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

Getting Real-Time Performance From A Full-Featured OS

Spend a few minutes at your local electronics store and it's obvious — the mobile phone is a device that far surpasses its original intent. With respect to functionality, today's mobile phone goes well beyond the ability to make calls and store phone numbers. It also synchs up with your desktop's calendar and address book, it can take pictures, play and store music, and receive emails.

Posted in: Articles, Articles, Electronics & Computers, Computer software / hardware, Electronic equipment

Wireless Electronic Patches Improve Medical Data and Patient Mobility

Non-invasive and ambulatory monitoring of body parameters is receiving much interest from the medical, sports and entertainment world. Possible applications are the monitoring of brain waves to detect epilepsy, monitoring of muscle activity during an athlete's training, and monitoring of heart rate during gaming. The idea is to develop small, low-power, autonomous biomedical monitoring systems that collect and process data from human body sensors and wirelessly transmit the data to a central monitoring system.

Posted in: Application Briefs, Application Briefs, Electronics & Computers, Sensors and actuators, Wireless communication systems, Diagnosis, Medical equipment and supplies

Omniscient Code Generation for 8-, 16- and 32-bit Microcontrollers

C-language programs are usually developed by teams of engineers who are often geographically dispersed, leading to redundant code and inconsistent variable declarations between modules. Traditional compilation technology compiles each module separately with no regard for what goes on in the other modules and with no information about how pointers, stacks, variables and functions are used throughout the whole program. Traditional compilers tend to over-allocate memory space for pointers, stacks and registers. They are unable to fully exploit the wide variety of memory maps, and register and stack configurations available in today’s micro-controllers. All too often, the programmer must resort to manual optimizations that compromise portability (Figure 1).

Posted in: Articles, Articles, Electronics & Computers, Design processes, Architecture, Computer software / hardware

Using AdvancedTCA and MicroTCA in High-Availability Military Systems

The complexity of military and aerospace systems is growing — more components, interfaces, power, bandwidth, processing, features, and data — and these systems are being networked to form even more complex "systems of systems." Modern networkcentric systems can contain hundreds, even thousands of electronic modules.

Posted in: Articles, Articles, Electronics & Computers, Architecture, Computer software / hardware, Data management, Defense industry, Systems management

Multipurpose Transaction Protocol: A New Data Transport Model

It is no secret that high-performance and the Internet are often seen as contradictory terms. Even private IP networks see serious performance challenges once they extend beyond the local building and around the globe. As devices and their users become more mobile, it has become critical to design with high-speed, Wide Area Networks in mind. But software and hardware designers are traditionally given few choices and little control for ensuring high network performance.

Posted in: Articles, Articles, Electronics & Computers, Communication protocols, Data exchange, Internet