Scattering of radiation by a system of point dipoles on a ring. Exact solution in two dimensions

Scattering of radiation by a system on N quasi-point like dipoles located on a circle (equidistantly in the polar angle) in two spatial dimensions is considered. The coupling of the dipoles is taken into account exactly. A closed-form expression for the electric fields at the points where the dipoles are located is given via the partial wave decomposition. Scattering and focusing properties are investigated for both dielectric and metallic scatterers.     

Band of Selective Transmission of Electromagnetic Radiation by an Absorbing Dielectric Layer

Equations for determining the frequency band near the frequency of selective reflectionless transmission of electromagnetic radiation by a layer of an absorbing dielectric which separates two nonabsorbing media with dissimilar optical densities have been obtained. The absorption band of the wave in the dielectric layer as a function of the dielectric properties and thickness of the layer and of the dielectric properties of the separated media has been evaluated.     

Measurement of electrostatic dipoles and net charge on particles suspended in air

Explanations of electrostatic behaviour of individual particulates have always invoked net electrostatic charge and neglected any fixed dipoles arising from nonuniform distribution of charge on their surface. Here for the first time, techniques are described to measure both net charge of each particle and its dipole moment by sampling, photography, and movement analysis of particles suspended in air. In this study, spherical dielectric particles were subjected to a non-uniform electric field (around a probe) and their trajectory was followed with a multi-flash high-speed video camera. These first results support the existence of fixed or “permanent” dipoles, on tribocharged particles.     

Mechanism analysis of BaTiO3 and polymer QAR composite humidity sensor

The humidity sensing mechanism of the composite material of nanometer barium titanate and polymer quaternary acrylic resin (QAR) is discussed in terms of d.c. property, dielectric loss and thermally stimulated depolarization current (TSDC). Various conducting carriers in different humidity ranges are identified by the direct current curves. The dielectric loss may be caused by the polarizations of dipole orientation and interface charge. The TSDC patterns show that the active energy and relaxation time of the dipoles in the composite materials take continuous, rather than discrete, values.     

Internal dipole radiation as a tool for particle identification

A numerical approach for the calculation of the internal dipole radiation associated with particles of arbitrary morphology is investigated by using the discrete-dipole approximation (DDA) method. The DDA and analytical solutions for the total radiated power and radiation pattern are compared in the case of spherical host particles. It is shown that the DDA can be quite accurate under the condition that m 相似文献   

High‐Quality‐Factor Mid‐Infrared Toroidal Excitation in Folded 3D Metamaterials

With unusual electromagnetic radiation properties and great application potentials, optical toroidal moments have received increasing interest in recent years. 3D metamaterials composed of split ring resonators with specific orientations in micro‐/nanoscale are a perfect choice for toroidal moment realization in optical frequency considering the excellent magnetic confinement and quality factor, which, unfortunately, are currently beyond the reach of existing micro‐/nanofabrication techniques. Here, a 3D toroidal metamaterial operating in mid‐infrared region constructed by metal patterns and dielectric frameworks is designed, by which high‐quality‐factor toroidal resonance is observed experimentally. The toroidal dipole excitation is confirmed numerically and further demonstrated by phase analysis. Furthermore, the far‐field radiation intensity of the excited toroidal dipoles can be adjusted to be predominant among other multipoles by just tuning the incident angle. The related processing method expands the capability of focused ion beam folding technologies greatly, especially in 3D metamaterial fabrication, showing great flexibility and nanoscale controllability on structure size, position, and orientation.     

Influence of dielectric substrate on the responsivity of microstrip dipole-antenna-coupled infrared microbolometers

We report on the influence of the dielectric substrate on the performance of microstrip dipole-antenna-coupled microbolometers. The location, the width, and the magnitude of the resonance of a printed dipole are altered when the dielectric substrate is backed by a ground plane. A thicker dielectric substrate shifts the antenna resonance toward shorter dipole lengths and leads to a stronger and slower detector response. The incorporation of an air layer into the antenna substrate further increases thermal impedance, leading to an even stronger response and shifting the antenna resonance toward longer dipole lengths.     

Modeling fluorescence collection from single molecules in microspheres: effects of position, orientation, and frequency

We present calculations of fluorescence from single molecules (modeled as damped oscillating dipoles) inside a dielectric sphere. For an excited molecule at an arbitrary position within the sphere we calculate the fluorescence intensity collected by an objective in some well-defined detection geometry. We find that, for the cases we model, integration over the emission linewidth of the molecule is essential for obtaining representative results. Effects such as dipole position and orientation, numerical aperture of the collection objective, sphere size, emission wavelength, and linewidth are examined. These results are applicable to single-molecule detection techniques employing microdroplets.     

Infrared and Optical Properties of Carbon Nanotube Dipole Antennas

The characteristics of armchair carbon nanotube dipole antennas are investigated in the infrared and optical regime. The analysis is based on a classical electromagnetic Halleacuten's-type integral equation, and an axial quantum mechanical conductance function for the tube. It is found that, within a certain frequency span in the GHz-THz range, finite-length carbon nanotube dipoles resonate at approximately integer multiples of one-half of a plasma wavelength. Outside of this range, current resonances are strongly damped. In the optical regime, antenna properties are strongly modulated by interband transitions. General antenna characteristics of finite-length carbon nanotube dipoles are presented, such as input impedance, current profile, gain, and efficiency, and radiation patterns are discussed     

Influence of orientation ratio on reverse erase-edge noise andtrack-edge dipole distribution

The cross-track profile of media noise is measured on a precision spinstand for oriented and nonoriented media. These data are correlated with magnetic force microscopy (MFM) images to determine the location of track-edge noise with high spatial resolution. A significant component of track-edge noise is located in a narrow band at the edge of bits recorded in opposition to the previously saturation-erased direction. This reverse erase-edge noise (REEN) increases as orientation ratio increases. The magnitude and distribution of REEN is consistent with a reverse-dc-erase mechanism. δM data indicate a greater influence of magnetostatic and/or exchange coupling for the oriented media. Together with larger on-track reverse-dc-erase noise and higher supralinear transition noise, these results suggest enhanced collective magnetization reversal for the oriented media relative to the nonoriented media. MFM images also reveal the presence of narrow magnetic-dipolar strips at the track edges. These dipolar strips are generated by cross-track components of the head field. The track-edge dipole moment decreases as orientation ratio increases due to preferential alignment of easy axes along the down-track direction. These dipoles contribute to base line shift and are not a significant source of media noise     

Interpretation of single-particle negative polarization at intermediate scattering angles

We study the interrelation of the internal field of irregular particles to the far-field scattering characteristics by modifying the internal field of dipole groups. In this paper, we concentrate on the longitudinal component, i.e., the internal-field component parallel to the incident wave vector. We use the discrete-dipole approximation to determine the internal field and switch off the longitudinal component from the dipoles that have the highest energy density above a preset cutoff value. We conclude that only a relatively small number of core dipoles, about 5% of all dipoles, contribute to the negative linear polarization at intermediate scattering angles. These core dipole groups are located at the forward part of the particles. The number of core dipoles in the group becomes greater as particle asphericity increases. We find that the interference between the scattered waves from the core dipole groups, which was studied previously for spherical particles, is preserved to a large extent for nonspherical particles.     

A Polarized Transfer Matrix for Electromagnetic Waves in Structured Media

Abstract

The study of electromagnetic systems with dielectric or magnetic properties that vary spatially on or below the scale set by the wavelength of the radiation considered is of interest both in the field of photonic band gap materials and in that of random multiple scattering media. A key calculation technique in both areas is the transfer matrix. We derive a new transfer matrix, written in the language of scattering between transverse polarized wave states. This could be used in either photonic band calculations or in disordered media calculations. We demonstrate the use of the new transfer matrix to describe transport through a layered random dielectric in the Rayleigh scattering regime. This problem has considerable similarities to that of non-interacting electrons in a one-dimensional random potential. A complete solution for one polarization can be given by the use of group theoretical results. The other polarization exhibits pronounced dipole effects which can easily be calculated to lowest order.     

Conductivity Measurements in Dissipative Media with Electrically Short Probes

In a dissipative medium, the radio-frequency input conductance of a linear dipole, whether a bare wire or an insulated wire with its terminals short-circuited to the medium, is simply related to the conductivity of that medium provided the electrical length of the dipole is short. Model measurements were made on dipoles in saline water of known conductivity to test the theory. The feasibility of deducing conductivity of the solution by using both types of antennas as probes was demonstrated. The technique has been utilized to evaluate the electrical conductivity of rock media from measurements on probes inserted into vertical drill holes. Examples are given of measurements variously to depths of 4000 ft. In one of the cases the rock type was (fractured) granite and, in another, anorthosite. In a geophysical crustal sense, data are typical of some near-surface or sedimentary rock conditions. Since such rock media are rarely uniform in their electrical characteristics, the deduced conductivity will be a gross average conductivity of that volume of the rock approximately within the antenna region of the probe.     

A Toroidal Metamaterial Switch

Toroidal dipole is a localized electromagnetic excitation that plays an important role in determining the fundamental properties of matter due to its unique potential to excite nearly nonradiating charge–current configuration. Toroidal dipoles are recently discovered in metamaterial systems where it is shown that these dipoles manifest as poloidal currents on the surface of a torus and are distinctly different from the traditional electric and magnetic dipoles. Here, an active toroidal metamaterial switch is demonstrated in which the toroidal dipole can be dynamically switched to the fundamental electric dipole or magnetic dipole, through selective inclusion of active elements in a hybrid metamolecule design. Active switching of nonradiating toroidal configuration into highly radiating electric and magnetic dipoles can have significant impact in controlling the electromagnetic excitations in free space and matter that can have potential applications in designing efficient lasers, sensors, filters, and modulators.     

Microwave detection and depth determination of disbonds in low-permittivity and low-loss thick sandwich composites

Nondestructive evaluation (NDE) of disbonded low-permittivity and low-loss dielectric multilayered composite media is of considerable interest in many applications. The ability of microwaves to penetrate inside dielectric materials makes microwave NDE techniques very suitable for interrogating structures made of multilayered dielectric composites. Additionally, the sensitivity of microwaves to the presence of dissimilar layers in such materials allows for accurate detection of a disbonded layer. In a multilayered composite, a disbond may occur between any two (or more) layers. The potential of utilizing microwave NDE techniques for the detection and depth estimation of disbonds in a thick sandwich composite is investigated. This study utilizes a theoretical model developed for investigating the interaction of microwave radiation from an open-ended rectangular waveguide sensor with ann-layer dielectric composite medium. The influence of the standoff distance between the sensor and the medium and the operating frequency on the sensitivity of disbond detection and depth estimation is studied to obtain an optimum set of parameters for enhanced detection sensitivity. Results of the theoretical study are presented with a discussion on the optimization process for a thick sandwich composite composed of 13 dielectric layers.     

Microwave absorbing properties of activated carbon-fiber felt dipole array/epoxy resin composites

Microwave absorbing properties of the composites containing activated carbon-fiber felt dipole arrays (ACFFDAs) were investigated. The results show that the absorbing performances of the composites containing ACFFDAs are affected greatly by the dimension parameters of the arrays, the resistance connecting the two arms and the materials of the dipoles. The absorption of the composites containing ACFFDAs presents anisotropy. When the dipoles are parallel to the incident electric field, the composites show better absorbing effect. The absorbing properties rise at first and then fall with increasing the resistance connecting arms or the space between dipoles. In this work, when the dipoles are parallel to the incident electric field, the composite obtains a reflection loss below −10 dB over 12.2 GHz and the minimum value reaches −32 dB. The bandwidth below −10 dB increases with increasing the length of the arms when the dipoles are parallel to the incident electric field. The bandwidth below −10 dB is 13.1 GHz when the length of the arms is 85 mm. Compared with copper plate, the dipole arrays whose arms are made of activated carbon-fiber felt exhibit better absorption properties.     

Broadband and mid-infrared absorber based on dielectric-thin metal film multilayers

We propose a periodic multilayer structure of dielectric and metal interlayers to achieve a near-perfect broadband absorber of mid-infrared radiation. We examine the influence of four factors on its performance: (1) the interlayer metal conductance, (2) the number of dielectric layers, (3) a nanopatterned antireflective layer, and (4) a reflective metallic bottom layer for backreflection. Absorption characteristics greater than 99% of the 300 K and 500 K blackbody spectra are found for the optimized structures. Incident angle and polarization dependence of the absorption spectra are examined. We also investigate the possibility of fabricating a nanopatterned antireflective layer to maximize absorption.     

Influences of d.c. and a.c. fields on the dielectric properties of relaxor ferroelectric ceramics

The influence of direct and alternating current fields on the dielectric properties of PMN-PZN-PT relaxor ferroelectric ceramics is examined. The reduction of both dielectric constant and dielectric loss by the applied d.c. bias field was demonstrated. An opposite trend was observed on the a.c. field dependence of dielectric response. The analysis revealed that d.c. bias reduces the degree of frequency dispersion, whereas a.c. drive increases it linearly. It is shown that the results obtained are consistent with the predictions of the glass model employing the concept of slow dipoles and frozen dipoles.