Dr. Peter Rejmstad Profile

Dr. Peter Rejmstad

at FOI-Swedish Defence Research Agency

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Publications (2)

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Proceedings Article | 23 October 2023 Presentation + Paper

Nanocellulose-based films for camouflage applications

Jennifer Silander, Peter Rejmstad, Tomas Hallberg, Christina Åkerlind

Proceedings Volume 12736, 1273608 (2023) https://doi.org/10.1117/12.2684079

KEYWORDS: Reflectivity, Chlorophyll, Camouflage, Cellulose, Materials properties, Absorption, Long wavelength infrared, Silver, Mid-IR, Optical properties

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Achieving low signature is much desired in forest and foliage dominated backgrounds. Cellulose nanofibres (CNF) or nanocellulose, is a non-toxic biopolymer that is biodegradable and renewable. Other physical and optical properties such as thermal stability, high mechanical strength and high infrared (IR) emissivity gives it potential to replace hazardous components for camouflage applications, where a more environmentally friendly alternative would be preferred. CNF based films were produced with optical properties similar to leaves in terms of colour. The investigated films were made with carboxymethylated CNF as a matrix, and by adding cenospheres (hollow spheres of alumino-silicate), chlorophyll as a green dye and other additives the films optical and physical properties could be modified to mimic a leaf. The physical structure had a rough paper-like texture and the optical properties could be altered through changing the amount of cellulose, cenospheres and other additives. Initial analysis using UV-VIS-NIR and IR spectroscopy show similar optical properties to a fresh maple leaf. In the UV-VIS region of 0.25 – 0.8 μm a clear chlorophyll peak and a red edge is visible. The CNF film give a high reflectance in the SWIR region 1 – 2.5 μm. A peak of higher reflectance is observed in the IR region 3 – 6 μm, while the reflectance decreases for longer wavelengths. However, silver nanowires could increase the reflectance at longer IR wavelengths. This early work in exploring the use of nanocellulose based films for camouflage applications gives a glimpse of what capabilities CNF might bring in the future.

Proceedings Article | 23 October 2023 Presentation + Paper

Optical properties of water absorbing textiles for camouflage

Eveline Örtenberg, Peter Rejmstad, Christina Åkerlind

Proceedings Volume 12736, 127360A (2023) https://doi.org/10.1117/12.2683969

KEYWORDS: Cotton, Short wave infrared radiation, Absorption, Reflectivity, Water, Camouflage, Optical properties, Nanoparticles, Visualization, Silica

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Background matching is an essential form of camouflage, adopted by humans especially within military applications in terms of signature reduction. Recent sensor developments have created a need for novel camouflage effective in shortwave infrared (SWIR). The absorption of electromagnetic radiation in SWIR is heavily influenced by water. In a forest environment, the water content in plants is of considerable importance. Therefore, it can be inferred that fabrics with higher moisture levels would exhibit reduced detectability in SWIR wavelengths when compared to their dry counterparts. In this study, the optical properties of different fabrics, both in their dry and hydrated state, was evaluated with SWIR imaging and UV-VIS-NIR spectroscopy and compared to foliage. Two methods of hydration were used, water and nanocellulose. In addition, an assessment of the evaporation of water from the hydrated fabrics samples was carried out. Two fabrics were surface treated with hydrophobic compounds in order to modify the evaporation. The treatments included water-repelling agents and silica nanoparticles (SNPs). The hydrophobic surface modifications did not appear to prolong the evaporation of water from the studied fabrics. Hydrating the fabrics appears to transform the electro-optical signature to closely resemble foliage.

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