Incident Electromagnetic Field Research Articles

Observation of zero-transmission dip in a single-layer electric metamaterial with finite non-radiative loss

We propose a theory for realizing a zero-transmission dip in the transmission spectrum of a reflectionless single-layer metamaterial designed based on the Brewster effect by variably controlling the radiative loss of the metamaterial in response to the non-radiative loss. The radiative loss can be controlled while maintaining broadband zero reflection by varying the relationship between the orientation of the constituent meta-atoms and the incident electromagnetic fields. As a verification of the proposed theory, we design a reflectionless metamaterial by arranging meta-atoms that exhibit a simple electric dipole resonance in a two-dimensional lattice. The numerically calculated and experimentally measured transmission spectra of this metamaterial demonstrate that the radiative loss can be controlled by changing the arrangement of the meta-atoms without altering their structure, and that a zero-transmission dip can be observed for a certain arrangement of the meta-atoms. This study could lead to the development of material sensing, especially for lossy materials based on resonant metamaterials.

Research on the efficient EM modeling method from multilayered anisotropic medium-metal composite targets

The paper presents a high-frequency modeling approach tailored for the electromagnetic (EM) scattering characteristics from electrically large radar targets coated with multi-layered anisotropic mediums (MLAMs). The approach begins by deriving the plane-wave spectrum expression for the incident EM field within MLAMs. It then employs spectral domain full-wave analysis method (SDFWAM) to obtain an analytical representation of the scattering field, further leveraging saddle point evaluation (SPE) to derive asymptotic solutions in the spatial domain. By integrating principles of physical optics (PO) and the tangent plane approximation, the far-field scattering characteristics of target enveloped in the specified medium are efficiently delineated. Validations against standard structure and the Misty satellite model reveal the method's pronounced alignment with the method of moments – finite element method (MoM-FEM) hybrid numerical algorithm, underscoring its notable computational efficiency. Furthermore, in conjunction with scattering sources decomposition technique, the approach is applied to optimize the radar cross-section (RCS) of the Su-57 aircraft, achieving precise and intelligent RCS control at minimal material cost. In conclusion, this research offers pivotal technological and theoretical foundations for EM scattering prediction, stealth design, and performance assessment in radar target domains.

Photonic approach in stacked slabs having periodic holes for enhancing photocatalytic activities.

Photonic approaches can improve the efficiencies of photo-electrochemical devices towards CO2 reduction and fossil fuel-free societies. In a system consisting of stacked dielectric slabs having periodic holes with each slab coated by photocatalyst layers at both sides, immersed in water, we show that an incident electromagnetic field is effectively confined in the photocatalyst layers, resulting in the enhancement of the photocatalytic activities. In addition, the antireflection effect was engineered by adjusting the distances between the photonic crystal slabs. Numerical results reveal an enhancement factor of 3 for the absorption of electromagnetic fields at the operation frequency in the 3rd band of the dispersion diagram, compared to the bulk photocatalyst. Our system has the feature of periodic holes allowing the movement of reaction products. An analytical model is developed using the revised plane wave method and perturbation theory, which captures the trends observed in numerical results.

The effect of frequency (64-498MHz) on specific absorption rate adjacent to metallic orthopedic screws in MRI: A numerical simulation study.

The imaging of patients with implanted electrically-conductive devices via magnetic resonance imaging at ultra-high fields is hampered by uncertainties relating to the potential for inducing tissue heating adjacent to the implant due to coupling of energy from the incident electromagnetic field into the implant. Existing data in the peer-reviewed literature of comparisons across field strengths of tissue heating and its surrogate, the specific absorption rate (SAR), is scarce and contradictory, leading to further doubts pertaining to the safety of imaging patients with such devices. The radiofrequency-induced SAR adjacent to orthopedic screws of varying length and at frequencies of 64 to 498MHz was investigated via full-wave electromagnetic simulations, to provide an accurate comparison of SAR across MRI field strengths. Dipole antennas were used for RF transmission to achieve a uniform electric field tangential to the screws located 120mm above the antenna midpoints, embedded in a bone-mimicking material. The input power to the antennas was constrained to achieve the following targets without the screw present: (i) E=100V/m, (ii) B1 + =2 μT, and (iii) global-average-SAR=3.2W/kg. Simulations were performed with a spatial resolution of 0.2mm in the volume surrounding the screws, resulting in 76-137 MCells, noting the maximum 1g-averaged SAR value in each case. Simulations were repeated at 128 and 297MHz for screws embedded in muscle tissue. The peak SAR, occurring at the resonant screw length, substantially increased as the frequency decreased when the input power to the dipole antenna was constrained to achieve constant electric field in background tissue at the screws' locations. A similar pattern was observed when constraining input power to achieve constant B1 + and global-average-SAR. The dielectric properties of the tissue in which the screws were embedded dominated the SAR comparisons between 297 and 128MHz. The study design allowed for a direct comparison to be performed of SAR across frequencies and implant lengths without the confounding effect of variable incident electric field. Lower frequencies produced substantially larger SAR values for implants approaching the resonant length for the worst-case uniform incident electric field along the screws' length. The data may inform risk-benefit assessments for imaging patients with orthopedic implants at the new clinical field strength of 7Tesla.

Modeling scanning near-field optical photons scattered from an atomic force microscope for quantum metrology

Scattering scanning near-field optical microscopy (s-SNOM) is a promising technique for overcoming Abbe diffraction limit and substantially enhancing the spatial resolution in spectroscopic imaging. The s-SNOM works by exposing an atomic force microscope (AFM) tip to an optical electromagnetic (EM) field, while the tip is so close to a dielectric sample that the incident beam lies within the near-field regime and displays nonlinear behavior. We suggest replacing the incident EM field by photons generated by a single photon emitter, and propose a theoretical model for the suggested system by employing electric-dipole approximation, image theory, and perturbation theory. The count rate of the scattered photons from the AFM tip is extracted through a single photon detector, which contains information about electrical permittivity of the dielectric material beneath the tip. The permittivity of the sample can be extracted through spectroscopic setups. Our proposed scheme is useful for enhancing the spatial resolution of the modern quantum spectroscopy configurations that utilize entangled single photons.

Detailed analysis for temperature-dependent and temperature-independent Goos–Hänchen shift

In this work, we have presented the deep insight of Goos–Hänchen shift depending upon the temperature when a plane incident electromagnetic beam of light enters from a rare to a denser medium, keeping conditions of total internal reflection intact. A simple well known Drude’s model has been used for the purpose of thermal analysis of this shift. Through this model, the temperature-dependent permittivity of absorbing or complex medium has been found through the temperature-dependent plasma and damping wavelengths. Both transverse electric and magnetic incident electromagnetic fields have been considered in this regard. On an air–metal interface, firstly, Goos–Hänchen shift has been found when a temperature-independent dielectric function of a complex medium has been considered, and secondly, by analyzing the temperature-dependent dielectric function in the simplest way by using the stationary-phase method. This study is useful to understand the behavior of Goos–Hänchen shift around the temperature-dependency of the medium and how the angle of incidence impacts in this scenario.

Multi-element metasurface system for imaging in the near-infrared

Metasurfaces are optically thin 2D arrays of subwavelength scatterers that modify scalar and vector properties of incident electromagnetic fields. Metasurface lenses are of particular interest for imaging applications for their flat form factor, compatibility with CMOS fabrication processes, and potential for correcting aberrations with a small number of elements. We advance this capability by realizing a millimeter-diameter, polarization-independent metalens triplet system with chromatic aberration correction over the wavelength range of 1.30–1.60 μm and monochromatic aberration correction enabling a field of view of 50°.

Ultra-Broadband Solar Absorber and High-Efficiency Thermal Emitter from UV to Mid-Infrared Spectrum.

Solar energy is currently a very popular energy source because it is both clean and renewable. As a result, one of the main areas of research now is the investigation of solar absorbers with broad spectrum and high absorption efficiency. In this study, we create an absorber by superimposing three periodic Ti-Al2O3-Ti discs on a W-Ti-Al2O3 composite film structure. We evaluated the incident angle, structural components, and electromagnetic field distribution using the finite difference in time domain (FDTD) method in order to investigate the physical process by which the model achieves broadband absorption. We find that distinct wavelengths of tuned or resonant absorption may be produced by the Ti disk array and Al2O3 through near-field coupling, cavity-mode coupling, and plasmon resonance, all of which can effectively widen the absorption bandwidth. The findings indicate that the solar absorber's average absorption efficiency can range from 95.8% to 96% over the entire band range of 200 to 3100 nm, with the absorption bandwidth of 2811 nm (244-3055 nm) having the highest absorption rate. Additionally, the absorber only contains tungsten (W), titanium (Ti), and alumina (Al2O3), three materials with high melting points, which offers a strong assurance for the absorber's thermal stability. It also has a very high thermal radiation intensity, reaching a high radiation efficiency of 94.4% at 1000 K, and a weighted average absorption efficiency of 98.3% at AM1.5. Additionally, the incidence angle insensitivity of our suggested solar absorber is good (0-60°) and polarization independence is good (0-90°). These benefits enable a wide range of solar thermal photovoltaic applications for our absorber and offer numerous design options for the ideal absorber.

Fast Full-Wave Electromagnetic Forward Solver Based on Deep Conditional Convolutional Autoencoders

This letter proposes a novel deep learning (DL) based fast solver for the electromagnetic forward (EMF) process. This proposed fast full-wave solver for EMF process is designed based on the deep conditional convolutional autoencoder (DCCAE), consisting of a complex-valued deep convolutional encoder network and its corresponding complex-valued deep convolutional decoder network. The encoder network makes use of the input consisting of the incident electromagnetic (EM) wave and the contrast (permittivities) distribution of the target domain, while the corresponding decoder network predicts the total EM field illuminated by the input incident EM wave. The training of the proposed DCCAE solver for EMF is merely based on the simple synthetic dataset. Thanks to its strong approximation capability, the proposed DCCAE can realize the prediction of the EM field of target domain by using the incident EM field and the distribution of contrasts (permittivities). Therefore, compared with conventional methods, the EMF problem could be solved with higher accuracy and the significant reduced computation time. Numerical examples have illustrated the feasibility of the newly proposed DL-based EMF solver. The newly proposed DL-based EMF solver presents its excellent performance for the real-time online application.

Wideband, Wearable, Printed Monopole Antenna System for Integration into an Electromagnetic Radiation Evaluation Device

This paper describes the design steps carried out to prove the concept of a wideband monopole antenna system to be used in a wearable device conceived for the evaluation of electromagnetic field radiation. Such a device is envisaged to be integrated into protective vests worn by professional users in their working space environment as part of intelligent multi-risk protection. Initially, the main characteristics of a simple straight monopole are reviewed to serve as a reference. A modified octagonal monopole antenna element is introduced, and a two dual-linearly polarized configuration of such monopoles is designed, fabricated, and tested to be used in the frequency range of 0.7-3.5 GHz. The expected radiation characteristics (input reflection coefficient and isolation between vertically and horizontally polarized ports) are confirmed experimentally. The effects of a thick lossy foam substrate layer used to mitigate the presence of the metal shield, employed in the vest lining as a Faraday cage protection, are analyzed both by simulation and experimentally. Finally, electromagnetic simulations are carried out to confirm that a system of five dual-linearly polarized monopole elements located in the chest, shoulders, back, and helmet of the user can provide an adequate estimation of the incident electromagnetic field radiation.

Nonlinear Molecular Electronic Spectroscopy via MCTDH Quantum Dynamics: From Exact to Approximate Expressions.

We present an accurate and efficient approach to computing the linear and nonlinear optical spectroscopy of a closed quantum system subject to impulsive interactions with an incident electromagnetic field. It incorporates the effect of ultrafast nonadiabatic dynamics by means of explicit numerical propagation of the nuclear wave packet. The fundamental expressions for the evaluation of first- and higher-order response functions are recast in a general form that can be used with any quantum dynamics code capable of computing the overlap of nuclear wave packets evolving in different states. Here we present the evaluation of these expressions with the multiconfiguration time-dependent Hartree (MCTDH) method. Application is made to pyrene, excited to its lowest bright excited state S2 which exhibits a sub-100-fs nonadiabatic decay to a dark state S1. The system is described by a linear vibronic coupling Hamiltonian, parametrized with multiconfiguration electronic structure methods. We show that the ultrafast nonadiabatic dynamics can have a remarkable effect on the spectral line shapes that goes beyond simple lifetime broadening. Furthermore, a widely employed approximate expression based on the time scale separation of dephasing and population relaxation is recast in the same theoretical framework. Application to pyrene shows the range of validity of such approximations.

Adjustment of eccentricity and split angle for improved SERS and refractive index sensing of TiN nanodonuts

The unique refractory plasmonic properties and strong enhancement of the electric field within the inherent gap of titanium nitride (TiN) nanodonuts make them excellent candidates for surface-enhanced Raman scattering (SERS)- and refractive index (RI)-sensing applications. The eccentricity and split angles are critical parameters for tuning the localized surface plasmon resonance (LSPR) properties of the donuts, which were numerically investigated using the finite element method herein. We demonstrated that the proposed donuts provided efficient SERS and RI sensing substrates capable of working in regions ranging from ultraviolet (UV) to near-infrared (NIR). By adjusting the eccentricity and split angles, the corresponding optimized RI sensitivity and SERS enhancement factor reached 1,374 nm RIU−1 and 6.8 × 104, respectively. Moreover, the effects of both incident polarisation and electromagnetic (EM) field distributions on the LSPR properties were elucidated and discussed. This study provides new insights for understanding the LSPR properties of TiN nanoparticles and enables the rational design of efficient refractory plasmon-based SERS and RI-sensing substrates.

Shielding Effectiveness of a PC Case Using Three-Axis Electro-optic Sensors

This paper presents a measurement method for the shielding effectiveness (SE) of a personal computer (PC) case using three-axis electrooptic sensors and a vector network analyzer (VNA). The SE is obtained by taking the difference between the logarithmic values of the ratios of transmitted power to the input power for conditions with and without the PC case. The SE measurements versus the incident angle and polarization of incident electromagnetic fields are performed in a fully anechoic chamber (FAC) in the frequency range of 1 GHz to 4 GHz. A computer simulation is conducted to compare the experimental and numerical results. Additionally, we measured the SE of the PC case in a reverberation chamber (RC). The SE values of the PC case for the three axes in the case of FAC and RC are within 4 dB. The results show that this SE measurement technique, using electro-optic sensors and a VNA, is useful for both FAC and RC.

Atomic-Scale Defects Might Determine the Second Harmonic Generation from Plasmonic Graphene Nanostructures.

In this work, we theoretically investigate the impact of the atomic scale lattice imperfections of graphene nanoflakes on their nonlinear response enhanced by the resonance between an incident electromagnetic field and localized plasmon. As a case study, we address the second harmonic generation from graphene plasmonic nanoantennas of different symmetries with missing carbon atom vacancy defects in the honeycomb lattice. Using the many-body time-dependent density matrix approach, we find that one defect in the nanoflake comprising over five thousand carbon atoms can strongly impact the nonlinear hyperpolarizability and override the symmetry constraints. The effect reported here cannot be captured using the relaxation time approximation within the quantum or classical framework. Results obtained in this work have thus important implications for the design of nonlinear graphene devices.

Graphene-based metamaterial absorber for refractive index sensing applications in terahertz band

A tunable triple-band absorption-based refractive index (RI) sensor with a combined graphene pattern in the terahertz (THz) band has been proposed in this paper. The proposed sensor has the potential to be used for biosensing applications. Graphene split-ring and patch resonators are combined and used as a metamaterial element. The combined array structures are used to localize the incident electromagnetic field. In the proposed absorber, using the surface plasmon resonance (SPR) phenomenon of graphene, three narrow absorption peaks arise at frequencies of 4.66 THz, 6.035 THz, and 8.72 THz with absorption efficiencies of 99.2 %, 99 %, and 89 %, respectively. The overall performance and the position of the resonance frequencies are adjustable using an external DC-bias voltage applied to the graphene. The RI sensor is based on detecting changes in the RI of the sample under test, has a maximum sensitivity, Q-factor, and figure-of-merit (FoM) of 1791 (GHz/RIU), 32.354 and 7.046 RIU−1, respectively. Therefore, according to the mentioned features, which are obtained based on numerical simulations, the designed sensor is a good choice for medical and biosensing applications.

100 GSM paper as an SERS substrate for trace detection of pharmaceutical drugs in an aqueous medium

Surface-enhanced Raman spectroscopy (SERS) is a unique technique that allows us to detect samples in trace quantities. The spectral intensities of the characteristic Raman peaks of the analyte molecule are enhanced manifold in the presence of noble metal nanoparticles (NPs). The existence of NPs is necessary to couple the incident electromagnetic field with NPs through the localized surface plasmon resonance phenomenon, which primarily contributes to the enhancement of an SERS signal. The present work demonstrates the working of a paper-based SERS substrate to detect and quantify two pharmaceutical drugs—paracetamol and aspirin—in water. The proposed SERS substrate was obtained by drop-casting silver NPs over printing grade 100 grams per square meter (GSM) paper. 100 GSM denotes the class of paper where 100 grams of raw materials (cellulose) is used per square meter to manufacture the paper. The performance of the designed SERS substrate was initially evaluated with two Raman active samples—malachite green and rhodamine-6G. The applicability of the proposed SERS substrate was evaluated further through monitoring the Raman spectra of the two aforementioned pharmaceutical drugs in different field-collected water samples, thus establishing the reliability of the scheme in a real field environment.

An Analytical Solution of the Multiple Scattering from a Buried Medium Coated Conducting Sphere

Based on the image method and addition theorem of spherical vector wave functions, an analytical solution of the multiple scattering by a buried medium-coated conducting sphere is proposed in this paper. An iterative process to obtain the scattered electromagnetic field is discussed on the basis of the continuous boundary condition in the plane boundary, the medium inner and the outer surface of a coated conducting sphere, respectively. Applying an image method and the addition theorem of spherical vector wave functions, the scattering electromagnetic fields by the plane in a local coordinate system can be transformed into the globe coordinate, and they can be regarded as the next incident electromagnetic fields to the buried medium-coated conducting sphere. This process does not end until the scattering electrical field on the plane boundary is accurate enough. Numerical results are given and compared with commercial software FEKO, they coincide enough; the calculation times of the present method are very short compared to those of the software FEKO, and some discussion is given at the end of this paper.

Modeling the Performance Impact of Anisotropic Unit Cells Used in Additively Manufactured Luneburg Lenses

Additively manufactured graded index lenses, such as the Luneburg lens, often result in some degree of uniaxial anisotropy in the effective permittivity distribution. A uniaxially anisotropic Luneburg lens modifies the polarization state of an incident electromagnetic field, thus giving rise to a polarization mismatch at the receiving antenna. Using 3D finite element simulation, the lens focal point polarization is analyzed and a model that fits the simulation data is created. The model allows prediction of polarization mismatch loss given any incident field and any receiving antenna polarization without resorting to further time-consumingsimulations.

On the excitation and radiative decay rates of plasmonic nanoantennas

Abstract Plasmonic nanoantennas have the ability to confine and enhance incident electromagnetic fields into very sub-wavelength volumes, while at the same time efficiently radiating energy to the far-field. These properties have allowed plasmonic nanoantennas to be extensively used for exciting quantum emitters—such as molecules and quantum dots—and also for the extraction of photons from them for measurements in the far-field. Due to electromagnetic reciprocity, it is expected that plasmonic nanoantennas radiate energy as efficiently as an external source can couple energy to them. In this paper, we adopt a multipole expansion (Mie theory) and numerical simulations to show that although reciprocity holds, certain plasmonic antennas radiate energy much more efficiently than one can couple energy into them. This work paves the way towards designing plasmonic antennas with specific properties for applications where the near-to-far-field relationship is of high significance, such as: surface-enhanced Raman spectroscopy, strong coupling at room temperature, and the engineering of quantum states in nanoplasmonic devices.

Induced Optical Bistability in Small Metal and Metal Coated Particles with Nonlinear Dielectric Functions

The theoretical and numerical study of the enhancement of the amplitude of the incident electromagnetic radiation in small metal ellipsoidal particles and spherical dielectric particles covered by a metal shell with nonlinear dielectric functions is carried out. If the frequency of the external radiation approaches the frequency of surface plasmons of a metal, the local field in the particle considerably increases. At intense incident electromagnetic fields (laser radiation), it is necessary to consider the nonlinear part of the dielectric functions of a metal and a dielectric. This results in the induced optical bistability (IOB) when one value of the amplitude of the incident field initiates three values of the local field in a particle. The domains of IOB are specified in the case where the radiation wavelength is much larger than the typical size of particles. The range of external fields and the IOB frequency are specified. A decrease of the IOB domain and an increase of the critical fields with increase in the damping of plasmon vibrations are discussed. The results of numerical computations for typical small silver particles are presented graphically.