Kolbun N.V., Pulko Е.A., Lynkov L.M.

Electromagnetic radiation (EMR) shielding is one of the most efficient techniques which are used to reduce the extraneous electromagnetic field intensity of radio electronic equipment. Its basшс principle is preventing electromagnetic waves from traveling into a certain space region by scattering, reflection of electromagnetic energy and its transformation into heat energy within the shielding materials possessing resistive, dielectric or magnetic losses. Technology of composite materials enables such shields and radioabsorbers manufacturing with a wide range of properties. A separate group of such materials include liquid-containing EMR shields based upon porous fiber and powder matrixes which absorb a solution with dielectric and resistive losses to attenuate the EMR. The EMR shielding efficiency of such materials 1.6 mm in thickness is about 13-40 dB in the frequency range 0.8-115 GHz while the reflectivity factor ranges 3 - 18 dB. Variation of technological parameters of manufacturing process enables composite-s electromagnetic properties obtaining in a wide range. Materials utilization under high humidity conditions (caused by climate features or manufacturing processes) results in intensification of microorganisms activity - such as bacteria, fungi etc. This can cause materials mechanical or dielectric properties deterioration. This work was aimed at investigation of the stability of composite liquid-containing material-s electromagnetic properties under liquid medium transformation on molecular level resulting from microorganisms - activity during long-term utilization or storage of product. Optical microphotographs of microorganisms appearing under high humidity conditions are given. Mould-s mycelium has branchy hyphae structure containing a significant volume of intracellular water. Its growth results in forming of spatial disperse water structure having dielectric properties which are defined by the bound water state and are significantly lower than those of the volume water. As a result the matching of wave impedance of the material to free space impedance is enhanced and the EMR reflection from the mediums - interface lowers. Moulds and bacterium activity influence on shielding effectiveness of liquid-containing materials is studied. The EMR energy attenuation produced by samples, which contain microorganisms, corresponds to the level of a control sample. Total electromagnetic radiation shielding efficiency provided by liquid-containing composite materials under microorganisms - activity influence does not change significantly. High liquid content of composite shielding materials ensures 14 dB suppression of EMR in the frequency range 8-11.5 GHz at 1.6 mm sample thickness and up to 50 dB if the thickness of the composite materials is increased up to 15 mm. The EMR reflection by liquid-containing materials under microorganisms activity is reduced by 1-2.5 dB ensured by liquid dispersed structure of mycelium forming resulting in composite surface scattering property enhance. It leads to a conclusion that EMR shielding properties of liquid-containing composite materials are relatively stable under the microorganisms - activity on their surface and within the porous space.