Equivalent Electric Dipole Research Articles

Reconfigurable terahertz stretchable spoof surface plasmon polariton waveguide for filter applications

In this paper, a reconfigurable terahertz spoof surface plasmon polariton (SPP) waveguide is proposed on a stretchable polydimethylsiloxane (PDMS) substrate. The SPP unit incorporates a folded stub and a conventional V-shaped SPP groove, enhancing the equivalent capacitance and consequently reducing the cutoff frequency. The cutoff frequency of the proposed SPP unit can be tuned from 285 to 390 GHz with stretchable factors of 1 ∼ 1.2, thereby achieving a reconfigurable operating frequency. The horizontal dimension of the proposed SPP waveguide can be tuned from 6.36 mm to 7.12 mm. Moreover, the SPP waveguide can generate transmission continuous phase shifts of −30°, −60°, −90°, and −120° with stretchable factors of 1.05, 1.1, 1.15, and 1.2, respectively, in the 150–190 GHz band. Applying the characteristic mode theory, a split ring resonator (SRR) functions as the equivalent magnetic dipole, which remains unaffected by stretchable deformation. When loaded with four SRR cells, the proposed SPP waveguide generates a tunable passband with a fixed notched frequency at 193 GHz. Another stretchable SPP resonator serves as the equivalent electric dipole, operating from 284 GHz to 256 GHz in 1∼1.2 stretchable states. By loading three SPP resonators, the SPP waveguide can achieve a passband for the initial state, and a tunable stopband is introduced under 1.1 and 1.2 stretchable states. The proposed stretchable method provides a promising solution for planar terahertz components and systems with reconfigurable functions.

Localization and Identification of EMI Sources in Shielding Enclosures Based on a Two-Step Source Reconstruction Method

Localization and identification of unknown electromagnetic interference (EMI) sources in shielding enclosures is a great challenge due to the complex electromagnetic environment. In this work, a two-step source reconstruction method is proposed to address this issue. The actual EMI sources are initially modeled by equally distributed equivalent electric dipoles in the shielding enclosure. Effects of surrounding environments are rigorously incorporated using the numerical Green's function which bridges between the equivalent dipoles and planar scanned tangential magnetic near-field. Next, the initial equivalent sources are downsized via evaluating the contribution of each equivalent dipole. The parameters of remaining equivalent dipoles are updated by another source reconstruction process, in which additional equivalent magnetic dipoles are added to improve precision of the equivalent model. The locations and geometries of EMI sources in the shielding enclosure can be identified clearly in terms of the updated equivalent dipoles. Furthermore, the radiated emissions from individual EMI sources can be estimated accurately. The effectiveness of this approach is validated by representative numerical examples.

An Electrically Small Antenna With Quasi-Isotropic Coverage for Linearly Polarized Receiver

An electrically small antenna (ESA) for a linearly polarized (LP) receiver with quasi-isotropic coverage is developed and investigated by theoretical and experimental analyses. This antenna comprises two perpendicular positioned split-ring resonators (SRRs) and a fixed pad. Each SRR could generate a quasi-isotropic radiation with a gain difference of around 3 dB, which is attributed to the fields’ combination of the equivalent magnetic and electric dipoles. By regulating the antenna configuration of the orthogonal substrates, the developed antenna could also produce a quasi-isotropic coverage. At the same time, a circularly polarized characteristic in the maximum radiation direction can be achieved, which is exactly the direction of the largest polarization mismatch level (PML) value of the developed ESA for the LP receiver. The measured results agree well with the simulated ones, which demonstrates that this proposed antenna could realize a quasi-isotropic coverage in the whole space for the LP receiver with the measured gain difference of about 1.42 dB. This developed ESA reveals an electrically small size (0.19 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times0.15\,\,\times 0.15\lambda ^{3}$ </tex-math></inline-formula> , ka <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$=0.89$ </tex-math></inline-formula> ) and radiation efficiency of 91% with a fractional bandwidth of 1.6% at the center frequency of 748.5 MHz. Moreover, the measured and simulated realized gain differences of the quasi-isotropic ESA are, respectively, 3.33 and 2.77 dB, which demonstrates that the ESA has a very good uniform quasi-isotropic coverage of the whole space.

Optimum frequency model research and experimental verification for suppressing CaCO3 scaling in copper tubes by an electromagnetic field

The electromagnetic frequency is one of the most important parameters in electromagnetic scale inhibition research, and most of the previous studies on the optimal frequency range used experimental analysis. In this paper, a computational model for the optimal frequency of CaCO3 scaling in copper pipes under the action of electromagnetic fields is introduced. By establishing the equivalent electric dipole pipeline physical propagation model of the two-layer medium of the pipe wall and the water body, the vector magnetic potential in the water body is deduced by the mirror method, and the electromagnetic field expression of the water body in the pipe is derived. According to the electromagnetic energy relationship, the optimal electromagnetic frequency range is calculated to be 70–75 kHz. Finally, experiments were performed to analyze the effect of electromagnetic fields in different frequency ranges on the scaling of CaCO3 in copper pipes, and the obtained results verified the accuracy of the optimal frequency calculation model for CaCO3 scaling in copper pipes under the action of electromagnetic fields.

Efficient EDM-PO Method for the Scattering From Electrically Large Objects With the High-Order Impedance Boundary Condition

This work proposes an efficient hybrid method consisting of the efficient iterative method of moments–physical optics (EI-MoM-PO) and the equivalent dipole moment (EDM) with the high-order impedance boundary condition (HOIBC) to explore the electromagnetic scattering from the object with an isotropic or anisotropic surface coating. By introducing the HOIBC into the EDM method, the relationship between the equivalent electric and magnetic dipole moments is established. Therefore, the EDM method is extended to general cases. For the composite scattering from electrically large objects including MoM and PO regions, the EDM method is implemented to fill the MoM impedance matrix and to accelerate the evaluation of the coupling between the MoM and PO regions, which considerably improves the computing efficiency. The numerical results indicate that the proposed hybrid method allows for a substantial decrease in computation time. Also, they also agree well with the traditional finite element method, MoM, or MoM-PO method, which proves the validity of the proposed method.

Broadband Dielectric Resonator Antenna Array With Enhancement of Isolation and Front-to-Back Ratio for MIMO Application

Dielectric resonator antenna (DRA) arrays with enhanced isolation and front-to-back ratio (FBR) are proposed in this letter. Specifically, each DRA element is mounted on a small and separated ground plane; all the DRA elements (with small ground planes) share a large common ground plane. Each DRA element is excited by two differential probes at its edges. The DRA element in its <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\boldsymbol{TE}}_{{\boldsymbol{\delta }}11}^{\boldsymbol{x}}$</tex-math></inline-formula> mode is equivalent to a magnetic dipole. Meanwhile, the differential probes also excite electric current on the small grounds that can be viewed as an electric dipole. The equivalent magnetic and electric dipoles are orthogonal, behaving like a magnetoelectric dipole (ME-dipole). By properly adjusting the small ground planes’ size and their height above a sizeable common ground plane, a broadside unidirectional radiation pattern with low backward radiation is realized; moreover, the small ground structures can provide neutralization paths to counteract the original coupling waves. A <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$1 \times 4$</tex-math></inline-formula> single-polarized DRA array is designed, fabricated, and measured. Measurements align well with the simulations, demonstrating significant isolation and FBR improvements compared with the conventional DRA array. The proposed array has about 20% relative bandwidth.

Numerical simulation research of circular dichroism based on a catenary-shaped ultrathin metasurface

The circular dichroism (CD) produced by chiral materials in nature is usually very weak, and is not easy to be detected and analyzed in experiment. In this paper, a catenary-shaped chiral metasurface (CCMS) is proposed to achieve giant CD. The unit of the CCMS is composed of a metal–insulator–metal structure. Its upper and lower layers are composed of catenary-shaped metal elements. Under the excitation of left circularly polarized light and right circularly polarized light, the coupling modes of the equivalent electric dipole moments on the upper and lower metal surfaces are different, which leads to giant CD approaching 0.55. In addition, the CD properties can be tuned by structure parameters, such as the thickness of the intermediate dielectric layer, the length of the catenary-shaped metal elements, the twisted angle of the catenary-shaped metal surfaces of the upper and lower layers, and the period of the structure. By optimizing structure parameters, the maximum CD signal can reach 0.68. The present results would be helpful for designing chiral structures with enhanced CD signal.

Orientation Effect of the Electromagnetic Field Coupling for Device in a TEM Cell

In this article, the orientation effect of electromagnetic coupling for a device in a transverse electromagnetic (TEM) cell is explained in the frame of the model with intercoupling of equivalent electric and magnetic dipoles taken into account. Different from the widely used model, which predicts a half-circle period of the orientation effect, the proposed model predicts a full-circle period due to the introduced intercoupling. The intercoupling of the electric and magnetic field interaction inside the TEM cell and the full-circle period orientation effect is demonstrated first by simple straight and meander microstrip lines, which is then compared to a segment of an integrated circuit (IC). For the application of the proposed model to a complex device, a limited number of pairs of intercoupling electric and magnetic field dipoles can be introduced to predict the complicated orientation effect of a running large-scale IC in TEM cell measurement. The extracted dipoles are in good agreement with the near-field scanning results. The widely used Wilson model should be checked carefully in the application of field to line analysis.

Mutual Impedance Computation of a Waveguide Slot-fed Arbitrary Patch Using Combined Conventional Moment Method and Equivalent Electric and Magnetic Dipole Method

Mutual Impedance Computation of a Waveguide Slot-fed Arbitrary Patch Using Combined Conventional Moment Method and Equivalent Electric and Magnetic Dipole Method

A Linearly Polarized Low-Profile Complementary Antenna With Enhanced Bandwidth and Wide Broadside Beamwidth

A linearly polarized low-profile complementary antenna with enhanced bandwidth and wide broadside beamwidth is proposed. To realize a wide half-power beamwidth (HPBW), an equivalent electric dipole is introduced by the strip on the bottom layer at first. As seen, it not only contributes to the beamwidth enlargement in yz-plane due to the superposition of complementary sources but also introduces a lower resonance. Then, in order to obtain a broad bandwidth, a stub is crossed on the strip to make the lower resonance move up, meanwhile merging with the higher one. After this, a tapered aperture structure is employed to reduce the input inductance for a further bandwidth enhancement. Finally, antenna prototype of center frequency 5 GHz is fabricated and tested. As experimentally demonstrated, a wide HPBW up to 180° and a broad bandwidth around 30% are achieved under a low-profile about 0.035λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> as well as excellent gain flatness property, which outperforms most of the reported counterparts.

Estimating Electrically Small Targets Using Equivalent Dipoles and Sparse Processing

We develop an algorithm for localizing and estimating electrically small targets using sparse processing framework and vector electric-field measurements. To model the sources of electromagnetic field, we use equivalent electric and magnetic dipoles, assuming that only a few of them are sufficient for accurate source representation. To find the locations and complex amplitudes of the equivalent dipoles, we apply the l <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> regularization, which mitigates the inherent ill-posedness of the inverse problem. The method includes a normalization scheme which harmonizes imbalances in the system matrix and, consequently, improves the numerical stability of the method. In addition, we develop an algorithm for finding the optimal value of the regularization coefficient, based on the L-curve approach. The performance of the algorithm has been extensively tested using experimental data collected over a wide frequency bandwidth.

An efficient method for predicting the shielding effectiveness of an enclosure with multiple apertures

ABSTRACT An efficient analytical method has been proposed for predicting the shielding effectiveness (SE) and resonances of a metallic enclosure with multiple apertures against an external incident plane wave. First, the electromagnetic (EM) field distribution within the enclosure through multiple apertures is represented by the equivalent electric and magnetic dipole moments based on the Bethe’s theory for small aperture coupling. Then, the EM fields in the enclosure can be obtained by using the scalar wave functions, where the unknown coefficients in the functions are related to the equivalent dipole moments. Finally, the analytical method is applied to handle the enclosure with multiple apertures, and corresponding inclusions about the SE and resonances can be obtained. Compared with the full-wave simulation software CST over the frequency range of 0–2.5 GHz, the analytical method is proved to be accurate and effective, which consumes less time than the conventional numerical methods.

Inversion of the Equivalent Electric Dipole Moment of Ship’s Corrosion-Related Static Electric Field in Frequency Domain

When evaluating the ship’s underwater electric field stealth, the underwater electric potential or the underwater electric field is often used, but it is easily affected by the environment conditions. As a result, the evaluating accuracy is not high. To solve this problem, the equivalent electric dipole moment is used as the evaluating factor in this paper. Firstly, the method of inverting the equivalent electric dipole moment in the frequency domain is proposed. However, the limited measuring range will also lead to some errors based on the proposed method. As a result, we improve the proposed method by applying an integral correction which uses a standard dipole source. To test the effectiveness of this method, a simulation experiment is carried out, and the results show that the method has high inversion accuracy even in a low signal-to-noise ratio (SNR) environment. This method has provided a new technological approach for evaluating the ship’s corrosion-related static electric field.

Active Control and Biosensing Application of Induced Chirality between Symmetric Metal and Graphene Nanostructures

Induced circular dichroism (ICD) is found between plasmonic nanostructures and chiral molecules, where at least one of them is chiral. However, it is a great challenge to generate ICD only through achiral structures with the simple coupling model. Here, we demonstrate that ICD is approximately contributed by the cross-electromagnetic coupling between equivalent electric dipole moments and magnetic dipole moments for two achiral plasmon nanostructures. To prove electromagnetic couplings between different wavebands, graphene belts are introduced into plasmon nanostructures composing achiral metal-nanorods with graphene-nanobelt arrays (AMGAs). Results showed that ICD signals are achieved in a near-infrared band of metal resonance and a micron band of graphene resonance. Near-field charge distributions of AMGAs reveal the coupling effect between metal-nanorods and graphene-nanobelts. The handedness of AMGAs can be actively controlled by adjusting the Fermi levels of graphene-nanobelts; the strength and reson...

A novel stacked patch antenna with dual band and diverse pattern characteristics

AbstractA dual‐band patch antenna with diverse radiation patterns is presented in this paper. Circular patch and turnstile‐shaped patch are placed up and down to obtain dual band characteristic. Two surface current loops on the circular patch and turnstile‐shaped patch work like equivalent magnetic dipole. Four rectangle slots and four PIN diodes are loaded on the circular patch to readjust the surface current. Due to the changed current path, an equivalent electric dipole is introduced and two dipoles with phase difference of 180° are combined with each other to achieve directional radiation pattern. By switching the states of the diode to control the connection states of the rectangle slot on the circular patch, then a dual‐band antenna with diverse patterns is designed. The measured results show that the overlapping bandwidths of lower band f1 is 2.9% (2.42‐2.49 GHz) and over 2.9 dBi gain, the overlapping bandwidths of upper band f2 is 2.0% (4.87‐4.97 GHz) and over 4.8 dBi gain. The measured patterns of f1 show that the proposed antenna can not only omnidirectional radiation but also directional radiation with a scan angle of 90°. Meanwhile, the measured patterns of f2 remain omnidirectional radiation.

Design of Low-Cost, Flexible, Uniplanar, Electrically Small, Quasi-Isotropic Antenna

A low-cost, flexible, uniplanar, electrically small, quasi-isotropic antenna with considerably simple structure is proposed and experimentally investigated in this letter. The antenna is composed of a pair of driven striplines and a split-ring resonator (SRR) with two extended strips on the same side of the substrate. The equivalent electric and magnetic dipoles generated by the SRR could realize omnidirectional radiation patterns oriented to x - and y -axis, respectively, with nearly the same amplitude of the realized gains. With the orthogonalized radiation patterns between the equivalent electric and magnetic dipoles, the measured results, in good agreement with the simulation values, demonstrated that the antenna has a quasi-isotropic radiation pattern with maximum gain difference around 3 dB in the whole sphere, an electrically small size (0.154 × 0.154 × 0.0004 λ 3, ka = 0.68), and an overall efficiency 77%. Moreover, the performance characteristics of the antenna remains unchanged even when bending the antenna in different ways by conforming it on cylinders of various radii, proving its suitability for conformal applications.

Analytical theory on electromagnetic shielding effectiveness of infinite conductor plate with periodic aperture array under plane wave illumination

Penetration of a plane electromagnetic wave through the apertures on a perfectly conducting flat plate is a classical electromagnetic problem. In some practical applications like electromagnetic shielding, where only the fields far from the apertures are concerned and the aperture sizes are small compared with a wavelength, the role of apertures can be represented by the equivalent electric and magnetic dipoles located in the centers of the apertures. In principle, the penetration field can be expressed as the superposition of the radiation fields of the dipoles. However, the direct superposition leads to a double series with complex form and poor convergence. On the other hand, this problem may also be solved by full wave numerical simulations. Even so, finding analytical solutions is still desirable considering that it is clear in physical significance and easy to implement. In this paper, the analytical formula of the penetration fields are derived for both TE and TM polarization mode with different angles of incidence. The derivation is carried out firstly by averagely distributing each dipole moment within each periodic unit. As a result, the dipole array is replaced with a flat sheet with uniform magnetization and polarization intensity. Then, the equivalent surface current and charge distributions are obtained directly from the polarization intensity. Finally, the penetration fields are treated as the radiation fields of the surface sources. It is shown that the amplitude of the penetration field is proportional to aperture magnetic polarization coefficient and wave frequency, and it is inversely proportional to the area of a periodic unit. In regard to the effect of the incidence angle, the amplitude of the penetration field is proportional to the cosine of the incidence angle for TE polarization. However, for the TM polarization, the relationship is a little complicated due to the coexistence of electric and magnetic dipoles: the field is not rigorously inversely proportional to the cosine of the incidence angle due to the existence of a correction term involving both the polarization coefficient and the sine of the angle. The formula is used to calculate the shielding effectiveness for several different aperture shapes and different incidence angles. The results are in good agreement with those from the full wave simulation software.

메타표면 반사계수 계산을 위한 정사각형 패치의 전기 분극률 계산

The tangential electric polarizability of a electrically small square patch, which is commonly used in metasurfaces, is calculated using electric potential continuity. Since the potential at the patch surface is not uniform due to the equivalent electric dipole located at the center, there is a problem in that the polarizability is not uniquely defined. To obtain equivalent polarizability, the meshes in the analysis area are divided on the patch surface, and the equivalent polarizability is calculated by averaging the polarizabilities obtained at each point. The results of the proposed method, third-power series approximation, and experimental equations are compared and verified. Finally, the magnitude and phase of the reflection coefficient of patch metasurface calculated by generalized sheet transition conditions(GSTCs) are in good agreement with the HFSS simulation results.

Induced chirality in micron wave through electromagnetic coupling between chiral molecules and graphene nanostructures

The intricate mechanisms of plasmon-induced circular dichroism (CD) in a visible region are considered based on chemical and physical influences, in which a simple model and formulations are required. Here, we demonstrate theoretically that plasmon-induced CD is approximately contributed by the cross-interaction between equivalent electric and magnetic dipole moments for chiral molecules and plasmon nanostructures. To prove electromagnetic couplings, we introduce graphene into plasmon nanostructures and design asymmetrically inscribed graphene dual-rings arrays (IGDAs) with high-order hybrid modes. Results show that ultrahigh-order plasmon-induced CD signals are achieved in micron wave, which is easily detected by mature microwave technology. The maximum enhancement factor of induced CD could reach up to four orders of magnitude. In addition, an induced CD signal could be tuned only by varying the Fermi energy of IGDAs rather than by varying geometric dimensions. For different molecules, the electromagnetic couplings still hold. The results could be used to dynamically design chiral sensors in biology and chemistry.

Mechanism of equivalent electric dipole oscillation for high-order harmonic generation from grating-structured solid-surface by femtosecond laser pulse

We theoretically study high-order harmonic generation (HHG) from relativistically driven overdense plasma targets with rectangularly grating-structured surfaces by femtosecond laser pulses. Our particle-in-cell (PIC) simulations show that, under the conditions of low laser intensity and plasma density, the harmonics emit principally along small angles deviating from the target surface. Further investigation of the surface electron dynamics reveals that the electron bunches are formed by the interaction between the laser field and the target surface, giving rise to the oscillation of equivalent electric-dipole (OEED), which enhances specific harmonic orders. Our work helps understand the mechanism of harmonic emissions from grating targets and the distinction from the planar harmonic scheme.