Biaxial and Shear Testing Apparatus With Force Controls

An apparatus for in-plane biaxial tension/compression and in-plane shear testing of fabrics, other flexible sheet materials, or relatively rigid thin plate materials has been invented. The apparatus is capable of applying, to a sheet material specimen, a controlled tensile or compressive force along each of two directions in the plane of the specimen. The force along each direction can differ from the force along the other direction. The directions of the applied forces can be orthogonal or can be set at an oblique angle, depending on the combination of stresses required to be applied to the specimen. Thus, depending on the angle between the applied-force directions, the sense (tensile or compressive) of each applied force, and the magnitude of each force, the specimen can be subjected to almost any combination of in-plane shear and biaxial tension/compression loading.

Posted in: Briefs, Mechanical Components

Effects of High-Power Microwave Pulses on Electronic Systems

A five-year program comprising several coordinated research efforts was devoted to increasing understanding and developing capabilities for computational modeling of the effects of highpower microwave (HPM) radiation upon electronic circuits and upon systems that comprise or include electronic circuits. The HPM radiation of primary interest in this program included both narrow-band and ultra- wide-band (UWB) pulsed radiation. Whether aimed at electronic equipment deliberately or inadvertently, either type of radiation can, potentially, cause damage and/or adversely affect operation. The knowledge gained from this program can help in designing future electronic circuits and systems to be less vulnerable to damage and disruption by incident HPM/UWB radiation.

Posted in: Briefs, Electronics & Computers

Near-Field Light Lenses for Nano-Focusing of Beams of Atoms

Near-field light lenses for focusing beams of light and beams of atoms to spots having a width of no more than several nanometers are undergoing development. There are numerous potential applications for such lenses:

•A capability to focus beams of light to nanometer-sized spots is essential for development of proposed nanoscale optical devices (e.g., optical switches and logic gates) based on near-field optical interactions.

•A capability to focus beams of atoms to nanometer-sized spots could contribute to the development of nanophotonic devices, including quantum dots, which must be sized and positioned with precision.

Posted in: Briefs, Photonics, Glass, Nanotechnology, Refractory materials

Developments in Adaptive Filtering and System Identification

Progress has been made on several fronts in a continuing program of research oriented toward the development of real-time algorithms, and computer and control systems that utilize the algorithms, for adaptive filtering, prediction, and system identification with improved efficiency and numerical stability in applications that involve large numbers of channels and high filter orders. Potential applications include adaptive optics, optical communications, target tracking, image processing, blind identification and deconvolution in wireless communications, and active control of noise and vibration.

Posted in: Briefs, Photonics

Electrochromic Devices for Controlling Infrared Emissivity

Electrochromic devices that exhibited adjustable infrared emissivity were developed in a research program that was part of a larger effort to develop adaptive infrared camouflage. Inasmuch as objects that one seeks to conceal by use of camouflage are generally hotter than their surroundings, the basic idea of adaptive infrared camouflage is to reduce the infrared emissivity of an object of interest by a controllable amount so that, as viewed via an infrared camera, the object blends into the background.

Posted in: Briefs, Materials

Aligned MWCNTs as Thermal Conductors in Adhesive Joints

A developmental method of increasing the thermal conductance of an adhesive joint in a composite-material structure (or between a composite-material structure and another structure) involves exploitation of the inherently large thermal conductances of multi-wall carbon nanotubes (MWCNTs) along their longitudinal axes. A composite material of the type to which the method applies is, somewhat more specifically, a polymer-matrix/fiber composite. Typically, the matrix polymer is an epoxy, and the adhesive used to bond the composite-material structure may not be an epoxy. In any event, the thermal conductivity of the adhesive is about 0.3 W/mK — a value that is insufficient for many applications in which there are requirements for efficient transfer of heat.

Posted in: Briefs, Materials

Infrared-Sensitive Photorefractive Polymer Composite Devices

Polymer composites that are photorefractive at visible and near- infrared wavelengths, and devices that exploit their photorefractivity, have been demonstrated. Potential applications for such devices could include real-time holography, medical imaging, imaging through light-scattering media, and beam cleanup in free-space optical communications. Especially notable products of this development effort include devices that exhibit one-photon photorefractivity with high diffraction efficiency at a wavelength of about 1 μm and devices that exhibit two-photon photorefractivity at a wavelength of about 1.5 μm. The polymer composites used in these devices are the first-demonstrated all-organic photorefractive materials suitable for wavelengths >0.83 μm, and are among the best infrared-sensitive photorefractive materials yet demonstrated under similar experimental conditions.

Posted in: Briefs, Physical Sciences, Imaging, Composite materials, Polymers, Refractory materials

Cooperative Control of Robotic Aircraft

A document reviews a multidisciplinary research program oriented toward development of a rigorous theoretical foundation, and scalable analytical tools and paradigms, for construction of cooperative, networked control for numerous autonomous and semi-autonomous aircraft. This research has addressed issues affecting the design of robust autonomous vehicle systems that could operate in highly uncertain environments, form teams, manage information, and cooperate in deployment, allocation of tasks, and searches. Significant accomplishments are reported in three areas:

Deployment and Task Allocation

Algorithms for deployment of aircraft for surveillance have been developed. The algorithms run in real time aboard the aircraft, routing the aircraft to optimal locations, coordinating among the aircraft, thereby enabling efficient deployment throughout a geographic region.

Verification and Hybrid Systems

Advances have been made in the theory of hybrid input-output automata and in techniques, based on this theory, that enable off-line automatic verification and validation of safety and liveness of cooperative control algorithms.

Information Management for Cooperative Control

An information theory produced in this research has yielded significant contributions to the design of robust communication protocols featuring cooperative routing schemes that take advantage of network layer diversity and delay adaptation to increase reliability over wireless networks with fading channels.

Posted in: Briefs, Information Technology, Electronic control systems, Collaboration and partnering, Research and development, Robotics, Unmanned aerial vehicles

Oxide and Nitride Films for Tunable Capacitors and HEMTs

A report describes research on thin oxide films intended for use as variable-high-permittivity dielectrics in advanced tunable capacitors and on thin nitride films as starting materials for advanced high-electron- mobility transistors (HEMTs). In this research, a custom molecular-beam-epitaxy system was used to grow thin films of TiO2, SrTiO3, Ba1-xSrxTiO3, MgO, and AlxGa1-xN (where 0 ≤ x ≤ 1). Growth parameters and properties of the films were investigated with a view toward developing processes for fabricating HEMTs using epitaxy of AlxGa1-xN, processes for fabricating varactors using epitaxy of Ba1-xSrxTiO3, and processes in which integration of Ba1-xSrxTiO3 onto AlxGa1-xN templates would be facilitated by use of MgO buffer layers. The films were characterized, variously, in situ by reflected-high-energy-electron diffraction, source-flux monitoring, and/or residual-gas analysis. The films were characterized, variously, ex situ by atomic-force microscopy, x-ray rocking-curve measurements, high-resolution x-ray diffraction, Rutherford backscattering, cross-section transmission electron microscopy and diffraction, and/or radio-frequency-loss metrology. In addition, the AlxGa1-xN films were characterized in situ by multi-beam optical stress-sensor analysis.

Posted in: Briefs, Materials

Flexible Biohybrid Nanomembranes for Multifunctional Sensors

A document describes recent activities in a continuing effort to develop devices, based on biohybrid nanomembranes, that would perform diverse sensory functions. The term "biohybrid nanomembranes" signifies flexible organic/inorganic composite membranes, of the order of tens of nanometers thick, typically comprising polymeric outer supporting layers and wholly or partly inorganic (e.g., biomineralized) inner sensory layers. This development is envisioned to yield novel acoustic, infrared, and photothermal sensors characterized by extreme degrees of miniaturization and sensitivity. The main focus of recent activities was on (1) synthesis of new branched and peptide-containing molecules to be incorporated into membranes and (2) further development of sophisticated freely standing membranes with micropatterned structures. In addition, membranes encapsulating arrays of carbon nanotubes and gold nanoparticles were fabricated and tested in micromechanical Raman-spectroscopic studies. Recent findings include the following:

Flexible nanomembranes with encapsulated silver nanowires and semiconducting quantum dots exhibit outstanding micromechanical, fluorescence, and conducting properties. Quantum-dot nanomembranes suspended over optical cavities exhibit exceptional backlight enhanced fluorescence intensity. Multifunctional hyperbranched molecules control the growth of monolayers of monodisperse silver nanoparticles at air-water interfaces. Silver-reducing peptides can be encapsulated in ultrathin polymer films and there utilized to effect formation of silver nanoparticles.
Posted in: Briefs, Materials