Reconfigurable Antennas

In this new book, we present a collection of the advanced developments in reconfigurable antennas and metasurfaces. It begins with a review of reconfigurability technologies, and proceeds to the presentation of a series of reconfigurable antennas, UWB MIMO antennas and reconfigurable arrays. Then, reconfigurable metasurfaces are introduced and the latest advances are presented and discussed

Gradient metasurfaces: a review of fundamentals and applications

In the wake of intense research on metamaterials the two-dimensional analogue, known as metasurfaces, has attracted progressively increasing attention in recent years due to the ease of fabrication and smaller insertion losses, while enabling an unprecedented control over spatial distributions of transmitted and reflected optical fields. Metasurfaces represent optically thin planar arrays of resonant subwavelength elements that can be arranged in a strictly or quasi periodic fashion, or even in an aperiodic manner, depending on targeted optical wavefronts to be molded with their help. This paper reviews a broad subclass of metasurfaces, viz. gradient metasurfaces, which are devised to exhibit spatially varying optical responses resulting in spatially varying amplitudes, phases and polarizations of scattered fields. Starting with introducing the concept of gradient metasurfaces, we present classification of different metasurfaces from the viewpoint of their responses, differentiating electrical-dipole, geometric, reflective and Huygens' metasurfaces. The fundamental building blocks essential for the realization of metasurfaces are then discussed in order to elucidate the underlying physics of various physical realizations of both plasmonic and purely dielectric metasurfaces. We then overview the main applications of gradient metasurfaces, including waveplates, flat lenses, spiral phase plates, broadband absorbers, color printing, holograms, polarimeters and surface wave couplers. The review is terminated with a short section on recently developed nonlinear metasurfaces, followed by the outlook presenting our view on possible future developments and perspectives for future applications.Comment: Accepted for publication in Reports on Progress in Physic

1-D broadside-radiating leaky-wave antenna based on a numerically synthesized impedance surface

A newly-developed deterministic numerical technique for the automated design of metasurface antennas is applied here for the first time to the design of a 1-D printed Leaky-Wave Antenna (LWA) for broadside radiation. The surface impedance synthesis process does not require any a priori knowledge on the impedance pattern, and starts from a mask constraint on the desired far-field and practical bounds on the unit cell impedance values. The designed reactance surface for broadside radiation exhibits a non conventional patterning; this highlights the merit of using an automated design process for a design well known to be challenging for analytical methods. The antenna is physically implemented with an array of metal strips with varying gap widths and simulation results show very good agreement with the predicted performance

Beam scanning by liquid-crystal biasing in a modified SIW structure

A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium

Research and technology, 1990: Goddard Space Flight Center

Goddard celebrates 1990 as a banner year in space based astronomy. From above the Earth's obscuring atmosphere, four major orbiting observatories examined the heavens at wavelengths that spanned the electromagnetic spectrum. In the infrared and microwave, the Cosmic Background Explorer (COBE), measured the spectrum and angular distribution of the cosmic background radiation to extraordinary precision. In the optical and UV, the Hubble Space Telescope has returned spectacular high resolution images and spectra of a wealth of astronomical objects. The Goddard High Resolution Spectrograph has resolved dozens of UV spectral lines which are as yet unidentified because they have never before been seen in any astronomical spectrum. In x rays, the Roentgen Satellite has begun returning equally spectacular images of high energy objects within our own and other galaxies

3D printing assisted development of bioinspired structure and device for advanced engineering

Smart materials with bio-inspired structure and stimuli responsive features can sense the external and internal condition changes, such as temperature, light intensity, pH or ion concentration. Those unique functions have been widely utilized in cutting edge engineering applications, such as flexible sensors, soft robotics and tissue engineering. Meanwhile, conventional manufacturing methods such as moulding, and lithography-based microfabrication still represent the mainstream force in scale up manufacturing. Considerable limitations for these technologies, such as on demand rapid prototyping, the high cost and low-volume production, remain to be overcome. In this PhD project, I explored the advanced manufacturing in facilitating the complex structure, with higher controllability, lower prototyping cost and extended applications (flexible sensors, soft robots, biomedical devices, etc.). The key practice is to utilize the high resolution 3D printing technology to create dedicated bio inspired structures based on functional materials. Combined with advanced micro/nano engineering, we have achieved a variety of techniques/prototypes for future applications, such as optical control, micro-fluidic and bio-medical systems, etc

NASA SBIR abstracts of 1992, phase 1 projects

The objectives of 346 projects placed under contract by the Small Business Innovation Research (SBIR) program of the National Aeronautics and Space Administration (NASA) are described. These projects were selected competitively from among proposals submitted to NASA in response to the 1992 SBIR Program Solicitation. The basic document consists of edited, non-proprietary abstracts of the winning proposals submitted by small businesses. The abstracts are presented under the 15 technical topics within which Phase 1 proposals were solicited. Each project was assigned a sequential identifying number from 001 to 346, in order of its appearance in the body of the report. Appendixes to provide additional information about the SBIR program and permit cross-reference of the 1992 Phase 1 projects by company name, location by state, principal investigator, NASA Field Center responsible for management of each project, and NASA contract number are included

NASA Tech Briefs, July 1992

Topics include: New Product Ideas; Electronic Components and Circuits; Electronic Systems; Physical Sciences; Materials; Computer Programs; Mechanics; Machinery; Fabrication Technology; Mathematics and Information Sciences; Life Sciences

Technology 2002: The Third National Technology Transfer Conference and Exposition, volume 2

Proceedings from symposia of the Technology 2002 Conference and Exposition, December 1-3, 1992, Baltimore, MD. Volume 2 features 60 papers presented during 30 concurrent sessions