Tech Briefs

Photonic-Crystal-Based Devices for Commercial Applications

Several analog-to-digital converter (ADC) devices and part of a multispectral receiver have been designed, fabricated, and tested to demonstrate their feasibility as part of an effort to establish the organizational and technological foundation for development of photonic-crystal-based devices for commercial and military applications. Also known as photonic-band-gap devices, photonic crystals contain periodic structures having feature sizes in the submicron range — less than the wavelengths of light that the devices are intended to handle. Photonic crystals can be fabricated by techniques used in the integrated-circuit and microelectromechanical systems (MEMS) industries.

Posted in: Briefs, Photonics, Optics
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Infrared Data Link Using an MQW Modulator on a Retroreflector

A n infrared data link between a ground station and a small uninhabited helicopter in flight has been demonstrated in an effort to develop a type of system for free-space optical communication between (1) a larger and relatively stationary platform, and (2) a smaller and relatively mobile platform. In a system of this type, rather than using laser transmitters with their associated gimbaled telescopes and pointing/tracking subsystems on both platforms, one uses only a single such laser transmitter on the larger platform (in this case, the ground station). The single laser transmitter is capable of tracking the smaller platform (in this case, the helicopter) and transmitting data to the smaller platform in the conventional way via modulation of the outgoing laser beam. The field of view of the receiver on the smaller platform is wide enough to capture the laser beam, without need for a large receiving telescope and its aiming subsystem. For transmitting data from the smaller to the larger platform, a large fraction of the laser power incident on the smaller platform is modulated and retroreflected to the larger platform, by means of an InGaAs-based multiple-quantum-well (MQW) light modulator on a cornercube retroreflector (see Figure 1).

Posted in: Briefs, Photonics, Data exchange, Optics, Rotary-wing aircraft
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Self-Lubrication of Hot YSZ-Ag-Mo Nanocomposite Coatings

An experimental study has been performed to learn about the physical and chemical mechanisms of self-lubrication of coatings that comprise nanostructured composites of yttria-stabilized zirconia (YSZ), silver, and molybdenum. These and other YSZ-based nanocomposite coatings have received increasing attention in recent years because they offer a combination of hardness, toughness, resistance to wear, and low-friction C properties that make them attractive for reducing wear and friction and increasing the lifetimes of hot, sliding components of mechanical systems. In addition to the excellent mechanical and thermal stability of the basic YSZ ceramic material, the nanocomposite structures of these coatings, consisting of combinations of amorphous and crystalline phases, provide a “chameleon” surface adaptation, in which different phases turn into lubricants in response to different test environments, contact loads, sliding speeds, and temperatures. Moreover, proper sizing of nanocrystalline grains can restrict crack sizes and create large volumes of grain boundaries, thereby increasing the toughness and contact-load-bearing capabilities of these coatings.

Posted in: Briefs, Materials, Lubricants, Coatings Colorants and Finishes, Composite materials, Nanomaterials, Wear
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Hybrid Three-Axis Vibration Reducers

Hybrid (passive/active) devices have been developed to reduce the magnitudes of possibly threedimensional vibrations coupled from vibrating equipment on platforms to bases that support the platforms. These hybrid devices are three-axis generalizations of singleaxis hybrid vibration reducers developed and reported previously. Each hybrid device includes rubber passive vibration-isolator pads, piezoelectric actuators, optional piezoelectric force sensors, and accelerometers. Each device operates in conjunction with a computer and control-and-actuation circuitry, which process accelerometer readings using feedforward and/or feedback control laws to excite the piezoelectric actuators with signals having amplitudes and phases chosen to minimize acceleration of the base.

Posted in: Briefs, Mechanical Components, Vibration
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Some Advances in Reducing Drag and Suppressing Convection

Theoretical and computational research has yielded some advances in the art of designing active feedforward and feedback controllers to suppress thermal convection and reduce drag (by suppressing turbulence) in boundary-layer flows. The advances include (1) improved means for designing reduced-order (and, hence, computationally more efficient) controllers and (2) discovery of a previously unknown phenomenon that could be exploited for feedforward control to reduce drag.

Posted in: Briefs, Mechanical Components, Electronic control systems, Drag
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Autonomous Vehicles Would Learn by Mimicking Human Drivers

A program initiated by the Defense Advanced Research Projects Agency (DARPA) and now also pursued by other agencies called “Learning Applied to Ground Robots” (LAGR), is developing control algorithms that would enable a robotic land vehicle, robotic underwater crawler, or other similar autonomous mobile robot to traverse terrain safely. Among the algorithms needed are navigation algorithms for finding and then following a safe path across terrain from a starting or current position to a destination.

Posted in: Briefs, Information Technology, Vehicle drivers, Robotics, Autonomous vehicles
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Advances in Algorithms for CFD and Finite-Element Simulation

A program of research and development has resulted in some advances in algorithms for computational fluid dynamics (CFD), finite-element simulation of solid objects undergoing large deformations, and some related topics. The main advances are summarized as follows:

Posted in: Briefs, Information Technology, Computational fluid dynamics, Finite element analysis
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