Paul-Henri Tichit

Waveguide taper engineering using coordinate transformation technology

Spatial coordinate transformation is a suitable tool for the design of complex electromagnetic structures. In this paper, we define three spatial coordinate transformations which show the possibility of designing a taper between two different waveguides. A parametric study is presented for the three transformations and we propose achievable values of permittivity and permeability that can be obtained with existing metamaterials. The performances of such defined structures are demonstrated by finite element numerical simulations.

Transformation media producing quasi-perfect isotropic emission

Using the idea of wave manipulation via transformation optics, we propose a way to create a quasi-perfect isotropic emission from a directional one. The manipulation is enabled by composite metamaterials that correspond to a space stretching around the source. It is shown that the directive radiation of a plane source larger than the operating wavelength can be transformed into an isotropic one by modifying the electromagnetic properties of the space around it. A set of parameters allowing practical realization of the proposed device is defined. Numerical simulations using Finite Element Method (FEM) are performed to illustrate the proposed coordinate transformation. This idea, which consists in strongly reducing the apparent size of a radiating source, can find various applications in novel antenna design techniques.

Spiral-like multi-beam emission via transformation electromagnetics

Transformation electromagnetics offers an unconventional approach for the design of novel radiating devices. Here, we propose an electromagnetic metamaterial able to split an isotropic radiation into multiple directive beams. By applying transformations that modify distance and angles, we show how the multiple directive beams can be steered at will. We describe transformation of the metric space and the calculation of the material parameters. Different transformations are proposed for a possible physical realization through the use of engineered artificial metamaterials. Full wave simulations are performed to validate the proposed approach. The idea paves the way to interesting applications in various domains in microwave and optical regimes.

Illusion optics: Optically transforming the nature and the location of electromagnetic emissions

Complex electromagnetic structures can be designed by using the powerful concept of transformation electromagnetics. In this study, we define a spatial coordinate transformation that shows the possibility of designing a device capable of producing an illusion on an antenna radiation pattern. Indeed, by compressing the space containing a radiating element, we show that it is able to change the radiation pattern and to make the radiation location appear outside the latter space. Both continuous and discretized models with calculated electromagnetic parameter values are presented. A reduction of the electromagnetic material parameters is also proposed for a possible physical fabrication of the device with achievable values of permittivity and permeability that can be obtained from existing well-known metamaterials. Following that, the design of the proposed antenna using a layered metamaterial is presented. Full wave numerical simulations using Finite Element Method are performed to demonstrate the performances of such a device.

Reducing physical appearance of electromagnetic sources

We propose to use the concept of transformation optics for the design of novel radiating devices. By applying transformations that compress space, and then that match it to the surrounding environment, we show how the electromagnetic appearance of radiating elements can be tailored at will. Our efficient approach allows one to realize a large aperture emission from a small aperture one. We describe transformation of the metric space and the calculation of the material parameters. Full wave simulations are performed to validate the proposed approach on different space compression shapes, factors and impedance matching. The idea paves the way to interesting applications in various domains in microwave and optical regimes, but also in acoustics.

Efficient control of a 3D optical mode using a thin sheet of transformation optical medium

We report on a mode adapter that transitions light between two SOI waveguides having different widths. The device has been designed using a two-dimensional embedded coordinate transformation and consists of a thin sheet of a controlled anisotropic material directly placed on top of the Si slab. We demonstrate that this layer effectively controls the flow of energy propagating in the Si slab by performing three-dimensional full-wave simulations. The proposed geometry can be implemented with planar optical metamaterials for various applications in guided optics.

Transformation Electromagnetics for Antennas With an Illusion on the Radiation Pattern

Using transformation electromagnetics concept, we introduce an approach to virtually delocalize radiating sources and to transform their radiation pattern at the same time. We propose the design of an electromagnetic device that can virtually change the location of the emission point. By applying radial transformations that compress space, and then match it to the surrounding environment, we show how the emission of a radiating element placed in a core region can be delocalized in a second impedance-matched region, corresponding to a space folding. Moreover, the radiation pattern of the virtual source can be modified such that an omnidirectional radiation can be changed into a directive one. We describe the space coordinate transformation and the calculation of the material parameters. Full-wave simulations are performed at different frequencies to validate the proposed approach.

Novel antenna concepts via coordinate transformation

Coordinate transformation is an emerging field which offers a powerful and unprecedented ability to manipulate and control electromagnetic waves. Using this tool, we demonstrate the design of novel antenna concepts by tailoring their radiation properties. The wave manipulation is enabled through the use of engineered dispersive composite metamaterials that realize the space coordinate transformation. Three types of antennas are considered for design: a directive, a beam steerable and a quasi-isotropic one. Numerical simulations together with experimental measurements are performed in order to validate the coordinate transformation concept. Near-field cartography and far-field pattern measurements performed on a fabricated prototype agree qualitatively with Finite Element Method (FEM) simulations. It is shown that a particular radiation pattern can be tailored at ease into a desired one by modifying the electromagnetic properties of the space around radiator. This idea opens the way to novel antenna design techniques for various application domains such as the aeronautical and transport fields.

Transformation Optics Concept: Definition and Tools

The exciting field of metamaterials has attracted the interest of researchers from all across the world over the past few years. With roots in the foundations of optics and electromagnetics, researchers are exploring the underlying physics of metamaterials. Electromagnetic metamaterials are artificially structured materials composed of periodic arrays of sub-wavelength resonating structures, scatterers or apertures, whose electric or magnetic response provides the ability to engineer dielectric or magnetic properties that do not exist in naturally occurring materials. The dielectric or magnetic properties can be tailored by changing the geometrical parameters of the constituent structure of the metamaterial.

Space Transformation Concept: Controlling the Path of Electromagnetic Waves

In this chapter, we will deal with devices designed using space transformation concept. Quasi-conformal transformation optics (QCTO) is applied for the design of electromagnetic devices at microwave frequencies. Antenna applications are targeted for focusing and collimating properties. Two lenses are studied and designed by solving the Laplace’s equation that describes the deformation of a medium in the space transformation. The material parameters of the lenses are derived from the analytical solutions of the Laplace’s equation. The first lens is conceived to produce an overall directive in-phase emission from an array of sources conformed on a cylindrical structure. The second lens allows steering a directive beam to an off-normal direction. Theoretical formulations are given to describe the transformations and full-wave simulations are performed to verify the functionality of the calculated lenses. Theoretical designs are adapted judiciously to be compatible with the constraints of realization technologies so as to have the best agreement between numerical calculations and experimental tests. Prototypes presenting a graded refractive index are fabricated through three-dimensional (3D) polyjet printing using all-dielectric materials and experimental measurements are carried out to validate the proposed lenses. Such easily realizable designs open the way to lowcost all-dielectric broadband microwave lenses for beam forming and collimation.