Bandwidth limit and synthesis approach for single resonance ultrathin metasurfaces

Abstract

Metasurfaces have emerged as a promising technology for the manipulation of electromagnetic waves within a thin layer. In planar ultrathin metasurfaces, there exist rigorous design methods, based on the equivalent surface impedance of patterned metallic layers on dielectric substrates. In this work, we derive a limit on bandwidth achievable in these metasurfaces, based on constraints that their meta-atoms should be passive, causal and lossless and that they should obey the time-bandwidth product rules of a single resonance structure. The results show that in addition to elementary design parameters involving variation of the surface impedance, the bandwidth is critically limited by the dielectric substrate thickness and permittivity. We then propose a synthesis method for broadband ultrathin metasurfaces, based on an LC resonance fit of the required surface impedance and experimentally verify a broadband dispersive structure at millimeter-wave frequencies. This results in a bandwidth enhancement of over 90%, relative to a reference metasurface created with the narrowband design process.

Characterization of Broadband Focusing Microwave Metasurfaces at Oblique Incidence

“…To understand the effect of oblique incidence, we synthesize and fabricate a broadband metasurface using the method reported in Ref. [24]. The metasurface is realized by tailoring the Q-factor of the resonant structures, which is equivalent to modifying the parameters of series and parallel LC circuits.…”

“…Here, the resistance R is obtained by fitting to the unit-cell numerical simulation results, while L and C are the inductance and capacitance obtained from the design procedure outlined in Ref. [24]. For the focusing metasurface as realized in Section II, the L, C and R profiles are plotted in Fig.…”

“…We use a broadband metasurface based on the design procedure presented in Ref. [24], utilizing dog-bone and inverse dog-bone structures, in a metallicdielectric meta-atom architecture. Experimental verification is performed in the X-band microwave frequency range, considering an incident plane wave with transverse electric (TE) polarization.…”

Recent advances in strongly resonant and gradient all-dielectric metasurfaces

“…As a result, a new generation of research on achromatic gradient metasurfaces has been recently established, aiming to increase their temporal bandwidth and render them more suited to practical applications. 124,[150][151][152][154][155][156][157][158] Fundamental limits for the bandwidth of achromatic metalenses have been discussed based on the time-bandwidth limit in any time-invariant system. 159 Dielectric achromatic metasurfaces were first demonstrated in the context of beam steering, where it was realized that to achieve the same deflection angle for different wavelengths the metasurface can no longer be periodic.…”

Squeezing a Prism into a Surface: Emulating Bulk Optics with Achromatic Metasurfaces

“…As a result, researchers have very recently focused on the search for achromatic gradient metasurfaces that retain their functionality over broad spectral bandwidths and are thus suitable for practical applications. [ 15–23 ]…”