An object of the invention is a method for obtaining a metamaterial and its use in devices operating within a range of radio- and microwaves.

A metamaterial is the material whose properties depend more on its structure than on physicochemical properties of the chemical compounds of which it is composed. Various types of metamaterials are known in state of the art, including electromagnetic metamaterials (US7855696 B2 [1], WO2014/145821A1 [2]), flexible (J. Page, Nature Materials 10, 565-566 (2011) [3]), acoustic metamaterials (US8579073 B2 [4]), structural metamaterials (http://www.caltech.edu/content/miniature-truss-work [5]), or non-linear metamaterials (US20120293854 Al [6]).

US7855696 B2 discloses a metamaterial and its use for shaping of a beam of radiation and switching a directional wave.

On the other hand, WO2014/145821 Al discloses a method and a device for creating an absorber with radio frequency (RFA) or an ideal surface absorbing microwave radiation (PMA). In this solution, a method for creating a printed circuit board (PCB) absorbing radio frequency (RFA) involves superimposing numerous metamaterial layers over numerous dielectric substrates, adding resistive layers, adding capacitive layers, shaping metamaterial layers into layers of RFA metamaterial and using numerous RFA layers for mounting on a board for absorption of electromagnetic radiation within target frequency range. The metamaterial according to the invention is used for a multi-layered system for the absorption of electromagnetic radiation within a range of frequencies, such as microwave frequency bands, in a final product, i.e. mobile phones, communication devices or other electronic devices.

In the case of metamaterials working as antennas, one significant performance parameter is a value of the reflection losses RL. Reflection losses are characterised by a power drop, between an incident wave Pi and a reflected wave P _r and are described by formula (1) [10]:

RL (dB) = Wlog ₁₀ ^ (1) where RL (dB) is reflection losses [in decibels], Pi - incident wave power, P _r - reflected wave power.

Reflection losses are simultaneously connected to a standing wave ratio (VSWR) and reflection coefficient (Γ via formulas (2) and (3) [10]:

20 ]<>g ₁₀ (2)

V . 1 _ r

(3) where VSWR is a reflection coefficient,

|Vmax| is a maximum voltage amplitude, wherein V _ma x = |Vfj +| Vr|, where Vf is a voltage of the incident wave, and Vr is a voltage of the reflected wave;

|Vmin| - minimum voltage amplitude, wherein |Vmin| = |Vf| - |Vr|, wherein Vf is a voltage of the incident wave, and Vr is a voltage of the reflected wave;

Increase of a value of the reflection losses RL results in lowering the VSWR ratio, which is significant for an use. Therefore, the reflection losses are a measure indicating how well elements of a device system or a transmission line are fitted. The fitting is better when a level of RL [10] is high.

The reflection losses RL is the ratio of the power of the signal reflected from the end of the transmission line to the power of the input signal. RL is measured in the frequency domain and expressed in dB. Since the reflected wave is always smaller than the incident wave, RL is always negative. Therefore, the higher the absolute value of RL (the lower the RL), the lower the reflected power compared to the transmitted power, thus, the better the efficiency of the transmitter-antenna system [11].

VSWR is the voltage standing wave ratio. It is the measure of the fitting of the transmission line impedance and its load. The lower the VSWR parameter, the better the adjustment of the transmission line with the antenna [11]. According to international certification, antennas having RL < -10 dB are considered to be suitable to be used in RFID radio identification (radio-frequency identification), which corresponds to a VSWR ratio < 2: 1 [12]. Values amounting to RL < -6 dB, which corresponds to VSWR < 3 : 1, are also acceptable, what indicates that 75% of wave power is absorbed by the antenna.

One of the valued properties of a finished antenna is width of the resonance band, i.e. the band where RL < -10 dB and it is constant.

In state of the art there are devices in which metamaterials are used as elements absorbing electromagnetic radiation. However, main barrier limiting use of metamaterials is a high cost of the production. Methods for producing metamaterials used today are quite complicated, what leads to high costs of producing metamaterials, and as a consequence into a low accessibility to metamaterials having varied RL and VSWR parameters, adjusted to various wave frequencies.

A goal of the present invention is providing a new way of producing an electromagnetic metamaterial having low RL and VSWR coefficients and large width of the resonance band to be used as RFID, an antenna, a dielectric substrate and other devices or elements of devices operating within a range of radio- and microwaves.

The object of the present invention is a method for producing an electromagnetic metamaterial, characterised in that a magnetic powder in the form of micro- or nano-powder, having a grain size ranging between 10 nm and 1 mm, is mixed with a binder in the volume ratio of 1 :99 to 99: 1, until a homogeneous mixture is obtained, followed by placing the mixture on a cuvette, subsequently placing the cuvette in a slit between the poles of an electromagnet, wherein it is possible to optionally place pole shoes between the cuvette and the poles, and the mixture is subsequently subjected to an impact of magnetic field until the mixture solidifies, wherein the magnetic field strength at an edge of a slit between pole shoes or the poles is from 5 A/m to 1600 kA/m, preferably between 7 A/m and 10 kA/m, more preferably 318 kA/m, and subsequently, once the mixture solidifies, the finished metamaterial is removed from the cuvette.

In the method according to the invention, ferro- or ferri-magnetic material in the form of micro or nano-powder is mixed with a liquid or semi-liquid binder having an adhesive properties, which exhibits high specific electrical resistance. The resulting mixture is subsequently put onto a cuvette between pole shoes placed between the poles of the electromagnet, or without use of pole shoes, and subjected to an impact of magnetic field until the binder solidifies (hardens). A constant magnetic field is established by means of a control device between the poles, as well as the pole shoes, on an edge of a slit in the core. Due to the impact of the magnetic field, the particles of a magnetic material in a mixture will align along the lines of a field, correspondingly to the shape of the pole shoes or an edges of a slit in the core. The use of pole shoes in the method according to the invention is optional, a change in the method of aligning particles in metamaterial being easier and more convenient to realise if pole shoes are replaced in the device (shape of the pole shoes is changed), compared to the possible replacement of the core, both options are falling within the scope of the invention.

The mixture is subjected to an impact of magnetic field until the binder contained in the mixture solidifies. The magnetic field is then deactivated and the resulting metamaterial is given the desired shape, imposed upon it by the shape of the cuvette. If necessary, the shape of the finished metamaterial can be changed correspondingly to the given application, e.g. by cutting it into strips with desired dimensions.

Preferably, in the method according to the invention, the magnetic powder in the form of micro- or nano-powder consists of iron, nickel, cobalt, manganese, rare earth elements, their alloys or ferrites, while the binder is, among others, single or multi -component plastic, epoxy glue, polyethylene, paraffin, glue, glass, plasticine, the volume ratio of the magnetic powder to the binder is to 1 :99 to 99: 1, preferably 1 :9, 1 :5, 1 :2 and 2: 1.

Preferably, in the method according to the invention, the grain size of the magnetic powder ranges between 500 nm and 5 μπι.

Preferably, in the method according to the invention, the binder exhibits specific electrical resistance amounting from 10 ^"1 Ω-m to 10 ¹⁴ Ω-m, preferably from 10 ³ Ω-m to 10 ¹⁴ Ω-m.

Preferably, in the method according to the invention, the pole shoes can be made of or contain elements made of a ferro- or ferrimagnetic material.

Preferably, in the method according to the invention, the production of metamaterial can be proceed without use of the pole shoes.

According to the method of the invention, a shape and other properties of the resulting metamaterials, such as resonance frequency, values of the reflection losses and the standing wave ratio, can change depending on a shape of the pole shoes or an edge of a slit in the core.

An electromagnetic metamaterial obtained via the method according to the invention has a high level of the reflection losses within a range of radio- and microwaves. For a metamaterial produced via the method according to the invention within a resonance area from 0.01 to 10 GHz, the value of the resulting reflection losses amounts to RL < - 10 dB, with the voltage standing wave ratio VSWR falling within a range of 2: 1, preferably 1.09: 1 to 1.8: 1.

Another object of the invention is an use of the metamaterial obtained in the method according to the invention as an antenna, dielectric substrate, RFID, electromagnetic wave absorber, in filters, manipulators and other devices or elements of devices operating within a range of radio- and microwaves. The invention is depicted in the figures, where

Fig.l shows a layout of a device for the production of metamaterials. The current, from a direct current source (11) controlled by a converter (12) for controlling the strength of the magnetic field, is applied to a solenoid (13) comprising from 1 to 10 000 coils. The solenoid (13) is wound around the core (14) made of soft ferro- or ferri-magnetic material (e.g., Armko, ferrite or other). The core (14) can have a shape of a toroid or a rectangle or another, but it necessarily has to comprise a slit, whose size does not significantly affect the method according to the invention. The cuvette (16) with the mixture and possibly the pole shoes (15) are placed in a slit. Due to the electromagnetic induction phenomenon, during flow of the current through the solenoid, magnetic field is induced in the core, which is directed along the core in such a manner that S and N poles appear at an edges of a slit, as well as the cuvette (16). The magnetic field generated in a slit, will on the other hand, cause the alignment of magnetic particles in the mixture along the lines of this field. The lines of the magnetic field may be controlled via shape of pole shoes, or via shape of an edge of the slit in the core.

Therefore, depending on the shape of pole shoes or an edge of a slit in the core, the corresponding structures of aligned magnetic particles will be generated in the resulting metamaterial, separated (dispersed) in the medium of the binder (the an adhesive substance), as depicted in Figs.5-7.

Figs. 2-7 show a various possible shapes of the pole shoes (Fig. 2-4) and metamaterials, obtained as a result of using these pole shoes (Figs. 5-7). In Figs. 2-4 reference marks 21, 31, 41 correspond to a ferromagnetic element, reference marks 22, 32, 42 correspond to a matrix of a dia- or paramagnetic material.

In Figs.5-7 reference marks 51, 61, 71 correspond to structured magnetic particles in the metamaterial, reference marks 52, 62, 72 correspond to the binder (an adhesive substance) in the metamaterial. Fig. 8 shows a plot of the reflection losses RL as a function of frequency within a range of 0.01-10 GHz for the samples from examples 1-4.

Fig. 9 shows a plot of the standing wave ratio VSWR as a function of frequency ranging of 0.01-10 GHz for the samples from Examples 1-4.

The invention is further presented in embodiments which do not limit its scope.

Example 1

Micrometric carbonyl iron (particles size from 100 nm to 10 μιη) was mixed with molten paraffin in the volume ratio of 1 :9. The resulting mixture was transferred to a cuvette 16. The cuvette 16 was placed in a slit between pole shoes 15, shaped as shown in Fig.2. Subsequently, using a direct current source, current was applied 11, which via a solenoid 13 and the core 14 generated magnetic field with a strength established by means of a converter 12 at the level of 318 kA/m. Due to the impact of the magnetic field, the magnetic particles aligned along the lines of the magnetic field. The magnetic field was maintained until the mixture solidified. The metamaterial with the shape of a cuboid as shown in Fig.5 was subsequently removed from the cuvette and subjected to tests, which resulted in checking the structure and the dependence between RL and VSWR ranging from 0.01 to 10 GHz. The results are presented in Table 1 and in Figs. 8-9.

Example 2

Micrometric carbonyl iron (particles size from 100 nm to 10 μπι) was mixed with molten paraffin in the volume ratio of 1 :5. The resulting mixture was transferred to a cuvette 16. The cuvette 16 was placed in a slit between pole shoes 15, shaped as shown in Fig.2. Subsequently, using a direct current source, current was applied 11, which by means of a coil 13 and the core 14 generated magnetic field with a strength fixed by means of a converter 12 at the level of 318 kA/m. Due to the impact of the magnetic field, the magnetic particles aligned along the lines of the magnetic field. The magnetic field was maintained until the mixture solidified. The metamaterial with the shape of a cuboid as shown in Fig.5 was subsequently removed from the cuvette and subjected to tests, which resulted in checking the structure and the dependence between RL and VSWR ranging from 0.01 to 10 GHz. The results are presented in Table 1 and in Figs. 8-9.

Example 3

Micrometric carbonyl iron (particles size from 100 nm to 10 μιη) was mixed with molten paraffin in the volume ratio of 1 :2. The resulting mixture was transferred to a cuvette 16. The cuvette 16 was placed in a slit between pole shoes 15, shaped as shown in Fig.2. Subsequently, using a direct current source, current was applied 11, which by means of a coil 13 and the core 14 generated magnetic field with a strength fixed by means of a converter 12 at the level of 318 kA/m. Due to the impact of the magnetic field, the magnetic particles aligned along the lines of the magnetic field. The magnetic field was maintained until the mixture solidified. The metamaterial with the shape of a cuboid as shown in Fig.5 was subsequently removed from the cuvette and subjected to tests, which resulted in checking the structure and the dependence between RL and VSWR ranging from 0.01 to 10 GHz. The results are presented in Table 1 and in Figs. 8-9.

Example 4

Micrometric carbonyl iron (particles size from 100 nm to 10 μπι) was mixed with molten paraffin in the volume ratio of 2: 1. The resulting mixture was transferred to a cuvette 16. The cuvette 16 was placed in a slit between pole shoes 15, shaped as shown in Fig.2. Subsequently, using a direct current source, current was applied 11, which by means of a coil 13 and the core 14 generated magnetic field with a strength fixed by means of a converter 12 at the level of 318 kA/m. Due to the impact of the magnetic field, the magnetic particles aligned along the lines of the magnetic field. The magnetic field was maintained until the mixture solidified. The metamaterial with the shape of a cuboid as shown in Fig.5 was subsequently removed from the cuvette and subjected to tests, which resulted in checking the structure and the dependence between RL and VSWR ranging from 0.01 to 10 GHz. The results are presented in Table 1 and in Figs. 8-9. Table 1. The structural and electromagnetic properties of metamaterials obtained using the method described in Examples 1-4.

References

[I] US7855696 B2.

[2] WO2014/145821 Al .

[3] J. Page, Nature Materials 10, 565-566 (2011). [4] US8579073 B2.

[ 5 ] http : //www . cal tech . edu/content/mi ni ature-truss-work

[6] US20120293854 Al .

[7] US20130128132 Al .

[8] US7826504 B2.

[9] EP2495621A1.

[10] T. S. Bird, Antennas and Propagation Magazine, IEEE,51, 166-167 (2009).

[I I] - http://www.pzk.bydgoszcz.pl/pdf/straty%20odbiciowe.pdf

[12] The RFID Certification Textbook, 3rd Edition, American RFID Solutions, 2007 - Electronic data processing, pp. 184-187.