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  • 1.
    He, Sailing
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Cui, Yanxia
    KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Ye, Yuqian
    KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Zhang, Pu
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Jin, Yi
    KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Optical nano-antennas and metamaterials2009In: MATERIALS TODAY, ISSN 1369-7021, Vol. 12, no 12, p. 16-24Article in journal (Refereed)
    Abstract [en]

    We review some recent approaches to transmission enhancement and light harvesting based on optical nano-antennas and metamaterials. Nano-cavity antennas are used to enhance the extraordinary transmission of TM-polarized light through vertical nano-slits in a metal film. The enhanced transmission of TE-polarized waves through an array of subwavelength-slits in a thin metal film at low frequencies (including microwave) is also investigated. Light harvesting with a metamaterial cloaking shell is also demonstrated.

  • 2.
    Jin, Yi
    et al.
    KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Zhang, Pu
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Abnormal enhancement of electric field inside a thin permittivity-near-zero object in free space2010In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 82, no 7, p. 075118-Article in journal (Refereed)
    Abstract [en]

    It is found that the electric field can be enhanced strongly inside a permittivity-near-zero object in free space, when the transverse cross section of the object is small and the length along the propagation direction of the incident wave is large enough as compared with the wavelength. The physical mechanism is explained in details. The incident electromagnetic energy can only flow almost normally through the outer surface into or out of the permittivity-near-zero object, which leads to large energy stream density and then strong electric field inside the object. Meanwhile, the magnetic field inside the permittivity-near-zero object may be smaller than that of the incident wave, which is also helpful for enhancing the electric field. Two permittivity-near-zero objects of simple shapes, namely, a thin cylindrical shell and a long thin rectangular bar, are chosen for numerical illustration. The enhancement of the electric field becomes stronger when the permittivity-near-zero object becomes thinner. The physical mechanism of the field enhancement is completely different from the plasmonic resonance enhancement at a metal surface.

  • 3.
    Jin, Yi
    et al.
    KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Zhang, Pu
    KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP. KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Squeezing electromagnetic energy with a dielectric split ring inside a permeability-near-zero metamaterial2010In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, no 8Article in journal (Refereed)
    Abstract [en]

    An electromagnetic energy squeezing mechanism is proposed based on the special properties of permeability-near-zero metamaterials. It is found that nearly no energy stream can enter a simply connected conventional dielectric material positioned inside a permeability-near-zero material. When the dielectric domain is shaped as a split ring (with a gap opened) surrounding a source, the electromagnetic energy generated by the source is forced to propagate through the gap. When the gap is narrow, the energy stream density becomes very large and makes the magnetic field enhanced drastically in the gap. The narrow gap can be long and bended. This provides us a method to obtain strong magnetic field without using resonance enhancement.

  • 4.
    Zhang, Pu
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Theory of transformation optics and invisibility cloak design2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Research on metamaterials has been growing ever since the first experimental realization of double negative media. The theory of transformation optics provides people with a perfect tool to make use of vast possibilities of the constitutive parameters for metamaterials. A lot of fascinating designs have been brought to us by transformation optics, with invisibility cloaks being the most intensely studied. The present thesis aims to develop the basic theory of transformation optics, and utilize it to design invisibility cloaks for various applications.

    After the background description of this field, the theory of transformation optics is first introduced. Formulas of transformation medium parameters and transformed fields are derived with every detail explained, so that the working knowledge of transformation optics can be grasped with minimal prerequisite mathematics. Proof of form invariance of full Maxwell’s equations with sources is presented. Design procedure of transformation optics is then demonstrated by creating perfect invisibility cloaks. The introduction to basic theory is followed by discussions on our works included in our published papers.

    As our first application, a method of designing two-dimensional reduced cloaks of complex shapes is proposed to relieve the difficulty of singularity occurring in perfect cloaks. The simple and intuitive method is the first way to design two-dimensional reduced cloaks of shapes other than cylindrical. Elliptical and bowtie shaped reduced cloaks are presented to verify the effectiveness of the method. Prominent scattering reduction is observed for both examples.

    Considering the practical realization, transformations continuous in the whole space must be the identity operation outside certain volume, and thus they can only manipulate fields locally. Discontinuous transformations are naturally considered to break the limitation. We study the possible reflections from such a transformation medium due to a discontinuous transformation by a new concept of inverse transformation. This way, the reflection falls into the framework of transformation optics as well. A necessary and sufficient condition for no reflection is derived as a special case.

    Unlike the invisibility realized by perfect cloaks, cloaking an object over a dielectric half-space has advantages in some particular applications. Starting from a perfect cloak, a half-space cloak is designed to achieve this. In our design, two matching strips embedded in the dielectric ground are used to induce proper reflection in the upper air space, so that the reflected field is the same as that from the bare dielectric ground.

    Cloaks obtained from singular transformations and even reduced models all have null principal value in their material parameters, making invisibility inherently very narrowband. In contrast, a carpet cloak designed by only coordinate deformation does not have the narrowband issue, and can perform well in a broad spectrum. The invisibility accomplished by the carpet cloak is also for the half-space case as our previous design. In this part, we extend the original version of a carpet cloak above a PEC sheet to a general dielectric ground.

  • 5.
    Zhang, Pu
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Jin, Y.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Cloaking an object on a dielectric half-space2008In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 16, no 5, p. 3161-3166Article in journal (Refereed)
    Abstract [en]

    Cloaking an object on a dielectric half-space for an observer in air is studied. The proposed cloaking configuration has two vertical matching strips of isotropic and homogeneous material under the two bottom surfaces of a semi-cylindrical cloaking cover. Simple expression for the material parameters of the matching strips is derived. The theoretical results of cloaking are verified numerically for the incidence of plane wave and line current source. The vertical matching strips can be terminated with a finite depth by introducing some loss to the matching material.

  • 6.
    Zhang, Pu
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Jin, Yi
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Inverse Transformation Optics and Reflection Analysis for Two-Dimensional Finite-Embedded Coordinate Transformation2010In: IEEE Journal of Selected Topics in Quantum Electronics, ISSN 1077-260X, E-ISSN 1558-4542, Vol. 16, no 2, p. 427-432Article in journal (Refereed)
    Abstract [en]

    Inverse transformation optics is introduced, and used to calculate the reflection at the boundary of a transformation medium under consideration. The transformation medium for a practical device is obtained from a 2-D finite-embedded coordinate transformation (FECT), which is discontinuous at the boundary. For an electromagnetic excitation of particular polarization, many pairs of original medium (in a virtual space V') and inverse transformation can give exactly the same anisotropic medium through the conventional procedure of transformation optics. Nonuniqueness of these pairs is then exploited for the analysis and calculation of the boundary reflection. The reflection at the boundary of the anisotropic FECT medium (associated with the corresponding vacuum virtual space V) is converted to the simple reflection between two isotropic media in virtual space V' by a selected inverse transformation continuous at the boundary. A reflectionless condition for the boundary of the FECT medium is found as a special case. The theory is verified numerically with the finite element method.

  • 7. Zhang, Pu
    et al.
    Jin, Yi
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Obtaining a nonsingular two-dimensional cloak of complex shape from a perfect three-dimensional cloak2008In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 93, no 24, p. 243502-Article in journal (Refereed)
    Abstract [en]

    A general method is proposed to construct an approximate nonsingular two-dimensional (2D) cloak by taking constitutive parameter tensors (CPTs) of a three-dimensional perfect cloak on a mirror-symmetric cross section in order to avoid any singularity at the inner boundary of a perfect 2D cloak. As two examples, reduced 2D models for an elliptic cloak and a bow-tie cloak are derived. The reduced 2D models are characterized explicitly with CPT of finite values and good cloaking effects are verified numerically.

  • 8.
    Zhang, Pu
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Lobet, Michael
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Carpet cloaking on a dielectric half-space2010In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 18, no 17, p. 18158-18163Article in journal (Refereed)
    Abstract [en]

    Carpet cloaking is proposed to hide an object on a dielectric half-space from electromagnetic (EM) detection. A two-dimensional conformal transformation specified by an analytic function is utilized for the design. Only one nonsingular material parameter distribution suffices for the characterization. The cloaking cover situates on the dielectric half-space, and consists of a lossless upper part for EM wave redirection and an absorbing bottom layer for inducing correct reflection coefficient and absorbing transmission. Numerical simulations with Gaussian beam incidence are performed for verification. The broadband behavior of the carpet cloaking is also illustrated.

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