Modeling Defects in Transparent Ceramics to Improve Military Armor

The dominant materials solution used for ballistic transparency protection of armored tactical platforms in commercial and military applications is low-cost glass backed by polycarbonate. Development of next-generation ceramics is critical to offering enhanced protection capability and extended service performance for future armored windows to the soldier. Among the potential ceramic materials considered for armor — sapphire, edge-form-growth sapphire, magnesium aluminate spinel, aluminium oxynitride — one was selected for the current pursuit: magnesium aluminate spinel (MgAl2O4).

Posted in: Briefs, Materials, Windows and windshields, Failure modes and effects analysis, Ceramics, Occupant protection, Military vehicles and equipment

Validation of Hazardous Air Pollutant (HAP)-Free Torque Seal Inspection Lacquer

The Army uses numerous adhesives and sealants, among other coating materials, that contain significant amounts of hazardous air pollutants (HAPs). This work examines laboratory and field demonstration/validation of one sealant, Torque Seal. A HAP-free alternative to Torque Seal containing ethanol as the carrier solvent has been identified. Laboratory testing including adhesion, resistance to fluids, resistance to humidity, and drying time validated that the HAP-free sealant performs very similarly to the baseline Torque Seal containing methanol (HAP). Furthermore, a demonstration study at Fort Rucker, AL, using a UH-1 helicopter rotor, shows that the HAP-free sealant performed as well as the Torque Seal.

Posted in: Briefs, Materials, Air pollution, Adhesives and sealants, Performance tests, Test procedures, Military aircraft, Military vehicles and equipment

Wireless Network Cocast: Location-Aware Cooperative Communications with Linear Network Coding

In wireless networks, reducing aggregate transmit power and having even power distribution increase the network lifetime. The conventional direct transmission (DTX) scheme results in high aggregate transmit power and uneven power distribution. In conventional DTX, where mobile units directly transmit their information to a common destination, the distant mobile units require more transmit power to provide a comparable quality of service (QoS) to that of the closer ones. Consequently, high aggregate transmit power (the sum of all transmit power of individual mobile units) and uneven power distribution among the units exist in the network. These two issues result in low network lifetime, which is defined as the time until the first mobile unit dies. It is wellknown that diversity techniques such as time diversity, frequency diversity, and spatial diversity result in reduction of transmit power and thus can be used to improve network lifetime. Three location- aware cooperation-based schemes considered in this work are immediateneighbor cooperation (INC), maximal cooperation (MAX), and wireless network cocast (WNC) that achieve spatial diversity to reduce aggregate transmit power and even power distribution.

Posted in: Briefs, Electronics & Computers

High Assurance Virtualization Engine (HAVEN)

Virtualization technology has been around since the late 1960s. Initially, it was conceived to maximize utilization of expensive hardware by running multiple instances of an operating system (OS) using virtual machines (VM). In the past decade, virtualization has become popular due to its cost and space-saving advantages.

Posted in: Briefs, Electronics & Computers, Virtual reality, Architecture, Computer software / hardware

Memory-Based, Structured, Application-Specific Integrated Circuit (ASIC)

For air, space, and ground-based systems, there is a clear need for highperformance, lightweight, low-power, highly reliable computing on data-intensive applications. A data-intensive application is one in which there is a very large volume of data, which is often accessed in irregular patterns. Yet, despite the fact that application-specific integrated circuits (ASICs) are becoming more memory- intensive, commodity memory and ASIC design and manufacturing technologies are still on divergent paths.

Posted in: Briefs, Electronics & Computers, Design processes, Integrated circuits, Data management, Fabrication

Solid-State, High-Energy Lasers Based on Rare-Earth Doped Gallium Nitride

Laser-based directed-energy weapons (DEW) are important components for future Army missile defense systems. The diode-pumped, rare-earth (RE)-doped, solid-state laser is a very promising path towards achieving a DEW-sufficient level of average power from a reasonably compact device. Even so, the extreme pump power densities, combined with the inevitable non-radiative losses in the pump-lase process, introduce severe thermal loading in the gain medium. Regardless of the sophistication of the heat removal technique and its efficiency, the gain medium itself is the bottleneck for non-distortive heat removal due to the low thermal conductivity of known gain media compared to that of heat-sinking materials. The bestknown laser hosts, e.g., yttrium aluminum garnet (YAG), possess thermal conductivities (10–11 W/(m-K)) that are ~1.5 orders of magnitude lower than those of known heat-sinking materials. In order to eliminate this technical hurdle, an innovative gain medium with a thermal conductivity on the same order as copper (~390 W/(m- K)) had to be engineered.

Posted in: Briefs, Photonics, Lasers, Thermal management, Military vehicles and equipment, Missiles

Analysis of Analog Photonic Links Employing Multiple-Channel (Arrayed) Receivers

Analog optical links are finding increased application in commercial and military systems ranging from radio-over-fiber applications, antenna remoting, and optical signal processing. As the performance of an analog link improves with received photocurrent, optical amplifiers — predominantly erbium-doped fiber amplifiers (EDFAs) — have been readily incorporated into a variety of systems. It is known that the addition of an optical amplifier (EDFA) raises the electrical noise floor in both digital and analog applications due to the presence of amplified spontaneous emission (optical) noise. To mitigate this additional noise in systems employing EDFAs prior to modulation, dualoutput optical modulators and balanced detection are frequently employed. This technique has been utilized alone to achieve the first multi-gigahertz bandwidth analog optical link with a noise figure

Posted in: Briefs, Photonics, Amplifiers, Architecture, Noise

Photonic Recirculating Delay Line for Analog-to-Digital Conversion

Aconventional analog fiber-optic link can be augmented with a recirculating optical delay loop so as to realize an optically assisted analogto- digital converter (ADC) that provides improved performance in terms of both speed and resolution using one (slower) electronic ADC (see figure). The overall architecture readily integrates with any electronic ADC system. Moreover, the highspeed ADC performance is fundamentally limited by the performance of the fiber-optic link.

Posted in: Briefs, Photonics, Amplifiers, Fiber optics, Performance upgrades, Test procedures

Design and Development of a Package for a Diluted Waveguide Electro-Absorption Modulator

Externally coupled electroabsorption modulators (EAMs) are commonly used in order to transmit RF signals on optical fibers. Recently, an alternative device design with diluted waveguide structures was developed. Bench tests show benefits of lower propagation loss, higher power handling (100 mW), and higher normalized slope efficiency. Bench tests were performed in order to characterize the optical coupling of the EAM. The photo current maximum was offset from the optical power output maximum. The transmissions vs. bias voltage curves were measured, and an XY scanner was used to record the mode field of the light exiting from the EAM waveguide in each position. The Beam Propagation Method was used to simulate the mode field and the coupling efficiency. Based on the bench tests and simulation results, a design including mechanical, optical, and RF elements was developed.

Posted in: Briefs, Photonics, Design processes, Fiber optics, Waveguides

Developing Fleets of Autonomous Underwater Vehicles

Autonomous underwater vehicles (AUVs) have a demonstrated capability to collect valuable data for scientific and military purposes. Historically, individual vehicles have been used. To reduce the overall time and cost of acquiring data over large areas, multiple vehicles must be used. A fleet of five AUVs, capable of underwater commendation, was fabricated. These AUVs include small submarines, referred to as “swimmers,” and small, two-tracked vehicles, referred to as “crawlers.” The control and communication algorithms developed in this work will enable AUVs to use formations to search for mines and to communicate with each other in order to implement cooperative behavior. Languages and logics were developed to enable collaborative operations among the vehicles.

Posted in: Briefs, Mechanical Components, Communication protocols, Electronic control systems, Fleet management, Autonomous vehicles, Marine vehicles and equipment