Studies of shielded properties of materials based on powdered shungite
From materials of Institute of Geology of Karelian Research Centre of Russian Academy of Sciences.
A serious problem of the industrial safety is protection of human organisms from EMR of non-ionizing nature. This problem can be resolved by electromagnetic shield. Nowadays, a wide range of nomenclature of shielding materials that have magnetic, dielectric, and electroconductive properties are used.
One of the forms of carbon is natural mineral shungite from Zazhoginskiy deposit (the Republic of Karelia). Shungite stones are natural compounds: equitable spread of highly-dispersed crystalline silicate particles in amorphous carbon matrix.
Shungite is characterized by having high strength, density, chemical resistance, and electroconductivity (Linkov and others, 2004). Due to bipolarity, powder of shungite rocks mixes with other different substances (water suspensions and ftoroplasts, rubber, resin, cement, etc.). Shungite is used for production of electroconductive paints, plastic with antistatic properties, construction materials that are resilient to poor liners conditions etc.
Effectiveness of shungite-based shielding powder depends on the level of its density. The study of impairing of shungite crumbs’ EMR of different fractions in frequency range of 100…800 MHz showed that impairing of 20 dB is reached when filling without compressing and if the size of the particle is larger than 5 mm and thickness of the layer of filling is larger than 15 cm. When there is thickening, thickness of layer can be decreased to 10 cm because of increase in contacts between the particles and increase in electroconductivity.
Significant disadvantage of homogenous conducting materials is their high electroconductivity that results in their having a high coefficient of reflection.
The use of such materials in room shielding leads to appearance of the following: remirrors of electromagnetic energy inside the room and regions where field tension can exceed the norm by hundreds. Both events have a negative impact on a person who spends time in such settings.
The goal of this research was to study shielding properties of materials that were obtained from shungite powder with soluble fillers containing water.
Studied samples of materials, powdered shungite with various water-containment of fraction up to 1 mm, were placed into a solid container made of radar-transparent material. Thickness of samples is 3 mm. Powder was not compressed.
Panoramic measuring devices of standing wave ratio (SWR) and of deamplification and waveguide guide lines were used in measurement of impairing and the coefficient of reflection of EMR in the ranges 8-12, 27-36, 80-115 MHz. After preliminary calibration of machinery, the studied sample was placed in between two horn antennas.
The results of measurements of deamplification and coefficient of reflection of studied materials are presented in Graph 1.
Shungite plate has maximum effectiveness of shielding in studied range of frequencies over 30 dB that is achieved due to high reflection coefficient (-2 dB). As a result of decrease of contact surface between different particles, the division of shungite (fraction under 1 mm) leads to a decrease in its electroconductivity resulting in the measurement of deamplification being 10-20 dB with the coefficient of reflection -5 -10 dB. Adding water containing fillers to the powdered shungite allows to increase effectiveness of shielding up to 25-35 dB by increasing productivity of the material.
Graph 1. Frequencies of dependence of shielding properties: a – impairing, b – coefficient of remirroring of shungite-based materials: 1 – powder with fraction up to 1 mm; 2 – powder with water containing fillers (water content – 43%); 3 – shungite plate.
Results of measurements of shielding characteristics of powdered shungite with various water content (% mass) within frequency range 8-12, 27-36, 80-115 MHz are presented on the Graphs 2 and 3.
Graph 2. Frequency dependencies of impairing (a) and coefficient of reflection (b) of EMR of water containing materials based on powdered shungite with various coefficient of water content: 1 – 53,1 %, 2 – 26,0 %, 3 – 12,3%.
Graph 3. Changes in frequencies of impairing (a) and mirroring coefficient (b) of EMR of powdered shungite with water content 12,3%.
Impairing of powdered shungite with water content 53,1 % leaves about 40 dB with the coefficient of mirroring within the frequency range of 8-12 MHz is -3 dB. The decrease in liquid leads to decrease of the coefficient of mirroring down to -4 dB resulting in a significant fall and impairing down to 10-15 dB.
Research of shielding characteristics of powdered shungite with water containing fillers with 12, 3% coefficient of water content within frequency range of 27-36, 80-115 MHz showed that the impairing of such material equals to 35 dB with mirroring coefficient of -3,5 -10 dB.
It is proven that by changing water content of powdered shungite, properties of such material can be controlled, in particular measurement of impairing and mirroring coefficient, that can be used for creation of shielding rooms, construction elements that lower EMR of mobile phones, and personal computers.
Authors of the study:
L.M. Linkov, T.V. Borbotko,
Y.K. Kalinin, L.M. Guzova.