|Posted on March 4, 2019 at 9:10 AM|
Ph.D. student Oshri’s paper (in collaboration with Rafael Advanced Defense Systems Ltd.) “Experimental demonstration and in-depth investigation of analytically designed anomalous reflection metagratings” was recently published in Physical Review B.
The paper verifies experimentally the analytical scheme we have previously developed for designing realistic (printed-circuit-board fabrication-ready) metagratings for perfect anomalous reflection. These metagratings feature only a single simple element (single degree of freedom) per period, yet couple 96% of the scattered power towards the desirable anomalous reflection mode. Multifunctionality and multichannel reflection features are observed, and important experimental aspects, such as the merits of the beam-integration technique for evaluating the coupling efficiency, as well as the origin of losses, are explored and discussed in detail.
|Posted on February 16, 2019 at 3:20 PM|
The book chapter “Advanced Huygens’ metasurfaces for beam manipulation and antenna applications” by Ariel Epstein and George V. Eleftheriades has been published in John L. Volakis’ Antenna Engineering Handbook, 5th edition [McGraw Hill Education, 2019].
|Posted on February 5, 2019 at 7:50 AM|
Congratulations to Oshri Rabinovich, a Ph.D. student in our group, who has been selected to receive an IEEE Antennas and Propagation Society Doctoral Research Grant.
Way to go, Oshri!
|Posted on January 4, 2019 at 2:00 AM|
Yaniv has formally joined our group as a M.Sc. student.
|Posted on September 12, 2018 at 4:35 AM|
Dr. Vinay Kumar Killamsetty has joined our group as a postdoctoral fellow.
|Posted on September 12, 2018 at 4:30 AM|
Ph. D. student Oshri Rabinovich’s paper was published on IEEE Transactions on Antennas and Propagation recently. The paper formulates for the first time a complete analytical synthesis procedure for printed circuit board (PCB) metagratings for perfect anomalous reflection. The manuscript derives the expressions for the scattered fields in a metal-dielectric-loaded wires formation, and formulates the conditions for achieving exclusive coupling to the first Floquet-Bloch mode (anomalous reflection) while conserving power. This leads to a fabrication-ready PCB layout (up to the required conductor trace geometry) obtained without even a single full-wave simluation. Such an efficient analytical design scheme, verified using commercial solvers, is expected to accelerate experimental demonstration of these novel devices for beam manipultation, as well as their application in realistic configurations.
|Posted on December 25, 2017 at 2:05 AM|
Our recent paper “Negative index effects from a homogeneous positive index prism” was just published in EPJ-Applied Metamaterials.
The paper sheds light on experiments conducted to verify effective negative index of refraction in artificial metamaterials. The investigation shows that certain observations typically associated with negative index effects, but can actually arise from a homogeneousn positive index (natural) material, if deformed to the usual cerrated prism configuration applied in metamaterial experiments. Thus, experimental evidence for negative index effects should be carefully examined in order to unambiguously verify the metamaterial properties.
|Posted on November 24, 2017 at 1:45 AM|
Our recent paper “Unveiling the Properties of Metagratings via a Detailed Analytical Model for Synthesis and Analysis” has just been published in Physical Review Applied, and was chosen as “Editors’ Suggestion”.
The paper explores the novel concept of metagratings, periodic arrays consisting of one or two subwavelength polarizable particles (meta-atoms) per period. Surprisingly, despite the utmost simplicity, these structures allow highly-efficient implementation of intricate beam-manipulating functionalities, such as perfect anomalous reflection. In our manuscript, we rigorously investigate metagratings based on capacitively loaded conduting wires for perfect wide-angle beam splitting, via a detailed analytical model. We show that based on this architecture, compatible with printed-circuit-board (PCB) manufacturing techniques, the synthesis can be completed almost completely analytically, prescribing the copper trace geometry required for reaching unitary coupling efficiencies.
Furthermore, the formulation allows analytical examination of the device susceptibility to conductor losses, fabrication imperfections, and frequency shifts. This examination reveals that metagratings feature distinct preferable working points, in which the sensitivity to these non-idealities is minor, directly realted to fundamental interference processes taking place within the device.
|Posted on March 28, 2017 at 2:50 AM|
Two of our papers (with Prof. Eleftheriades and Dr. Abdo-Sanchez) have made it to the top 5 best paper award contest finalists of EuCAP2017, in the Electromagnetics and Antenna Theory category.
Ariel Epstein and George V. Eleftheriades, “Emulating Arbitrary Antenna Arrays with Low-Profile Probe-Fed Cavity-Excited Omega-Bianisotropic Metasurface Antennas”.
Elena Abdo-Sánchez, Ariel Epstein, and George V. Eleftheriades, “Bianisotropic Huygens’ Metasurface Leaky-Wave Antenna with Flexible Design Parameters”.
|Posted on December 19, 2016 at 9:45 AM|
Our recent work, suggesting to harness auxiliary fields to facilitate advanced metasurface-based beam manipulations, was published in Physical Review Letters. In this Letter, we show that certain basic diffraction engineering problems (e.g., beam splitting, engineered reflection) feature mode interference that does not allow local power conservation. The latter is required to generate passive lossless metasurface designs to implement the desirable functionalities. Thus, recent reports that examined these problems, marked them as significant challenges, and suggested approximated solutions or exotic ones.
In the manuscript, we propose a new paradigm to tackle these challenges. The key concept involves the utilization of evanescent modes to manipulate the flow of real power, in both lateral and longitudinal directions, assisting the establishment of local power conservation. Being evanescent, these auxiliary fields do not affect the device functionality in the far field, while guaranteeing a passive and lossless solution.
We demonstrate this concept for the problems of wide-angle beam splitting and perfect engineered reflections, showing that both functionalities can be implemented using standard, local, reciprocal, passive, and lossless omega-bianisotropic meta-atoms. Interestingly, the auxiliary fields are not bound to any specific form; although the designed metasurfaces are periodic, in certain cases the auxiliary fields are not Floquet-Bloch modes of the incident fields.
|Posted on July 9, 2016 at 9:25 PM|
Our invited review paper “Huygens’ metasurfaces via the equivalence principle: design and applications” featured the “10 top downloaded papers in JOSA B” for 4 months in a row (Jan, Feb, Mar, Apr 2016).
|Posted on July 9, 2016 at 8:50 PM|
Our paper on general field transformations using passive lossless omega-type bianisotropic metasurfaces (O-BMSs) has been accepted for publication in IEEE Transactions on Antennas and Propagation, and is available online. The paper proves that any field transformation that satisfies local power conservation, i.e. for which the real power is conserved at each point along the metasurface, can be implemented with a passive and lossless O-BMS. This allows extensive control over the transmission properties of the metasurface, as for Huygens’ metasurfaces, but also over its reflection coefficients; the latter is made possible by the additional degree of freedom provided by O-BMSs, namely, the magnetoelectric coupling effect.
The design procedure is demonstrated by engineering three O-BMSs for reflectionless wide-angle refraction (not possible with Huygens’ metasurfaces), independent surface wave guiding, and highly-directive low-profile cavity-excited O-BMS antennas. These examples show how the O-BMS can be designed to exhibit zero reflection, full reflection, or partial reflection, respectively, with precise control of the phase and magnitude of reflected and transmitted fields.
Importantly, the paper also shows that an asymmetric three-layer impedance sheet structure can be used to implement omega-type meta-atoms, paving the way for PCB-compatible O-BMS realizations.
The combined macroscopic (metasurface) and microscopic (meta-atom) design schemes provide new general tools for designing realistic metasurfaces that can be implemented using standard fabrication techniques for a myriad of advanced electromagnetic applications.
|Posted on April 14, 2016 at 7:45 AM|
Our paper on truly-reflectionless wide-angle refracting metasurfaces has been officially published in IEEE Antennas and Wireless Propagation Letters. The paper shows that in order to get perfect refraction to arbitrarily-large angles, one has to design the metasurface unit cells to match the wave impedance of both incident and refracted fields. Unlike Huygens’ metasurfaces, this requirement dictates an asymmetric meta-atom structure which can be implemented by cascading 3 asymmetric impedance sheets. The paper ties the achieved functionality to an equivalent 2-port microwave network theory, based on generalized scattering matrices. Full-wave simulations demonstrate a refraction of nomally-incident beam towards an angle of 80 degrees with as little as 0.35% reflected power. In a subsequent paper, we show that the resultant meta-atoms adhere omega-type bianisotropic sheet transition conditions, and derive a general theory for arbitrary power-conseving field transformations based on this class of metasurfaces; the case of wide-angle reflectionless refraction can be seen as a private case of that theory.
|Posted on January 21, 2016 at 11:25 AM|
Our recent paper “Cavity-excited Huygens’ metasurface antennas for near-unity aperture illumination efficiency from arbitrarily large apertures” have been published in Nature Communications and is available at http://www.nature.com/ncomms/2016/160121/ncomms10360/full/ncomms10360.html.
In this paper we provide a solution to a long-standing problem in antenna engineering: how to generate highly-dricetive beams from a low-profile structure using a singe simple source and without incurring edge-taper losses. The solution is given by a cavity-excited Huygens’ metasurface, fed by a single localized source. The cavity configuration is optimized to guarantee uniform aperture illumination, while the metasurface facilitates the phase-purity of the radiating aperture fields. As verified by full-wave simulations and an experimental demonstration, this results in low-profile radiators with near-unity aperture illumination efficiency, not degrading even for very large apertures.
From a fundamental point of view, the ability of the Huygens’ metasurface, designed following the equivalence principle, to introduce discontinuities to the electromagnetic fields, allows decoupling the excitation and radiation spectra, which is crucial for achieving the demonstrated performance.
|Posted on January 21, 2016 at 11:15 AM|
Our recent review “Huygens’ metasurfaces via the equivalence principle: design and applications” has been published in JOSA B (special issue) and is available at https://www.osapublishing.org/josab/abstract.cfm?uri=josab-33-2-A31.
In this paper we provide a tutorial for the macroscopic (metasurface) and microscopic (meta-atom) design procedures of Huygens’ metasurface, relying on the equivalence principle and the generalized sheet transition conditions (GSTCs). Basic concepts and nomenclature are reviewed, and the rigour of the equivalence-principle-based approach, yielding surface impedance design requirements, in contrast to the more common phase-shift stipulation approach, is stressed and deomnstrated. Finally, the formulated design procedure is utilized to demonstrate the usage of Huygens’ metasurfaces in various beam forming applications.
|Posted on December 16, 2014 at 10:25 AM|
Our recent paper “Floquet-Bloch analysis of refracting Huygens metasurfaces” was published in Physical Review B and can be accessed via http://journals.aps.org/prb/abstract/10.1103/PhysRevB.90.235127. The paper rigorously anlyzes the scattering of an arbitrary plane-wave off a Huygens metasurface designed to refract a wave with a particular angle of incidence towards a prescribed angle. Our analysis reveals that, in consistency with experimental evidence, the Huygens metasurface refracts well even if the angle of incidence deviates significantly from the designated angle.
This phenomenon can be interpreted via an intuitive ray-optical model which describes the scattering, in correspondence with the closed-form solution obtained from Floquet-Bloch analysis. According to this model, the metasurface forms a virtual (zero-thickness) region with constant wave impedance acting as a Fabry-Perot etalon. Incident power incouples to this region and outcouples to successively higher-order Floquet-Bloch modes. Due to the order of this successive outcoupling, the incident wave first couples to the first (refracted) mode; only the fraction of the power remaining in the virtual region after this event (which is usually dmall) can couple to other (undesirable) modes.
We use the Floquet-Bloch analysis to examine further the limitations of realistic implementation of such metasurfaces, mitigating problems related to the singular values and infinite spatial bandwidth inherent in the cotangent impedance modulation. We suggest a realizable (finite-value finite-bandwidth) alternative impedance modulation resembling the ideal cotangent modulation, and show that it does not significantly deteriorate the device efficiency.
The generality of the formulation and the appealing physical interpretation may shed light on the operation of other types of metasurfaces, as well as pave the path for ray-oriented design of novel devices.
|Posted on November 11, 2014 at 9:20 AM|
Our papr “On the Relevance of Two-Dimensional Models for Radiation of Statistical Sources in Stratified Media” was accepted for publication in Radio Science and is now available online at http://onlinelibrary.wiley.com/doi/10.1002/2014RS005543/full.
The paper systematically and rigorously formulate radiation pattern expressions for various 2D and 3D sources in stratified media, integrating the effects of statistical incoherence and orientational randomness. This is facilitated by an original decomposition of the sources to TE-generating and TM-generating current distributions at the source level (typically done at the fields level). It is shown that for statistical sources which are incoherent and randomly oriented the transverse electric (TE) radiation pattern arising from a 2D electric line source coincides with the normalized TE radiation pattern of a realistic scenario, in which the sources are arbitrary 3D dipoles. The relations between 2D magnetic line source radiation and transverse magnetic (TM) radiation patterns are also discussed. This allows accurate analysis of 3D configurations via 2D models, which are usually much simpler. The results also indicate how the different source properties are typically expressed in power quanatities in general geometrical optics scenarios. Radiation associated with different sources usually differ in the reflection coefficient and orienatation factor.
|Posted on October 21, 2014 at 12:55 AM|
Our paper “Passive lossless Huygens metasurfaces for conversion of arbitrary source field to directive radiation” was accepted for publication in IEEE Transactions on Antennas and Propagation and is now available online at http://dx.doi.org/10.1109/TAP.2014.2354419.
The paper formulates a procedure to excite Huygens metasurfaces with arbitrary 2D source fields, enabling design of novel directive radiators excited by localized sources. The proposed semianalytical method is based on plane-wave spectral decomposition of the fields, and derives sufficient conditions for passive lossless implementaion: local power conservation and local impedance equalization. Comparison of the semianalytical results with finite-element numerical simulations using realistic unit cells show good agreement, demonstrating the effectiveness of the mehod for source configurations including localized excitations and planar interfaces.
Our work facilitates, for the first time to the best of our knowledge, design of antennas that can be excited by a general 2D current distribution, rather than by beams or plane-waves as was previously demonstrated.
|Posted on June 11, 2014 at 12:45 AM|
Our paper “Analytical estimation of emission zone mean position and width in organic light-emitting diodes from emission pattern image-source interference fringes” was accepted for publication in Jounral of Applied Physics and is now available online at http://scitation.aip.org/content/aip/journal/jap/115/22/10.1063/1.4880737.
The paper derives in detail an analytical scheme to relate the main features of the emission pattern to the principal properties of the distribution of radiating excitons (emission zone) in OLEDs. The proposed method is verified using simulated and measured emission patterns, and a thorough discussion of the interpretation of the results is included as well.
|Posted on July 20, 2013 at 3:25 AM|
Our second son, Eshel (Shelli) was born a couple of weeks ago.
|Posted on June 4, 2013 at 8:30 AM|
The paper “On the Relevance of Two-Dimensional Sources for Modelling Optical Emission from Layered Media” (with Prof. N. Tessler and Prof. P. D. Einziger) won the Young Scientist Best Paper Award (1st prize) in the International Symposium on Electromagnetic Theory (EMTS2013) held by URSI Commission B at Hiroshima, Japan, on May 2013.