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Electromagnetic Metasurface
An electromagnetic metasurface refers to a kind of artificial sheet material with sub-wavelength thickness. Metasurfaces can be either structured or unstructured with subwavelength-scaled patterns in the horizontal dimensions. In electromagnetic theory, metasurfaces modulate the behaviors of electromagnetic waves through specific boundary conditions, rather than constitutive parameters in three dimensional (3D) space, which is commonly exploited in natural materials and metamaterials. Metasurfaces may also refer to the two-dimensional counterparts of metamaterials. Definitions Metasurfaces have been defined in several ways by researchers. 1, “An alternative approach that has gained increasing attention in recent years deals with one- and two-dimensional (1D and 2D) plasmonic arrays with subwavelength periodicity, also known as metasurfaces. Due to their negligible thickness compared to the wavelength of operation, metasurfaces can (near resonances of unit cell constituents) ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Metasurface (5941035620)
An electromagnetic metasurface refers to a kind of artificial sheet material with sub-wavelength thickness. Metasurfaces can be either structured or unstructured with subwavelength-scaled patterns in the horizontal dimensions. In electromagnetic theory, metasurfaces modulate the behaviors of electromagnetic waves through specific boundary conditions, rather than constitutive parameters in three dimensional (3D) space, which is commonly exploited in natural materials and metamaterials. Metasurfaces may also refer to the two-dimensional counterparts of metamaterials. Definitions Metasurfaces have been defined in several ways by researchers. 1, “An alternative approach that has gained increasing attention in recent years deals with one- and two-dimensional (1D and 2D) plasmonic arrays with subwavelength periodicity, also known as metasurfaces. Due to their negligible thickness compared to the wavelength of operation, metasurfaces can (near resonances of unit cell constituents) ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diffraction Limit
The resolution of an optical imaging system a microscope, telescope, or camera can be limited by factors such as imperfections in the lenses or misalignment. However, there is a principal limit to the resolution of any optical system, due to the physics of diffraction. An optical system with resolution performance at the instrument's theoretical limit is said to be diffraction-limited. The diffraction-limited angular resolution of a telescopic instrument is inversely proportional to the wavelength of the light being observed, and proportional to the diameter of its objective's entrance aperture. For telescopes with circular apertures, the size of the smallest feature in an image that is diffraction limited is the size of the Airy disk. As one decreases the size of the aperture of a telescopic lens, diffraction proportionately increases. At small apertures, such as f/22, most modern lenses are limited only by diffraction and not by aberrations or other imperfections in the co ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ptychography
Ptychography (/t(ʌ)ɪˈkogræfi/ t(a)i-KO-graf-ee) is a computational method of microscopic imaging. It generates images by processing many coherent interference patterns that have been scattered from an object of interest. Its defining characteristic is translational invariance, which means that the interference patterns are generated by one constant function (e.g. a field of illumination or an aperture stop) moving laterally by a known amount with respect to another constant function (the specimen itself or a wave field). The interference patterns occur some distance away from these two components, so that the scattered waves spread out and "fold" ( grc, πτύξ is 'fold') into one another as shown in the figure. Ptychography can be used with visible light, X-rays, extreme ultraviolet (EUV) or electrons. Unlike conventional lens imaging, ptychography is unaffected by lens-induced aberrations or diffraction effects caused by limited numerical aperture. This is particula ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polarization (waves)
Polarization (also polarisation) is a property applying to transverse waves that specifies the geometrical orientation of the oscillations. In a transverse wave, the direction of the oscillation is perpendicular to the direction of motion of the wave. A simple example of a polarized transverse wave is vibrations traveling along a taut string ''(see image)''; for example, in a musical instrument like a guitar string. Depending on how the string is plucked, the vibrations can be in a vertical direction, horizontal direction, or at any angle perpendicular to the string. In contrast, in longitudinal waves, such as sound waves in a liquid or gas, the displacement of the particles in the oscillation is always in the direction of propagation, so these waves do not exhibit polarization. Transverse waves that exhibit polarization include electromagnetic waves such as light and radio waves, gravitational waves, and transverse sound waves (shear waves) in solids. An electromagnetic wa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Meta-waveguide
In photonics, a meta-waveguide is a physical structures that guides electromagnetic waves with engineered functional subwavelength structures. Meta-waveguides are the result of combining the fields of metamaterials and metasurfaces into integrated optics. The design of the subwavelength architecture allows exotic waveguiding phenomena to be explored. Meta-waveguides can be classified by waveguide platforms or by design methods. If classified by underlying waveguide platform, engineered subwavelength structures can be classified in combination with dielectric waveguides, optical fibers, or plasmonic waveguides. If classified by design methods, meta-waveguides can be classified as either using design primarily by physical intuition, or by computer algorithm based inverse design methods. Meta-waveguides can provide new degrees of design freedom to the available structural library for optical waveguides in integrated photonics. Advantages can include enhancing the performance of co ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electromagnetic Waves
In physics, electromagnetic radiation (EMR) consists of waves of the electromagnetic (EM) field, which propagate through space and carry momentum and electromagnetic radiant energy. It includes radio waves, microwaves, infrared, (visible) light, ultraviolet, X-rays, and gamma rays. All of these waves form part of the electromagnetic spectrum. Classically, electromagnetic radiation consists of electromagnetic waves, which are synchronized oscillations of electric and magnetic fields. Depending on the frequency of oscillation, different wavelengths of electromagnetic spectrum are produced. In a vacuum, electromagnetic waves travel at the speed of light, commonly denoted ''c''. In homogeneous, isotropic media, the oscillations of the two fields are perpendicular to each other and perpendicular to the direction of energy and wave propagation, forming a transverse wave. The position of an electromagnetic wave within the electromagnetic spectrum can be characterized by either its ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Optical Waveguides
An optical waveguide is a physical structure that guides electromagnetic waves in the optical spectrum. Common types of optical waveguides include optical fiber waveguides, transparent dielectric waveguides made of plastic and glass, liquid light guides, and liquid waveguides. Optical waveguides are used as components in integrated optical circuits or as the transmission medium in local and long-haul optical communication systems. Optical waveguides can be classified according to their geometry (planar, strip, or fiber waveguides), mode structure (single-mode, multi-mode), refractive index distribution (step or gradient index), and material (glass, polymer, semiconductor). Total internal reflection The basic principles behind optical waveguides can be described using the concepts of geometrical or ray optics, as illustrated in the diagram. Light passing into a medium with higher refractive index bends toward the normal by the process of refraction (Figure a.). Take, for exampl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Radiation-absorbent Material
In materials science, radiation-absorbent material, usually known as RAM, is a material which has been specially designed and shaped to absorb incident RF radiation (also known as non-ionising radiation), as effectively as possible, from as many incident directions as possible. The more effective the RAM, the lower the resulting level of reflected RF radiation. Many measurements in electromagnetic compatibility (EMC) and antenna radiation patterns require that spurious signals arising from the test setup, including reflections, are negligible to avoid the risk of causing measurement errors and ambiguities. Introduction One of the most effective types of RAM comprises arrays of pyramid shaped pieces, each of which is constructed from a suitably lossy material. To work effectively, all internal surfaces of the anechoic chamber must be entirely covered with RAM. Sections of RAM may be temporarily removed to install equipment but they must be replaced before performing any tes ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Radar Cross-section
Radar cross-section (RCS), also called radar signature, is a measure of how detectable an object is by radar. A larger RCS indicates that an object is more easily detected. An object reflects a limited amount of radar energy back to the source. The factors that influence this include: *the material with which the target is made; *the size of the target relative to the wavelength of the illuminating radar signal; *the absolute size of the target; *the incident angle (angle at which the radar beam hits a particular portion of the target, which depends upon the shape of the target and its orientation to the radar source); *the reflected angle (angle at which the reflected beam leaves the part of the target hit; it depends upon incident angle); *the polarization of the transmitted and the received radiation with respect to the orientation of the target. While important in detecting targets, strength of emitter and distance are not factors that affect the calculation of an RCS becaus ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stealth Technology
Stealth technology, also termed low observable technology (LO technology), is a sub-discipline of military tactics and passive and active electronic countermeasures, which covers a range of methods used to make personnel, aircraft, ships, submarines, missiles, satellites, and ground vehicles less visible (ideally invisible) to radar, infrared, sonar and other detection methods. It corresponds to military camouflage for these parts of the electromagnetic spectrum (i.e., multi-spectral camouflage). Development of modern stealth technologies in the United States began in 1958, where earlier attempts to prevent radar tracking of its U-2 spy planes during the Cold War by the Soviet Union had been unsuccessful. Designers turned to developing a specific shape for planes that tended to reduce detection by redirecting electromagnetic radiation waves from radars. Radiation-absorbent material was also tested and made to reduce or block radar signals that reflect off the surfaces of air ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Superlenses
A superlens, or super lens, is a lens which uses metamaterials to go beyond the diffraction limit. For example, in 1995, Guerra combined a transparent grating having 50nm lines and spaces (the "metamaterial") with a conventional microscope immersion objective. The resulting "superlens" resolved a silicon sample also having 50nm lines and spaces, far beyond the classical diffraction limit imposed by the illumination having 650nm wavelength in air. The diffraction limit is a feature of conventional lenses and microscopes that limits the fineness of their resolution depending on the illumination wavelength and the numerical aperture NA of the objective lens. Many lens designs have been proposed that go beyond the diffraction limit in some way, but constraints and obstacles face each of them. History In 1873 Ernst Abbe reported that conventional lenses are incapable of capturing some fine details of any given image. The super lens is intended to capture such details. The limitation o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Metamaterials
A metamaterial (from the Ancient Greek, Greek word Meta, μετά ''meta'', meaning "beyond" or "after", and the Latin word ''materia'', meaning "matter" or "material") is any material engineered to have a property that is not found in naturally occurring materials. They are made from assemblies of multiple elements fashioned from composite materials such as metals and plastics. The materials are usually arranged in Periodic function, repeating patterns, at scales that are smaller than the wavelengths of the phenomena they influence. Metamaterials derive their properties not from the properties of the base materials, but from their newly designed structures. Their precise shape, geometry, dimensions, size, orientation (geometry), orientation and arrangement gives them their smart properties capable of manipulating Electromagnetism, electromagnetic waves: by blocking, absorbing, enhancing, or bending waves, to achieve benefits that go beyond what is possible with conventional materi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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