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Metamaterial Based Ultra-Wideband Antennas for Portable Wireless Applications
Abstract and Figures
Antennas are essential for wireless communication systems. The size of a conventional antenna is dictated mainly by its operating frequency. With the advent of ultra-wideband systems (UWB), the size of antennas has become a critical issue in the design of portable wireless devices. Consequently, research and development of suitably small and highly compact antennas are challenging and have become an area of great interest among researchers and radio frequency (RF) design engineers. Various approaches have been reported to reduce the physical size of RF antennas including using high permittivity substrates, shorting pins, reactive components, and more recently, metamaterials (MTM) based on composite right-/left-handed transmission-lines (CRLH-TLs). MTM exhibit unique electromagnetic response that cannot be found in the nature. In this chapter, the properties of CRLH-TL are used to synthesize novel and highly compact planar UWB antennas with radiation properties suitable for wireless mobile devices and systems.
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Multiband functionality in antennas has become a fundamental requirement to equip wireless devices with multiple communication standards so that they can utilize the electromagnetic spectrum more efficiently and effectively. This is necessary to ensure global portability and enhance system capacity. To meet these requirements, microstrip technology is increasingly being used in communication systems because it offers considerable size reduction, cost-effectiveness as they can be easily manufactured in mass production, are durable and can conform to planar or cylindrical surfaces. Unfortunately, such antennas suffer from intrinsically narrow bandwidth. To overcome this deficiency, various techniques have been investigated in the past. In this chapter, a novel approach is presented to design antennas for applications that cover radio frequency identification (RFID) and WiMAX systems.
In this chapter, a review of the recent advances in optical metalenses is presented, with special emphasis in their experimental implementation. First, the Huygens’ principle applied to ultrathin engineered metamaterials is introduced for the purpose of giving curvature to the wavefront of free-space wave fields. Primary designs based on metallic nanoslits and holey screens occasionally with variant width are first examined. Holographic plasmonic lenses are also explored offering a promising route to realize nanophotonic components. More recent metasurfaces based on nano-antenna resonators, either plasmonic or high-index dielectric, are analyzed in detail. Furthermore, 2D material lenses in the scale of a few nanometers enabling the thinnest lenses to date are here considered. Finally, dynamically reconfigurable focusing devices are reported for creating a scenario with new functionalities.
Optical metasurfaces are two-dimensional arrays of nano-scatterers that modify optical wavefronts at subwavelength spatial resolution. They are poised to revolutionize optics by enabling complex low-cost systems where multiple metasurfaces are lithographically stacked and integrated with electronics. For imaging applications, metasurface stacks can perform sophisticated image corrections and can be directly integrated with image sensors. Here, we demonstrate this concept with a miniature flat camera integrating a monolithic metasurface lens doublet corrected for monochromatic aberrations, and an image sensor. The doublet lens, which acts as a fisheye photographic objective, has a small f-number of 0.9, an angle-of-view larger than 60°×60°, and operates at 850 nm wavelength with 70% focusing efficiency. The camera exhibits nearly diffraction-limited image quality, which indicates the potential of this technology in the development of optical systems for microscopy, photography, and computer vision.
We design plano–concave silicon lenses with coupled gradient-index plasmonic metacoatings for ultrawide apertured focusing utilizing a reduced region of ∼ 20 λ 2 . The anomalous refraction induced in the planar input side of the lens and in the boundary of the wavelength-scale focal region boosts the curvature of the emerging wavefront, thus significantly enhancing the resolution of the tightly focused optical wave. The formation of a light tongue with dimensions approaching those of the concave opening is here evidenced. This scheme is expected to have potential applications in optical trapping and detection.
Optical activity is the rotation of the plane of linearly polarized light along the propagation direction as the light travels through optically active materials. In existing methods, the strength of the optical activity is determined by the chirality of the materials, which is difficult to control quantitatively. Here we numerically and experimentally investigated an alternative approach to realize and control the optical activity with non-chiral plasmonic metasurfaces. Through judicious design of the structural units of the metasurfaces, the right and left circular polarization components of the linearly polarized light have different phase retardations after transmitting through the metasurfaces, leading to large optical activity. Moreover, the strength of the optical activity can be easily and accurately tuned by directly adjusting the phase difference. The proposed approach based on non-chiral plasmonic metasurfaces exhibits large optical activity with a high controllable degree of freedom, which may provide more possibilities for applications in photonics.
This paper introduces a left-handed metamaterial traveling-wave antenna (TWA) based on metamaterial transmission-line structure to enhance the gain and radiation efficiency of the antenna without trading on its fractional bandwidth. The antenna consists of a series of coupled unit-cells comprising “X-shaped” slots which are inductively terminated to ground. Effective aperture of the antenna can be increased by increasing the number of unit-cells. The consequence of this is enhanced gain and radiation efficiency performance with no adverse affect on its fractional bandwidth. The antenna’s characterizing parameters were extracted using 3D electromagnetic simulation tool (HFSS™), and the antenna was fabricated using standard PCB manufacturing techniques on a 1.6 mm thick dielectric substrate with permittivity of 2.2. The antenna operates from 0.4 GHz to 4.7 GHz. The antenna has an electrical size of 0.017λ0 0.006λ0 0.002λ0, where λ0 is free space wavelength at 400 MHz. The proposed antenna is significantly smaller than its conventional counterparts. Antenna’s measured optimum gain and radiation efficiency are 2 dBi and 65%, respectively, at 2.5 GHz. These features make the antenna attractive for use in multiple wireless communication applications.
The constructive and destructive interference of waves is often exploited in optics and signal transmission. The interference pattern is a direct measure of the phase difference between two or more beams. Such a phase difference may result from the difference between the optical paths traversed by the light beams. However, phase can change for a single beam if it propagates through an “anisotropic parameter space,” a medium that curves the light; this property is called geometric or topological phase ( 1 – 4 ). On page 1202 of this issue, Maguid et al. ( 5 ) use metasurfaces—ultrathin, planar engineered structures ( 6 – 9 )—to form shared-aperture antenna arrays that impart geometric phase to optical signals. These devices can control photonic spin and enable multiple optical functions.
Multifunction planar optics
Specially designed two-dimensional (2D) arrays of nanometer-scale metallic antennas, or metasurfaces, may allow bulky optical components to be shrunk down to a planar device structure. Khorasaninejad et al. show that arrays of nanoscale fins of TiO can function as high-end optical lenses. At just a fraction of the size of optical objectives, such planar devices could turn your phone camera or your contact lens into a compound microscope. Maguid et al. interleaved sparse 2D arrays of metal antennas to get multifunctional behavior from the one planar device structure (see the Perspective by Litchinitser). The enhanced functionality of such designed metasurfaces could be used in sensing applications or to increase the communication capacity of nanophotonic networks.
Science , this issue pp. 1190 and 1202 ; see also p. 1177
We design and fabricate metasurface on the facet of conventional G.652 single mode fiber (SMF). We also experimentally investigate the linearly polarized mode (LP11) generation in SMF using the fabricated metasurface at the wavelength of 632.8 nm.