Method and system with fragmented metastructures formed with a plurality of metasurface arrays
An exemplary method and system are disclosed comprising retroreflective metastructures formed with a plurality of metasurface arrays configured to destructively cancel or interfere, in part, with one another to reduce specular mode associated scattering or reflection. In some embodiments, the retroreflective metastructures are formed by a combination of metasurfaces with different lattice spacings that can exhibit enhanced bandwidth and angular range at near-grazing angles to provide enhanced retroreflective electromagnetic responses.
1 . An apparatus comprising:
a substrate defining a top layer of the apparatus, the substrate comprising a retroreflective metasurface comprising a plurality of unit cells defining a macro-pattern, each unit cell comprising two or more types of pixelated-array metasurfaces that define a sub-pattern within the respective unit cell, including a first pixelated-array metasurface and a second pixelated-array metasurface, the first pixelated-array metasurface and the second pixelated-array metasurface being configured to reflect a signal wavefront at a pre-defined range of angle of incidence to generate a scattered wavefront having a resulting first scattered wavefront portion and a second scattered wavefront portion that destructively cancel or interfere, in part, of one another to reduce specular mode of the scattered wavefront,
wherein the first pixelated-array metasurface has a first pattern having a first associated periodicity, and
wherein the second pixelated-array metasurface has a second pattern having a second associated periodicity; and
a ground plane coupled to the substrate and defining a bottom layer of the apparatus, the ground plane having a reflective surface to the signal wavefront,
wherein the top layer is transparent to a first frequency and retroreflective to a second frequency, and wherein the bottom layer functions at the second frequency and is retroreflective to the first frequency.
2 . The apparatus of claim 1 , wherein the first pixelated-array metasurface or second pixelated-array metasurface include a pixelated pattern comprising a plurality of pixel elements, each having a first reflective surface or a second reflective surface.
3 . The apparatus of claim 1 , wherein the first pixelated-array metasurface and the second pixelated-array metasurface are located on a same plane on the substrate.
4 . The apparatus of claim 1 , wherein the substrate is transparent to the signal wavefront, wherein the first pixelated-array metasurface is located on a first surface of the substrate, and wherein the second pixelated-array metasurface is located on a second surface of the substrate, and wherein the first surface is parallel to the second surface, and wherein the first pixelated-array metasurface overlaps with the second pixelated-array metasurface for the pre-defined range of angle of incidence.
5 . The apparatus of claim 4 , wherein the first surface is orthogonal to the second surface.
6 . The apparatus of claim 4 , wherein the first pixelated-array metasurface has a first retroreflective frequency characteristic and a transparent frequency characteristic, and wherein the second pixelated-array metasurface has a second retroreflective frequency characteristic.
7 . The apparatus of claim 1 , wherein the first pixelated-array metasurface and the second pixelated-array metasurface each has a size defined by wavelength parameter and an angle of incidence.
8 . The apparatus of claim 1 , wherein one or more of the plurality of unit cells are configured for dual-polarized retroreflection.
9 . The apparatus of claim 1 , wherein one or more of the plurality of unit cells are configured for single-polarized retroreflection.
10 . The apparatus of claim 1 , wherein one or more of the plurality of unit cells are configured for dual-band retroreflection, including a first retroreflection frequency range having a first center frequency and a second retroreflection frequency range having a second center frequency, and wherein the reduced specular mode of the scattered wavefront increases a bandwidth and angular range of retro-reflectivity of the apparatus.
11 . The apparatus of claim 1 , wherein the first pixelated-array metasurface and the second pixelated-array metasurface collectively provide an overall response of the retroreflective metasurface as a weighted average of the first pixelated-array metasurface and the second pixelated-array metasurface.
12 . The apparatus of claim 1 , wherein the first pattern of the first pixelated-array metasurface and the second pattern of the first pixelated-array metasurface each comprises a binary Huygens metasurface.
13 . The apparatus of claim 1 , wherein the apparatus is configured as a passive or active radio-frequency identification (RFID) tag, optical or RF tagging device, or a smart surface for wireless communication.
14 . The apparatus of claim 1 , further comprising:
an electrical circuit component located in proximity to the retroreflective metasurface.
15 . The apparatus of claim 1 , wherein the first pixelated-array metasurface and the second pixelated-array metasurface are configured for steep angle operation, broad-or multi-band operation, dual-polarized operation, or low CSWAP (cost, size, weight, and power) operation.
16 . The apparatus of claim 1 , wherein the first pixelated-array metasurface and the second pixelated-array metasurface are configured to reflect the signal wavefront having visible light in a visible light portion of the electromagnetic spectrum.
17 . The apparatus of claim 1 , wherein the first pixelated-array metasurface and the second pixelated-array metasurface are configured to reflect the signal wavefront having a frequency in an RF portion of the electromagnetic spectrum.
18 . The apparatus of claim 1 , wherein the pre-defined range of angle of incidence is greater than 0 degrees and less than 90 degrees from normal, and wherein the first associated periodicity and the second associated periodicity establish an angle at which retroreflection is most efficient for a given frequency.
19 . A system comprising:
an apparatus, the apparatus comprising:
a substrate defining a top layer of the apparatus, the substrate comprising a retroreflective metasurface comprising a plurality of unit cells defining a macro-pattern, each unit cell comprising two or more types of pixelated-array metasurfaces that define a sub-pattern within the respective unit cell, including a first pixelated-array metasurface and a second pixelated-array metasurface, the first pixelated-array metasurface and the second pixelated-array metasurface being configured to reflect a signal wavefront at a pre-defined range of angle of incidence to generate a scattered wavefront having a resulting first scattered wavefront portion and a second scattered wavefront portion that destructively cancel or interfere, in part, of one another to reduce specular mode of the scattered wavefront,
wherein the first pixelated-array metasurface has a first pattern having a first associated periodicity, and
wherein the second pixelated-array metasurface has a second pattern having a second associated periodicity; and
a ground plane coupled to the substrate and defining a bottom layer of the apparatus, the ground plane having a reflective surface to the signal wavefront, wherein the top layer is transparent to a first frequency and retroreflective to a second frequency, and wherein the bottom layer functions at the second frequency and retroreflective to the first frequency; and
a controller configured to interrogate the apparatus.
20 . A method of fabricating the apparatus of claim 1 , the method comprising:
setting a retroreflection angle of interest for a unit cell;
partitioning the unit cell into two or more parts;
modeling reflected fields from two subcells and computing a relative phase value between the subcell reflections of a current pattern;
varying patterns of the two subcells until the determined relative phase value of the current pattern of the two subcells is 180 degrees; and
verifying design performance for the two subcells.