NZ752904B2 - Artificial dielectric material and focusing lenses made of it - Google Patents

Abstract

artificial dielectric material containing plurality of sheets of a lightweight dielectric material piled up together and plurality of short conductive tubes placed in layers inside of holes made in sheets of a lightweight dielectric material. A cross section of the short conductive tubes may be in a shape of a circle or a polygon for example square, hexagon or octagon. The lightweight dielectric material may be a foam polymer. Sheets of a foam polymer containing the short conductive tubes are separated by sheets of a foam polymer without the short conductive tubes. The short conductive tubes placed in odd and even layers could be placed above each other or be shifted from each other. The provided artificial dielectric material suits for manufacturing focusing lenses for antennas, for example cylindrical lenses. n a shape of a circle or a polygon for example square, hexagon or octagon. The lightweight dielectric material may be a foam polymer. Sheets of a foam polymer containing the short conductive tubes are separated by sheets of a foam polymer without the short conductive tubes. The short conductive tubes placed in odd and even layers could be placed above each other or be shifted from each other. The provided artificial dielectric material suits for manufacturing focusing lenses for antennas, for example cylindrical lenses.

Description

ARTIFICIAL DIELECTRIC MATERIAL AND FOCUSING LENSES MADE OF IT CROSS-REFERENCE TO RELATED APPLICATION The present invention application claims priority from Provisional NZ patent application 741978, filed April 27, 2018, entire content of which is incorporated herein by reference.

FIELD OF THE INVENTION The present invention relates to artificial dielectric material and focusing lenses made of it for focusing electromagnetic waves of radio frequency band.

BACKGROUND Modern mobile communication market needs multi beams antennas creating narrow beams and operating in different frequency bands. Focusing dielectric lens is the main part of the most efficient multi beam antennas. Diameter of a focusing lens has to be several wave length of the operating frequency to create a narrow beam therefore some lenses of multi beams antennas for mobile communication have diameter more than 1 m. Such lenses made of usual dielectric materials are too heavy therefore many researches were done to create light and low loss lenses.

The most of known lightweight artificial dielectric materials consist of randomly oriented conductive parts mixed with nonconductive parts made of lightweight dielectric material. It is very difficult to manufacture uniform material having desirable dielectric properties by randomly mixing of conductive and nonconductive parts therefore focusing lens is the most expensive component of multi beams antennas. Due to improve properties and decrease cost of focusing lens development of such materials is constantly continuing.

US Pat.8518537 B2 describes the lightweight artificial dielectric material comprising plurality of randomly orientated small particles of lightweight dielectric material like polyethylene foam containing conductive fibers placed inside of each particle.

Patent application US 2018/0034160 A1 describes the lightweight artificial dielectric material comprising plurality of randomly orientated small multilayer particles of lightweight dielectric material containing thin conductive patches between layers. It is written in this application such multilayer particles provides more dielectric permittivity than particles containing conductive fibers.

Patent application US 2018/0279202 A1 describes other kings of the lightweight artificial dielectric material comprising plurality of randomly orientated small particles. One described material small multilayer particles of lightweight dielectric material containing thin conductive sheets between layers.

All mentioned above lightweight artificial dielectric materials are made by randomly mixing of small particles. It is need to eliminate metal-to-metal contacts within the material to that could lead to passive intermodulation distortion therefore manufacturing of such materials comprises many stages and its cost is high.

Randomly mixing provides isotropic properties of a final material consisting of small particles but some applications need dielectric material having anisotropic properties. For example cylindrical lens made of anisotropic dielectric material can reduce depolarization of electromagnetic wave passed through cylindrical lens and improve cross polarization ratio of multi beam antenna (US Pat.9819094 B2). The cylindrical lens made of isotropic artificial dielectric material creates depolarization of the electromagnetic wave passed through such lens therefore an antenna comprising such lens can suffer from high cross polarization level.

Thus, there is a need for lightweight dielectric material providing desirable properties including anisotropic properties.

SUMMARY The first objective of the invention is to overcome deficiencies of known lightweight artificial dielectric materials and provide a light artificial dielectric material which is simpler for manufacturing compare with known analogous and suitable for production of focusing lenses and dielectric antennas for radio communication.

Accordingly, provided herein is an artificial dielectric material containing a plurality of sheets of a foam dielectric material having density less than 500 kg/m3 piled up together and a plurality of short conductive tubes placed in holes made in the sheets of the foam dielectric material, wherein the sheets of the foam dielectric material containing the short conductive tubes placed in the holes are separated by sheets of the foam dielectric material without the short conductive tubes.

Also provided is a cylindrical focusing lens made of the artificial dielectric material described.

The provided material has to provide desirable dielectric properties and reliable isolation of conductive particles from each other.

The present invention provides the light artificial dielectric material including a plurality of short conductive tubes having thin walls and placed inside of a lightweight dielectric material.

A cross section of the tube could be a circle or a polygon for example square, hexagon or octagon. The short conductive tubes are placed in layers. One layer comprises a sheet of the lightweight dielectric material containing a plurality of holes. The lightweight dielectric material can be a foam polymer. Tubes are placed in the holes made in a sheet of the lightweight dielectric material and contain air inside of the tubes. Layers containing the tubes are separated by layers of a lightweight dielectric material without tubes. Separating layers also could contain holes having smaller diameter than diameter of the holes for tubes to provide air ventilation through the lightweight dielectric material. The tubes placed at neighboring layers could be placed above each other at the same axes or shifted from each other and have different axes.

Diameter of the conductive tubes is about twenty times less than wave length of the operating frequency to provide acceptable dependence of properties of the artificial dielectric material versus frequency. A length of the conductive tubes may be 0.2-5.0 of their respective diameter depends of desirable properties of the artificial dielectric material.

Density of the provided artificial dielectric material mainly depends of tubes’ weight and density of the lightweight dielectric material. Polyethylene foam has density in the range 40- 100 kg/m3. Aluminum tubes having diameter 6 mm and walls’ thickness 0.1 mm have density 180 kg/m3. The provided artificial dielectric material containing such tubes and polyethylene foam has density approximately 140 kg/m3 and dielectric permittivity (Dk) approximately 1.7 when distances between the tubes and the layers are approximately 1 mm. There is possible to decrease density of the provided artificial dielectric material by decreasing thickness of walls of the conductive tubes. Sputtering or chemical precipitation of a conductive material on walls of the holes made in the dielectric material can provide conductive tubes having thickness of walls less than 0.01 mm.

Dk of the provided artificial dielectric material depends of a shape of the tubes and distances between the tubes and between the layers. Also its Dk depends of polarization and direction of electromagnetic wave spreading through the material. Thus the provided artificial dielectric material is mainly an anisotropic material but one also can provide isotropic properties. For example when electromagnetic wave crosses material along the axes of the short tubes, Dk doesn’t depend of polarization when distances between the short tubes disposed at one layer are equal.

When electromagnetic wave crosses the provided material in perpendicular to the axes of the short tubes, Dk depends of polarization. Big Dk dependence of polarization occurs when distances between the short tubes disposed at one layer significantly less or bigger than distances between the layers. Dk for E polarization directed along the axes of the short tubes is bigger than Dk for E polarization directed across the axes of the short tubes when distances between the short tubes disposed at one layer significantly bigger than distances between layers. Dk for E polarization along the axes of the short tubes is smaller than Dk for E polarization across the axes of the short tubes when distances between the short tubes disposed at one layer significantly smaller than distances between the layers. Such materials can transfer the linear polarized electromagnetic wave to circular polarized one.

Dk for both polarizations could be equal or slightly different when distances between the short tubes disposed at one layer and distances between the layers are approximately equal.

Thus the provided material could be useful for several applications.

Repeatability of Dk of the provided material dependents of how correct the short tubes and distances between ones were made on a production line. Several samples of the provided material were assembled using made by punching tubes having diameter 6 mm and length 6 mm. Holes in sheets of polyethylene foam were made by laser cutting. Measured values of Dk were 1.68 +/- 0.006. Thus dielectric properties of the provided material are very repeatable.

Other known technologies could be also used for production of the tubes and the supporting lightweight dielectric material.

The second objective of the invention is to provide focusing lenses made of the provided artificial dielectric material. The short tubes placed at one layer could form a structure providing desirable distribution of Dk along the layer therefore different kinds of focusing lens could be made of the provided artificial dielectric material. For example a cylindrical lens could be made of round sheets of the lightweight dielectric material placed above each other and containing the short conductive tubes. Several embodiments of described below cylindrical lenses show different distribution of Dk along the round sheets of lightweight dielectric material. Process of manufacturing of such lenses doesn’t include mixing of small parts. The structure of provided artificial dielectric material eliminates moving and settling of conductive tubes under vibration and other environmental factors providing the long term physical stability and performance of the lens. It is the first advantage of the provided artificial dielectric material.

The reliable isolation of conductive tubes by the lightweight dielectric material eliminates a possibility of metal-to-metal contacts that could lead to passive intermodulation distortion.

Therefore the provided artificial dielectric material is suitable for manufacturing of lenses for base station antennas having very tight specification for passive intermodulation distortion. It is the second advantage of the provided artificial dielectric material.

The provided artificial dielectric material can provide as homogenous Dk so as variable along the layer Dk. It is the third advantage of the provided artificial dielectric material.

The provided artificial dielectric material could be made with air ventilating channels therefore high power electromagnetic wave could be focused by lenses made of such artificial dielectric material. It is the fourth advantage of the provided artificial dielectric material.

BRIEF DESCRIPTION OF THE DRAWINGS Figs.1a-1f show top views of a one layer of several embodiments of the present invention containing the tubes of different shapes and forming different structures.

Figs. 2a and 2b show reciprocal dispositions of round tubes placed in two layers shifted from each other.

Fig. 3a shows the top view of even layer of a cylindrical lens containing round tubes placed in the holes made in the lightweight dielectric material.

Fig. 3b shows the top view of odd layer of a cylindrical lens made of the lightweight dielectric material.

Fig. 3c shows the top view of odd layer of a cylindrical lens made of the lightweight dielectric material with holes for air ventilation.

Fig. 3d shows the cross section of a cylindrical lens containing 8 layers with round tubes and 9 layers without tubes.

Fig. 3e shows the cross section of a cylindrical lens containing 8 layers with round tubes and 9 layers with holes for air ventilation.

Fig. 3f shows the cross section of a cylindrical lens containing 9 layers without tubes and 8 layers with round tubes where layers 4, 8, 12 and 16 are turned around axis of a cylinder at 30 degrees from layers 2, 6, 10 and 14.

Fig. 3g shows reciprocal positions of the tubes placed in layers 2 and 4.

Fig. 4a and 4b show another embodiment of the present invention where two neighboring layers of the lightweight dielectric material are made as an entire part 5 containing the tubes 1.

Fig. 5 shows one layer of a cylindrical lens containing equal tubes forming three areas providing different Dk.

Fig. 6 shows one layer of a cylindrical lens containing equal tubes placed along radiuses of a cylinder. Distances between the tubes increase towards the edge of a cylinder providing Dk decreasing towards the edge of a cylinder.

Fig. 7 shows one layer of a cylindrical lens containing the tubes having three different diameters and forming three areas providing different Dk.

DETAILED DESCRIPTION The present invention provides the lightweight artificial dielectric material including a plurality of the short conductive tubes having thin walls and placed inside of the lightweight dielectric material. The short conductive tubes are placed in layers. One layer comprises a sheet of the lightweight dielectric material containing a plurality of the holes. The short conductive tubes are placed in the holes made in the sheet of the lightweight dielectric material and contain air inside of the tubes. The layers containing the tubes are separated by layers of the lightweight dielectric material without tubes.

Such structure delays electromagnetic wave passing through and acts like a dielectric material when dimensions of the conductive tubes are much less than wave length.

Some embodiments of the present invention containing the tubes of different shapes and forming different structures are shown in Figs.1a-1f.

Fig. 1a shows the top view of a one layer containing round tubes placed in rows where distances between tubes disposed at neighboring rows and distances between neighboring tubes of one row are equal.

Fig. 1b shows the top view of a one layer containing round tubes placed in rows shifted on half of a distance between neighboring tubes placed in one row and distances between any neighboring tubes are equal. Such disposition provides bigger value of Dk in compare with disposition shown in Fig. 1a if both structures have equal gaps between the tubes.

Fig. 1c shows the top view of a one layer containing square tubes placed in rows where distances between tubes disposed at neighboring rows and distances between neighboring tubes of one row are equal. The tubes of a square shape could provide bigger value of Dk in compare with tubes of a round shape but its weight is bigger.

Fig. 1d shows the top view of a one layer containing square tubes placed in rows shifted on half of a distance between neighboring tubes placed in one row and distances between any neighboring tubes are equal.

Fig. 1e shows the top view of a one layer containing tubes having hexagonal cross section and placed in positions providing equal distances between any edges of any neighboring tubes.

Fig. 1f shows the top view of a one layer containing tubes having octagonal cross section placed in rows where distances between tubes disposed at neighboring rows and distances between neighboring tubes of one row are equal.

The tubes having any other shape of cross section also could be used for manufacturing the artificial dielectric material. The artificial dielectric material containing the tubes of one size only is the simplest for production but for some applications the material could contain tubes having different sizes to provide desirable dielectric properties.

Fig. 2a shows round tubes of a two layers containing round tubes placed as shown in Fig. 1a where the top layer are shifted along rows and perpendicular to rows on half of a distance between neighboring tubes placed in one row.

Fig. 2b shows the top view of a two layers containing round tubes placed as shown in Fig. 1b where the top layer is shifted along rows on half of a distance between neighboring tubes placed in one row and perpendicular to rows on a distance providing equal distances between axis of a tube placed in the top layer and axes of three neighboring tubes placed in the bottom layer. The shift of neighboring layers decrease dependence Dk from direction of electromagnetic wave spreading perpendicular to axes of the tubes.

Figs.3a-3g show some embodiments of cylindrical lenses made of the provided lightweight artificial dielectric material.

Fig. 3a shows the top view of even layers containing round tubes 1 placed in holes made in a sheet of a lightweight dielectric material 2 of a round shape. The tubes 1 contain air 3 inside.

Fig. 3b shows the top view of odd layers made of the lightweight dielectric material without tubes.

Fig. 3c shows the top view of odd layers made of the lightweight dielectric material with holes 4 having smaller diameter than diameter the holes for the tubes.

Fig. 3d shows the cross section of a cylindrical lens containing 8 layers with round tubes placed as shown in Fig. 3a and 9 layers without tubes shown in Fig. 3b.

Fig. 3e shows the cross section of a cylindrical lens containing 8 layers with round tubes shown in Fig. 3a and 9 layers with holes 4 shown in Fig. 3c. Holes 4 and tubes 1 form vertical channels for air ventilation therefore high power electromagnetic wave could be focused by such lens made of the provided lightweight artificial dielectric material.

Fig. 3f shows the cross section of a cylinder containing 8 layers with round tubes shown in Fig. 3a and 9 layers without tubes shown in Fig. 3b. Layers 4, 8, 12 and 16 are turned around an axis of the cylinder by 30 degrees in relation to layers 2, 6, 10 and 14.

Fig. 3g shows reciprocal positions of tubes placed in layers 2 and 4.

Turn by 30 degrees of neighboring layers containing tubes in relation to each other decreases dependence Dk from azimuth angle of electromagnetic wave crossing the lens in direction perpendicular to cylinder axis.

Fig. 4a and 4b show another embodiment of the present invention where two neighboring layers of the lightweight dielectric material are made as an entire part 5 containing tubes 1.

Such shape of the supporting lightweight dielectric material decreases quantity of dielectric parts and simplifies assembling of the focusing lens.

Other embodiments of the present invention showing different dispositions of the short tubes forming one layer of a cylindrical lens are shown in Figs. 5-7.

Fig. 5 shows one layer with equal tubes forming three areas providing different Dk.

The first area is the circle placed at the middle. The second area is the first ring placed nearly the circle. The third area is the second ring placed nearly the first ring. Distances between the tubes of the circle are smaller than distances between the tubes of the first ring and distances between the tubes of the second ring are smaller than distances between the tubes of the second ring. As a result Dk of the first area is bigger than Dk of the second area and Dk of the second area is bigger than Dk of the third area.

Fig. 6 shows one layer with equal tubes placed radially. Distances between the tubes increase towards the edge of the cylinder providing Dk decreasing towards the edge of the cylinder.

Fig. 7 shows one layer containing the round tubes of three different sizes forming three areas providing different Dk. The first area is the circle placed at the middle and containing the tubes of the big size. The second area is the first ring placed nearly the circle and containing the tubes of the middle size. The third area is the second ring placed nearly the first ring and containing the tubes of the small size. Distances between tubes of the circle are smaller than distances between tubes of the first ring and distances between tubes of the first ring are smaller than distances between tubes of the second ring therefore Dk of the first area is bigger than Dk of the second area and Dk of the second area is bigger than Dk of the third area.

A focusing lens concentrating a flat electromagnetic wave in a focus also can be made of many layers having different diameters. In such type of a lens electromagnetic wave spreads along axes of tubes placed in layers.

Claims (21)

1. An artificial dielectric material containing a plurality of sheets of a foam dielectric material having density less than 500 kg/m3 piled up together and a plurality of short conductive tubes placed in holes made in the sheets of the foam dielectric material, wherein the sheets of the foam dielectric material containing the short conductive tubes placed in the holes are separated by sheets of the foam dielectric material without the short conductive tubes.

2. The artificial dielectric material according to claim 1, wherein the short conductive tubes have cross section in a shape of a circle or a polygon.

3. The artificial dielectric material according to claim 1, wherein the short conductive tubes are made of aluminium.

4. The artificial dielectric material according to claim 1, wherein the short conductive tubes are made by sputtering of conductive material on walls of the holes made in the foam dielectric material.

5. The artificial dielectric material according to claim 1, wherein the short conductive tubes are made by chemical precipitation of conductive material on walls of holes made in the foam dielectric material.

6. The artificial dielectric material according to claim 1, wherein the short conductive tubes have a length in the range 0.2-5.0 of their respective diameter.

7. The artificial dielectric material according to claim 1, wherein the foam dielectric material is a foam polymer.

8. The artificial dielectric material according to claim 7, wherein the foam polymer is made of a material in a group consisting of: polyethylene, polystyrene, polypropylene, polyurethane, silicon and polytetrafluoroethylene.

9. The artificial dielectric material according to claim 8, wherein sheets of the foam polymer without the short conductive tubes contain holes providing air ventilation through the material.

10. The artificial dielectric material according to claim 1, wherein the sheets of foam dielectric material containing the short conductive tubes and the sheets of the foam dielectricmaterial without the short conductive tubes are made as one sheet containing gaps for the short conductive tubes disposed on one surface of the sheet.

11. The artificial dielectric material according to claim 1, wherein the short conductive tubes placed in one layer form a square structure providing equal distances between neighbouring tubes disposed at the same row or at the same column.

12. The artificial dielectric material according to claim 1, wherein the short conductive tubes placed in one layer form a honeycomb structure providing equal distances between any neighbouring tubes.

13. The artificial dielectric material according to claim 1, wherein the short conductive tubes placed in even layers are disposed at the same longitudinal axes as the short conductive tubes placed in odd layers.

14. The artificial dielectric material according to claim 1, wherein the short conductive tubes placed in even layers are shifted along the layer in relation to the short conductive tubes placed in odd layers.

15. A cylindrical focusing lens made of the artificial dielectric material according to any one of claims 1-14.

16. A cylindrical focusing lens made of the artificial dielectric material according to claim 15, wherein the short conductive tubes placed in one layer and having the same size form the middle area in a shape of circle and at least one area in a shape of ring surrounding the middle area where distances between the short conductive tubes are bigger than the distances between the short conductive tubes in the middle area.

17. A cylindrical focusing lens made of the artificial dielectric material according to claim 15, wherein even and odd layers of the short conductive tubes are shifted by 30 degree in relation to one another around an axis of the cylindrical focusing lens and the short conductive tubes placed in one layer and having the same size form a middle area in a shape of a circle and at least one area in a shape of a ring surrounding the middle area where distances between the short conductive tubes are bigger than the distances between the short conductive tubes in the middle area.

18. A cylindrical focusing lens made of the artificial dielectric material according to claim 15, wherein the short conductive tubes placed in one layer form a middle area in a shape of a circle and at least one area in a shape of a ring surrounding the middle area where diameters of the short conductive tubes are smaller than diameters of the short conductive tubes in the middle area.

19. A cylindrical focusing lens made of the artificial dielectric material according to claim 15, wherein the short conductive tubes placed in one layer are disposed radially and distances between the short conductive tubes increase towards an outer contour of the lens.

20. An artificial dielectric material according to claim 1, substantially as herein described or exemplified with reference to the accompanying drawings.

21. A cylindrical focusing lens according to claim 1, substantially as herein described or exemplified with reference to the accompanying drawings.