Direction Of Dipole Research Articles

Design of a Wideband Coupled Feed Dipole Antenna for PCL Array Systems

This article proposes the design of a wideband coupled feed dipole antenna for Passive Coherent Location (PCL) systems. The proposed antenna consists of an internal direct feed dipole and an external coupled feed dipole. This coupled feed mechanism, which is often used in microstrip patch antennas, is applied to the dipole element for a wide matching bandwidth. To verify the operating principle of the proposed antenna, an equivalent circuit model is investigated along with some parametric studies of the coupling effect. The proposed antenna is then extended to an eight-element uniform circular array to confirm the beamforming performance for PCL systems. The results demonstrate that the coupled feed dipole element is more suitable to enhance the matching bandwidth compared to a conventional dipole antenna.

Exploring Light Polarization Effects of Photovoltaic Actions in Organic-Inorganic Hybrid Perovskites with Asymmetric and Symmetric Unit Structures.

Hybrid perovskites are known as electrically polarizable semiconductors based on theoretical prediction and experimental information. Here we show the light polarization effects on the photovoltaic actions in perovskite solar cells by optically generating directional and random electronic transition dipoles within asymmetric and symmetric unit structures. In an asymmetric tetragonal unit structure, we observed the stripes with different orientations onto perovskite grains and that the randomly polarized photoexcitation can generate a higher photocurrent (Jsc) by 6.5 ± 0.5% as compared to the linearly polarized photoexcitation at same intensity in the hysteresis-free perovskite solar cells [ITO/PEDOT:PSS/MAPbI3/PC61BM/PEI/Ag]. Clearly, switching the photoexcitation between linear and random polarizations leads to a ΔJsc, which provides an experimental indication that all-directional and one-directional transition dipoles generate higher and lower photocurrents in organic-inorganic hybrid perovskites (MAPbI3) with an asymmetric tetragonal unit structure. This implies that all-directional and one-directional transition dipoles develop stronger and weaker dissociative interactions, consequently giving rise to more and less dissociation toward generating photocurrent. This is confirmed by the experimental observation that the ΔJsc almost disappears when the temperature increases up to 55 °C, where the asymmetric tetragonal structure is changed to a symmetric cubic structure. Furthermore, the ΔJsc is shown to decrease with increasing light intensity. This indicates that the electronic transition dipoles encounter a polarization relaxation caused by mutual interaction. We show that the polarization relaxation time in MAPbI3 is comparable to exciton dissociation time (∼ps). This presents the necessary condition to demonstrate light polarization effects of photovoltaic actions in perovskite solar cells.

Design for a New “Dipole-sorter” for Direct and Dose Effective Magnetic Dipole Measurement

Design for a New “Dipole-sorter” for Direct and Dose Effective Magnetic Dipole Measurement

Giant Gaussian process models of geomagnetic palaeosecular variation: a directional outlook

SUMMARY Assessment of long-term palaeosecular variation (PSV) of the geomagnetic field is frequently based on simplified versions of a class of statistical models known as giant Gaussian processes (GGP) used to represent temporal variations in spherical harmonic descriptions of the field. Here we propose a new type of analysis to assess the shape and dispersion of the directional distributions caused by PSV. The quantities analysed in this study are equal-area coordinates of rotated distributions of palaeomagnetic directions, ${x_E}$ (east−west) and ${x_N}\ $(north−south) and their standard deviations (${\sigma _E}$ and ${\sigma _N}$). These are easy to determine, and can readily be numerically predicted for any GGP model, avoiding the need for the numerous simulations generally used to determine the scatter and/or elongation of directional distributions. Mean predictions of $\overline {{x_N}} $ for a simplified GGP model are different from the expected geocentric axial dipole (GAD) directions, in agreement with inclination differences noted in previous studies. The best estimates for palaeomagnetic inclination are the expected directions from the mean of virtual geomagnetic poles (VGPs) calculated using an iterative angular cut-off process. Predictions of ${\sigma _{\rm E}}$ and ${\sigma _{\rm N}}$ vary with latitude and are symmetric about the Equator. The N–S direction (${\sigma _{\rm N}}$) is always larger than E–W (${\sigma _{\rm E}}$), but the difference decreases from a maximum at the Equator to the poles, where ${\sigma _{\rm N}} = \ {\sigma _{\rm E}}$. A simplified GGP model is used to show that the parameter α (affecting variances in all Gauss coefficients) is positively correlated with ${\sigma _{\rm E}}$ and ${\sigma _{\rm N}}\ $ while the β parameter, the ratio of dipole to quadrupole family standard deviations, modifies the latitudinal dependence of ${\sigma _{\rm E}}$ and ${\sigma _{\rm N}}$. Experimental error in ${\sigma _{\rm E}}$ and ${\sigma _{\rm N}}$ can be accommodated using the common statistical parameters found in palaeomagnetic data sets, as ${\alpha _{95}}$ from site-mean directions. Predictions of simplified GGP models are compared with both numerical simulations and real data spanning the last 10 Ma. The latitudinal dependence of the proposed measures of PSV (${\sigma _{\rm E}}$ and ${\sigma _N}$) provide useful diagnostics for testing the validity of a GGP model. For the past 10 Ma the best-fitting GGP model with a mean GAD field set to $g_1^0 = \ - 18\ \mu T$ has α = 6.7 µT and β = 4.2. These new directional diagnostics will be used to investigate changes in overall geomagnetic field behaviour over other geological time intervals.

Tunable toroidal Fano resonance in the multiple split-ring resonators metamaterials

We investigate the tunable toroidal Fano resonance in the multiple split-ring resonators (SRRs) metamaterial. The toroidal Fano resonance is theoretically and experimentally demonstrated. The Fano resonance can be excited by introducing a big-SRR in the multiple small-SRRs. Fano resonance results from the mutual coupling between toroidal and magnetic dipoles. The Fano lineshape can be tuned by changing the size of big-SRR. Moreover, the authors discover that the direction of toroidal dipole also can be tuned by properly controlling the size of big-SRR. The strength of Fano resonance can be enhanced by introducing two small-SRRs. The double Fano resonances can be excited by tuning the size ratio between two small-SRRs. The structure provides more dielectric information of the analyte. In the design, by introducing two small-SRRs in the structure and using Fano resonance, the sensitivity has been improved. The two small-SRRs structure increases the sensitivity of the final design, up to two times compare to the one small-SRRs structure. The tunable toroidal Fano resonance offers the potential for application in the microwave and terahertz sensing.

Oligothiophene‐Based Phosphonates for Surface Modification of Ultraflat Transparent Conductive Oxides

AbstractThe self‐assembly of electroactive organic molecules on transparent conductive oxides is a versatile strategy to engineer the interfacial energy‐level alignment and to enhance charge carrier injection in optoelectronic devices. Via chemical grafting of an aromatic oligothiophene molecule by changing the position of the phosphonic acid anchoring group with respect to the organic moiety (terminal and internal), the direction of the main molecular dipole is changed, i.e., from parallel to perpendicular to the substrate, to study the molecular arrangement and electronic properties at the organic–inorganic interface. It is found that the observed work function increase cannot solely be predicted based on the calculated molecular dipole moment of the oligothiophene‐based phosphonates. In addition, charge transfer from the substrate to the molecule has to be taken into account. Molecular assembly and induced electronic changes are analogous for both indium‐tin oxide (ITO) and zinc oxide (ZnO), demonstrating the generality of the approach and highlighting the direct correlation between molecular coverage and electronic effects.

Rhodium-Catalyzed Highly Diastereo- and Enantioselective Synthesis of a Configurationally Stable S-Shaped Double Helicene-Like Molecule.

An S-shaped double helicene-like molecule (>99 % ee), possessing stable helical chirality, has been synthesized by the rhodium(I)/difluorphos complex-catalyzed highly diastereo- and enantioselective intramolecular double [2+2+2] cycloaddition of a 2-naphthol- and benzene-linked hexayne. The collision between two terminal naphthalene rings destabilizes the helical chirality of the S-shaped double helicene-like molecule, but the introduction of two additional fused benzene rings significantly increases the configurational stability. Thus, no epimerization and racemization were observed even at 100 °C. The enantiopure S-shaped double helicene-like molecule forms a trimer through the multiple C-H⋅⋅⋅π and C-H⋅⋅⋅O interactions in the solid-state. The trimers stack to form columnar packing structures, in which neighboring stacks have opposite dipole directions. The accumulation of helical structures in the same direction in the S-shaped double helicene-like molecule enhanced the chiroptical properties.

Rhodium‐Catalyzed Highly Diastereo‐ and Enantioselective Synthesis of a Configurationally Stable S‐Shaped Double Helicene‐Like Molecule

AbstractAn S‐shaped double helicene‐like molecule (>99 % ee), possessing stable helical chirality, has been synthesized by the rhodium(I)/difluorphos complex‐catalyzed highly diastereo‐ and enantioselective intramolecular double [2+2+2] cycloaddition of a 2‐naphthol‐ and benzene‐linked hexayne. The collision between two terminal naphthalene rings destabilizes the helical chirality of the S‐shaped double helicene‐like molecule, but the introduction of two additional fused benzene rings significantly increases the configurational stability. Thus, no epimerization and racemization were observed even at 100 °C. The enantiopure S‐shaped double helicene‐like molecule forms a trimer through the multiple C−H⋅⋅⋅π and C−H⋅⋅⋅O interactions in the solid‐state. The trimers stack to form columnar packing structures, in which neighboring stacks have opposite dipole directions. The accumulation of helical structures in the same direction in the S‐shaped double helicene‐like molecule enhanced the chiroptical properties.

Dissipative couplings in cavity magnonics

Cavity magnonics is an emerging field that studies the strong coupling between cavity photons and collective spin excitations such as magnons. This rapidly developing field connects some of the most exciting branches of modern physics, such as quantum information and quantum optics, with one of the oldest sciences on Earth, the magnetism. The past few years have seen a steady stream of exciting experiments that demonstrate novel magnon-based transducers and memories. Most of such cavity magnonic devices rely on coherent coupling that stems from the direct dipole–dipole interaction. Recently, a distinct dissipative magnon–photon coupling was discovered. In contrast to coherent coupling that leads to level repulsion between hybridized modes, dissipative coupling results in level attraction. It opens an avenue for engineering and harnessing losses in hybrid systems. This article gives a brief review of this new frontier. Experimental observations of level attraction are reviewed. Different microscopic mechanisms are compared. Based on such experimental and theoretical reviews, we present an outlook for developing open cavity systems by engineering and harnessing dissipative couplings.

Matching the Directions of Electric Fields from Triboelectric and Ferroelectric Charges in Nanogenerator Devices for Boosted Performance.

SummaryEmbedding additional ferroelectric dipoles in contacting polymer layers is known to enhance the performance of triboelectricnanogenerator (TENG) devices. However, the influence of dipoles formed between the triboelectric surface charges on two contacting ferroelectric films has been ignored in all relevant studies. We demonstrate that proper attention to the alignment of the distinct dipoles present between two contacting surfaces and in composite polymer/BaTiO3 ferroelectric films can lead to up to four times higher energy and power density output compared with cases when dipole arrangement is mismatched. For example, TENG device based on PVAc/BaTiO3 shows energy density increase from 32.4 μJ m−2 to 132.9 μJ m−2 when comparing devices with matched and mismatched dipoles. The presented strategy and understanding of resulting stronger electrostatic induction in the contacting layers enable the development of TENG devices with greatly enhanced properties.

Optimization of Shell packaging for cilium MEMS bionic vector hydrophone

Packaging of vector hydrophone influences its engineering application scope. However, the sensitivity of vector hydrophone is greatly reduced after packaging in previous works. Moreover, the vector hydrophone with dipole directivity has the problem of left-right ambiguity. To solve these problems, the shell packaging of cilium MEMS bionic vector hydrophone is optimized in terms of sound-transparent cap and the capability of underwater localization. A blue nitrile butadiene rubber is used as the material for the sound-transparent cap to solve the problem of poor sensitivity after packaging. And in order to solve the problem of left-right ambiguity of a single vector hydrophone, a piezoelectric ceramic tube is integrated into the shell to obtain sound pressure information. In this paper, the packaging process of optimized shell is introduced in detail. Then, the sensitivity test, directivity test and pressure-resisting test of optimized shell are finished. The testing results show that sensitivity of vector information part is increased average 5.6 dB after packaging. And the sensitivity curve depicts that the sensitivity increases 6 dB per octave in the working bandwidth in the range of 63−1000 Hz. Therefore, the optimized vector hydrophone shows a good performance in engineering application.

Two Numerical Methods for the 3D Anisotropic Propagation of Galactic Cosmic Rays

Abstract Conventional cosmic-ray propagation models usually assume an isotropic diffusion coefficient to account for the random deflection of cosmic rays by the turbulent interstellar magnetic field. Such models very successfully explain many observational phenomena related to the propagation of Galactic cosmic rays, such as broken power-law energy spectra, secondary-to-primary ratios, etc. However, the isotropic diffusion presupposition is facing severe challenges from recent observations. In particular, such observations on the large-scale anisotropy of TeV cosmic rays show that the dipole direction differs from the prediction of the conventional model. One possible reason is that the large-scale regular magnetic field, which leads to an anisotropic diffusion of cosmic rays, has not been included in the model provided by the public numerical packages. In this work, we propose two numerical schemes to solve the three-dimensional anisotropic transport equation: the pseudo-source method and Hundsdorfer–Verwer scheme. Both methods are verified by reproducing the measured B/C and proton spectrum and the radial variation of spectral index expected by former 2D simulation. As a demonstration of the prediction capability, dipole anisotropy is also calculated by a toy simulation with a rough magnetic field.

Fast neutrino flavor instability in the neutron-star convection layer of three-dimensional supernova models

Neutrinos from a supernova (SN) might undergo fast flavor conversions near the collapsed stellar core. We perform a detailed study of this intriguing possibility, analyzing time-dependent state-of-the-art 3D SN models of 9 and 20 Msun. Both models were computed with multi-D three-flavor neutrino transport based on a two-moment solver, and both exhibit the presence of the lepton-number emission self-sustained asymmetry (LESA). The transport solution does not provide the angular distributions of the neutrino fluxes, which are crucial to track the fast flavor instability. To overcome this limitation, we use a recently proposed approach based on the angular moments of the energy-integrated electron lepton-number distribution. With this method we find the possibility of fast neutrino flavor instability at radii <~20 km, which is well interior to the neutrinosphere. Our results confirm recent observations in a 2D SN model and in 2D/3D models with fixed matter background, which were computed with Boltzmann neutrino transport. However, the flavor unstable locations are not isolated points as discussed previously, but thin skins surrounding volumes where electron antineutrinos are more abundant than electron neutrinos. These volumes grow with time and appear first in the convective layer of the proto-neutron star (PNS), where a decreasing electron fraction (Ye) and high temperatures favor the occurrence of regions with negative neutrino chemical potential. Since Ye remains higher in the LESA dipole direction, where convective lepton-number transport out from the nonconvective PNS core slows down the deleptonization, flavor unstable conditions become more widespread in the opposite hemisphere. This interesting phenomenon deserves further investigation, since its impact on SN modeling and possible consequences for SN dynamics and neutrino observations are presently unclear. (abridged)

Conformational analysis of selected [2.2]heterophanes: A comparison of stereochemical switching via computational chemistry

Conformational switching of selected [2.2]heterophanes was investigated by computational chemistry. Analyses were carried out by various methods, including Conformational Search in HyperChem, and forced conformational transformations with Energy Profile in Spartan. Stable anti and syn conformers arising from flipping of aromatic rings within the molecules were observed. The activation energies of the ring flipping process, as well as dipole moments and directions, were obtained by molecular mechanics. The present work shows that simple computational techniques can be employed to screen certain compounds as potential candidates for molecular machinery. Thus, heterophanes demonstrated reversible shifts between two or more configurations which are energetically stable and have different electronic properties, constituting a basic requirement for possible applications as molecular switches.

Quantum Simulation of Non‐Perturbative Cavity QED with Trapped Ions

AbstractThe simulation of non‐perturbative cavity‐QED effects is discussed using systems of trapped ions. Specifically, the implementation of extended Dicke models with both collective dipole‐field and direct dipole–dipole interactions is addressed, which represent a minimal set of models for describing light–matter interactions in the ultrastrong and deep‐strong coupling regime. It is shown that this approach can be used in state‐of‐the‐art trapped ion setups to investigate excitation spectra or the transition between sub‐ and superradiant ground states, which are currently not accessible in any other physical system. The analysis also reveals the intrinsic difficulty of accessing this non‐perturbative regime with larger numbers of dipoles, which makes the simulation of many‐dipole cavity QED a particularly challenging test case for future quantum simulation platforms.

Two-year Cosmology Large Angular Scale Surveyor (CLASS) Observations: A First Detection of Atmospheric Circular Polarization at Q band

Abstract The Earth’s magnetic field induces Zeeman splitting of the magnetic dipole transitions of molecular oxygen in the atmosphere, which produces polarized emission in the millimeter-wave regime. This polarized emission is primarily circularly polarized and manifests as a foreground with a dipole-shaped sky pattern for polarization-sensitive ground-based cosmic microwave background experiments, such as the Cosmology Large Angular Scale Surveyor (CLASS), which is capable of measuring large angular scale circular polarization. Using atmospheric emission theory and radiative transfer formalisms, we model the expected amplitude and spatial distribution of this signal and evaluate the model for the CLASS observing site in the Atacama Desert of northern Chile. Then, using two years of observations at 32.°3 to 43.7 GHz from the CLASS Q-band telescope, we present a detection of this signal and compare the observed signal to that predicted by the model. We recover an angle between magnetic north and true north of −5.°5 ± 0.°6, which is consistent with the expectation of −5.°9 for the CLASS observing site. When comparing dipole sky patterns fit to both simulated and data-derived sky maps, the dipole directions match to within a degree, and the measured amplitudes match to within ∼20%.

A highlight effects generation model for translucent materials perception based on directional subsurface scattering

Usually the highlights can be calculated with the specular term of the bidirectional reflectance distribution functions developed for glossy or matte materials. However, as for the translucent materials, complex appearance could be caused by the scattering of light inside the medium. An efficient highlight generation model is presented to simulate the highlight effects on smooth or rough surfaces or around the boundaries of objects made from translucent materials. The presented model is derived from the directional dipole model approximation of the diffusive part of the bidirectional scattering surface reflectance distribution function. Unlike the previous specular reflection models, the presented model builds a relationship between the highlights and the scattered lights inside the medium by considering the refracted ray of the incident point and the ray toward the emergent point, which could represent the variation in fluence due to the internal scattering at the surface. By integrating a rendering process with the directional dipole model, the resulting highlight effects term could be represented in a similar way by the specular term of a bidirectional reflectance distribution function model. The number and the strength of the generated highlight pixels were compared among typical highlight generation models. It is demonstrated that the presented model could generate highlight effects at the appropriate positions and enhance the perceptual translucency of specific edge areas greatly.

Design and Optimization of Genetic Algorithm (GA) based High Gain and Directive CPW-Fed Slot Dipole Antenna for Wideband Applications

Genetic Algorithm (GA) is proposed in this paper for the design of a wide bandwidth, high gain and directive CPW-fed slot-dipole antenna. The proposed antenna is built on a FR4 substrate that is cheap and easy to produce. Genetic Algorithm is used to select parameters that reflect antenna geometry to achieve wider bandwidth and reduced return loss (parameter S11) and high gain values at resonant frequency. The antenna design shows a wide operating bandwidth of 1.4 GHz (simulated) and 1.3 GHz (measured) over the X-band, a return loss (S11) of -25.83 dB (simulated) and -23.08 (measured) and a gain and directivity of 5.61 dB (simulated) and 11.87 dB (simulated) at 10.5 GHz resonating frequencies. In this work, all simulations were performed using the ANSYS HFSS v14.0 software. A prototype antenna was produced and then characterized using VNA to validate the design. Measurement results were in good agreement with the results simulated using ANSYS HFSS.

Burying the Inverted Surface Dipole: Self-Assembled Monolayers Derived from Alkyl-Terminated Partially Fluorinated Alkanethiols

The direction and magnitude of surface dipoles directly affect the interfacial properties and can be tuned through molecular design. This article examines the effect of a hydrocarbon–fluorocarbon, ...

Structures, stabilities and piezoelectric properties of Janus gallium oxides and chalcogenides monolayers

Due to losing out-of-surface symmetry and the induced built-in dipole, two-dimensional (2D) Janus structures were believed to have various potential applications in the fields of piezoelectric devices, photocatalysis and electrochemical catalysis. In this work, 2D gallium oxides and chalcogenides (GaX) derived Janus monolayers Ga2XY (X/Y = O, S, Se, and Te) were designed. Our first-principles calculations showed that apart from Ga2OTe, all the monolayers are thermodynamically, dynamically and mechanically stable. These monolayers are demonstrated to be semiconductors with the band gaps in a wide range of 1.00–3.24 eV. The calculated in-plane piezoelectric coefficients of Janus monolayers (d11 = 3.09–5.67 pm V−1) are demonstrably enhanced with respect to the pristine monolayers (d11 = 0.41–3.04 pm V−1). Meanwhile, the yielding additional out-of-plane piezoelectric coefficients range from 0.11 to 0.34 pm V−1. Interestingly, O-participated Janus monolayers display distinctive properties: dipole direction flipping from O to S/Se, high stabilities and moderate direct-band-gaps. Particularly, Ga2OSe monolayer was found to have the largest piezoelectric coefficient of 5.67 pm V−1, which can be ascribed to the highly imbalanced charge distribution on O and Se as well as the largest bond length differences between Ga–O and Ga–Se. Our study revealed that the Janus Ga2XY monolayers, especially O-related systems, could be pretty promising as candidates in optoelectronic, piezoelectric sensors and energy conversion devices.