Broadband filter using multi-layer sub-wavelength high-contrast grating structure

In this study, the effect of different numbers of layers of reduced graphene oxide (RGO) on the ferromagnetic behavior of zinc oxide–reduced graphene oxide (ZnO–RGO) hybrid architectures has been investigated. Scanning and transmission electron microscopy along with x-ray diffraction of these hybrids confirm that ZnO nanorods are wrapped with different numbers of layers of RGO in a controlled way and their hexagonal phase is unaffected by these layers. Raman and photoelectron spectroscopy of these hybrids reveals that RGO does not alter the nonpolar optical phonon E2 (high) mode and chemical state of Zn2+ in ZnO. Electron paramagnetic resonance (EPR) spectra show that RGO passivates singly charged oxygen vacancies () in ZnO. It correlates the passivation efficiency of to the number of RGO layers and this has been achieved up to 90% by ∼31 layers of RGO. Due to passivation of in ZnO by RGO, the ferromagnetic behavior (saturation magnetization and divergence between zero field cooled and field cooled) in ZnO–RGO hybrids is suppressed as compared to ZnO. Combining the EPR and magnetic behavior, a direct link between the passivation of the singly charged oxygen vacancies present on the surface of ZnO nanorods and the number of RGO layers is established.

In this study, the behavior of composite material produced using basalt, a natural fabric, under ballistic and Charpy impact loads was investigated. The damage resistance of target plates under ballistic loads is an important design parameter in the structures that will be exposed to these loads. Cross‐ply fiber‐reinforced composite plates were produced with different numbers of layers. The composite specimens are produced using the vacuum infusion method, cross‐ply laminated with 3, 6, 9, and 12 layers ([0/90]3, [0/90]6, [0/90]9, and [0/90]12). Carbon/Epoxy specimens were also produced in identical sequences to be used as comparison material. The study aimed to understand the absorbed energy under ballistic loads and the required energy level under the Charpy impact loads of Basalt/Epoxy composite specimens with different thicknesses. Ballistic loads are applied to the specimens using a test set‐up including the sample holder mechanism and a firing system. Charpy impact tests were conducted using a standard test machine. According to the results, for 12‐layer specimens, the residual velocity difference between Basalt/Epoxy and Carbon/Epoxy is approximately 1.5 times. For the Basalt/Epoxy plate, increasing number of layers from 3 to 12 increases the amount of energy absorbed approximately 13 times. Although this increase is approximately 19 times for the Carbon/epoxy plate, when Basalt/Epoxy and Carbon/Epoxy plates are compared, Basalt/Epoxy absorbs more energy for all layer numbers. For the Charpy impact cases, it has been observed that Basalt/Epoxy absorbs approximately 34% more energy for flat wise impact and approximately 24% more energy for edgewise impact.Highlights The behavior of composite material produced using basalt, a natural fabric. Cross‐ply fiber‐reinforced composite plates. Effect of different number of layers considered. The damage resistance of target plates under ballistic loads. Comparison of basalt and carbon‐reinforced composites.

Blood vessels exhibit a common structure composed of layers of cells encircling a central lumen. Arteries generally have more layers than veins have, and different arteries in the same individual can have different numbers of layers. Because all blood vessels are built around a monolayer of endothelial cells, the variation in wall structure is due to variable numbers of smooth muscle-containing layers in the tunica media. Indeed, Wolinsky and Glagov's classic article showed that the relation between lumen diameter and wall thickness across a wide range of mammalian species is a function of the number of layers of smooth muscle and elastic fibers that are present in the arterial media.1 Yet precisely how layers of smooth muscle are formed during vascular development and what molecular mechanisms operate to produce different numbers of layers in different blood vessels is still poorly understood. Article see p 314 For many years the prevailing hypothesis has been that wall thickness is determined by wall tension, and the number of layers found in a given blood vessel is that number sufficient to normalize wall tension to values (dynes/cm2) within a narrow physiological range per layer.2 The advent of transgenic mouse technology generated new animal models that provided for interesting tests of the accepted paradigms for the development of vessel wall structure. For example, mice expressing a growth hormone transgene driven by a metallothionein promoter (MtGH) reached a body mass 1.8-fold that of wild-type littermate mice.3 Most of the internal organs in these mice exhibited proportional increases in mass in comparison with wild-type littermates (eg, kidney=1.9-fold; heart= 1.8-fold).4 To accommodate the increases in blood flow required to support these larger bodies, the aortas of transgenic MtGH mice exhibited a number of structural changes. For example, aortic lumen diameter was increased (1.22-fold), …

During the lifespan, graphic products are exposed to various external factors. During their use, their properties(physical, mechanical, visual, etc.) change to a greater or lesser extent. It is necessary to observe/monitor changesand influence of external factors on their properties as soon as the product is created. The aim of this research is toexamine the impact of the aging process on the quality of inkjet printing. A different number of layers of black ink (in10 % tonal value (TV) and 100 % TV) and a different number of varnish layers were printed on PVC foil material. The samples were exposed to xenon light (λ > 300 nm) to accelerate the ageing process over a period of 72 and 216 h. They were measured by Datacolor spectrophotometer. As expected, with longer exposure time, greater changes occurred. According to the CIE ΔE*00 formula, the differences ranged from an imperceptible to a large colour change. After 72 h, the biggest changes in colour occurred in the K10 % with one ink layer and three layers of varnish. The smallest changes were in K100 % with one ink layer and no varnish. After 216 h, the greatest changes were observed in the K10 % sample with three layers of ink and two layers of varnish. The smallest differences were K10 % sample with one ink layer and without varnish.

In this review, we summarize and discuss our recent studies of subwavelength grating (SWG) structures for engineering the refractive index of silicon microphotonic waveguides. The SWG effect allows control of the effective refractive index of a waveguide core over a range spanning the values of the cladding material and silicon by lithographic patterning. We demonstrate this effect with the example of segmented photonic wire waveguides, which are shown to exhibit low propagation loss, and can be used to make highly efficient waveguide crossings and in-plane fiber-chip coupling structures. Other applications of SWG structures in silicon photonic waveguide devices include surface grating couplers with enhanced performance and simplified fabrication requirements, as well as a novel curved waveguide sidewall grating micro-spectrometer, in which an SWG structure fulfills a dual purpose by acting as an effective slab waveguide for diffracted light and as a lateral cladding for a channel waveguide.

Rapid development of automotive, aviation, aerospace and defense industries are necessitated the use of lightweight and high strength materials. For this purpose, glass fiber reinforced plastic composite materials are began to be produced and widely used. These materials are in proportion to weight have higher strength and rigidity so that has found wide usage. In this study, glass fibre reinforced plastic composite materials were produced with hand lay-up as different number of layers of glass fibre. Mechanical properties of produced composite materials were investigated. Avarage strength values of produced composite materials are obtained with three point bending and tensile tests. In addition to these tests, impact strength of materials were investigated by low speed impact test. Macro and micro photographs of samples were taken before and after the tests. Samples were characterized by metallographic respect. The damage zones of resin and glass fibre materials were examined in detail in the test images. The variation of mechanical properties depending on the number of fibre layers were identified considering the experimental results. Mechanical properties of GFRP materials were investigated; mechanical properties of fibre composite materials had a good outcome, depending on the number of layers. When impact test results are examined, between the number of fibre layers and the values of the energy absorbed by GFRP were observed approximately linearity.

The high-Q resonances observed in subwavelength gratings support many applications, including optical phase arrays, refractive index sensing, enhancement of nonlinear effects, and spectral filtering. Integrating these functions with active devices opens new possibilities for microscale optical systems. GaAs high-contrast gratings (HCGs) simplify the integration of resonant structures with active III–V semiconductor devices. These structures are particularly useful in the mid-wave infrared (5–7 μm), overcoming several limitations of the material systems presented in previous works. By selectively removing an underlying AlGaAs layer, a high index contrast is introduced between suspended GaAs gratings and air without using an exotic low-index substrate. Furthermore, epitaxial growth enables precise device thickness. In this work, we demonstrate GaAs/air HCG transmittance filters for operation in the mid-wave infrared. A numerical study investigates the dependence of filter performance on substrate proximity. We fabricate experimental filters using an HBr-based plasma etch and a selective wet etch. Optical characterization demonstrates quality factors >50 and transmittance peak efficiency >50%. The observed filter performance is comparable to other mid-wave infrared subwavelength grating filters. This work concludes with discussion of experimental nonidealities, emphasizing the considerable influence of grating size and optical measurement conditions. The suspended GaAs HCG filters show potential for direct integration with active devices such as photodetectors and lasers.

Efficient polarization management is a key issue for on-chip silicon photonic integrated circuits. Here, we propose a compact and broadband on-chip silicon polarization beam splitter (PBS) using tilted subwavelength grating (SWG) structure. The key polarization separation region consists of an input tapered SWG, a titled SWG, and two output tapered SWGs at both output ports. The tilted SWG has a strong polarization dependence for the mode coupling, and we have introduced different grating duty cycles, positional offset, and a new, to the best of our knowledge, output mode transition structure to enhance the device performance. Based on these techniques, the key coupling length of the proposed PBS is only 5 µm (total length, 12 µm), together with polarization extinction ratio (ER) 21.2 dB (19.7 dB) and insertion loss 0.21 dB (0.39 dB) for the TE (TM) mode. Moreover, the device working bandwidth can be extended to 311 nm (154 nm) by keeping E R > 15 d B ( E R > 18 d B ), satisfying the on-chip broadband applications. We believe the proposed device could become a good candidate to boost the on-chip polarization management toward compact and broadband directions.

Firstly, three groups of fiber curve laminates with different numbers of layers and different fiber curve angles were designed and prepared. A cantilever plate free vibration test was used to analyze the influence of the fiber curve angle on the vibration free attenuation characteristics of the laminates. The three groups of contrast test results show that the fiber curve angle has a significant effect on the loss factor of the laminate structure. When the angle change of the fiber curve was ±<45|60>, the loss factor of the laminates reached the maximum value, and the vibration damping performance of the laminates was the best. Secondly, modal tests were carried out on the laminates, the modeling and simulation of the variable stiffness laminate were completed, and the influence of the fiber curve angle on the natural frequency of the laminate was explored. The results showed that when the number of laminate layers was the same, the natural frequencies of the laminates first increased and then decreased with an increase in the fiber curve angle. The first three natural frequencies of the laminates reached the maximum value when the fiber curve angle was ±<45|60 > or ±<60|75>. Finally, it is concluded that when the fiber curve angle of the laminates varies between ±<45|60>, the damping ratio and the first three natural frequencies of the laminates reach the maximum value, and the vibration damping performance is the best.

Bulletproof vest is also known as ballistic vest and it is used to provide ballistic protection to the body of law enforcement and military personnel from injury through bullet impact, fragments, stab attacks and other treats. In this project, shear thickening fluid/ultra-high molecular weight polyethylene, STF/UHMWPE fabrics composites were prepared in order to design a low cost and lightweight bulletproof vest with high mechanical properties (impact energy and stab resistance). There are 2 categories that are prepared (UHMWPE with and without STF) and each category has 10 different numbers of layers. For the “UHMWPE with STF”, 10 of them were impregnated with shear thickening fluid that prepared by sonochemical method by mixing dry silica nanopowders, polyethylene glycol and ethanol. The effects of number of layers of UHMWPE fabrics and STF/UHMWPE fabrics on the impact properties for both UHMWPE without STF and UHMWPE with STF fabrics were investigated by using drop tower impact testing. Results from this study showed, absorption of impact energy is increased with increase in the number of penetrated witness papers. Besides, it is also indicated that the impact energy absorbed by witness paper/s is increased when the number of UHMWPE fabric and STF/UHMWPE layers are increased. The comparison between 2 categories is discussed. The result showed that STF/UHMWPE fabrics have better performance than UHMWPE fabrics in term of impact energy absorption, stab resistance and number of fabrics layers.

3D-Printing with precise layer-wise dose adjustments for paediatric use via pressure-assisted microsyringe printing

All-optical switching based on a subwavelength metallic grating structure containing nonlinear optical materials has been proposed and numerically investigated. Metal-dielectric composite material is used in the switching for its larger third-order nonlinear susceptibility (approximately 10(-7)esu) and ultrafast response properties. The calculated dependence of the signal light intensity on the pump light intensity shows a bistable behavior, which results in a significant switch effect. It rests on a surface plasmon's enhanced intensity-dependent change of the effective dielectric constant of Kerr nonlinear media, corresponding to a transition of the far-field transmission from a low- to high-transmission state. The study of this switching structure shows great advantages of smaller size, lower requirement of pump light intensity, and shorter switching time at approximately the picosecond level.

High contrast grating (HCG) is the structure made up of the sub-wavelength grating of high-index and the surrounding layer of low-index, which reveals high contrast between two materials. Its advantages include high reflectivity over a broad bandwidth, polarization and wavelength selectivity, optical high-Q resonator, and phase modulation. In this work, the HCG structure comprising of indium tin oxide (ITO) and Silicon (Si), for the surrounding layer and the grating layer respectively, was studied. Its theoretical model was established, and transmittance, phase and optical behavior were calculated by rigorous coupled-wave analysis and finite element method. Furthermore, the established structure was fabricated to validate its feasibility. The fabricated structure shows the focusing capability whose length is about 10 μm, and the feasibility of the structure was demonstrated. It is also meaningful that ITO layer can contribute to the fabrication of the HCG structure, leading to enable the structure to be electrical-driven.

For GaN-based microcavity light emitters, such as vertical-cavity surface-emitting lasers (VCSELs) and resonant cavity light emitting diodes (RCLEDs) in the blue-green wavelength regime, achieving a high reflectivity wide bandwidth feedback mirror is truly challenging. The material properties of the III-nitride alloys are hardly compatible with the conventional distributed Bragg reflectors (DBRs) and the newly proposed high-contrast gratings (HCGs). Alternatively, at least for the top outcoupling mirror, dielectric materials offer more suitable material combinations not only for the DBRs but also for the HCGs. HCGs may offer advantages such as transverse mode and polarization control, a broader reflectivity spectrum than epitaxially grown DBRs, and the possibility to set the resonance wavelength after epitaxial growth by the grating parameters. In this work we have realized an air-suspended TiO2 grating with the help of a SiO2 sacrificial layer. The deposition processes for the dielectric layers were fine-tuned to minimize the residual stress. To achieve an accurate control of the grating duty cycle, a newly developed lift-off process, using hydrogen silesquioxan (HSQ) and sacrificial polymethyl-methacrylate (PMMA) resists, was applied to deposit the hard mask, providing sub-10 nm resolution. The finally obtained TiO2/air HCGs were characterized in a micro-reflectance measurement setup. A peak power reflectivity in excess of 95% was achieved for TM polarization at the center wavelength of 435 nm, with a reflectivity stopband width of about 80 nm (FWHM). The measured HCG reflectance spectra were compared to corresponding simulations obtained from rigorous coupled-wave analysis and very good agreement was found.

We propose an original diffraction grating demultiplexer (spectrometer) device with a very small footprint, designed for the silicon-on-insulator waveguide platform. The wavelength dispersive properties are provided by a second-order diffraction grating lithographically defined and etched in the sidewall of a curved Si waveguide. The grating is blazed to maximize the -1^st order diffraction efficiency. The diffracted light is coupled into the silicon slab waveguide via an impedance matching sub-wavelength grating (SWG) graded-index (GRIN) anti-reflective interface. The waveguide is curved in order to focus the light onto the Rowland circle, where different wavelengths are intercepted by different output waveguides. The phase errors were substantially reduced using an apodized design with a chirped grating pitch, which assures a constant effective index along the grating length. The simulated crosstalk is -30 dB. The device has 15 channels with a spacing of 25 nm, thus a broadband operational bandwidth of 375 nm. Its performance approaches the diffraction limit. The device layout size is 90 &mu;m &times; 50 &mu;m, which is the smallest footprint yet reported for a mux/dmux device of a similar performance.