Physical Sciences

Compressive Oversampling for Robust Data Transmission in Sensor Networks

A paper discusses recent developments in the area of Compressive Sensing (CS) for data loss in wireless sensing applications. Since many physical signals of interest are known to be sparse or compressible, employing CS not only compresses the data and reduces the effective transmission rate, but also improves the robustness of the system to channel erasures. This is possible because reconstruction algorithms for compressively sampled signals are not hampered by the stochastic nature of wireless link disturbances, which has traditionally plagued attempts at proactively handling the effects of these errors.

Posted in: Briefs, Physical Sciences, Mathematical models, Data exchange, Wireless communication systems, Reliability

Forehead-Mounted Sensor Measures Oxygen Saturation for Hypoxia Early Detection and Warning

Symptoms of hypoxia – a deficiency in the amount of oxygen reaching body tissues - have been documented among rotary-wing pilots and aircrew flying at altitudes as low as 8,000 feet. Effective hypoxia-related mishap prevention relies upon rapid recognition of hypoxia symptoms and expeditious execution of emergency procedures. This is particularly challenging in rotary wing aircraft, where the lack of adequate training makes reliance on hypoxia self-detection an ineffective solution. An automated warning would be preferable, but currently no military aviation platform is outfitted with a physiological monitoring system to alert pilots and aircrew of impending hypoxic episodes.

Posted in: Briefs, Physical Sciences, Measurements, Sensors and actuators, Medical, health, and wellness, Personnel, Oxygen

Manifold-Based Image Understanding

The rapid growth of sensing and imaging technology, combined with the need for near-real-time action based on the sensed data, has rendered automatic processing, understanding, and decision-making vital to our national security. A unified theory and practical toolset was developed for the analysis and processing of signal and image manifolds for signal and image understanding purposes. The unifying theme is the multiscale geometric structure of signal and image families and manifolds. Specifically, theory and tools were developed for (1) model-based signal and image recognition and registration, (2) sensing and compressing data on manifolds, and (3) data-driven manifold modeling and learning.

Posted in: Briefs, Physical Sciences, Mathematical models, Imaging, Security systems, Data management

Battery Electrolyte Level Detector Apparatus

An apparatus has been developed for checking the electrolyte level in a battery, providing a safer and more efficient means to do so. The result is a non-intrusive apparatus and method of checking the electrolyte level that reduces the need to open the caps on the battery by checking the level externally.

Posted in: Briefs, Physical Sciences, Batteries, Sensors and actuators, Electrolytes

Outdoor Synthetic Aperture Acoustic Ground Target Measurements

A novel outdoor synthetic aperture acoustic (SAA) system consists of a microphone and loudspeaker traveling along a 6.3-meter rail system. This is an extension of a prior indoor laboratory measurement system in which selected targets were insonified while suspended in air. Here, the loudspeaker and microphone are aimed perpendicular to their direction of travel along the rail. The area next to the rail is insonified and the microphone records the reflected acoustic signal, while the travel of the transceiver along the rail creates a synthetic aperture allowing imaging of the scene.

Posted in: Briefs, Physical Sciences, Measurements, Acoustics, Test equipment and instrumentation

Portable, Rapid-Test Fuel Tank Leak Detection System

In 1988, the EPA issued Underground Storage Tank (UST) regulations for fuel storage in order to implement monthly monitoring and annual tightness testing. Monthly monitoring requires that the leak detection system be certified for a leak rate of 0.2 gallons per hour (GPH), and annual tightness testing requires a certified leak rate of 0.1 GPH, both with a probability of detection of at least 95%, and a probability of false alarm of no more than 5%. The DoD owns and operates hundreds of underground storage tanks that are less than 100,000 gallons. These tanks, commonly operating at base fuel farms, must comply with EPA, state, and local regulations, and require that either an annual tightness test with monthly inventory reconciliation or monthly monitoring tests be conducted in accordance with published performance standards. Existing technologies either cannot meet performance standards for the large 50-K to 100-K gallon USTs or do not provide a cost-effective solution. The Portable Rapid Test (PRT) is designed and recommended for testing tanks containing lower-volatile, heavier-type fuels such as diesel, JP-5, JP-8, etc.

Posted in: Briefs, Physical Sciences, Defense industry, Fuel tanks, Certification, Inspections, Test procedures

Uncooled Tunable LWIR Microbolometers

Uncooled infrared detectors have significant potential capabilities that have been little explored. Micro-machined uncooled detectors with tunable spectral characteristics across the long-wave infrared (LWIR, λ~8-12 μm) have been developed. In the middle wavelength infrared (MWIR) and LWIR regions, the fabrication of Fabry-Perot filters is more complex because the optical materials must be infrared-compatible and the layer thicknesses must be larger. It is very difficult to build filters for uncooled LWIR thermal detectors, which has limited previous researchers to demonstrations of discretely tunable 2- or 3-color thermal detectors rather than continuously tunable ones.

Posted in: Briefs, Physical Sciences, Architecture, Sensors and actuators, Thermal testing

Fluid Helmet Liner for Protection Against Blast-Induced Traumatic Brain Injury

An Advanced Combat Helmet liner design uses the novel idea of including filler materials inside channels in the liner. An energy-absorbing foam was selected for the main liner structure, and several filler material candidates of widely varying properties are being considered. To date, material has been evaluated both experimentally and numerically. Numerical studies will include coupled simulations with a detailed finite element head model, providing insight into the effect of the new liner on the brain’s response to a blast wave impact.

Posted in: Briefs, Physical Sciences, Finite element analysis, Foams, Head injuries, Protective equipment, Military vehicles and equipment

Performance of Steel Stud Walls Subjected to Blast Loads

Construction trends have brought about an increase in the use of cold-formed steel studs in Air Force facilities. These steel stud walls have significant potential for mitigating large blast events. The current state of steel stud research, however, has not addressed all the variables that can influence the behavior of typical wall systems. As a result, there is a research gap that exists in the blast-resistant design of conventional steel stud wall systems.

Posted in: Briefs, Physical Sciences, Materials properties, Steel, Protective structures, Construction vehicles and equipment

Through-the-Wall Small Weapon Detection Based on Polarimetric Radar Techniques

Detecting concealed small weapons carried by people has received significant interest from law enforcement agencies as well as the military, most frequently for application in controlling checkpoints (in airports, border crossings, public spaces, etc.). Imaging systems for concealed weapons based on radar or other sensor technologies have been recently developed and tested. Most of the existing electromagnetic (EM) sensors suitable for this application operate at very high frequencies, usually in the millimeter or terahertz frequency bands and produce high-resolution images. Although these EM waves can penetrate through clothing (textile materials), they have very poor penetration properties through many common construction materials (such as brick or concrete). Most through-the-wall radars must operate at much lower frequencies, usually below 4 GHz, in order to “see” targets behind walls. However, at those low frequencies, the image resolution is degraded, so small weapons carried by humans may be difficult to detect directly in the image domain.

Posted in: Briefs, Physical Sciences, Imaging, Radar, Security systems, Sensors and actuators