Seminar: Electro-Optics and Microelectronics Seminar
Nonlocal Metasurfaces and Time Gratings: Rigorous Degrees of Freedom for Extreme Electromagnetic Field Manipulation
Date:
October,27,2025
Start Time:
14:30 - 15:30
Location:
1061, Meyer Building
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Lecturer:
Amit Shaham
Research Areas:
| The need for sophisticated control over electromagnetic (EM) fields has driven the development of metamaterials and metasurfaces (MSs), enabling a wide range of applications from beam shaping to analog computing. This ever-growing demand calls for extreme constitutive properties, including nonlocality for governing the angular response of metasurfaces and time modulation for surpassing fundamental bounds. In this work, we investigate rigorous degrees of freedom within these two advanced EM paradigms to unveil their foundations and perfect their performance. In the first part, we systematically explore how incorporating both tangential and normal susceptibilities in MSs can dramatically extend their spatial bandwidth, enabling robust nonlocal functionality across all angles of incidence. As a central result, we establish the generalized Huygensโ conditionโa unique balance between tangential and normal susceptibilities that enables all-angle transparency. By thoroughly analyzing its properties, particularly the role of grazing incidence, we rigorously derive a universal link between such susceptibility mixtures and cascaded admittance sheets, forming a basis for practical printed-circuit-board (PCB) realizations (for the transverse-electric polarization). We demonstrate the versatility and performance of our framework by designing and characterizing all-angle transparent radomes (experiment), as well as all-angle spatial differentiators and all-angle artificial magnetic conductors (simulation)โkey components for antenna technologies, radar systems, and analog image processing. These results are expected to significantly expand the capabilities of nonlocal metasurfaces, with potential applications in optical computers and spaceplates. In the second part, we turn to the rich realm of time-varying media. Specifically, we report the first experimental observation of temporal Woodโs anomalyโa theoretically predicted fundamental phenomenon of time-periodic interfacesโusing a compact and economical platform of a folded time grating. By enclosing a single time-varying element within waveguide surroundings, we exploit image theory to reduce the complexity and power consumption demanded of the modulation network. We support our results with a rigorous Floquet-Bloch analysis that exhibits excellent agreement with measurements. Importantly, we utilize our framework to reveal a new regime of temporal Wood’s anomaly, where coupling to negative surface-wave frequencies manifests the emergence of tunable parametric amplification. Beyond this fundamental milestone, our results pave the path toward universal synthesis of intricate temporal apertures for enhancing dynamic filtering and leaky-wave antennas. Collectively, our findings rigorously identify and harness the fundamental spatial and temporal degrees of freedom in nonlocal metasurfaces and time gratings to unlock extreme electromagnetic performance. These results lay the groundwork for diversifying and perfecting nonlocal and time-modulated devices.Ph.D. student under the supervision of Prof. Ariel Epstein.
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