Mantle Cloaking Research Articles

Overcoming limitations of passive invisible antennas through bianisotropic nonreciprocal mantle cloaks

Overcoming limitations of passive invisible antennas through bianisotropic nonreciprocal mantle cloaks

Square Rod Antenna Covered by Mantle Cloak with Rejection Band at Lower Frequency Side of Operating Frequency

Square Rod Antenna Covered by Mantle Cloak with Rejection Band at Lower Frequency Side of Operating Frequency

Cloaking of Equilateral Triangle Patch Antennas and Antenna Arrays with Planar Coated Metasurfaces

We have proposed an effective metasurface design to accomplish the cloaking of equilateral patch antennas and their array configuration. As such, we have exploited the concept of electromagnetic invisibility, employing the mantle cloaking technique with the intention to eliminate the destructive interference ensuing between two distinct triangular patches situated in a very congested arrangement (sub-wavelength separation is maintained between the patch elements). Based on the numerous simulation results, we demonstrate that the implementation of the planar coated metasurface cloaks onto the patch antenna surfaces compels them to become invisible to each other, at the intended frequencies. In effect, an individual antenna element does not sense the presence of the other, in spite of being in a rather close vicinity. We also exhibit that the cloaks successfully reinstate the radiation attributes of each antenna in such a way that it emulates its respective performance in an isolated environment. Moreover, we have extended the cloak design to an interleaved one-dimensional array of the two patch antennas, and it is shown that the coated metasurfaces assure the efficient performance of each array in terms of their matching as well as radiation characteristics, which in turn, enables them to radiate independently for various beam-scanning angles.

Scattering suppression with dual-band single-layer mantle cloak for cylindrical metasurface

This paper investigates scattering suppression with a dual-band and single-layer mantle cloak by using the proper structure for cylindrical objects. The mantle cloak’s surface impedance is calculated according to the Mie Theory to obtain considerable scattering reduction at all angles of the cylinder. The analytical formulation assists in determining the proper unit cell dimensions to obtain design parameters. Firstly, the patch array geometry is applied on the mantle cloak for a single operating frequency with different unit cell numbers. Then a new design of a dual-band single-layer mantle cloak is made with the findings obtained. Simulations are conducted for both mantle cloaks, and bi-static Radar Cross-Section (RCS) analyses are carried out, generating simulated outcomes for cylinders that are both cloaked and uncloaked. The comparison of the scattering suppression between them reveals that the cloaked cylinders demonstrate a significant reduction in scattering. These achievements apply to both single-band and dual-band designs. A novel dual-band single-layer mantle cloak is presented with a new design method and scattering suppression is observed in more than one operating frequency. As evidence of the subject, a dual-band cloaked cylinder is designed with a total radius of 0.13λ0, a total length of 2.59λ0, and a thin dielectric layer’s thickness of 0.0127λ0(λ0i s the wavelength at design frequency f0=3 GHz). This dual-band cloaked cylinder has 7.6 dB absolute RCS reduction at f=2.05 GHz and 5.6 dB absolute RCS reduction at f=3.75 GHz. An efficient scattering suppression is achieved for these two different frequencies in all directions. The considerable degree of invisibility observed in this study opens up possibilities for future investigations in various fields, including radar applications, sensing applications, and antenna isolation for the purpose of blockage reduction.

Design and implementation of elliptical mantle cloaks for polarization decoupling of two tightly spaced interleaved co-frequency patch array antennas

In this paper, we utilized the method of mantle cloaking to decouple/isolate two densely packed interleaved patch array antennas operating at the same frequency but with orthogonal polarizations. To reduce mutual coupling between the adjacent elements, vertical strips, as a type of elliptical mantle cloaks, are located in close proximity to the patches. At the operating frequency of f0 = 3.7 GHz, the edge-to-edge spacing of the elements of the two interleaved arrays is less than λ0/80 (1 mm) and the center-to-center spacing of each array element is 0.7 λ0 (57 mm). The proposed design is implemented using 3D printing technology, and its performance in terms of return loss, efficiency, gain, radiation patterns, and isolation is measured for evaluation. The results show the radiation characteristics of the arrays are perfectly retrieved after cloaking similar to the isolated arrays. Decoupling tightly spaced patch antenna arrays on a single substrate paves the way to achieve miniaturized communication systems with full duplex operation or dual polarization communication.

Cloaking of Slot Antennas at C-Band Frequencies Using Elliptical Metasurface Cloaks

In this letter, we endeavor to curb the adverse effects of mutual coupling between two-slot antennas (operating at C-band frequencies), situated at a subwavelength separation. The effects of mutual coupling become extremely apparent at such close proximity and leads to the deterioration of the radiation aspects of each antenna. To mitigate these detrimental effects, we exploit the concept of mantle cloaking for the design of specialized cloaks, consisting of elliptical dielectric regions integrated with capacitive metallic strips. It is demonstrated through simulation results that by enclosing each radiating edge of the individual slots with these uniquely designed metasurfaces, the slot antennas are decoupled in the near field. Moreover, the metasurface cloaks also facilitate restoration of the far field radiation properties of the slots. In this regard, our cloak design ensures that the slot antennas do not sense the presence of each other, enabling each slot antenna to operate individually, as if they were isolated.

On the Use of Nonlinear Metasurfaces for Circumventing Fundamental Limits of Mantle Cloaking for Antennas

The aim of this communication is to investigate and demonstrate the possibility to overcome the fundamental limitations of mantle cloaking for antennas by exploiting nonlinear metasurfaces. First, we recap and give additional physical insights about the fundamental bounds that apply to the electric properties of an antenna that is made invisible at its own resonance frequency. Then, an innovative strategy is proposed to circumvent these limits through the introduction of nonlinear elements that are able to dynamically transform the geometry of the cloaking metasurface depending on the power level of the impinging field. Different nonlinear designs are discussed, and their effectiveness is assessed through the relevant benchmark example of a half-wavelength dipole antenna able to efficiently transmit high-power signals while being invisible to low-power ones. In addition, the capability of such nonlinear mantle cloaks to enable the shaping of the radiation pattern of an antenna array depending on the power level of the received/transmitted signal is demonstrated. These innovative cloaking devices may find applications in different radiating systems enabling unprecedented functionalities.

Optical cloaking and invisibility: From fiction toward a technological reality

Optical invisibility, which started in the pages of fiction before becoming an intriguing quest of humankind for over a century, has blossomed into a remarkable scientific journey toward reality over the last two decades. Perfect optical cloaking requires the total scattering of electromagnetic waves around an object at all angles, all polarizations, over a wide frequency range, irrespective of the medium. Such a device is still far-fetched, requiring the transformation of space around a cloaked region such that the phase velocity is faster than other areas to preserve the phase relationships. However, by simplifying the invisibility requirements, pioneering work on spherical transformation cloaks, carpet cloaks, plasmonic cloaks, and mantle cloaks has been realized in narrowband microwave, infrared, and even optical wavelengths. In this Tutorial, we review the theoretical basis for invisibility cloaking, from spherical transformational optics to non-Euclidian cases, and discuss their limitations. Subsequently, we highlight the recent trends in realizing reconfigurable intelligent cloaks to overcome the traditional limitations of wideband operation and parallel efforts in unidirectional cloaking. Because the human eye is insensitive to the phase and polarization of visible light, a class of ray optics cloaking devices has been recently developed by eliminating phase preservation requirements. Notably, we focus on the recent progress achieved on invisibility cloaks that function in natural incoherent light and can be realized using standard optical components. We conclude this Tutorial with a prospective of potential applications and the practicality of optical cloaks in everyday life.

Design investigation of mantle-cloak for a PEC cylindrical object under oblique incidence of TM and TE waves

In this paper, the possibility of cloaking a metallic cylinder is investigated for a wide range of angles of obliquely incidence TE and TM wave using the well-known mantle cloaking technique. Initially, the scattered field is formulated analytically using the circumferential waves in cylindrical coordinates. A full tensor is utilized for modeling the sheet impedance of an ideal metasurface wrapped around the cylinder to be cloaked. Then, a capacitive rectangular patch metasurface is designed and its parameters are optimized to suppress both the co- and cross-polarized components of the scattered fields. The analytical results are verified with those obtained using the full wave simulation investigation performed by CST Microwave Studio, and a very good agreement is observed between the obtained results.

Theory and algorithm for tunable mantle cloaking through bulk Dirac semimetal metasurfaces around elliptical cylinders

In recent years, invisibility has become a research area of increasing interest due to the advances in material engineering. It may be possible to achieve invisibility through cloaking structures based on one or more layers of materials with proper electromagnetic properties. In this regards, we propose and analyze a bulk Dirac semimetal (BDS) cloaking metasurface to achieve scattering cancelation in the terahertz (THz) spectrum. A monolayer of the BDS as a mantle cloak is applied around a dielectric elliptical cylinder to achieve a tunable scattering width. The effectiveness of the designed cover is checked with a full-wave simulation based on the finite element method (FEM) as well as an analytical approach. A good agreement is observed between the results of the analytic method and those of the full-wave simulation. To achieve a mantle cloaking for TE and TM polarizations, an anisotropic metasurface should be applied. Therefore, we introduce the BDS strips as a mantle cloaking around an SiO2-coated PEC elliptical cylinder and propose an algorithm to determine the features of the anisotropic cover.

Optimization of Frequency Selective Surfaces for the Design of Electromagnetic Mantle Cloaks

A full optimization procedure that combines the parallel self-adaptive low-high evaluation-evolutionary algorithm with the finite element method-robin boundary condition iteration numerical method is proposed for the design of electromagnetic mantle cloaks enclosing arbitrary objects. The procedure is efficiently applied to optimize an ultrathin, conformal frequency selective surface (FSS), placed around an inhomogeneous dielectric cylinder to be made invisible. Two very different optimal solutions have been found, and this can be a great advantage for the designer using the proposed optimization strategy.

Improving performance of mantle cloak for electrically large PEC cylinders by reducing higher-order scattering coefficients

Based on the scattering cancellation technique, an approach is proposed to improve the mantle cloak’s performance for electrically large cylinders. The procedure is based on the observation that the number of dominant scattering coefficients and corresponding magnitudes for a cylinder decreases when oriented obliquely to the incident wave. Thus, it is quite advantageous to design a mantle cloak under the oblique incidence than the normal incidence. The proposed method starts with determining the optimum angle of incidence at which if the object is oriented with respect to the incident wave, the maximum scattering reduction can be obtained with a mantle cloak explicitly designed for that orientation. The procedure is applied to cylinders of radii and , where is the design wavelength. The proposed approach’s advantages are highlighted by comparing it with the previously published literature. Additionally, the mantle cloak is realized using a periodic grid of metallic patches, and simulations in Ansys HFSS are performed to verify the design.

Progress and perspective on advanced cloaking metasurfaces: from invisibility to intelligent antennas

Among the different cloaking applications proposed in the literature, the antenna framework has emerged as one of the most fruitful and mature field. In particular, mantle cloaking approach has proven to be a powerful tool for enabling unprecedented possibilities in antenna design. Here, we provide a review of the most significant works in the field of electromagnetic invisibility for antenna applications, demonstrating the versatility of cloaking metasurfaces in antenna scenarios. We also discuss our recent results and investigations on the design of advanced cloaking metasurfaces equipped with electronic components and circuits and able enriching the antenna intelligence.

Restoration of antenna performance in the vicinity of metallic cylinder in implantable scenario

In this study, the authors propose an innovative solution based on mantle cloaking method to restore the performance of an implantable antenna, which is degraded due to the scattering from an adjacent metallic body. In an implantable device, the metallic body is generally used as a house for electronic circuitry. Initially, they investigate the deteriorating effects of metallic body on the antenna input impedance and radiation characteristics. Finally, by covering the metallic body with the designed metasurface, most of the antenna parameters are successfully retrieved. The proposed model is fabricated and measured with the in vitro test by immersing the antenna inside a muscle emulating gel, as well as, inside the minced pork.

Revealing radiationless sources with multi-harmonic mantle cloaking

A general formula for the scattering suppression of simultaneous cylindrical harmonic waves is reported for a bare dielectric cylinder. A proper surface impedance condition is imposed at the boundary between dielectric and background regions, revealing a parity-time condition for the internal electromagnetic field in order to be nonradiating. Depending on the maximum number of cylindrical harmonic waves to suppress along the azimuthal variable φ, such surface impedance function profile reveals several higher order nonradiating modes. The determination of is consistent with the degrees of freedom of the scattered fields. Moreover, the multi-harmonic mantle cloaking technique automatically generates radiationless sources suitable for the implementation with metal-dielectric metasurfaces or all-dielectric metamolecules.

Analysis and realization of a wideband mantle cloak with improved cloaking performance

ABSTRACT An approach for improving the invisibility performance of mantle cloak is proposed. It is based on an interesting observation that the cloaking performance of mantle cloak can be significantly enhanced if the cloak is operated under tilted conditions with respect to the incident radiation (such that the wave is incident obliquely onto the cloak). The mantle cloak is thus designed by judiciously choosing the value of surface impedance corresponding to the tilt angle. It is because the optimum value of surface impedance changes with the tilt angle. An analytical method is devised for the calculation of optimum surface impedance under tilted conditions and subsequently verified with Ansys HFSS simulations. It is also shown that by deliberately tilting the mantle cloak, numerous advantages over normal incidence scenario, are obtained, such as (a) significant reduction in total scattering width, (b) considerable enhancement in bandwidth, and (c) increase in performance robustness with respect to the dispersion of surface impedance. These advantages of operating under tilted conditions are well elucidated by comparing it with that for normal incidence scenario previously presented in various literatures. The metasurface cloak is subsequently realized using I-shaped unit cell structure and varactor diodes, and cloaking performance is analyzed using HFSS simulations.

Mantle cloaking due to ideal magnetic dipole scattering

One of the most exciting applications of metaparticles and metasurfaces consists in the magnetic light excitation. However, the principal limitation is due to parasitic extra multipoles of electric family excited in magnetic dipole meta-particles characterized by a radiating nature and corresponding radiating losses. In this paper, we propose the “ideal magnetic dipole” with suppressed additional multipoles except of magnetic dipole moment in the scattered field from a cylindrical object by using mantle cloaking based on metasurface and on anapole concept. The considered metasurface consists of a periodic width modulated microstrip line, with a sinusoidally shaped profile unit cell printed on a dielectric substrate.

Electrically tunable mantle cloaking utilizing graphene metasurface for oblique incidence

An analytic formulation to achieve mantle cloaking of a dielectric cylinder using scattering cancellation method for TMz polarized oblique incidence is presented. To obtain this goal, a closed form expression for the required surface impedance of the covering metasurface is derived. By properly tuning the chemical potential of graphene, its surface impedance is adjusted for the invisibility of the considered cylinder for arbitrary angles of the impinging plane wave. The scattering width reduction of 15.7 dB and 21.27 dB is obtained with 3-dB bandwidth of 18.7% and 10.6% at 1 THz and 1.5 THz, respectively for the incident angle of 60 degrees. Furthermore, by optimizing the surface impedance of graphene, finite cylinders can also be cloaked. The results indicate 11.4 dB and 13.5 dB radar cross section (RCS) reduction with 30% and 22% 3-dB bandwidth for the incident angles of 45 and 80 degrees, respectively. Full-wave simulations verify the analytical results. The effect of the cloaking is examined by comparing the input impedance of a pyramidal horn antenna when it is loaded with an array of bear and cloaked cylinders positioned in the aperture.

Tunable mantle cloaking utilizing graphene metasurface for terahertz sensing applications.

Design of sensors which are able to probe electromagnetic radiation with larger cross section and at the same time with having negligible perturbation in measurement has attracted significant attention. For this purpose, scattering-cancellation sensors or cloaking sensors are introduced. However, tunable cloaking sensors are very challenging. In this regards, here, a metasurface based on graphene strips is proposed to cloak a dielectric cylinder under illumination of TEz and TMz polarized incident waves in terahertz range. According to the in plane effective surface impedance tensor for the considered metasurface and the required surface impedance for achieving invisibility under TE and TM polarized impinging waves, the geometrical parameters of the covering structure and characteristics of graphene are obtained. Numerical simulations show radar cross section reduction for both TE and TM polarizations. Furthermore, the introduced metasurface is able to cloak the cylinder for incoming waves with circular polarization. In addition, it is shown that by properly adjusting the chemical potential of graphene, the required surface impedance to have cloaking for the two polarizations in other frequencies can also be achieved, which results in a tunable dual polarized cloaking. The proposed structure provides 2-11 dB reduction in scattering strength relative to the uncloaked configuration for 0.3eV variation of graphene chemical potential.

Application of the mantle cloak in near vertical incidence skywave/ground wave high frequency communication

In this study, the authors propose a new idea to employ mantle cloaking in order to reduce the mutual coupling between electrically small antennas (ESAs) placed on man-pack radio systems. They determined and numerically optimised the parameters of the mantle cloak on loop and monopole antennas; these antennas are to provide near vertical incidence skywave (NVIS) and ground wave high frequency (HF) communication in man-pack radio systems. The authors’ designed cloak can effectively minimise the mutual coupling between the ESAs – in the man-pack radios – for only a very small impact on the antenna's radiation characteristics. The authors believe that these improvements pave the way toward effectively applying these compact radio structures in emergency HF communication in areas with limited access to conventional communication links.