Invisibility Cloak Research Articles

Third order differential subordination and superordination results for analytic functions involving the Hohlov operator

The problems of third order differential subordination as well as superordination for functions analytic in the open unit disk seem to be new and have been of interest after the seminal work of Antonino and Miller, and Tang. In the present paper by considering suitable classes of admissible functions associated with Hohlov operator, various third order differential subordination as well as differential superordination results are obtained. As a consequence, the dual problems which gives the sandwich-type relations are presented. Upon suitable choice of the parameters, the results obtained in this paper include some classical as well as recently studied results. An attempt has also been made to illustrate the applications of the new results in the context of electromagnetic cloaking problem.

Design and parametric analysis of a wide-angle polarization-insensitive metamaterial absorber with a star shape resonator for optical wavelength applications

Optical wavelengths considered as the key source of electromagnetic waves from the sun, and metamaterial absorber (MMA) enables various applications for this region like real invisible cloaks, color imaging, magnetic resonance imaging, light trapping, plasmonic sensor, light detector, and thermal imaging applications. Contemplated those applications, a new wide-angle, polarization-insensitive MMA is presented in this study. The absorber was formatted with three layers that consisted of a sandwiched metal-dielectric-metal structure. This formation of metamaterial absorber showed a good impedance match with plasmonic resonance characteristics. The structure was simulated using the FIT and validated with the FEM. A variety of parametric studies were performed with the design to gain best physical dimension. The mechanism of absorption also explained immensely by various significant analysis. The design had average 96.77% absorption from wavelengths of 389.34 nm to 697.19 nm and a near-perfect absorption of 99.99% at a wavelength of 545.73 nm for TEM mode. For an ultra-wide bandwidth of 102 nm, the design exhibited above 99% absorbance. The proposed is wide-angle independent up to 60° for both TE and TM mode, which is useful for solar energy harvesting, solar cell, and solar thermophotovoltaics (STPV). This MMA can be used for an optical sensor or as a light detector. Moreover, this proposed design can be employed in some applications mentioned above.

Cloaking Using the Anisotropic Multilayer Sphere

We studied a Spherically Radially Anisotropic (SRA) multilayer sphere with an arbitrary number of layers. Within each layer permittivity components are different from each other in radial and tangential directions. Under the quasi-static approximation, we developed a more generalized mathematical model that can be used to calculate polarizability of the SRA multilayer sphere with any arbitrary number of layers. Moreover, the functionality of the SRA multilayer sphere as a cloak has been investigated. It has been shown that by choosing a suitable contrast between components of the permittivity, the SRA multilayer sphere can achieve threshold required for invisibility cloaking.

Scattering Cancellation by a Monolayer Cloak in Oxide Dispersion‐Strengthened Alloys

AbstractIn addition to wave‐based fields, metamaterials can manipulate diffusion fields at will, for example, the scattering cancellation of particle flow in natural materials. In this paper, a monolayer cloak is proposed to eliminate electron scattering and improve the total conductivity in commonly used aluminum‐oxide‐dispersion‐strengthened copper alloys (Cu‐Al2O3) after a multiscale model is established to theoretically explain the dependence of conductivity on scattering behavior. Intense electron scattering caused by dispersed alumina nanoinclusions dominates the drastic drop in the conductivity in the Cu‐Al2O3 system. The Drude model is expanded to a generalized form to explain the multiscale scattering regime in Cu‐Al2O3 after unifying the macro‐ and nanoscale considerations into the mesoscopic multibody scattering process of a Monte Carlo simulation. The results indicate that the conductivity is closely related to the overall electron density and relaxation time of electrons. Then, a cloak is designed based on scattering cancellation to improve the conductivity by reducing electron collisions, whose structure is simplified into a monolayer cloak by adopting an imaginary insulating layer. Both simulation and experiment confirm a substantial improvement of the total conductivity. The invisible cloaks manipulating particle flow expands the research scope of metamaterials to innovatively improve the properties of traditional materials.

Design of annulus-based dielectric metamaterial cloak with properties of illusion optics

We propose a feasible design for an annulus-based dielectric metamaterial cloak to not only reduce Ohmic losses from metallic metamaterials but also avoid manual misalignment when utilizing discrete dielectric metamaterials. The designed cloak is authenticated by the finite-integration method, and the corresponding field distributions without and with hidden objects are found to reveal the invisibility of the cloak. In addition, illusion optics are comprehended by comparing the field distributions of the dielectric-metamaterial-cloak-based illusion-device and an illusion object. With the abovementioned characteristics of the proposed cloak using an annulus-based dielectric metamaterial, in simulation, we successfully approach the features of the reciprocal cloak, which conceals multiple objects with vision and movement.

General design of 3D piecewise homogeneous illusion devices with arbitrary shapes

In this work, a general method is presented for the design of arbitrarily shaped 3D illusion devices with piecewise homogeneous parameters based on geometric divisions and linear coordinate transformations. Three illusion devices that can reshape the sizes or positions of the wrapped objects are demonstrated, namely, shrinking, amplifying, and shifting devices. The shrinking device can shrink a larger object into a smaller one with different material parameters, whereas the amplifying device can enlarge a smaller object into a larger one, and a shifting device can generate a new image with an identical size but located at a different position. In addition, based on the presented shrinking device, a perfect 3D invisibility cloak is achieved by shrinking the wrapped object to sufficiently small dimensions as compared to the operating frequency. An electromagnetic concentrator is also obtained by replacing the coated object of the amplifying device with a compression medium. The presented design approach can be easily extended to the design of other electromagnetic devices and even to other physical fields. It is believed that the presented piecewise homogeneous devices are more practicable in reality and can accelerate the potential applications of illusion devices in both military and commercial fields.

The meaning of dignity for older adults: A meta-synthesis.

Dignified care is a central issue in the nursing care of older adults. Nurses are expected to treat older adults with dignity, and older adults wish to be treated in a dignified manner. Researchers have recommended investigating the concept of dignity based on specific contexts and population groups. This meta-synthesis study aims to explore the understandings of dignity from the perspective of older adults in the Nordic countries. Synthesising findings from qualitative studies on older adults’ experiences of dignity has provided important insight into what can be essential for dignified care in a Nordic context. The importance of visibility and recognition for the experience of dignity is an overarching theme in all the studies. The participants’ descriptions mostly implicated an existence dominated by a lack of recognition. The older adults do not feel valued as people or for their contribution to society and strive to tone down their illnesses in an attempt to become more visible and acknowledged as people. Toning down their illnesses and masking their needs can protect their independence. At the same time, becoming less visible can leave them without a voice. The metaphorical phrase protected and exposed by a cloak of invisibility is used to express the authors’ overall interpretation of the findings. Lack of recognition and being socially invisible is a genuine threat to older adults’ dignity.

SYMBOLS OF THE DEATHLY HALLOWS IN J.K. ROWLING’S “HARRY POTTER AND THE DEATHLY HALLOWS”

This research aimed to describe what the Deathly Hallows symbolized in J.K. Rowling’s “Harry Potter and the Deathly Hallows”. This was a qualitative content analysis with hermeneutic approach. The primary data was from the novel of Harry Potter and the Deathly Hallows. The results of this research were the Deathly Hallows symbolized the thirst of the greatest power which could make the owner immortal, but for Harry Potter they symbolized a test, which tested his mission to defeat Voldemort. The Hallows themselves consisted of three objects which were the Elder Wand, the Resurrection Stone, and the Invisibility Cloak. Each of the Hallows also symbolized different things. The Elder Wand symbolized a wizard’s desire for power, the Resurrection Stone symbolized deep longing towards the loved one who had died, and the Invisibility Cloak symbolized protection.

Active control cloak of the elastic wave metamaterial

The invisible cloak has attracted great attention due to its significant influences on science and engineering. Active elastic wave metamaterials provide superior controllable characteristics for the flexural wave cloak that is obviously different from the conventional structure. In this work, a broadband flexural wave cloak is designed and fabricated by the coordinate transformation method and active control system. The cloaking configuration consists of 16 alternative concentric layers with the polydimethylsiloxane (PDMS) and piezoelectric (PZT) patches which are connected with the active control systems. The results of the finite element simulations and experiments show that the effective frequency range of the flexural wave cloak with the active control systems is extended from 900 Hz to 1200 Hz. The design and fabrication of the elastic cloak with broadband characteristics have shielding applications.

Intestinal stem cells promote crypt fission during postnatal growth of the small intestine

ObjectiveWnt-β-catenin signalling is essential for intestinal stem cells. Our aim was to investigate the relationship between intestinal stem cells and crypt fission which peaks during infancy.DesignDuodenal biopsies were obtained during...

Fast Exponentially Convergent Solution of Electromagnetic Scattering From Multilayer Concentric Magnetodielectric Cylinders by the Spectral Integral Method

The multilayer surface integral equations (SIEs) for electromagnetic scattering by infinitely long magnetodielectric cylinders with an arbitrary number of layers are derived and solved by the spectral integral method (SIM). Singularity subtraction for the 2-D Green's function is used to enhance the computation accuracy and achieve exponential convergence. The final matrix equation after discretization is formed in the Fourier spectral domain rather than the spatial domain, which greatly expedites the SIM solution by accelerating the convolution via the fast fourier transform (FFT) algorithm. A recursive method is proposed to solve the spectral integral equations instead of using an iterative method to lower the computation complexity. Numerical examples for ordinary multilayer cylinders and invisibility cloak cylinders are presented to validate the SIM results by comparing the total fields, scattered fields, and radar cross section (RCS) to analytical solutions or finite-element simulations. They verify that the recursive solution has a complexity of O(MN log N) for an M-layer cylinder with N discrete points on each interface. Meanwhile, the SIM outperforms the analytical method because only the 0th-order and 1st-order special functions (Bessel functions and Hankel functions) are used in the SIM but higher-order functions are necessary for the analytical method to maintain the accuracy.

Generation of high-saturation two-level iridescent structures by vibration-assisted fly cutting

The submicron-level structured surface induces viewing-angle-dependent iridescence, and has wide applications in multi-color printing, micro-display projection, invisibility cloak technology. In this study, several types of two-level structures, which consist of the first-order micro geometric features corresponding to the pattern shape and the second-order submicron grooves corresponding to the diffraction grating, are designed to directly induce a variety of iridescent patterns based on their shape regulations. To fabricate these two-level iridescent structures with high accuracy in a single step, vibration-assisted fly cutting (VAFC) is proposed. VAFC involves the low-frequency vibration of the workpiece in the vertical direction during the feed in the horizontal direction and the high-speed rotation of the diamond cutting tool. A 3D theoretical model is established for the numerical simulation of the generating process of the iridescent structures and the regulation of the first-order geometric feature by vibration parameters. As the key parameter to the iridescent color, the spacing of the second-order submicron grooves is flexibly controlled by the feed rate. A VAFC platform is developed to fabricate the two-level structures and an optical detection system is setup to test the surface iridescence. Various vivid colors are regulated by the two-level structures with high saturation and uniformity.

Inhibition of Histone Deacetylase (HDAC) Enhances Checkpoint Blockade Efficacy by Rendering Bladder Cancer Cells Visible for T Cell-Mediated Destruction.

Inhibitory checkpoint blockade therapy is an immunomodulatory strategy that results in the restoration of T cell functions, and its efficacy depends on the recognition of tumor cells for destruction. Considering the factors at play, one could propose that anti-tumor responses will not occur if tumor cells are immunologically invisible to T cells. In this study, we tested a strategy based on the modulation of cancer cell's immunovisibility through HDAC inhibition. In a model (heterotopic and orthotopic) of mouse urothelial bladder cancer, we demonstrated that the use of intratumoral or intravesical HDACi in combination with systemic anti-PD-1 was effective at inducing curative responses with durable anti-tumor immunity capable of preventing tumor growth at a distal site. Mechanistically, we determined that protective responses were dependent on CD8 cells, but not NK cells. Of significance, in an in vitro human model, we found that fully activated T cells fail at killing bladder cancer cells unless tumor cells were pretreated with HDACi. Complementary to this observation, we found that HDACi cause gene deregulation, that results in the upregulation of genes responsible for mediating immunorecognition, NKG2D ligands and HSP70. Taken together, these data indicate that HDAC inhibition results in the elimination of the tumor cell's “invisibility cloak” that prevents T cells from recognizing and killing them. Finally, as checkpoint blockade therapy moves into the adjuvant setting, its combined use with locally administrated HDACi represents a new approach to be included in our current therapeutic treatment toolbox.

Multi-wavelength carpet cloaking based on an ultrathin single layer metamaterial microstructure

Ultrathin metasurfaces provide a completely new route to achieve an invisibility cloak through local phase compensation. However, conventional carpet cloaking only works at a single frequency. Here, we propose a dual-wavelength carpet cloaking based on a single layer metasurface. Based on the electromagnetic coupling effect between the outside split square loop and inner metal structure array, the independent phase compensation and reconstruction of the reflected wavefront can be realized. The cloaking can effectively suppress the unexpected scattering and hide an object with arbitrary shape. This ultrathin metasurface cloaking can be applied in illusion optics, radars and antenna systems.

An electric concentrator and thermal cloaking device

The concentration and cloaking phenomena of physical fields in Metamaterials has captured the attention of the researchers due to their simplified approaches. However most of the work conducted is focussed on controlling single physical field. Transformation optics has paved the way for developing intelligent bifunctional devices. Bifunctional devices are such controlled devices which execute two different physical functions simultaneously and independently. In this work we have applied the transformation optics theory to design a multilayered two dimensional spherical bifunctional device which behaves like an electric concentrator and thermal invisibility cloak simultaneously. Moreover, we have also observed the normalized behavior of the proposed device. The simulation performance confirms the feasibility of our suggested model.

Invisibility Cloak using Color Detection and Segmentation with Open CV

Have you ever thought of making visible things invisible, just like the Harry Potter? Have you ever thought how does one supersede backgrounds and add effects in a movie? The cloak was magical and invisible in Harry Potter, the movie. As we know there is no magic and no invisible cloak which exists in the world. It’s all about the graphics tricks. The concept of an invisibility cloak is a mixture of science, fantasy, and the collective imagination. This paper helps to create one’s own ‘Invisibility Cloak’.It will make use of Python and OpenCV module specifically targeting Image Processing and Image Segmentation to create a false sense of invisibility in the frame. It will explore how an object of a specific color or texture can be manipulated using the OpenCV library of python. To achieve this, initially we’ll be capturing and storing the backdrop frame . Thereafter we’ll be identifying the red coloured fabric by making use of the above mentioned algorithms. Then we’ll segment out the red colored fabric by generating a mask and then finally , we’ll generate the final augmented(magical) output to create Invisibility cloak. These steps are discussed deeper in the paper.

Dabo Swinney, Universal Whiteness, and a “Sin Problem”

Clemson University head football coach Dabo Swinney was asked to respond to Colin Kaepernick’s protest of police killings of unarmed black men and women by kneeling for the national anthem. Swinney’s response was surprisingly comprehensive and illuminating into his stance on race, religion, and sport. He crystallizes his overall interpretation of societal problems with the statement, “It’s so easy to say we have a race problem, but we got a sin problem.” In this essay, I examine “whiteness” as that which endows whites with a kind of universal authority to establish norms as well as provide a protective cloak of invisibility that effectively hides the identity of those constructing the norms. I argue that Swinney’s unconscious display of his own whiteness coupled with the additional cloak of universal sin, that purportedly knows no color, serves to downplay and dismiss Kaepernick’s call for racial justice.

All‐Angle Self‐Collimation‐Based Invisibility Cloaking in 2D Square Lattice Photonic Crystals

AbstractHere, a two‐dimensional (2D) hole‐type square lattice photonic crystal is shown to achieve invisibility cloaking based on all‐angle self‐collimation. The proposed structure, which is composed of the high‐refraction‐index dielectric material PbTe (nPbTe ≈ 6), is applicable in the mid‐infrared (mid‐IR) frequency range. The cloaking region is capable of hiding any object of any shape and size since the incoming wave does not interact with the cloaked object. The optimization process and the functionality of the proposed structure are investigated by equal frequency contour analysis and the finite difference time domain (FDTD) method.

Frequency‐Agile Temporal Terahertz Metamaterials

AbstractSpatiotemporal manipulation of electromagnetic waves has recently enabled a plethora of exotic optical functionalities, such as non‐reciprocity, dynamic wavefront control, unidirectional transmission, linear frequency conversion, and electromagnetic Doppler cloak. Here, an additional dimension is introduced for advanced manipulation of terahertz waves in the space‐time, and frequency domains through integration of spatially reconfigurable microelectromechanical systems and photoresponsive material into metamaterials. A large and continuous frequency agility is achieved through movable microcantilevers. The ultrafast resonance modulation occurs upon photoexcitation of ion‐irradiated silicon substrate that hosts the microcantilever metamaterial. The fabricated metamaterial switches in 400 ps and provides large spectral tunability of 250 GHz with 100% resonance modulation at each frequency. The integration of perfectly complementing technologies of microelectromechanical systems, femtosecond optical control and ion‐irradiated silicon provides unprecedented concurrent control over space, time, and frequency response of metamaterial for designing frequency‐agile spatiotemporal modulators, active beamforming, and low‐power frequency converters for the next generation terahertz wireless communications.

3D-printed woodpile structure for integral imaging and invisibility cloaking

We present here the design, fabrication and experimental demonstration of a composite woodpile structure for integral imaging and invisibility cloaking. The structure composed of two layers of 3D-printed woodpile structure and a designed screen beneath it. The 3D display capability is first demonstrated by projecting a real 3D image from the screen. An invisibility carpet cloak is then demonstrated to hide an object on the ground in the visible regime by projecting a 3D virtual image of the ground from a pyramidal-shape screen. Comparing to transformation-optics-based or metasurface-based carpet cloaks, the current cloak can be both easily fabricated in large-scale simply using 3D printing and has an ultra-thin thickness with only 1.4 mm comparing to the height of the object of 4.7 mm. A polar viewing angle up to 20° with an arbitrary azimuthal viewing angle can be obtained with the present cloak. Our approach enables a cost-effective way towards practical 3D-printed optical components using the straight-forward fused deposition modeling method, leading to potential applications in 3D displays, integral microscopy, smart windows and augmented reality.