Mechanical mode engineering with orthotropic metamaterial membranes

Metamaterials are structures engineered at a small scale with respect to the wavelength of the excitations they interact with. These structures behave as artificial materials whose properties can be chosen by design, mocking and even outperforming natural materials and making them the quintessential tool for manipulation of wave systems. In this Letter we show how the acoustic properties of a silicon nitride membrane can be affected by nanopatterning. The degree of asymmetry in the pattern geometry induces an artificial anisotropic elasticity, resulting in the splitting of otherwise degenerate mechanical modes. The artificial material we introduce has a maximum Ledbetter-Migliori anisotropy of 1.568, favorably comparing to most bulk natural crystals. With an additional freedom in defining arbitrary asymmetry axes by pattern rotation, our approach can be useful for fundamental investigation of material properties as well as for devising improved sensors of light, mass or acceleration based on micromechanical resonators

Macro-micro relationship in nanostructured functional composites

This paper examines the results of the characterization of two functional composites: Poly(methyl methacrylate) (PMMA)-Ce:YAG (yttrium aluminium garnet doped with cerium) and PMMA-cobalt hexacyanoferrate (CoHCF). The composites were prepared as possible emitters in the fields of lighting thermal sensors. The prepared composites were characterized using transmission electron microscopy (TEM), nuclear magnetic resonance (NMR) spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) analyses to study the correlation between micro and macro characteristics. We found that the molecular interactions of the two different fillers with the matrix were localized in different sites of the polymer chains. Moreover, the composites showed an increased thermal strength and stiffness, in particular the PMMA-Ce:YAG composite

Interferometric control of absorption in thin plasmonic metamaterials: General two port theory and broadband operation

In order to extend the Coherent Perfect Absorption (CPA) phenomenology to broadband operation, the interferometric control of absorption is investigated in two-port systems without port permutation symmetry. Starting from the two-port theory of CPA treated within the Scattering Matrix formalism, we demonstrate that for all linear two-port systems with reciprocity the absorption is represented by an ellipse as function of the relative phase and intensity of the two input beams, and it is uniquely determined by the device single-beam reflectance and transmittance, and by the dephasing of the output beams. The basic properties of the phenomenon in systems without port permutation symmetry show that CPA conditions can still be found in such asymmetric devices, while the asymmetry can be beneficial for broadband operation. As experimental proof, we performed transmission measurements on a metal-semiconductor metamaterial, employing a Mach-Zehnder interferometer. The experimental results clearly evidence the elliptical feature of absorption and trace a route towards broadband operation

Metodologia para a determinação da intensidade de coloração em grãos de milho.

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