Defense-related Applications Research Articles

Critical quality indicators of high-performance polyetherimide (ULTEM) over the MEX 3D printing key generic control parameters: Prospects for personalized equipment in the defense industry

Additive Manufacturing (AM) can provide customized parts that conventional techniques fail to deliver. One important parameter in AM is the quality of the parts, as a result of the material extrusion 3D printing (3D-P) procedure. This can be very important in defense-related applications, where optimum performance needs to be guaranteed. The quality of the Polyetherimide 3D-P specimens was examined by considering six control parameters, namely, infill percentage, layer height, deposition angle, travel speed, nozzle, and bed temperature. The quality indicators were the root mean square (Rq) and average (Ra) roughness, porosity, and the actual to nominal dimensional deviation. The examination was performed with optical profilometry, optical microscopy, and micro-computed tomography scanning. The Taguchi design of experiments was applied, with twenty-five runs, five levels for each control parameter, on five replicas. Two additional confirmation runs were conducted, to ensure reliability. Prediction equations were constructed to express the quality indicators in terms of the control parameters. Three modeling approaches were applied to the experimental data, to compare their efficiency, i.e., Linear Regression Model (LRM), Reduced Quadratic Regression Model, and Quadratic Regression Model (QRM). QRM was the most accurate one, still the differences were not high even considering the simpler LRM model.

Smart mid-infrared metasurface microspectrometer gas sensing system

Smart, low-cost and portable gas sensors are highly desired due to the importance of air quality monitoring for environmental and defense-related applications. Traditionally, electrochemical and nondispersive infrared (IR) gas sensors are designed to detect a single specific analyte. Although IR spectroscopy-based sensors provide superior performance, their deployment is limited due to their large size and high cost. In this study, a smart, low-cost, multigas sensing system is demonstrated consisting of a mid-infrared microspectrometer and a machine learning algorithm. The microspectrometer is a metasurface filter array integrated with a commercial IR camera that is consumable-free, compact ( ~ 1 cm3) and lightweight ( ~ 1 g). The machine learning algorithm is trained to analyze the data from the microspectrometer and predict the gases present. The system detects the greenhouse gases carbon dioxide and methane at concentrations ranging from 10 to 100% with 100% accuracy. It also detects hazardous gases at low concentrations with an accuracy of 98.4%. Ammonia can be detected at a concentration of 100 ppm. Additionally, methyl-ethyl-ketone can be detected at its permissible exposure limit (200 ppm); this concentration is considered low and nonhazardous. This study demonstrates the viability of using machine learning with IR spectroscopy to provide a smart and low-cost multigas sensing platform.

Polarization Independent Ultra-wideband Meta-material Absorber Using Conductive Ink Resonator

A wideband meta-material absorber with square and circular split rings that is based on a frequency selective surface of conductive ink is proposed. With over 90% absorptivity, the structure demonstrates broad absorption for the C, X, KU and K bands, as well as polarization independent characteristics for both TE and TM, at angles of up to 45°. Research has been performed to better understand the absorption phenomenon by looking into real and imaginary permittivity, permeability, normalized impedance, and surface current density. The meta-material absorber (MA) discussed in this study finds use in defense-related applications, such as radar surveillance, stealth technology, terrestrial and satellite communications.

Polarization-independent wideband meta-material absorber based on resistor-loaded hexagonal ring resonators

A polarization-independent meta-material-based absorber with wideband response is presented in this study. The proposed absorber’s unit cell consists of a resistance-loaded metallic hexagonal ring and four rectangular metal strips placed inside the hexagonal ring patterned on the upper surface of a dielectric substrate. The absorber exhibits wideband absorption with absorptivity more than 90% in the frequency range 7.14 to 13.68 GHz. The Full-Width Half Maxima (FWHM) of the absorber is 8.8 GHz (5.2–14 GHz). The four-fold symmetrical structure of the absorber confirms polarization-insensitive behaviour. The absorber performance is also validated with fabrication and measurement. There is a fair degree of agreement between simulated and measured results. The novelty of the proposed absorber is having wideband absorption with high packing density due to its hexagonal shape. The metamaterial absorber finds its use in defence-related applications such as radar surveillance, stealth technology, terrestrial communications, and satellite communication.

Uncertain multi-objective dynamic weapon-target allocation problem based on uncertainty theory

<abstract><p>The weapon-target allocation (WTA) problem is a fundamental subject of defense-related applications research, and previous studies assume that the parameters in the model are determinate. For the real battlefield, asymmetric information usually leads to the failure of the above assumption, and there are uncertain factors whose frequency is hard to pinpoint. Based on uncertainty theory, we study a WTA problem in indeterminate battlefield in this paper. First, we analyze the uncertain factors in indeterminate battlefield and their influence on WTA problem. Then, considering the target threat value, the protected asset value and the extra cost of interception as uncertain variables, the uncertain multi-objective dynamic WTA (UMDWTA) model is established, where three indices including the value of destruction of targets, the value of surviving assets and the cost of operation are regarded as objective functions, and on this basis, an equivalent transformation is presented to convert the UMDWTA model into a determinate multi-objective programming (MOP) problem by expected value and standard deviation principle. To solve the proposed model efficiently, an improved multi-objective evolutionary algorithm based on decomposition (MOEA/D) is designed, which employs three new evolutionary operators and the weight vectors adaptation mechanism to improve the convergence and uniformity of the Pareto front obtained. Finally, a case of the UMDWTA problem is carried out to be solved by the designed algorithm, and the results verify the feasibility of the proposed model.</p></abstract>

Research on Dynamic Weapon Target Assignment Based on Cross-Entropy

The weapon target assignment (WTA) is a classical problem of defense-related applications which is proved to be a NP-complete problem. In this paper, a practical and available dynamic weapon target assignment (DWTA) formulation is given which incorporates two meaningful and conflicting objectives, that is, minimizing weapon costs and maximizing combat benefits. As we know, heuristic methods have some shortcomings such as slow convergence speed and local optimum in solving the nonlinear integer optimization problem. To this end, a novel DWTA algorithm based on cross-entropy (CE) method is introduced, where the resources requirement condition for targets is taken into consideration. The CE method associates an estimation problem with the DWTA optimization problem, and then, the estimation problem is transformed into a convex optimization problem. The Karush–Kuhn–Tucker conditions are applied to solve the convex optimization problem, and the iteration formulas to find the optimal solution are deducted. Furthermore, in order to verify the performance of CE method in dealing with the DWTA problem, several simulations in different combat scenarios are implemented. The results reveal that, compared with the benchmark heuristic and Monte-Carlo (MC) methods, there are some notable advantages in solving the DWTA problem based on CE method with regard to the solution quality and time consumption.

Design and Analysis of a Variable Buoyancy System for Efficient Hovering Control of Underwater Vehicles with State Feedback Controller

The design process for Variable Buoyancy System (VBS) is not known in full, and existing approaches are not scalable. Furthermore, almost all the small size Autonomous Underwater Vehicles/Gliders (AUVs/G’s) use very low capacity of buoyancy change (in the range of few milliliters) and the large size AUVs require large buoyancy change. Especially for adverse weather conditions, emergency recovery or defense-related applications, higher rate of rising/sinking (heave velocity) is needed along with an ability to hover at certain depth of operation. Depth of UVs can be controlled either by changing the displaced volume or by changing the overall weight and, herein, our focus is on the later. This article presents the problem of design and analysis of VBS for efficient hovering control of underwater vehicles at desired depth using the state feedback controller. We formulate and analyze the design and analysis approach of VBS using the fundamental of mechanics, system dynamics integration and control theory. Buoyancy is controlled by changing the overall weight of the vehicle using the ballasting/de-ballasting of water in ballast tanks through the use of Positive Displacement Pump (PDP) for control in heave velocity and hovering depth. Furthermore, detailed mass metric analysis of scalable design of VBS for different buoyancy capacities is performed to analyze the overall performance of the VBS. Also, the performances of AUVs integrated with VBS of different buoyancy capacities are investigated in both the open loop and closed loop with the LQR state feedback controller. Hovering performance results are presented for three Design Examples (DEs) of AUVs with 2.8 m, 4.0 m and 5.0 m length and they are integrated with various buoyancy capacities at 9 kg/min rate of change of buoyancy. Results indicate that the AUVs achieve the desired depth with almost negligible steady state error and when they reach the desired hovering depth of 400 m the maximum pitch angle achieved of 16.5 degree for all the Des is observed. Maximum heave velocity achieved during sinking is 0.44 m/s and it reduces to zero when the vehicle reaches the desired depth of hovering. The presented computer simulation results indicate good performance and demonstrate that the designed VBS is effective and efficient in changing the buoyancy, controlling and maintaining the depth, controlling the heave velocity and can be used in rescue/attack operations of both the civil and defense UVs.

Influence of Design Parameters on Multilayered Nanoplasmonic Structures in Modified Kretschmann-Raether Configurations

Surface Plasmon Resonance (SPR) technique has been of recent interest in many fields such as biological and chemical sensing, defense-related applications, etc. The introduction of graphene sheet (metal-like optical properties) over a thin-film layers plays a significant role in generating SPR. Different nanoplasmonic structures like Coupled Waveguide SPR (CWSPR) and Long Range SPR (LRSPR) are considered with modified Kretschmann-Raether configurations for different wavelengths in visible range for plasmonic sensors application. Characteristic Transfer Matrix (CTM) method in MATLAB environment is employed to obtain the theoretical results of LRSPR-based nanoplasmonic structures. Based on different compositions, minimum reflectivity as obtained is reported here. Due to the incorporation of additional graphene thin layer, keeping the angle of incidence constant, the percentage of reflectivity is being increased significantly, thereby reducing the transmission within the layers. With the variation of thickness, refractive index of different layers as well as wavelength of the LASER source, one may optimize the structures to obtain best possible performance.

(Invited) Efficient pH-Gradient-Enabled Microscale Bipolar Interfaces in High Performance Direct Borohydride Fuel Cells

Electrochemical energy conversion devices usually operate at uniform pH or over a narrow pH range. The uniform pH environment of these devices frequently hampers the facility of one of the half-cell reactions. In proton exchange membrane fuel cells (PEMFCs)/ proton exchange membrane water electrolyzers (PEMWEs), where both the anode and cathode operate at acidic pH, the H2 oxidation/evolution reaction is quite facile while the O2 reduction/evolution reaction is sluggish. In anion exchange membrane fuel cells (AEMFCs)/ anion exchange membrane water electrolyzers (AEMWEs), the converse is true. Moreover, the chemical stability of some reactants depends strongly on the pH. Direct borohydride fuel cells (DBFCs), operating with NaBH4 as a fuel and H2O2 as the oxidant have attracted a lot of attention due to their high theoretical cell voltages and tactical advantages, particularly for defense-related applications. DBFCs have a high energy density of 9.3 kWh kg-1 and specific capacity of 5.67 kAh kg-1 based on NaBH4 oxidation in alkaline media [1], although the practical energy density will be lowered upon accounting for the added weight of KOH solution required to stabilise NaBH4. Using liquid hydrogen peroxide as the oxidant, the DBFC is a safe and attractive low temperature power source for unmanned underwater vehicles (UUVs) as they exhibit excellent energy and power density, are safe, given the high flash point of NaBH4, and do not release any gaseous effluents, enabling operation at neutral buoyancy [2]. One challenge for this system is the separation between the anolyte fuel (1.5M NaBH4 in 3M KOH) and catholyte oxidant streams (15% H2O2 in 1.5M H2SO4), while another is the high instability of NaBH4 in acidic or even neutral pH [3]. Herein, a pH-gradient-enabled microscale bipolar interface (PMBI) is demonstrated for maintaining pH control of the anolyte and catholyte compartments of the fuel cell. The PMBI employed to separate anolyte and catholyte was based on an anion exchange membrane (AEM) interface in conjunction with a cation exchange membrane (Nafion®) separator. The DBFC with the PMBI yielded a current density of 330 mA/cm2 at 1.5 V and a promising peak power density of 630 mW cm-2 at 1 V in a 25-cm2 active area cell [4]. Using a recessed planar electrode (RPE) in conjunction with TEM, we show that the PMBI maintained a sharp local pH gradient (0.82 pH units/nm on average) at the electrocatalytic reaction site.

Scattering Cancellation-Based Cloaking for the Maxwell-Cattaneo Heat Waves

In this work we theoretically propose scattering cancellation-based cloaks for heat waves that obey the Maxwell-Cattaneo equation. The proposed cloaks possess carefully tailored diffusivity to cancel the dipole scattering from the object that they surround, and thus can render a small object invisible in the near and far fields, as demonstrated by full-wave finite-element simulations. Mantle heat cloaking is further analyzed and proposed to simplify the design and bring this cloaking technology one step closer to its practical implementation, with promising applications in nanoelectronics and defense related applications.

Improved Precision in Surface-Enhanced Raman Scattering Quantification of Analyte through Dual-Modality Multisite Sensing.

Accurate quantification of analyte using surface-enhanced Raman spectroscopy (SERS) is a desired, yet unfulfilled, ability that could enable a plethora of diagnostic- and defense-related applications. The major hurdles to overcome to achieve this goal are expensive manufacturing for highly ordered and reproducible substrates and low reproducibility of substrates produced through low cost methods. A technology that can set industry standards for manufacturing/processing of SERS substrates is still yet to be achieved. A dual-modality multisite sensing approach was developed, that overcomes the limitations experienced when fabricating bottom-up, reproducible, sensitive, and low-cost SERS substrates. Electrochemistry was combined with SERS for dual-modality sensing to improve precision by adding redundancy and encoding features, thus increasing measurement robustness and predictability. This technique works by calibrating SERS response with respect to active surface area, a parameter known to be proportional to charge, which can be estimated via electrochemical measurements. The dual-modality multisite measurement demonstrates at least 2.8× improvement in assay precision compared to the traditional single-site Raman measurements. The technique yields overall improved precision of measurement and is not limited to any particular SERS substrate or geometry, and thus it can be adapted and incorporated readily in any SERS sensing assay.

Bipolar Polymer Electrolyte Interfaces As Separators for High Performance Direct Borohydride Fuel Cells

Direct borohydride fuel cells (DBFCs), operating with NaBH4 as a fuel and H2O2 as the oxidant have attracted a lot of attention due to their high theoretical cell voltages and tactical advantages, particularly for defense-related applications. DBFCs have a high energy density of 9.3 kWh kg-1 and specific capacity of 5.67 kAh kg-1 based on NaBH4 oxidation in alkaline media [1]. Using liquid hydrogen peroxide as the oxidant, the DBFC is a safe and attractive low temperature power source for unmanned underwater vehicles (UUVs) as they exhibit excellent energy and power density, are safe, given the high flash point of NaBH4, and do not release any gaseous effluents, enabling operation at neutral buoyancy[2]. One challenge for this system is the separation between the anolyte fuel (1.5M NaBH4 in 3M KOH) and catholyte oxidant streams (15% H2O2 in 1.5M H2SO4), while another is the high instability of NaBH4 in acidic or even neutral pH. Herein, a bipolar interface membrane electrode assembly is demonstrated for maintaining pH control of the anolyte and catholyte compartments of the fuel cell. The bipolar interface employed to separate anolyte and catholyte was based on an anion exchange membrane (AEM) interface in conjunction with a cation exchange membrane (Nafion®) separator. Studies of ion-containing block copolymers have provided clear evidence that the phase separation between hydrophilic and hydrophobic phases can produce materials with excellent ionic conductivity [3, 4]. The DBFC with the bipolar interfaces yielded a promising peak power density of 300 mW cm-2 in a 5-cm2 active area cell. Different operating conditions such as catalyst loading, operation temperature, flow rate and thickness of separator were investigated. The bipolar junction offers improved performance in the DBFC when compared with the use of a typical AEM or PEM configuration in the MEA.

Adjoint of Generalized Outflow-Based Functionals Applied to Hypersonic Inlet Design

The continuous adjoint method for the Reynolds-averaged Navier–Stokes (RANS) equations offers an efficient approach for computing gradients of a functional, particularly in high-dimensional design problems where gradient calculations can otherwise be expensive and difficult to obtain. Existing work has generally been limited to the use of a single, simple functional in the formulation of the adjoint. As a result, the full potential of adjoint-based design has not yet been realized. This work focuses on the derivation and implementation of an adjoint formulation of the RANS equations for generalized outflow-based functionals that allows information from external models to be coupled with the high-fidelity gradient calculation, and expands the range and complexity of objectives that can be used. As an example application this is applied to supersonic combustion ramjets (scramjets), which have the potential to enable more efficient transatmospheric flight, airplane-like operations of launch vehicles, and defense-related applications. Challenges in their design can be addressed by optimization as well as by other gradient-dependent techniques. Optimization studies using the generalized outflow-based functional show that different inlet design results are obtained when incorporating full-engine performance as compared with an inlet-only objective, and illustrate a trade-off between inlet surface heat flux and thrust.

A Concept of Minimizing an Electric Power Supply System for Portable Gear and Arms

Abstract Currently a much higher number of portable devices with improved functionality supporting our job-related and social activities require higher and higher capacity and power offered by sources of power supply. Theoretical analysis of the possibility to achieve exploitation features of currently known portable sources of electric current has led the author to a conclusion that even the best solutions will not meet the desired mass and volume magnitudes in relation to the energy supplied. Therefore, if the sources of energy have reached the physically and economically justified capability limits and they are characterized by significantly varied exploitation properties, a solution combining the advantages of various sources of energy through energy management seems to be sensible. In this connection this article presents the idea of a system of energy control, which using available cells will allow for reducing the weight of power supply systems. The considerations are based on defense-related applications, this, however, does not exclude applications for civilian purposes.

Optical Cavity Interrogation for MEMS Accelerometers

MEMS accelerometers utilizing electrostatic, piezoelectric, and magnetic proof mass displacement readout approaches have achieved success in both commercial- and defense-related applications. However, there is a desire for improved acceleration resolution suitable for navigation-grade applications. Optical readout of mechanical displacements has demonstrated high levels of resolution in macro-scale applications including precision movement and placement systems. In addition, optical techniques are common in high performance inertial sensors such as fiber optic gyros and ring laser gyros. Incorporating optical readout approaches into MEMS acceleration devices may yield sufficient resolution to achieve navigation-grade performance. Therefore, the U.S. Army AMRDEC is developing MEMS accelerometers based on optical cavity resonance readout. In the device, an optical cavity is formed between a MEMS proof mass and a reference reflector. A tunable laser excites the cavity on the edge of its resonance peak. Small displacements of the cavity from its rest position are detected by frequency shifts of the resonance, leading to high-resolution proof mass displacement detection and therefore high acceleration resolutions. This paper will present modeling associated with the design concept, as well predictions of device geometries and performance with the goal of achieving less than 1 micro-g bias instability and a velocity random walk of better than 0.2 micro-g/rt.Hz.

File Integrity Maintenance Tool for Secure Information Storage in Cloud

In current scenario, modern technologies have completely changed the lives of the people. Every facility is available online through internet. People do their business through online services by being at home. This changing trend brought the concept of Cloud Computing where various physical servers(may be at different locations) are collaborated together and cloud services are provided to the users in the same fashion. When millions of people access business applications to perform their transactions, there arises a susceptibility for personal information security to get leaked through hackers/intruders etc. [1] [2] [3]. To avoid certain circumstances, data security becomes prime essential component as building block for the development of a safer and convenient system. The users require a prominent and secure portal. The risk levels get enhanced in case of access of highly confidential information through their accounts within the portal such as Banking websites, Defense or brokerage related applications. Safeguard of security through internet becomes streamlined concern for the service providers. A lot of research work has been pursued in order to ensure higher safety levels [4][5][6]. General Terms Cloud Computing, Data Integrity.

One Pot Synthesis of Multifunctional Aramid Aerogels

ABSTRACTAerogels are quasi-stable, low-density, three-dimensional assemblies of nanoparticles, but they are commonly associated with poor mechanical properties. The most successful efforts to improve their mechanical properties involve cross-linking of the skeletal nanoparticles with polymers. However, post gelation cross-linking is time-consuming. Hence, it is reasonable to seek robust all-polymer aerogels among polymers known for their high mechanical strength. As a result, here we report the facile one-pot synthesis of a new class of Kevlar-like aerogels based on the rather underutilized reaction of multifunctional isocyanates and carboxylic acids. The resulting materials are up to 84% v/v porous with surface areas as high as 380 m2 g-1. The ultimate compressive strength per unit density is within 10% equal to that of Kevlar 49. The high specific energy absorption (37 J g-1) and Styrofoam-like thermal conductivity (0.028 W m-1 K-1) combined with thermal stability up to 350 °C render aramid aerogels multifunctional materials suitable for defense, civil and transportation related applications. Upon pyrolysis at 800 °C they can be converted to 80% (v/v) porous, electrically conducting carbons with surface areas as high as 474 m2 g-1.

The Behaviour of Naturally Debonded Composites Due to Bending Using a Meso-Level Model

Numerical simulations and analytical models are increasingly being sought for the design and behaviour prediction of composite materials. The use of high-performance composite materials is growing in both civilian and defence related applications. With this growth comes the necessity to understand and predict how these new materials will behave under their exposed environments. In this study, the displacement behaviour of naturally debonded composites under out-of-plane bending conditions has been investigated. An analytical approach has been developed to predict the displacement response behaviour. The analytical model supports multi-layered composites with full and partial delaminations. The model can be used to extract bulk effective material properties in which can be represented, later, as an ESL (Equivalent Single Layer). The friction between each of the layers is included in the analytical model and is shown to have distinct behaviour for these types of composites. Acceptable agreement was observed between the model predictions, the ANSYS finite element model, and the experiments.

CoFiDS: A Belief-Theoretic Approach for Automated Collaborative Filtering

Automated Collaborative Filtering (ACF) refers to a group of algorithms used in recommender systems, a research topic that has received considerable attention due to its e-commerce applications. However, existing techniques are rarely capable of dealing with imperfections in user-supplied ratings. When such imperfections (e.g., ambiguities) cannot be avoided, designers resort to simplifying assumptions that impair the system's performance and utility. We have developed a novel technique referred to as CoFiDS-Collaborative Filtering based on Dempster-Shafer belief-theoretic framework-that can represent a wide variety of data imperfections, propagate them throughout the decision-making process without the need to make simplifying assumptions, and exploit contextual information. With its DS-theoretic predictions, the domain expert can either obtain a hard” decision or can narrow the set of possible predictions to a smaller set. With its capability to handle data imperfections, CoFiDS widens the applicability of ACF to such critical and sensitive domains as medical decision support systems and defense-related applications. We describe the theoretical foundation of the system and report experiments with a benchmark movie data set. We explore some essential aspects of CoFiDS' behavior and show that its performance compares favorably with other ACF systems.

Molecular basis of the structural stability of a Top7-based scaffold at extreme pH and temperature conditions

The development of stable biomolecular scaffolds that can tolerate environmental extremes has considerable potential for industrial and defense-related applications. However, most natural proteins are not sufficiently stable to withstand non-physiological conditions. We have recently engineered the de novo designed Top7 protein to specifically recognize the glycoprotein CD4 by insertion of an eight-residue loop. The engineered variant exhibited remarkable stability under chemical and thermal denaturation conditions. In the present study, far-UV CD spectroscopy and explicit-solvent MD simulations are used to investigate the structural stability of Top7 and the engineered variant under extreme conditions of temperature and pH. Circular dichroism measurements suggest that the engineered variant Top7(CB1), like Top7, retains its structure at high temperatures. Changes in CD spectra suggest that there are minor structural rearrangements between neutral and acidic environments for both proteins but that these do not make the proteins less stable at high temperatures. The anti-parallel beta-sheet is well conserved within the timescale simulated whereas there is a decrease of helical content when low pH and high-temperature conditions are combined. Concerted alanine mutations along the alpha-helices of the engineered Top7 variant did not revert this trend when at pH 2 and 400K. The structural resilience of the anti-parallel beta-sheet suggests that the protein scaffold can accommodate varying sequences. The robustness of the Top7 scaffold under extreme conditions of pH and temperature and its amenability to production in inexpensive bacterial expression systems reveal great potential for novel biotechnological applications.