Tech Briefs

RASCAL Facility

AFRL's Radiation and Scattering Compact Antenna Laboratory (RASCAL) enables researchers to develop and evaluate advanced aperture technologies that support electronic warfare, radar, communication, and navigation— technologies supplementing a variety of applications as the "eyes and ears" of the warfighter. Current research efforts are concentrated on developing relatively small and inexpensive broadband, multifunctional antennas, as well as conformal and structurally integrated antennas for manned and unmanned air vehicles. Using the RASCAL facility, researchers can perform the necessary fabrication, simulation, testing, and measurement of aperture technologies.

Posted in: Briefs, Electronics & Computers, Antennas, Test facilities, Military aircraft
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Response Surface Mapping Technique Aids Warfighters

When weaponeering a target, military planners pinpoint a detonation location that will result in the desired damage to the entire target, or even a particular area within the target. The warfighter then selects the most suitable delivery platform— aircraft, weapon, guidance package, release altitude, and speed— for inflicting the appropriate damage to the target. Determining the proper combination of variables capable of producing the desired effect on a hardened target requires the warfighter to understand the penetration dynamics of the weapon; it also relies on the individual's ability to adjust the variables within his or her control, as necessary. For a scenario in which the destruction of a specific target is often coupled with the mitigation of collateral damage, it is imperative that the warfighter make proper decisions regarding weapons selections. AFRL scientists, collaborating with other Department of Defense agencies, applied innovative data mining and visualization methods to aid warfighter efficiency and effectiveness in making these choices.

Posted in: Briefs, Information Technology, Cartography, Data acquisition and handling, Imaging, Terrain, Military vehicles and equipment
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Microelectromechanical Systems Inertial Measurement Unit Flight Test

AFRL and Boeing engineers conducted successful flight tests of microelectromechanical systems (MEMS) inertial measurement units (IMU) on the Joint Direct Attack Munition (JDAM). They collected flight data and validated the MEMS IMU technology's capability to provide stable navigation performance and accurate weapon guidance, both with and without Global Positioning System (GPS) updates. Researchers will use this flight data to further refine MEMS IMU technology to enhance future capabilities of air-launched munitions.

Posted in: Briefs, Mechanical Components, Microelectricmechanical device, Navigation and guidance systems, Flight tests
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Fruit Flies

He refers to them as "nature's fighter jets" and has devoted his life's work and an entire lab to monitor their every move. Thus is the relationship existing between Dr. Michael Dickinson and the objects of his attention—fruit flies. Career pursuits aside, Dr. Dickinson's connection to the insects is one he predicts will eventually lead to the development of flying robots capable of performing various covert tasks, such as spying and surveillance.

Posted in: Briefs, Mechanical Components, Surveillance, Biological sciences, Robotics
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Active Flow Control Demonstrated on “Airborne Wind Tunnel”

AFRL engineers, collaborating with aerospace manufacturers and other Air Force groups, recently demonstrated the first-ever airborne active flow control system when they manipulated the airflow behind an F-16 external pod. They significantly altered the turbulent wake using small, electrically controlled, piezoelectric synthetic jet (PESJ) actuators. This demonstration is just one part of AFRL's multiphase Aeroelastic Load Control program aimed at reducing the weight, complexity, and signature of air vehicles through the introduction of active control technologies.

Posted in: Briefs, Mechanical Components, Aerodynamics
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Coordination of Autonomous Unmanned Air Vehicles

Future autonomous unmanned air vehicles (UAV) will need to work in teams to share information and coordinate activities in much the same way as current manned air systems. Funded by AFRL, Professor Hugh Durrant-Whyte and his research staff (see Figure 1) at the Australian Research Council's Center of Excellence for Autonomous Systems have been developing mathematical models and simulation studies to understand—and ultimately provide— this future UAV capability.

The team's research focuses on coordination and cooperation for teams of autonomous UAVs engaged in information gathering and data fusion tasks, including cooperative tracking, ground picture compilation, area exploration, and target search. The underlying mathematical model for coordination and cooperation employs quantitative probabilistic and information-theoretic models of platform and sensor abilities. This information-theoretic approach builds on established principles for distributed data fusion in sensor networks, extending these ideas to problems in the distributed control of sensing resources. The researchers have made substantial progress towards formulating, solving, and demonstrating these methods for multi-UAV systems. In particular, they have developed distributed algorithms that enable UAV team-based search and exploration operations. These search and exploration algorithms can incorporate realistic constraints on platforms and sensors—a priori constraints from the environment and weak information from external sources. To date, Prof Durrant-Whyte's research team has successfully demonstrated these algorithms on a flight simulator of midlevel fidelity (see Figure 2).

Recently, the team presented its findings to AFRL researchers at Wright- Patterson Air Force Base (AFB), Ohio, and Eglin AFB, Florida. Based on the promising results of this research effort, AFRL is funding two additional projects to further explore the mathematical aspects of the technology and facilitate real-world application through demonstrations. The first round of demonstrations will involve high-fidelity, hardware-in-the-loop simulations, culminating in a large-scale demonstration involving a UAV fleet operated by the University of Sydney (see Figure 3). AFRL's two research projects will provide significant scientific and technical advancement in the cooperative control of autonomous systems.

The availability of autonomous UAV teams capable of complex cooperative behavior will enable warfighters to execute highly complex missions effectively and safely removed from harms way (i.e., remotely). In addition to providing these advantages, the UAV technology's imaging and atmospheric sampling capabilities have the potential to support both homeland security emergency scenarios and real-time forest fire monitoring tasks.

Dr. Tae-Woo Park, of the Air Force Research Laboratory's Air Force Office of Scientific Research, and Prof Hugh Durrant-Whyte, of the University of Sydney (Australian Research Council Federation Fellow), wrote this article. For more information, contact TECH CONNECT at (800) 203-6451 or place a request at http://www.afrl.af.mil/techconn/index.htm. Reference document OSR-H-05-06.

Posted in: Briefs, Information Technology, Mathematical models, Simulation and modeling, Unmanned aerial vehicles
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Surface-Emitting Laser Arrays Bring Light to the Top

Laser diodes are an integral part of everyday life, incorporated into commonplace items as diverse in function as laser pointers, fiber-optic communications systems, and DVD players. Manufacturers make most laser diodes by layering specially doped semiconductor materials on a wafer. By slicing tiny chips from these wafers to attain two perfectly smooth, parallel edges, they create very thin (tens of microns) waveguides. These waveguides define a resonating cavity that causes stimulated light to combine in a way that embodies a "laser" and propagates its lasing action. Although this process represents a highly successful and wellengineered means for producing semiconductor lasers, the lasers do not produce an optimum beam. Beam emission occurs from the small rectangular opening at the end of the chip, a configuration that results in an elliptically distorted beam as well as the loss of output efficiency. In addition, the output aperture's relatively small size can lead to destruction of the cleaved and polished end facet during the laser's high-power operation. Laser diodes produced using this process are also susceptible to substantial fluctuations in output wavelength and beam quality as a function of temperature. Furthermore, since the chip emits beam output from an edge instead of its top or bottom surface, manufacturers experience difficulty both in packaging various diode configurations and in combining the output beams of multiple laser diodes.

Posted in: Briefs, Photonics, Fiber optics, Lasers
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Geo*View

Visualization of geospatially correct, remotely sensed data is a key element of many government and commercial applications. It enables a user to analyze and assess ground activities and other conditions of interest. Because remotely sensed data can include a diversity of data types reflecting many different data formats, users may experience difficulty visualizing and interpreting these varying data types and formats due to data structure complexity. In addition, important supplemental information often accompanies the data. This supplemental information—or metadata— may include pertinent information of significant value to the user with respect to where, when, and how data collection occurred. Whereas some applications require metadata to support geospatial analysis functions such as positioning and measurement, many others are unable to interpret such metadata and it may thus go unnoticed. Multiband data and motion imagery further compound the task of visualization with spectral components and complex video streams interlaced with other geospatial information.

Posted in: Briefs, Software, Data acquisition and handling, Imaging
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New Capability to Characterize the Mechanical Properties of Explosive Materials

Improved targeting accuracy and the long-standing desire to minimize collateral damage are causing current and future munitions to become much smaller. As munitions size decreases, the explosive materials packed within bomb cases begin to carry a significant portion of the structural loads experienced by the warhead. In an ongoing program effort to determine the mechanical properties of explosives and other energetic materials, scientists at AFRL's High Explosives Research and Development (HERD) facility (Eglin Air Force Base, Florida) acquired a miniaturized split Hopkinson pressure bar (MSHPB) (see Figure 1). Designed and built by Mr. Clive Siviour under the guidance of Drs. John Field, Bill Proud, and Stephen Walley (of the United Kingdom's University of Cambridge, Physics and Chemistry of Solids Group), the MSHPB is capable of strain rates up to 105 s-1 in material samples. AFRL's European Office of Aerospace Research and Development sponsored the project.

Posted in: Briefs, Materials, Materials properties, Hazardous materials
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Ceramic Matrix Composites Research

AFRL scientists characterized and evaluated the high-temperature mechanical behavior of fiber-reinforced ceramic matrix composite (CMC) materials used in aerospace structural applications. Researchers examined four principal characteristics of a porous matrix composite that General Electric developed for the aerospace industry. Their evaluations resulted in an increased understanding of the materials and their potential for applications in military and commercial aerospace products.

Posted in: Briefs, Materials, Research and development, Ceramics, Composite materials
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Characterizing Mechanical Properties at the Microscale

Scientists from AFRL, Pratt & Whitney Aircraft, and General Electric Aircraft Engines, working under the Defense Advanced Research Projects Agency's Accelerated Insertion of Materials (AIM) program, have invented a new method for characterizing the single-crystal properties of aerospace alloys using micron-size test samples. The research team based the new characterization method on focused ion beam (FIB) microscopy and a commercially available nanoindentation-based test instrument. Further development of these methodologies, in conjunction with their continued integration with simulation methods devised under the AIM program, will enable engineers to consider local changes in material microstructure and their effect on properties in the design process. The integration of advanced mechanical property measurements, materials representation, and simulation methods will dramatically decrease the time required for new materials insertion and will transform microstructure into a design variable for engineered systems. These advancements will directly benefit combat systems and readiness.

A primary challenge to the rapid insertion of new materials into the design cycle is the need to understand both the intrinsic properties of an engineering material at the microscopic level and the influence of defects on these properties at the macroscopic level. Historically, scientists have been unable to develop model parameters or validate continuum materials behavior models that are based upon discrete microstructural information. Continuum crystal plasticity models are at the frontier of techniques that incorporate direct microstructural information. However, a major deficiency of these models is the need to obtain required input information: the single-crystal mechanical properties of individual grains, or microconstituents. Acquiring this information is particularly difficult when such parameters must reflect the subtleties of material process history or the local influence of material defects.

Under the AIM program, AFRL researchers have sought to measure the single-crystal mechanical properties, such as the critical resolved shear stresses and strain hardening rates, of micro- and nanoscale samples extracted from relevantly processed structural alloys (see figure). Scientists are currently developing direct methods to automatically and rapidly characterize both the mechanical response of relevant microstructural elements and the stochastic nature of material property variation to establish the mechanical properties of a material's representative volume elements (RVE).

It is essential for scientists building continuum models to quickly determine the mechanical properties of RVEs in order to quantify the inherent variability in material properties, the observed variability in experimental measurements, and the uncertainty in predicted properties. They can then establish "confidence metrics" for the data they incorporate into the designer's knowledge base. Without such confidence, scientists can add new materials (or old materials in new applications) to the knowledge base only after extremely difficult and costly testing.

The new characterization method uses FIB milling to isolate and prepare single-crystal mechanical test specimens from individual grains, or precipitates, of a conventionally processed alloy. Scientists then move the prepared specimens to a conventional nanoindenter device outfitted with a flatpunch indentation tip. The nanoindenter imposes uniaxial compression on the microsamples and records highfidelity load-displacement measurements as the samples deform. With the development of this novel mechanical behavior test capability, researchers now envisage sampling the local mechanical effects of material microstructure and statistically incorporating these results in improved constitutive response surfaces, which could be used in simulations of critical component features.

Dr. Dennis M. Dimiduk, Dr. Michael D. Uchic, and Dr. Peter S. Meltzer (Anteon Corporation), of the Air Force Research Laboratory's Materials and Manufacturing Directorate, wrote this article. For more information, contact TECH CONNECT at (800) 203-6451 or place a request at http://www.afrl.af.mil/techconn/index.htm. Reference document ML-H-04-10.

Posted in: Briefs, Materials
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Total In-Flight Simulator 50th Anniversary

AFRL's Total In-Flight Simulator (TIFS), a Convair C-131 Samaritan aircraft, entered service on March 22, 1955. The C-131 aircraft had performed various transport operations for approximately a decade up to that point, and the Air Force (AF) Flight Dynamics Laboratory—now AFRL— subsequently chose it for a very special mission: developing next-generation air vehicles.

Posted in: Briefs, Mechanical Components
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F-35 Antenna Measurement Program

Engineers are conducting sophisticated performance testing of F-35 Joint Strike Fighter (JSF) antennas at the AFRL Newport Research Facility, New York. Through an agreement with the F-35 Joint Program Office, engineers from Lockheed Martin and AFRL's Rome Research Site are collaborating on the test effort. Because antenna testing is occurring early in the aircraft development cycle, the team is using a model—a full-scale F-35 replica—to measure the installed performance of the aircraft's communications, navigation, identification, and electronic warfare antennas. The goal of this testing program is to optimize antenna performance and identify and correct antenna problems before the aircraft design is finalized and antenna system changes consequently become more difficult and expensive to incorporate.

Posted in: Briefs, Electronics & Computers
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A New Method for Determining Aeroballistic Parameters From Flight Data

Dr. Gregg Abate, an AFRL exchange engineer, developed a new method for determining aeroballistic parameters from projectile flight data. Assigned to the Fraunhofer Institute for High-Speed Dynamics (commonly known as the Ernst-Mach Institute), Freiburg, Germany, Dr. Abate was a participant in the AFRL-managed Engineer and Scientist Exchange Program, a Department of Defense effort to promote international cooperation in military research, development, and acquisition through the exchange of defense engineers and scientists.

Posted in: Briefs, Mechanical Components
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Fire-Resistant Hydraulic Fluid

An AFRL-developed fire-resistant hydraulic fluid recently completed a B-52 flight test, and based on successful test results, systems engineers from Oklahoma City Air Logistics Center (OC-ALC) will adopt the fluid (MILPRF- 87527) for use in over 90% of the aircraft's hydraulic systems. OC-ALC engineers will conduct further tests to determine whether they can also convert the hydraulic systems controlling the B-52's landing gear and wingtip protection struts to the fire-resistant fluid. AFRL expects the improved fluid's higher flash point and reduced flammability to increase the B-52 aircraft's survivability and overall operational safety. Further, the fluid's associated thermal stability measurements and fluid film thickness data indicate it performs well over extended periods of time in hightemperature environments and in temperatures as low as -65°F.

Posted in: Briefs, Materials
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Predicting the Composition of Metallic Glasses

AFRL scientists made significant progress in developing bulk metallic glasses to improve the durability and performance of aerospace components. They also successfully created working scientific models that can predict the composition of new metallic glasses, a capability that helps researchers determine in advance whether a particular glass can be manufactured in bulk form. As a direct result of their effort, researchers recently discovered several new bulk metallic glasses. Their work also led to the successful development of a new technique to illustrate the topology of amorphous (noncrystalline) metal alloys.

Posted in: Briefs, Materials
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Innovative Processes Strengthen F-15E Vertical Stabilizers

AFRL materials engineers resolved a potentially serious problem that affects the operational life of F-15E vertical stabilizers. Working with engineers from Warner Robins Air Logistics Center (WR-ALC), Georgia, they successfully developed, demonstrated, and transitioned an adhesive bonding process and nondestructive inspection (NDI) technique that ensure the stiffening doublers attached to both sides of the aircraft's two vertical stabilizers remain adequately secured (see figure on next page). Successful transition of these innovative methods restores the operational life of the vertical stabilizers.

Posted in: Briefs, Materials
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