Waveguide Characterization of S-Band Microwave Mantle Cloaks for Dielectric and Conducting Objects

An object illuminated by an electromagnetic wave can be actively cloaked using a surface conformal array of radiating sources to cancel out scattering. this method is promising as elementary antennas can be used as sources while its active nature can surpass passivity-based performance limitations. While this technique has been conceptually extended to accommodate complex geometries, experimental validation past simple uniform scatterers is lacking. to address this scarcity, the design and experimental demonstration of a low-profile, active cloak capable of concealing a complex, metallic, polygonal target is presented. this cloak is constructed with commercially available monopoles and enclosed within a parallel-plate waveguide-based apparatus to approximate a quasi-2D environment. performance is then assessed when the target is illuminated at either frontal or oblique incidence by a 1.2 GHz cylindrical wave. Overall, the cloak reduces the target's scattering cross-section by an average of 7.2 dB at frontal incidence and 8.6 dB at oblique incidence. These results demonstrate the feasibility of this kind of active cloaking for more complex scatterers containing flat surfaces and edges. Further analysis shows that the cloak possesses a functional bandwidth of 14% and can be reconfigured for single frequency operation over 0.8-1.8 GHz. Developments in artificial media, such as metamaterials, have given rise to new applications focused on advancing the ability to control electromagnetic waves. Electromagnetic cloaking comprises one such area and focuses on preventing an object from scattering impinging electromagnetic waves. This is achieved by either redirecting an incident wavefront around an object 1-4 or by altering the properties of a target to reduce or cancel out natural scattering 5-7. Although much research focuses on managing microwaves, cloaks at other bands 8,9 along with thermal 10 , acoustic 11 , and temporal 12 devices have been proposed. Presently, the majority of research into cloaking has focused on passive techniques. While elegant and operationally simpler, passivity imposes fundamental design and performance limitations. These often require compromises on: operational bandwidth, directionality, polarization, along with the permissible size, geometry, and material of the cloak and target 13,14. While more complex and less popular, active techniques provide a potential means of relaxing or mitigating passivity based constraints. One avenue of development is to use metasurfaces 15,16 and metamaterials 17,18 augmented with active components or networks. The resultant devices function similarly to passive cloaks but exhibit expanded capabilities 19 , reconfigurability 20,21 , or unidirectional reflectivity 22,23. This present work focuses on an alternative concept, analogous to acoustic noise cancellation, where an active mechanism is employed to directly manage scattering 24,25. Here, an illuminated object is surrounded by a surface conformal array of radiating elements which are configured to radiat...

Section: Resultsmentioning

confidence: 99%

Active Cloaking of a Non-Uniform Scatterer

Ang

Eleftheriades

2020

“…Scattering cancellation-based cloaking mainly using metamaterial, meta-surfaces, graphene and/or plasmonic materials to eliminate the scattering field of target object, and it can also be used in some physical fields [7][8][9][10][11][12][13][14][15][16][17][18] . As some of the literatures suggests that each cloaking technique has its own advantages and disadvantages 7,19 , exploring the new methods, for example, the illusion optics, or the common materials that can also make targets invisible from different ways, will significantly promote the practical application of relevant research results [20][21][22] .At presents some researchers have reported that the invisibility cloak can be widely used in electromagnetic waves [23][24][25][26] , mechanical waves 27 , elastic waves 28,29 , matter waves 30 , water waves 31 , magnetic fields 32 , DC magnetic or electric fields [33][34][35] , current 36 , and thermal fields [37][38][39] . Based on the metamaterial, people can also design an electrostatic field concentrator 3 , magnetic field concentrator 40 , asymmetric universal and invisible gateway 41 , the perfect lens 42,43 , perfect transmission channel 44 , general illusion device 21 , transparency coating 45 , dc electric concentrator 46 , tunable invisibility cloaking 47 , special imaging probe 48 and so on [48][49][50][51] .…”

mentioning

confidence: 99%

“…At presents some researchers have reported that the invisibility cloak can be widely used in electromagnetic waves [23][24][25][26] , mechanical waves 27 , elastic waves 28,29 , matter waves 30 , water waves 31 , magnetic fields 32 , DC magnetic or electric fields [33][34][35] , current 36 , and thermal fields [37][38][39] . Based on the metamaterial, people can also design an electrostatic field concentrator 3 , magnetic field concentrator 40 , asymmetric universal and invisible gateway 41 , the perfect lens 42,43 , perfect transmission channel 44 , general illusion device 21 , transparency coating 45 , dc electric concentrator 46 , tunable invisibility cloaking 47 , special imaging probe 48 and so on [48][49][50][51] .…”

mentioning

confidence: 99%

Equivalence between positive and negative refractive index materials in electrostatic cloaks

Wang

Zhang

2021

We investigate, both theoretically and numerically, the equivalence relationship between the positive and negative refraction index dielectric materials in electrostatic invisibility cloak. We have derived an analytical formula that enables fast calculate the corresponding positive dielectric constant from the negative refraction index material. The numerical results show that the negative refraction index material can be replaced by the positive refractive index materials in the static field cloak. This offers some new viewpoints for designing new sensing systems and devices in physics, colloid science, and engineering applications.

“…The enormous progress in the field of metamaterials paved the way in recent years to a new era for novel devices able to realise exotic electromagnetic responses, some of them impossible to achieve with natural materials, ranging from negative refraction 1 and superlensing 2 to enhanced transmission 3 , perfect absorption 4 , cloaking 5 6 and, more generally, to those properties based on coordinate transformation design 7 . The electric and magnetic responses achieved by metamaterials derive microscopically from the geometry of their unit cells and are preserved in the macroscopic medium.…”

mentioning

confidence: 99%

A hybrid tunable THz metadevice using a high birefringence liquid crystal

Chikhi

Lisitskiy

Papari

et al. 2016

Self Cite

We investigate a hybrid re-configurable three dimensional metamaterial based on liquid crystal as tuning element in order to build novel devices operating in the terahertz range. The proposed metadevice is an array of meta-atoms consisting of split ring resonators having suspended conducting cantilevers in the gap region. Adding a “third dimension” to a standard planar device plays a dual role: (i) enhance the tunability of the overall structure, exploiting the birefringence of the liquid crystal at its best, and (ii) improve the field confinement and therefore the ability of the metadevice to efficiently steer the THz signal. We describe the design, electromagnetic simulation, fabrication and experimental characterization of this new class of tunable metamaterials under an externally applied small voltage. By infiltrating tiny quantities of a nematic liquid crystal in the structure, we induce a frequency shift in the resonant response of the order of 7–8% in terms of bandwidth and about two orders of magnitude change in the signal absorption. We discuss how such a hybrid structure can be exploited for the development of a THz spatial light modulator.