| 1. |
- Jiang, Wei, et al.
(författare)
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Room-temperature broadband quasistatic magnetic cloak
- 2017
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Ingår i: NPG ASIA MATERIALS. - : Nature Publishing Group. - 1884-4049 .- 1884-4057. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- In the past decade, invisible cloaks have experienced rapid research development in the metamaterial community driven by their revolutionary practical potentials. Among them, magnetic cloaks, which are able to conceal metallic or magnetic objects from electromagnetic induction detection, have attracted a great amount of attention. However, applications of these reported devices are limited by their low-temperature environment requirement because of the involvement of superconductors to acquire the perfect diamagnetic response. In this work, we remove this temperature hurdle by fully taking the diamagnetic features of usual metals and demonstrate a three-dimensional room temperature quasistatic magnetic cloak using a ferromagnetic metallic bilayer structure. Experimentally, our device exhibits a prominent cloaking effect in a wide frequency range from 5 to 250 kHz with a maximum field disturbance ratio < 0.5%. The practical potential is verified through a commercial handheld metal probe working at 25 kHz. Our results unambiguously show that an invisible cloak may be realized in the low-frequency region for scenarios where screening an external magnetic field without disturbance is specifically demanded.
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| 2. |
- Jiang, Wei, et al.
(författare)
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Static Magnetic Cloak without a Superconductor
- 2018
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Ingår i: Physical Review Applied. - : American Physical Society. - 2331-7019. ; 9:5
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Tidskriftsartikel (refereegranskat)abstract
- Similar to its electromagnetic counterpart, magnetic cloaking also has very important technological applications. However, the traditional method to build a static magnetic cloak requires the use of superconducting materials as the diamagnetic component, which seriously limits the practical potential because of the cryogenic condition. We show that a diamagnetic active current boundary combined with a high-permeability magnetic inner shell (MIS) can be designed to solve this problem, rendering an ideal magnetic cloaking effect at zero frequency. We first theoretically prove that a current boundary could magnetically behave as a superconductor to external observers. Based on this phenomena, we introduce a high-permeability MIS made of magnetically ultrasoft metallic sheets (permeability mu > 10(3)) and experimentally prove that the bilayer combination can exactly balance out the disturbance to the external probing field and, meanwhile, have a large invisible inner space. We also show that the active boundary currents can be accordingly configured to overcome the permeability and frequency band limits, leading to a robust cloak over the entire quasistatic frequency region. Our work creates an efficient way to circumvent the traditional limits of metamaterials to build magnetic cloaks for ultralow frequencies. The active-passive hybrid approach could be generally extended to yield other artificial magnetic devices or systems as well.
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| 3. |
- Liu, Yichao, et al.
(författare)
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An efficient plate heater with uniform surface temperature engineered with effective thermal materials
- 2014
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Ingår i: Optics Express. - 1094-4087. ; 22:14, s. 17006-17015
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Tidskriftsartikel (refereegranskat)abstract
- Extended from its electromagnetic counterpart, transformation thermodynamics applied to thermal conduction equations can map a virtual geometry into a physical thermal medium, realizing the manipulation of heat flux with almost arbitrarily desired diffusion paths, which provides unprecedented opportunities to create thermal devices unconceivable or deemed impossible before. In this work we employ this technique to design an efficient plate heater that can transiently achieve a large surface of uniform temperature powered by a small thermal source. As opposed to the traditional approach of relying on the deployment of a resistor network, our approach fully takes advantage of an advanced functional material system to guide the heat flux to achieve the desired temperature heating profile. A different set of material parameters for the transformed device has been developed, offering the parametric freedom for practical applications. As a proof of concept, the proposed devices are implemented with engineered thermal materials and show desired heating behaviors consistent with numerical simulations. Unique applications for these devices can be envisioned where stringent temperature uniformity and a compact heat source are both demanded.
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| 4. |
- Liu, Yichao, et al.
(författare)
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Broadband Electromagnetic Wave Tunneling with Transmuted Material Singularity
- 2020
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Ingår i: Physical Review Letters. - : American Physical Society (APS). - 0031-9007 .- 1079-7114. ; 125:20
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Tidskriftsartikel (refereegranskat)abstract
- Subwavelength channels filled with near-zero-index (NZI) media can realize extraordinary optical functionalities, for example, tunneling electromagnetic wave without reflections, but usually confined in a narrow wavelength band due to the material singularity (refractive index n approximate to 0), which seriously limits the practical potentials. In this Letter, we show this limit can be fundamentally overcome by an alternative, named near-zero-index-featured (NZIF) structure, with the singularity transmuted via a controlled optical conformal mapping, enabling the device implementation with nonmagnetic normal dielectrics (i.e., relative permittivity >1). Their equivalence is strictly examined through a subwavelength tunneling waveguide. Classic wave tunneling features in a broad frequency range are revealed in various confined geometries. These properties are robust against the disturbance of several kinds of structural defects benefited from the infinite effective local wavelength. The broadband and lossless NZIF medium proposed here provides a promising way to pursue the fascinating light controlling functionalities as initially enabled by singular NZI materials.
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| 5. |
- Liu, Yichao, et al.
(författare)
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Controlling the plasmonic surface waves of metallic nanowires by transformation optics
- 2015
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 107:1
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Tidskriftsartikel (refereegranskat)abstract
- In this letter, we introduce the technique of using transformation optics to manipulate the mode states of surface plasmonic waves of metallic nanowire waveguides. As examples we apply this technique to design two optical components: a three-dimensional (3D) electromagnetic mode rotator and a mode convertor. The rotator can rotate the polarization state of the surface wave around plasmonic nanowires by arbitrarily desired angles, and the convertor can transform the surface wave modes from one to another. Full-wave simulation is performed to verify the design and efficiency of our devices. Their potential application in photonic circuits is envisioned.
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| 6. |
- Ma, Yungui, et al.
(författare)
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A transient thermal cloak experimentally realized through a rescaled diffusion equation with anisotropic thermal diffusivity
- 2013
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Ingår i: NPG Asia Materials. - : Springer Science and Business Media LLC. - 1884-4049 .- 1884-4057. ; 5:11, s. e73-
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Tidskriftsartikel (refereegranskat)abstract
- Transformation optics has made a major contribution to the advancement of modern electromagnetism and related research assisted by the development of metamaterials. In this work, we applied this concept to the thermodynamics using the coordinate transformation to the time-dependent heat diffusion equation to manipulate the heat flux by predefined diffusion paths. Experimentally, we demonstrated a transient thermal cloaking device engineered with effective thermal materials and successfully hid a centimeter-sized vacuum cavity. A rescaled heat equation accounting for all the pertinent parameters of various ingredient materials was proposed to greatly facilitate the fabrication. Our results unambiguously demonstrate the practical possibility of implementing complex transformed thermal media with high accuracy and acquiring several unprecedented thermodynamic functions, which we believe will help to broaden the current research and pave a new path to manipulate heat for novel device applications.
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| 7. |
- Ma, Yungui, et al.
(författare)
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Experimental Demonstration of a Multiphysics Cloak : Manipulating Heat Flux and Electric Current Simultaneously
- 2014
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 113:20, s. 205501-
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Tidskriftsartikel (refereegranskat)abstract
- Invisible cloaks have been widely explored in many different physical systems but usually for a single phenomenon for one device. In this Letter we make an experimental attempt to show a multidisciplinary framework that has the capability to simultaneously respond to two different physical excitations according to predetermined scenarios. As a proof of concept, we implement an electric-thermal bifunctional device that can guide both electric current and heat flux "across" a strong 'scatterer' (air cavity) and restore their original diffusion directions as if nothing exists along the paths, thus rendering dual cloaking effects for objects placed inside the cavity. This bifunctional cloaking performance is also numerically verified for a line-source nonuniform excitation. Our results and the fabrication technique presented here will help broaden the current research scope for multiple disciplines and may pave a way to manipulate multiple flows and create new functional devices, e.g., for on-chip applications.
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| 8. |
- Ma, Yungui, et al.
(författare)
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First experimental demonstration of an isotropic electromagnetic cloak with strict conformal mapping
- 2013
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Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 3, s. 2182-
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Tidskriftsartikel (refereegranskat)abstract
- In the past years quasi-conformal mapping has been generally used to design broadband electromagnetic cloaks. However, this technique has some inherit practical limitations such as the lateral beam shift, rendering the device visible or difficult to hide a large object. In this work we circumvent these issues by using strict conformal mapping to build the first isotropic cloak. Microwave near-field measurement shows that our device (with dielectric constant larger than unity everywhere) has a very good cloaking performance and a broad frequency response. The present dielectric approach could be technically extended to the fabrication of other conformal devices at higher frequencies.
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| 9. |
- Ma, Yungui, et al.
(författare)
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Transformation thermodynamics : Heat flux control and device applications
- 2014
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Ingår i: 2014 XXXITH URSI GENERAL ASSEMBLY AND SCIENTIFIC SYMPOSIUM (URSI GASS). - : IEEE.
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Konferensbidrag (refereegranskat)abstract
- Extended from its electromagnetic counterpart [1,2], transformation thermodynamics applied to thermal conduction equations can map a virtual geometry into a physical thermal medium, realizing the manipulation of heat flux with almost arbitrarily desired diffusion paths, which provides unprecedented opportunities to create thermal devices unconceivable or deemed impossible before [3,4]. In this talk we report our recent work on manipulation of transient heat flux employing this technique and showed two thermal devices: a heat flux cloak and an efficient plate heater. In the cloaking device we will show that heat flux can be guided by a transformed medium to flow around a vacuum obstacle and restore its diffusion direction as if nothing inhomogeneous exists in their trajectories [5]. In the second experiment we design an efficient plate heater that can transiently achieve a large surface of uniform temperature powered by a small thermal source [6]. As opposed to the traditional approach of relying on the deployment of a resistor network, our approach fully takes advantage of an advanced functional material system to guide the heat flux to achieve the desired temperature heating profile. Our research results are good examples of the powerful application of coordinate transformation on wave/flux manipulation and may help to broaden research in acquiring extraordinary ways to control and utilize heat energy or configure novel heat devices.
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| 10. |
- Man, Shahid, et al.
(författare)
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FeGaB(25 nm)/Al2O3/FeGaB(25 nm) Multilayer Structures : Effects of Variation of Al(2)O(3)Thickness on Static and Dynamic Magnetic Properties
- 2018
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Ingår i: Xiyou jinshu cailiao yu gongcheng. - : NORTHWEST INST NONFERROUS METAL RESEARCH. - 1002-185X. ; 47:7, s. 1951-1957
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Tidskriftsartikel (refereegranskat)abstract
- Iron-gallium (FeGa) thin film has the unique advantages in designing integrated magnetic sensors or chips due to its relatively large magnetostrictive constant compared with other soft magnetic materials. In this work, non-magnetic doping and laminating methods have been employed to control the magnetic and electric properties of this alloy film. By doping a certain amount of boron (B), the coercivities are largely decreased for samples of thickness less than similar to 30 nm. For thicker films, we find that inserting an ultrathin Al2O3 middle layer is very helpful to control the coercivities with negligible influence on saturation magnetization (M-s). The smallest easy-axis coercivity of 0.98x79.6 A/m is obtained in the multilayer film FeGaB(25 nm)/Al2O3(0.5 nm)/FeGaB(25 nm). In this case, the resistivity is enhanced by 1.5 times compared with the 50 nm single layer film. Structural characterizations indicate the reductions of crystalline quality and physical dimension of the magnetic grains playing important roles in softening the magnetic properties. Besides, the influences of magnetostatic interaction and morphology characteristics are also considered in facilitating domain reversal. High permeability spectra with gigahertz response are obtained for our multilayer films. The methodology applied here, i.e., enhancing magnetic and electric performance by introducing ultrathin non-magnetic layers, could be translated to other species of soft magnetic materials as well.
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