Tech Briefs

The Impact of Video Compression on Remote Cardiac Pulse Measurement Using Imaging Photoplethysmography

Remote measurement of physiological signals has a number of advantages over traditional contact methods. It allows the measurement of vital signals unobtrusively and concomitantly. In recent years, a number of approaches for imaging-based measurement of physiology using digital cameras have been proposed. Imaging photoplethysmography (iPPG) captures variations in light reflected from the body due to blood volume changes in microvascular tissue. It has been demonstrated that sub-pixel variations in color channel measurements from a digital single lens reflex (DSLR) camera, when aggregated, could be used to recover the blood volume pulse. Subsequently, it was shown that iPPG methods can allow accurate measurement of heart rate, heart rate variability, breathing rate, blood oxygenation and pulse transit time.

Posted in: Briefs, Aerospace, Test & Measurement

Subjective Mapping of Dust-Emission Sources by Using MODIS Imagery

Dust storms (5 to 100 km across) often originate from multiple dust-emission sources (1 to 10 km across). Remote-sensing-based dust-source identification is a challenge. A previous study developed a subjective approach for mapping dust sources by using enhanced MODIS satellite imagery; therefore, this study conducted mapping exercises to assess the reproducibility of this technique amongst multiple analysts and in different regions.

Posted in: Briefs, Aerospace, Test & Measurement

Custom Data Logger for Real-Time Remote Field Data Collections

The U.S. Army Corps of Engineers (USACE), CHL, FRF, had a need for a remote real-time data collection system to control instruments and log and communicate data from five observing stations in the Currituck Sound Estuary, NC1. These stations, referred to as the Currituck Sound Array (CSA), collect a suite of meteorological and oceano-graphic data including wind, air temperature, humidity, incoming solar radiation (above and below water), waves, currents, water level, salinity, and water temperature, as well as turbidity and many other water quality parameters. This array of instruments has a variety of control commands, sample routines, and output data formats. Additionally, the CSA was designed to act as a natural laboratory for estuarine research and as an instrument and model test bed. These capabilities required a reliable and flexible system that would allow easy modification of sampling schemes, the ability to log as many as 15 instruments with a single logger, and allow the incorporation of additional and novel instrumentation with minimal effort and expense.

Posted in: Briefs, Aerospace, Test & Measurement

Initial Validation of Ballistic Shock Accelerometers

Method 522.2 of MIL-STD-810G CN1 defines ballistic shock as “a high-level shock that generally results from the impact of projectiles or ordnance on armored combat vehicles”. Typical engagements of interest also include Kinetic Energy projectiles, land mines, and improvised explosive devices. For the purposes of this TOP, ballistic shock is generally referred to as the sudden high-rate loading resulting from under body blast (UBB) testing designed to assess the crew-survivability of military vehicles. Historical testing conducted in both areas have proven the relative similarities between the two environments.

Posted in: Briefs, Aerospace, Sensors

Topology Control in Aerial Multi-Beam Directional Networks

In multi-beam directional networks, nodes are able to simultaneously transmit to all neighbors or receive from all neighbors. This spatial reuse allows for high throughputs, but in dense networks can cause significant interference. Topology control (i.e., selecting a subset of neighbors to communicate with) is vital to reduce the interference. Good topology control balances the number of links utilized to achieve fewer collisions while maintaining robust network connectivity.

Posted in: Briefs, Aerospace, Test & Measurement

Hydrodynamic Drag Force Measurement of a Functionalized Surface Exhibiting Superhydrophobic Properties

With superhydrophobic properties being extended to a variety of metallic substrates through the process of ablation due to femto-second laser surface processing (FLSP), it is important to understand the hydrodynamic benefits of such a material, as well as its resiliency. This research focuses on the skin friction drag effects of a superhydrophobic flat plate compared to an untreated flat plate of the same material and geometry. The resiliency of this material will also be tested through the use of an accelerated corrosion fog chamber using both treated and untreated aluminum samples.

Posted in: Briefs, Aerospace, Lasers, Metal finishing, Aluminum alloys, Corrosion resistant alloys, Materials properties

High-Power Broadband Multispectral Source on a Hybrid Silicon Chip

For applications in manufacturing, remote sensing, medicine, military, and fundamental science, an ideal laser would have high output power and a diffraction-limited beam. The figure-of-merit to describe this property is the brightness, which scales proportional to output power and inverse to the beam quality factor M2.

Posted in: Briefs, Aerospace, Integrated circuits, Lasers, Waveguides, Silicon alloys

Stimulated Brillouin Scattering (SBS) Suppression and Long Delivery Fibers at the Multikilowatt Level with Chirped Seed Lasers

One obstacle in the scaling of high-power fiber lasers arises because of nonlinear effects (e.g., stimulated Brillouin scattering [SBS]) due to the large intensity times length product. Efforts to raise the power threshold include:

Posted in: Briefs, Aerospace, Fiber optics, Lasers, Performance upgrades

Erbium Doped GaN Lasers by Optical Pumping

The main objective of this research was to construct an optical pump system that would allow the study of Er:GaN materials under 980 nm resonant excitation to be carried out. The results obtained from the optically pumped studies could then be utilized to guide crystal growth and laser design.

Posted in: Briefs, Aerospace, Lasers, Optics, Materials properties, Refractory materials, Pumps

New Class of Excimer-Pumped Atomic Lasers (XPALS)

The focus of this research program was the investigation of XPAL properties, and new pumping schemes, as well as modeling, and measuring critical photoionization and excited state-excited state reaction rates in order to improve the performance of XPALs.

Posted in: Briefs, Aerospace, Lasers, Research and development, Pumps

Measuring Propellant Stress Relaxation Modulus Using Dynamic Mechanical Analyzer

Structural analysis of solid rocket motors is challenging for several reasons, but the most important of these is the complex behavior of the propellant. The mechanical response of a solid propellant is time and temperature dependent. The complexity of the mathematical analysis of the propellant depends on the loading conditions, but for some loading situations, the linear viscoelasticity assumption is reasonable. In particular, linear viscoelasticity is perhaps the most appropriate material behavior description for use in the simulations of stresses related to storage conditions. Typically, simulations use a viscoelastic model in the form of a Prony series and a Williams–Landel–Ferry (WLF) equation. The parameters in these models are derived from stress relaxation experiments, making the stress relaxation experiment a key viscoelastic test, analogous to the tensile test for linear elastic materials.

Posted in: Briefs, Aerospace, Defense, Fluid Handling, Propulsion, Solid propellants, Spacecraft fuel, Performance tests

Combustion Characteristics of Hydrocarbon Droplets Induced by Photoignition of Aluminum Nanoparticles

In the study of combustion characteristics of liquid rocket fuels, it is customary to either study the combustion of liquid fuel droplets or the combustion of fuel sprays. However, the two are closely related to each other, because in a typical rocket combustion chamber, the burning of droplets, droplet clusters, and fuel sprays occur simultaneously.

Posted in: Briefs, Aerospace, Defense, Propulsion, Test & Measurement, Spacecraft fuel, Aluminum, Combustion and combustion processes, Liquid propellant rocket engines

Vapor Pressure Data and Analysis for Selected Organophosphorous Compounds: DIBMP, DCMP, IMMP, IMPA, EMPA, and MPFA

Knowledge of the physical properties of materials is critical for understanding their behavior in the environment as well as in the laboratory. Vapor pressure is an important physical property for a wide variety of chemical defense-related applications, including estimation of persistence, prediction of downwind time-concentration profiles after dissemination, generation of controlled challenge concentrations for detector testing, evaluation of toxicological properties, and assessment of the efficiency of air filtration systems.

Posted in: Briefs, Aerospace, Defense, Emergency management, Chemicals, Materials properties, Hazardous materials

Coupling of Coastal Wave Transformation and Computational Fluid Dynamics Models for Seakeeping Analysis

This research focused on depth-integrated modeling of coastal wave and surf-zone processes in support of computational fluid dynamics (CFD) simulation of ship motions. There were two components of the project. The first was the development of a numerical dispersion relation for a family of Boussinesq-type equations commonly used in modeling of coastal wave transformation. The relation depicts numerical dissipation and dispersion in wave propagation and provides guidelines for model setup in terms of temporal and spatial discretization. The second component was an extension of existing depth-integrated wave models to describe overtopping of coastal reefs and structures along with a series of CFD and laboratory experiments for model validation. The basic approach utilizing the HLLS Riemann solver performs reasonably well and produces stable and efficient numerical results for practical application.

Posted in: Briefs, Aerospace, Defense, Computational fluid dynamics, Marine vehicles and equipment

Assessment of Non-Traditional Isotopic Ratios by Mass Spectrometry for Analysis of Nuclear Activities

The objective of this work is to identify isotopic ratios suitable for analysis via mass spectrometry that distinguish between commercial nuclear reactor fuel cycles, fuel cycles for weapons grade plutonium, and products from nuclear weapons explosions. Methods will also be determined to distinguish the above from medical and industrial radionuclide sources.

Posted in: Briefs, Aerospace, Defense, Nuclear energy, Identification, Test procedures

Imaging Detonations of Explosives

An effort has been made within the US Army Research Laboratory (ARL) to extract quantitative information on explosive performance from high-speed imaging of explosions. Explosive fireball surface temperatures are measured using imaging pyrometry (2-color 2-camera imaging pyrometer; full-color single-camera imaging pyrometer). Framing cameras are synchronized with pulsed laser illumination to measure fireball/shock expansion velocities, enabling calculation of peak air-shock pressures. Multicamera filtering at different wavelengths enables visualization of light emission by some reactant species participating in energy release during an explosion. Measurement of incident and reflected shock velocities is used to calculate shock energy on a target.

Posted in: Briefs, Aerospace, Imaging, Imaging, Thermodynamics, Defense industry, Missiles

Laser Integration on Silicon Photonic Circuits Through Transfer Printing

The purpose of this project was to develop a transfer printing process for the massively parallel integration of III-V lasers on silicon photonic integrated circuits. Silicon has long offered promise as the ultimate platform for realizing compact photonic integrated circuits (PICs). That promise stems in part from the material's properties: the high refractive-index contrast of silicon allows strong confinement of the optical field, increasing light-matter interaction in a compact space—a particularly important attribute for realizing efficient modulators and high-speed detectors.

Posted in: Briefs, Aerospace, Photonics, Integrated circuits, Lasers, Fabrication, Materials properties, Semiconductors

Determining Detection and Classification Potential of Munitions Using Advanced EMI Sensors in the Underwater Environment

Hazardous ordnance items are present along coastlines and in rivers and lakes in waters shallow enough to cause concerns for human recreational and industrial activities. The presence of water makes it difficult to detect and remove these hazardous legacies induced from wars, military training and deliberate disposal. Various techniques have been proposed to detect and characterize Unexploded Ordnances (UXO) and discarded military munitions (DMM) in the underwater environment including acoustic waves, magnetometery, and electromagnetic induction (EMI).

Posted in: Briefs, Aerospace, Sensors, Sensors and actuators, Water, Defense industry, Conductivity, Hazardous materials, Marine vehicles and equipment, Missiles

High Energy Computed Tomographic Inspection of Munitions

An advance computed tomography (CT) system was recently built for the U.S. Army Armament Research, Development and Engineering Center, Picatinny Arsenal, NJ, for the inspection of munitions. The system is a charged coupled device (CCD) camera based CT system designated with the name “experimental Imaging Media” (XIM). The design incorporated shielding for use up to 4MeV x-ray photons and integrated two separate cameras into one single field of view (FOV). Other major distinguishing characteristics include its processing functions to digitally piece the two cameras together, use of advanced artifact reduction principles, performing reconstruction simultaneously during acquisition, and its development in accurate beam hardening corrections through digital means.

Posted in: Briefs, Aerospace, Photonics, Charge coupled devices, Imaging, Defense industry, Inspections, Missiles

Terahertz (THz) Radar: A Solution For Degraded Visibility Environments (DVE)

An accurate view of the physical world is frequently vital. For example, rotary wing aircraft pilots must have knowledge of the terrain in order to safely fly their aircraft. Therefore, systems capable of generating images of the environment of sufficient quality to facilitate the decision process are necessary. The product of such a system is illustrated in Figure 1.

Posted in: Briefs, Aerospace, Imaging, Cartography, Imaging, Radar, Terrain

Development of Photoacoustic Sensing Platforms

In recent years, photoacoustic spectroscopy (PAS) has emerged as an attractive and powerful technique well suited for sensing applications. The development of high-power radiation sources and more sophisticated electronics, including sensitive microphones and digital lock-in amplifiers, have allowed for significant advances in PAS. Furthermore, photoacoustic (PA) detection of IR absorption spectra using modern tunable lasers offers several advantages, including simultaneous detection and discrimination of numerous molecules of interest. Successful applications of PAS in gases and condensed matter have made this a notable technique and it is now studied and employed by scientists and engineers in a variety of disciplines.

Posted in: Briefs, Aerospace, Photonics, Amplifiers, Electronic equipment, Lasers, Sensors and actuators, Spectroscopy, Acoustics

Experimental Confirmation of an Aquatic Swimming Motion Theoretically of Very Low Drag and High Efficiency

It has been established theoretically that self-propulsion of deformable bodies in ideal fluid can occur with a careful specification of the deformation mode shape. With the fluid assumed ideal, vortex shedding, rotational wake, and induced drag would not occur. The implication is that for a real fluid, provided the existence of a thin boundary layer, similarly configured bodies with the same deformation mode shape self-propel without vortex shedding, rotational wake, and induced drag. Only viscous drag effects, due to the existence of the thin boundary layer, are present and unavoidable. The motion mode in question is the little-exploited anguilliform mode exhibited in some aquatic animal swimming. The Anguilla includes the snake, eel, lamprey, and leach, among others.

Posted in: Briefs, Aerospace, Automation, Water, Biological sciences, Robotics, Drag, Marine vehicles and equipment

Gesture-Based Controls for Robots: Overview and Implications for Use by Soldiers

Afuture vision of the use of autonomous and intelligent robots in dismounted military operations is for soldiers to interact with robots as teammates, much like soldiers interact with other soldiers. Soldiers will no longer be operators in full control of every movement, as the autonomous intelligent systems will have the capability to act without continual human input. However, soldiers will need to use the information available from, or provided by, the robot. One of the critical needs to achieve this vision is the ability of soldiers and robots to communicate with each other. One way to do that is to use human gestures to instruct and command robots.

Posted in: Briefs, Aerospace, Automation, Robotics, Optics, Sensors and actuators, Human machine interface (HMI), Robotics

A Guide for Developing Human-Robot Interaction Experiments in the Robotic Interactive Visualization and Experimentation Technology (RIVET) Simulation

ARL's Intelligent Systems Enterprise vision is to enable the teaming of autonomous intelligent systems with soldiers in dynamic, unstructured combat environments, as well as in non-combat military installations and base operations. To accomplish this vision for interdependent soldier-robot teaming, there has been a paradigm shift in robotic research conducted by ARL from the current instantiation of fielded remote-controlled or teleoperated robots to systems with increased intelligence, decision-making capability, and autonomy. This type of teaming is needed for future joint, interdependent, network-enabled operations.

Posted in: Briefs, Aerospace, Automation, Computer simulation, Imaging, Human machine interface (HMI), Robotics, Autonomous vehicles, Military vehicles and equipment

Identifying the Flow Physics and Modeling Transient Forces on Two-Dimensional Wings

The main objective of this research was to better understand the flow physics of aircraft wings undergoing highly unsteady maneuvers. Reduced-order models play a central role in this study, both to elucidate the overall dynamical mechanisms behind various flow phenomena (such as dynamic stall and vortex shedding), and ultimately to guide flight control design for vehicles for which these unsteady phenomena are important.

Posted in: Briefs, Aerospace, Automation, Robotics, Wings, Mathematical models, Aerodynamics

The Scaling of Loss Pathways and Heat Transfer in Small Scale Internal Combustion Engines

The rapid expansion of the remotely piloted aircraft market includes an interest in 10 kg to 25 kg vehicles (Group 2) for monitoring, surveillance, and reconnaissance. Power plant options for those aircraft are often 10 cm3 to 100 cm3 displacement internal combustion engines. Both power and fuel conversion efficiency decrease increasingly rapidly in the aforementioned size range, with fuel conversion efficiency falling from approximately 30% for automotive and larger scale engines (greater than 100 cm3 displacement) to less than 5% for micro glow fuel engines (less than 10 cm3 displacement).

Posted in: Briefs, Aerospace, Automation, Heat transfer, Combustion and combustion processes, Engine efficiency, Two stroke engines, Unmanned aerial vehicles

Luminescence Materials as Nanoparticle Thermal Sensors

The purpose of this research program was to create and study novel luminescence particles (phosphors} capable of sensing and retaining the time-temperature information to which they were exposed, therefore acting as nano- and microsized thermosensors. The thermometric property is the latent thermoluminescence (TL) signal associated with electron/hole pairs trapped at defect energy levels, which are differently affected by the environmental temperature.

Posted in: Briefs, Aerospace, Data Acquisition, Defense, Nanotechnology, Photonics, Sensors, Architecture, Sensors and actuators, Research and development, Nanomaterials, Thermal testing

Using Dempster-Shafer Fusion for Personnel Intrusion Detection

The Dempster-Shafer (D-S) mass function is used in effect as a common representation of heterogeneous sensor data. In order to cast each data source in this form, first the raw data is reduced to points in a multi-dimensional feature space specific to each sensor. From there, an approach is outlined that uses a distance metric in the feature space to assign mass to each state in the class hierarchy. This hierarchy begins with the full frame of discernment which represents complete uncertainty. From there it proceeds as an n-array tree broken down into further subclasses until the finest granularity of classification for the specific sensor is reached.

Posted in: Briefs, Aerospace, Defense, Detectors, Sensors, Mathematical models, Sensors and actuators, Data management, Reliability

Using Fisher Information Criteria for Chemical Sensor Selection via Convex Optimization Methods

The design of chemical sensor arrays from the standpoint of chemical sensor selection and error quantification has historically proceeded as an ad hoc process. Frequently, chemical sensors are developed not as general purpose sensing devices, but as analyte or chemical class specific detectors. When such single purpose devices are integrated together as a chemical sensor array, it is unclear a priori how well they will function in concert with each other to provide expanded capabilities, an observation that is true of the integration of analytical instruments as well.

Posted in: Briefs, Aerospace, Sensors, Optimization, Neural networks, Sensors and actuators, Identification, Chemicals

Development of an Optically Modulated Scatterer Probe for a Near-Field Measurement System

Near-field radiation patterns are useful in diagnosing antenna array defects, measuring far-field antenna patterns where the far-field is prohibitively far, and locating field concentrations in high power microwave applications, which could lead to material breakdown. There are two categories of near-field measurements: direct and indirect. In a direct measurement, the field from the antenna-under-test (AUT) is directly measured by a probe whereas, in an indirect measurement, the field is inferred from the scattering off of a probe that is placed in the near-field.

Posted in: Briefs, Aerospace, Sensors, Finite element analysis, Measurements, Antennas, Radiation