Selective Shielding Research Articles

Optical Metacages.

We suggest a novel strategy for spectrally selective optical shielding of arbitrary shaped volumes by arranging specifically designed two- or three-layer nanowires around an area that needs to be protected. We show that such nanowire shields preserve their functionality for almost arbitrary geometry, and we term such structures optical metacages. We analyze several designs of such optical metacages made from either metallic or dielectric materials with experimentally measured parameters. We employ a semianalytical approach and also verify our results by numerical simulations. We further study optical properties of the introduced metacages in both near- and far-field regions, as well as analyze their frequency selectivity and the vanishing backscattering regime.

Preparation of reduced graphene oxide/Ni0.4Zn0.4Co0.2Fe2O4 nanocomposites and their excellent microwave absorption properties

A novel reduced graphene oxide/Ni0.4Zn0.4Co0.2Fe2O4 nanocomposite was firstly prepared by a facile and efficient mechanical mixing method with good safety, high controllability and excellent quantifiability. The microstructure and morphology were examined by FTIR, XRD, TG, SEM and EDS. The measured electromagnetic parameters indicated that the rGO/NZCF-15 composite exhibited excellent microwave absorption properties and extraordinary broad absorption bandwidths due to both dielectric loss and magnetic loss. The minimum reflection loss of the rGO/NZCF-15 composite was −38.7dB at 15.2GHz for a layer of only 1.9mm thickness, and the bandwidth corresponding to RL less than −10dB can reach 6.2GHz (11.8–18.0GHz). This novel composite with such strong microwave absorption could be used as a new candidate for selective frequency shielding and lightweight EM wave absorbing material.

A Circular-Ring Miniaturized-Element Metasurface With Many Good Features for Frequency Selective Shielding Applications

A novel circular-ring miniaturized-element (CRME) metasurface is proposed for frequency selective electromagnetic shielding applications in this paper. The proposed structure exhibits good performance in many aspects. The CRME size can be easily reduced to 0.088 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> × 0.088 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> , where λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> is the wavelength at resonance. Such small size can be useful in applications with limited space. The newly proposed metasurface not only shows the stability to incidence angles and polarizations, but also demonstrate negligible polarization crossing. The metasurface also presents low coupling between elements, which leads to the insensitivity of periodicity fluctuation in fabrication process. Moreover, the frequency responses can be varied through the modification of the element pattern of the metasurface. It provides flexible frequency responses to use in frequency selective shielding applications. Also, this element is suitable for constructing a metasurface aligned in either square or even hexagonal lattice, which owns the best adaptability to a doubly curved surface or a spherical one. Without revising the CRME, both the squareand hexagonal-lattice metasurfaces constructed can perform competently at the same time. Finally, the metasurface prototype is fabricated and tested in a fully anechoic chamber to verify the design. The measured results well agree with the simulated ones.

Omni-Directional Selective Shielding Multilayered Material for High Frequency Radiation

The selective microwave absorption properties of individual and multiple CoFe-glass coated amorphous microwires (GCAW) with small negative value of magnetostriction <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$(\lambda\sim-1\times 10^{-7})$</tex></formula> , positioned in various configurations are investigated. The deep minimum in the transmission spectra correspond to the first antenna resonance for each length of the individual microwire indicating a selective stop filter behavior. A new type of shielding material in the shape of a multilayered material based on CoFe-GCAW with desired shielding effectiveness and selective absorption of the microwave frequency range by controlling the number of the layers and the length of microwires is proposed and the omni-directional selective shielding properties in the microwave frequency range are determinated. The shielding effectiveness measurements results were <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">${\rm SE}=4\ {\rm dB}$</tex></formula> to 9.5 dB for the samples with two layers, <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm SE}=18\ {\rm dB}$</tex></formula> to 33 dB for sample with 14 layers, and <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm SE}=36\ {\rm dB}$</tex></formula> to 48 dB for sample with 28 layers, respectively.

Angular independent frequency selective surfaces for interference control in indoor wireless environments

A study of electromagnetic wave propagation in buildings using a finite-difference time-domain algorithm has demonstrated that waves are incident on walls over a wide range of angles. If wall mounted frequency selective shielding is desired, it is argued that this behaviour requires shielding solutions that are angle insensitive. A simple single-layer annular ring frequency selective surface (which is relatively economic to fabricate) is shown to offer adequate angular stability of the transmission response, and is thus suitable for electromagnetic interference control in indoor wireless environments.

Omni-directional selective shielding material based on amorphous glass coated microwires

The shielding effectiveness of the omni-directional selective shielding material based on CoFe-glass coated amorphous wires in 0.8 GHz-3 GHz microwave frequency range is investigated. The measurements were done in a controlled medium using a TEM cell and in the free space using horn antennas, respectively. Experimental results indicate that the composite shielding material can be developed with desired shielding effectiveness and selective absorption of the microwave frequency range by controlling the number of the layers and the length of microwires.

Design and Characterization of a Multilevel DRAM

Multilevel DRAM (MLDRAM) increases the storage density of DRAMs by using more than two signal levels in the data storage cells. Our MLDRAM uses reference and data cell signals that are generated in the cell array using charge sharing. The single-step sensing method uses multiple reference signals in parallel. We describe an operational 19200-cell MLDRAM test chip in 1.8-V, 180-nm mixed-signal CMOS that allows 1, 1.5, 2, 2.25, and 2.5 bits-per-cell operation using 2, 3, 4, 5, and 6 data signal levels, respectively. Characterization features include a partitioned memory array with four different data cell sizes, two sense amplifier sizes, and selective bitline shielding. New tests were developed using an MLDRAM fault model covering basic functionality, retention time, multilevel march, inter-bitline coupling and cell plate voltage bump tests. We show that, with short bitlines, MLDRAM's noise margins can be similar to DRAM's to more reliably store two bits in a 1T1C cell.

Plasma Lithography Surface Patterning for Creation of Cell Networks

Systematic manipulation of a cell microenvironment with micro- and nanoscale resolution is often required for deciphering various cellular and molecular phenomena. To address this requirement, we have developed a plasma lithography technique to manipulate the cellular microenvironment by creating a patterned surface with feature sizes ranging from 100 nm to millimeters. The goal of this technique is to be able to study, in a controlled way, the behaviors of individual cells as well as groups of cells and their interactions. This plasma lithography method is based on selective modification of the surface chemistry on a substrate by means of shielding the contact of low-temperature plasma with a physical mold. This selective shielding leaves a chemical pattern which can guide cell attachment and movement. This pattern, or surface template, can then be used to create networks of cells whose structure can mimic that found in nature and produces a controllable environment for experimental investigations. The technique is well suited to studying biological phenomenon as it produces stable surface patterns on transparent polymeric substrates in a biocompatible manner. The surface patterns last for weeks to months and can thus guide interaction with cells for long time periods which facilitates the study of long-term cellular processes, such as differentiation and adaption. The modification to the surface is primarily chemical in nature and thus does not introduce topographical or physical interference for interpretation of results. It also does not involve any harsh or toxic substances to achieve patterning and is compatible for tissue culture. Furthermore, it can be applied to modify various types of polymeric substrates, which due to the ability to tune their properties are ideal for and are widely used in biological applications. The resolution achievable is also beneficial, as isolation of specific processes such as migration, adhesion, or binding allows for discrete, clear observations at the single to multicell level. This method has been employed to form diverse networks of different cell types for investigations involving migration, signaling, tissue formation, and the behavior and interactions of neurons arraigned in a network.

Plasma Lithography Surface Patterning for Creation of Cell Networks

Systematic manipulation of a cell microenvironment with micro- and nanoscale resolution is often required for deciphering various cellular and molecular phenomena. To address this requirement, we have developed a plasma lithography technique to manipulate the cellular microenvironment by creating a patterned surface with feature sizes ranging from 100 nm to millimeters. The goal of this technique is to be able to study, in a controlled way, the behaviors of individual cells as well as groups of cells and their interactions.This plasma lithography method is based on selective modification of the surface chemistry on a substrate by means of shielding the contact of low-temperature plasma with a physical mold. This selective shielding leaves a chemical pattern which can guide cell attachment and movement. This pattern, or surface template, can then be used to create networks of cells whose structure can mimic that found in nature and produces a controllable environment for experimental investigations. The technique is well suited to studying biological phenomenon as it produces stable surface patterns on transparent polymeric substrates in a biocompatible manner. The surface patterns last for weeks to months and can thus guide interaction with cells for long time periods which facilitates the study of long-term cellular processes, such as differentiation and adaption. The modification to the surface is primarily chemical in nature and thus does not introduce topographical or physical interference for interpretation of results. It also does not involve any harsh or toxic substances to achieve patterning and is compatible for tissue culture. Furthermore, it can be applied to modify various types of polymeric substrates, which due to the ability to tune their properties are ideal for and are widely used in biological applications. The resolution achievable is also beneficial, as isolation of specific processes such as migration, adhesion, or binding allows for discrete, clear observations at the single to multicell level.This method has been employed to form diverse networks of different cell types for investigations involving migration, signaling, tissue formation, and the behavior and interactions of neurons arraigned in a network.

A Ligand Structure–Activity Study of DNA‐Based Catalytic Asymmetric Hydration and Diels–Alder Reactions.

AbstractA structure–activity relationship study of the first generation ligands for the DNA‐based asymmetric hydration of enones and Diels–Alder reaction in water is reported. The design of the ligand was optimized resulting in a maximum ee of 83 % in the hydration reaction and 75 % in the Diels–Alder reaction, and some guidelines for ligand design were formulated. A comparison between these two reaction classes using salmon testes DNA/Cu2+‐L catalysts, showed that the enantioselectivity in the hydration reaction was not the result of selective shielding of one π face of the enone. In contrast, the structure of the ligand was suggested to be crucial to position and orient the substrate bound Cu2+ complex optimally with respect to the structured first hydration layer of the DNA. Likely, the DNA activates and directs the H2O nucleophile for attack to one preferred π face of the enone.

An EM Absorber and Frequency Selective Shielding by Use of Metal Fiber Array Composites

The construction of EM absorber and frequency selective shielding has been investigated by using two dimensional metal fiber array (MFA) composites. The MFA composite shows a resonant type frequency dispersion in the complex relative permittivity spectra (er = e'r - je ''r) having a negative e'r region. The frequency characteristics of the conventional ferrite-rubber EM absorber can be improved by combining with the negative permittivity property of the MFA composite. A frequency selective shielding can be achieved by the evanescent EM wave propagation in the layered MFA composite structure.

Selective shielding technique to eliminate crosstalk transitions

With CMOS process technology scaling to deep submicron level, propagation delay across long on-chip buses is becoming one of the main performance limiting factors in high-performance designs. Propagation delay is very significant when adjacent wires are transitioning in opposite direction as compared to transitioning in the same direction. As opposite transitions on adjacent wires (called as crosstalk transitions ) have significant impact on propagation delay, several bus encoding techniques have been proposed in literature to eliminate such transitions. We propose selective shielding technique to eliminate crosstalk transitions. We show that the selective shielding technique requires ⌈3 n /2⌉ wires to encode a n -bit bus. SPICE simulations by considering 90nm technology nodes reveal that, for uniformly distributed random data, our technique achieves nearly 39% (21%) delay savings over 10 mm -length uncoded 32-bit bus for pipelined (nonpipelined) data transmission at the cost of nearly 7% energy overhead.

Selective passive shielding and the Faraday bracelet

We describe a general approach for the design of passive conducting structures that preferentially shield the ac magnetic field produced by a specific coil geometry. We demonstrate the utility of selective passive shielding with the Faraday bracelet, an open-access shield for saddle-shaped rf coils. Our data also corroborate the poorly known fact that effective shielding can occur when the ratio of shield thickness to skin depth is much less than unity.

Antioxidant Nanoreactor Based on Superoxide Dismutase Encapsulated in Superoxide-Permeable Vesicles

We designed and tested an antioxidant nanoreactor based on encapsulation of Cu,Zn superoxide dismutase in amphiphilic copolymer nanovesicles, the membranes of which are oxygen permeable. The nanovesicles, made of poly(2-methyloxazoline)-poly(dimethylsiloxane)-poly(2-methyloxazoline), successfully encapsulated the protein during their self-assembling process, as proved by confocal laser-scanning microscopy and fluorescence-correlation spectroscopy. Electron paramagnetic resonance spectroscopy and circular dichroism analyses showed that no structural changes appeared in the protein molecules once inside the inner space of the nanovesicles. The function of this antioxidant nanoreactor was tested by pulse radiolysis, which demonstrated that superoxide dismutase remains active inside the nanovesicles and detoxifies the superoxide radical in situ. The membrane of our triblock copolymer nanovesicles plays a double role, both to shield the sensitive protein and to selectively let superoxide and dioxygen penetrate to its inner space. This simple and robust hybrid system provides a selective shielding of sensitive enzymes from proteolytic attack and therefore a new direction for developing drug delivery applications.

Quantitative assessment of selective in-plane shielding of tissues in computed tomography through evaluation of absorbed dose and image quality

This study aimed at assessment of efficacy of selective in-plane shielding in adults by quantitative evaluation of the achieved dose reduction and image quality. Commercially available accessories for in-plane shielding of the eye lens, thyroid and breast, and an anthropomorphic phantom were used for the evaluation of absorbed dose and image quality. Organ dose and total energy imparted were assessed by means of a Monte Carlo technique taking into account tube voltage, tube current, and scanner type. Image quality was quantified as noise in soft tissue. Application of the lens shield reduced dose to the lens by 27% and to the brain by 1%. The thyroid shield reduced thyroid dose by 26%; the breast shield reduced dose to the breasts by 30% and to the lungs by 15%. Total energy imparted (unshielded/shielded) was 88/86 mJ for computed tomography (CT) brain, 64/60 mJ for CT cervical spine, and 289/260 mJ for CT chest scanning. An increase in image noise could be observed in the ranges were bismuth shielding was applied. The observed reduction of organ dose and total energy imparted could be achieved more efficiently by a reduction of tube current. The application of in-plane selective shielding is therefore discouraged.

Raman Enhancement Factor of a Single Tunable Nanoplasmonic Resonator

We have developed a novel technique to precisely determine the Raman enhancement factor in single nanoplasmonic resonators (TNPRs). TNPRs are lithographically defined metallodielectric nanoparticles composed of two silver disks stacked vertically, separated by a silica layer. At resonance, the local electromagnetic fields are enhanced at the TNPR surface, making it an ideal surface-enhanced Raman scattering (SERS) active substrate. The ability to control the dimensions of the metallic and dielectric layers offers the unique advantage of fine-tuning the plasmon resonance frequency to maximize the enhancement of the Raman signal. Furthermore, by selective shielding of the outer surface of the metallic structure, the efficiency can be further enhanced by guiding the molecular assembly to the locations that exhibit strong electromagnetic fields. We experimentally demonstrate SERS enhancement factors of (6.1+/-0.3)x10(10), with the highest enhancement factor being achieved by using an individual nanoparticle. By using nanofabrication techniques, we eliminate the issues such as large size variations, cluster aggregation, and interparticle effects common in preparing SERS substrates using conventional chemical synthesis or batch fabrication methods. TNPRs produce very controllable and repeatable SERS signals at the desired locations and, thus, make an ideal candidate for device integration.

Renal Dysfunction after Total-Body Irradiation

A retrospective analysis was conducted on the outcome of total-body irradiation (TBI) followed by bone marrow transplantation (BMT) on leukemia patients. Also studied was the risk of renal dysfunction after TBI/BMT with or without the use of selective renal shielding blocks. The cases of 109 leukemia patients who received TBI as a component of the conditioning regimen for their BMT were reviewed. They received 12 Gy of TBI in six fractions over 3 consecutive days. Doses to eyes and lungs were reduced to 7 Gy and 8 Gy, respectively, by customized organ shielding blocks. After March 1999, renal shielding blocks were used to constrain the renal dose to 10 Gy. The patients were followed for a median period of 16.6 months (range: 0.3–180.1 months). The 2-year and 5-year overall survival rates were 55.4% and 43.2%, respectively. Renal dysfunction-free rates were different between those with and without renal shielding blocks: 100% and 78.5%, respectively, at 2 years. Overall survivals were not significantly different among these patients: 60.4% and 52.9%, respectively, at 2 years in patients with and without renal shielding blocks (p = 0.53). The use of selective renal shielding blocks provided evidence for reducing radiation-induced renal toxicities without decreasing the overall survival rate.

Boc–phenylglycine: a chiral solvating agent for the assignment of the absolute configuration of amino alcohols and their ethers by NMR

The absolute configuration of β-amino alcohols and their ethers can easily be determined by comparison of the 1H NMR spectra of the mixture formed by the substrate amino alcohol or amino ether plus one equivalent of ( R)-Boc–α-phenylglycine (BPG) with that of the mixture formed by the substrate plus one equivalent of ( S)-BPG. Several examples of known absolute configuration have been used to validate the results, which are explained in terms of the selective shielding experienced by protons of the substrate located on the complex on the same side of the phenyl group of BPG. A graphical model has been proposed in which the use of the Δ δ RS parameters for Cα–H, Cβ–H and the L group allow the direct configurational assignment from the NMR data.

Stereoselective Synthesis of 1,2‐ and 1,4‐Dihydropyridines by Using Cation‐π Interaction as a Conformation‐Controlling Tool.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Face‐Selective Addition to a Cation—π Complex of a Pyridinium Salt: Synthesis of Chiral 1,4‐Dihydropyridines.

AbstractFor Abstract see ChemInform Abstract in Full Text.