Electronics & Computers

PCI Cards Feature 4 GigaSamples of Memory

Two 8-bit resolution arbitrary waveform generator cards with up to 4 gigasamples of onboard memory are available from Strategic Test Corp. (Woburn, MA).

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Textile Capacitor

The Air Force (AF) is evolving from a Cold War-era force with a large, containment- focused infrastructure to a smaller, more responsive and affordable Air and Space Expeditionary Force. In support of this transformation, AFRL is developing affordable, sustainable, and scalable force applications, including directed energy weapons, kinetic energy weapons, electromagnetic guns and launchers, and high-power microwaves.

Capacitors are an essential component in all of these systems because of their ability to store prime electrical energy and expel it in short, fast energy pulses. If they were to be made using conventional technology, however, the capacitors required to support such advanced systems would be bulky and could weigh thousands of pounds. Consequently, AFRL researchers are exploring ways to integrate load-bearing capacitor fibers into air vehicle structures to reduce airframe weight, free up valuable space, and offer fuel cost savings.

Three AFRL scientists, Mr. William Baron, Dr. Maxwell Blair, and Mrs. Sandra Fries-Carr, recently received a patent entitled “Airframe Structure- Integrated Capacitor” (see inset). The term “structural capacitance” implies that in addition to carrying load, the aircraft or spacecraft structure maintains a capacitive charge that permits energy storage and power conditioning for use in a variety of applications, both pulsed and continuous. The specific objectives of the scientists’ work effort were to identify a plausible design concept, conduct experimental trials, and characterize the concept’s structural and electrical efficiency.

In selecting from available capacitor types, the team considered only those configurations capable of carrying normal, shear, and bending loads. Two common capacitors— parallel plate and cylindrical—met this requirement. While evaluating parallel plate capacitors, the researchers considered laminated structural systems constructed from metal and dielectric material; they envisioned bonding sheets of aluminum to the chosen dielectric material. Commercially available, structural precedents such as Arall™ use this procedure. Although not designed for electrical purposes, Arall is a structurally durable material constructed from impregnated aramid fibers and bonded with aluminum sheets into a laminate. Technicians apply this design approach to the structural capacitor application by laminating a good dielectric with a conductive lamina. Because the parallel plate capacitor concept is quite efficient, the team members initially believed it had significant potential. However, they later abandoned the concept because of associated developmental challenges, including the control of dielectric layer properties, damage tolerance, and repair issues.

The team then focused on an alternative approach—designing a cylindrical capacitor capable of reacting structural loads. To fabricate this concept, technicians would cover a dielectric-coated conductor with a conductive metal layer. Next, they would integrate the coaxial system into a hybridized, composite weave with carbon tow for additional reinforcement. Finally, they would lay up the material on a tool and inject it with resin to create an air vehicle’s primary load-bearing structure. Dielectric characteristics, which are the Achilles’ heel of any electrostructural system, govern capacitor performance. While the cylindrical capacitor approach enables precise control over dielectric layer quality, designing the energy’s ingress and egress paths into the structure is more complicated than simply using the parallel plate capacitor concept. Nevertheless, using the cylindrical capacitor composite allows engineers to integrate tens of thousands of feet of capacitor into an air vehicle’s structure.

To demonstrate the basic concept, AFRL researchers used a commercially available copper wire with Kapton™, an aromatic polyamide dielectric material available in numerous manufactured forms. Kapton material has voltage breakdown strengths of around 4500 V/mil and offers low electromagnetic losses. While designers did not intend for this material to form the basis of a transitionable solution, they did believe it capable of showing concept feasibility and establishing future research activity parameters. For the purposes of the initial feasibility investigation, technicians fabricated the first specimens with a conductive copper paint offering a uniform coat and good adhesion. The team conducted an initial capacitor test to examine performance using a Hewlett-Packard 4284A precision impedance meter. Results showed good capacitance, inductance, and resistance from 1 kHz to 1 MHz. The team considered these results significant, given the limited time spent optimizing the system.

The team then integrated the design into an experimental piece of carbon fabric material, evaluated its ability to maintain structural capacitance, and demonstrated the weaving process viability. This process required a significant amount of capacitive wire, since 1.0 sq ft of plain weave fabric requires 120 ft of cylindrical capacitor when used only in the fabric warp direction at 10 pics/in. The team created a small, taskspecific weaving machine to produce a structural capacitor fabric coupon measuring 8.0 in. wide by 14.0 in. long. Testing this first-generation specimen (see Figure 1) verified the capacitor concept’s preliminary feasibility. Researchers subsequently used this demonstrated performance in an integrated conceptual air vehicle fuselage design that ultimately generated 168.92 μF at high-voltage operation.

In the future, superior dielectrics that offer improved structural and electrical performance will increase the structure’s energy density storage capacity. The AFRL team is working with researchers from the University of Dayton Research Institute (UDRI) to develop highperformance resins for achieving dielectric performance with good structural properties. This work involves doping resins to improve the voltage breakdown strength, provide low electromagnetic losses, and increase the material dielectric constant. In addition, the team is developing material that is compatible with the injected structural resin and also has low moisture uptake, since the dielectric is not hermetically sealed. The researchers are synthesizing this resin material for use in the precision dielectric coating pultrusion process that AFRL is currently developing to produce the next generation of coaxial structural capacitors. Figure 2 shows a scanning electron microscope image of the doped resin.

Researchers have also made significant progress in lowering the structural capacitor concept’s specific weight and improving its durability. The first improvement was in eliminating the copper paint electrode. This step involved thorough consideration of several options, including metal foil bonding, electroless plating, metal coating flame spray, vapor deposition, and braiding of a conductive surface with composite fibers. For the second-generation device, researchers used a conductive fiber overbraid to improve structural and electrical performance. They tested several varieties of this overbraid, including variations fabricated from titanium, copper zirconium alloy, and carbon tow. These braids provided an overall thickness of approximately 4 mils, enabling a small profile for integration into the composite architecture. Researchers evaluated these materials based on cost, electrical resistance, weight, and ease of fabrication, ultimately choosing the carbon braid electrode (see Figure 3) for future development activity. The team also evaluated copper zirconium options for the center electrode. Although the zirconium contained in the copper improved structural fatigue resistance with minimal impact to electrical conductivity, the desire to further reduce weight has since inspired additional efforts to fabricate the center electrode using carbon fiber tow in a pultrusion process.

Finally, researchers used the Textile Composite Analysis for Design (TEXCAD) computer program to model the plain weave unit cell structure used in the feasibility study. TEXCAD is a general-purpose micromechanics code that models yarn architecture to predict three-dimensional thermal and mechanical properties, damage initiation and progression, strength under tension, compression, and shear. These analyses guided the development of an advanced textile architecture and resulted in a new weave that provided significant fiber volume fraction increase and improved weight efficiency. Researchers then worked with the UDRI team to model this new weave using a novel finite element approach in ABAQUS, a finite element analysis software suite that uses embedded elements. ABAQUS’ embedded elements enabled detailed modeling of the complex architecture, which established mechanical performance estimates that the team will use to baseline empirical results and update vehicle conceptual design application studies. In addition, the researchers performed preliminary analyses characterizing the Lorentz forces induced during structural capacitor system discharge. These forces arise from electrostatic and electromagnetic fields and can induce significant mechanical stresses in the dielectric layers. The team’s parametric studies characterized both physical and operational effects on the stress levels induced into the dielectric material.

The researchers also developed and demonstrated several approaches for busing energy into and out of the structure. These methods encompass various attempts at designing an integrated bus structure capable of transferring critical loads through joints to prevent disruption of the load path. Technicians have fabricated prototype panels to validate these approaches, and researchers are using validation results to optimize structural performance and develop improved fabrication methods and bus integration designs. It is likely that implementing this technology in the future will involve integrating an active switching network into the bus system. This type of network would allow the creation of parallel networks of series circuits to provide power handling tailored to weapon system requirements. This network would offer another advantage as well: if any loadbearing capacitor elements were shorted due to in-service structural damage, the active network could eliminate those components from the circuit.

Developing this technology is an important step toward fulfilling future AF needs. One day, engineers will use AFRL-developed capabilities to design smaller air vehicles capable of delivering short pulses of electrical energy to power directed energy weapons and provide necessary power for air vehicle subsystems. These future air vehicles will play an important role in tomorrow’s AF and will forever change the face of warfare.

Mr. William Baron and Ms. Melissa Withrow (Azimuth Corporation), of the Air Force Research Laboratory’s Air Vehicles 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.asp. Reference document VA-H-06-06.

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Adaptable Miniature Initiation System Technology

The ever-changing nature of warfare presents constant challenges to weapon system designers, who must carefully consider various perspectives of mutual importance. Specifically, designers must address constraints associated with newly developed aircraft, such as the F-22 and F-35, which carry their stores internally and thus have size limitations on their payloads. Weapons designers must also recognize the weight of political pressures that fuel concerns about a given weapon’s potential to cause collateral damage to civilian populations. At the same time, they must respond adequately to warfighter demand for the flexibility to employ the most effective weapon against a given target.

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Collapsing and Closing Unmanned Air Vehicle Swarms

AFRL researchers are exploring an adaptive and reconfigurable unmanned air vehicle (UAV) swarm configuration known as “collapsing and closing UAV swarms.” This approach to developing UAV swarms is suitable for a number of multifunction radio frequency (RF) applications in challenging environments such as urban and mountainous regions. Figures 1a-1c illustrate the basic approach. In Figure 1a, a long-range search UAV swarm collectively forms a scanning RF aperture. The swarm’s scanning RF aperture interrogates a region of interest to detect high-clutter, discrete objects such as buildings or mountains. As depicted in Figure 1b, once the swarm detects these large, obscuring objects, it “collapses and closes” in on the region between the objects. This allows the swarm configuration to interrogate the embedded channels between the buildings or mountains to look for signal leakage points within these large objects, and once detected, these leakage points facilitate cavity interrogation.1 After the swarm has finished interrogating the embedded channels and cavities, it reconfigures itself for RF long-range remote sensing with regard to the next region of interest, as illustrated by Figure 1c.

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Eddy Current Inspection System

AFRL manufacturing technology engineers, working with personnel from the 76th Maintenance Wing’s Software and Propulsion Maintenance Groups at the Oklahoma City Air Logistics Center (OC-ALC) and Wyle Laboratories (formerly Veridian Engineering), delivered a major configuration upgrade and improved the inspection process for the Air Force (AF) Eddy Current Inspection System (ECIS) at OC-ALC, Tinker Air Force Base (AFB), Oklahoma. These ECIS improvements are part of AFRL’s Engine Rotor Life Extension program. With investments exceeding $80 million, the ECIS program addresses an AFRL initiative to extend the useful life of turbine engine components and reduce the cost of replacing aging engine components in the AF’s fighter and bomber fleets.

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Low-Cost Transmit/Receive Module for Satellite Control and Communications

A multidisciplinary team led by AFRL scientists is developing a geodesic dome phased-array antenna (GDPAA) for a proposed future Air Force (AF) technology demonstration.1 AFRL is also developing a second-generation S-band electronic scanning array (ESA) proof-of-concept (POC) panel to support the demonstration efforts.

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The Next Frontier of Networking—The Airborne Network

It is the next frontier of networking—a frontier where communication nodes may move at Mach speeds, wireless line of sight covers hundreds of miles, and weather affects communications capabilities such as chat and e-mail. It is the airborne network (AN). In the coming years, the military services and commercial aviation enterprises will internetwork their respective fleets of airborne assets. For the military, these assets range from unmanned aircraft, smart munitions, and fast-moving fighter aircraft to “air stationary” tankers and slow-moving cargo planes. This fast-paced, ever-changing environment presents challenges across all network layers—from basic connectivity and linking/routing challenges to management of the proposed global network. Accordingly, military entities define the AN as the sum total of all capabilities required for conducting airborne network-centric operations to shorten the kill chain and facilitate the synchronized flow of relevant information by extending the Global Information Grid (GIG) to the airborne domain (see figure).

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Weapon Data Link Demonstration

One of the US Air Force’s goals is to reduce the time needed to strike timesensitive targets, thus minimizing the adversary’s perceived mobility advantage and leaving concealment as that enemy’s primary defensive measure. One potential way to meet this challenge relies on a capability to redirect and update weapons with new target coordinates while they are in flight—a solution that requires weapons developers to outfit weapons with a data link enabling communications between warfighters operating in the air and on the ground. This Weapon Data Link (WDL) approach would allow the warfighter to directly communicate with and control air-launched weapons to strike moving or otherwise time-sensitive targets, while continually gathering information about the weapon’s performance against those targets. The scenario could involve something as simple as a weapon communicating its position and system status back to the release aircraft, or something as complex as a weapon operating in the Global Information Grid (GIG), wherein a secondary ground/air controller assumes the weapon’s control after a positive handoff from the release platform, with the weapon’s sensor and video information autonomously distributed throughout the GIG.

Figure 1. Depiction of WDLAFRL engineers recently accomplished a critical step in demonstrating the WDL approach. Held at Langley Air Force Base (AFB), Virginia, the demonstration’s primary objective was to show that two WDL terminals, connected to Tactical Air Control Party (TACP) laptop computers, could successfully transmit and receive J-series messages within a Link-16 network (see Figures 1 and 2). The network included a legacy Fighter Data Link (FDL) terminal provided by the 46th Test Squadron (Eglin AFB, Florida), two WDL terminals, and local aircraft equipped with Link-16 radios.

Engineers from AFRL and Rockwell Collins partnered to develop the 50 in3, software-defined WDL radio used in the demonstration. This radio provides multiple operators with the flexibility to port and upload communication waveforms. The device has three software waveforms loaded into its memory; the operator can switch between these waveforms as required. Although the test team limited this demonstration to Link-16 operation, future demonstrations will highlight the radio’s capacity to receive and transmit ultra-high-frequency satellite communications and line-of-sight waveforms as well. The TACP Modernization program supplied the TACPCASS (Close Air Support System) software, laptop computers, and a trained operator. During the first part of the demonstration, one TACP computer generated target coordinates and transmitted them as J-series messages from one WDL terminal to the other. The TACP-CASS software on the second TACP computer interpreted and displayed the transmitted messages as target tracks. This test showed that messages generated by the TACP-CASS software could be correctly interpreted by the two networked WDL terminals and that this information could be shared between them. In the second phase of the demonstration, test engineers integrated the FDL terminal into the network. One of the TACP computers transmitted target information via Link-16 network protocol to the FDL terminal, which correctly interpreted and displayed the information on the Improved Multilink Translator and Display System (IMTDS). In the next phase, both computers correctly received, interpreted, and displayed target messages transmitted by the FDL terminal. In a final demonstration of system capability, several aircraft from Langley AFB joined the network for short periods of time, transmitting information that was subsequently displayed on both the TACP and IMTDS computers.

Figure 2. Setup of WDL demonstration equipmentAll demonstration participants gained valuable insight into using Link-16 networks for passing J-series messages between aircraft, weapons, and ground troops. The test team did not intend for the demonstration to provide an in-depth look at integrating weapons into battlefield networks. Rather, its purpose was to provide a rudimentary understanding of how an aircraft, weapon, and TACP could join and operate in an existing Link-16 network, while specifically demonstrating the capability of a software-defined WDL radio to transmit and receive J-series messages. The demonstration achieved its twofold purpose, both providing overall insight regarding the system and establishing the flexibility of a softwaredefined WDL radio in processing J-series messages within a representative network.

Ms. Michelle White, of the Air Force Research Laboratory’s Munitions 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 MN-H-05-14.

Reference

1 “China-America: The Great Game.” Interview With Lt Gen Liu Yazhou. Eurasian Review of Geopolitics, Gruppo Editoriale L’Espresso/Cassan Press-HK, Jan 05.

Posted in: Briefs, Electronics & Computers, Data acquisition and handling, Personnel, Military aircraft
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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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Switching Chassis Enables Ethernet Control of 3U Modules in LXI Environment

Designed to enable the use of PXI test modules in a LAN extensions for Instrumentation (LXI) environment, Pickering Interfaces’ (Woburn, MA) 60-100 and 60-101 chassis are fully compliant with Functional Class C of the LXI standard. They allow 3U PXI switching modules to be supported in a LXI-compliant environment. The 60- 100 is suitable for modules occupying 7 or fewer slots, and the 60-101 can support up to 13 slots.

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