Heterodyne RF/Optical Links Utilizing Integrated Photonics

A program of research and development has been directed toward the goals of demonstrating (1) ultra-low-noise communication links in which information is conveyed by phase-modulated radio-frequency (RF) carrier signals that are, in turn, used to modulate laser-generated optical carrier signals and (2) implementation of transmitters and receivers in such links by means of several key integrated optoelectronic and photonic components. Notably, the scheme for integrating these components is based on the use of asymmetric twin optical waveguides (see figure) that afford design versatility in that they enable the use of a broad range of components useful in RF/photonic applications.

Posted in: Briefs, Photonics, Optics, Waveguides, Research and development

Microwave Sources Utilizing Linear Induction Accelerators

Progress has been reported in a continuing effort to develop pulsed, high-power microwave signal sources based on (1) oscillators in the form of relativistic magnetrons containing transparent cathodes, and (2) hybrid antenna/ amplifiers powered via electronbeam generators. The underlying concept is that a compact, high-power microwave source could be constructed by integrating an electron-beam accelerator with a radiating antenna and an electrodynamic-interaction space.

Posted in: Briefs, Electronics & Computers, Amplifiers, Antennas

Accomplishments of the Microwave Power Research Initiative

Research performed under the auspices of the Microwave Power Research Initiative (MiPRI) between May 1, 2005 and April 30, 2006 has been reported. [The MiPRI is a congressionally mandated Air Force program to advance the science of high-power electron- beam-driven microwave and millimeter- wave signal sources.] The reported research was performed by a consortium of three universities led by the University of New Mexico and including the University of Michigan and the Massachusetts Institute of Technology (MIT). The research pertains to two signal sources of current interest to the Air Force: a relativistic Lband magnetron and a W-band source.

Posted in: Briefs, Electronics & Computers, Telecommunications, Research and development, Technical reference, Radiation

Microstrip Patch Antennas Containing Multi-PBG Structures

Microstrip patch antennas of a proposed type would contain photonic- bandgap (PBG) structures characterized by multiple bandgaps. In a given antenna, the PBG structure(s) could be one or more periodic dielectric and/or metal structures that could be embedded in the dielectric substrate of the antenna and/or formed on either or both faces of the dielectric substrate. As explained below, the incorporation of PBG structures would facilitate the design of a smaller antenna capable of providing a given amount of gain at a given frequency.

Posted in: Briefs, Electronics & Computers, Antennas, Architecture, Insulation

Assembly of Nanowire-Based Computing Systems

A program to develop ultra-dense integrated digital data-processing systems and circuits based on nanowires involves utilization of hybrid top-down and bottom-up assembly techniques to implement designs representative of a highly reliable defect- and fault-tolerant architecture. This program has included fabrication and assembly of molecular- scale logic blocks based on arrays of overlapping semiconducting nanowires, using novel wafer-scale assembly techniques. On the basis of breakthrough addressing techniques, these logic blocks have been connected to ultradense memory blocks and to external complementary oxide/semiconductor (CMOS)-process lithographic interfaces for testing. One of the main underlying ideas is to construct highly reliable components out of high-defect-density logic and memory elements, using recently developed sublithographic-scale programmable- logic-array architectures that incorporate novel reliable-circuit concepts and higher-level redundancy mechanisms. Using state-of-the-art modeling techniques and computational simulations, test designs have been optimized, various defect-tolerance approaches have been developed, and development and optimization of larger systems are continuing.

Posted in: Briefs, Electronics & Computers, Architecture, Integrated circuits, Semiconductor devices, Nanotechnology

Compensating for Parasitic Effects in Low-Pass Filters

Techniques to compensate for the effects of parasitic inductances and capacitances have been developed as part of an effort to improve the performances of low-pass filters in electronic power circuits. As used here, "parasitic" refers to departure from an ideal inductive or capacitive characteristic. No inductor, capacitor, or other electronic component is ideal: wherever a current loop exists, there is inductance, and wherever two conductors are near each other, there is a capacitance between them. Parasitic capacitances in inductors and parasitic inductances in capacitors degrade the performances of low-pass filters, especially at high frequencies.

Posted in: Briefs, Electronics & Computers, Capacitors, Power electronics, Performance upgrades

Fast Liquid-Crystal-on-Silicon Spatial Light Modulators

Stressed-liquid-crystal (SLC) light-modulating devices suitable for use as liquidcrystal- on-silicon (LCOS) spatial light modulators (SLMs) that could operate in nearand mid-infrared wavelength ranges have been demonstrated. These SLC devices were conceived to exploit the SLC electrooptical effect, which makes it possible to obtain response times shorter than those of prior infrared LCOS SLMs.

Posted in: Briefs, Photonics, Optics, Semiconductors, Silicon alloys

Detecting Change in 3D by Use of an Evidence Grid

Astudy has been undertaken to evaluate a method of detecting change in a three-dimensional (3D) terrain map generated from data acquired by an imaging ladar system carried aboard a moving unmanned ground vehicle (UGV) on patrol. The proposed method involves the use of an evidence grid (described below) in comparing data acquired on a second patrol with data acquired on the first patrol along the same route, in order to determine which, if any, volume elements (voxels) in a 3D map representing the terrain have changed from free space to occupied or vice versa. For the purpose of the method, it is assumed that the terrain is static during each patrol and the only changes of interest occur between patrols. It was recognized in the study that these assumptions are unlikely to hold in realistic scenarios. This study was intended to be a precursor to a study of a method for recognizing a moving obstacle C, particularly a moving pedestrian C during a patrol by an autonomous UGV.

Posted in: Briefs, Photonics, Cartography, Lidar, Surveillance, Terrain, Autonomous vehicles, Military vehicles and equipment

Accelerated Evaluation of Properties of Polyphase Alloys

A methodology for accelerated evaluation of mechanical properties of polyphase alloys is based on digital representations of the alloys. For a given alloy material system, this representation is utilized in concert with (1) software tools and probes that simulate traditional laboratory testing equipment and instrumentation, and (2) real laboratory mechanical testing by nontraditional methods.

Posted in: Briefs, Materials, Computer simulation, Alloys, Materials properties, Test equipment and instrumentation, Test procedures

Plasma-Spray Coating as an Alternative to Chromium Plating

Plasma-spray application of coating materials that include tungsten carbide has been investigated as an alternative to electroplating of hard chromium onto internal metal surfaces that are required to be protected against wear or to be restored to within dimensional tolerances. Prime examples of such wear surfaces are the inner walls of cylinders in aircraft hydraulic actuators and dampers. The need for an alternative to chromium plating arises partly because chromium plating involves the use of hexavalent chromium, which is a highly toxic carcinogen subject to increasingly stringent government regulation and, therefore, increasingly expensive to use. Another reason for developing an alternative arises from a desire to reduce process time: To remove hydrogen that is unavoidably incorporated during chrome plating, it is necessary to perform a 24-hour bakeout. Process time could be reduced substantially if this bakeout could be eliminated. Plasma spraying involves fewer process steps than does electroplating, and for plasma-sprayed coatings, no hydrogen bakeout is necessary.

Posted in: Briefs, Materials, Spraying, Coatings Colorants and Finishes