The subject-matter of the invention is a solution for impregnation of materials shielding low-frequency electric field characterized and the shielding material itself.

The flow of electric current is accompanied by the presence of both the electric (EF) and magnetic fields (MF) in the surroundings of the electric wires and close to the appliances. Electromagnetic field (EMF), a combination of EF and MF, propagates in a wave-manner throughout the space and interacts with matter in various ways, depending on its energy (frequency).

With ra pid adva nces i n electric, e lectron ic a n d communication technologies we are increasingly exposed to EF and MF. Everyday use of electrical household equipments and the boom in communication (internet, cellular phone networks and satellite navigation systems) result in an electromagnetic smog. The electromagnetic smog is hazardous to human health.

Electric currents naturally exist in the huma n body as an essential part of the functioning body. Electric processes are involved both in transmitting nerve signals and in biochemical reactions related to digestion, brain activity etc. The problem of adverse health effect of EMF has been studied repeatedly and it is accepted that long-term exposure to EMF, even if of minor strength, may influence people's well being as has been published by Radiation and Environmental Health Department of the Human Environment of the World Health Organization (Report 2002). Recently, M. Blank and R. Goodman from the Columbia University, NY, USA (Pathophysiology 16, 71: 2009), reported that EMF of extremely low frequencies (ELF - of frequencies 50/60 Hz and lower) was found to interact with DNA inducing the stress response whereas- EMF of higher energy, in the radiofrequency (RF) and ionizing range, can result in breaking of double DNA strands. The impact of light-dark cycle on the regulation of various cellular processes of living organisms and the immune system response has been studied in many outstanding laboratories: Claredon Hall Labs, Blanch Lane, UK (SJ. Collins, SJ. Boulton), University of California, Berkeley, USA (E. M. Gibson, W. P. Williams, LJ. Kriegsfeld), Claveland State University, USA (R.V. Kondratov) and The Scripps Research Institute, La JoIIa, USA (F. F. Shadan). As it has been reported by Collins and Boulton (Chromosoma 116, 331 :2007) the light-dark cycle, related to planetary rotation with respect to our Sun, may play a role in DNA repairing processes in the cells. The cell cycle is linked to the circadian clock at the molecular level so that the protein synthesis and DNA replication are at a higher level during the night. It limits the synthesis and repairing processes of DNA to the nighttime (no UV damage to DNA made by the Sun and the reactive oxygen species resulting from metabolism are minimized).

Thus it appears that the adverse health effect of EMF has to be minimized by EMF shielding. Commonly used shields are based on conductive media which need grounding. Various electric field shielding solutions as Faraday cages, polymer or glass housed metal meshes, conducting polymers and soft materials made of cotton/polyester blended with microfine silver or stainless steel fibers are available. According to US 4704413 a resin composition comprising 35 to 90 wt % of an ABS resin or a mixture of the ABS resin and an AS resin, 1 to 25 wt % of a plasticizer and 5 to 40 wt % of carbon fibers, having an electromagnetic wave shielding effect is provided.

I n U S 5241132 shielding connecting structure is disclosed, composed of conductive solid membrane with rubber hoses. US 5349133 describes magnetic field and electric field shield having an electrically conductive layer and two layers of thin, soft magnetic material wrapped in opposite directions about a common axis. Patent US 6028266 EMF discloses shield for shielding against low frequency electromagnetic fields comprises two pairs of domain refined steel sheets stacked orthogonally with spacer sheet between them and corrosion protective coating on outside surfaces. In US 6226450 electric field shielding apparatus used with an electrical device is described, comprising a housing body at least partially surrounding the electrical device and a conductive shield medium arranged with the shape of the housing body.

It is an object of present invention to develop a method of obtaining materials with properties which provide protection of living organisms and food-stuffs from EMF damage, and these materials may possess, also various properties dependent on the applied primary material. It is a further object of present invention to provide shields of ELF and RF (up to 100 kHz) EMF which do not need grounding. The heart of the matter, according to our invention of EMF shield, lies in a composite which consists of a matrix in which water is randomly dispersed in various ways (in form microdrops or hydrates, confined etc).

It is a still further object of present invention to provide a flexible shield that can be tailored to various applications (bed sheets, pillow, laptop shields etc) and does not need any grounding cord. The product should exhibit EF .shielding abilities in the frequency range from ELF to RF.

According to the invention, the heart of the solution to impregnate the material (matrix) for EMF shields is an aqueous solution of hydrated salt and/or salt mixtures with hydration abilities, i.e. salts with sulphate ^2" , phosphate ^3' , carbonate ^2" , Cl ^" anions and Mg ²⁺ , Ca ²⁺ , Cu ²⁺ , Na ⁺ , K ⁺ cations with hydration abilities. Preferably such solution contains at least one salt with hydration ability absorbing moisture from the air. Further, preferably the impregnating solution is an aqueous solution of at least one hydrated salt. Moreover, preferably the weight ratio of the salt with hydration ability to water falls within the range from 1:0.01 up to 1 : 1000. Moreover, preferably the weight ratio of the hydrate to water falls within the range from 1:0 up to 1: 1000. The idea of the shielding material according to the invention to be applied to ELF and RF EMF shielding consists in that this material has a matrix that can easily soak up the aqueous solution of the hydrate. According to the invention material with such properties is soaked up with the solution as described above. Preferably, this matrix is provided with pores and/or apertures and/or capillarity. Also preferably, such matrix of the material belongs to the set including fabrics, knitted fabrics, nonwovens, ceramics, wood, plastics, construction materials, concrete, plaster and compositions of the above. Moreover, preferably when the hydrate to water ratio is 1 : 10 and lower, the modified material containing polyester fabric is slow-burning.

The invention shall be introduced on the ground of examples, which nevertheless does not limit it in any respect. Flexible shields can be produced in a variety of sizes, shapes, thicknesses and designed for various applications to reduce the EF from appliances which surround us at home and at work. Example I Shield developed for protection of large areas from EF of ELF and RF frequency (up to 100 kHz). As larger appliances will need larger screen the bedding is being produced on a production line. Viscose/PES (60/40) fabric (basic weight 70g/m ² ) being unrolled from a horizontally placed bale, passes through a bath containing impregnating solution (at room temperature), su bseq uently is pressed i n a ma ngle-type engine, dried at 80 ⁰ C (during 5 min on 5 m distance) and wound on a roller. The fabric is being fed at a rate of 1 m/min. The impregnating solution consists of a mixture of aqueous solution of MgCh-δhbO and with hydrate to water weight ratio 1:10 and aqueous solution of polyvinyl acetate (PVAc) with weight ratio of PVAc:H ₂ O amounting to of 1 : 10. The basic weight of the modified Viscose/PES (60/40) increased by 50% in comparison with that of non-modified fabric. When having been dried, the said fabric absorbs EF component of EMF as shown in Figure 1. Electric field strength distribution above an electric cable connected to a power socket (50 Hz) measured with an ESM-100 3D H/E field meter (Maschek Elektronik) is shown in Figure Ia. The cable was covered with 0.3mx0.3m sheet of the said modified fabric and as seen in Figure Ib the EF strength was decreased considerably.

Figure 1. EF distribution above an electric cable connected to a power socked without the Viscose/PES shield and with the shield.

EF shielding ability of the said impregnated Viscose/PES (60/40) fabric is characterized also by high dielectric losses measured by the tanδ value. Frequency dependence of tanδ was measured in the frequency range 10 ^"2 - 10 ⁷ Hz at room temperature using a NOVOCONTROL dielectric spectrometer. Figure 2 shows frequency dependence of tanδ. Maximum of dielectric losses is apparent between 1 kHz and 10 kHz, however the tanδ values are still high in the ELF range of EF.

10 ^'2 10 ^'1 10° 10 ¹ 10 ² 10 ³ 10 ⁴ 10 ⁵ 10 ^s f [Hz]

Figure 2. Dielectric losses of Viscose/PES (60/40) modified with aqueous solution of MgCI ₂ '6H ₂ O (hydrate:water weight ratio 1:10)

Example H

Excellent shielding qualities exhibits also polyester fabric modified at laboratory level with impregnating solution of various hydrate-to-water ratio. Fabric made of polyester (PES- 100g/m ² ) is being impregnated with a solution of MgCI ₂ -6 H2O at the temperature not exceeding 117 ⁰ C in order to produce an EMF shield. The solution is being prepared in a weight ratio of MgCI ₂ -6 H ₂ O to H ₂ O 1:20, 1:10 and 1:5. Next it is being dried at 80 ⁰ C for few min.

When having been dried, the said fabric absorbs EF component of EMF as shown in Figure 3. The strength E ₀ of EF produced by a C&C FG-220C generator was measured at well defined position with an ESM-100 3D H/E field meter (Maschek Elektronik). To measure the shielding ability the probe of the field meter was screened by modified (1 : 20, 1 : 10 and 1 :5) PES fabric and the field strength E _e was measured. One can observe (Rg. 3) that relative field strength (E _o -E _e )/Eo, which can be taken as a measure of shielding ability of the fabric, depends the on the hydrate:water ratio of impregnating solution. The higher is the hydrate concentration the greater is the shielding ability.

Figure 3. Relative changes in EF strength due to shielding by non- modified PES (control) by PES matrix modified by aqueous solutions of MgCI ₂ -6 H ₂ O (hydrate: water weight ratio = 1:5, 1:10, 1:20) versus the EF frequency f

Example III

As claimed the shields made of fabrics impregnated with various hydrates can protect against ELF and RF (up to 100 kHz) EFs resulting in an adverse health effect. Hydrophilic fabric made of Viscose/PES (60/40) (basic weight 70g/m ² ) is being impregnated on the production line described in Example I with an aqueous solution of four various hydrates: 1) MgCl ₂ "6H ₂ O (1: 10 weight ratio of hydrate to water)

2) Na ₃ PO ₄ - 12H ₂ O (1 : 10 weight ratio of hydrate to water)

3) CuSO ₄ -5H ₂ O (1:10 weight ratio of hydrate to water)

4) Na ₂ CO ₃ -IOH ₂ O (1: 10 weight ratio of hydrate to water). When having been dried, the four said fabrics were found to exhibit EF shielding properties. The measurements of shielding efficiency were done in the following way. The strength E ₀ of EF produced by a C&C FG-220C generator was measured at well defined position with an ESM-100 3D H/E field meter (Maschek Elektronik). To measure the shielding efficiency the probe of the field meter was screened by Viscose/PES (60/40) fabric modified with four various hydrates and the field strength E _e was measured. One can observe (Figure 4) that relative field strength (Eo-E _e )/Eo, which can be taken as a measure of shielding efficiency, depends the on the type of the hydrate. At ELF the differences in the shielding efficiency of the fabric impregnated with various hydrates are rather small. At RF the highest shielding efficiency exhibits Viscose/PES (60/40) impregnated with MgCI ₂ -6H ₂ O, whereas the lowest efficiency shows the fabric modified with Cu ₂ SO ₄ -5H ₂ O.

f [Hz]

Fig.4 Frequency dependence of relative changes in EF strength due to shielding by non-modified VIS/PES (control) and VIS/PES matrix modified by aqueous solutions of MgCI ₂ -6H ₂ O; Na ₃ PO ₄ -12H ₂ O; CuSO ₄ -5H ₂ O and Na ₂ CO ₃ -IOH ₂ O (hydrate:water weight ratio = 1:10)

With the purpose to obtain the composite many fabrics and porous materials such as e.g. ceramics have been applied, and it has been proved that absorption rate of electric field depends on a hydrate type, and then - its concentration which is connected with dilution degree, temperature of impregnating with a solution received from the said hydrate, kind of material from which such fabric is made, porosity ratio, hydrophility or capillarity of this material, and in the case of fabric - its basis weight.

Materials produced in accordance with the invention can be applied in manufacturing of all kinds of enclosures, shields and covers protecting living organisms and food-stuffs against effects of a variable electric field. Particularly essential seems to be application of the materials according to the invention to manufacturing of covers for electronic appliances of personal use such as mobile phones, palmtops, all types of image and sound reproducers. Such appliances are permanently carried close to the human body producing electric field which is variable depending on the operating mode. The said field is characterized by a relatively low intensity, but its effect is long- lasting and its absorption constitutes an important factor increasing users' safety. Also directly shielding materials can be applied in e.g . electric sockets and electric wires. Another application of the composite is manufacturing of mats e.g. to be put on chairs, under chairs or on the entire bed. The said materials can also form at least one layer of materials applied to shoe pads or directly as an element of shoes. The above materials can be also applied in manufacturing of apparel as well as sheets, duvets, tents, sleeping-bags, foam mattresses. One more application area is construction industry, for example manufacturing of roofing nonwovens, bricks, ceramic tiles, masonry mortar and plasters or wooden elements used as variable electric field shields.

The issue of health protection of human beings does not limit further applications of the said solutions. The above can be also applied with the aim to protect rooms and buildings against possible outflow of electronic information, interferences caused by low-frequency electric fields, and the like.