WO2018106181A1

WO2018106181A1 - Antenna embedded into concrete and method for embedding antenna into concrete

Info

Publication number: WO2018106181A1
Application number: PCT/SG2017/050558
Authority: WO
Inventors: Yee Loon Sum; Vanessa RHEINHEIMER; Boon Hee Soong; Paulo J.M. Monteiro
Original assignee: Nanyang Technological University; The Regents Of The University Of California
Priority date: 2016-12-05
Filing date: 2017-11-07
Publication date: 2018-06-14
Also published as: WO2018106181A8

Abstract

Various embodiments provide for an antenna structure, including an antenna configured to send and/or receive an electromagnetic signal. The antenna is embedded in a concrete including at least a cement. The concrete further includes additions in the form of particles, and the particles comprise a magnetic and/or a metallic material. Various embodiments also provide for a method for forming an antenna structure.

Description

ANTENNA EMBEDDED INTO CONCRETE AND METHOD FOR EMBEDDING

ANTENNA INTO CONCRETE

Cross-reference to Related Applications

[0001] The present application claims the benefit of the US provisional patent application No. 62/430,172 filed on 05 December 2016, the entire contents of which are incorporated herein by reference for all purposes.

Technical Field

[0002] Embodiments relate generally to an antenna structure and a method for forming an antenna structure.

Background

[0003] Antennas have the ability of converting radio frequency (RF) signals into electrical signals and vice versa. Most antennas are electrically large between 0.25 λ to 1 λ, where λ is the wavelength, which has excellent Sn of less than -20 dB and a percentage bandwidth of up to 180%. As the size of antenna reduces to less than 0.25 λ, the Sn increases and the bandwidth narrows. This limits the capability of the antenna.

[0004] A method of improving this is to perform impedance matching where the impedance of the antenna can be adjusted to a desired value such as 50 ohms to maximize power transfer. This method, however, introduces losses as the non-ideal matching components have inherent resistance. This is especially so when the antennas are electrically small and the frequency increases.

[0005] It is known that many objects such as metal surfaces, bodies of water, and thick layers of isolating materials can negatively affect the transmission of electromagnetic (EM) waves, and change the properties of the antenna such as changing the radiation pattern, shifting the resonant frequency, and reducing the bandwidth. Despite this, efforts have been done to select some other materials that can benefit the antenna by improving certain qualities of the antenna, however not improving the media properties in order to enhance the antenna performance.

[0006] For example, normal concrete, plaster, gypsum, are isolating materials, presenting very poor conducting characteristics, however their electromagnetic properties can be changed by adding conductive materials to the mixture.

[0007] Magnetic and metallic particles application in concrete is still very limited and focuses only in the need for disposing the industry residues (environmental aspect). Existing studies in this composite material are restricted to concrete performance and durability, thus far not applying the use of metallic and/or magnetic particles in concrete for enhancing the electromagnetic shielding, or energy harvesting abilities of the concrete structure. Furthermore, the use of conductive concrete for the electromagnetic shielding has been explored before, but up until now not using magnetic/metallic particles to improve the properties of concrete.

[0008] Wireless communications are essential in buildings for many Internet of things (IOT) applications. However, materials used in buildings do not allow good propagation of wireless signals within, and in and out of the buildings. This is especially so for embedded antennas in building materials. With increasing interest to use such embedded antennas in building materials for concrete health monitoring, wireless powering of embedded sensors and radio -frequency identification (RFID) applications, investigations have been done to study the effects of building materials on electromagnetic (EM) propagation. It is known that common building materials such as concrete, gypsum and plaster have high shielding effectiveness due to their nature. Direct measurements, and analysis using finite-difference time-domain (FDTD), and method of moments (MOM) techniques show that building materials have more than 80 dB to 100 dB of shielding effectiveness. Previously, particles application in concrete focused only in the need of disposing industry residues (environmental aspect). Existing studies in this composite material are restricted to concrete performance and durability, thus far not applying the use of magnetic and/or conductive particles in concrete for enhancing the electromagnetic properties of the concrete structure for embedded antennas. Furthermore, the use of conductive concrete for the electromagnetic applications has been explored before, but up until now commonly used to improve the shielding effectiveness of concrete. Earlier work developed on conductive concrete for electromagnetic applications mainly use carbon fibers in polymer concretes for frequencies from 30 MHz to 5 GHz to increase the shielding effectiveness of materials. It has been shown that very high shielding effectiveness of several dozen dB may be achieved.

Summary

[0009] Various embodiments provide an antenna structure. The antenna may be configured to send and/or configured to receive an electromagnetic signal. Various embodiments may further include the antenna being embedded in a concrete. The concrete may include at least a cement. The concrete may further include additions in the form of particles. The particles may include a magnetic and/or a metallic material.

[0010] Various embodiments provide a method for forming an antenna structure. The method for forming the antenna structure may include providing an antenna. The antenna may be configured to send and/or configured to receive an electromagnetic signal. The method may further include providing a concrete composition. The concrete composition may include at least a cement. The concrete composition may further additions in the form of particles. The particles may include a magnetic and/or a metallic material. The method may further include providing a mold for pouring the concrete composition in. The method may further include pouring the concrete composition into the mold. After arranging the antenna in the mold and after pouring the concrete into the mold, the antenna may be at least partially surrounded by the concrete. The antenna may be arranged in the mold before the pouring of the concrete composition into the mold. The antenna may be arranged in the mold after the pouring of the concrete composition into the mold.

Brief Description of the Drawings

[0011] In the following description, various embodiments are described with reference to the following drawings, in which:

Fig. 1 shows a schematic illustration of an antenna structure 10 according to the invention, including an antenna 20, able to receive an electromagnetic signal 12, embedded in a concrete 30; Fig. 2 shows a Sii plot over a frequency of 2 to 3 GHz of an electrically small antenna designed for wireless LAN of 2.4 GHz, with the solid line 200 representing the plot as measured and the dotted line 201 representing the plot as simulated;

Fig. 3 shows a Sii plot over a frequency (f) of 2 to 3 GHz, with the antenna in air for comparison (solid line 301), an antenna structure according to the invention (long dashed line 302), and a comparative example wherein an antenna is embedded into concrete only (short dashed line 303);

Fig. 4 shows a flowchart illustrating a method for forming an antenna structure according to various embodiments.

Fig. 5 shows the geometry of an exemplary antenna used for the experiments, in front view (left) and back view (right).

Fig. 6 shows a schematic representation of the exemplary antenna used for the experiments (a) and of the antenna arranged in concrete (b). Fig. 6 (c) to (e) show the geometry of a second, a third, and a fourth antenna structure according to various embodiments.

Fig. 7 (a) is a schematic representation of antenna structures as prepared according to the invention. Fig. 7 (b) and Fig. 7 (c) illustrate the experimental setup for measuring of Sn (Fig. 7 (b)) and S21 or S12 (Fig. 7 (c)).

Fig. 8 shows six Si 1 plots over a frequency (f) of 2 to 3 GHz, for a comparative example wherein an antenna is embedded into concrete only (solid line 801), the antenna in air (small spaced dotted line 802), and according to the invention for micro-sized iron (III) oxide (long dashed line 803), nano-sized iron (III) oxide (large spaced dotted line 804), micro-sized magnetite (short dashed line 805), and nano-sized magnetite (dash-dot line 806);

Fig. 9 shows six S21 plots over a frequency (f) of 2 to 3 GHz, for a comparative example wherein an antenna is embedded into concrete only (solid line 901), the antenna in air (small spaced dotted line 902), and according to the invention for micro-sized iron (III) oxide (long dashed line 903), nano-sized iron (III) oxide (large spaced dotted line 904), micro-sized magnetite (short dashed line 905), and nano-sized magnetite (dash-dot line 906); Fig. 10 shows a Sii plot over a frequency of 2 to 3 GHz of antennas in air before embedding into concrete, the short dashed line 1001 corresponds to the antenna before embedding into concrete with lweight% of micro-sized iron oxide particles, the long dashed line 1002 corresponds to the antenna before embedding into concrete with 2weight% of micro-sized iron oxide particles, and the solid line 1003 is for the antenna of the comparative example wherein an antenna is embedded into concrete only;

Fig. 11 shows a S21 plot, corresponding to the plots in Fig. 10, over a frequency of 2 to 3 GHz of antennas in air before embedding into concrete, the short dashed line 1101 corresponds to the antenna before embedding into concrete with lweight% of micro-sized iron oxide particles, the long dashed line 1102 corresponds to the antenna before embedding into concrete with 2weight% of micro-sized iron oxide particles, and the solid line 1103 is for the antenna of the comparative example wherein an antenna is embedded into concrete only;

Fig. 12 shows a Sn plot over a frequency of 2 to 3 GHz of an antenna structure according to the invention for lweight% of micro-sized iron oxide particles (short dashed line 1201) and 2weight% of micro-sized iron oxide particles (long dashed line 1202), and further a comparative example wherein an antenna is embedded into concrete only (solid line 1203);

Fig. 13 shows a S21 plot, corresponding to the plots in Fig. 12, over a frequency of 2 to 3 GHz of antenna structure according to the invention for lweight% of micro-sized iron oxide particles (short dashed line 1301) and 2weight% of micro-sized iron oxide particles (long dashed line 1302), and further a comparative example wherein an antenna is embedded into concrete only (solid line 1303);

Fig. 14 shows a S n plot over a frequency of 2 to 3 GHz of antennas in air, before embedding into concrete, the short dashed line 1401 corresponds to the antenna before embedding into concrete with 3weight% of micro-sized iron oxide particles, the long dashed line 1402 corresponds to the antenna before embedding into concrete with 4weight% of micro-sized iron oxide particles, and the solid line 1404 is for the antenna of the comparative example wherein an antenna is embedded into concrete only;

Fig. 15 shows a S21 plot, corresponding to the plots in Fig. 14, over a frequency of 2 to 3 GHz of antennas in air, before embedding into concrete, the short dashed line 1501 corresponds to the antenna before embedding into concrete with 3weight% of micro- sized iron oxide particles, the long dashed line 1502 corresponds to the antenna before embedding into concrete with 4weight% of micro-sized iron oxide particles, and the solid line 1503 is for the antenna of the comparative example wherein an antenna is embedded into concrete only;

Fig. 16 shows a Sn plot over a frequency of 2 to 3 GHz of an antenna structure according to the invention for 3weight% of micro- sized iron oxide particles (short dashed line 1601) and 4weight% of micro-sized iron oxide particles (long dashed line 1602), and further a comparative example wherein an antenna is embedded into concrete only (solid line 1603);

Fig. 17 shows a S21 plot, corresponding to the plots in Fig. 12, over a frequency of 2 to 3 GHz of an antenna structure according to the invention for 3weight% of micro- sized iron oxide particles (short dashed line 1701) and 4weight% of micro-sized iron oxide particles (long dashed line 1702), and further a comparative example wherein an antenna is embedded into concrete only (solid line 1703);

Fig. 18 shows the improvement in transmission, in relation to the comparative example, with the increase of the concentration of the additions.

Detailed Description

[0012] The following detailed description refers to the accompanying drawings that show, by way of illustration, specific details and embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments may be utilized, and structural and logical changes may be made without departing from the scope of the invention. The various embodiments are not necessarily mutually exclusive, as some embodiments can be combined with one or more other embodiments to form new embodiments.

[0013] Various embodiments provide an antenna structure and a method for forming an antenna structure.

[0014] Embodiments described below in context of the antenna structure are analogously valid for the method for forming an antenna structure and vice versa.

Furthermore, it will be understood that the embodiments described below may be combined, for example, a part of one embodiment may be combined with a part of another embodiment.

[0015] The term "and/or" within the context of the present disclosure, including the claims, means that the respective components may be connected by "and" and may be connected by "or". For example, for components "a" and "b", the expression "a and/or b" means "one of: a, b, a and b". For example, a magnetic and/or metallic material may mean a metallic material, a magnetizable material, or a metallic magnetizable material.

[0016] In the present disclosure, a method of adding certain magnetic and/or metallic particles in building composites, such as concrete, mortar, gypsum plaster, among others, to increase the performance of the antenna is described.

[0017] To improve the performance of the antenna, especially in the context of buildings, is to take advantage of the building elements such as partitions, walls, ceilings, floors, and fagade to enhance the behavior of the antenna.

[0018] It will be understood that any property described herein for a specific antenna structure may also hold for any antenna structure described herein.

[0019] In order that various embodiments may be readily understood and put into practical effect, particular embodiments will now be described by way of examples and not limitations, and with reference to the figures.

[0020] In the present disclosure it was surprisingly found that the addition of metallic and/or magnetic particles to concrete improves the electromagnetic properties of concrete for embedded antennas. The performance of the antenna in terms of at least the return loss, and bandwidth is improved by embedding the antenna in enhanced building composite by the use of metallic and/or magnetic particles.

[0021] In various embodiments, the antenna may be an electrical small antenna. The antenna may also be a metamaterial resonator or an array of resonators. Antennas are considered electrically small if the diameter of the sphere containing the antenna is small compared to the wavelength of operating frequency. The definition of electrically small is generally taken as any maximum length smaller than Ο. ΐλ. As such, there is a range of values that an antenna can take to be considered electrically small. In summary, if the antenna maximum dimension is less than Ο. ΐλ to 0.0795λ, it is considered small. [0022] The antenna structure may be configured such that the antenna is able to receive an electromagnetic signal. The antenna structure may be configured such that the antenna is able to send electromagnetic signal. The antenna structure may be configured such that the antenna is able to receive and send electromagnetic signal.

[0023] The antenna structure may be configured to operate in the frequency range above 1 GHz, for example between 2 GHz and 60 GHz, or 2 GHz to 6 GHz. The antenna in the antenna structure may include an operational frequency within this range. To "operate" as in "operational frequency" may mean that the antenna structure is configured to send and/or configured to receive the electromagnetic signal. An operational frequency may mean the frequency for which the transmission coefficient is close of a maximum, for example is a maximum. In various embodiments, the antenna structure may be configured to operate in a wireless LAN frequency range, thus configured to send and receive wireless LAN data, wireless LAN frequency range may refer to the frequency ranges including the frequencies used by the IEEE 802.11 protocols, for example the IEEE 802.11-2016 protocols variants a/b/g/n/ac/ad. Within the context of the present disclosure, the terms "wireless LAN" and "Wifi" have the same meaning and may be used interchangeably. "LAN" stands for local area network.

[0024] In various embodiments, the antenna is embedded in a concrete, mortar or cementitious materials. Within the context of the present disclosure, the term "embedded" may mean to be firmly fixed in the concrete, wherein the concrete surrounds the antenna. In various embodiments, the antenna may be completely embedded into the concrete, for example completely surrounded by concrete, so that no part of the antenna is accessible (as in direct physical contact). For example, no part of the antenna may be accessible without breaking the concrete. In various embodiments, the concrete surrounding the antenna may include a thickness of at least 1cm. An electrical connection may be envisaged, which allow for transmission of electrical signal from and/or to the antenna, for example via a coaxial cable. Such electrical connection may itself be at least partially embedded into the concrete. Such electrical connection may include at least a part which is not embedded into concrete, thus enabling external electrical connection, for example to a radio equipment. An example of a radio equipment is a wireless LAN router.

[0025] Within the context of the present disclosure, the term "concrete" may mean a building composite including a building composite material. Typically, concrete is formed by an aggregate, for example a silica aggregate, and a cement that, when fluid, hardens over time. Example of such concrete are mortar, gypsum plaster.

[0026] In various embodiments, the concrete may include at least a cement. The cement may be any hydraulic material, for example any hydraulic inorganic material. Any material with cementing properties when in contact with water may be used as hydraulic inorganic material. For example, all types of Portland cement, alumina cement, water glass cement, magnesia cement, gypsum, either alone or in combination. One exemplary cement is of the type ordinarily called Portland cement (which does not necessarily need to come from Portland).

[0027] In various embodiments, the concrete may further include additions. The additions may be in the form of particles.

[0028] In various embodiment, the concrete may further include at least an additive. The additive may be liquid.

[0029] In various embodiment, the concrete may further include a superplasticizer. Superplaticizers are high range water reducers widely used in concrete to improve the workability and reduce the water consumption in the mixture (by reducing the water in the mixture the concrete strength increases). Superplasticizers are chemical admixtures which may be used where well-dispersed particle suspension is required in concrete.

[0030] In various embodiments the particles may include a magnetic and/or a metallic material. When the particles include a magnetic and/or a metallic material, the transmission of the signal can be improved in the antenna structure. The particles may include or essentially consist of magnetic and/or metallic material, for example the particle may include or essentially consist of a material which can be magnetized. The particle may be magnetized, for example by exposing the particle to a magnetic field. For example, the magnetic material, and the magnetic particle, may be from "hard" magnetic materials or from "soft" magnetic materials. "Hard" magnetic metals tend to stay magnetized over a long period while "soft" magnetic metals can be magnetized but lose their magnetism quickly. In another example a composition of a particle of the particles may be at least 40% of metallic material. One example of a metallic material, which is also a magnetic material is iron (III) oxide. One example of a magnetic material is magnetite.

[0031] In the present disclosure, the term "particles" may refer to granular material, wherein each particle (or also named each grain) may include a plurality of atoms. The plural "particles", according to the invention, may include an average size from about 10 nm and up to about 5 micrometers. The average size may be calculated over the size of the particles that are according to the invention, for example, only considering the particles including metallic and/or magnetic materials. The size of each particle may be determined as the largest diameter of each particle.

[0032] In various embodiments, a concrete composition may be used for forming the concrete. The concrete composition may include the cement and the additions. The concrete composition may further include an aggregate, for example a mixture of materials selected from at least one of: coarse gravel, crushed rocks, granite, sand, and a mixture thereof. Typically water, for example in liquid form, is mixed to the concrete composition to form a slurry, which, after hardening, forms the concrete.

[0033] In various embodiments, the additions may be included in a weight percentage to the total sum of dry concrete compositions, depending on the type of additions. This ensures that a sufficient workability and strength are achieved in the concrete.

[0034] In the context of the present disclosure, other elements embedded in a building structure, which building structure includes a concrete according to the invention, are not comprised in the definition of concrete. For example a metal steel frame may be part of a building structure, and may be surrounded by concrete, however the metal steel frame is neither part of the concrete composition nor part of the definition of "a concrete" or "the concrete" in accordance with the invention.

[0035] In various embodiments, the method for forming an antenna structure may include providing a mold. An example of a mold is a structural concrete mold, such as used for building construction. In another example, the mold may be a cavity in a building structure in which the antenna structure may be formed. This allows for example, for establishing of a telecommunications infrastructure, after a building structure is formed.

[0036] In some embodiments, the antenna may be arranged into the mold before pouring the concrete composition into the mold. Arranging the antenna into the mold before the pouring of the concrete composition may facilitate an exact positioning of the antenna, since it can be fixed in relation to the mold, and thus be fixed in relation to the concrete, once the antenna structure is formed. Alternatively, in other embodiments, the antenna is arranged in the mold, after the pouring of the concrete. At this stage of "pouring", the concrete composition is still in a non-set stage, for example mixed with water in the form of a slurry. Arranging the antenna into the mold with concrete may have the advantage of not requiring to fix the antenna to the mold, thus saving time and fixing material, as the antenna may be secured in place by the slurry. Another advantage is that no auxiliary structure is needed, for example to fix the antenna to the mold. The antenna could also be arranged into the mold after the concrete composition is partially poured into the mold, wherein after arranging the antenna, the concrete composition is further poured, thus completing the process. Such case could present advantages, for example, if the mold is very deep and thus not easily accessible, therefore, the antenna may be arranged over the concrete composition on a certain height of the mold, which can then be further filled.

[0037] In various embodiments, after arranging the antenna in the mold and after pouring the concrete composition into the mold, the antenna is at least partially surrounded by the concrete. At least partially surrounded means embedded into concrete, as explained above. The antenna may also be completely surrounded by the concrete, meaning that it is fully embedded into the concrete.

[0038] In various embodiments, the antenna may be arranged in the mold keeping a distance of at least 1 cm to a closest mold wall.

[0039] It was surprisingly found, that by providing metallic and/or magnetic particles into the concrete composition, and therefore providing metallic and/or magnetic particles into the concrete, it was possible to significantly improve transmission of electromagnetic signal, significantly improve the Sn and/or S21 of the antenna in the antenna structure. The improvements, in comparison to normal concrete without the additions, are of such magnitude, that the antenna structure even allows for wireless LAN signal transmission, which was not feasible before the present invention.

[0040] An improvement of Sn refers to an improve of the reflection coefficient. In this context "improvement" may refer to less reflection than a comparative case.

[0041] An improvement of S21 or S 12 refers to an improve of the transmission coefficient. In this context "improvement" may refer to a stronger transmission coefficient than a comparative case. In the present disclosure, S21 and S 12 can be used interchangeably.

[0042] In various embodiments, the particles including a magnetic and/or a metallic material is comprised in an amount of at least 0.5 weight% of the concrete, for example in an amount of from 0.5 weight% to 4 weight%. The weight percentage may refer to the percentage of particles according to the invention in relation to the total sum of the dry concrete composition.

[0043] In various embodiments, the particles may be of a non-uniform shape. A nonuniform shape may refer to random shape, for example sand grain shaped. A non-uniform shape may also refer to grinded material. The grinded material may be filtered material, for providing a certain particle size of the particles.

[0044] In various embodiments, the particles' average size may be from about 5 nm to about 5 micrometers. In various embodiments, the particles' average size may be from about 100 nm to about 5 micrometers. The size of a single particle may be the largest diameter of the particle.

[0045] The particles used in various embodiments, may be obtained from commercial sources. For example, micro sized iron oxide particles are commercially available.

[0046] In various embodiments, the particles may be homogeneously distributed in the concrete. For providing a homogeneous distribution, the concrete composition may be mixed, for example before and/or after the addition of water. In one example, the particles may be dispersed in water, for example with ultra- sound, before mixing the dispersion with cement.

[0047] The invention further relates to use of antenna embedded or in the surface of conductive building elements for either cloaking/transparency or shielding/attenuation to certain wavelengths, focusing on several different usages.

[0048] Electromagnetic shielding is necessary in certain structures such as for medical, defense, databases, or scientific applications, normally through a Faraday cage. On the other hand, some structures require electromagnetic transparency to enhance the transmission of certain wavelengths through walls for example, such as office space, underground structures, etc. The present conductive composite material for building applications used with antenna permits adjusting the properties of the material in order to attain these benefits depending on the usage.

[0049] The addition of metallic/magnetic particles in concrete was proven to increase its electrical conductivity. The results show that, compared to the control concrete samples, the addition of particles proved to increase the bandwidth and decrease the return loss. That is, using metallic and/or magnetic particles in the composite material mixture enhances the electrical properties, useful for electromagnetic shielding and/or EH. [0050] The performance depends on the type of particles used, as well as the size distribution, as described in the present disclosure.

[0051] Fig. 1 shows a schematic illustration of an antenna structure 10 according to the invention, including an antenna 20, configured to send and/or receive an electromagnetic signal 12, wherein the antenna is embedded in a concrete 30, the concrete comprising at least a cement. The concrete further comprises additions in the form of particles, wherein the particles comprise a magnetic and/or a metallic material.

[0052] Fig. 2 shows a Sn plot over a frequency of 2 to 3 GHz of an electrically small antenna designed for wireless Lan of 2.4 GHz, with the solid line 200 representing the plot as measured and the dotted line 201 representing the plot as simulated. The simulated and measured results vary slightly due to fabrication limitations. From the graph, it can be seen that both simulated and measured results have a bandwidth just wide enough to cover the wireless LAN spectrum from 2.412 GHz to 2.472 GHz. The center frequency of 2.442 GHz is the lowest point of the graph, which is also the resonant frequency. The two main disadvantages of this is that firstly, although through simulations, the simulated resonant frequency has a Sn of less than -25 dB, the measured value was much lesser at -16 dB. Although any value below -16 dB is considered very good, this antenna is easily affected by the surrounding environment such as the presence of humans or metallic objects. Secondly, the bandwidth of the antenna is very narrow. This is a typical issue with electrically small antennas. With a narrow bandwidth, the extreme wireless LAN channels will encounter a greater loss than the center resonant frequency.

[0053] Fig. 3 shows a Sn plot over a frequency (f) of 2 to 3 GHz, with the antenna in air for comparison (solid line 301), an antenna structure according to the invention (long dashed line 302), and a comparative example (short dashed line 303). The plots of Fig. 3 are results of test cases created to show the effects of embedding antenna in concrete, for example cement paste, enhanced with metallic and/or magnetic particles.

[0054] Fig. 4 shows a flowchart illustrating a method 400 for forming an antenna structure according to various embodiments. The method 400 may include providing (410) an antenna configured to send and/or receive an electromagnetic signal. The method may include providing (420) a concrete composition; wherein the concrete composition comprises a cement and additions in the form of particles, wherein the particles comprise a magnetic and/or a metallic material. The method may include providing (430) a mold for pouring the concrete composition in. The method may further include (440) arranging the antenna in the mold; and pouring the concrete composition into the mold. The method may also be characterized by after arranging the antenna in the mold and after pouring the concrete composition into the mold, the antenna being at least partially surrounded by the concrete (450).

[0055] The concrete composition was mixed in water to form a paste, the paste was poured into a mold with inner volume of 8cm x 8cm x 8cm. Ordinary Portland cement was used with water/cement volume ratio 0.35 and including additions as articles in weight% to the total dry weight. Superplasticizer was used at 260 ml per lOOKg cement to improve the workability. The antenna (in the present example an antenna array) was arranged at the center of the samples, which were demolded from the mold after hardening and kept in a closed container. The antenna array was also measured in air and in a control sample without the particles added.

[0056] The experimental setup comprised a network analyzer connected to a sample via a coaxial cable, for the present examples, a N5242A PNA-X network analyzer was used. The data plot of the Sn is captured and various frequency ranges are displayed. From this plot, the resonant frequency can be seen, together with the bandwidth and Sn values at the various frequencies. A reference antenna was connected to another port to measure the S21 parameter.

[0057] Fig. 5 shows the structure of an exemplary antenna used for the experiments, in front view 501 (left) and back view 502 (right).

[0058] The antenna used for the examples includes seven metamaterial split ring resonators 100, arranged adjacent to each other in an array 550. Each metamaterial split ring resonator includes a first split ring including a first split at a first edge of the first split ring and a second split at a second edge of the first split ring. The first edge is opposite to the second edge. Each metamaterial split ring resonator may further include a second split ring inside the first split ring and concentric with the first split ring, wherein the second split ring includes a third split at a first edge of the second split ring adjacent to the first edge of the first split ring. The first split ring includes a first pair of stubs extending inwardly from the first split, and the second split ring includes a second pair of stubs extending inwardly from the third split. Although Fig. 5 shows an embodiment wherein the metamaterial split ring resonator array includes six resonators surrounding one resonator located in the center, it is understood that the metamaterial split ring resonator array 550 may include any suitable number of resonators arranged in any suitable form of array in various embodiments. In exemplary embodiments, the plurality of metamaterial split ring resonators may be arranged in a one-dimensional array, or in a two-dimensional array (e.g. in rows and columns).

[0059] Fig. 5(left) shows a top view 510 of a fabricated metamaterial split ring resonator array 550. The array 550 may be fabricated as a planar array on a top surface of a substrate. As shown in Fig. 5(left), the top side of the substrate has seven metaresonators 100, which are linked to a bottom layer of the substrate via two through hole vias 530 of each metaresonator 100.

[0060] Fig. 5(right) shows a bottom view 520 of the fabricated metamaterial split ring resonator array 550 according to various embodiments. At the bottom layer of the substrate as shown in Fig. 5(c), each metaresonator is connected via DC lines 540, as the current can be treated as uniform.

[0061] Fig. 6 (a) shows a schematic illustration of the exemplary antenna 610 including a metaresonator array 100 on a substrate 612 used for the experiments. A cable 650 with a connector 652 and tag 654 is shown connected to the antenna 610. Fig. 6 (b) shows an exemplary mold structure 660 comprising 3 molds 670. The two right molds include each an antenna embedded in concrete and a cable 650 connected to the antenna. Only the cables can be seen, marked with ".2" and ".3", each arranged in concrete in a corresponding mold. The right mold comprises concrete without an antenna for forming an antenna-free block may be used for other comparative experiments.

[0062] The fabricated metaresonator is formed on a substrate, for example, a front surface of the substrate. The fabricated metaresonator includes through hole vias at the front surface of the substrate. The width of the metaresonator in this exemplary embodiment is about 1.2cm, and the width of the substrate in this exemplary embodiment is about 1.3cm. In order to reduce the cost of fabrication for the fabricated metaresonator, standard PCB processes and FR-4 as a substrate are used. In PCB technologies, there are four classes of printed boards according to the IPC standards. In most cases, Class 2 has a good balance between cost and standard. For the design, the trace width of the split ring required in an exemplary embodiment is about 0.127mm with a trace separation of about 0.0889mm, and accordingly Class 2 was selected. The exemplary values of parameters of the fabricated metaresonator are listed in Table 1. The parameters of the metaresonator according to various embodiments of this specification may be in any other suitable values or range of values depending on the design need.

Table 1

[0063] Fig. 6 (c) to (e) show the geometry of a second, a third, and a fourth antenna structure according to various embodiments.

[0064] Fig. 6 (c) shows a patch antenna 670, comprising a microstrip patch 672 on a first side of a substrate 673, and a ground layer 674 on a second side of the substrate 673. The exemplary values of parameters of the fabricated antenna 670 are listed in Table 2.

Table 2

[0065] Fig. 6 (d) shows a quarter wavelength monopole antenna 680 comprising a microstrip 682 on a first side of a substrate 683, and a ground layer 684 on a second side of the substrate 683. The exemplary values of parameters of the fabricated antenna 680 are listed in Table 3. Parameter Property Units

Substrate

Material FR4 -

Thickness, H 0.6 to 1.6 mm

Trace

Material copper -

Thickness 12.7 to 50.8 μ m

L 20 to 30 mm

W 1 to 2 Mm

Table 3

[0066] Fig. 6 (e) shows a meander line antenna 690 comprising a microstrip 692 on a first side of a substrate 693, and a ground layer 694 on a second side of the substrate 693. The exemplary values of parameters of the fabricated antenna 690 are listed in Table 4.

Table 4

[0067] Any other antenna structure may be used. For example an omnidirectional antenna may be used in the present invention.

[0068] Fig. 7 (a) shows a schematic illustration 700 of demolded antenna structures according to the invention. Each concrete block 710 of an antenna structure 720 is marked by writing the code on the concrete block. Each antenna is marked before embedding with a tag 754 secured to the coaxial cable 750. The marking of the antennas is represented in Fig. 7 (a) as with a "." followed by a number, for illustrative purposes only. The cable 750 may include a connector 752. Concrete blocks used as reference are also prepared in a similar manner, for example, the block 730 does not include an embedded antenna. [0069] Fig. 7 (b) and Fig. 7 (c) illustrate the experimental setup for measuring of S n (Fig. 7 (b)) and S21 or S12 (Fig. 7 (c)). In Fig. 7 (b) the measurement setup 760 for measuring Sn is schematically demonstrated, the device under test 768 (e.g. antenna structure) is connected to the port 1 762 of the network analyzer 761. In Fig. 7 (b) the measurement setup 770 for measuring S21 (or S12) is schematically demonstrated, the device under test 778 (e.g. antenna structure) is connected to the port 2 776 of the network analyzer 771, a reference antenna 774 (in air) is connected to port 1 772 of the network analyzer 771.

[0070] Around the frequency range of wireless LAN, in a sweep of 2 GHz to 3 GHz, as shown in the Fig. 3, it is observed that when the antenna is included in concrete only (without the additions) (short dashed line 303), the S n performance of the antenna is bad, when compared to the performance of the antenna in air (solid line 301). The frequency response is distorted to a significant degree. On the other hand, when the antenna is placed in the concrete with the additions (long dashed line 302), the Sn is improved. In addition, the bandwidth of the antenna also increases allowing the antenna to operate in a wider frequency span. A point to take note is that the resonant frequency is shifted to the right. The reason is that the antennas used in these samples are optimized in air, not in a composite media. Even with such antenna, the improvements are significant. With a better optimization of the antenna for the particular composites, the resonant frequency can be tuned to the desired frequencies.

[0071] In conclusion, by adding metallic and/or magnetic particles in concrete, the performance of the antenna improves at least in terms of S n and bandwidth, thus the performance of the antenna structure is improved in comparison with a comparative example.

[0072] Without wanting to be bound by theory, the hypothesis is that by changing the surrounding dielectric from air to other composites that are more conductive and magnetic, at least two properties of Sn and bandwidth of the antenna can be improved. In order to achieve a high electric conductivity composite, the mixture includes any hydraulic inorganic material and metallic and/or magnetic particles, at different contents.

[0073] Magnetite, cementite, carbon-coated nickel, cobalt, iron, or any other kind of magnetic particles in any size may be used as the material for the particles. For example, cobalt oxide particles, and nickel oxide particles may be used. The material for the particles provide for permittivity to the building material, alone or in combination, and at different ratios, always assuring that the mechanical and durability properties of the structural element are not compromised.

[0074] Changing the medium surrounding an antenna changes its behavior due to the different characteristic impedances. The material of the antenna form capacitors and/or inductors which are coupled to its surrounding medium. Any metallic, magnetic, and/or dielectric material in the near field affects these inductive and capacitive values. When discussing small resonant antennas, such as metaresonators, the quality factor is important, as they typically have a small bandwidth, BW. The quality factor provided by the Chu- limit is given as

[0075] where * = ¥ Λ , and a is the radius of the sphere enclosing the antenna.In general, the quality factor can be written as

mW

Q ₌

^rad

where ω is the angular frequency, W is the average stored energy, and rad is the radiated power. It is beneficial that Q is small as BW is inversely proportional to Q, by having as little energy stored in the antenna, and increasing the power radiated. One way to decrease the Q and improve the BW is to analyze the antenna using series and parallel resonance transmission lines (TLs). If the transverse electromagnetic is regarded, TEM wave propagation on a two-wire conductor, and assuming sinusoidal steady-state, the complex propagation constant can be obtained:

where a is the attenuation constant, β = _{is the phase constant}, v ' ^" is the propagation constant (wave number) of a plane wave in free space, R is the series resistance per unit length (co/m), L is the series inductance per unit length (H/m), G is the shunt conductance per unit length (S/m), and C is the shunt capacitance per unit length ( /m).From this perspective, the quality factor can be written as

[0076] Therefore, to lower the Q, it is possible to load the antenna with materials that have lower relative permittivity, ε_Γ, and relative permeability, μ_Γ. From the results obtained, the Q is decreased as the BW increased for all four samples. The cement paste containing micro-sized iron-based magnetic particles improve the BW of the antenna by a larger extend while maintaining the shape of the Sn curve. Among the two cement pastes with micro-sized particles samples, iron (III) oxide had a better effect on S21 for frequencies between 2 to 2.54 GHz, which suggests that more electromagnetic waves are passing into the sample. Within the wireless LAN spectrum, the cement paste with micro-sized iron (III) oxide particles allows the most electromagnetic waves to penetrate into the sample.

[0077] By adding magnetic and/or metallic particles in the composite material, the electrical permittivity and permeability may be changed in a way that can positively impact the performance of the antenna. Having the particles, the aim is to increase the bandwidth by lowering the overall reflection coefficient.

[0078] Therefore, the experiments support the hypothesis of improvement of an antenna structure by using magnetic and/or metallic particles included in the concrete with the antenna embedded.

[0079] Comprehensive experiments were done as will be explained further below. Different types of particles were included in the concrete compositions used for embedding a metaresonator antenna array to simulate embedded wireless applications. It was observed, for all samples, 1) an increase in the bandwidth of the embedded antenna compared to the antenna in air, and 2) a shift in the resonance frequency smaller than pure concrete alone. In the analysis of the effects of different sizes of the iron-based particles have on the antennas, it is observed that micro-sized particles enhanced concrete increases the bandwidth, while maintaining the general shape of the Sn of the antenna compared to other samples and control. Good results were obtained with iron-based particles, however, the invention is not limited thereto, as similar results were also obtained with other kind of particles. In addition, for the intended wireless LAN spectrum, micro-sized iron (III) oxide enhanced concrete improved the transmission coefficient of the antenna by as much as 10 dB.

Effects on reflection coefficient

[0080] Fig. 8 shows six Sn plots over a frequency range of 2 to 3 GHz, for a comparative example (solid line), the antenna in air (small spaced dotted line), and according to the invention for micro-sized iron (III) oxide (long dashed line), nano-sized iron (III) oxide (large spaced dotted line), micro-sized magnetite (short dashed line), and nano-sized magnetite (dash-dot line).

[0081] Figure 8 shows the measured reflection coefficient, Sn of several examples. The solid line 801 represents the measured Sn of the comparative example with an antenna in concrete only. As there may be slight deviations in the performance of each antenna used, the Sn of one sample antenna measured in air medium (small spaced dotted line 802) is shown as a reference. The frequency range between the two vertical dashed lines represents the intended wireless LAN spectrum. When this antenna is embedded in pure concrete only (solid line 801), the behavior of the antenna is changed significantly. At the designed frequency of 2.442 GHz, the Sn is changed to -13 dB. Within the 2 GHz to 3 GHz bandwidth, there is no noticeable resonance, although in general, the Sn is less than -10 dB. This shows that the impedance of the antenna is not well matched throughout this bandwidth. To improve the performance of embedded antenna, four types of iron-based magnetic particles are added to concrete; 1) micro-sized magnetite (short dashed line 805), 2) nano-sized magnetite (dash-dot line 806), 3) micro-sized iron (III) oxide (long dashed line 803), and 4) nano-sized iron (III) oxide (large spaced dotted line 804). The table below summaries the effects of the different particles have on the antenna. The changes in Sn (in dB) and frequency shifts (in percentage), where positive values indicate shifting to higher frequencies, and negative value indicate shifting to lower frequencies, are compared to the measurement of the antenna in air. The change in Sn is taken as the decrease in the smallest Sn value within the 2 to 3 GHz frequency range of the antenna measured before and after embedding into the materials.

[0082] For pure concrete only sample (control, solid line 801), the Sn is decreased by - 2.01 dB compared to the measurement done in air. As there is no noticeable dip in S n within this 2 to 3 GHz range, the lowest point of Sn at 3 GHz is taken as the resonance frequency for comparison purposes. For nano-sized particles enhanced concrete, it is observed that both magnetite and iron (III) oxide lower the Sn by 6.19 dB and 9.07 dB respectively. For micro-sized particles enhanced concrete, the magnetite and iron (III) oxide samples lower the Sn by 17.26 dB and 19.28 dB respectively. Comparing the type of particles, iron (III) oxide particles enhanced concrete lower the S more than magnetite particles enhanced concrete, giving a better effect on the embedded antenna. Comparing the size of the particles, micro-sized particles enhanced concrete were able to lower the Sn of the embedded antenna to be even better than the sample reference antenna measured in air. This shows that when the sample antennas are embedded into micro-sized magnetic iron-based particles enhanced concrete, the Sn is significantly better than just the antenna in air. Nano-sized magnetic iron based enhanced concrete could also lower the Sn of the antenna, although less than for iron oxide. In all samples, the Sn is reduced to less than - 10 dB within the intended wireless LAN bandwidth. A reading of -10 dB or less indicates a sufficient performance of the antenna where at least 90% of the input power is delivered to the antenna, and 10% is reflected.

[0083] Observing the shift in resonance frequency (Fig. 8), assuming the resonance frequency of the control at 3 GHz (lowest value within the test spectrum), the shift in frequency is 23.2%. For the magnetite particles enhanced concrete, the shift in frequency is -3.87% and 3.66% for micro-sized and nano-sized particles respectively. Comparing with iron (III) oxide particles enhanced concrete, the shift is 12.20% and 8.35% for the micro-sized and nano-sized particles respectively. In general, other than the micro-sized magnetite particles enhanced concrete, the other three particle enhanced concrete shifted the resonance frequency to the right (higher frequency). In terms of the magnitude of shifting, iron (III) oxide shifted the resonance frequency more than magnetite, with micro- sized iron (III) oxide particle enhanced concrete shifting the most towards higher frequency. A small shift in frequency shows that the material has little detuning effect on the antenna.

[0084] When observing shape of the Sn, micro-sized particles enhanced concrete maintain the general shape of the Sn curves with a single distinct resonance frequency that can be noted. The nano-sized particles enhanced concrete exhibit two resonance frequencies, altering the single resonance frequency shape of the antenna. In terms of bandwidth, both micro-sized particles enhanced concrete increased the bandwidth, with magnetite particles enhanced concrete having the bigger effect than iron (III) oxide enhanced concrete. For the nano-sized particles, the double dip shape also has an increased bandwidth when compared to the bandwidth of the reference antenna in air.

[0085] From the observations of Sn of the different samples, adding iron-based magnetic particles showed the strongest positive effect on the embedded antenna. The micro-sized particles enhanced concrete showed an improved effect over the nano-sized particles enhanced concrete on the antenna in terms of the decrease in Sn, bandwidth, and shape of the Sn curve.

Effects on transmission coefficient

[0086] Fig. 9 shows six S21 plots over the frequency (f) of 2 to 3 GHz, for a comparative example (solid line 901), the antenna in air (small spaced dotted line 902), and according to the invention for micro-sized iron (III) oxide (long dashed line 903), nano-sized iron (III) oxide (large spaced dotted line 904), micro-sized magnetite (short dashed line 905), and nano-sized magnetite (dash-dot line 906). The frequencies between two vertical dotted lines indicates the wireless LAN 802.11 b/g/n spectrum. A reference measurement of the sample antenna used (small spaced dotted line) is shown to indicate the in air performance of the antenna. At the frequency range of wireless LAN 802.1 lb/g/n, the S21 has a range of between -30 dB to -37 dB. When the antenna is placed in pure concrete only (solid line), the S21 reduces by about 16 to 20 dB. This shows that the amount of electromagnetic radiation that can pass through into the concrete is significantly reduced.

[0087] When the antenna is embedded in iron-based magnetic particles enhanced concrete, most of the S21, within frequencies of from 2.412 GHz to 2.472 GHz, are improved except for the micro-sized magnetite particles, for which the improvement is shifted to higher frequencies. The antenna may be adjusted such that, when embedded in concrete, the improvement peak corresponds to the required frequency.

[0088] Both nano-sized particles enhanced concrete have the same behavior in this range. For iron (III) oxide particles enhanced concrete, the improvement to S21 is the most. This shows that by enhancing concrete with iron-based magnetic particles, the amount of electromagnetic radiation passing through the material increase compared to concrete alone. [0089] A set of experiments were conducted to measure the influence of the variation of the concentration of the particles on the properties of the antenna. For these experiments, micro-sized iron oxide of identical composition was used as exemplary particle type. A total of 15 samples were produced with 3 of each of 0% (control, solid line 901), 1%, 2%, 3%, and 4% iron oxide enhanced building materials. Measurements in Sn and S12 were taken. The results show that in general, increasing the concentration of iron oxide improves the matching of the embedded antenna, and the transmission of electromagnetic signal.

[0090] A set of antennas was selected, having similar Sn values, in air and before embedding in concrete. The Sn and the S12 of the antennas was firstly measured in air, so that properties could be better compared to the antenna structure in concrete and to the control sample embedded in concrete without particles. The plots are shown in sets of 3 for ease of comparison.

[0091] The antennas were embedded in concrete using the method as described herein. One sample was prepared as control sample, wherein the antenna was embedded into concrete without magnetic and/or metallic particles (sample 1). Another sample was prepared according to the invention, wherein the antenna was embedded into concrete including micro-sized iron oxide particles in a concentration of 1 weight% (sample 2). A third sample was prepared according to the invention, wherein the antenna was embedded into concrete including micro-sized iron oxide particles in a concentration of 2 weight% (sample 3). A fourth sample was prepared according to the invention, wherein the antenna was embedded into concrete including micro-sized iron oxide particles in a concentration of 3 weight% (sample 4). A fifth sample was prepared according to the invention, wherein the antenna was embedded into concrete including micro-sized iron oxide particles in a concentration of 4 weight% (sample 5).

[0092] Fig. 10 shows the respective Sn of antennas for samples 1 to 3 before embedding in concrete, and Fig. 11 shows the respective S12 of the antennas for samples 1 to 3 before embedding in concrete. It is shown that the antennas have comparable Sn and S12 properties. The solid lines 1003 and 1103 correspond to the antenna for sample 1, before it is embedded in concrete alone. The short dashed lines 1001 and 1101 correspond to the antenna for sample 2 before it is embedded in concrete comprising micro- sized iron oxide particles in a concentration of 1 weight%. The long dashed lines 1002 and 1102 correspond to the antenna for sample 3 before it is embedded in concrete comprising micro-sized iron oxide particles in a concentration of 2 weight%. [0093] Fig. 12 shows the S n of the prepared samples 1 to 3, and Fig. 13 shows the S12 of the prepared samples 1 to 3. For Figs. 12 and 13, the Sn and S12 of sample 1 are represented by solid lines 1203 and 1303 respectively, the S n and S12 of sample 2 are represented by the short dashed lines 1201 and 1301 respectively, and the Sn and S12 of sample 3 is represented by the long dashed lines 1202 and 1302 respectively.

[0094] By comparing Fig. 12 and Fig. 10, the Sn are generally decreased which shows better matching, and the frequencies are shifted towards the higher frequency after the antennas are embedded into the respective concrete samples.

[0095] It is shown in Fig. 13, at frequencies from 2.45 GHz to about 2.15 GHz which are lower than the wireless LAN frequencies, that the enhanced concrete increases the transmission of electromagnetic signal. At the range of up to 2.7 GHz, sample 3 allows more electromagnetic signal to be transmitted through it. Above 2.9 GHz, sample 3 acts more like a shield while sample 2 allows more electromagnetic signal to be transmitted through from 2.7 GHz to 2.9 GHz, and acting like a shield for frequencies above 2.9 GHz. At the range of the frequencies from 2.37 GHz to 2.6 GHz which includes the wireless LAN range of frequencies, sample 3 allows for more transmission of electromagnetic signal (6dB).

[0096] Fig. 14 shows the respective Sn of the antennas for samples 1, 4 and 5 before embedding in concrete, and Fig. 15 shows the respective S12 of the antennas for samples 1,

4 and 5 before embedding in concrete. The Sn and S 12 of the control antenna for sample 1 is represented by solid lines 1403 and 1503 respectively, for ease of comparison. It is shown that the other antennas for samples 4 and 5 and the control antenna have comparable S n and S12 properties. The short dashed lines 1401 and 1501 correspond to the antenna for sample 4 before it is embedded in concrete comprising micro-sized iron oxide particles in a concentration of 3 weight%. The long dashed lines 1402 and 1502 correspond to the antenna for sample 5 before it is embedded in concrete comprising micro- sized iron oxide particles in a concentration of 4 weight%.

[0097] Fig. 16 shows the Sn of the prepared samples 1, 4 and 5, and Fig. 17 shows the S12 of the prepared samples 1, 4 and 5. For Figs. 16 and 17, the Sn and S12 of sample 1 is represented by solid lines 1603 and 1703 respectively, the Sn and S12 of sample 4 is represented by short dashed lines 1601 and 1701 respectively, and the Sn and S12 of sample

5 is represented by long dashed lines 1602 and 1702 respectively. [0098] By comparing Fig. 16 and Fig. 14, the Su are generally decreased which shows better matching, and the frequencies are shifted towards the higher frequency after the antennas are embedded into the respective concrete samples. Fig. 16 also shows that the matching is greatly improved for sample 5 with the Su at -44 dB with a shift in the frequency to 2.84 GHz.

[0099] Fig. 17 shows the S12 of the antennas after embedding. At frequencies from 2.45 GHz to 2.15 GHz, which are lower than the wireless LAN frequencies, the enhanced concrete increases the transmission of electromagnetic signal. At the range of the frequencies from 2.37 GHz to 2.6 GHz, which includes the wireless LAN range of frequencies, sample 5 allows more electromagnetic signal to pass through the sample. Beyond 2.6 GHZ, samples 4 and 5 act more like shield compared to concrete alone.

[00100] Fig. 18 summarizes the results of the improvement in transmission. It can be seen that the transmission is improved, in relation to the comparative example, with the increase of the concentration of the additions. There is an increasing trend of increasing transmission of electromagnetic signal with increase in the concentration of iron oxide in building materials. The most significant increase is when 4% iron oxide is added to building materials, the transmission coefficient increases by 5.5 dB, which translates to about 1.9 times more transmission compared to concrete alone.

[00101] This experiment confirms that effect of adding iron oxide to building materials positively affects the matching of the antenna (as can be seen by improvement in Su). In addition, the transmission of electromagnetic signal into the material can also be improved (as can be seen by improvement in S12 in the frequency of 2.45 GHz) other than the conventional understanding that placing antenna in lossy materials reduces electromagnetic signal transmission.

[00102] While the invention has been particularly shown and described with reference to specific embodiments, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. The scope of the invention is thus indicated by the appended claims and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced.

Claims

Claims What is claimed is:

1. An antenna structure, comprising: an antenna configured to send and/or receive an electromagnetic signal; wherein the antenna is embedded in a concrete comprising at least a cement; wherein the concrete further comprises additions in the form of particles, and wherein the particles comprise a magnetic and/or a metallic material.

2. The antenna structure of claim 1, wherein the particles comprise at least one of: iron, nickel, and cobalt.

3. The antenna structure of claim 2, wherein the particles comprise carbon-coated nickel.

4. The antenna structure of claim 2, wherein the particles comprise magnetite, cementite, or a mixture thereof.

5. The antenna structure of claims 2, wherein the particles comprise iron in the form of an iron oxide.

6. The antenna structure of claim 1, wherein the particles comprising a magnetic and/or a metallic material are comprised in an amount of at least 0.5 weight% of the concrete.

7. The antenna structure of claim 1, wherein the particles' average size is between 5 nm and 5 micrometers.

8. The antenna structure of claim 7, wherein the particles' average size is between 100 nm and 5 micrometers.

9. The antenna structure of claim 7, wherein the particles are homogeneously distributed in the concrete.

10. The antenna structure of claim 7, wherein the particles comprise a non-uniform shape.

11. The antenna structure of claim 1, further comprising a cable electrically coupled to the antenna; wherein the cable is partially embedded in the concrete.

12. The antenna structure of claim 1, wherein the antenna is configured to have a resonant frequency equal or above 2 GHz.

13. The antenna structure of claim 1, wherein the concrete in proximity with the antenna comprises a thickness of at least 1 cm.

14. A method for forming an antenna structure, comprising: providing an antenna configured to send and/or receive an electromagnetic signal; providing a concrete composition; wherein the concrete composition comprises: a cement; additions in the form of particles, wherein the particles comprise a magnetic and/or a metallic material; providing a mold for pouring the concrete composition in; arranging the antenna in the mold; and pouring the concrete composition into the mold, wherein after arranging the antenna in the mold and after pouring the concrete composition into the mold, the antenna is at least partially surrounded by the concrete.

15. The method of claim 14, wherein the antenna is arranged in the mold before the pouring of the concrete composition into the mold.

16. The method of claim 14, wherein the antenna is arranged in the mold after the pouring of the concrete composition into the mold.

17. The method of claim 14, wherein the antenna is arranged in the mold keeping a distance of at least 1 cm to a closest mold wall.