TM Waves Research Articles

Visible and NIR transparent broadband microwave absorption metamaterial based on silver nanowires

In this study, a visible and near infrared (NIR) transparent and broadband microwave metamaterials absorber based on resistive silver nanowires (AgNW) films is designed and fabricated. The metamaterial unit consists of a concentric annular resonant pattern, a continuous conductive AgNW film and a transparent polymer frame. By using different types of support frames, the absorber can switch between rigidity and flexibility. The absorber has over 90% broadband microwave absorption from 4.1 to 18.2 GHz with 75% visible transparency and 66% NIR transparency. The absorber is polarization insensitive and can keep efficient absorption of TM or TE waves with an oblique incidence angle less than 30°. The radar cross section (RCS) of the absorber is reduced to more than 10 dB, covering all reflection angles and matching the absorption bandwidth range. Compared with traditional transparent microwave absorber (TMA) with indium tin oxide (ITO), the TMA in this work, specifically with high transparent in NIR has a great application in transparent electromagnetic windows of near infrared hyperspectral sensors and optical/laser seekers.

Tunable dual-band linear-to-circular polarization conversion based on the electromagnetically induced transparency utilizing the graphene metamaterial

A tunable dual-band linear-to-circular polarization conversion (LTCPC) related to electromagnetically induced transparency (EIT) is theoretically proposed by employing the graphene metamaterial in the terahertz (THz) regime. Since the electric resonance (bright mode) and the magnetic resonance (quasi-dark mode) for the x - and y -polarized (TM and TE) waves are mutually coupled, the EIT behavior is realized due to the destructive interference. Two transparent EIT windows have emerged in 1.452–1.661 THz and 1.348–1.683 THz when the TM and TE waves are incidents. The corresponding values of the maximum group delay and group index respectively are 225 ps, 162 ps, 1636, and 1177. The LTCPC is achieved at 1.432 THz and 1.676 THz when the graphene does not exist. While the graphene is introduced, the LTCPC is dynamically adjustable by controlling the Fermi energy ( E f ) of the graphene. The optimal ARs can dynamically change between 1.438 (1.689) THz and 1.452 (1.696) THz while the E f changes from 0.1 eV to 0.9 eV. A theoretical investigation of two-oscillator model further confirms the effectiveness and consistency of the simulation results. The presented metamaterial with a thickness of subwavelength and high transparency for the electromagnetic waves opens a new path to the applications in beam steering and polarization controls. • The dual-band linear-to-circular PC of EIT phenomenon can be simultaneously realized. • The structure is equipped with graphene which can adjust the EIT behavior and circular polarization features. • The presented structure is great transparency for the EM wave, and its thickness is subwavelength. • The proposed structure provides a new idea to manipulate the polarization state of the EM wave. • The device is stable for the circular polarization feature within 10°.

Photon Spectra of a Bragg Microresonator with Bigyrotropic Filling

In this article, we have obtained the transmission spectra of a microresonator structure with Bragg mirrors, the working cavity of which is filled with a magnetically active finely layered ferrite-semiconductor structure with material parameters controlled by an external magnetic field. It is shown that a change in the external field and the size of the cavity (filling layer thickness) provokes a controlled rearrangement of the transmission spectrum of TM and TE waves. The polarization characteristics of the microcavity, their dependence on the external field, and the ratio of the thicknesses of the layers that make up the period of the ferrite-semiconductor structure are investigated.

Design and analysis of a wideband and wide angle 3D metamaterial absorber

In this paper, we proposed a three-dimensional (3D) metamaterial absorber joint by lightweight 3D grid structure and traditional magnetic materials, which can achieve wideband and wide-angle perfect absorption at 5–20 GHz. By simulation, the broadband absorption remained almost 90% from 0° to 80° for TM wave. The surface current and power loss distributions were investigated to interpret the physical mechanism of wideband and wide-angle absorption. The broadband and wide-angle absorption were derived from magnetic and electric resonances between the top resistive film, background plane and magnetic loss of magnetic materials. The results proved that different layers of the proposed absorber play different loss roles, and finally contributed to the wideband and wide-angle absorption. The polarization insensitive stability of the proposed absorber was also demonstrated at different polarized angles. The present study provided a new design to achieve a polarization insensitive, wideband and wide-angle absorber. Moreover, the structure absorber has potential applications in other fields, including the solar cell, imaging and detection etc.

Achieving polarization control by utilizing electromagnetically induced transparency based on metasurface

In this study, a design of transmissive linear-to-circular polarization conversion (LCPC) related to electromagnetically induced transparency (EIT) by arranging four sets of asymmetric resonators on a metasurface in a cross-shaped distribution is theoretically reported in the terahertz (THz) regime. It has numerically demonstrated that the bright modes and quasi-dark modes can also be mutually coupled when the x-polarized (TM) and y-polarized (TE) waves are incidents, resulting in a famous EIT phenomenon. Subsequently, when the direction of the electric fields of the electromagnetic (EM) waves are incident along the x-axis with an angle of 45°, the electric fields can be decomposed into the x- and y-directions. At this time, the corresponding amplitude and phase meet the conditions of the LCPC. Furthermore, for the TM and TE waves, the values of the maximum transmission coefficients respectively reach up to 0.910 at 1.384 THz and 0.890 at 1.277 THz. Correspondingly, two brand-new bright transparent windows are located in 1.276-1.454 THz for the TM waves and 1.206-1.373 THz for the TE waves. Concurrently, the band of the maximum 3 dB axial ratio is obtained from 1.308 THz to 1.343 THz with a relative bandwidth of 3%.

Graphene-based ultra-wideband absorber for terahertz applications using hexagonal split ring resonators

In this paper, a hexagonal split ring ultra-wideband absorber is proposed at THz frequency. The proposed structure consists of four graphene based hexagonal split rings, a dielectric substrate and graphene layer at the bottom. The proposed absorber achieves an ultra-wideband absorption characteristics from 0.95 THz to 2.96 THz with percentage bandwidth of 102.8% and bandwidth of 2.1THz with absorptivity beyond 90%. Also, 100% absorption is achieved from 2.07 to 2.33 THz making this unique feature for THz applications. Ultra-wideband response is mainly resulted because of overlapping of strong Electromagnetic (EM) resonance of the four split rings. The modes generated within the graphene split rings are merged for achieving ultra wide band response. Furthermore, the proposed absorber is polarization insensitive because of symmetry geometry and also exhibits absorption greater than 90% for incidence angle up to 75° for both TE and TM waves. In addition, tunability is achieved by varying the graphene chemical potential. These features make the proposed metal free absorber useful for terahertz applications and future nanoscale systems. The proposed absorber shows narrow absorption characteristics for higher graphene chemical potential values which can also be utilized for sensor applications.

Bound states in the continuum in metal–dielectric photonic crystal with a birefringent defect

By using the difference of the band structure for the TE and TM waves in the metal–dielectric photonic crystals beyond the light cone and the birefringence of the anisotropic crystal, a one-dimensional photonic system is constructed to realize the bound states in the continuum (BICs). In addition to the BICs arising from the polarization incompatibility, the Friedrich–Wintgen BICs are also achieved when the leaking TM wave is eliminated due to the destructive interference of its ordinary and extraordinary wave components in the anisotropic crystal. A modified scheme favorable for practical application is also proposed. This scheme for BICs may help to suppress the radiation loss in the metal–dielectric photonic crystal systems.

Smile face array: Generating oblique incident and front output vortex beam for both TE and TM waves

A single layer reflective array is designed to generate orbital angular momentum (OAM) beam at microwave frequency. The unit cell of this design is smile face shape distributed over a planar surface. Phase modulation can be realised by changing the size of each unit cell, with very low variation in reflection amplitude. By careful design, oblique incident can be obtained, reducing feed blockage to the output beam. The direction of the output beam can also be intendedly designed. In this work, the front output is chosen as a demonstrative example. In addition, the input beam can be either TE or TM wave, enable dual-mode operation. Furthermore, it is flexible to design the topological mode of the output OAM. The smile array is developed by cutting slots on circular patch array to produce perturbation on TE and TM waves, so that the difference in TE and TM incidence is reduced. As an instance, the topological modes of l = (−2, −1, 1, 2) are simulated, and the mode l = 1 is fabricated and measured. Measurements are conducted for both near field and far field. The measured results show good agreement with the simulated ones, indicating that this dual mode design works satisfactorily when oblique feed is used.

Tunable photonic bandgap and reflection phase shift properties of 1D binary photonic crystal consisting of double negative and magnetic cold plasma materials

In this manuscript, by using alternate layers of double negative and magnetic cold plasma materials, we have studied the reflection and reflection phase shift properties of 1D binary photonic crystals. The simulations of the proposed work have been carried out by using the transfer matrix method with the help of MATLAB software. It has been found that the combination of the angle of incidence and external magnetic field under both right hand polarized and left handed polarized configurations can be used for right and left tuning of photonic bandgap (PBG) of the proposed structure under consideration. Under the aforementioned circumstances, the reflection phase shift corresponding to TE and TM waves can be smoothly switched between 0 to π and –π to 0, respectively, across PBGs of the proposed structure. The variation in external magnetic field values from 0 to 6 T and angle of incidence from 0° to 80° can be used for precise tuning of PBG and reflection phase shift between –π and π depending upon TM and TE polarization cases, respectively. This study may open a new gateway for designing externally tunable microwave devices like single to multichannel band-stop filters, buffers that can hold data temporarily, tunable wave plates, and tunable phase retarders.

Switchable tri-function terahertz metasurface based on polarization vanadium dioxide and photosensitive silicon.

A terahertz switchable metasurface with the function of absorption and polarization conversion is proposed. It consists of metal pattern layer - dielectric layer - VO2 layer - dielectric layer - metal pattern layer, and the photosensitive silicon is embedded in the metal pattern. When VO2 is in insulated state, the metasurface behaves as a linear polarization converter. The polarization conversion rate (PCR) is more than 90% at two frequency bands of 1.64 THz ∼ 1.91 THz and 2.35 THz ∼ 2.75 THz. The polarization converter has good asymmetric transmission ability. Moreover, the polarization conversion performance can be dynamically controlled by changing the conductivity of the photosensitive silicon. When VO2 is in metallic state, the metasurface becomes a terahertz bidirectional absorber, which exhibits different absorption properties under TE and TM waves with the maximum absorptance reaching to 100%. In addition, the absorption of TE and TM terahertz waves can be controlled at the specific frequency by changing the conductivity of photosensitive silicon. We also explore the application of dynamic control of polarization waves in the near-field image display.

Alternative modification of KBM for solving equations of TE wave spreading in depth of kerr substarte with linear absorbtion

K8M method, specialy modified for solving a pair of first order differential equations for TM wave spreading in depth of kerr substrate with linear absorbtion. is used to solve the same problem in the case of TE polarization. Solution, obtained by this alternative modification of KBM. is in full agreement with the solution to Helmgolts's equation, previously found by another modification of KBM. It is shown that the one of asymptotic series obtained with the method is convergent.

Распространение электромагнитных ТМ волн в нелинейной подложке с линейным поглощением

The scheme used in asymptotical methods of Krilov- Bogolubov-Mytropolsky is modified to solve a set of two Maxwell's equations in propogation problem of stationary optical TM waves in nonlinear substrate with linear absorption. Simplicity of structures of recurrent calculations affords us to easily obtain solution accurate to enough high order of small parameter.

Хоёр атомт бодисоос тогтсон шугаман бус нимгэн илтсээс гэрэл сарних бодлогын формаль шийд

Formal solution of Maxwell equations for stationary TE and TM wave in nonlinear thin film of two lewel atoms are obtained. Parameter domains of possible wave regims are estabilished.

Broadband refractive index sensor based on localized surface plasmon for highly sensitive detection of fluid pressure

Localized surface plasmon resonance (LSPR) in gold (Au) nanoparticles is the research hotspot in various fields, due to its high chemical and physical stability, ease of preparation and multiple optical properties. However, the anisotropic response to polarized light of LSPR has been rarely studied. Here, we report optical refractive index sensors based on the polarization sensitive response of LSPR in gold nanoparticles, and its application in the highly sensitive detection of fluid species and hydraulic pressure. The polarization-sensitive absorption characteristics of the interfacial nanoparticles rendering it different absorption properties for TM and TE mode waves under the condition of total reflection, which is also strongly affected by the refractive index of medium n2 in contact with it. On this basis, the refractive index sensor based on LSPR in gold nanoparticles is successfully realized. In addition, the refractive index sensor features broadband response (from 200 to 1000 nm) in a wide range of incident angle δ (from −10° to 25°), exhibiting great application potential in various scenarios. To evaluate the practical applicability of the proposed sensor, we constructed an optical refractive index sensing system that can distinguish between liquid species and accurately detect hydraulic pressure in real time.

Dual-directional group delays during optical topological transitions in black phosphorus-based asymmetric hyperbolic metamaterials.

We theoretically study the optical properties of TM waves when their magnetic field direction is perpendicular to the armchair and zigzag optical axes of black phosphorus, respectively. It is found that hyperbolic dispersion and elliptic dispersion coexist in periodically arranged black phosphorus multilayers. Interestingly, by tilting the symmetric multilayers to be asymmetric, the elliptical part of the original two dispersions disappears as the wavelength increases. As such only the hyperbolic dispersion remains, showing an optical topological transition. In the region of the topological transition, a large transmitted group delay (3ps) and a reflected group delay (0.2ps) of the TM waves occurs simultaneously. The corresponding group velocities are slowed down to approximately c/1000 and c/100 (c is the speed of light in a vacuum), respectively. This dual-directional group delays significantly increase the wave-matter interaction so that nonreciprocal perfect absorptions can be realized in the mid-infrared band. Such asymmetrical black phosphorus hyperbolic metamaterials can be applied to the directional, tunable, and nonreciprocal perfect absorbers and also to devices based on strong wave-matter interactions.

Дважды отрицательные среды на основе антиферромагнитных полупроводников для терагерцевого диапазона частот

The paper presents the results of a theoretical study of the dispersion characteristics of electromagnetic waves (EMW) existing in a transversely magnetized antiferromagnetic (AFM) semiconductor with loss. An AFM semiconductor is an infinite bi-gyrotropic medium, the effective material parameters of which are twice negative in several frequency ranges. It was found that these frequency regions are in the terahertz range and there are four backward EMEs in them, two of which are TE waves, and the other two are TM waves.

Double negative media based on antiferromagnetic semiconductors for the terahertz frequency range

The paper presents the results of a theoretical study of the dispersion characteristics of electromagnetic waves (EMW) existing in a transversely magnetized antiferromagnetic (AFM) semiconductor with loss. An AFM semiconductor is an infinite bi-gyrotropic medium, the effective material parameters of which are twice negative in several frequency ranges. It was found that these frequency bands are in the terahertz range, and there are four backward EMEs in them, two of which are TE waves, and the other two are TM waves. Keywords: left-handed media, antiferromagnets, semiconductors, spin waves.

Focusing of the surface plasmon wave on the nanoapex of a scanning metal microtip near a plane-layered structure

A generalized method of mirror reflections of electrostatics for a point charge located near a flat-layered structure is formulated and proved. The method is generalized to the case of an arbitrary system of charges. It is shown in detail how to apply the obtained method to finding the focal distribution of the electric field in the vicinity of the nanoapex of a metal micropoint located near the flat-layered structure, which is obtained when a surface plasmon TM wave converges to the nanoapex. The penetration of the field into the area of the surface layer of the flat-layered structure (photoresist) with a size of the order of the tip rounding radius is demonstrated. Keywords: nanofocusing, surface plasmons, optical sensors.

Фокусировка поверхностной плазмонной волны на нановершине сканирующего металлического микроострия у плоскослоистой структуры

A generalized method of mirror reflections of electrostatics for a point charge located near a flat-layered structure is formulated and proved. The method is generalized to the case of an arbitrary system of charges. It is shown in detail how to apply the obtained method to finding the focal distribution of the electric field in the vicinity of the nanoapex of a metal micropoint located near the flat-layered structure, which is obtained when a surface plasmon TM wave converges to the nanoapex. The penetration of the field into the area of the surface layer of the flat-layered structure (photoresist) with a size of the order of the tip rounding radius is demonstrated.

Nonlinear and self-consistent single-mode formulation for TM-mode gyrotrons.

This work develops a nonlinear and self-consistent framework for the single-mode simulation of TM-mode gyrotrons. Unlike TE modes, a nonlinear TM wave equation is derived by considering the additional axial modulation on the electron beam due to the interaction with the axial electric field. Together with the electrons' equations of motion, particle tracing simulation is conducted to model TM-mode oscillation. For a uniform structure, the electron-beam efficiency of the TM_{11}-mode gyrotron at the W band can achieve 30% over broad parameter space. Its beam-current, beam-voltage, and pitch-factor tuning properties are investigated under different magnetic fields. By optimizing the interaction structure of the proposed gyrotron backward-wave oscillator (gyro-BWO), the maximum interaction efficiency is higher than 30% with a frequency tuning range of more than 6 GHz at the pitch factor of 1.5. The peak efficiency can remain high of 32% at low beam voltage (10 kV) and low magnetic field (32.8 kG), indicating additional operating conditions. These special features may facilitate the development of low-cost and compact gyrotron systems and show great potential in the applications for TM-mode gyro-BWOs.