to 120 nm, and the intensity increases to 1.18.