Transverse Magnetic Incident Waves Research Articles

Sub-Millimeter-Wave Polarization-Independent Spatial Power Divider for a Two-Port Dual-Polarized Antenna

An antenna system is proposed that uses a novel polarization-independent spatial power divider to align the beams from two orthogonally oriented dual-polarized feeds. This antenna system uses a common aperture for transmitting and receiving and provides high port isolation while maintaining compatibility with fully polarimetric radar. Unlike conventional two antenna radar systems, a radar using this antenna does not suffer from the parallax problem. The spatial power divider is designed using an all-dielectric metasurface approach and is fabricated on a silicon wafer using standard micromachining technology. The measured device exhibits at most 0.9 dB of difference between the reflection and transmission for both transverse electric and transverse magnetic incident waves at 45° incidence, over a band from 221 to 250 GHz. Conical horns are fabricated as feeds and together with the spatial power divider, a focusing lens, and microwave absorbers, are assembled in a three-dimensional-printed housing to complete the antenna system. Its measured gain is approximately 39 dB for each port and polarization, and isolation between ports is at least 40 dB for all polarization combinations over the band of interest.

Wideband absorber based on conductive ink frequency selective surface with polarization insensitivity and wide-incident-angle stability

In this article, a wideband, polarization-insensitive, and wide-incident-angle stable absorber based on conductive ink frequency selective surface is presented. The presented absorber is compatible with screen printing technology. The design and absorption principle of the proposed absorber is presented, and simulation analysis is conducted. The simulation results show that in the frequency range 6.58–16.38 GHz, the absorptivity of the proposed absorber is greater than 90%, while the relative absorption bandwidth is 85.4%. The whole absorber structure is relatively thin, having a total thickness of 3.3 mm, corresponding to 0.126λ0 at its center frequency. In addition, for both transverse electric and transverse magnetic incident waves, the proposed absorber achieves the absorptivity of more than 80% at the incident angle of up to 45°. A prototype of the proposed absorber is fabricated and used in experimental verification. The obtained experimental results show a good agreement with the numerical simulations. This absorber has great potential applications in the field of microwave sensing and absorbing.

A Unidirectional TM-Wave Cloak With Full Parameters

Unidirectional cloaks or carpet cloaks have become an essential branch of invisibility cloaks due to non-extreme parameters that are relatively easy for realization and potential applications. So far, a unidirectional cloak for transverse electric (TE) polarized wave has been successfully realized to hide an object in the air along a single direction with almost ideal performance. However, a practical method to achieve a unidirectional cloak for transverse magnetic (TM) polarization is still missing. In this paper, we successfully have designed, fabricated, and measured a full-parameter unidirectional TM-wave cloak in free space. In comparison to the previously-realized TE-wave counterpart, our cloak uses a perfect electric conductor boundary to obey the free-space symmetry condition of the TM incident wave and is therefore much more convenient to fabricate. The cloaking performance of the fabricated sample has been demonstrated via both full-wave numerical simulation and near-field measurement.

Reflection and transmission properties of a wire grid embedded in a SNG or SZ medium

The reflection and transmission properties of a wire grid embedded in lossless Single Negative (SNG) or Single Zero (SZ) medium have been analytically studied. The wires of the grid are taken to be lossless as well as lossy. It is shown that a lossy grid has approximately identical reflection characteristics for the Transverse Magnetic incident wave with Epsilon Negative and Mu Negative background medium. The lossy grid with Epsilon Zero background medium acts as a perfect reflector for the normally incident wave. Likewise, it is further studied that a lossy wire grid embedded in Mu Zero medium can be cloaked for the incoming normally incident wave.

Multi-band polarization-insensitive metamaterial absorber based on Chinese ancient coin-shaped structures

In this paper, the design, simulation, fabrication, and measurement of the five-band metamaterial absorber (MMA) based on Chinese ancient coin-shaped structure are proposed. Simulation results show that the proposed absorber has five distinctive absorption peaks at frequencies of 2.538 GHz, 7.092 GHz, 9.702 GHz, 13.302 GHz, and 15.588 GHz with the absorptivity of 0.99, 0.99, 0.99, 0.98, and 0.99, respectively. Experiment results matches well with the simulation. Both simulation and experiment results exhibit that the MMA sample is polarization insensitive for transverse electric and transverse magnetic incident wave. It also shows that high absorption for wide angle of incidence is up to 60°. Finally, the current distribution for the MMA is presented to gain an insight into the physics behind the multiple absorption mechanism. The five-band absorber is promising candidates as absorbing elements in scientific and technical applications because of its multiband absorption, polarization insensitive, and wide angle incidence.

Multipole Plasmons in Metal Nanorods: Scaling Properties and Dependence on Particle Size, Shape, Orientation, and Dielectric Environment

T-matrix formalism was used to study the multipole resonances excited by electromagnetic plane waves in gold and silver nanorods whose shape was modeled by prolate spheroids and cylinders with flat or semispherical ends (s-cylinders). The particle diameters and aspect ratio were varied from 20 to 80 nm and from 2 to 20, respectively. By using extended precision T-matrix codes, we calculated the extinction, absorption, and scattering spectra for random and fixed orientations of the particle axis with respect to the incident transverse magnetic (TM) and transverse electric (TE) polarized light, where the reference plane is defined by the particle axis and the incident wave vector. We found that the parity of a given spectral resonance number n coincides with the parity of their multipole contributions l, where l is equal to or greater than n, and the total resonance magnitude is determined by the lowest multipole contribution. The random-orientation resonances are excited most effectively by the TM scattering configurations, except for the short-wavelength resonance, which equals the sum of the dominant dipole TE resonance and the other multipole contributions. The even multipole resonances are maximal at intermediate orientations, whereas the odd multipoles can effectively be excited at both perpendicular and intermediate orientations of the rod axis with respect to the TM incident wave. In particular, the quadrupole resonance can be excited only by the TM incident wave, and the resonance magnitude is maximal for orientation of the particle symmetry axis near 54° with respect to the incident light. Finally, we found that the multipole resonance wavelengths obey a universal linear scaling when plotted versus the particle aspect ratio divided by the resonance number. This remarkable property of multipole resonances can be understood in terms of a simple concept based on plasmon standing waves excited in metal nanowires by an electric field of incident light (Schider et al. Phys. Rev. B 2003, 68, 155427). The refractive index sensitivity of the multipole resonance wavelength to a dielectric environment also exhibits linear scaling properties. Specifically, the relative shift of the resonance wavelength is proportional to the relative refractive index increment with a universal angular slope coefficient.

A neural network approach to the microwave inverse scattering problem with edge‐preserving regularization

A neural network approach to the inverse scattering problem for microwave tomographic reconstruction is presented. Although the technique of microwave tomography has been developed for more than two decades, it is still in its infancy in that it is necessary to solve the inverse scattering problem, which is well known as an ill‐posed and nonlinear problem and therefore difficult to deal with. To improve the inherent ill‐posedness of the problem, good regularization procedures are required. In this paper, an edge‐preserving regularization is proposed with a set of line processes to preserve the edge of the reconstructed image. Since the unknown dielectric permittivities are continuous complex variables and the line processes are binary variables, an augmented Hopfield network is applied to the mixed‐variable optimization problem. With this method, a priori knowledge can be conveniently incorporated into the optimization process, and inversions of large matrices are avoided. A numerical example of a simple model illuminated by the transverse magnetic incident waves is reported, and the advantages and limitations of the method are discussed.

On uniqueness for anisotropic inhomogeneous inverse scattering problems

The problem of determining the shape of a two-dimensional inhomogeneous orthotropic scatterer from far-field data is considered. In particular, by using integral equation techniques we prove that the support of the scatterer is uniquely determined if the far-field pattern is known for all incident directions. We point out that this uniqueness result may be useful also for practical applications, since in previously treated cases (isotropic inhomogeneous objects in the case of transverse magnetic incident waves and homogeneous orthotropic objects in the case of transverse electric incident waves) the theorems proving uniqueness have been quite straightforwardly extended to formulate a simple method for solving the inverse scattering problem.

A combined finite element-nonlinear conjugate gradient spatial method for the reconstruction of unknown scatterer profiles

The inversion of microwave imaging data is treated by means of a novel iterative spatial domain reconstruction technique. The latter combines the Finite Element Method (FEM) and a Nonlinear Conjugate Gradient (NCG) optimization scheme. The method is applied to the reconstruction of the complex permittivity profile of cylindrical inhomogeneous objects, that are illuminated by transverse magnetic incident waves, and is based on scattered far field measurements. Starting from an initial guess of the scatterer profile, the FEM is used to solve the forward problem, resulting in an estimate of the scattered field. The inverse process of updating the constitutive parameters of the scatterer is performed by the Polak-Ribiere algorithm by the use of which the difference between the measured and the estimated scattered data is minimized. The minimization procedure is carried out by a sensitivity analysis scheme based on the FEM and the introduction of the adjoint state vector. The proposed method is applied to various cases of scatterer profiles.

CFIE MM solution for TE and TM incidence on a 2-D conducting body with dielectric filled cavity

The problem of determining the scattering cross section of an arbitrarily shaped two-dimensional conducting body with an arbitrarily shaped dielectric filled cavity is considered. The problem is solved using a method-of-moments solution for the combined field integral equations. The particular form of the method of moments solution used here uses a minimum number of expansion coefficients. Results are given for transverse electric and transverse magnetic incident waves.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>