Time-varying Huygens' meta-devices for parametric waves

Huygens' metasurfaces have demonstrated almost arbitrary control over the shape of a scattered beam, however, its spatial profile is typically fixed at fabrication time. Dynamic reconfiguration of this beam profile with tunable elements remains challenging, due to the need to maintain the Huygens' condition across the tuning range. In this work, we experimentally demonstrate that a time-varying metadevice which performs frequency conversion can steer transmitted or reflected beams in an almost arbitrary manner, with fully dynamic control. Our time-varying Huygens' metadevice is made of both electric and magnetic meta-atoms with independently controlled modulation, and the phase of this modulation is imprinted on the scattered parametric waves, controlling their shapes and directions. We develop a theory which shows how the scattering directionality, phase and conversion efficiency of sidebands can be manipulated almost arbitrarily. We demonstrate novel effects including all-angle beam steering and frequency-multiplexed functionalities at microwave frequencies around 4 GHz, using varactor diodes as tunable elements. We believe that the concept can be extended to other frequency bands, enabling metasurfaces with arbitrary phase pattern that can be dynamically tuned over the complete 2\pi range

Terahertz focusing of multiple wavelengths by graphene metasurfaces

Metasurfaces can achieve nearly arbitrary wavefront control based on manipulation of the wave phase profile. We propose a metasurface based on double graphene cut-wire resonators which can cover the complete 2p phase region with high reflection efficiency. This full phase coverage is essential for efficient wavefront manipulation, without reflecting energy into unwanted channels. A mirror capable of focusing multiple wavelengths is demonstrated numerically based on the proposed structure. The mirror can effectively focus terahertz (THz) waves from 1.2 to 1.9 THz to the same focal point by changing the Fermi level of each graphene resonator separately. The presented metasurface could provide a powerful platform for controlling THz waves, including focusing, beam steering, beam shaping, and holography

Nivel de incidencia y principales factores de la desnutrición infantil

TablasEl presente documento muestra un compendio de información acerca de la Desnutrición infantil , esto teniendo en cuenta que durante la infancia se produce el mayor desarrollo y crecimiento de la vida de una persona. Por eso es muy importante que los niños tengan una buena alimentación para que no se presenten problemas de salud por la desnutrición. Además se muestra como la desnutrición causa diferentes problemas de salud y enfermedades, algunas leves, otras crónicas y algunas muy graves, afectando el desarrollo y crecimiento normal, llegando a ocasionar retraso mental e intelectual o hasta la muerte. El problema de la desnutrición es colosal para la humanidad: más de mil niños están desnutridos y hambrientos. En la mayor parte de los casos es originado por la falta de alimentos, pero otras veces tiene su raíz en el desconocimiento de los correctos hábitos alimenticios. De acuerdo a lo anterior, la investigación se divide en cuatro fases: determinación del problema, sustentación teórica, análisis de la información y propuesta. Esto con el fin de proponer medidas preventivas contra esta problemática social que día a día esta afectando más a la población.This document presents a summary of information about child malnutrition This considering that occurs during childhood further development and growth of a person's life. It is therefore very important that children have a good diet to avoid health problems arise from malnutrition. Also shown as malnutrition causes different diseases and health problems, some minor, some chronic and some very serious, affecting the normal growth and development, leading to mental retardation and intellectual cause or death. The problem of malnutrition is colossal for mankind: more than a thousand children are malnourished and hungry. In most cases it is caused by lack of food, but sometimes is rooted in the lack of proper eating habits. According to this, the research is divided into four phases: defining the problem, theoretical support, information analysis and proposal. This in order to propose preventive measures against this social problem that every day is affecting more people

Tunable focusing by a flexible metasurface

An efficient reflective metasurface with elastically tunable focal length is proposed and experimentally demonstrated. The metasurface consists of electric resonators embedded in a stretchable elastic substrate which allows continuous elongation of the system. Our theory and numerical simulations predict how the focal length is controlled by means of the stretching, which we experimentally verify. By performing phase-sensitive measurements of the scattered field, we are able to differentiate the true focus, where all scattered waves are in phase, from the point of maximum amplitude. These phase measurements further enable us to characterise an axial aberration in the stretched structure, due to rays projected from distinct parts of the structure converging at different focal lengths. Additionally, we characterise the efficiency of our structure, showing that 78–95% of the incident power is reflected, depending on the degree of tuning. We also quantify the fraction of incident power which is directed into the beam waist. Our results demonstrate that metamaterials integrated with engineered elastic structures are an effective platform for functional devices

Time-varying metasurfaces for arbitrary parametric wave control

Huygens' metasurfaces allow almost arbitrary wave-front shaping. However, it remains highly nontrivial to achieve dynamic and arbitrary control of the amplitude and phase response. Here we show that in a system consisting of both electric and magnetic meta-atoms with independently controlled modulation, the incident wave can be efficiently converted to sidebands of new frequencies, whose scattering directionality, phase and conversion efficiency can be manipulated almost arbitrarily

Elastic metamaterials for tuning circular polarization of electromagnetic waves

Electromagnetic resonators are integrated with advanced elastic material to develop a new type of tunable metamaterial. An electromagnetic-elastic metamaterial able to switch on and off its electromagnetic chiral response is experimentally demonstrated. Such tunability is attained by harnessing the unique buckling properties of auxetic elastic materials (buckliballs) with embedded electromagnetic resonators. In these structures, simple uniaxial compression results in a complex but controlled pattern of deformation, resulting in a shift of its electromagnetic resonance, and in the structure transforming to a chiral state. The concept can be extended to the tuning of three-dimensional materials constructed from the meta-molecules, since all the components twist and deform into the same chiral configuration when compressed