Meta Atoms Research Articles

Near-perfect sound absorption using hybrid resonance between subwavelength Helmholtz resonators with non-uniformly partitioned cavities

We present near-perfect sound absorption using a metasurface composed of meta-atoms (MAs) which are subwavelength Helmholtz resonators (HRs) with cavities non-uniformly partitioned by membranes. By embedding the membranes at different horizontal locations in the cavities, we break geometrical symmetry between the MAs so as to derive hybrid resonance between the MAs at our target frequency. The resonance frequency of each MA is determined by delicately adjusting the locations of the membranes, resulting in perfect absorption at the target frequency which is different from the resonance frequencies of MAs. The metasurface is designed to satisfy impedance matching conditions with air at one or more target frequencies with the aid of a theoretical model for frequency-dependent effective acoustic impedance. The theoretical model is established with physical reality by considering the higher-order eigenmodes of the membrane, the visco-thermal losses in narrow orifices, and the end corrections of the subwavelength HR. The designed metasurface is fabricated and its absorption performance is verified experimentally in an impedance tube. Near-perfect absorption of sound is achieved at the target frequency of 500 Hz, which is 12.3% lower than that of near-perfect absorption by previous metasurfaces inducing hybrid resonance between HRs without membranes.

Investigations of generalized Pancharatnam-Berry phase in all-dielectric metasurfaces

As one of the main approaches to implement phase gradient in metasurfaces, Pancharatnam-Berry (PB) phase originated from the spin–orbit interaction (SOI) of light has attracted enormous interest during the past several decades. Different from classical PB phase in linear optics that equals to twice the rotational angle of anisotropic elements for half wave plate distance and circular polarization, the recently proposed generalized PB phase indicates that phase gradient equals to multiple times the rotation angle could be achieved by high-order symmetry metallic meta atoms. Here, we show that the generalized PB phase can also be implemented in all-dielectric metasurfaces with higher efficiency than their metallic counterparts. Besides, by merging generalized PB phase and propagation phase, several functional devices are designed that the symmetric performance of PB phase can be decoupled. Moreover, a detailed comparison between meta atoms with C2, C3, and C6 rotational symmetries is conducted to illustrate the difference between classical and generalized PB phase. These results may further supplement the concept of generalized PB phase and could find many applications in optics and photonics..

(Invited) Two-color soliton meta-atoms and molecules

We present a detailed overview of the physics of two-color soliton molecules in nonlinear waveguides, i.e. bound states of localized optical pulses which are held together due to an incoherent interaction mechanism. The mutual confinement, or trapping, of the subpulses, which leads to a stable propagation of the pulse compound, is enabled by the nonlinear Kerr effect. Special attention is paid to the description of the binding mechanism in terms of attractive potential wells, induced by the refractive index changes of the subpulses, exerted on one another through cross-phase modulation. Specifically, we discuss nonlinear-photonics meta atoms, given by pulse compounds consisting of a strong trapping pulse and a weak trapped pulse, for which trapped states of low intensity are determined by a Schr\"odinger-type eigenproblem. We discuss the rich dynamical behavior of such meta-atoms, demonstrating that an increase of the group-velocity mismatch of both subpulses leads to an ionization-like trapping-to-escape transition. We further demonstrate that if both constituent pulses are of similar amplitude, molecule-like bound-states are formed. We show that z-periodic amplitude variations permit a coupling of these pulse compound to dispersive waves, resulting in the resonant emission of Kushi-comb-like multi-frequency radiation.

Bioinspired multiple-degrees-of-freedom responsive metasurface by high-entropy-alloy ribbons with hierarchical nanostructures for electromagnetic wave absorption

The compound eyes of the dragonfly, Pantala flavescens Fabricius, are covered by micro-scaled ocelli capable of sensing polarized light, an attractive property for radar stealth and counterreconnaissance. In this work, we fabricated biomimetic electromagnetic wave absorption materials (EAMs) by analyzing the covert information identifications of biological systems and focusing on the design of metastructures and microstructures. Several bionic metasurfaces with anisotropic double-V meta atoms made up of (FeCoNiSi8.9Al8.9)C0.2 high-entropy-alloy (HEA) ribbons for multiple-degrees-of-freedom recognition and broadband absorption are presented. The covert phase, amplitude, and angular momentum of electromagnetic waves were controlled and recognized as information by manipulating the rotation angle θ of meta atoms. A vortex wave with a topological charge of 1 was generated to recognize linearly polarization and left- and right-handed circular polarization. In addition, the polarization conversion enhanced absorption. The hierarchical nanostructures of HEA ribbons give rise to suitable electromagnetic loss and a superior impedance match. Finally, inspired by the structure of compound eyes, the designed multilayer metamaterials realized effective absorption (reflection loss (RL) ≤ − 10 dB) within the 4.5–18 GHz regime under 2.8 mm thickness. These materials provide evidence for a new way for integrated EAMs and metamaterials.

Identification and Strategies to Mitigate High Total Clearance of Benzylamine-Substituted Biphenyl Ring Systems.

For most oral small-molecule projects within drug discovery, the extent and duration of the effect are influenced by the total clearance of the compound; hence, designing compounds with low clearance remains a key focus to help enable sufficient protein target engagement. Comprehensive understanding and accurate prediction of animal clearance and pharmacokinetics provides confidence that the same can be observed for human. During a MERTK inhibitor lead optimization project, a series containing a biphenyl ring system with benzylamine meta-substitution on one phenyl and nitrogen inclusion as the meta atom on the other ring demonstrated multiple routes of compound elimination in rats. Here, we describe the identification of a structural pharmacophore involving two key interactions observed for both the MERTK program and an additional internal project. Four strategies to mitigate these clearance liabilities were identified and systematically investigated. We provide evidence that disruption of at least one of the interactions led to a significant reduction in CL that was subsequently predicted from rat hepatocytes using in vitro/in vivo extrapolation and the well-stirred scaling method. These tactics will likely be of general utility to the medicinal chemistry and DMPK community during compound optimization when similar issues are encountered for biphenyl benzylamines.

Numerical investigation of metasurface narrowband perfect absorber and a plasmonic sensor for a near-infrared wavelength range

Herein, we have presented a computation study of a metasurface (MS) narrowband perfect absorber performed utilizing the three-dimensional finite element method. In the first part of the paper, the periodic sequence of silicon meta-atoms (MAs) is positioned on a ∼100 nm gold thin-film. The gold thin-film obstructs a broadband light at normal incidence, and silicon MAs are utilized to stimulate the surface plasmon by scattering light through it. The highest absorption of 96% is procured at 930.26 nm in the air medium which can be further enhanced by using a layered structure of MAs deposited on gold. The MAs are composed of Si/SiO2/Si with an optimized layers height. Consequently, the perfect impedance matching of the electric and magnetic dipoles takes place providing a 99% of absorption insensitive to the incidence angle of light and almost negligible reflection at a resonating wavelength of 889.4 nm. This feature allows us to utilize this device as a plasmonic sensor. That is why, in the second part of the paper, the proposed device design is studied for the detection of the refractive index of the surrounding medium. The sensitivity and figure of merits of the MS device are in the range of 460–492 nm RIU−1 and 76.7–82 RIU−1, respectively. We claim that the anticipated MS element can be employed in solar photovoltaic and biomedical sensing purposes.

Subwavelength, polarimetric color sorting by densely interleaved nano-resonators

Sorting light by spectrum in subwavelength scale emerges as important research due to its potential applications in nanoscale optical devices. Diverse research activities are explored to achieve efficient spectral sorting based on nanostructured metasurfaces by leveraging plasmonic and dielectric resonances. While they show many advantages of controlling light in nanoscale with compact form factor, practical realization of the efficient sorting of light in visible spectrum is still elusive due to the strong optical coupling and crosstalk between nanostructures that are arranged in subwavelength scale. Here, we demonstrate silicon-based ultrathin metasurfaces composed of densely interleaved one-dimensional nano-resonators (meta atoms) with three different widths that function both as efficient spectral sorter and light absorber in the visible regime. We find that the geometric aspect ratio of meta atoms and specific mode of resonance play a crucial role in realizing efficient subwavelength spectral splitting with significantly suppressed crosstalk. The sorting efficiency up to 78% is reported by optimally designing the metasurface. We believe that suggested designing scheme paves an important way to realize ultrathin, subwavelength spectral sorters and to develop nano-scale optical sensors.

Narrowband perfect metasurface absorber based on impedance matching

We presented a numerical investigation of a metamaterial narrowband perfect absorber conducted via a finite element method based on commercially available COMSOL software. The periodic array of silicon meta-atoms (MAs) are placed on 80 nm thick gold layer. The broadband light at normal incidence is blocked by the gold layer and silicon MAs are used to excite the surface plasmon by scattering light through it. Maximum absorption of 95.7 % is obtained at the resonance wavelength of 1137.5 nm due to the perfect impedance matching of the electric and magnetic dipoles. The absorption is insensitive to the wide-angle of incidence ranging from 0 to 80 degrees. We believe that the proposed metamaterial device can be utilized in solar photovoltaic and biochemical sensing applications. Full Text: PDF ReferencesY. Cheng, X.S. Mao, C. Wu, L. Wu, R.Z. Gong, "Infrared non-planar plasmonic perfect absorber for enhanced sensitive refractive index sensing", Optical Materials, 53, 195-200 (2016). CrossRef S. S. Mirshafieyan, D.A. Gregory, "Electrically tunable perfect light absorbers as color filters and modulators", Scientific Reports,8, 2635 (2018). CrossRef D.M. Nguyen, D. Lee, J. Rho, "Control of light absorbance using plasmonic grating based perfect absorber at visible and near-infrared wavelengths", Scientific Reports, 7, 2611 (2017). CrossRef Y. Sun, Y. Ling, T. Liu, L. Huang, "Electro-optical switch based on continuous metasurface embedded in Si substrate", AIP Advances, 5, 117221 (2015). CrossRef H. Chu, Q. Li, B. Liu, J. Luo, S. Sun, Z. H. Hang, L. Zhou, Y. Lai, "A hybrid invisibility cloak based on integration of transparent metasurfaces and zero-index materials", Light: Science & Applications, 7, 50 (2018). CrossRef S. K. Patel, S. Charola, J. Parmar, M. Ladumor, "Broadband metasurface solar absorber in the visible and near-infrared region", Materials Research Express, 6, 086213 (2019). CrossRef Q. Qian, S. Ti, C. Wang, "All-dielectric ultra-thin metasurface angular filter", Optics Letters, 44, 3984 (2019). CrossRef P. Yu et al., "Broadband Metamaterial Absorbers", Advanced Optical Materials, 7, 1800995 (2019). CrossRef Y. J. Kim et al., "Flexible ultrathin metamaterial absorber for wide frequency band, based on conductive fibers", Science and Technology of advanced materials, 19, 711-717 (2018). CrossRef N.L. Kazanskiy, S.N. Khonina, M.A. Butt, "Plasmonic sensors based on Metal-insulator-metal waveguides for refractive index sensing applications: A brief review", Physica E, 117, 113798 (2020). CrossRef H. E. Nejad, A. Mir, A. Farmani, "Supersensitive and Tunable Nano-Biosensor for Cancer Detection", IEEE Sensors Journal, 19, 4874-4881 (2019). CrossRef

Dipole Response of a Dielectric Sphere

Most of the effects of metamaterial physics are associated with a resonance response, particularly electric and magnetic dipole resonances. For dielectric meta atoms with high refractive indices of 3 to 10, formulas are derived that describe the positions of the first dipole resonances, the characteristic size of particles, and their refractive index. A criterion for the validity of a dipole approximation for replacing a dielectric sphere with a pair of dipoles is constructed for the first time.

Depiction and analysis of a modified H-shaped double-negative meta atom for satellite communication

AbstractA modified H-shaped metamaterial is imparted in this paper that has a multiple band coverage for reflection and transmission coefficient. The proposed structure exhibits triple band coverage for the permittivity and permeability. Two split ring resonators (SRR) are connected with the substantial H-shaped structure. The 12 × 12 mm2 structure has been printed on FR-4 and a correlation is made between the basic unit-cell and array structures. A comparison is made among 1 × 2, 2 × 2, and 4 × 4 array structures with 1 × 2, 2 × 2, and 4 × 4 unit-cell configurations to validate the performance of the proposed metamaterial. A great transmission coefficient having a band of 13 GHz with a 500 MHz band gap in the middle is demonstrated for all of these configurations. The effective parameters of the resonators cover C, X, and Ku bands independently with double-negative phenomena at X and Ku bands with a frequency range of about 2.5 GHz. The reflection and transmission coefficients of the unit cell are obtained by CST microwave studio. Having an auspicious design and wide range double-negative characteristics, this structure can be applied to satellite communication.

Parametric studies on split S-shaped composite meta atom for X-band communication

AbstractThe aim of this paper is to describe a split S-shaped composite meta atom which shows double negative characteristics at resonance frequency. The proposed meta-atom structure exhibits an almost 3.70 GHz bandwidth when the operating frequency from 8 to 14 GHz (X-band). In this study, the ring width, split width, size of substrate material, and the substrate material itself are varying to investigate their effect on the resonance frequencies. Metal strips of the outer resonator are the splits and the inner ring resonator is designed in a way that it forms a split S-shaped structure on the epoxy resin fibre (FR-4) substrate material. The CST Microwave Studio electromagnetic simulator software was used for the design and simulation purposes, and an Agilent N5227A vector network analyser was used for practical measurements.

Multiband left handed biaxial meta atom at microwave frequency

Left handed meta atoms are special class materials that characterized by the negative refractive index. In this paper, a left handed biaxial meta-atom is reported that has 5.81 GHz wide bandwidth and applicable for C-, X- and Ku-band applications. The meta atom is developed by an outer and the inner split ring resonator with inverse E-shape metal strips of copper, which are connected with the outer ring resonator that look like a mirror-shape structure. A finite integration technique based CST Microwave Studio is utilized to design, simulation and analysis purposes, where the Agilent N5227A vector network analyzer is utilized for measurement purpose. Measurements show that, the measured and simulated results are well complied together and negative index bandwidth from 3.27 to 6.55 GHz (bandwidth of 3.28 GHz) and 7 to 12.81 GHz (bandwidth of 5.81 GHz) along the z-axis wave propagation. The total dimensions of the designed structure are 0.2λ × 0.2λ × 0.035λ and the effective medium ratio 5, makes the proposed biaxial meta-atom is suitable for practical applications.

The Influence of Element Deformation on Terahertz Mode Interaction in Split-Ring Resonator-Based Meta-Atoms

The interaction between terahertz (THz) resonance modes and element deformation in rectangular split-ring resonator (RSRR)-based meta-atoms (MAs) is investigated experimentally. Two types of RSRR-based MAs are presented: lateral-varied SRR (LV-SRR) and arm-twisted SRR (AT-SRR). When the distances from the gaps to the opposite sides of above meta-atoms increase from 10 to 40 μm, the inductive-capacitive (LC) resonance modes and dipole oscillation modes exhibit redshift behavior. The quality factor (Q factor) of LC resonance decreases while that of dipole oscillation modes increases. The THz mode interaction is subject to the distance between the gap and opposite side. An extension of lateral side contributes much more to the enhancement of Q factor of dipole oscillation mode than the twisted arms. The relationship between the near-field coupling effect and THz modes is revealed by the analysis of surface currents as well as the electric energy density distribution, as is in agreement with the experimental results.

Terahertz response of fractal meta-atoms based on concentric rectangular square resonators

We investigate the terahertz electromagnetic responses of fractal meta-atoms (MAs) induced by different mode coupling mechanisms. Two types of MAs based on concentric rectangular square (CRS) resonators are presented: independent CRS (I-CRS) and junctional-CRS (J-CRS). In I-CRS, each resonator works as an independent dipole so as to result in the multiple resonance modes when the fractal level is above 1. In J-CRS, however, the generated layer is rotated by π/2 radius to the adjacent CRS in one MA. The multiple resonance modes are coupled into a single mode resonance. The fractal level increasing induces resonance modes redshift in I-CRS while blueshift in J-CRS. When the fractal level is below 4, the mode Q factor of J-CRS is in between the two modes of I-CRS; when the fractal level is 4 or above, the mode Q factor of J-CRS exceeds the two modes of I-CRS. Furthermore, the modulation depth (MD) decreases in I-CRS while it increases in J-CRS with the increase in fractal levels. The surface currents analysis reveals that the capacitive coupling of modes in I-CRS results in the modes redshift, while the conductive coupling of modes in J-CRS induces the mode blueshift. A high Q mode with large MD can be achieved via conductive coupling between the resonators of different scales in a fractal MA.

Electric and Magnetic Response in Dielectric Dark States for Low Loss Subwavelength Optical Meta Atoms

Artificially created surfaces or metasurfaces, composed of appropriately shaped subwavelength structures, namely, meta‐atoms, control light at subwavelength scales. Historically, metasurfaces have used radiating metallic resonators as subwavelength inclusions. However, while resonant optical metasurfaces made from metal have been sufficiently subwavelength in the propagation direction, they are too lossy for many applications. Metasurfaces made out of radiating dielectric resonators have been proposed to solve the loss problem, but are marginally subwavelength at optical frequencies. Here, subwavelength resonators made out of nonradiating dielectrics are designed. The resonators are decorated with appropriately placed scatterers, resulting in a meta‐atom with an engineered electromagnetic response. As an example, a metasurface that yields an electric response is fabricated, experimentally characterized, and a method to obtain a magnetic response at optical frequencies is theoretically demonstrated. This design methodology paves the way for metasurfaces that are simultaneously subwavelength and low loss.

Microwave meta-atom enhanced spintronic rectification

An artificial meta-atom (MA), or alternatively, a plasmonic antenna, has been demonstrated to significantly enhance the microwave spin rectifying photovoltage by more than two orders in magnitude (∼280) in the ferromagnetic resonance regime. The large enhancement is attributed to the unique structure of the MA which magnifies both microwave electric (∼5) and magnetic (∼56) fields in the same near-field spatial region. Our work develops the interdisciplinary direction with artificial and natural magnetism and may find promising applications in high-frequency or opto-spintronic devices and wireless microwave energy harvesting.

Role of duality symmetry in transformation optics

Maxwell's equations in curved space-time are invariant under electromagnetic duality transformations. We exploit this property to constraint the design parameters of metamaterials used for transformations optics. We show that a general transformation must be implemented using a dual-symmetric metamaterial. This can be accomplished constraining the polarisability tensors of their individual constituents, i.e. the meta atoms. We obtain explicit expressions for these constraints. We also show that the spatial part of the coordinate transformation depends only on the electric-electric tensorial coupling of the polarisability tensor, while the spatio-temporal part depends only on the electric-magnetic tensorial coupling. In our derivations, we find that two dipoles located at the same point, one electric (p) and one magnetic (m), are needed to produce a total field with well defined helicity equal to +1 or -1, and that they must be related as p=im/c or p=-im/c, respectively.

Chromophores Arranged as “Magnetic Meta Atoms”: Building Blocks for Molecular Metamaterials

Benzoperylenetriscarboximides were parallel arranged by stiff spacers where exciton interactions could be controlled by their distance. The most bathochromic electronic transition of the chromophores essentially exhibits only an electric component where an orthogonal magnetic component was established by the distance-controlled interaction of chromophores. Such arrangements were discussed as building blocks for molecular metamaterials.

Reductive dechlorination of polychlorinated biphenyls (PCBs) by ultrasound-assisted chemical process (UACP)

The dechlorination of aqueous polychlorinated biphenyls (PCBs) using the ultrasound-assisted chemical process (UACP), which is a combination of ultrasonic irradiation and radical generations using di-tert-butyl peroxide as a radical initiator and ferrous ion as a catalyst at moderate temperature in alkaline 2-propanol, was demonstrated with a high reduction of PCBs. A commercial PCB-containing compound, Aroclor 1260, was also decomposed with the removal efficiency of 97 % achieved within 3 h of UACP. The gas chromatograph was used as a quantitative method to measure the decomposition rate of PCBs. The competitive elimination among the ortho (2-position), meta (3-position), and para (4-position) chlorine atoms of PCB was also identified.

Hepatic microsomal cytochrome P450 enzyme activity in relation to in vitro metabolism/inhibition of polychlorinated biphenyls and testosterone in Baltic grey seal (Halichoerus grypus)

Among other factors, cytochrome P450 (CYP) enzyme activity determines polychlorinated biphenyl (PCB) bioaccumulation, biotransformation, and toxicity in exposed species. We measured the oxidative metabolism in vitro of 12 PCB congeners, representing structural groups based on the number and position of the chlorine atoms, by the hepatic microsomes of one Baltic grey seal (Halichoerus grypus). Microsomal metabolism was observed for several PCBs with vicinal H atoms exclusively in the ortho and meta positions and without any ortho-Cl substituents (CB-15 [4,4'-Cl2] and CB-77 [3,3',4,4'-Cl4]), vicinal meta and para-H atoms (CB-52 [2,2',5,5'-Cl4], and -101 [2,2',4,5,5'-Cl5]) or with both characteristics in combination with either only one ortho-Cl (CB-26 [2,3',5-Cl3], CB-31 [2,4',5-Cl3]) or two ortho-Cl substituents (CB-44 [2,2',3,5'-Cl4]). To allocate PCB biotransformation to specific CYPs, the inhibitive effect of compounds with known CYP-specific inhibition properties was assessed on in vitro PCB metabolism and on regio- and stereospecific testosterone hydroxylase activities. Metabolic inhibition was considered relevant at concentrations < or = 1.0 microM because these inhibitors became decreasingly selective at higher concentrations. At < 1.0 microM, ellipticine (CYPIAI/2 inhibitor) selectively inhibited CB-15, -26, -31, and -77 metabolism, with no significant inhibition of CB-44, -52, and -101 metabolism. Inhibition of CB-52 and -101 metabolism by chloramphenicol (CYP2B inhibitor) started at 1.0 microM and maximized at about 100% at 10 microM. Ketoconazole (CYP3A inhibitor) appeared to selectively inhibit CB-26, -31, and -44 metabolism relative to CB-15, -77, and -52 at concentrations < or = 1.0 microM. Major testosterone metabolites formed in vitro were 2beta-(CYP3A), 6beta- (CYP3A, CYPIA), and 16beta- (CYP2B) hydroxytestosterone and androstenedione (CYP2B, CYP2C11). The CYP forms indicated are associated with the specific metabolism of testosterone in laboratory animals. Inhibition of 2beta- and 6beta-hydroxytestosterone formation at ellipticine and ketoconazole concentrations < or = 1.0 microM suggested that both inhibitors were good substrates of CYP3A-like enzymes in grey seal. Chloramphenicol (model for CYP2B) is apparently not a good inhibitor of CYPI A and CYP3A activities in grey seal because the chemical did not inhibit any metabolic route of testosterone at concentrations from 0.1 to 10 microM. Our findings demonstrated that at least CYP1A- and CYP3A-like enzymes in the liver of grey seals are capable of metabolizing PCBs with ortho-meta and/or meta-para vicinal hydrogens. A CYP2B form might also be involved, but this could not be proven by the results of our experiments. Defining the profiles of CYP enzymes that are responsible for PCB biotransformation is necessary to fully understand the bioaccumulation, toxicokinetics, and risk of PCB exposure in seals and other free-ranging marine mammals.