Simultaneously manipulating multiple physical fields plays an important role in the increasingly complex integrated systems,aerospace equipment,biochemical productions,etc.For on-chip systems with high integration lev...Simultaneously manipulating multiple physical fields plays an important role in the increasingly complex integrated systems,aerospace equipment,biochemical productions,etc.For on-chip systems with high integration level,the precise and efficient control of the propagation of electromagnetic waves and heat fluxes simultaneously is particularly important.In this study,we propose a graphical designing method(i.e.,thermal-electromagnetic surface transformation)based on thermal-electromagnetic null medium to simultaneously control the propagation of electromagnetic waves and thermal fields according to the pre-designed paths.A thermal-electromagnetic cloak,which can create a cloaking effect on both electromagnetic waves and thermal fields simultaneously,is designed by thermal-electromagnetic surface transformation and verified by both numerical simulations and experimental measurements.The thermal-electromagnetic surface transformation proposed in this study provides a new methodology for simultaneous controlling on electromagnetic and temperature fields,and may have significant applications in improving thermal-electromagnetic compatibility problem,protecting of thermal-electromagnetic sensitive components,and improving efficiency of energy usage for complex onchip systems.展开更多
In the present paper, a physical model is proposed for reducing the problem of the drag reduction of an attached bow shock around the nose of a high-speed vehicle with on-board discharge, to the problem of a balance b...In the present paper, a physical model is proposed for reducing the problem of the drag reduction of an attached bow shock around the nose of a high-speed vehicle with on-board discharge, to the problem of a balance between the magnetic pressure and gas pressure of plane shock of a partially ionized gas consisting of the environmental gas around the nose of the vehicle and the on-board discharge-produced plasma. The relation between the shock strength and the discharge-induced magnetic pressure is studied by means of a set of one-fluid, hydromagnetic equations reformed for the present purpose, where the discharge-induced magnetic field consists of the electron current （produced by the discharge）-induced magnetic field and the partially ionized gas flow-induced one. A formula for the relation between the above parameters is derived. It shows that the discharge-induced magnetic pressure can minimize the shock strength, successfully explaining the two recent experimental observations on attached bow shock mitigation and elimination in a supersonic flow during on-board discharge [Phys. Plasmas 9 （2002） 721 and Phys. Plasmas 7 （2000） 1345]. In addition, the formula implies that the shock elimination leaves room for a layer of higher-density plasma rampart moving around the nose of the vehicle, being favourable to the plasma radar cloaking of the vehicle. The reason for it is expounded.展开更多
The concentrically layered thermal cloaks with isotropic materials could realize the equivalent thermal cloaking effect with Pendry＇s cloak, while the effectiveness is scarcely investigated quantitatively. Here we ex...The concentrically layered thermal cloaks with isotropic materials could realize the equivalent thermal cloaking effect with Pendry＇s cloak, while the effectiveness is scarcely investigated quantitatively. Here we examine the cloaking effectiveness quantitatively by evaluating the standard deviation of the temperature difference between the simulated plane with the layered thermal cloak and Pendry＇s thermal cloak. The design rules for the isotropic materials in terms of thermal conductivity and layer thickness are presented. The present method could quan- titatively evaluate the cloaking effectiveness, and could open avenues for analyzing the cloaking effect, detecting the （anti-） cloaks, etc.展开更多
Electromagnetic cloaking based on the scattering cancellation method have been reviewed. The possibility of designing the tunable electromagnetic cloaking is analytically suggested with a single cloak composed of homo...Electromagnetic cloaking based on the scattering cancellation method have been reviewed. The possibility of designing the tunable electromagnetic cloaking is analytically suggested with a single cloak composed of homogeneous materials,including semiconductor,superconductor,ferrite and ferroelectrics by using Mie scattering theory. The simulated results demonstrate that the cloaks with these homogeneous materials can drastically reduce the total scattering cross sections of the cloaked system by using the finite element method. These cloaking frequencies can be controlled by external field through tuning the permittivity or permeability of these materials by the applied field,such as temperature,magnetic field and electric field. These may provide some potential ways to design tunable cloaking with considerable flexibility.展开更多
In cloaking, a body is hidden from detection by surrounding it by a coating consisting of an unusual anisotropic nonhomogeneous material. The permittivity and permeability of such a cloak are determined by the coordin...In cloaking, a body is hidden from detection by surrounding it by a coating consisting of an unusual anisotropic nonhomogeneous material. The permittivity and permeability of such a cloak are determined by the coordinate transformation of compressing a hidden body into a point or a line. The radially-dependent spherical cloaking shell can be approximately discretized into many homogeneous anisotropic layers;each anisotropic layer can be replaced by a pair of equivalent isotropic sub-layers, where the effective medium approximation is used to find the parameters of these two equivalent sub-layers. In this work, the scattering properties of cloaked dielectric sphere is investigated using a combination of approximate cloaking, where the dielectric sphere is transformed into a small sphere rather than to a point, together with discretizing the cloaking material using pairs of homogeneous isotropic sub-layers. The back-scattering normalized radar cross section, the scattering patterns are studied and the total scattering cross section against the frequency for different number of layers and transformed radius.展开更多
Acoustic cloaking is an important application of acoustic metamaterials.This article proposes a novel design scheme for acoustic cloaking based on the region partitioning and multi-origin coordinate transformation.The...Acoustic cloaking is an important application of acoustic metamaterials.This article proposes a novel design scheme for acoustic cloaking based on the region partitioning and multi-origin coordinate transformation.The cloaked region is partitioned into multiple narrow strips.For each strip,a local coordinate system is established with the local origin located at the strip center,and a coordinate transformation in the local coordinate system is conducted to squeeze the material along the strip length direction to form the cloaked region.To facilitate the implementation of the acoustic cloak,the multilayer effective medium is used to approximate the non-uniform anisotropic material parameters.The effectiveness of the proposed coordinate transformation method is verified by comparing the results from our method with those in the literature.Firstly,the results of a circular acoustic cloak in the literature are reproduced by using our finite element(FE)simulations for validation.Then,a comparison is made between the traditional coordinate transformation scheme and our new scheme for simulating an elliptical acoustic cloak.The results indicate that the proposed multi-origin coordinate transformation method has a better cloaking effect on the incident wave along the ellipse minor axis direction than the traditional method.This means that for the same object,an appropriate transformation scheme can be selected for different incident wave directions to achieve the optimal control effect.The validated scheme is further used to design an arch-shaped cloak composed of an upper semicircular area and a lower rectangular area,by combining the traditional single-centered coordinate transformation method for the semicircular area and the proposed multi-origin method for the rectangular area.The results show that the designed cloak can effectively control the wave propagation with significantly reduced acoustic pressure level.This work provides a flexible acoustic cloak design method applicable for arbitrary shapes and different wave incident directions,enriching the theory of acoustic cloaking based on coordinate transformation.展开更多
A novel cloaking scheme to hide an object in a half space from electromagnetic （EM） detection without reflection is firstly presented. The proposed cloaking scheme contains a couple of matching strips, which consist...A novel cloaking scheme to hide an object in a half space from electromagnetic （EM） detection without reflection is firstly presented. The proposed cloaking scheme contains a couple of matching strips, which consist of an isotropic material layer and an anisotropic UPML layer, located right under the bottom surface of a semi-cylindrical cloaking shell. Simple expressions for the material parameters of the cloaking scheme are derived. Numerical simulations are also performed, and a good cloaking effect is achieved. The cloaking scheme is effective to hide the local object with strong scattering characters placed on mobile carders, such as the radar antenna system on an aircraft.展开更多
Transformation optics provides great versatility for precisely manipulating electromagnetic waves. It has been extended to other fields including acoustics, thermotics, and electrics. Taking advantage of the transform...Transformation optics provides great versatility for precisely manipulating electromagnetic waves. It has been extended to other fields including acoustics, thermotics, and electrics. Taking advantage of the transformation electrics method, we demonstrate that the square-shaped cloak can guide electric current around the cloaked region smoothly without perturbing the exterior electric current. And the cylindrical rotator can rotate the electric current.Inside the enclosed domain of the rotator, the electric current from the outside will appear as if it is coming from a different angle. Finally, the related experimental realizations and potential applications are also discussed.展开更多
Thermal rectification refers to the asymmetry in heat transfer capability when subjected to forward and reverse temperature gradients.A thermal cloak can render objects invisible in thermal fields by redirecting heat ...Thermal rectification refers to the asymmetry in heat transfer capability when subjected to forward and reverse temperature gradients.A thermal cloak can render objects invisible in thermal fields by redirecting heat flux pathways.In this paper,we present a thermal diode model based on a bi-layer thermal cloak system that incorporates a composite heat-fluxattracting layer with asymmetric,temperature-dependent thermal conductivity.In the forward case,the heat flux bypasses the cloaking region while maintaining undistorted background isotherm contours,whereas in the reverse case,the thermal cloak fails to function and the device effectively insulates heat.Consequently,thermal rectification occurs in the bi-layer thermal cloak system.A significant increase in the thermal rectification ratio is observed as the temperature gradient increases.By optimizing the system dimensions,a peak rectification ratio of 11.06 is achieved.This study provides physical insight and a design framework for developing novel thermal diodes with dual-functional thermal management capabilities.展开更多
The existing knowledge on the electrodynamics of invisibility cloaking based on transformation optics is reviewed from an integrated science and engineering perspective.Several significant electromagnetic problems tha...The existing knowledge on the electrodynamics of invisibility cloaking based on transformation optics is reviewed from an integrated science and engineering perspective.Several significant electromagnetic problems that have resulted in intense discussions in the past few years are summarized in terms of propagation,scattering,radiation and fabrication.Finally,the road ahead toward invisibility cloaking and transformation optics is discussed from the viewpoint of the author.展开更多
In view of the fact that most invisibility devices focus on linear polarization cloaking and that the characteristics of mid-infrared cloaking are rarely studied,we propose a cross-circularly polarized invisibility ca...In view of the fact that most invisibility devices focus on linear polarization cloaking and that the characteristics of mid-infrared cloaking are rarely studied,we propose a cross-circularly polarized invisibility carpet cloaking device in the mid-infrared band.Based on the Pancharatnam–Berry phase principle,the unit cells with the cross-circular polarization gradient phase were carefully designed and constructed into a metasurface.In order to achieve tunable cross-circular polarization carpet cloaks,a phase change material is introduced into the design of the unit structure.When the phase change material is in amorphous and crystalline states,the proposed metasurface unit cells can achieve highefficiency cross-polarization conversion,and reflection intensity can be tuned.According to the phase compensation principle of carpet cloaking,we construct a metasurface cloaking device with a phase gradient using the designed unit structure.From the near-and far-field distributions,the cross-circular polarization cloaking property is confirmed in the broadband wavelength range of 9.3–11.4μm.The proposed cloaking device can effectively resist detection of cross-circular polarization.展开更多
We consider the approximate acoustic cloaking in an inhomogeneous isotropic background space.By employing transformation media,together with the use of a sound-soft layer lining right outside the cloaked region,we sho...We consider the approximate acoustic cloaking in an inhomogeneous isotropic background space.By employing transformation media,together with the use of a sound-soft layer lining right outside the cloaked region,we show that one can achieve the near-invisibility by the"blow-up-a-small-region"construction.This is based on novel scattering estimates corresponding to multiple multi-scale obstacles located in an isotropic space.We develop a novel system of integral equations to decouple the nonlinear scattering interaction among the small obstacle components,the regular obstacle components and the inhomogeneous background medium.展开更多
Making the propagation of sound waves immune to interference from obstacles with high transmission efficiency is a long-term pursuit in acoustic science and engineering.Recent proposal pointed out that perfect transmi...Making the propagation of sound waves immune to interference from obstacles with high transmission efficiency is a long-term pursuit in acoustic science and engineering.Recent proposal pointed out that perfect transmission through obstacles can be achieved by deploying a bulky gain-loss distribution in parity-time(PT)symmetry.Here we demonstrate a modified methodology to achieve the extraordinary physical property of acoustic cloaking accompanied by perfect transmission at the exceptional points(EPs).Systematically probing reveals two complementary solutions of EPs corresponding to acoustic cloaking,in the system composed of an equivalent medium slab sandwiched by a pair of PT-symmetric admittance metasurfaces.To model the crucial acoustic gains that are not present in nature,we employ actively controlled ultra-thin carbon nanotube dimer films to mimic admittance metasurfaces perfectly via thermoacoustic effect,and manipulate acoustic cloaking over a wide frequency band in experiments.This divergent strategy releases restrictions on the operating frequency,shape and size of the obstacle,which can be applied to acoustic sensing,directional imaging,and other related wave disciplines.展开更多
In this paper we present a rigorous derivation of the material parameters for both the cylinder and rectangle cloaking structures.Numerical results using these material parameters are presented to demonstrate the cloa...In this paper we present a rigorous derivation of the material parameters for both the cylinder and rectangle cloaking structures.Numerical results using these material parameters are presented to demonstrate the cloaking effect.展开更多
In this work,we investigate wave propagation through a zero index meta-material(ZIM)waveguide embedded with triangular dielectric defects.We provide a theoretical guidance on how to achieve total reflection and total t...In this work,we investigate wave propagation through a zero index meta-material(ZIM)waveguide embedded with triangular dielectric defects.We provide a theoretical guidance on how to achieve total reflection and total transmission(i.e.,cloaking)by adjusting the defect sizes and/or permittivities of the defects.Our work provides a systematical way in manipulating wave propagation through ZIM in addi-tion to the widely studied dielectric defects with cylindrical and rectangular geome-tries.展开更多
Thermal-electric bilayer invisibility cloak can prevent the heat flux and electric current from touching the object without distorting the external temperature and electric potential fields simultaneously.In this pape...Thermal-electric bilayer invisibility cloak can prevent the heat flux and electric current from touching the object without distorting the external temperature and electric potential fields simultaneously.In this paper,we design an omnidirectional thermal-electric invisibility cloak with anisotropic geometry.Based on the theory of neutral inclusion,the anisotropic effective thermal and electric conductivities of confocal elliptical bilayer core-shell structure are derived,thus obtaining the anisotropic matrix material to eliminate the external disturbances omnidirectionally.The inner shell of the cloak is selected as an insulating material to shield the heat flux and electric current.Then,the omnidirectional thermal-electric cloaking effect is verified numerically and experimentally based on the theoretical anisotropic matrix and manufactured composite structure,respectively.Furthermore,we achieve the thermal-electric cloaking effect under a specific direction of heat flux and electric current using the isotropic natural materials to broaden the selection range of materials.The method proposed to eliminate anisotropy and achieve the omnidirectional effect could also be expanded to other different physical fields for the metadevices with different functions.展开更多
In this paper,a design method for an acoustic cloak in the presence of background mean flows is proposed by using topology optimization,which enables the associated fabrication of the cloaking design.The density-based...In this paper,a design method for an acoustic cloak in the presence of background mean flows is proposed by using topology optimization,which enables the associated fabrication of the cloaking design.The density-based topology optimization method is used to allocate the designated materials,thus providing the structure of the cloak.The optimization problem is efficiently solved with the gradient-based globally convergent method of moving asymptotes,which utilizes the derivative information from the finite element simulation studies of the linearized acoustic potential equation.This paper introduces the whole design method first then numerically demonstrates the corresponding performance,which shall constitute the main contribution of the present work.展开更多
Metamaterials are artificial composite materials engineered to have properties that may not be found in nature. By exploring locally resonant effect of the building units, elastic metamaterials are able to possess neg...Metamaterials are artificial composite materials engineered to have properties that may not be found in nature. By exploring locally resonant effect of the building units, elastic metamaterials are able to possess negative values of effective mass, effective bulk or shear modulus. Mass-spring and continuum material versions of these elastic metamaterials are reported and the physical mechanisms of negative effective parameters are demonstrated. Applications of metamaterials to acoustic cloaking and superlensing are also discussed.展开更多
In this paper, acoustic scattering from the system comprised of a cloaked object and the multilayer cloak with only one single pair of isotropic media is analyzed with a recursive numerical method. The designed acoust...In this paper, acoustic scattering from the system comprised of a cloaked object and the multilayer cloak with only one single pair of isotropic media is analyzed with a recursive numerical method. The designed acoustic parameters of the isotropic cloak media are assumed to be single-negative, and the resulting cloak can reduce acoustic scattering from an acoustic sensor while allowing it to receive external information. Several factors that may influence the performance of the cloak, including the number of layers and the acoustic dissipation of the medium are fully analyzed. Furthermore, the possibility of achieving acoustic invisibility with positive acoustic parameters is proposed by searching the optimum value in the parameter space and minimizing the scattering cross-section.展开更多
基金supported by the National Natural Science Foundation of China (Nos. 61971300, 12274317, 12374277, 61905208)Open Foundation of China-Belarus Belt and Road Joint Laboratory on Electromagnetic Environment Effect (No. ZBKF2022031202)+1 种基金Scientific and Technological Innovation Programs (STIP) of Higher Education Institutions in Shanxi (Nos. 2019L0159 and 2019L0146)2022 University Outstanding Youth Foundation of Taiyuan University of Technology
文摘Simultaneously manipulating multiple physical fields plays an important role in the increasingly complex integrated systems,aerospace equipment,biochemical productions,etc.For on-chip systems with high integration level,the precise and efficient control of the propagation of electromagnetic waves and heat fluxes simultaneously is particularly important.In this study,we propose a graphical designing method(i.e.,thermal-electromagnetic surface transformation)based on thermal-electromagnetic null medium to simultaneously control the propagation of electromagnetic waves and thermal fields according to the pre-designed paths.A thermal-electromagnetic cloak,which can create a cloaking effect on both electromagnetic waves and thermal fields simultaneously,is designed by thermal-electromagnetic surface transformation and verified by both numerical simulations and experimental measurements.The thermal-electromagnetic surface transformation proposed in this study provides a new methodology for simultaneous controlling on electromagnetic and temperature fields,and may have significant applications in improving thermal-electromagnetic compatibility problem,protecting of thermal-electromagnetic sensitive components,and improving efficiency of energy usage for complex onchip systems.
基金Project supported by the National Natural Science Foundation of China （Grant Nos 40390150 and 10005001）.
文摘In the present paper, a physical model is proposed for reducing the problem of the drag reduction of an attached bow shock around the nose of a high-speed vehicle with on-board discharge, to the problem of a balance between the magnetic pressure and gas pressure of plane shock of a partially ionized gas consisting of the environmental gas around the nose of the vehicle and the on-board discharge-produced plasma. The relation between the shock strength and the discharge-induced magnetic pressure is studied by means of a set of one-fluid, hydromagnetic equations reformed for the present purpose, where the discharge-induced magnetic field consists of the electron current （produced by the discharge）-induced magnetic field and the partially ionized gas flow-induced one. A formula for the relation between the above parameters is derived. It shows that the discharge-induced magnetic pressure can minimize the shock strength, successfully explaining the two recent experimental observations on attached bow shock mitigation and elimination in a supersonic flow during on-board discharge [Phys. Plasmas 9 （2002） 721 and Phys. Plasmas 7 （2000） 1345]. In addition, the formula implies that the shock elimination leaves room for a layer of higher-density plasma rampart moving around the nose of the vehicle, being favourable to the plasma radar cloaking of the vehicle. The reason for it is expounded.
基金Supported by the National Natural Science Foundation of China under Grant Nos 51576078 and 51376070
文摘The concentrically layered thermal cloaks with isotropic materials could realize the equivalent thermal cloaking effect with Pendry＇s cloak, while the effectiveness is scarcely investigated quantitatively. Here we examine the cloaking effectiveness quantitatively by evaluating the standard deviation of the temperature difference between the simulated plane with the layered thermal cloak and Pendry＇s thermal cloak. The design rules for the isotropic materials in terms of thermal conductivity and layer thickness are presented. The present method could quan- titatively evaluate the cloaking effectiveness, and could open avenues for analyzing the cloaking effect, detecting the （anti-） cloaks, etc.
基金Supported by the National Natural Science Foundation of China(11174147,11104144)
文摘Electromagnetic cloaking based on the scattering cancellation method have been reviewed. The possibility of designing the tunable electromagnetic cloaking is analytically suggested with a single cloak composed of homogeneous materials,including semiconductor,superconductor,ferrite and ferroelectrics by using Mie scattering theory. The simulated results demonstrate that the cloaks with these homogeneous materials can drastically reduce the total scattering cross sections of the cloaked system by using the finite element method. These cloaking frequencies can be controlled by external field through tuning the permittivity or permeability of these materials by the applied field,such as temperature,magnetic field and electric field. These may provide some potential ways to design tunable cloaking with considerable flexibility.
文摘In cloaking, a body is hidden from detection by surrounding it by a coating consisting of an unusual anisotropic nonhomogeneous material. The permittivity and permeability of such a cloak are determined by the coordinate transformation of compressing a hidden body into a point or a line. The radially-dependent spherical cloaking shell can be approximately discretized into many homogeneous anisotropic layers;each anisotropic layer can be replaced by a pair of equivalent isotropic sub-layers, where the effective medium approximation is used to find the parameters of these two equivalent sub-layers. In this work, the scattering properties of cloaked dielectric sphere is investigated using a combination of approximate cloaking, where the dielectric sphere is transformed into a small sphere rather than to a point, together with discretizing the cloaking material using pairs of homogeneous isotropic sub-layers. The back-scattering normalized radar cross section, the scattering patterns are studied and the total scattering cross section against the frequency for different number of layers and transformed radius.
基金supported by the opening project of State Key Laboratory of Explosion Science and Technology (Beijing Institute of Technology)(No. KFJJ22-08M)the State Key Laboratory of Mechanics and Control of Mechanical Structures (No. MCMS-E-0221G02)Shanghai Supercomputer Center
文摘Acoustic cloaking is an important application of acoustic metamaterials.This article proposes a novel design scheme for acoustic cloaking based on the region partitioning and multi-origin coordinate transformation.The cloaked region is partitioned into multiple narrow strips.For each strip,a local coordinate system is established with the local origin located at the strip center,and a coordinate transformation in the local coordinate system is conducted to squeeze the material along the strip length direction to form the cloaked region.To facilitate the implementation of the acoustic cloak,the multilayer effective medium is used to approximate the non-uniform anisotropic material parameters.The effectiveness of the proposed coordinate transformation method is verified by comparing the results from our method with those in the literature.Firstly,the results of a circular acoustic cloak in the literature are reproduced by using our finite element(FE)simulations for validation.Then,a comparison is made between the traditional coordinate transformation scheme and our new scheme for simulating an elliptical acoustic cloak.The results indicate that the proposed multi-origin coordinate transformation method has a better cloaking effect on the incident wave along the ellipse minor axis direction than the traditional method.This means that for the same object,an appropriate transformation scheme can be selected for different incident wave directions to achieve the optimal control effect.The validated scheme is further used to design an arch-shaped cloak composed of an upper semicircular area and a lower rectangular area,by combining the traditional single-centered coordinate transformation method for the semicircular area and the proposed multi-origin method for the rectangular area.The results show that the designed cloak can effectively control the wave propagation with significantly reduced acoustic pressure level.This work provides a flexible acoustic cloak design method applicable for arbitrary shapes and different wave incident directions,enriching the theory of acoustic cloaking based on coordinate transformation.
基金Project supported by the Program for New Century Excellent Talents in University of China (Grant No. NCET-10-0894)
文摘A novel cloaking scheme to hide an object in a half space from electromagnetic （EM） detection without reflection is firstly presented. The proposed cloaking scheme contains a couple of matching strips, which consist of an isotropic material layer and an anisotropic UPML layer, located right under the bottom surface of a semi-cylindrical cloaking shell. Simple expressions for the material parameters of the cloaking scheme are derived. Numerical simulations are also performed, and a good cloaking effect is achieved. The cloaking scheme is effective to hide the local object with strong scattering characters placed on mobile carders, such as the radar antenna system on an aircraft.
基金Support by Young Teacher Training Program of Shanghai Municipal Education Commission under Grant No.egd11005by Innovation Program of Shanghai Municipal Education Commission under Grant No.12YZ177+3 种基金by National Natural Science Foundation of China under Grant No.11304195financial support by the National Natural Science Foundation of China under Grant Nos.11075035 and 11222544by Fok Ying Tung Education Foundation under Grant No.131008by Shanghai Rising-Star Program under Grant No.12QA1400200
文摘Transformation optics provides great versatility for precisely manipulating electromagnetic waves. It has been extended to other fields including acoustics, thermotics, and electrics. Taking advantage of the transformation electrics method, we demonstrate that the square-shaped cloak can guide electric current around the cloaked region smoothly without perturbing the exterior electric current. And the cylindrical rotator can rotate the electric current.Inside the enclosed domain of the rotator, the electric current from the outside will appear as if it is coming from a different angle. Finally, the related experimental realizations and potential applications are also discussed.
文摘Thermal rectification refers to the asymmetry in heat transfer capability when subjected to forward and reverse temperature gradients.A thermal cloak can render objects invisible in thermal fields by redirecting heat flux pathways.In this paper,we present a thermal diode model based on a bi-layer thermal cloak system that incorporates a composite heat-fluxattracting layer with asymmetric,temperature-dependent thermal conductivity.In the forward case,the heat flux bypasses the cloaking region while maintaining undistorted background isotherm contours,whereas in the reverse case,the thermal cloak fails to function and the device effectively insulates heat.Consequently,thermal rectification occurs in the bi-layer thermal cloak system.A significant increase in the thermal rectification ratio is observed as the temperature gradient increases.By optimizing the system dimensions,a peak rectification ratio of 11.06 is achieved.This study provides physical insight and a design framework for developing novel thermal diodes with dual-functional thermal management capabilities.
文摘The existing knowledge on the electrodynamics of invisibility cloaking based on transformation optics is reviewed from an integrated science and engineering perspective.Several significant electromagnetic problems that have resulted in intense discussions in the past few years are summarized in terms of propagation,scattering,radiation and fabrication.Finally,the road ahead toward invisibility cloaking and transformation optics is discussed from the viewpoint of the author.
基金This work was supported by the National Key R&D Program of China(No.2018YFF01013005)the Natural Science Foundation of Zhejiang Province(Nos.LY22F050001,LZ21A040003,and LY20F050007)+2 种基金the National Natural Science Foundation of China(Nos.52076200 and 62175224)the Newshoot Talents Program of Zhejiang province(Nos.2021R409042 and 2021R409012)the Fundamental Research Funds for the Provincial Universities of Zhejiang.
文摘In view of the fact that most invisibility devices focus on linear polarization cloaking and that the characteristics of mid-infrared cloaking are rarely studied,we propose a cross-circularly polarized invisibility carpet cloaking device in the mid-infrared band.Based on the Pancharatnam–Berry phase principle,the unit cells with the cross-circular polarization gradient phase were carefully designed and constructed into a metasurface.In order to achieve tunable cross-circular polarization carpet cloaks,a phase change material is introduced into the design of the unit structure.When the phase change material is in amorphous and crystalline states,the proposed metasurface unit cells can achieve highefficiency cross-polarization conversion,and reflection intensity can be tuned.According to the phase compensation principle of carpet cloaking,we construct a metasurface cloaking device with a phase gradient using the designed unit structure.From the near-and far-field distributions,the cross-circular polarization cloaking property is confirmed in the broadband wavelength range of 9.3–11.4μm.The proposed cloaking device can effectively resist detection of cross-circular polarization.
基金supported by National Natural Science Foundation of China(Grant Nos.1110141411201453+1 种基金91130022 and 91130026)National Science Foundation of USA(Grant No.DMS 1207784)
文摘We consider the approximate acoustic cloaking in an inhomogeneous isotropic background space.By employing transformation media,together with the use of a sound-soft layer lining right outside the cloaked region,we show that one can achieve the near-invisibility by the"blow-up-a-small-region"construction.This is based on novel scattering estimates corresponding to multiple multi-scale obstacles located in an isotropic space.We develop a novel system of integral equations to decouple the nonlinear scattering interaction among the small obstacle components,the regular obstacle components and the inhomogeneous background medium.
基金supported by the National Key Research and Development Program of China(Grant No.2022YFA1404400)the National Natural Science Foundation of China(Grant Nos.11834008,11904035,12074183,12225408,and 12227809)+2 种基金the Qing Lan Project of Jiangsu Provincethe Natural Science Foundation of the Jiangsu Higher Education Institutions of China(Grant No.23KJD140001)Changzhou Sci&Tech Program(Grant No.CJ20220256)。
文摘Making the propagation of sound waves immune to interference from obstacles with high transmission efficiency is a long-term pursuit in acoustic science and engineering.Recent proposal pointed out that perfect transmission through obstacles can be achieved by deploying a bulky gain-loss distribution in parity-time(PT)symmetry.Here we demonstrate a modified methodology to achieve the extraordinary physical property of acoustic cloaking accompanied by perfect transmission at the exceptional points(EPs).Systematically probing reveals two complementary solutions of EPs corresponding to acoustic cloaking,in the system composed of an equivalent medium slab sandwiched by a pair of PT-symmetric admittance metasurfaces.To model the crucial acoustic gains that are not present in nature,we employ actively controlled ultra-thin carbon nanotube dimer films to mimic admittance metasurfaces perfectly via thermoacoustic effect,and manipulate acoustic cloaking over a wide frequency band in experiments.This divergent strategy releases restrictions on the operating frequency,shape and size of the obstacle,which can be applied to acoustic sensing,directional imaging,and other related wave disciplines.
基金The first author is supported by National Science Foundation grant DMS-0810896This work is also inspired by the workshop “Metamaterials:Applications,Analysis and Modeling”held at the Institute for Pure and Applied Mathematics(IPAM)located at University of California at Los Angeles(UCLA)during January 25-29,2010.+1 种基金As Co-Chair of this workshop,he highly appreciated IPAM’s kind support for sponsoring this workshopThe second author is supported in part by the NSFC Key Project 11031006 and Hunan Provincial NSF project 10JJ7001.
文摘In this paper we present a rigorous derivation of the material parameters for both the cylinder and rectangle cloaking structures.Numerical results using these material parameters are presented to demonstrate the cloaking effect.
基金Prof.Yunqing Huang is partially supported by NSFC Key Project 91430213,IRT1179 of PCSIRT and MOST 2010DFR00700Prof.Jichun Li is Partially supported by NSFC project 11271310 and a grant from the Simons Foundation(#281296 to Jichun Li).
文摘In this work,we investigate wave propagation through a zero index meta-material(ZIM)waveguide embedded with triangular dielectric defects.We provide a theoretical guidance on how to achieve total reflection and total transmission(i.e.,cloaking)by adjusting the defect sizes and/or permittivities of the defects.Our work provides a systematical way in manipulating wave propagation through ZIM in addi-tion to the widely studied dielectric defects with cylindrical and rectangular geome-tries.
基金This work was financially supported by the National Natural Science Foundation of China(Grant No.11572090)the Fundamental Research Funds for the Central Universities(Grant No.3072022GIP0202).
文摘Thermal-electric bilayer invisibility cloak can prevent the heat flux and electric current from touching the object without distorting the external temperature and electric potential fields simultaneously.In this paper,we design an omnidirectional thermal-electric invisibility cloak with anisotropic geometry.Based on the theory of neutral inclusion,the anisotropic effective thermal and electric conductivities of confocal elliptical bilayer core-shell structure are derived,thus obtaining the anisotropic matrix material to eliminate the external disturbances omnidirectionally.The inner shell of the cloak is selected as an insulating material to shield the heat flux and electric current.Then,the omnidirectional thermal-electric cloaking effect is verified numerically and experimentally based on the theoretical anisotropic matrix and manufactured composite structure,respectively.Furthermore,we achieve the thermal-electric cloaking effect under a specific direction of heat flux and electric current using the isotropic natural materials to broaden the selection range of materials.The method proposed to eliminate anisotropy and achieve the omnidirectional effect could also be expanded to other different physical fields for the metadevices with different functions.
基金This work was supported by the Beijing Municipal Science&Technology Commission(Grant Z181100001018030)the National Natural Science Foundation of China(Grant 11561130148)the Newton Advanced Fellowship from the Royal Society(Ref.NA14081).
文摘In this paper,a design method for an acoustic cloak in the presence of background mean flows is proposed by using topology optimization,which enables the associated fabrication of the cloaking design.The density-based topology optimization method is used to allocate the designated materials,thus providing the structure of the cloak.The optimization problem is efficiently solved with the gradient-based globally convergent method of moving asymptotes,which utilizes the derivative information from the finite element simulation studies of the linearized acoustic potential equation.This paper introduces the whole design method first then numerically demonstrates the corresponding performance,which shall constitute the main contribution of the present work.
基金supported by the National Natural Science Foundation of China (10832002,11172038,10972036)
文摘Metamaterials are artificial composite materials engineered to have properties that may not be found in nature. By exploring locally resonant effect of the building units, elastic metamaterials are able to possess negative values of effective mass, effective bulk or shear modulus. Mass-spring and continuum material versions of these elastic metamaterials are reported and the physical mechanisms of negative effective parameters are demonstrated. Applications of metamaterials to acoustic cloaking and superlensing are also discussed.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11274168,11374157,11174138,11174139,11222442,and 81127901)the National Basic Research Program of China(Grant Nos.2010CB327803 and 2012CB921504)
文摘In this paper, acoustic scattering from the system comprised of a cloaked object and the multilayer cloak with only one single pair of isotropic media is analyzed with a recursive numerical method. The designed acoustic parameters of the isotropic cloak media are assumed to be single-negative, and the resulting cloak can reduce acoustic scattering from an acoustic sensor while allowing it to receive external information. Several factors that may influence the performance of the cloak, including the number of layers and the acoustic dissipation of the medium are fully analyzed. Furthermore, the possibility of achieving acoustic invisibility with positive acoustic parameters is proposed by searching the optimum value in the parameter space and minimizing the scattering cross-section.
