Constant Permeability Design of Cylindrical Invisibility Cloaks with Hyperbolic Coordinate Transformation Based on Transformation Electromagnetics

2018 ◽  
Author(s):  
Yuma Takano ◽  
Tsutomu Nagayama ◽  
Atsushi Sanada
Keyword(s):  
Coordinate Transformation ◽  
Invisibility Cloaks

An Elastic Cloak Model Based on Coordinate Transformation

2010 ◽  
Author(s):  
M. Brun ◽  
S. Guenneau ◽  
A. B. Movchan
Keyword(s):  
Coordinate Transformation ◽  
Elastic Waves ◽  
Pressure Waves ◽  
Plane Shear ◽  
Initial Form ◽  
Model Based ◽  
Elasticity Equations ◽  
Invisibility Cloaks ◽  
Fully Coupled

We propose a class of cylindrical cloaks for elastic waves which are deduced from geometric transform. In particular we implement a radially symmetric linear geometric transform which depends upon a parameter and depending upon the value of such parameter, the transform is applied to the design of neutral (invisibility) cloaks and to obtain mirage effects. Interestingly, the cloaking device has been designed for fully-coupled in-plane shear and pressure waves and, moreover, the chosen reparameterization is such that the elasticity equations maintain their initial form under the transformation, which is generally untrue in the elasticity case.

scholarly journals The required acoustic parameters simplification of invisibility cloaks and concentrators using the impedance-tunable coordinate transformation

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Jun Cao ◽  
Fenghua Qi ◽  
Senlin Yan
Keyword(s):  
Coordinate Transformation ◽  
Two Dimensional ◽  
Acoustic Metamaterials ◽  
Acoustic Parameters ◽  
Acoustic Design ◽  
Impedance Distribution ◽  
Invisibility Cloaks ◽  
Impedance Functions ◽  
Transformation Acoustics ◽  
Tunable Impedance

AbstractTransformation acoustics, as an unconventional theory, provides a powerful tool to design various kinds of acoustic devices with excellent functionalities. However, the required ideal parameters, which are prescribed by the method, are both complex and hard to implement-even using acoustic metamaterials. Furthermore, simplified parameter materials are generally favored in transformation-acoustic design due to its easier realization with artificial structures. In this letter, we propose a coordinate transformation methodology for achieving simplified parameters by tuning the impedance distribution in the geometric limit, where the transformation media parameters can be derived by setting tunable impedance functions in the original space and a combination of suitable linear or nonlinear coordinate transformation. Based on this approach, both two-dimensional acoustic cloak and concentrators are designed with different sets of simplified parameters. Numerical simulations indicate good performance of these devices with minimized scattering at higher frequencies. The proposed method provides more opportunities to realize the designed acoustic devices experimentally, and can also be used for other transformation-acoustic designs including 3D cases.

scholarly journals Transformation optics beyond the manipulation of light trajectories

2015 ◽  
Vol 373 (2049) ◽  
pp. 20140361 ◽  
Author(s):  
Vincent Ginis ◽  
Philippe Tassin
Keyword(s):  
Electromagnetic Fields ◽  
Coordinate Transformation ◽  
Quadratic Function ◽  
Cherenkov Light ◽  
Transformation Optics ◽  
Optical Material ◽  
Optical Forces ◽  
Light Waves ◽  
Light Rays ◽  
Invisibility Cloaks

Since its inception in 2006, transformation optics has become an established tool to understand and design electromagnetic systems. It provides a geometrical perspective into the properties of light waves without the need for a ray approximation. Most studies have focused on modifying the trajectories of light rays, e.g. beam benders, lenses, invisibility cloaks, etc. In this contribution, we explore transformation optics beyond the manipulation of light trajectories. With a few well-chosen examples, we demonstrate that transformation optics can be used to manipulate electromagnetic fields up to an unprecedented level. In the first example, we introduce an electromagnetic cavity that allows for deep subwavelength confinement of light. The cavity is designed with transformation optics even though the concept of trajectory ceases to have any meaning in a structure as small as this cavity. In the second example, we show that the properties of Cherenkov light emitted in a transformation-optical material can be understood and modified from simple geometric considerations. Finally, we show that optical forces—a quadratic function of the fields—follow the rules of transformation optics too. By applying a folded coordinate transformation to a pair of waveguides, optical forces can be enhanced just as if the waveguides were closer together. With these examples, we open up an entirely new spectrum of devices that can be conceived using transformation optics.

scholarly journals Modification to the Hawking temperature of a dynamical black hole by a flow-induced supertranslation

2020 ◽  
Vol 2020 (12) ◽  
Author(s):  
Hsu-Wen Chiang ◽  
Yu-Hsien Kung ◽  
Pisin Chen
Keyword(s):  
Black Hole ◽  
Coordinate Transformation ◽  
Information Loss ◽  
Hawking Temperature ◽  
Asymptotic Region ◽  
Unruh Effect ◽  
Anisotropic Flow ◽  
Information Loss Paradox ◽  
History Of ◽  
Entire History

Abstract One interesting proposal to solve the black hole information loss paradox without modifying either general relativity or quantum field theory, is the soft hair, a diffeomorphism charge that records the anisotropic radiation in the asymptotic region. This proposal, however, has been challenged, given that away from the source the soft hair behaves as a coordinate transformation that forms an Abelian group, thus unable to store any information. To maintain the spirit of the soft hair but circumvent these obstacles, we consider Hawking radiation as a probe sensitive to the entire history of the black hole evaporation, where the soft hairs on the horizon are induced by the absorption of a null anisotropic flow, generalizing the shock wave considered in [1, 2]. To do so we introduce two different time-dependent extensions of the diffeomorphism associated with the soft hair, where one is the backreaction of the anisotropic null flow, and the other is a coordinate transformation that produces the Unruh effect and a Doppler shift to the Hawking spectrum. Together, they form an exact BMS charge generator on the entire manifold that allows the nonperturbative analysis of the black hole horizon, whose surface gravity, i.e. the Hawking temperature, is found to be modified. The modification depends on an exponential average of the anisotropy of the null flow with a decay rate of 4M, suggesting the emergence of a new 2-D degree of freedom on the horizon, which could be a way out of the information loss paradox.

scholarly journals Correction and accuracy improvement of non-parallel shear zone model

2018 ◽  
Vol 207 ◽  
pp. 02002
Author(s):  
Yaoke Wang ◽  
Meng Kou ◽  
Wei Ding ◽  
Huan Ma ◽  
Liangshan Xiong
Keyword(s):  
Experimental Data ◽  
Cutting Force ◽  
Shear Zone ◽  
Coordinate Transformation ◽  
Chip Thickness ◽  
Zone Model ◽  
Aisi 1045 Steel ◽  
Aisi 1045 ◽  
Experimental Values ◽  
1045 Steel

When applying the non-parallel shear zone model to predict the cutting process parameters of carbon steel workpiece, it is found that there is a big error between the prediction results and the experimental values. And also, the former approach to obtain the relevant cutting parameters of the non-parallel shear zone model by applying coordinate transformation to the parallel shear zone model has a theoretical error – it erroneously regards the determinant (|J|) of the Jacobian matrix (J) in the coordinate transformation as a constant. The shape of the shear zone obtained when |J| is not constant is drew and it is found that the two boundaries of the shear zone are two slightly curved surfaces rather than two inclined planes. Also, the error between predicted values and experimental values of cutting force and cutting thrust is slightly smaller than that of constant |J|. A corrected model where |J| is a variable is proposed. Since the specific values of inclination of the shear zone (α, β), the thickness coefficient of the shear zone (as) and the constants related to the material (f0, p) are not given in the former work, a method to obtain the above-mentioned five constants by solving multivariable constrained optimization problem based on experimental data was also proposed; based on the obtained experimental data of AISI 1045 steel workpiece cutting force, cutting thrust, chip thickness, the results of five above-mentioned model constants are obtained. It is found that, compared with prediction from uncorrected model, the cutting force and cutting thrust of AISI 1045 steel predicted by the corrected model with the obtained constants has a better agreement with the experimental values obtained by Ivester.

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