Near Zero Index Perfect Metasurface Absorber using Inverted Conformal Mapping

Abstract

The geometry of the characteristic element forming the artificial structure of an electromagnetic metamaterial defines the way the metamaterial will interact with electromagnetic waves, and accordingly, how it will transmit, reflect, and absorb electromagnetic energy. Metamaterials have been discovered that can manipulate electromagnetic waves to create perfect absorption of incident electromagnetic energy using relatively simple elemental geometries. But the phenomenon is confined to very narrow frequency bandwidths owing to the mono-resonance characteristics of simple cellular structures. Complex cellular geometries based on the combination of many different fundamental building blocks may be able to constructively couple many more resonances and broaden the perfect absorption bandwidth. We describe here a metasurface based upon geometric inversion of a set of conformal mapping contours. The resulting geometry forms a nearly continuous series of perfect absorption resonances within an ultrathin (λ/165) metasurface to develop broadband absorption in a frequency range of interest for downhole chemical spectroscopy. The metasurface is derived from a geometric inversion of the Rhodonea, or more commonly called four-leaf roses, conformal mapping contours and was found to exhibit a near zero index metamaterial (NZIM) behavior. An uncooled microbolometer design is described that uses the metasurface geometry on a single VO2 thermometric substrate leading to an infrared detector with predicted maximum absorption of 99.94% at 4.3 μm and an absorption bandwidth of 170% FWHM on 15.8 μm center wavelength, coincident with important chemical spectra of downhole hydrocarbons. The infrared detector design has a predicted maximum detectivity D* = 1.5 × 109 cm$$\sqrt{\text{Hz}}$$Hz/W and noise equivalent difference temperature NEDT of 70 mK at a frame rate of 60 Hz. These levels of detector performance conventionally would be achievable only with cryogenically cooled technologies and could represent a significant step in the effort towards deploying an in situ infrared chemical spectroscopy sensor into downhole logging applications.

Carbon Dioxide Gas Sensor Based on Polyhexamethylene Biguanide Polymer Deposited on Silicon Nano-Cylinders Metasurface

“…The transmission, reflection, absorption and electric-field distribution of the proposed device are calculated by utilizing the finite element method (FEM), based on a commercially available COMSOL Multiphysics software. By considering a single unit cell, the additional simulation volume is avoided which leads to a reduced simulation time [ 40 ]. On four sides of the unit cell, Floquet-periodic boundary conditions are applied to mimic the unbounded 2D array.…”

Near Centimeter-scale FT-MIR Spectrometer based on NZIM Perfect Absorption using Inverted TanCirc Conformal Mapping Geometry

“…Fundamentally, the miniaturized downhole spectrometer is built upon a perfect metasurface absorber for the uncooled microbolometer detector and thermal infrared source. In a previous work Swett 6 described how a broadband electromagnetic absorption could be achieved from a metamaterial built upon complex sub-cellular geometries derived from geometric inversion of a Rhodonea conformal mapping set of contours. Here we use a similar approach and report an electromagnetic metamaterial derived from a geometric inversion of the canonical TanCirc conformal mapping contours leading to a metamaterial also with near zero index metamaterial (NZIM) behavior and broad perfect absorption bandwidth.…”

“…For the free metasurface in the absence of substrate or reflector the scattering parameters for forward/backward propagation are identical owing to symmetry. The effective properties calculations were made using a conventional retrieval process 8 slightly modified as outlined in Swett 6 for the selection of the phase complex root which considers the case made by Markel 9 that material passivity fully constrains the imaginary part of permittivity to be positive, but does not preclude negativity in the imaginary part of permeability. Since the quantities of relative impedance and refractive index are not independent parameters but derived values from fundamental properties, the selection of one root fixes the value of the other 10 .…”

Carbon Dioxide Gas Sensor Based on Polyhexamethylene Biguanide Polymer Deposited on Silicon Nano-Cylinders Metasurface

“…HAu, respectively. The HAu is fixed at 100 nm throughout the paper which is bigger than the skin By considering a single unit cell, the additional simulation volume is avoided which leads to the reduced simulation time [29]. On four sides of the unit cell, Floquet-periodic boundary conditions are applied to mimic the unbounded 2D array.…”