Phase-Induced Frequency Conversion and Doppler Effect with Time-Modulated Metasurfaces

TL;DR

This paper introduces a novel time-modulated metasurface that can induce a Doppler-like frequency shift in electromagnetic waves without physical movement, enabling dynamic frequency control for advanced communication and sensing applications.

Contribution

It presents the first analytical and practical design of a time-modulated metasurface capable of artificial Doppler effects through controlled surface admittance modulation.

Findings

Analytical derivation of the required surface admittance modulation.

Numerical demonstration of frequency up- and down-conversion.

Potential applications in telecommunication, radar, and sensing.

Abstract

Metasurfaces consisting of electrically thin and densely packed planar arrays of subwavelength elements enable an unprecedented control of the impinging electromagnetic fields. Spatially modulated metasurfaces can efficiently tailor the spatial distribution of these fields with great flexibility. Similarly, time modulated metasurfaces can be successfully used to manipulate the frequency content and time variations of the impinging field. In this paper, we present time-modulated reflective metasurfaces that cause a frequency shift to the impinging radiation, thus realizing an artificial Doppler effect in a non-moving electrically thin structure. Starting from the theoretical analysis, we analytically derive the required time modulation of the surface admittance to achieve this effect, and present a realistic time-varying structure, based on a properly designed and dynamically tuned high-impedance surface. It is analytically and numerically demonstrated that the field emerging from the metasurface is up-,down-converted in frequency according to the modulation profile of the metasurface. The proposed metasurface concept, enabling a frequency modulation of the electromagnetic field on-the-fly, may find application in telecommunication, radar, and sensing scenarios.