Far-field subwavelength acoustic imaging by deep learning

Seeing and recognizing an object whose size is much smaller than the illumination wavelength is a challenging task for an observer placed in the far field, due to the diffraction limit. Recent advances in near and far field microscopy have offered several ways to overcome this limitation; however, they often use invasive markers and require intricate equipment with complicated image post-processing. On the other hand, a simple marker-free solution for high-resolution imaging may be found by exploiting resonant metamaterial lenses that can convert the subwavelength image information contained in the near-field of the object to propagating field components that can reach the far field. Unfortunately, resonant metalenses are inevitably sensitive to absorption losses, which has so far largely hindered their practical applications. Here, we solve this vexing problem and show that this limitation can be turned into an advantage when metalenses are combined with deep learning techniques. We demonstrate that combining deep learning with lossy metalenses allows recognizing and imaging largely subwavelength features directly from the far field. Our acoustic learning experiment shows that, despite being thirty times smaller than the wavelength of sound, the fine details of images can be successfully reconstructed and recognized in the far field, which is crucially enabled by the presence of absorption. We envision applications in acoustic image analysis, feature detection, object classification, or as a novel noninvasive acoustic sensing tool in biomedical applications

Metamaterials for enhanced light control: from high resolution focusing to invisibity

Artificial dielectrics and their descendants – metamaterials, have unusual electromagnetic parameters and provide more abilities than naturally available dielectrics for control of the light. The first experimental realization of a double negative medium gave an enormous impulse for research in the field of electromagnetism. As result, a lot of fascinating electromagnetic devices have been developed since then, including metamaterial lenses, beam steerers and even invisibility cloaks. The aim of this master thesis is to contribute to the development of such devices, especially metamaterial lenses and invisibility cloaks. First, a background of metamaterial and metasurfaces is introduced. The main aspects of metamaterials and their characteristics are reviewed, so that the working principles of metamaterials can be acquired with minimal prerequisite mathematics. Then we review the design process of several metamaterial lenses, including a zoned fishnet metamaterial lens and a Soret lens, a member of Fresnel zone plate lenses. Finally we design a carpet cloak, using a metasurface with double ring resonators. In the first application, the time-honored zoning technique is used to reduce the volume, and therefore weight, of a fishnet metamaterial lens. By properly optimizing a profile of the zoned lens we are able to reduce a volume of the lens up to 60% and broaden the fractional bandwidth up to 3 times. With this optimization technique the bandwidth of the zoned lens, which usually is narrow band, increases without causing any deterioration in its performance. The second metamaterial lens is a member of the well-known Fresnel zone plate’s family and consists of alternating and opaque concentric rings. Since half of the power is blocked by opaque rings the efficiency of such lenses is low. In order to improve the coupling and illumination efficiency we propose using an array of subwavelength holes instead of the transparent ring. Also by supporting the lens with a block of fishnet metamaterial working in near-zero index regime it is possible to improve radiation characteristics of a metalens antenna, such as directivity and side lobe level. Finally, in the third application a ground cloak design is described as simulation results. The presented ground cloak is based on a metasurface, an array of closed ring resonators, and, therefore, has an ultrathin design and relatively simple in fabrication. The proposed cloak has been successfully employed to conceal an electrically large object (1.1λ0) for wide range of incident angles and relatively wide frequency range.The author acknowledges Spanish Ministerio de Economía y Competitividad for the financial support (under grant FPI BES-2012-054909) of his study at UPNA.Máster Universitario en ComunicacionesUnibertsitate Masterra Komunikazioeta

PENGARUH EKSTRAK DAUN GINSENG JAWA (Talinum triangulare) TERHADAP KADAR MALONDIALDEHYDE (MDA) PADA TIKUS (Rattus novergicus) HIPERKOLESTEROLEMIA

Latar Belakang : Hiperkolesterolemia merupakan penyebab stres oksidatif dalam tubuh yang menyebabkan terjadinya peroksidasi lipid dan berperan utama pada perkembangan awal aterosklerosis. Ekstrak daun ginseng jawa (Talinum triangulare) mengandung senyawa flavonoid, asam fenolat dan antosianin yang memiliki fungsi sebagai antioksidan. Tujuan : Membuktikan pengaruh pemberian ekstrak daun ginseng jawa (Talinum triangulare) terhadap kadar MDA pada tikus hiperkolesterolemia. Metode : True Experimental, Post Test Only Control Group Design dengan kelompok kontrol negatif, kontrol positif diberi diet tinggi lemak saja, serta 3 kelompok perlakuan ekstrak Daun Ginseng Jawa yaitu dosis 25mg/200gBB/hari, 50mg/200gBB/hari, 100mg/200gBB/hari Hasil Penelitian dan Pembahasan : Dari hasil uji one way anova didapatkan pengaruh yang bermakna (p<0,05) pada kelompok kontrol dan kelompok perlakuan. Hasil uji post hoc didapatkan perbedaan yang bermakna (p<0,05) pada kelompok perlakuan 2 dan 3 dengan kontrol positif yang berarti terdapat pengaruh ekstrak daun ginseng jawa terhadap kadar MDA tikus hiperkolesterol pada dosis 50mg/200gBB dan 100mg/200gBB. Hasil uji regresi linier didapatkan R2=0,72 (ekstrak daun ginseng jawa memberikan pengaruh sebanyak 72% sementara 28% lain adalah faktor yang tidak diteliti). Berdasarkan hasil uji yang dilakukan menunjukkan semakin tinggi dosis ekstrak yang diberikan, semakin rendah kadar MDA tikus. Kesimpulan : Pemberian Ekstrak Daun Ginseng Jawa (Talinum triangulare) berpengaruh dapat menurunkan kadar MDA tikus hiperkolesterolemia

Tunable beam steering enabled by graphene metamaterials

We demonstrate tunable mid-infrared (MIR) beam steering devices based on multilayer graphene-dielectric metamaterials. The effective refractive index of such metamaterials can be manipulated by changing the chemical potential of each graphene layer. This can arbitrarily tailor the spatial distribution of the phase of the transmitted beam, providing mechanisms for active beam steering. Three different beam steerer (BS) designs are discussed: a graded-index (GRIN) graphene-based metamaterial block, an array of metallic waveguides filled with graphene-dielectric metamaterial and an array of planar waveguides created in a graphene-dielectric metamaterial block with a specific spatial profile of graphene sheets doping. The performances of the BSs are numerically analyzed, showing the tunability of the proposed designs for a wide range of output angles (up to approximately 70°). The proposed graphene-based tunable beam steering can be used in tunable transmitter/receiver modules for infrared imaging and sensing.This work was supported in part by the Spanish Government under Contract TEC2014- 51902-C2-2-R and the Government of the Russian Federation [Grant No. 074-U01]. B. O. is sponsored by the Spanish Ministerio de Economía y Competitividad under grant FPI BES- 2012-054909. M.B. is sponsored by the Spanish Government via RYC-2011-08221. I.K. is sponsored by the Russian Foundation for Basic Research under grant No. 14-07-31272

Tripod-loop metasurfaces for terahertz-sensing applications: a comparison

The high electric field intensity achieved on the surface of sensors based on metasurfaces (metasensors) makes them an excellent alternative for sensing applications where the volume of the sample to be identified is tiny (for instance, thin-film sensing devices). Various shapes and geometries have been proposed recently for the design of these metasensors unit-cells (meta-atoms) such as split ring resonators or hole arrays, among others. In this paper, we propose, design, and evaluate two types of tripod metasurfaces with different complexity in their geometry. An in-depth comparison of their performance is presented when using them as thin-film sensor devices. The meta-atoms of the proposed metasensors consist of a simple tripod and a hollow tripod structure. From numerical calculations, it is shown that the best geometry to perform thin-film sensing is the compact hollow tripod (due to the highest electric field on its surface) with a mean sensitivity of 3.72 × 10−5 nm−1. Different modifications are made to this structure to improve this value, such as introducing arms in the design and rotating the metallic pattern 30 degrees. The best sensitivity achieved for extremely thin film analytes (5–25 nm thick) has an average value of 1.42 × 10−4 nm, which translates into an extremely high improvement of 381% with respect to the initial hollow tripod structure. Finally, a comparison with other designs found in the literature shows that our design is at the top of the ranking, improving the overall performance by more than one order of magnitude. These results highlight the importance of using metastructures with more complex geometries so that a higher electric field intensity distribution and, therefore, designs with better performance can be obtained.This research was funded by Spanish Ministerio de Ciencia, Innovación y Universidades, Project RTI2018-094475-B-I00 (MCIU/AEI/FEDER,UE)