Using the freedom of design that metamaterials provide, we show how electromagnetic fields can be redirected at will and propose a design strategy. The conserved fields-electric displacement field D, magnetic induction field B, and Poynting vector B-are all displaced in a consistent manner. A simple illustration is given of the cloaking of a proscribed volume of space to exclude completely all electromagnetic fields. Our work has relevance to exotic lens design and to the cloaking of objects from electromagnetic fields.

/pdf/controlling-electromagnetic-fields-3ryxkryf1t.pdf

Controlling Electromagnetic Fields

A recently published theory has suggested that a cloak of invisibility is in principle possible, at least over a narrow frequency band. We describe here the first practical realization of such a cloak; in our demonstration, a copper cylinder was "hidden" inside a cloak constructed according to the previous theoretical prescription. The cloak was constructed with the use of artificially structured metamaterials, designed for operation over a band of microwave frequencies. The cloak decreased scattering from the hidden object while at the same time reducing its shadow, so that the cloak and object combined began to resemble empty space.

/pdf/metamaterial-electromagnetic-cloak-at-microwave-frequencies-1qj4zdgl8e.pdf

Metamaterial Electromagnetic Cloak at Microwave Frequencies

Conventional optical components rely on gradual phase shifts accumulated during light propagation to shape light beams. New degrees of freedom are attained by introducing abrupt phase changes over the scale of the wavelength. A two-dimensional array of optical resonators with spatially varying phase response and subwavelength separation can imprint such phase discontinuities on propagating light as it traverses the interface between two media. Anomalous reflection and refraction phenomena are observed in this regime in optically thin arrays of metallic antennas on silicon with a linear phase variation along the interface, which are in excellent agreement with generalized laws derived from Fermat’s principle. Phase discontinuities provide great flexibility in the design of light beams, as illustrated by the generation of optical vortices through use of planar designer metallic interfaces.

http://www.zenogaburro.it/papers/LightPropagation.pdf

Light Propagation with Phase Discontinuities: Generalized Laws of Reflection and Refraction

We present the design for an absorbing metamaterial (MM) with near unity absorbance A(omega). Our structure consists of two MM resonators that couple separately to electric and magnetic fields so as to absorb all incident radiation within a single unit cell layer. We fabricate, characterize, and analyze a MM absorber with a slightly lower predicted A(omega) of 96%. Unlike conventional absorbers, our MM consists solely of metallic elements. The substrate can therefore be optimized for other parameters of interest. We experimentally demonstrate a peak A(omega) greater than 88% at 11.5 GHz.

Perfect metamaterial absorber.

Metamaterials are artificially fabricated materials that allow for the control of light and acoustic waves in a manner that is not possible in nature. This Review covers the recent developments in the study of so-called metasurfaces, which offer the possibility of controlling light with ultrathin, planar optical components. Conventional optical components such as lenses, waveplates and holograms rely on light propagation over distances much larger than the wavelength to shape wavefronts. In this way substantial changes of the amplitude, phase or polarization of light waves are gradually accumulated along the optical path. This Review focuses on recent developments on flat, ultrathin optical components dubbed 'metasurfaces' that produce abrupt changes over the scale of the free-space wavelength in the phase, amplitude and/or polarization of a light beam. Metasurfaces are generally created by assembling arrays of miniature, anisotropic light scatterers (that is, resonators such as optical antennas). The spacing between antennas and their dimensions are much smaller than the wavelength. As a result the metasurfaces, on account of Huygens principle, are able to mould optical wavefronts into arbitrary shapes with subwavelength resolution by introducing spatial variations in the optical response of the light scatterers. Such gradient metasurfaces go beyond the well-established technology of frequency selective surfaces made of periodic structures and are extending to new spectral regions the functionalities of conventional microwave and millimetre-wave transmit-arrays and reflect-arrays. Metasurfaces can also be created by using ultrathin films of materials with large optical losses. By using the controllable abrupt phase shifts associated with reflection or transmission of light waves at the interface between lossy materials, such metasurfaces operate like optically thin cavities that strongly modify the light spectrum. Technology opportunities in various spectral regions and their potential advantages in replacing existing optical components are discussed.

Flat Optics With Designer Metasurfaces

In this paper, we present a novel method of electromagnetic field focusing applicable to 3D implantable devices. Focusing is achieved using two lines that guide the incident wave deeper into the body and concentrate it around their respective tips. The small gap between the tips of the lines provides constructive coupling and augments the focused field. Compared to the case where no lines are used, the focused power is 8 times and 16 times larger if one line and two lines are utilized, respectively. The proposed design can be modified to focus fields with arbitrary polarizations at different depths inside the body. We propose a method to create this focusing structure by extrusion inside the body using heat-activated polymer-based conductors.

Field Focusing for Implanted Medical Devices

A digital memory device includes a moveable element that is configured to move between a first stable position and a second stable position, where the moveable element comprises a first conducting area The digital memory device further includes a second conducting area on the surface of a substrate At the first stable position of the moveable element, a first gap exists between the first conducting area and the second conducting area At the second stable position of the moveable element, a second gap that is smaller than the first gap exists between the first conducting area and the second conducting area In at least the second stable position, an attractive Casimir force between the moveable element and the substrate holds the moveable element in the stable position

Casimir effect memory cell

We propose methods to determine beam-forming excitation phase profiles for arbitrarily oriented arrays of antennas and scatterers, made of arbitrarily polarized elements. Our generalized analytical phasing (GAP) method provides rapid near-optimal phasing, enabling real-time beam steering with high-element-count, and dynamically configured arrays. In addition, we propose a reduced-order numerical phasing (RONP) method that converts an N -dimensional unknown parameter space (the N unknown phases) to a 2-D space (the optimal beam polarization). Though not as fast as the GAP, this method introduces no reduction in phasing accuracy. Both methods are suitable for a wide range of antenna array and metasurface designs.

Fast Beamforming for Dynamic, Randomly Configured Antenna Arrays and Metamaterials

A technique for designing optimal near-field plates is presented in this work. This technique relies on signal estimation concepts to choose the smallest set of coils that minimizes the power of the error field distribution as well as the complexity of the resulting near-field plate. Furthermore, our technique can be applied to the design of a variety of near-field plates, and provides an path for the reduction of complexity of the design with minimal degradation on performance. An optimized near-field plate capable of generating an evanescent Bessel beam was designed through this procedure to demonstrate its performance. Near-field plates designed using this technique will be strong candidates to use in applications in the areas of wireless power transfer, lithography, near-field imaging, magnetic recording, etc.

Using signal estimation for near-field plate optimization

A method of constructing a concealing volume comprises constructing a plurality of concealing volume elements around a concealable volume. Each concealing volume element has a material parameter arranged to direct a propagating wave around the concealable volume.

David Schurig

Papers

Field Focusing for Implanted Medical Devices

Casimir effect memory cell

Fast Beamforming for Dynamic, Randomly Configured Antenna Arrays and Metamaterials

Using signal estimation for near-field plate optimization

Method of constructing a diverting volume