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.

We present a metamaterial that acts as a strongly resonant absorber at terahertz frequencies. Our design consists of a bilayer unit cell which allows for maximization of the absorption through independent tuning of the electrical permittivity and magnetic permeability. An experimental absorptivity of 70% at 1.3 terahertz is demonstrated. We utilize only a single unit cell in the propagation direction, thus achieving an absorption coefficient alpha = 2000 cm(-1). These metamaterials are promising candidates as absorbing elements for thermally based THz imaging, due to their relatively low volume, low density, and narrow band response.

We present the design, fabrication, and characterization of a metamaterial absorber which is resonant at terahertz frequencies. We experimentally demonstrate an absorptivity of 0.97 at 1.6 terahertz. Importantly, this free-standing absorber is only 16 microns thick resulting in a highly flexible material that, further, operates over a wide range of angles of incidence for both transverse electric and transverse magnetic radiation.

We present the theory, design, and realization of a polarization-insensitive metamaterial absorber for terahertz frequencies. We derive geometrical-independent conditions for effective medium absorbers in general, and for resonant metamaterials specifically. Our fabricated design reaches and absorptivity of 65% at 1.145 Thz.

Invisibility is a notion that has long captivated the popular imagination. However, in 2006, invisibility became a practical matter for the scientific community as well, with the suggestion that artificially structured metamaterials could enable a new electromagnetic design paradigm, now termed transformation optics. Since the advent of transformation optics and subsequent initial demonstration of the microwave cloak, the field has grown rapidly. However, the complexity of the transformation optics material prescription has continually forced researchers to make simplifying approximations to achieve even a subset of the desired functionality. These approximations place profound limitations on the performance of transformation optics devices in general, and cloaks especially. Here, we design and experimentally characterize a two-dimensional, unidirectional cloak that makes no approximations to the underlying transformation optics formulation, yet is capable of reducing the scattering of an object ten wavelengths in size. We demonstrate that this approximation-free design regains the performance characteristics promised by transformation optics.

The past decade has seen a revolution in electromagnetics due to the development of metamaterials. These artificial composites have been fashioned to exhibit exotic effects such as a negative index of refraction. However, the full potential of metamaterial devices has only been hinted at. By combining metamaterials with transformation optics (TO), researchers have demonstrated an invisibility cloak. Subsequently, quasi-conformal mapping was used to create a device that exhibited a broadband cloaking effect. Here we extend this latter approach to a strictly conformal mapping to create reflection less, inherently isotropic, and broadband photonic devices. Our method combines the novel effects of TO with the practicality of all-dielectric construction. We show that our structures are capable of guiding light in an almost arbitrary fashion over an unprecedented range of frequencies.

We introduce an approach to the design of three-dimensional transformation optical (TO) media based on a generalized quasiconformal mapping approach. The generalized quasiconformal TO (QCTO) approach enables the design of media that can, in principle, be broadband and low loss, while controlling the propagation of waves with arbitrary angles of incidence and polarization. We illustrate the method in the design of a three-dimensional carpet ground plane cloak and of a flattened Luneburg lens. Ray-trace studies provide a confirmation of the performance of the QCTO media, while also revealing the limited performance of index-only versions of these devices. DOI: 10.1103/PhysRevLett.105.193902 PACS numbers: 42.79.Àe, 42.15.Ài Transformation optics (TO) is a unique tool for the design of complex electromagnetic media [1]. TO makes use of the form invariance of Maxwell's equations to mimic spatial transformations using distributions of inhomogeneous and anisotropic material constitutive parameters. TO has inspired many exotic devices, one of the most compelling of which being the electromagnetic ''invisibility'' cloak. However, the use of TO as a design methodology typically comes at high cost; the media derived from coordinate transformations generally involve spatial gradients in all nine components of the permittivity and permeability tensors. Though it is possible to find a basis that diagonalizes these tensors, the diagonal basis will generally be a function of position for all but the most simplistic and symmetric designs. Moreover, the required response is generally outside of the range of natural materials.Electromagnetic metamaterials (MMs) are used to access the extreme material parameters required by TO media. MMs, for example, were used to demonstrate a negative index of refraction [2,3] and electromagnetic cloaking [4]. However, the performance of these initial MM constructs was limited by a combination of narrow bandwidth and relatively large absorption. The typical limitation for MM designs has been the requirement of constitutive parameters that have a large range of values for both permittivity and permeability. The implementation of artificial paramagnetism, in particular, requires resonant inclusions that are inherently lossy and dispersive, leading to absorption and reduced bandwidth. More recently, the development of coordinate transformation methods in optical design approaches has significantly advanced MM complexity: independent magnetic and electric responses are required in all directions for general TO designs, yet most MM elements provide a controlled response in one or two directions. Were one to attempt to control all of the tensor elements of a MM simultaneously, multiple MM elements would need to be either colocated or closely positioned, introducing very complicated magnetoelectric coupling difficult to control or even quantify using current MM retrieval techniques [5].Fortunately, the enormous degree of flexibility available in coordinate transformations can alleviate many of the c...

We report stereolithographic polymer-based fabrication and experimental operation of a microwave X-band cloaking device. The device is a relatively thin (about one wavelength thick) shell of an air-dielectric composite, in which the dielectric component has negligible loss and dispersion. In a finite band (9.7-10.1 GHz), the shell eliminates the shadow and strongly suppresses scattering from a conducting cylinder of six-wavelength diameter for TE-polarized free-space plane waves. The device does not require an immersion liquid or conducting ground planes for its operation. The dielectric constant of the polymer is low enough (ϵ 2.45) The possibility to make large and nontransparent objects electromagnetically undetectable has been the subject of intense research following the introduction of the transformation optics (TO) concept [1,2] and its microwave implementation [3]. In theoretical TO scenarios, an inhomogeneous shell around an object eliminates backward reflection and forward shadow, thus by virtue of the optical theorem also suppressing the scattering in all other directions. Currently, however, no technique is available for fabrication of invisibility devices capable of hiding objects with cross sections exceeding 5 free-space wavelengths (λ) [4]. Inherent in TO-based proposals are exotic material properties, such as large or near-zero magnetic permeability and/or dielectric permittivity, both with negligible imaginary parts. To date, virtually all TO medium proposals involved metallic components behaving as conducting [3][4][5] or plasmonic [6,7] media. Propagation loss is a major limitation for cloaks already at microwave frequencies [3,4], and it becomes overwhelming at visible wavelengths.The attenuation issue prompted a search for invisibility scenarios that could be based entirely on low-loss dielectric materials with a dielectric constant ϵ < 1. Naturally birefringent dielectric crystals such as calcite [8,9] were used in visible-wavelength cloaking experiments. Having refractive indexes n o;e > 1, such media are only capable of cloaking if submerged in a high-index immersion liquid whose refractive index n im satisfies 1 < n o∕e < n im . Immersion helps avoid the most fundamental limitation of TO-based cloaking-the need for superluminal phase velocities [10,11]-while rendering these cloaks useless for free-space applications such as sensing countermeasures.In this Letter, we present a general design and fabrication methodology that yields 2D microwave cloaks composed of only one, virtually lossless, dispersionless, dielectric medium with ϵ 2.45. The cloaks are multidirectional, i.e., invisible with respect to several propagation directions, are capable of hiding objects many wavelengths in diameter, and are thinner relative to the object size than in any previous experimental demonstrations [3][4][5]. Here, we apply the technique to TE-polarization waves, however, it also yields cloaks with similar performance metrics for TM polarization. Our choice of TE polarization is dictated by the testin...