Signature Reduction Research Articles

Inverted cones grating for flexible metafilter at optical and infrared frequencies

By combining the antireflective properties from gradual changes in the effective refractive index and cavity coupling from cone gratings and the efficient optical behavior of a tungsten film, a flexible filter showing very broad antireflective properties from the visible to short wavelength infrared region and, simultaneously, a mirror-like behavior in the mid-infrared wavelength region and long-infrared wavelength region has been conceived. Nanoimprint technology has permitted the replication of inverted cone patterns on a large scale on a flexible polymer, afterwards coated with a thin tungsten film. This optical metafilter is of great interest in the stealth domain where optical signature reduction from the optical to short wavelength infrared region is an important matter. As it also acts as selective thermal emitter offering a good solar-absorption/infrared-emissivity ratio, interests are found as well for solar heating applications.

Design of Degaussing System and Demonstration of Signature Reduction on Ship Model through Laboratory Experiments

Magnetic fields of naval vessels are widely used all over the world for detection and localization of naval vessel. Magnetic Anomaly Detectors (MADs) installed on air borne vehicles are used to detect submarine operating in shallow waters. Underwater mines fitted with magnetic sensor are used for detection and destruction of naval vessels in the times of conflict. Reduction of magnetic signature of naval vessels is carried out by deperming and installation of degaussing system onboard the vessel. Present paper elaborates details of studies carried out at Magnetics Division of Naval Science and Technological Laboratory (NSTL) for minimizing the magnetic signature of naval vessels by designing a degaussing system. Magnetic fields of a small ship model are predicted and a degaussing system is designed for reducing magnetic detection. The details of the model, methodology used for estimation of magnetic signature of the vessel and design of degaussing system is brought out in this paper with details of experimental setup and results.

Wideband Radar Cross Section Reduction of Slot Antennas Arrays

A comprehensive analysis aimed at reducing the radar cross section (RCS) of array antennas, preserving at the same time their radiating performance, is presented. A microstrip slot array is considered as a test case to illustrate the proposed strategy for radar cross section reduction (RCSR). It is shown that a remarkable reduction of the radar signature can be accomplished over a frequency band as wide as two octaves by employing an array of periodic resistive elements in front of the radiating apertures. The monostatic and bistatic RCS of the proposed structures are investigated both for normal and oblique incidence. Different arrangements and geometries of the periodic resistive pattern are thoroughly analyzed showing the benefits and the drawbacks in terms of antenna gain and level of the scattered fields. Furthermore, the use of metallic parasitic elements for enhancing the antenna gain is considered, and the scattering phenomena caused by their presence are addressed, taking into account the appearance of grating lobes. The antenna designs are also analyzed by resorting to a bidimensional color plot presenting the variation of the reradiated field both in frequency and spatial domain. The guidelines illustrated by the proposed examples can be easily applied to other antenna architectures.

Ordering and structural changes at the glass–liquid transition

Ordering types of amorphous solids and structural changes which occur at glass–liquid transition are discussed focusing on configuron percolation theory (CPT) of glass transition. The glass transition temperature can be calculated using bond thermodynamic parameters e.g. enthalpy Hd and entropy of formation Sd. Explicit equations have been derived to assess Hd and Sd from available data on viscosity of amorphous materials using the CPT viscosity equation. A universal equation for the variable activation energy of viscous flow Q(T) has been found. The glass–liquid transition is accompanied by formation of a percolation macroscopic cluster made up of broken bonds – configurons – which are dynamic in nature. The characteristic linear size of dynamic clusters formed is given by correlation length which universally depends on formation Gibbs free energy of configurons Gd=Hd−TSd and becomes macroscopic at glass transition. Fractal-type medium range order (MRO) is revealed at correlation length sizes and homogeneous and isotropic disordered state (DS) characteristic for macroscopic sizes larger than the correlation length. The reduction of topological signature (Hausdorff dimensionality) of disordered bonding lattice from 3 for glass to fractal Df=2.4−2.8 for melt is the main signature change to explain the drastic changes of material behaviour at glass transition.

무인항공기 노즐 형상 변화에 따른 IR 신호 영향성 연구

The effects of various nozzle configurations on infrared signature are investigated for the purpose of analysing the infrared signature level of aircraft propulsion system. A virtual subsonic aircraft is selected and then a circular convergent nozzle, which meets the mission requirements, is designed. Convergent nozzles of different configurations are designed with different geometric profiles. Using a compressible Navier-Stokes-Fourier CFD code, an analysis of thermal flow field and nozzle surface temperature distribution is conducted. From the information of plume flow field and nozzle surface temperature distribution, IR signature of plume and nozzle surface is calculated through the narrow-band model and the RadThermIR code. Finally, qualitative information for IR signature reduction is obtained through the analysis of the effects of various nozzle configurations on IR signature.

Microwave Absorption of Substituted M-type Lead Hexaferrite Nanopowders

M-type lead hexaferrites with compositions of PbFe12O19 and PbSnZnFe10O19 were synthesized by the citrate sol–gel method. The structural and magnetic properties of resultant particles were investigated by X-ray diffraction (XRD), transmission electron microscope (TEM), vibrating sample magnetometer (VSM) and vector network analyzer. The magnetic properties such as saturation magnetization (Ms) and coercivity (Hc) were calculated from the hysteresis loops. Microwave absorption properties of ferrite–polymer composites prepared with different ferrite ratios of 50%, 60%, 70% and 80% have been investigated in the frequency range of 12–20 GHz. The composite powder with 80 wt% lead ferrite possesses good microwave absorption properties. The minimum reflection loss of the composite powder reaches –30 dB at the thickness of 2 mm for composite powder with 80 wt% ferrite. The composite with 80% ferrite content has shown a minimum reflection loss of -24.5 dB at 18.6GHz with the -15 dB bandwidth over the extended frequency range of 16.3– 19.4GHz for an absorber thickness of 1.8 mm. The prepared composites can fruitfully be utilized for suppression of electromagnetic interference (EMI) and reduction of radar signatures (stealth technology). Keywords: Lead hexaferrite, nano-crystalline materials, microwave absorption, magnetic properties.

함정 적외선 신호의 관리방법 연구

In the development process of new naval ships, it is necessary to make the effort of the signature management and reduction of ship infrared(IR) signature to increase the ship survivability(susceptibility). So far the ship's contrast radiant intensity is used as a ship IR signature design criteria during the naval ship design stages. However, nowaday it is in a state of disorder at the basic design stage because of the lack of any related studies and methods. In this study, the IR signature management methods for improving the signature reduction and ship survivability are suggested by the comparison analysis of the advantages and disadvantages of signature management techniques. And also the criteria for the ship signature management are suggested when considering the infrared signature measuring assets and sea trial environments of the Korean peninsula.

Thiopurine treatment in patients with Crohn's disease leads to a selective reduction of an effector cytotoxic gene expression signature revealed by whole-genome expression profiling

Crohn's disease (CD) is characterized by chronic inflammation of the gastrointestinal tract, as a result of aberrant activation of the innate immune system through TLR stimulation by bacterial products. The conventional immunosuppressive thiopurine derivatives (azathioprine and mercaptopurine) are used to treat CD. The effects of thiopurines on circulating immune cells and TLR responsiveness are unknown. To obtain a global view of affected gene expression of the immune system in CD patients and the treatment effect of thiopurine derivatives, we performed genome-wide transcriptome analysis on whole blood samples from 20 CD patients in remission, of which 10 patients received thiopurine treatment, compared to 16 healthy controls, before and after TLR4 stimulation with LPS. Several immune abnormalities were observed, including increased baseline interferon activity, while baseline expression of ribosomal genes was reduced. After LPS stimulation, CD patients showed reduced cytokine and chemokine expression. None of these effects were related to treatment. Strikingly, only one highly correlated set of 69 genes was affected by treatment, not influenced by LPS stimulation and consisted of genes reminiscent of effector cytotoxic NK cells. The most reduced cytotoxicity-related gene in CD was the cell surface marker CD160. Concordantly, we could demonstrate an in vivo reduction of circulating CD160+CD3−CD8− cells in CD patients after treatment with thiopurine derivatives in an independent cohort.In conclusion, using genome-wide profiling, we identified a disturbed immune activation status in peripheral blood cells from CD patients and a clear treatment effect of thiopurine derivatives selectively affecting effector cytotoxic CD160-positive cells.

Revealing ordering and structural changes at glass transition

ABSTRACTOrdering types in the disordered structure of amorphous materials and structural changes which occur at glass-liquid transition are discussed revealing medium range order and reduction of topological signature of bonding system.

Carbon nanotube composite for electromagnetic interference shielding and thermal signature reduction

We have developed a new method of electron beam cross-linking to improve electrical conductivity without deteriorating optical transparency of carbon nanotube films. Nano- and micro-patterning on carbon nanotube films are found to be effective in improving optical transparency, but comes at a cost of reducing electrical conductivity. Thermal conductivity of carbon nanotube films can be significantly reduced by nanopatterning. A decreased thermal conductivity may not be all negative, as it could help thermal energy harvesting through increasing Seebeck coefficient and ZT. Multifunctional nanocomposites of carbon nanotube and poly( N-isopropylacrylamide) were prepared and they showed high electromagnetic interference shielding efficiencies and thermal signature reduction while remain optically transparent.

Barium titanate flakes based composites for microwave absorbing applications

Barium titanate (BT) has attained research focus in recent past owing to considering its high dielectric constant and stealth capabilities in microwave region. Shape effects of BT viz. powder, micron size flakes, nano particles and nanotubes have been studied vastly for its stealth capabilities. Present study aims at the preparation of millimetric size barium titanate flakes (BTFs) via controlled sol-gel process followed by tape casting. BTFs were mixed in varied weight ratio (50-90 wt.%) with polyurethane resin to fabricate composite laminates. Electromagnetic properties measurement in X and Ku band revealed high values of real and imaginary permittivity. Reflection loss measurements demonstrated more than 20 dB loss in wide frequency range (11.4-13.6 GHz). For single layer microwave absorber, reflection loss values have been calculated and it is observed that calculated and measured reflection loss values are in good agreement to each other. Developed material can find applications in broadband radar signature reduction.

Synthesis and absorbing mechanism of two-layer microwave absorbers containing polycrystalline iron fibers and carbonyl iron

Polycrystalline iron fibers were fabricated by α-FeOOH fiber precursors. Two-layer microwave absorber had been prepared by as-prepared polycrystalline iron fibers and carbonyl iron. The structure, morphology and properties of the composites were characterized with X-ray diffraction, scanning electron microscope and Network Analyzer. The complex permittivity and reflection loss (dB) of the composites were measured employing vector network analyzer model PNA 3629D vector in the frequency range between 30 and 6000MHz. The thickness effect of the carbonyl iron layer on the microwave loss properties of the composites was investigated. A possible microwave-absorbing mechanism of polycrystalline iron fibers/carbonyl iron composite was proposed. The polycrystalline iron fibers/carbonyl iron composite can find applications in suppression of electromagnetic interference, and reduction of radar signature.

Infrared properties of randomly oriented silver nanowires

We experimentally investigated the infrared properties of a set of randomly oriented silver nanowires films deposited onto glass substrate. Infrared emission of the obtained films was characterized in the long infrared range, i.e., 8–12 μm, by observing their temperature evolution under heating regime with a focal plane array infrared camera as well as a thermocouple. The obtained experimental results showed that the infrared emission from a mesh composed of silver nanowires might be tailored by opportunely assessing preparation condition, such as the metal filling factor. From the theoretical point of view, the real and imaginary part of the electrical permittivity components were retrieved from the calculations of effective permittivities of in-plane randomly oriented metallic wires, thus giving the refractive index and extinction coefficients for the four different silver nanowires meshes. Due to the correspondence between emissivity and absorbance, the experimental results are interpreted with the reconstructed corresponding absorbance spectra, thus suggesting that these coatings are suitable for infrared signature reduction applications.

엔진 노즐 형상이 Plume 적외선 신호에 미치는 영향에 관한 연구

A study on the effect of engine nozzle configuration on the engine plume Infra-red (IR) signature characteristics is performed. Configuration design of an engine nozzle with high aspect ratio to reduce IR signature level and a cylindrical nozzle which is typically used for conventional aircraft which does not require IR signature reduction is performed. And CFD analysis for the two nozzles is performed to compare the flowfields characteristics of the two nozzles. Finally IR signature analysis for the two nozzles is accomplished to calculate the total intensity level at mid-wave infra-red and investigate the differences of IR signature characteristics between the two nozzles.

Organic matter sources for tidal marsh sediment over the past two millennia in the Minho River estuary (NW Iberian Peninsula)

Environmental changes during the last 2 millennia in the Minho River tidal marsh (NW Portugal–Spain border) were reconstructed. Changes in the sources of organic matter (OM) delivered to the marsh were evaluated from elemental, isotopic and molecular composition using a 1m sediment core. Carbon isotopic composition (δ13C) and organic carbon to total nitrogen ratio (Corg/N) provided valuable information concerning the origin of the OM. These parameters indicated a major input from land plants, reaching a maximum at 1100–1200 and 1750–1850AD. These periods match with major flood events in the NW of the Iberian Peninsula, as reported by several authors. A significant reduction in the terrestrial signature occurred at 6–4cm (ca. 1960–1985AD), which is contemporaneous with the construction of several major dams on the Minho River. The distribution of selected lipid biomarkers, including n-alkanes, n-fatty acids and n-alkan-2-ones and specific parameters derived from the molecular distributions, were useful for refining bulk geochemical results. Long chain n-alkanes with an odd number of carbons are indicators of soil-and vascular plant-derived terrestrial OM and were dominant throughout the core. In addition, a greater contribution of plankton-derived lipids was observed in the sections corresponding to ca. 1960–1985AD (6–4cm) and ca. 100–200AD (96–94cm). Although different degradation rates for individual compounds might have partly affected biomarker assemblages, the variations could be attributed to a sharp decrease in the freshwater contribution to the Minho River estuary (dam construction) and a possible marine highstand, respectively. In addition, several parameters suggested changes in land use (including deforestation and farming) and probably the effects of mining exploitation during the Roman occupation of the area.

Synthesis and absorbing mechanism of two-layer microwave absorbers containing flocs-like nano-BaZn1.5Co0.5Fe16O27 and carbonyl iron

Flocs-like nano-barium ferrite (BaZn1.5Co0.5Fe16O27) was synthesized by sol–gel method using the absorbent cotton as template for the first time. A possible mechanism for the formation of flocs-like nano-barium ferrite had been proposed. Two-layer microwave nano-BaZn1.5Co0.5Fe16O27/carbonyl iron composite has been prepared by as-prepared material. The structure, morphology and properties of the composites are characterized with X-ray diffraction (XRD), scanning electron microscope (SEM), Net-work Analyzer. The complex permittivity and reflection loss (dB) of the composites have been measured at different microwave frequencies from 30 MHz to 6000 MHz employing vector network analyzer model PNA 3629D vector. The effect of the layer thickness of carbonyl iron on the microwave loss properties of the composites is investigated. A possible microwave absorbing mechanism of nano-BaZn1.5Co0.5Fe16O27/carbonyl iron composite has been proposed. The nano-BaZn1.5Co0.5Fe16O27/carbonyl iron composite can find applications in suppression of electromagnetic interference (EMI), and reduction of radar signature.

레이더 신호 간섭의 최소화를 위한 풍력 발전기 설계

The use of wind energy is gaining importance because of its many advantages. Nations worldwide are promoting the installation of wind farms to produce electricity in an attempt to tackle climate change and increasing oil costs. But, wind turbines can generate undesired signals which disturb the performance of military radar systems. Because the current generation of on and off-shore three bladed wind turbines have radar signatures consistent with their very large physical size. So this study considers the options available for the reduction of wind turbine radar signature and presents solutions for each of the main external turbine components. The radar signature reduction approaches are based on existing technologies developed for aerospaces stealth applications. However, the realization of these for the purposes of reduction wind turbine radar signatures is a novel development, particularly in the solutions proposed. This paper is presented techniques which reduce radar signatures of wind turbine. We know that radar signatures of wind turbine reduce by using these techniques.

A review and analysis of microwave absorption in polymer composites filled with carbonaceous particles

Carbon (C) is a crucial material for many branches of modern technology. A growing number of demanding applications in electronics and telecommunications rely on the unique properties of C allotropes. The need for microwave absorbers and radar-absorbing materials is ever growing in military applications (reduction of radar signature of aircraft, ships, tanks, and targets) as well as in civilian applications (reduction of electromagnetic interference among components and circuits, reduction of the back-radiation of microstrip radiators). Whatever the application for which the absorber is intended, weight reduction and optimization of the operating bandwidth are two important issues. A composite absorber that uses carbonaceous particles in combination with a polymer matrix offers a large flexibility for design and properties control, as the composite can be tuned and optimized via changes in both the carbonaceous inclusions (C black, C nanotube, C fiber, graphene) and the embedding matrix (rubber, thermoplastic). This paper offers a perspective on the experimental efforts toward the development of microwave absorbers composed of carbonaceous inclusions in a polymer matrix. The absorption properties of such composites can be tailored through changes in geometry, composition, morphology, and volume fraction of the filler particles. Polymercomposites filled with carbonaceous particles provide a versatile system to probe physical properties at the nanoscale of fundamental interest and of relevance to a wide range of potential applications that span radar absorption, electromagnetic protection from natural phenomena (lightning), shielding for particle accelerators in nuclear physics, nuclear electromagnetic pulse protection, electromagnetic compatibility for electronic devices, high-intensity radiated field protection, anechoic chambers, and human exposure mitigation. Carbonaceous particles are also relevant to future applications that require environmentally benign and mechanically flexible materials.

Prediction of the Rear Fuselage Temperature with Radiation Shield

� Abstract—In order to enhance the aircraft survivability, the infrared signatures emitted by hot engine parts should be determined exactly. For its reduction it is necessary for the rear fuselage temperature to be decreased. In this study, numerical modeling of flow fields and heat transfer characteristics of an aircraft nozzle is performed and its temperature distribution along each component wall is predicted. The radiation shield is expected to reduce the skin temperature of rear fuselage. The effect of material characteristic of radiation shield on the heat transfer is also investigated. Through this numerical analysis, design parameters related to the susceptibility of aircraft are examined. Keywords—Infrared signature, Nozzle flow, Radiation shield, Rear fuselage temperature, Susceptibility I. INTRODUCTION URVIVABILITY of aircraft has been a one of the important factors in modern battlefield in which the standard of technology determines the supremacy. Military forces are engaged in equipping a stealth function to the fighter plane at the early stage of design. The importance of susceptibility problem has been strengthened related to detection and tracking by enemy missiles or seekers. It is well known that aircraft survivability is threatened by detection using radar and thermal infrared(IR) sensor as well as by primary ways such as visual and sound sources. Several varieties of detection systems have been developed and their technology has been more sensitive, therefore signature reduction technology is excessively in need of development. Advanced countries lead the survivability and susceptibility research (1, 2), but they strongly control the outflow of these technologies overseas. High level of infrared signature emitted by aircraft rear fuselage is an easy target for IR detectors, therefore reduction of IR signature is essential for the improvement of survivability. IR signature can be predicted by figuring out the distribution of the rear fuselage temperature, because IR signature is a function of temperature. The numerical analysis of nozzle flow needs to be preceded to estimate the skin temperature precisely,

Multidisciplinary Optimization of Supersonic Aircraft Including Low-Boom Considerations

This paper presents a multidisciplinary optimization framework developed by the authors and applied to small-size supersonic aircraft. The multidisciplinary analysis suite is based on the combination of low (empirical) and high-fidelity computational fluid dynamics (CFD) and computational structure mechanics (CSM) tools for predicting the overall aircraft performance and the sonic boom overpressure at supersonic flight, which represents the most challenging environmental constraint for supersonic aircraft. The analysis suite is coupled with a multi-objective optimization strategy for quantifying the trade-off between the maximum take-off weight, mission range, and the sonic boom overpressure. The optimization framework is applied to a small-size supersonic business-jet cruising at Mach number M = 1.8 and featuring a double delta wing. The trade-offs between disciplines are well captured and an optimized configuration achieving the target mission range with a lower maximum take-off weight, and a moderate sonic boom signature is obtained through changes in wing dihedral and sweep. A more drastic reduction of the sonic boom signature is also obtained but at the cost of a significant reduction of the aircraft performance.