Archana Rajput

Design of a two-dimensional metamaterial cloak with minimum scattering using a quadratic transformation function

The presence of extreme material properties and undesired scattering make practical implementation of transformation optics based cloaks an extremely challenging issue. To overcome these problems, a simplified quadratic cloak has been proposed which provides finite material properties at the inner radius of the cloak and impedance match with the free space at the outer radius of the cloak simultaneously. The simultaneous occurrence of finite material properties and impedance match with the free space at the respective boundaries reduces the scattering cross section significantly. The material properties of the proposed simplified quadratic cloak can be realized with two dimensional (2D) metamaterials. The performance of the proposed cloak is examined by plotting the normalized total scattering cross section (SCSt,norm), and the scattering patterns in azimuthal plane. The proposed simplified quadratic cloak shows 10 dB reduction of the scattered field in both the forward and backward directions with respec...

Composite-Shaped External Cloaks With Homogeneous Material Properties

Two composite-shaped external cloaks are proposed based on the concept of linear transformation method and complementary media. Each composite-shaped cloak is subdivided into regions of rectangular and triangular shapes. The advantage of the proposed cloak designs is that the material properties are finite, homogeneous, and nonsingular within all subregions of the cloaks, which is good for practical realization. The cloak size of each of the proposed designs is smaller compared to the conventional external cloaks. Moreover, the cloaking area of the proposed cloaks can be increased in the vertical direction without any change in material parameters of core and complementary regions, which is an additional benefit for hiding long objects. Full-wave simulations reveal that the proposed cloaks have good performance even for hiding multiple objects of different shapes and sizes inside them for all angles of incidence of electromagnetic wave.

Approximated Complementary Cloak With Diagonally Homogeneous Material Parameters Using Shifted Parabolic Coordinate System

In this communication, a parabolic shaped complementary cloak is proposed which makes the object invisible by reducing its scattering under different incidence angles of electromagnetic wave. The proposed design is based on transforming a line segment into an enclosed space that is surrounded by the core region. The enclosed space is symmetrically divided into two regions, namely, cloaked region and complementary region. The shifted parabolic coordinate system introduced in the present work enhances the area of cloaked region and provides diagonally anisotropic but optimized homogeneous material properties in the core region. The cloaked region is mapped onto the complementary region using a simple one directional folding transformation, which yields homogeneous and isotropic material properties in the complementary region and also eases the creation of antiobject. Numerical results confirm the cloaking effect of the proposed approximate complementary cloak. The metamaterial unit cell designs are also presented for realizing the proposed material properties of core and complementary regions.

Triple band Planar Inverted-F antenna loaded with LC resonator

In this paper, a conventional Planar Inverted-F antenna is loaded with a LC resonator to achieve triple band behavior. The LC resonator enables the excitation of two modes (one lower and one higher) in addition to reference PIFA mode. The radiation patterns at the lower and reference PIFA mode bears the quasi-omnidirectional property while an endfire pattern is achieved for the higher mode. Prototype of the proposed antenna is fabricated to validate the result obtained in simulation.

Hexagonal shaped reciprocal external cloak with homogeneous material properties

Based on the concept of transformation optics and complementary media, a hexagonal shaped reciprocal external cloak is proposed which hides an object inside it perfectly. The hexagonal shape has been sub-divided into regions of rectangular and triangular shapes. The rectangular sub-regions have diagonal material properties whereas the triangular sub-regions have complete anisotropic tensor properties. The advantage of proposed cloak is that the material properties are homogeneous within all sub-regions. The other advantage is that its cloaked area can be increased without any change in material parameters. Full-wave simulations reveal that the proposed cloak has good performance even for hiding multiple objects of different shapes and sizes inside it.

Arbitrary Shaped Reciprocal External Cloak with Nonsingular and Homogeneous Material Parameters Using Expanding Coordinate Transformation

Arbitrary shaped reciprocal external cloak with homogeneous and nonsingular material parameters in complementary and core regions is designed by decomposing cloak geometry into several triangles. In each triangle, proposed expanding coordinate transformation is applied to cancel the space and a two-step compressing transformation is applied to restore the canceled space. The choice of transformation function is to ensure homogeneous material parameters which is the main advantage of the proposed design. Proposed design procedure is a generalized approach and can be used for any arbitrary polygonal geometries. Full-wave simulations confirm the theoretical design, and it is observed that proposed cloak shows significant invisibility effect in hiding multiple objects in the cloaked region for different cloak geometries.

Effect on scattering cross section for scaled anti-object and coordinate transformed anti-object in external cloaking

In this paper, the performance of external cloaking has been studied for coordinate transformed anti-object and scaled (without coordinate transformation) anti-object. To compare the effects on scattering cross section for scaled and coordinate transformed anti-object, numerical simulations have been performed for three different dimensions of rectangular object. The numerical results of total scattering cross section under different angles of incidence confirm that there is a considerable degradation in cloaking performance with increase in the size of the object for external cloak with scaled anti-object.

A metamaterial-inspired triple band dual polarized monopole antenna

In this paper, a triple-band dual-polarized microstrip-fed monopole antenna using a rectangular complementary split-ring resonator (CSRR) and an inverted L-shaped slit (ILS) has been proposed. The CSRR induces an additional lower resonant frequency in the antenna, whereas the ILS etched from the partial ground plane causes another higher frequency resonance. Linearly polarized quasi-monopolar radiation pattern is observed in the two lower frequency bands. The higher frequency band due to the ILS exhibits circularly polarized bi-directional radiation characteristics. The performance of the proposed antenna is validated through HFSS simulations and measurements on fabricated antenna prototype.

Reverse reciprocal external cloak without strict positional dependence of object to anti-object

In this paper, a reverse reciprocal cloak design has been proposed which removes the strict positional dependence of object in the cloaked region to its corresponding anti-object in the complementary region. The complementary region and cloaked region of reciprocal cloak are interchanged in the proposed reverse reciprocal cloak design, this results in smaller anti-object in complementary region for a large hidden object in the cloaked region. The governing transformation equations and material parameters are derived for the proposed design. Full wave simulations are performed to confirm the external invisibility effect. It is observed that the scattering cross-section for the proposed reverse reciprocal external cloak remains less compared to the previous external cloak designs with angular shift of the object from anti-object.

Cylindrical simplified cloak with enhanced bandwidth

A simplified cloak design has been proposed with radial permeability as 1, whereas angular permeability and axial permittivity are radially varying within the cloak shell for transverse electric wave. The proposed simplified cloak is perfectly matched at the outer boundary (when the outer radius of the cloak is twice the inner radius of the cloak) with the free space. The proposed cloak shows approximately 11% bandwidth for 50% SCS reduction from 8.7 GHz to 9.7 GHz. There is a 10 dB and 5 dB reduction in the scattered field with respect to the perfect electric conductor (PEC) cylinder in the forward and backward directions, respectively.