Browsing by Subject "metamaterials"

Now showing 1 - 4 of 4
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    Supporting data for "Shaping contactless radiation forces through anomalous acoustic scattering"
    (2022-09-15) Stein, Matthew; Keller, Sam; Luo, Yujie; Ilic, Ognjen; ilic@umn.edu; Ilic, Ognjen; University of Minnesota Ilic Research Group
    Waves impart momentum and exert force on obstacles in their path. The transfer of wave momentum is a fundamental mechanism for contactless manipulation, yet the rules of conventional scattering intrinsically limit the radiation force based on the shape and the size of the manipulated object. Here, we show that this intrinsic limit can be broken for acoustic waves with subwavelength-structured surfaces (metasurfaces), where the force becomes controllable by the arrangement of surface features, independent of the object’s overall shape and size. Harnessing such anomalous metasurface scattering, we demonstrate complex actuation phenomena: self-guidance, where a metasurface object is autonomously guided by an acoustic wave, and tractor beaming, where a metasurface object is pulled by the wave. Our results show that bringing metasurface physics of acoustic waves, and its full arsenal of tools, to the domain of mechanical manipulation opens new frontiers in contactless actuation and enables diverse actuation mechanisms that are beyond the limits of traditional wave-matter interactions.
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    Supporting data for Surface Structure Dependent Circular Dichroism in Single and Double Gyroid Metamaterials
    (2022-06-16) William, Lenart R; Ellison, Christopher J; Ferry, Vivian E; Cote, Bryan M; veferry@umn.edu; Ferry, Vivian E.; Materials Research Science & Engineering Center
    Data includes the processed FDTD simulation results needed to recreate the figures in "Surface Structure Dependent Circular Dichroism in Single and Double Gyroid Metamaterials". The data files include single and double gyroids' reflection, transmission, and absorption spectra, near-field electric field intensity enhancements, and the gyroid 3D models used in the FDTD simulations.
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    A Theoretical and Experimental Investigation on Infrared Metamaterial Absorbers
    (2020-01) JIA, WEI
    Metamaterials are artificially engineered structure with unique electromagnetic properties that can not be found in nature. They have many potential applications, and one of its most important applications is metamaterial absorbers. The designing of metamaterial absorbers is based on simultaneous ex citations of an electric dipole and a magnetic dipole resonances. Metamaterial absorber is typically a tri-layer structure with top metallic patterns structured at a sub-wavelength scales, a bottom metallic ground layer and a insulator layer in the middle. The top periodic structure functions as electric resonators driven by the electric field of the incident electromagnetic waves. The magnetic response of the structure is determined by the coupling of the two metallic layers and the dielectric layer. The metallic ground plane needs to be thicker than the skin depth to block any transmission. By altering the geometry sizes of the elements in the structure, the effective permittivity and permeability can be tuned to match the free space impedance, leading to a perfect absorption at certain wavelength. In the past few years, due to the demands of chemical detection and biological sensing, mid-infrared perfect metamaterial absorbers have been studied. For the broadband metamaterial absorber, we proposed a metal-dielectric-metal structure with top metallic patterns based on uniform raindrop shape. The absorption spectra and electromagnetic field distributions of the structure were numerically calculated by the finite element method based on commercial package COMSOL Multiphysics. Then we designed a braodband metamaterial absorber based on multiple sizes of raindrop shaped resonators. The fabrication of the proposed metamaterial absorbers was performed by E-beam lithography method. Following is the measurement of the absorption spectra using Fourier transform infrared spectrometer and the comparison with simulation results. Also, a five-band terahertz absorber with high absorbance was proposed and designed. The designed absorber is insensitive to both TE and TM polarization incident waves. The physical origins of the characteristics exhibited by this absorber can be attributed to dipolar and hexapolar resonances, as established by analyzing the electrical field density. Moreover, the influences of the main structural parameters and configurations on the absorption frequencies were studied. By varying several structural parameters, such as square ring length, dielectric thickness, and cross length, the absorption frequencies can be shifted to higher or lower values. In addition to the adjustment of absorption frequencies, the number of total resonance bands can also be adjusted by revising the structural configurations.
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    Tuning the Chiral Optical Response of Metamaterial and Metamaterial-Semiconductor Nanocrystal Hybrid Systems
    (2020-06) Pachidis, Pavlos
    Chiral metamaterials have been proposed as a promising platform for exotic optoelectronic applications such as ultrasensitive sensors, 3D displays, and ultrafast optical circuits. The functionality of such devices depends on their ability to dynamically change their optical response when a stimulus is applied. However, there are few examples and strategies for designing chiral systems with dynamically tunable optical response without necessitating reconfiguration of the chiral assembly. This thesis presents nanostructures with chiroptical response that can be tuned by modifying the refractive index of non-metallic components, and examines the effect of different design parameters on both circular dichroism and circularly polarized photoluminescence (PL). We show a chiral metamaterial system with metallic and dielectric components, where the refractive index of the dielectric component tunes the dissymmetry in transmission of right and left circularly polarized light (RCP, LCP). We then study the polarization of PL from chiral gold nanorod dimer arrays coated with poly(lauryl methacrylate) - CdSe/CdS quantum dot (QD) composite films. For these studies, we constructed a Fourier space polarimeter and demonstrated how changing the pitch of the periodic array, altering the luminescent material, introducing a dielectric spacer layer, and modulating the refractive index of the underlying substrate affects the handedness and directionality of the PL of the QD film. Finally, we show using finite-difference time-domain simulations that the placement of luminescent nanostructures within the unit cell of metallic arrays leads to enhanced degrees of circularly polarized PL compared to luminescent films that coat the metallic arrays uniformly. In this fashion, metamaterials with highly tailored directionality and polarization of PL can be designed and built. We fabricate assemblies of gold nanorods with QD nanopillars as well as assemblies of nanostructured QD solids via direct-write electron beam lithography, and show that these assemblies exhibit substantial chiroptical response. The results of this thesis encourage the integration of dielectric, phase change, or other materials with switchable optical properties in the design of chiral optical metamaterials, and expand the range of architectures and strategies for dynamically tunable chiroptical properties.