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Radiative cooling forms an emerging direction in which objects are passively cooled via thermal radiation to cold space. Cooling materials should provide high thermal emissivity (infrared absorptance) and low solar absorptance, making cellulose an ideal and sustainable candidate. Broadband solar-reflective or transparent coolers are not the only systems of interest, but also more pleasingly looking colored systems. However, solutions based on wavelength-selective absorption generate not only color but also heat and thereby counteract the cooling function. Intended as coatings for solar cells, we demonstrate a transreflective cellulose material with minimal solar absorption that generates color by wavelength-selective reflection, while it transmits other parts of the solar spectrum. Our solution takes advantage of the ability of cellulose nanocrystals to self-assemble into helical periodic structures, providing nonabsorptive films with structurally colored reflection. Application of violet-blue, green, and red cellulose films on silicon substrates reduced the temperature by up to 9 degrees C under solar illumination, as result of a combination of radiative cooling and reduced solar absorption due to the wavelength-selective reflection by the colored coating. The present work establishes self-assembled cellulose nanocrystal photonic films as a scalable photonic platform for colored radiative cooling. Funding Agencies|Knut and Alice Wallenberg foundation; Linkoping University; Wallenberg Wood Science Center; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009 00971]; Swedish Foundation for Strategic Research; Wenner-Gren Foundations; Olle Engkvist Foundation [194-0679]; Swedish Research Council

Radiative cooling passively removes heat from objects via emission of thermal radiation to cold space. Suitable radiative cooling materials absorb infrared light while they avoid solar heating by either reflecting or transmitting solar radiation, depending on the application. Here, we demonstrate a reflective radiative cooler and a transparent radiative cooler solely based on cellulose derivatives manufactured via electrospinning and casting, respectively. By modifying the microstructure of cellulose materials, we control the solar light interaction from highly reflective (> 90%, porous structure) to highly transparent (approximate to 90%, homogenous structure). Both cellulose materials show high thermal emissivity and minimal solar absorption, making them suitable for daytime radiative cooling. Used as coatings on silicon samples exposed to sun light at daytime, the reflective and transparent cellulose coolers could passively reduce sample temperatures by up to 15 degrees C and 5 degrees C, respectively. Funding Agencies|Linkoping University

In this paper the results of development and investigation on textile-based radar absorbing materials for protection against battlefield radar are presented. This research has been carried out within the Project “Adaptive Camouflage for the Soldier” (ACAMSII) which has received funding from the European Union’s Preparatory Action for Defence Research—PADR programme under grant agreement No 800871. To develop the fabrics with microwave shielding and absorbing properties samples of woven fabrics were coated with compositions containing inherently conducting polymers (ICPs), carbon-based formulations or their mixtures. For coating screen printing and knife-over-roll techniques were applied, as our aim was to develop the fabrics coated with conductive layer only on the back side of camouflage pattern printed fabric, that it could be integrated in the military camouflage clothing system. In the radar threat evaluation, as a part of ACAMSII project, it was pointed up that a major threat to dismounted soldiers are battlefield radars commonly operating within X and Ku-bands. Consequently, the investigation of reflection and transmission properties of developed textile fabrics was performed in a frequency range of 6–18 GHz, which cover the defined frequencies relevant to the application. It was found that shielding effectiveness (SE) as well as absorption properties depend not only on the amount and type of conductive paste topped on the fabric, but also resides in the construction parameters of fabrics and their finishing before coating.

The development of new sensing abilities, such as hyperspectral sensors, small man-portable infrared sensors, battlefield radars and faster AI based data processing requires new capabilities of camouflage materials. Military systems also have to work in changing environments calling for adaptivity. ACAMSII is an EU funded project within the Preparatory Action for Defence Research (PADR) programme under grant agreement No 800871. Scientists from Sweden, Germany, Portugal, France, Lithuania and the Netherlands cooperate in the project. ACAMSII conducts applied research on improved Camouflage for the Soldier with purpose to provide increased survivability in diversified environments. The ACAMSII multifunctional camouflage demonstrator consists of three main parts: • The IR adaptivity is realized by integrating phase changing and low emissivity materials in the printed camouflage patterned textile. • Adaption to background colours and lighting conditions in the visible range is managed by operating and driving light emitting diodes (LEDs) embedded in a panel of clothing textile material. The LEDs are controlled by means of a camera and a light sensor placed in the back. Thermochromic materials give further adaptation. • Woven fabric is coated with microwave shielding and absorbing materials reduces the radar signature. For a soldier combat system, not only camouflage properties are of importance but also the comfort properties of the system is evaluated. In this paper emphasis is put on military needs (top-down or market pull) and scientific aspects and technical readiness level of available technology and materials (technology push or down-up), on how to build a consortium in an international collaboration during a pandemic. The concept of EDA Overarching Strategic Research Agenda is introduced and the projects relation to this explained. Only general aspects and results from the three-year project, ending 2021, is presented here whereas specific details of the camouflage system are presented in other papers presented during the session.

Radiative cooling passively removes heat from objects via emission of thermal radiation to cold space. Suitable radiative cooling materials absorb infrared light while they avoid solar heating by either reflecting or transmitting solar radiation, depending on the application. Here, we demonstrate a reflective radiative cooler and a transparent radiative cooler solely based on cellulose derivatives manufactured via electrospinning and casting, respectively. By modifying the microstructure of cellulose materials, we can control the solar light interaction from highly reflective (>90%, porous structure) to highly transparent (≈90%, homogenous structure). Both cellulose materials show strong thermal emissivity and minimal solar absorption, making them suitable for daytime radiative cooling. Used as coatings on silicon samples exposed to sun light at daytime, the reflective and transparent cellulose coolers could passively reduce sample temperatures by up to 32 °C and 15 °C, respectively.

Materials that provide independent control of infrared thermal radiation and haze in the visible could benefit many areas and applications, including clothing, packaging and photovoltaics. Here, we study this possibility for a metamaterial composite paper based on cellulose nanofibrils (CNF) and silicon dioxide (SiO2) microparticles with infrared (IR) Frohlich phonon resonances. This CNF-SiO2 composite shows outstanding transparency in the visible wavelength range, with the option of controlling light diffusion and haze from almost zero to 90% by varying the SiO2 microparticle concentration. We further show that the transparent metamaterial paper could maintain high thermal emissivity in the atmospheric IR window, as attributed to strong IR absorption of both the nanocellulose and the resonant SiO2 microparticles. The high IR emissivity and low visible absorption make the paper suitable for passive radiative cooling and we demonstrate cooling of the paper to around 3 degrees C below ambient air temperature by exposing it to the sky. Funding Agencies|Knut and Allice Wallenberg Foundation via a Wallenberg Scholarship; Knut and Alice Wallenberg foundationKnut & Alice Wallenberg Foundation; Linkoping University; Wallenberg Wood Science Center; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009 00971]; Swedish Foundation for Strategic ResearchSwedish Foundation for Strategic Research; Swedish Armed Forces Research and Technology programme

The scattering properties of materials such as coated and painted surfaces are important in the design of low observable materials. These properties are also important to enable accurate modeling of targets in a scene of different background materials. The distribution of light scatter from surfaces can be determined by measurements of the Bidirectional Reflectance Distribution Function (BRDF) using devices such as scatterometers. The BRDF should ideally be possible to measure both in and outside the plane-of-incidence in order to characterize both isotropic and anisotropic scatter and with suitably high angular resolving power and signal to noise ratio at the wavelengths of interest. Both narrow-band light sources (e.g. lasers) and broad-band light sources in combination with spectral band pass filters may be used in combination with appropriate detectors. This type of instrumentation may consist of complex mechanically moving parts and optics requiring careful alignment to the sample surface to be measured. To understand the synergies and discrepancies between the outputs of different BRDF instruments measuring the same sample set, we have compared BRDF measurement results between our research laboratories in a round robin comparison of an agreed set of sample surfaces and measurement geometries and wavelengths. In this paper, the results from this study will be presented and discussed.

As the sensor technology for polarimetric imaging is advancing into more robust commercial systems such sensors could soon be expected for, e.g., military surveillance and reconnaissance applications in addition to more conventional sensor systems. Thus, there might be an upcoming need to understand limitations on present camouflage systems to meet this new sensor threat. Some of the reasons why polarimetric imaging has drawn attention is the ability to achieve a higher contrast for artificial surfaces against natural backgrounds, by analyzing the degree of linear polarization, which in this work has been analyzed for different types of surfaces as a function of wavelength. We also compare with the polarimetric vision of horse-flies and other aquatic insects via the polarization properties of different colors of horse coat hair in order to give some further insight into polarimetric vision techniques developed by nature. In this work we have used different measurement techniques, such as angle dependent polarimetric spectral directional hemispherical reflectance and polarimetric imaging.

Polarimetric imaging sensors in the electro-optical region, already military and commercially available in both the visual and infrared, show enhanced capabilities for advanced target detection and ...

In this work a spectral designed coating from SPECTROGON is evaluated. Spectral design in this case means that the coating has a reflectivity equal to one at 3-5 and 8-12 microns were sensors operate and a much lower reflectivity in the other wave length regions. Three boxes are evaluated: one metallic, one black-body and one with a spectral designed surface, all with a 15 W radiator inside the box. It is shown that the box with the spectral designed surface can combine the two good characteristics of the other boxes: low signature from the metallic box and reasonable inside temperature from the black-body box. The measurements were verified with calculations using RadThermIR.

In this work, spectroscopic ellipsometry and vector network analysis are used to determine the electromagnetic response of three samples, an epoxy polymer, a sample with ferrit-based nanoparticles in a polymer matrix and silicon, in the wavelength ranges 0.4-30 µm and 0.75- 7.59 cm. Both methods measure amplitude and phase changes due to interaction with a sample and can be used to measure the full complex-valued dielectric response to electromagnetic radiation. The data from the two methods show similar levels of the response at the two ends of the spectral gap between the ranges of the two methods.

This new security development is expected to increase interest fromNorthern European states in supporting the development of conceptually newstealthy ground platforms, incorporating a decade of advances in technology andexperiences from stealth platforms at sea and in the air. The scope of thiscase study is to draw experience from where we left off. At the end of the1990s there was growing interest in stealth for combat vehicles in Sweden. Anambitious technology demonstrator project was launched. One of the outcomes wasa proposed Systems Engineering process tailored for signature managementpresented to SPIE in 2002.(Olsson et.al, A systems approach…, Proc. SPIE 4718 )The process was used for the Swedish/BAE Systems Hägglunds AB development of amultirole armored platform (The Swedish acronym is SEP). Before development wascompleted there was a change of procurement policy in Sweden from domesticdevelopment towards Governmental Off-The-Shelf, preceded by a Swedish ArmedForces change of focus from national defense only, towards expeditionarymissions. Lessons learned, of value for future development, are presented. Theyare deduced from interviews of key-personnel, on the procurer and industrysides respectively, and from document reviews.

Optical properties of natural photonic structures can inspire material developments in diversified areas, such as the spectral design of surfaces for camouflage. Here, reflectance, scattering, and polarization properties of the cuticle of the scarab beetle Cyphochilus insulanus are studied with spectral directional hemispherical reflectance, bidirectional reflection distribution function (BRDF) measurements, and Mueller-matrix spectroscopic ellipsometry (MMSE). At normal incidence, a reflectance (0.6–0.75) is found in the spectral range of 400–1600 nm and a weaker reflectance 1600 nm . A whiteness of 𝑊=42 is observed for mainly the elytra of the beetle. Chitin is a major constituent of the insect cuticle which is verified by the close similarity of the measured IR spectrum to that of 𝛼 -chitin. The BRDF signal shows close-to-Lambertian properties of the beetle for visible light at small angles of incidence. From the MMSE measurement it is found that the beetles appear as dielectric reflectors reflecting linearly polarized light at oblique incidence with low gloss and a low degree of polarization. The measured beetle properties are properties that can be beneficial in a camouflage material.

In development of visual (VIS) and infrared (IR) camouflage for signature management, the aim is the design of surface properties of an object to spectrally match or adapt to a background and thereby minimizing the contrast perceived by a threatening sensor. The so called 'ladder model" relates the requirements for task measure of effectiveness with surface structure properties through the steps signature effectiveness and object signature. It is intended to link materials properties via platform signature to military utility and vice versa. Spectral design of a surface intends to give it a desired wavelength dependent optical response to fit a specific application of interest. Six evaluation criteria were stated, with the aim to aid the process to put requirement on camouflage and for evaluation. The six criteria correspond to properties such as reflectance, gloss, emissivity, and degree of polarization as well as dynamic properties, and broadband or multispectral properties. These criteria have previously been exemplified on different kinds of materials and investigated separately. Anderson and Åkerlind further point out that the six criteria rarely were considered or described all together in one and same publication previously. The specific level of requirement of the different properties must be specified individually for each specific situation and environment to minimize the contrast between target and a background. The criteria or properties are not totally independent of one another. How they are correlated is part of the theme of this paper. However, prioritization has been made due to the limit of space. Therefore all of the interconnections between the six criteria will not be considered in the work of this report. The ladder step previous to digging into the different material composition possibilities and choice of suitable materials and structures (not covered here), includes the object signature and decision of what the spectral response should be, when intended for a specific environment. The chosen spectral response should give a low detection probability (DP). How detection probability connects to image analysis tools and implementation of the six criteria is part of this work.

Gold, silver, and copper substrates were immersed in aqueous solutions of a simulant mineral flotation agent, potassium O,O-di(para-fluorophenyl) dithiophosphate. The adsorbed molecules on gold wer ...

The chemisorption of dimethylphenyl-, methyldiphenyl- and triphenylphosphine on evaporated gold, silver, copper, rhodium, iridium, palladium, platinum and nickel surfaces has been studied by means of infrared reflection–absorption spectroscopy (IRAS). Multilayers of physisorbed phosphine are formed on the surfaces of all metals studied except nickel after deposition from dilute toluene solution. The deposition rate varies for different metal surfaces and it is sometimes quite slow. The standard immersion time was 20 h in this study to secure that an equilibrium between the surface and the solution is reached. Several minutes of ultrasonic treatment are required to get rid of the physisorbed phosphine, leaving a very thin layer of chemisorbed phosphine on the metal surface. Most of the absorption bands in IRAS spectra of these thin layers show significant shifts, which are especially large for dimethylphenylphosphine. It is evident that the electron distribution in the entire phosphine molecules is changed and that the chemisorption to the coinage and platinum group metal surfaces is strong. Infrared spectra of coordination compounds of gold(I), silver(I) and copper(I) with dimethylphenyl-, methyldiphenyl- and triphenylphosphine and of the corresponding phosphine oxides have served as reference material for the chemisorbed phosphines. The spectra of the coordination compounds show similar shifts and intensity changes as the IRAS spectra of tertiary phosphines chemisorbed on the coinage and platinum group metals. This suggests that the studied phosphines are as strongly bound to the coinage and platinum group metal surfaces as to the monovalent coinage metal ions known to form very stable complexes with tertiary phosphines.

Tricyclohexylphosphine (TCHP) adsorbates on rhodium, prepared both from solution and by sublimation in UHV are studied by X-ray photoelectron spectroscopy (XPS), infrared reflection-absorption spectroscopy (IRAS), and temperature-programmed desorption (TP

The adsorption of 3-(2-thioethyl)pyrrole (3-TEP) and 1-(2-thioethyl)pyrrole (1-TEP) on gold has been studied in ultrahigh vacuum with infrared reflection absorption spectroscopy, X-ray photoelectron spectroscopy, and temperature-programmed desorption mass

To try to solve the problem of delamination of polypyrrole from gold during electrochemical cycling, 1-(2-thioethyl)pyrrole and 3-(2-thioethyl)pyrrole were synthesized as adhesion promoters. These compounds were designed to bind to gold through the sulfur atom to form monolayers, and their alkyl chains were made short to permit electron transfer to and from the pyrrole moieties. It was hoped that during electropolymerization of unmodified pyrrole in solution, the pyrrole moieties of the monolayer would be incorporated into the growing film. In this first paper of the series, the synthesis and characterization of the monomers and their electrochemical polymerization to form thin films is presented. Nuclear magnetic resonance and infrared, Raman, UV−vis−NIR, and mass spectroscopy measurements form a basis for comparison with monolayers adsorbed on gold surfaces in the following papers.

The adsorption of dimethylphenylphosphine (dmpp) on gold, silver, and copper has been studied with infrared reflection absorption spectroscopy and temperature programmed desorption mass spectroscop...

Some of the ongoing studies at our laboratory of gas-sensitive field-effect devices with catalytic metal gates are reviewed. More particularly, we discuss the use of such devices in so-called electronic noses due to the possibility of changing the selectivity patterns of the devices by the choice of catalytic metal and operation temperature. Several examples of the application of electronic noses consisting of field-effect devices in combination with metal oxide-based sensors are given. Finally, a summary is given of some remaining scientific problems and studies related to the understanding and development of gas-sensitive field-effect devices.

Optical properties in terms of the complex-valued dielectric function were determined for spin-coated films of a Rose Bengal derivative using variable angle of incidence spectroscopic ellipsometry in the visible and infrared wavelength regions. In addition, the thickness and roughness of the films were determined and related to the solution concentration of Rose Bengal. Switching between two different oxidation states of the Rose Bengal derivative was investigated. The two states were chemically induced by exposure to vapors of hydrochloric acid and ammonia, respectively. A substantial and reversible change of the optical properties of the films was observed. Original Publication: C Akerlind, Hans Arwin, Fredrik Jakobsson, H Kariis and Kenneth Järrendahl, Optical properties and switching of a Rose Bengal derivative: A spectroscopic ellipsometry study, 2011, THIN SOLID FILMS, (519), 11, 3582-3586. http://dx.doi.org/10.1016/j.tsf.2011.01.269 Copyright: Elsevier Science B.V., Amsterdam. http://www.elsevier.com/

The geometric and electronic structure of condensed phase organic conducting polymer PEDOT:PSS blends has been investigated by periodic density functional theory (DFT) calculations with a generalized-gradient approximation (GGA) functional, and a plane wave basis set. The influence of the degree of doping of the PEDOT polymer on structural and optical parameters such as the reflectivity, absorbance, conductivity, dielectric function, refractive index and the energy-loss function is studied. A flip from the benzoid to the quinoid structure is observed in the calculations when the neutral PEDOT is doped by negatively charged PSS. Also the optical properties are affected by the doping. In particular, the reflectivity was found to be very sensitive to the degree of doping, where higher doping implies higher reflectivity. The reflectivity is highly anisotropic, with the dominant contribution stemming from the direction parallel to the PEDOT polymer chain. Original Publication:Annika Lenz, Hans Kariis, Anna Pohl, Petter Persson and Lars Ojamäe, The electronic structure and reflectivity of PEDOT:PSS from density functional theory, 2011, Chemical Physics, (384), 03-jan, 44-51.http://dx.doi.org/10.1016/j.chemphys.2011.05.003Copyright: Elsevier Science B.V., Amsterdam.http://www.elsevier.com/

Thermochromic metal oxides with a Mott transition, such as vanadium dioxide (VO 2 ) exhibit an extensive alteration in their infrared reflectivity when heated above the transition temperature. For VO 2 the infrared reflectivity increases as the material becomes more metal-like above the transition temperature at 68°C. Given these dynamic electromagnetic properties in the IR-range, it is interesting to study the reflection of the material also in other wavelength ranges. The microwave properties of VO 2 as a function of temperature have been investigated here. Measurements were made with an automated network analyzer combined with an electrical heating unit. Reflection properties of VO 2 in the microwave region were determined. Above the transition temperature, an increase in the reflection of the surface was observed. The VO 2 became more metal-like in the whole measured microwave frequency range, as in the infrared region. It is concluded that VO 2 not only can be used to adapt the thermal emissivity of a surface but also to control the microwave reflectivity. Possible applications are switchable radomes, switchable radarabsorbers and heat protection for antenna apertures.

The market demand for bright laser pointers has led to the development of readily available devices that can pose a threat to road safety. Laser pointers can be involved in accidents caused by laser users who do not realise the dangers involved, but laser pointers can also enable deliberate criminal activity. There are technologies available that can counter the threat in different ways. A number of protective principles are outlined below. Some technologies built upon Liquid Crystal Devices are described in greater detail. Without any knowledge of what laser pointers a potential aggressor has access to, a frequency agile filter seems to be the most promising way to avoid the most severe consequences of dazzle from laser pointers. Protective systems incorporating suitable glasses or visors holding frequency agile filters of this kind however, are not commercially available today.

In the present work the infrared-transmission of PEDOT:PSS (poly(3,4-ethylenedioxythiophene):poly(styrensulfonat)) is being investigated using three different kind of electrochromic devises. PEDOT:PSS is an electrochromic conducting polymer able to change its optical properties when it is doped and undoped. The doping is achieved by a voltage applied across the cell. The optical properties are reversible if the polarity of the voltage is changed. We report here, to our knowledge, the first cell with adaptive transmission in the infrared wavelength range. The issue for this type of cell is that all the layers in the device must be transmissive in the whole relevant wavelength range. The results were further verified by construction of similar cells with different configuration giving adaptable reflectivity.

A combination of analytical techniques was used to examine monolayers of 1-(2-thioethyl)pyrrole (1-TEP) and 3-(2-thioethyl)pyrrole (3-TEP) adsorbed on gold, including infrared, UV−vis−NIR, mass spe...

The electrochemical oxidation of 1-(2-thioethyl)pyrrole (1-TEP) and 3-(2-thioethyl)pyrrole (3-TEP) monolayers on gold was studied. Their cyclic voltammograms were different, with, for example, 1-TEP having three oxidation peaks and 3-TEP just one. Moreover, the cyclic voltammetry of both TEP monolayers was unusual and did not follow the expected behavior for simple electron transfer from an adsorbed monolayer. The chronoamperometry for 1-TEP was also surprising, showing nucleation-like peaks; this was not seen for 3-TEP. Air exposure left the 1-TEP, but not the 3-TEP, surface electrochemically inert. Spectroscopic data on the oxidation products of surface-bound pyrroles are presented for the first time. IRAS, XPS, and UV−vis−NIR showed that, after electrochemical cycling, all the pyrrole rings were absent. This demonstration that the molecules decompose calls into question the generality of the grafting mechanism of adhesion promotion for this type of compound.