Near-field Coupling Effects Research Articles

A Novel Design Method for Wide-Angle Beam-Scanning Phased Arrays Using Near-Field Coupling Effect and Port Self-Decoupling Techniques

A Novel Design Method for Wide-Angle Beam-Scanning Phased Arrays Using Near-Field Coupling Effect and Port Self-Decoupling Techniques

Scattered beam control of encoded metasurface based on near-field coupling effects of elements

The coupling effect between the element structures of the traditional Huygens metasurface is easy to cause the efficiency of the designed functional devices to be reduced. In order to eliminate or reduce the coupling effect between the element structures, a border-type Huygens metasurface element structure is proposed. In order to confirm that the bounding element structure can significantly reduce the coupling effect, the near-field distribution and far-field properties of two Huygens metasurfaces with and without bounding are compared. Through comparative analysis, we find that the bounding Huygens element structure can significantly reduce the coupling effect between the element structures, and the far-field scattering angle is more consistent with the theoretical calculation value. In order to realize the free regulation of the far-field scattering angle of THz waves, we introduce the Fourier convolution principle in digital signal processing, and operate the element sequence of Huygens metasurface on the addition principle to realize the free regulation of scattered beams. In addition, we performed functional addition operations on the bounding and unbounding coding sequences. The bounding code structure can accurately achieve the synthesis of functions.

Manipulating multiple plasmon modes by coupling fields for broadband filtering in terahertz metamaterials

Multiple modes resonance provides the possibility of broadband filtering and has great potential applications in terahertz devices, including miniaturized spectrometers, hyperspectral imagers and optical switches in communication systems. However, it is difficult to further expand the bandwidth range due to the inability to stack an infinite number of resonant structures in a finite space. Here, an innovative method is reported for manipulating two localized surface plasmon polaritons (LSPP) modes by multiscale-coupled plasmonic fields to realize broadband filtering at terahertz (THz) frequencies. The interaction between two LSPP modes was verified theoretically and experimentally, exhibiting a prominent Rabi splitting and two peaks with high transmittance. Particularly, broadband filtering is accomplished by utilizing a double-layer structure that can be regarded as a cavity for inducing far-field interference. Experimental result demonstrates that the maximum transmission range of the bilayer metamaterial reaches 0.63 THz. Besides, the two wide bands can be integrated into one broadband through near-field coupling effects. The integration of strong coupling and far-field interference expands the transmission range of the double-layer metamaterial, further enhancing its capability for broadband filtering. This unique approach for manipulating multi-mode plasmonic coupling forges a convenient route for realizing broadband filtering.

Near-Field Coupling Effect Analysis of SMD Inductor Using 3D-EM Model

In this paper, we propose a methodology for analyzing the near-field coupling between two surface mount device (SMD) inductors using a 3-dimensional electromagnetic (3D-EM) model. To develop the 3D-EM model, we first constitute the equivalent circuit of the SMD inductor from the measured impedance and derive the loss tangent using circuit parameters. Secondly, the loss tangent using damped harmonic oscillator model is introduced to extract the effective permeability of core magnetic material in the SMD inductor. The optimization algorithm is used to compare the two loss tangents. Then the effective permeability is used in the magnetic material for the 3D-EM modeling of the SMD inductor. The validity of the proposed 3D-EM model is confirmed by comparing the impedance and S-parameters obtained from both measured and EM-simulated values for the two near-field coupled SMD inductors. Finally, the near-field coupling effects between the two adjacent SMD inductors are visualized in terms of coupling path visualization (CPV) using the proposed 3D-EM model, which demonstrates its usefulness for near-field coupling analysis.

Near-Field Electromagnetic Coupling Effects in Dimers of Three-Layer Metalorganic Nanoparticles with a J-Aggregate Dye Outer Shell

Near-Field Electromagnetic Coupling Effects in Dimers of Three-Layer Metalorganic Nanoparticles with a J-Aggregate Dye Outer Shell

EMI characteristics analysis and suppression technique of magnetic near-field coupling in power delivery adapter

With the continuous improvement of the power density of the power delivery (PD) adapter, switching frequency increases and volume decreases. The EMI issues caused by magnetic near-field coupling effects have become bottlenecks in the PD adapter’s EMI suppression. In this paper, the coupling characteristics of the magnetic field are deeply analyzed, and the equivalent circuit considering near-field coupling effects is derived. According to the electromagnetic field theory, the mathematical models of near-field coupling between transformer as well as power PCB circuits and the input plug are established. Based on this, the influence of the structure parameters of the input plug is studied. Finally, a new input plug loop structure is proposed, which can reduce the near-field coupling effects between the transformer as well as power PCB circuits and input plug. The experimental results verify the theoretical analysis to be correct and effective.

Near-Field Electromagnetic Coupling Effects in Optical Spectra of One-Dimensional and Two-Dimensional Arrays of Metal Nanoparticles

Near-Field Electromagnetic Coupling Effects in Optical Spectra of One-Dimensional and Two-Dimensional Arrays of Metal Nanoparticles

Monitoring allergic reaction to penicillin based on ultrasensitive detection of penicilloyl protein using alkyne response SERS immunosensor

The evaluation of true penicillin allergy is significant to reduce its occurrence and the overdiagnosis before anti-infective treatment. However, the currently available methods with high specificity still face the problem of low sensitivity, thereby easily leading to false negatives. Herein, an alkyne responsive surface-enhanced Raman scattering (SERS) immunosensor is reported for ultrasensitive detection of penicillin allergen penicilloyl protein (P-protein) by using Au-Ag alloy nanoparticles@(antibody + alkyne probe) (as SERS immunoprobe) together with Ag nanofilm modified by antibody (as SERS capture substrate). The SERS immunoassay integrates the interference-free Raman response of high wavenumber region (2212 cm−1) and specific capture antibody with high affinity to selectively recognize P-protein from complicated sample. Meanwhile, the target-induced near-field coupling effect between localized surface plasmon resonances of individual SERS immunoprobe and capture substrate enables the detection of P-protein as low as pg/mL level, and the limit of detection can reach 0.329 pg/mL that is about 6 orders of magnitude lower than the limit defined protein residue (causing penicillin allergy). With the ultrasensitivity and specific selectivity, the proposed SERS immunoassay platform can precisely evaluate the content of P-protein in blood sample or penicillin drugs. It will be a potential tool to monitor allergic reaction to penicillin and better understand the mechanism of penicillin hypersensitivity.

Plasmonic Au Nanoparticle Arrays for Monitoring Photopolymerization at the Nanoscale

The localized surface plasmon resonance (LSPR) of Au nanoparticles (NPs) was used to monitor photopolymerization at the nanoscale by in situ monitoring the optical response of AuNPs during the light-induced polymerization process. To show the interest of this approach, two configurations were used, which correspond to a resonant and a nonresonant excitation regime between the photopolymer and the AuNPs used as nanoprobes. We show that not only this method enables the progress monitoring of the photopolymerization reaction at the nanometric scale but also can highlight the near-field coupling effect responsible for the acceleration of the photoinduced reaction. This methodology appears very interesting to study the photoinduced nanofabrication processes of metal/polymer hybrid nanoparticles and more globally to study the photopolymerization reactions at the nanometric scale.

Super-Absorbers by Randomly Distributed Titanium Spheres

Electromagnetic wave absorbers have been widely investigated in these years. Nevertheless, the structural models were mainly based on the metal-insulator-metal metamaterials. In this work, we show a study on the achievement of ultra-broadband perfect absorption via a randomly distributed titanium spheres in the hydrogel layer. In the visible and near-infrared range ( $0.38-2.0\,\,\mu \text{m}$ ), the spectral average absorption reaches 93.6%. Taking the absorption efficiency above 90% into account, the bandwidth of the spectral window is 1386 nm. Moreover, the maximal absorption is even up to 98.9% in this open structure since there is no metal reflector back. In particular, these impressive absorption properties can be well maintained under complex electromagnetic surroundings, indicating the insensitive response to the polarization and incident angles. The particle plasmons and the near-field coupling effects for the adjacent spheres in-plane and out-of-plane are the main contributions for the ultra-broadband absorption. The absorption properties together with the simple structural characteristics including the flexible hydrogel layer will hold wide applications in the solar energy related technologies such as the solar thermal steam generation, desalination, macula-removing, and biological sterilization.

Double-Resonant Plasmonic Molecule: Enhanced Vibrational Induced Scattering Modulation

The present publication investigates the optical scattering behavior of an artificial near-field coupled double-resonant plasmonic molecule on a glass substrate formed by a linear arrangement of three gold nanobars. The aim of the proposed symmetrical structure arrangement is to achieve a significant increase in the feedback of optically induced coherent mechanical oscillations on the scattering cross-section. Based on the description of isolated dipole-like plasmonic nanostructures, it is shown how an increase of the modulation strength can be achieved by systematic utilization and modification of the inherent near-field coupling effect. It is shown which differences exist compared to an isolated plasmonic nanostructure, especially for the NIR spectral range. To the best of our knowledge, this is the first investigation showing the behavior of coherent acoustic vibrations in such artificial plasmonic molecules at an optical carrier wavelength of 1560 nm which is particularly interesting for applications in the field of optical communication.

Collective photonic response of high refractive index dielectric metasurfaces

Sub-wavelength periodic nanostructures give rise to interesting optical phenomena like effective refractive index, perfect absorption, cloaking, etc. However, such structures are usually metallic which results in high dissipative losses and limitations for use; therefore, dielectric nanostructures are increasingly considered as a strong alternative to plasmonic (metallic) materials. In this work, we show light-matter interaction in a high refractive index dielectric metasurface consisting of an array of cubic dielectric nano-structures made of very high refractive index material, Te in air, using computer modelling. We observe a distinct band-like structure in both transmission and reflection spectra resulting from the near-field coupling of the field modes from neighboring dielectric structures followed by a sharp peak in the transmission at higher frequencies. From the spatial distribution of the electric and magnetic fields and a detailed multipole analysis in both spherical harmonics and Cartesian components, the dominant resonant modes are identified to be electric and magnetic dipoles. Specifically at lower frequency (60 THz) a novel anapole-like state characterized by strong-suppression in reflection and absorption is observed, reported very recently as ‘lattice-invisibility’ state. Differently, at higher frequency (62 THz), strong absorption and near-zero far field scattering are observed, which combined with the field profiles and the multipole analysis of the near-fields indicate the excitation of an anapole. Notably the observed novel modes occur in the simple geometry of dielectric cubes and are a result of collective response of the metasurfaces. Periodicity of the cubic metasurface is shown as the significant material tuning parameter, allowing for the near-field and far-field coupling effects of anapole metasurface. More generally, our work is a contribution towards developing far-fetching applications based on metamaterials such as integrated devices and waveguides consisting of non-radiating modes.

Plasmonic wavy surface for ultrathin semiconductor black absorbers.

In this work, we propose and demonstrate a near-unity light absorber in the ultra-violet to near-infrared range (300-1100 nm) with the average efficiency up to 97.7%, suggesting the achievement of black absorber. The absorber consists of a wavy surface geometry, which is formed by the triple-layer of ITO (indium tin oxide)-Ge (germanium)-Cu (copper) films. Moreover, the minimal absorption is even above 90% in the wide wavelength range from 300 nm to 1015 nm, suggesting an ultra-broadband near-perfect absorption window covering the main operation range for the conventional semiconductors. Strong plasmonic resonances and the near-field coupling effects located in the spatially geometrical structure are the key contributions for the broadband absorption. The absorption properties can be well maintained during the tuning of the polarization and incident angles, indicating the high tolerance in complex electromagnetic surroundings. These findings pave new ways for achieving high-performance optoelectronic devices based on the light absorption over the full-spectrum energy gap range.

Interplay between Near-Field Radiative Coupling and Space-Charge Effects in a Microgap Thermionic Energy Converter under Fixed Heat Input

We investigate the performance of a micro gap vacuum thermionic energy converter considering the loss mechanisms due to the space charge effect and interelectrode radiative heat transfer. The dependencies of the space charge effect and near-field radiative heat exchange on the interelectrode distance are derived based on established theories. The electrode temperatures are determined by solving the steady-state energy balance equations in a numerical, iterative process and considering a constant energy flux input to the emitter. The resultant behaviour of the different mechanisms of energy flow from the electrodes is studied for a wide range of interelectrode distances, which provides new insights into the device operation. The maximum efficiency of the converter is obtained by optimizing the operating voltage and interelectrode distance. Considering the interplay between space charge and near-field radiative heat transfer, an optimal range is determined for the interelectrode distance. The optimal value of the distance and the lower limit of this range are found to be significantly higher than previously reported, where constant electrode temperatures had been assumed.

Toroidal dipolar bound state in the continuum and antiferromagnetic in asymmetric metasurface

The toroidal dipole (TD) with weak coupling to the electromagnetic fields promises tremendous capability in sensing, light absorption and optical nonlinearities. Here, we analyze the near-field coupling effects of an asymmetric all-dielectric metasurface with an array of high-index Mie-resonant dielectric tetramer cluster. Two distinct optical toroidal dipolar bound states in the continuum are identified from the asymmetric metasurface. One occurs at the internal gap of the tetramer cluster array (intra-cluster toroidal modes), and the other arises from two neighboring clusters (inter-cluster toroidal modes). Via control of the asymmetry of the cluster, the TD could transform from bound states in the continuum into leaky resonances with high-Q factors. The optical antiferromagnetic response could also be identified from the tetramer cluster arrays. The toroidal and antiferromagnetic effects come from the trapped modes with symmetry breaking. These robust responses of the asymmetric metasurface remain stable as the asymmetry degree increases and the polarization of the incident light changes. The proposed metasurface with efficient light–matter interaction serves as a platform for controlling and exploiting optical toroidal and antiferromagnetic excitations.

Dual-band isotropic metamaterial absorber based on near-field interaction in the Ku band

We numerically and experimentally investigate single-band and dual-band isotropic metamaterial absorbers (IMAs) based on metallic disks. By optimizing the diameter of the metallic disks and the thickness of the dielectric substrate, the single-band IMA is observed at 16.2 GHz with absorptivity of 97%. When adding one disk-pair to the structure, the dual-band IMA is obtained at 12.8 and 15.5 GHz due to the symmetry breaking. The physical mechanics is explained by near-field coupling effect and equivalent LC circuit model. The measurement results performed in the range 12–18 GHz show a good agreement with simulation and theoretical analysis. Our findings demonstrate a new approach to achieve dual-band and multi-band IMAs.

High-performance asymmetric optical transmission based on coupled complementary subwavelength gratings

Asymmetric transmission (AT) devices are fundamental elements for optical computing and information processing. We here propose an AT device consisting of a pair of coupled complementary subwavelength gratings. Different from previous works, asymmetric dielectric environment is employed for unidirectional excitation of surface plasmon polaritons (SPPs) and thus asymmetric optical transmission, and near-field coupling effect inherent in the coupled complementary structure is exploited to enhance forward transmission and AT behavior, and determine operation bandwidth as well. The influence of asymmetric dielectric environment, effect of vertical and lateral couplings, interactions of electric- and magnetic-dipole moments and the realization of Kerker conditions, are investigated in depth to unearth the AT mechanism and performance. High-performance AT with large forward transmittance of 0.96 and broad bandwidth of 174 nm is achieved at wavelength 1250 nm. Our work helps people to gain a better understanding of near-filed coupling effect in coupled complementary structures, expand their application fields, and it also offers an alternate way to high-performance AT devices.

Dual-band asymmetric optical transmission of both linearly and circularly polarized waves using bilayer coupled complementary chiral metasurface.

It is highly desirable to develop asymmetric transmission (AT) devices for both linearly and circularly polarized light. However, currently existing metamaterial-based AT devices require multi-step micro-nano fabrication processes and usually realize AT responses only for linearly or circularly polarized waves, not simultaneously for both. We here propose a dual-band AT device for both linearly and circularly polarized waves in the near-infrared region by using a bilayer coupled complementary chiral metasurface, which includes a half-gammadion-shape gold (Au) structural layer and its Babinet's complimentary copy. Unlike other multilayer AT devices working at optical frequencies, it takes less micro-nano fabrication steps. Besides, with the help of chirality and the inherent near-field coupling effect between the two complementary Au layers, the maximal AT parameters for linearly and circularly polarized waves can reach up to 0.45 and 0.56, respectively. The underlying mechanisms of dual-band AT responses are also investigated in depth from the perspectives of chirality and coupling effect. Our work offers a new and simple approach to high-performance AT devices, helps to better understand near-filed coupling effect in coupled complementary metasurfaces, and also expands their application fields.

Simulation and Analysis of Conductive Electromagnetic Interference in Near-Field Magnetic Coupling

Inductors, common-mode inductors, transformers and other magnetic components are important components of power converters. Their layout and wiring may affect the ability to suppress EMI noise. As a result of miniaturization and higher power density, the composition of power converter becomes more and more compact, which leads to the near-field coupling effect between components. In our study, the mechanism of near-field magnetic coupling between magnetic elements is analyzed, and the accuracy of the parameters of near-field magnetic coupling is further verified by experiments.

Narrow-band and high-contrast asymmetric transmission based on metal-metal-metal asymmetric gratings

A narrow-band and high-contrast asymmetric transmission (AT) device based on metal-metal-metal (M-M-M) asymmetric grating structure is proposed and investigated. Significantly distinct from previous reports, the upper and lower metallic silver (Ag) gratings are connected by a very thin metallic Ag film, without any dielectric spacer layer or subwavelength slit. Under forward incidence, the M-M-M structure supports efficient surface plasmon polaritons (SPPs) excitation and tunneling, more importantly, it promotes direct and thus high-efficiency SPPs decoupling, enabling high forward transmittance. While under backward incidence, the M-M-M structure offers not only high reflection by the Ag film but also a strong near-field coupling effect between the upper and lower gratings, which further suppresses backward transmittance, leading to near-zero backward transmittance. In addition, the M-M-M structure is optimized for narrow-band operation by employing grating groove depth effect and multiple interference effect. Numerical simulation results demonstrate that high-performance AT with high-quality factor (Q≈91), narrow-bandwidth (6.7 nm) and high contrast ratio is achieved, with forward transmittance of 0.72 and backward transmittance of 0.0015 at visible light (610 nm). Our work provides an alternative and simple way to high-performance AT devices.