Nowadays, modern uniforms and military camouflage systems for objects and buildings can do more than just use camouflage prints that are specially made to blend in with the environment to prevent them from being seen.
Special materials can also provide screening against tell-tale infrared heat radiation (IR radiation). Until now, it has been the IR-absorbing vat dyes of the camouflage print that generally ensure that the wearers are largely "invisible" to the CCD sensors on night-vision devices. However, the dye particles soon reach the limits of their absorption capability.
As part of a research project, (AiF No. 15598), scientists at the Hohenstein Institute in Bönnigheim and the ITCF Denkendorf have developed a new type of IR-absorbent textiles. By dosing (covering) or coating chemical fibres with nanoparticles of indium tin oxide (ITO), the heat radiation can be far more effectively absorbed and so a better screening effect is achieved than with conventional camouflage prints.
ITO is a transparent semiconductor which is also used, for example, in the touch screens of smartphones. The challenge for the researchers was to bind the ITO particles to the textiles in such a way that there was no detrimental effect on their other properties, such as their physiological comfort. The treatment on the textile also had to be made resistant to washing, abrasion and weathering.
To evaluate the screening effect of the textile treatment, the absorption, transmission and reflection were measured in the wave range 0.25 – 2.5 μm, i.e that of UV radiation, visible light and near infrared (NIR). The NIR screening effect in particular, which is important for night-vision devices, was markedly better when compared with untreated textile samples.
In their spectroscopic investigations, the team of experts was able to make use of the wealth of expertise and the state-of-the-art spectroscopy equipment at the Hohenstein Institute. This is also used in other ways as well as for research projects: for example, at the customer’s request, the specialists can calculate the UV protection factor (UPF) of textiles and check that colour requirements and tolerances are as specified in the technical terms of delivery.
Building on the latest research results, in future projects the IR-absorbent textiles will be further optimised with regard to their heat and sweat management capabilities. The aim is to prevent the tell-tale near and mid-range IR radiation, in the form of heat radiated from the body, from even forming, so making detection even harder. By keeping the physiological processes in the human body running as smoothly as possible, the textiles also help ensure that the soldiers can perform to the best of their abilities even in extreme climatic conditions or under great physical stress. The researchers are benefiting from the decades of experience at the Hohenstein Institute in the objective assessment and optimisation of functional textiles. This experience has fed into many internationally standardised test methods which the team of experts can use in its work.