Physical Sciences

Target Detection and Classification Using Seismic and PIR Sensors

Unattended ground sensors (UGS) are widely used in industrial monitoring and military operations. Such UGS systems are usually lightweight devices that automatically monitor the local activities in-situ, and transfer target detection and classification reports to the processing center at a higher level of hierarchy. Commercially available UGS systems make use of multiple sensing modalities (e.g., acoustic, seismic, passive infrared, magnetic, electrostatic, and video). Efficacy of UGS systems is often limited by high false alarm rates because the onboard data processing algorithms may not be able to correctly discriminate different types of targets (e.g., humans from animals). For example, discriminating human footstep signals from other targets and noise sources is a challenging task, because the signal-to-noise ratio (SNR) of footsteps decreases rapidly with the distance between the sensor and the pedestrian.

Posted in: Briefs, Physical Sciences, Mathematical models, Security systems, Sensors and actuators

Component Identification in Multi-Chemical Mixtures with Swept-Wavelength Resonant-Raman Spectroscopy

The utilization of ultraviolet resonance Raman spectroscopy for the detection and identification of chemical, biological, and nuclear hazards is of great interest due to the sensitivity and specificity afforded by this technique. Detection by means of optical probing is a fast, non-contact method that requires little to no sample preparation and can be performed remotely by an operator. In addition, this method is also well suited for use by an automated monitor or a mobile autonomous system, such as an in-situ environmental detector or a sensorequipped unmanned vehicle. In addition, this technique offers the ability for a single detector to identify multiple species of targets. However, for Raman detection to become practicable as a forensic tool, the method must demonstrate the ability to distinguish the target elements while operating in a complex environment.

Posted in: Briefs, Physical Sciences, Remote sensing, Spectroscopy, Chemicals, Materials identification, Biohazards, Radiation

Wheel Force Transducer for Field Testing

This project endeavors to develop, validate, and calibrate cost-effective field test equipment for measuring tire characteristics on vehicles while driving off-road. The four wheel force transducers are designed for use on the High Mobility Multipurpose Wheeled Vehicle (HMMWV or Humvee).

Posted in: Briefs, Physical Sciences, Wheels, Test equipment and instrumentation, Off-highway vehicles and equipment

Thermal Mechanical Fatigue Crack Growth Testing

Turbines in aircraft turbojet engines are being subject to increasingly higher temperatures to improve fuel efficiency. High turbine efficiency requires the ability of turbine blades to withstand gas temperature of the order of 1350 to 1550 °C. In polycrystalline materials, these increased temperatures would cause creep strains along grain boundaries that would be unacceptable. Even single-crystal materials must be pushed to their limits to insure that engine performance is maximized. Airfoils in modern gas turbine aircraft use a systems approach for cooling to achieve required component life. There are three basic components to these systems: a cast nickel single-crystal superalloy in combination with thermal barrier coatings, and a sophisticated cooling scheme consisting of intricately designed channels and holes through the core and surface of the airfoil.

Posted in: Briefs, Physical Sciences, Fatigue, Turbojet engines, Test procedures, Thermal testing

Evaluation of Three Extremity Armor Systems

The US Marine Corps and the US Army have been engaged in efforts to evaluate improved body armor, including armor to protect the extremities. These efforts are focused on both body armor performance (i.e., ballistic protection) and armor effects on the physical performance of personnel (e.g., body flexibility, mobility, and agility).

Posted in: Briefs, Physical Sciences, Kinematics, Defense industry, Protective clothing, Military vehicles and equipment

Development of High-Resolution Eddy Current Imaging Using an Electromechanical Sensor

An oscillating current flowing through a coil produces an oscillating magnetic field. When an electrically conducting material like a metal is brought close to the coil, the oscillating magnetic field produces eddy currents in the metallic material. The strength of the eddy current depends on the electrical conductivity of the material, the distance between the coil and the material, and the frequency of the excitation of the coil. The eddy currents in the electrical conductor produce a magnetic field opposing the magnetic field generated by the coil. The electrical impedance of the coil, placed in close proximity to a metal, is altered due to the eddy currents in the metal. Measurement of the change in the impedance is a method to determine the electrical conductivity of the metal.

Posted in: Briefs, Physical Sciences, Measurements, Sensors and actuators, Conductivity, Magnetic materials, Metals

Fuzzy Fiber Sensors for Structural Composite Health Monitoring

The onset of local damage in structures, such as delamination, cracking, and fastener loosening, can often be difficult to detect and has long-term implications on the performance of the composite structure. These structures are often exposed to a variety of conditions, including impact, shock loading, and extreme changes in temperature. Because of both manufacturing requirements and design specifications, large and complex sections often need to be joined together to form the final structures. It is important to understand the failure behavior of these joints under a variety of static and dynamic loading conditions.

Posted in: Briefs, Physical Sciences, Failure modes and effects analysis, Fiber optics, Sensors and actuators, Composite materials

Fatigue Crack Detection Via Load-Differential Guided Wave Methods

Guided waves (e.g., Lamb waves) have been considered for many structural health monitoring (SHM) applications because of their ability to travel long distances and maintain sensitivity to damage. One conventional approach to detect damage is to compare in situ signals to baselines recorded from the undamaged structure. By comparing current signals to damage-free baselines, signal changes caused by structural damage can be tracked. Such methods can handle some structural complexity, but have unwanted sensitivity to variations in environmental and operational conditions (e.g., temperatures and loads).

Posted in: Briefs, Physical Sciences, Failure modes and effects analysis, Waveguides, Fatigue

Distributed Fiber Optic Sensing for Homeland Security

To address the need to protect our borders and critical infrastructure, fiber optic sensing technology developed for antisubmarine warfare applications has been adapted to homeland security applications. Ground-based seismic sensing applications have significantly different requirements than traditional underwater acoustic applications. As a result, new optical interrogation and signal processing techniques are needed. Border and critical infrastructure sensor systems must be able to monitor long lengths (several km to several 10s of km) with reasonable spatial resolution (5 to 100 m), and have sufficient seismic sensitivity to detect targets of interest. A fiber optic distributed seismic sensor system was developed that is capable of meeting these requirements.

Posted in: Briefs, Physical Sciences, Architecture, Fiber optics, Security systems, Sensors and actuators

Computational Cameras

A computational camera uses a combination of optics and software to produce images that cannot be taken with traditional cameras. A variety of computational cameras has been demonstrated; some designed to achieve new imaging functionalities, and others to reduce the complexity of traditional imaging.

Posted in: Briefs, Physical Sciences, Computer software / hardware, Imaging