4
Electronics
The panel met on November 13-14, 2018, at the National Academies of Sciences, Engineering, and Medicine (National Academies) facility in Washington, D.C., to review the In-House Laboratory Independent Research (ILIR) program projects in electronics conducted in 2018 at the U.S. Army Communications–Electronics Research, Development, and Engineering Center (CERDEC). The panel received an overview presentation on CERDEC and technical presentations describing the CERDEC projects. During each presentation, the panel engaged in question-and-answer sessions with the presenter, and a general discussion with CERDEC staff after the panel had formulated initial impressions and developed additional questions during its closed-session deliberations, conducted after the CERDEC staff had concluded their presentations.
COMMUNICATIONS–ELECTRONICS RESEARCH, DEVELOPMENT, AND ENGINEERING CENTER
Project: A Mathematical Transformation from Metamaterial to Matching Circuit for a Conformal Antenna
A matter of strategic and tactical importance to soldiers is command and control on the battlefield. To facilitate this, radio frequency (RF) communication is critical to coordinate efforts of various components of a military unit. However, adversaries are fully aware of the criticality of radio communication and typically target vehicles and personnel carrying antennas. In fact, vehicles with on-board antennas are by far the most often attacked by adversaries. To obviate this problem, it is desirable to hide radio antennas on vehicles in a manner that communication is not degraded, and the antennas are unrecognizable.
Numerous military platforms are equipped with antennas for communications and electronic warfare. Since Army vehicle antennas are not sufficiently stealthy, they need to be redesigned to achieve
required results. However, the challenges in hiding communication antennas on vehicles are two-fold. First, in order to communicate effectively through a cluttered environment (e.g., foliage, dust, smoke, or buildings) low frequencies are needed. These low-frequency waves typically require a very large antenna to perform effectively—these antennas are often so large that no amount of camouflage can hide their presence. The other challenge in this area is the presence of the vehicle itself. A planar antenna that is placed close to a metal object (e.g., a vehicle door, hood, or roof) tends to be significantly degraded in performance unless it is placed some specific distance from the vehicle. At the frequencies under consideration, this distance is unreasonably large.
To overcome these challenges, a high-dielectric-value substrate is often used between the radiating antenna and the large metallic surface. This choice tends to reduce the distance required to place the antenna; however, it also generally requires very heavy and very brittle materials. To eliminate the need for these materials, the proposed work investigates the possibility of placing the radiating element close to the conducting surface without using any high-dielectric material, which is replaced with a lumped element-matching network.
Impedance matching of antennas is a subject of extensive work over the past century and remains a significant area of opportunity for improved antenna performance. Proper matching can allow antennas to be reduced in size and sometimes can lead to very wide beams in the far field. However, impedance matching alone does not always lead to radiation in the desired directions because other means of radiation may occur, such as substrate modes. Additionally, coupling to the vehicle may occur, which degrades performance of the overall communication system.
The proposed research has demonstrated the ability for a properly impedance-matched antenna to provide an adequate far-field pattern; however, antenna pattern validation was initially conducted at a single frequency. While broadband impedance matching was achieved (500 MHz – 1,000 MHz), it is not clear that the antenna pattern remains stable across the same band. Additionally, the impacts of a lossy impedance-matching network on overall antenna efficiency was not clearly analyzed. These are additional goals that need to be evaluated in future research.
Three distinct antenna topologies were considered by the researchers, each with a different substrate: a hexaferrite substrate, a metamaterial substrate, and an air substrate. The simplest design proof of concept is a simple dipole over a ground plane, which was accurately modeled and measured to validate methodology of wider applicability, promising greater cost-effectiveness of the research. Polynomial curve fitting for these geometries, which connects materials with design parameters, was accomplished. The research could be expanded to develop a fully generalizable true mathematical transformation that is applicable to a wide variety of antenna topologies, not simply the specific geometry and operating frequency bandwidth that was used in recent studies. This is often the least costly way of introducing a new technology: demonstrate it theoretically, validate the initial results, and then extend the methodology to a wider domain of applicability to achieve much greater military utility.
Currently, ultra-high frequency (UHF) antennas employed on Army combat vehicles do not have the minimal physical thickness to minimize their observability and vulnerability to detection, although they are conformal and otherwise demonstrate superior electrical performance, as measured by gain and electrical properties related to their efficiency and observability. A reverse-design methodology has been hypothesized to redesign such antennas from metamaterial-based to impedance-matching-based designs. In addition, mathematical transformations were defined to map metamaterial parameters (i.e., electrical permittivity, magnetic susceptibility, and thickness) to the equivalent matching circuit, and proof of concept was addressed based on a particular design that could lead to follow-on validation for other potential designs. This research activity focuses on improving Army communications based on antenna improvements that would increase bandwidth and gain; reduce size, weight, power, and cost (SWPaC); render a more flexible design; and reduce their visual signature. In addition, with the elimination of
metamaterials, costs would be reduced further, and, as a spinoff, optimal antenna design algorithms would emerge that could affect a prolific range of applications. Low visual-profile, wideband, conformable antennas are a critical Army need that would also favorably impact Army network connectivity.
In order to achieve the research goals of this project, the Army uses full-wave electromagnetic codes to simulate antennas and compare with measurements in support of model validation. Polynomial functions are generated and used to transform material properties to impedance parameters. A simple dipole above a ground plane was the first proof-of-concept test to validate this approach, although certain dimensional constraints apply. Further work will flesh out the dimensional constraints and gain improvements from distributing antenna loads.
Project: Mimicking Biological Visual Navigation Systems via Holographic Polymer Dispersed Liquid Crystals (H-PDLC)
The need for accurate, reliable, and redundant navigation systems is an ongoing challenge for the warfighter. The advent of the Global Positioning System (GPS) in 1978, and subsequent revisions of the constellation, have provided a solid source of accurate navigation information. However, because the satellites reside in geosynchronous orbit, the signal that reaches the earth’s surface is very weak, subject to jamming and, in extreme cases, spoofing (which provides false information to a GPS receiver). In addition, some scenarios seen by the warfighter make the GPS signal ineffective, which drives the need for alternative methods to generate navigation information.
One source to look at for guidance in navigation is the biological realm. Insects and animals achieve extensive feats of navigation without the need to resort to satellites, gyroscopes, or other methods. One of the many differences among humans, insects, and animals is the way in which each perceives the world. Humans generally perceive only three distinct colors: blue, green, and red; all other colors that they see are processed by their brains as combinations of these three colors. Other creatures, however, see different colors, and some see light in the infrared and the ultraviolet spectrum. It is postulated that these differences in perception are critical factors in biological navigation. Changing how humans process the different frequencies of light may give rise to additional information that may be used in navigation when GPS is not available.
The proposed research aims to address this problem with the development of a stack of optical filters made by a volume hologram recorded in a liquid crystal material sandwiched between transparent conductive coatings, which allow one to control the efficiency of the holographic filter with the application of a proper voltage. These optical elements can be used to extract color features from local scenes within and beyond the visible band, and such structures have been demonstrated to pass visible light through when their conductive coatings allow a voltage to be placed across the liquid crystal. They also vary the strength of the liquid crystal filter. If properly designed, the liquid crystal will then act as a filter to block a specific, narrow band of wavelengths from passing through the stack, which will then form a switchable optical filter. Investigating this filter capability, in combination with additional biological cues to select specific wavelengths of light, constitutes a multipronged crosscutting research program that offers the possibility of novel solutions not previously exploited.
In order to fully utilize the biological information, a significant level of signal processing is required to combine the specific wavelengths of light in a manner that approximates the true sight seen by the animal or insect model. This signal processing effort, however, is expected to be quite extensive, and appropriate tools and collaborators need to be pursued to assist with this portion of the effort.
The right tools and collaborations have the potential to enable radically different sensed data alternatives to those from GPS navigation, in particular by suggesting sensors that can image and filter the plethora of colors possible within and beyond the visual range of humans. Moreover, the prospect of
such alternative data sources needs to be explored in terms of their utility to combine with other data to enable actual navigation (including GPS data).
The color data also need to be robust to dynamic scene variations and potentially supply an operationally effective maximum set of features across multiple bands of the electromagnetic spectrum. Vision-aided navigation represents a technology that could also augment or complement the GPS, supplying assured positioning, navigation, and timing (APNT) to users in GPS-degraded and denied environments, especially locally. APNT is a crosscutting capability for many Army functions in support of cross-functional teams, and PNT is currently a critical component of the Army’s warfighting mission, as well as a technology enabler to support the warfighter in clear (i.e., unjammed) environments.
Several alternative technologies could also support the acquisition of multiple colors, of which the most prominent examples are multispectral and hyperspectral imaging. Nevertheless, for nascent research purposes one convenient technology cited above is holographic liquid crystals used as color filters when operated in transmissive and reflective modes in laboratory-based experiments. These are electrically addressed and can be stacked for controlling the wavelength distribution. When no electric field is applied, each layer is a distributed Bragg grating, associated with the refractive index periodicity of the layer. When an electric field is applied across the layer, the liquid crystal rotates and aligns with the field, changing the refractive index and disrupting the Bragg condition.
This research offers a physical-layer solution that might otherwise be addressed by using alternative multispectral or hyperspectral focal plane arrays (FPAs) with digital algorithms in lieu of direct spectral filtering. FPAs suggest a greater potential for diversification of applications in different environments where such technologies may be more mature, robust, and flexible. Having multiple options (e.g., holographic and hyperspectral technology) may be beneficial to early research goals because of the addition of bioinspired solutions, which are potentially unique and more compact than generic FPA-based technology; however, significant strides in the latter technology cannot be ignored. Significant trades remain to be addressed and represent future challenges to optimize design, robustness, and application utility (both multispectral and holographic filters demonstrate substantial sensitivity to the angle of observation, and whether a true color is transmitted through the filter signal depends strongly upon the angle of view on the scene). The implications of this research go beyond the currently adopted holographic technology and may harbor a much greater impact because of the yet to be examined synergism between other, broader spectrum color features and traditional kinematic or GPS navigation technology.
This research addresses color sensing applied to navigation in analogy with how biological systems navigate using a broad range of sensing abilities. Given the premise that bioinspired attributes may be potentially more robust, and apply more broadly to various environmental conditions, if performed by just a single-band sensor, it is hoped that from this research an effective alternative navigation capability will also be possible. Methods of research in this project will focus on laboratory experimentation that addresses filter spectral characteristics, modeling biological color perception, and eventually conducting field experiments incorporating authentic environments for performing visual navigation. Data analysis will address spectral filter matching to biophotoreceptors, wavefront distortion effects, and time-domain analyses of switching and synchronization, but the connection to more accurate navigation functionality needs to be included.
The holographic liquid crystal device has undergone initial testing to establish switching and color selectivity as well as extending sensitivity into the ultraviolet and permitting 20-85 percent transmission at the desired wavelengths in the visible spectrum. Preliminary conclusions indicate that visual characteristics of biological sources can be created using switchable filters, and the choice of the mixtures used would affect the transmission and reflection characteristics. In addition, it is possible to capture time-dependent visual data, which would mimic physiological visual changes of a biological source, depending on changes in the environment. Future anticipated activities include spectral color space
remapping to understand the color perception characteristic of a given biological color vision system, and the simulation of physiological visual changes versus time. It is expected that the amount of information embedded in multiple colors of distinct animal visual responses will grow exponentially with the dimensions of color and spatial sampling, for which significant effort will be necessary to screen the data to the desired wavelengths that would potentially maximize discrimination and, eventually, navigation performance. This is a well-recognized problem in sensor-data fusion (the so-called curse of dimensionality) that every application needs to address. The value-added of bioinspired color feature selection may be to obviate an otherwise time-consuming and expensive cluster analysis, which can be the bane of standing up a widely applicable and operationally effective pattern recognition and navigation methodology. Considering what is discussed above, two cases of data fusion can be identified depending on the nature (or physics) of the sensors. In the case when all sensors involved differ by the spectral band only, but have the same operational principles, the integrated scene can be achieved by using a homogeneous data fusion technique. Alternatively, when exploiting sensors of a different nature (e.g., spectral and GPS data), delivering a common scene can be achieved by applying the heterogonous data fusion technique. Such techniques were not employed in this project.
This project involves basic research and is complex because the connection between color sensing and navigation is not well defined. The research goals appear to be potentially novel; however, the utility of multispectral and hyperspectral imaging has been previously well established and needs to be accounted for. The use of color sensing to complement or enable navigation also signifies a nonconventional approach. A simplistic notion is that navigation can be at least minimally initiated with a cue predicated on finding unique scene content containing a critical color feature. The question is: What is the exact connection between the relevant navigation features needed to replace a GPS-enabled solution and the color features acquired through multispectral sensing? Given that the accuracy of GPS is nominally within a very localized CEP (circular error probable, a measure of GPS accuracy), what color features within that environment are critical cues for establishing not only position but also orientation? That has not been articulated in sufficient detail by the researcher to give confidence in the overall color sensing approach, and multispectral or hyperspectral solutions may already exist. However, if bioinspired color features are indeed leveraged, what additional functions could facilitate the navigation competence of those exemplars found in nature, and do those aspects help prescreen the optimal features needed for effective navigation? This tack would suggest that perhaps the subsumed approach of using color features might already contain a solution that would otherwise require a laborious and complex cluster analysis, which would be prudent to avoid. Hence, a large gap exists on the data processing tasks needed to determine a successful outcome (albeit this research initiative is relatively new). The challenge is to reframe the approach to better identify the connection between sensing and navigation as well as the prescreening methodology needed to derive traceable navigation algorithms in the absence of GPS but with performance equal to GPS, at least locally. This work appears to be reviewed at the CERDEC level, as well as being served by a thesis advisor for the Ph.D. candidate researcher, but further review is needed to further validate the research agenda. Additional spectral data sources are desirable, and bionavigation models are needed to more fully articulate the research agenda, which could indeed be a breakthrough if the hypothesis promoted turns out to be significantly supported by all relevant data.
Project: Harvesting Energy to Reduce the Metabolic Expenditure of Soldiers (HERMES Boots)
Warfighters carry heavy loads, which include electronics and computers, communication and navigation devices, radios, and mobile phones. These loads may total more than 31.75 kg (70 lb). Additional weight can increase a soldier’s risk of injury and can impact his or her mobility, safety, and efficiency. Over the past several decades the mean weight carried by the warfighter has risen by 17 kg, from 30 to
47 kg, which well exceeds the roughly 40 percent relative load-to-body-weight ratio that historically has been most efficiently sustained. Because this increase is attributed to gains from adding body armor, electronic devices, and batteries, development of an effective energy harvesting (EH) technique that would reduce the weight the soldier would be required to haul could substantially enhance warfighter performance. The Army aims to develop such an energy harvester that would be incorporated into combat boots for soldiers. Such a device could have a net zero or positive effect on the soldier’s metabolic rate, obtained by only harvesting energy during certain stages of the gait cycle.
This is desired without incurring any significant changes to the appearance of the boot. Therefore, both metabolic rate (i.e., energy burned) and gait kinematics (i.e., soldier motion) are key measurements. It is plausible to expect that energy can be harvested during the negative work phase of the gait, while reducing soldier fatigue and the risk of musculoskeletal injury. In addition to assisting the gait, this would reduce the total soldier mass-load from batteries by leveraging the electrical energy produced by the boots, and in turn this would enhance mission duration. An additional benefit, for instance, would be to power or enable assured APNT/GPS-denied technologies.
This research is very relevant to Army needs, and it provides a new way of solving critical problems related to the warfighter’s overall performance. Positive test results may contribute to reduced soldier fatigue and injury risk, as well as improved overall performance for extended missions.
The objectives of this program are clearly identified, and tasks for FY17–18 have been completed as planned, including (1) systematic design of a system capable of meeting system requirements for subsequent development, (2) ready-to-manufacture computer-aided design (CAD) tools, (3) initial modeling and optimization of EH utility and operability, and (4) an assembled EH device has been initially tested, culminating with integration into existing boots. Accomplishments to date have resolved a design that meets the intended function of reducing metabolic rate. A CAD model has been implemented to support manufacturing, and initial modeling and optimization have been addressed to support harvester functional capability. Prior experimental results were leveraged from soldier biomechanical tests to determine forcing inputs for simulation purposes. Subsequently, a device mechanism was constructed to perform iterative testing, and these and prior results were submitted for patent application. Follow-on work will refine the design and prototyping process, and human trials will establish reduced metabolic impact on solders and added power output. This work could afford future soldiers greater endurance in conjunction with the added features of body armor, sensors, and communications and is consonant with Army modernization priorities for enhanced soldier lethality. This work distinguishes the new capabilities expected from the prior state of energy harvesters that did not reduce metabolic rate.
Successful execution of this effort has also identified major challenges and concerns for further development of the proposed EH capability. First, though initial design and integration of EH in the boot has been accomplished, limited space in the boot sole is still a challenge that needs to be resolved. Fielding the EH-furnished boot and its acceptance by military personnel also remain to be accomplished. Additionally, the EH-equipped boot weight and rigidity still remain to be precisely defined.
FY19 tasks include design refinement and validation through human trials in test and realistic environments, the completion of which would lead to program success. Practical implementation and validation of the EH device and demonstrated improvement of actual personnel performance in a mission area context would constitute a nominal military measure of effectiveness. Although the studies performed were methodical and systematic, and the analyses of projected EH performance from laboratory tests and validations are within the context of established models for such devices, it would be useful if performance of the boot-based EH were to be compared with alternative solutions, such as the bionic power knee harvester.
It was reported that CERDEC EH research suggests that other EH systems do not appear to be as efficient as the proposed design. Analyses and comparisons need to be pursued to explore the utility of
CERDEC results to exoskeletons, allowing for performance tests when embedding EH in the Army standard HERMES and Belleville 390 boots. Specifically, the EH design could be extended to the alternator (i.e., power source). Results of studies performed to date contain technology innovations, and certain intellectual property elements may need to be protected by patent application. Study results within this program have been reported at Energy Harvesting Society meetings and workshops.
Energy harvesting, although not new as a research area, has yet to make a significant impact on actual warfighter efficiency, which is of particular interest to the Army in the functional enhancement of boots to alleviate physical fatigue. This project approaches this challenge by addressing the implementation of a mechanism that generates electrical power from the gait action of the soldier, which indirectly relieves the weight burden imposed on the soldier from the additional batteries and new electronic gear required for modern combat operations. This project has elements that point to a transition to applied research soon, because it is well along and holds the prospect of transitioning in the near term to soldier testing and training to evaluate the effectiveness of the technology. The researcher’s expectation is that this technology will do what has not been accomplished so far: extract energy from the negative work portion of the gait cycle without further taxing the soldier.
Project: Topology Optimization of an Electromagnetic Generator
Success on the battlefield depends on the correct equipment being in place for the duration of a mission. One of the most significant challenges in achieving this goal is the fuel required to sustain operations for the duration of a mission. Typically, the fuel requirements of any asset depend directly on the weight of the object—the larger the mass, the more fuel required to provide support to the warfighter. One of the largest and heaviest components of vehicle assets is the electric generator. The purpose of the generator is to provide electric power from the combustion of fuel in order to provide command and control, reconnaissance, and other functions as needed.
To reduce the mass of generators, it is desirable to reduce or eliminate as much of the iron core as possible from both the rotor and the stator. However, iron is used to guide magnetic flux through the generator and is the enabling physical mechanism for power generation. And so, although the iron core cannot be entirely removed, it may be possible for the shape of the iron to change in such a way as to reduce the overall mass without significantly impacting the flow of magnetic flux, therefore retaining the efficiency of the generator.
This CERDEC research is proposed in a multi-disciplinary way, which combines the topics of electromagnetics, thermodynamics, rotational kinematics, and materials science. It is pursued using a multipronged approach with validation steps throughout the process. The initial work begins with numerical modeling of a standard topology with fabrication and experimental test data for validation. The performance of the fabricated generator was very close to the expected result. The work continues into a two-dimensional thermodynamic analysis that will presumably be used to determine the heat dissipation through the modified core of the final generator design.
With these preliminary steps complete, optimization of the topology using various methods is under way. The researcher has developed multiple conceptual approaches to determine the optimal design and has selected multiple candidate engines for these approaches, which, in addition to optimality, include the method of moving asymptotes. Other options will be considered as necessary.
Research challenges for this project begin with the final topology optimization program. This program represents the crux of the research goals and represents both the most significant risk to the project and the most significant potential reward. The development of a generalizable algorithm to optimize generator design for power output with reduced mass could have significant and far-reaching impacts for the broader Army community.
Other fundamental challenges in this work include manufacturability and the uncertainty of a locally optimal solution instead of a globally optimized solution. The problem of manufacturability is a serious one that plagues research like this one (as well as numerous other areas of manufacturing). It is very likely possible to find a significantly improved design with the proposed method. However, the use of iron necessitates subtractive manufacturing, which cannot effectively create features such as voids within a solid volume of material. These manufacturability constraints are difficult to address in a semi-automated process and will require a certain amount of human (haptic) involvement in the design.
The Army desires to achieve increased mission duration, enhanced agility, and reduced logistics for the operation of electromagnetic devices, such as motors and generators, as found, for instance, in helicopter rotors and similar electromechanical systems, as well as for other applications for soldier lethality. An innovative way to do this is to optimize electromagnetic topology, arising from the design of critical components in motors, which will also impact their efficiency. This approach seeks optimization within any alternator configuration space by solving a dynamic simulation while simultaneously optimizing topology. The optimality criteria are power and magnetic flux, and the simulation tools rely on two-dimensional and three-dimensional finite element (FE) analyses. Heat transfer emerges as another scalar field problem to solve in concert with that of the electromagnetic field. Different approaches have been considered in the interest of minimizing computational costs, and FE tools are combined with topology optimization, as well as fine-tuning components, to achieve accurate and meaningful results. Other future challenges include manufacturability, design through iterations that incorporate penalties and sensitivity analyses, distinguishing global versus local maxima, and minimization of their uncertainty.
This project is at the threshold of transition to applied research, has a well-defined research goal, and is relevant to the Army’s need for improving efficiency across a number of platforms. The focus on the ubiquitous electric motor provides a well-defined basis for simulation and testing to achieve a closeable design. The theoretical basis is sound, based on joint or parallel optimization of electromagnetic, thermal, and topology simulations, as well as FE models, to ensure a robust approach. Challenges include the definition of uncertainty in evaluating optimization results as well as the impact of results on manufacturability. Since this project seeks an outcome that has not been achieved, it appears novel and could be game changing if successful. Progress to date has been significant and therefore places the project success very much in the direction of applied research for completion of the development cycle. So far, publications and reviews have been limited to a patent application and internal CERDEC review. Although publications are limited, cited described progress is promising and is being pursued as a Ph.D. dissertation.
Although this work is closer to applied research than basic research, it has a well-articulated research goal, approach, hypothesis, and theoretical basis. Its relevance to the Army’s mission is clear and appropriate, and it has the potential to be widely applicable to a variety of other missions and physical geometries. The measurements, modeling, and simulation results are all excellent and consistent, and the conclusions are reasonable given that the research is still in an early phase.
Project: Signal Degradation Analysis in Laser-Illuminated Scenes
The Army and other DoD services rely on optical technologies for target detection for their real-time tracking, identification, and discrimination (RTID). While direct intensity imaging remains essential for target identification, the retrieved data degrade dramatically when the detection is performed through perturbed media, such as turbulent atmosphere, or against complex cluttered backgrounds. This is of particular importance when dealing with coherent and laser-illuminated targets. Alternatively, using a polarimetric technique for signal detection allows the sensor to preserve and retrieve information
essential for characterizing and discriminating returned target signals, especially when operating in a cluttered environment.
The studies performed in this program address aspects related to the improved detectability of the target backscattered radiation, especially when RTID is performed through detection of the polarization-encoded signatures of the target, scattered and with transmitted light as a discriminator reference. The recent research program focuses on characterization of the target-returned signal using the adjustable frame rate of the sensor in combination with temporal modulation of the target-illuminating laser light. In essence, this is an innovative approach that proves to be more effective than the use of high frame-rate sensors. It may also provide better signature detectability, considering that high intensity target illumination may not be suitable for concealed missions, while high-speed sensors and imaging cameras do not perform well at low-illumination intensity.
On the other hand, as detailed in the presented results of the studies, modulation of the laser beam at frequencies contiguous with the sensor frame rate reveals the benefit of better signal detectability through anti-aliasing processing of the returned signal and imaging camera. This was experimentally demonstrated in the laboratory. The combination of the anti-aliasing method and detection of the polarization signatures from the test objects using the Mueller matrix with measured data would enable enhanced detectability and discrimination in a cluttered environment. Such an approach represents an innovative research program also relevant to CERDEC’s Night Vision and Electronic Sensors Directorate.
While active laser target illumination is frequently used for target designation, detection of the target-return signals in cluttered environments often remains difficult. Improvements can be sought by thorough characterization of the returned signal using polarization signatures as the source of information and, more specifically, developing methods that enable categorization of distinct polarization states and discriminants. Although laboratory studies have shown reliable detectability of the signatures of simple selected test samples, the technology eventually needs to be validated against realistic targets in operationally equivalent test environments. In those conditions, various components that may be viewed in a scene, either as clutter or targets of interest, will have different polarization properties, as evidenced by extant literature discussing Mueller matrices of various components.
The program is adequately supported in terms of research and technical staff. This study also combines the efforts of several collaborators, including senior engineers and scientists at CERDEC’s Intelligence and Information Warfare Directorate and its Electronic Warfare Air/Ground Survivability Division and a professor at the University of North Carolina at Charlotte (UNC); and so, it can potentially access UNC’s facilities for experimental studies. Its content fits well in the technology portfolio of CERDEC and fills an appropriate research niche critical to various Army missions. Key customers include (1) the project manager for aircraft survivability equipment, including infrared countermeasures and missile and radar warning; and (2) the product manager for vehicle protection suites, including hard kill, soft kill, active protection, hostile fire detection, pre-shot detection, laser warning receivers, obscurants, reactive armor, active blast, and signature management.
The methodology and technical approach used in this program has been reported at an International Society for Optics and Photonics (SPIE) meeting, has been published in a refereed journal, and is based on a well-established model of detection of Mueller matrices of scattered light. Mueller and Stokes matrices are well-established techniques that are widely used to characterize the polarization state of detected light, and so their use in evaluating laboratory tests is suitable.
Current Army-sponsored research in this domain addresses the characterization of both human-made objects and natural scenery for the purposes of intelligent discrimination using active (laser) illumination and eventually using passive sensors that fully image broader-band target details to attain early warning of threats. The use of lasers is potentially more effective, because laser illumination polarization and
wavelength are well defined, whereas noncoherent broadband light has more wavelength information but less well-defined polarization. And so, in addition to simple intensity imaging of potential threats, polarization image sensing modes may allow enhanced rejection of backgrounds as well as characterizing features that disclose the pose, symmetry, or even the identity of objects over useful operational ranges, including standoff distances (where spatial resolution may be compromised). Such intelligent systems offer the potential for augmenting the warfighter’s threat engagement capabilities or even supplying information autonomously to enhance weapon systems effectiveness.
Polarization is a complex feature of light that changes its state when scattered off objects and is more sophisticated than just measuring pure intensity. Polarization offers potential gains for clutter rejection, increased operational range, and possibly object orientation and symmetry estimation. One application is the Army concern for rotary wing aircraft protection, which is being addressed by research characterizing the utility of polarization to augment laser and vision sensors. Laboratory measurements recapitulate full-scale geometries encountered in combat. Polarization rotation is typically something that humans ignore or reject, but it offers the potential to provide subtle clues about a sensed object’s orientation and surface properties, and it affords better background rejection. By leveraging such technology using advanced sensors, the warfighter can widen the missions that can be pursued and expand the envelope of operational ranges.
This research is closely allied with the Army’s night vision work and overlaps numerous mission requirements and a variety of desired operational capabilities. The research requires the collection of the complex reflection properties of surfaces and object shapes to characterize natural and human-made objects as well as validating models that support proof-of-concept design studies. This approach tests hypotheses for system effectiveness using the above models in a more cost-effective manner and needs to be followed by field experimentation before substantial funding is applied to actual hardware system design. Complex object reflection models, even for elementary test objects, are constructed and incorporated into laboratory measurements to enable a rigorous scientific validation. Preliminary efforts show general agreement with extant measurements from other research studies. Further work will be required to extrapolate performance for more realistic field tests employing greater variations in object geometry, surface morphologies, shapes, textures, and wavelengths to expand the utility of this approach to realistic engagement scenarios. Preliminary measurements and analyses of laser signatures and solar clutter indicate the discrimination potential of these findings, but further statistical tests remain to be accomplished to fully prove actual realistic and operationally effective performance through more applied and collaborative research. Future work will address additional sample bench testing as well as upgrading to an expanded set of modeling, field-testing, and simulation efforts.
This research is well focused on Army mission needs and appears to have both basic and applied elements in its approach. Its basis in the theory of scattering from finite surfaces is well grounded. The measurement tools appear to be adequate but will require expansion to additional sensors and illuminators to accommodate finite beamwidths, incoherent illumination (which would need to be discriminated against a broadband illuminator), and broadband sources and sensors. The hypotheses generated appear to be well defined, and the selection of polarization as a critical variable offers the possibility that such a singular feature expressed in the Mueller matrix (in addition to wavelength and spatial extent) could be critical in achieving significant performance gains over conventional imaging sensors. This includes enhanced clutter rejection and pose and symmetry estimation without necessarily fully resolving the target. Issues were addressed concerning aliasing from the mismatch between laser modulation and imaging frame rate, indicating a careful research methodology to avoid potential sensor artifacts from compromising closer-to-optimal performance. The uses of noncoherent illumination and wideband imagery, however, need to be considered and their potential utility assessed before adding them as
additional features. Doing so would potentially expand the variety of sensors accessible, despite the fact that wavelength and angular resolution can complicate and even partially compromise acquiring clearly separable data for feature extraction. This research is in an early stage, and a full agenda of research has not fully emerged, although the Ph.D. researcher is aware of some of these caveats that need to be accommodated.
CERDEC Crosscutting Findings
CERDEC’s ILIR program is funding and directing fundamental research and development in electronics that is designed to achieve transitions to advanced development and, ultimately, fielded systems. The ILIR is focused on specific areas for technology innovations as well as specific system enhancements in the areas of sensing, communications, navigation, energy harvesting, and efficient mobility, while serving missions that address command, control, communication, computers, cybersecurity, intelligence, surveillance, and reconnaissance. Although this research is defined as basic, it often contains elements of and bears a direct benefit to related efforts in applied research that directly impacts diverse fielded capabilities.
The ILIR culture at CERDEC is in a nascent stage and, as such, is still evolving the necessary oversight, staff guidance, and mentoring that would be well tuned to the Army’s fundamental research needs as well as being well connected to other branches of Army research. CERDEC conducts internal reviews using its senior technical staff, including Senior Technical (STs) and management staff. However, CERDEC does not avail itself of external reviewers. At a minimum, it needs to consider outreach to ARL staff, especially Army Research Office (ARO) program managers. To improve research quality and to develop staff skills, outreach to external reviewers is a logical step. Given the relatively low level of funding and the small number of projects, CERDEC needs to regularly assess the effective number of projects, the distribution of funds-per-project, and project lifetime to optimize the total innovation and impact of CERDEC on the Army mission. In transitioning to a longer-term strategy, collaboration with other Army research laboratories needs to be fostered to make the impact of CERDEC more significant and broader in scope, consistent with its mission.
The stated goal of the ILIR program at CERDEC is to maintain research competence. To accomplish this CERDEC needs to incorporate suitable tools for assessing research success, including a range of metrics, such as the number of publications in high-impact journals, number of citations, or participation in external panels and boards. This assessment also needs to reflect a recurrent assessment of its strategic or mission focus, as well as a comparison with other Army laboratory missions, strategies, competencies, and joint service trends. CERDEC has attempted to invest in early doctoral candidate research, for which its budget seems initially well suited, but as current research expands, additional career opportunities in basic research and professional maturation incentives and recognition need to reflect that growth.
Recommendation: CERDEC should collaborate with other Army laboratories, including the Army Research Laboratory and the Army Research Office, to assess and improve research quality, develop staff skills, and make its impact more significant and broader in scope.
Recommendation: CERDEC should incorporate suitable tools for assessing research success, including a range of metrics, such as the number of publications in high-impact journals or participation in external panels and boards.
