WO2019069712A1

WO2019069712A1 - Electromagnetic wave transmission cable

Info

Publication number: WO2019069712A1
Application number: PCT/JP2018/035000
Authority: WO
Inventors: 康雄細田; 一智小幡; 知幸宮本
Original assignee: パイオニア株式会社
Priority date: 2017-10-02
Filing date: 2018-09-21
Publication date: 2019-04-11

Abstract

This electromagnetic wave transmission cable comprises: one or more dielectric waveguides which are formed of a dielectric body and transmit electromagnetic waves; and a resin foam material which is provided along the longitudinal direction of the one or more dielectric waveguides and covers the outer circumferential surfaces of the one or more dielectric waveguides.

Description

Electromagnetic wave transmission cable

The present invention relates to an electromagnetic wave transmission cable.

A waveguide made of a dielectric such as resin is lighter in weight and more flexible than a metal cable such as a coaxial cable or a metal waveguide. In the case of using PTFE (polytetrafluoroethylene) or the like having a low refractive index and a dielectric whose diameter is shorter than the wavelength, the transmission loss is also small and the transmission efficiency is good, so millimeter waves (30 to 300 GHz) are mainly used. Is effective as a cable for transmitting electromagnetic waves in the THz band (0.1 to 100 THz).

However, if the waveguide is made of a single-layer dielectric having a diameter smaller than the wavelength of the electromagnetic wave, the electromagnetic wave will propagate while leaking out from the surface of the waveguide. When it touches the outer wall of the dielectric waveguide, the electromagnetic wave gets out of the waveguide and scatters. Here, when PTFE or the like having a low refractive index is rod-shaped and used as a waveguide material, there arises a problem that there is no dielectric material which can be a clad layer having a single layer with a lower refractive index than the waveguide.

Therefore, a transmission path for confining and transmitting an electromagnetic wave has been proposed by constructing a Bragg mirror in which two or more kinds of dielectrics are stacked in contact with the outer peripheral portion of the dielectric waveguide (for example, Patent Document) 1).

U.S. Patent Application Publication 2009/0097809

In the prior art described above, several layers of different materials have to be stacked to form a Bragg mirror. Therefore, there is a problem that the number of steps is increased and the manufacturing cost is increased. In addition, the thickness of each layer must be designed in accordance with the wavelength of the electromagnetic wave to be transmitted, and there is a problem that there is wavelength dependency.

The problem to be solved by the present invention is, for example, the problem that the confinement effect of the electromagnetic wave is impaired when another object is in contact with the waveguide.

The invention according to claim 1 comprises one or more dielectric waveguides made of dielectrics and transmitting electromagnetic waves, and provided along the longitudinal direction of the one or more dielectric waveguides, And a foamed resin material covering the outer peripheral surface of the dielectric waveguide.

It is a figure which shows the electromagnetic wave transmission cable of Example 1 typically. FIG. 2 is a longitudinal sectional view of the electromagnetic wave transmission cable of the first embodiment. FIG. 8 is a longitudinal sectional view showing a modification of the electromagnetic wave transmission cable of the first embodiment. It is a figure which shows typically the modification of the electromagnetic wave transmission cable of Example 1. FIG. It is sectional drawing of the direction perpendicular | vertical to the central axis of the modification of the electromagnetic wave transmission cable of Example 1. FIG. FIG. 8 is a longitudinal sectional view showing a modification of the electromagnetic wave transmission cable of the first embodiment. FIG. 8 is a longitudinal sectional view showing a modification of the electromagnetic wave transmission cable of the first embodiment. FIG. 7 is a view schematically showing an electromagnetic wave transmission cable of Example 2; FIG. 7 is a cross-sectional view of the electromagnetic wave transmission cable of the second embodiment in the longitudinal direction. It is a figure which shows the relationship between the presence or absence of outer covering, and a transmission loss. It is a figure which shows the relationship between the presence or absence of outer coating | cover, and effective refractive index.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the description of the following embodiments and the accompanying drawings, substantially the same or equivalent parts are denoted by the same reference numerals.

FIG. 1 is a view schematically showing a configuration of the electromagnetic wave transmission cable 100 of the present embodiment. The electromagnetic wave transmission cable 100 includes a dielectric waveguide 10 made of a dielectric such as resin, and a foamed resin material 20 that covers the outer surface of the dielectric waveguide 10. The dielectric waveguide 10 is a waveguide for transmitting the electromagnetic wave EW. The electromagnetic wave EW is, for example, a millimeter wave having a frequency of 30 to 300 GHz or a THz wave having a frequency of 0.1 to 100 THz.

FIG. 2 is a cross-sectional view of the electromagnetic wave transmission cable 100 along the longitudinal direction. The dielectric waveguide 10 has a cylindrical shape centered on the central axis CA. That is, the dielectric waveguide 10 has a rotationally symmetric shape about the central axis CA. However, the dielectric waveguide 10 does not necessarily have to be cylindrical as long as the desired performance can be obtained. For example, FIG. 1 shows the case where the outer edge of the cross section of the dielectric waveguide 10 perpendicular to the central axis CA is circular, but it may be oval, elliptical, rectangular or the like.

The dielectric waveguide 10 is made of, for example, PTFE (polytetrafluoroethylene) which is a fluorocarbon resin, or e-PTFE (expanded polytetrafluoroethylene) obtained by subjecting the same to a drawing process. e-PTFE is obtained, for example, by stretching a PTFE material in at least one direction to give continuous porosity (structure having a large number of continuous pores) and then sintering and fixing (fixing by firing) at high temperature . The dielectric waveguide 10 is stretched in the longitudinal direction, and pores continuous in the stretching direction are formed. In the following description, among the continuous porosity, one having pores continuous in the stretching direction is also referred to as particularly stretched porosity. The dielectric waveguide 10 has a refractive index of about 1.5 when composed of PTFE, and a refractive index of about 1.1 to 1.2 when composed of e-PTFE. Have.

The dielectric waveguide 10 is configured such that the diameter of the waveguide (the diameter of the cross section in the direction perpendicular to the central axis CA) is sufficiently shorter than the wavelength of the electromagnetic wave EW to be transmitted. For example, when the electromagnetic wave EW has a frequency of 300 GHz and a wavelength of 1 mm, and the dielectric waveguide 10 is made of e-PTFE, the diameter of the dielectric waveguide 10 is set to, for example, 0.8 mm.

The foamed resin material 20 extends in the longitudinal direction of the dielectric waveguide 10 and covers the outer surface (that is, the outer peripheral surface) of the dielectric waveguide 10 so as to surround the outer periphery of the dielectric waveguide 10 . In addition, the foamed resin material 20 has, as its simplest shape, a cross-sectional shape that is rotationally symmetric about the central axis CA of the dielectric waveguide 10. However, the shape is arbitrary as long as a desired performance can be obtained. For example, although FIG. 1 shows the case where the outer edge of the cross section of the foamed resin material 20 in the direction perpendicular to the central axis CA is circular, it may be an oval, an ellipse, a rectangle or the like. The outer edge of the cross section of the foamed resin material 20 may have the same shape as the outer edge of the cross section of the dielectric waveguide 10, or may have a different shape.

The foamed resin material 20 is made of, for example, expanded polystyrene. Expanded polystyrene has a structure in which air (pores) of refractive index 1 is finely interspersed in polystyrene having a refractive index of 1.6, and a large number of fine reflective interfaces between polystyrene, which is a dielectric, and air are present. ing. For example, the average refractive index in the bulk state of the low-foam polystyrene foam used as a packaging material (refractive index assuming that the bulk material is a homogeneous medium of single substance) is 0.1 The average refractive index for electromagnetic waves of ̃0.5 THz was about 1.1. From this result, it can be confirmed that a large amount of air is mixed in the expanded polystyrene.

Thus, the foamed resin material 20 contains a large amount of air, and the proportion of polystyrene in contact with the surface of the dielectric waveguide 10 is very small. Therefore, even when metal, a human body or the like contacts the outer surface of the foamed resin material 20 (that is, the surface opposite to the surface in contact with the dielectric waveguide 10), the leakage of electromagnetic waves can be greatly reduced. .

If the thickness of the foamed resin material 20 is too thin, the effect of confining electromagnetic waves (that is, the effect of reducing the leakage of electromagnetic waves) is reduced. For example, in an experiment using a foamed polyethylene coating for a dielectric waveguide composed of PTFE with a waveguide frequency of 300 GHz and an outer diameter of 0.9 mm, sufficient electromagnetic wave confinement effects can be obtained if the coating thickness is less than 1 mm. It was not done. For example, the thickness of the foamed resin material 20 (the thickness of the coated portion) is desirably equal to or greater than the thickness (wavelength × average refractive index) corresponding to the wavelength of the electromagnetic wave to be transmitted. Moreover, since it will be difficult to handle if it is too thick, the thickness of the foamed resin material 20 is desirably set to 50 mm or less, preferably 10 mm or less.

In addition, the foamed resin material 20 may have a three-dimensional structure. For example, FIG. 3 (a) is a cross-sectional view of an electromagnetic wave transmission cable in which a concavo-convex or notch-shaped structure (for example, shown as 20a in FIG. 3 (a)) is provided on the outer surface of the foamed resin material 20. . By having such a structure, the electromagnetic wave transmission cable 100 can be easily bent. Further, as shown in FIG. 3 (b), by providing an uneven or notched structure (for example, shown as 20b in FIG. 3 (b)) on the inner surface in contact with the dielectric waveguide 10, it is possible to The confinement effect can be enhanced. Also, in order to protect the electromagnetic wave transmission cable 100 and to prevent it from collapsing, as shown in FIG. 3 (c), the outside covering the outer surface of the foamed resin material 20 along the longitudinal direction of the dielectric waveguide 10. A coating OC may be provided.

In addition, the electromagnetic wave transmission cable 100 may be configured as a multi-lumen cable in which the foamed resin material 20 covers a plurality of dielectric waveguides. For example, as shown in FIG. 4, the electromagnetic wave transmission cable 100 has a configuration in which the first dielectric waveguide 11 and the second dielectric waveguide 12 are provided, and the foamed resin material 20 covers them in common. It is good. According to such a configuration, it becomes possible to transmit a plurality of signals and a plurality of electromagnetic waves of different wavelengths (shown as EW1 and EW2 in the figure).

Further, in the multi-lumen type cable, the outer edge of the cross section of the foamed resin material 20 may not be circular, but may be oval or the like as shown in FIG. 5A. Further, the number of dielectric waveguides in the multi-lumen cable is not limited to two, and as shown in FIG. 5B, the number of

dielectric waveguides

11, 12 and 13 of three or more is more It may have a body waveguide. Moreover, the cross section of the foamed resin material 20 may be a polygon such as a square. For example, as shown in FIG. 5C, the outer edge of the cross section of the foamed resin material 20 is a quadrangle, and has a configuration covering the three

dielectric waveguides

11, 12, and 13 having a circular cross section. You may

Further, as shown in FIG. 5D, the plurality of dielectric waveguides in the multi-lumen cable may have mutually different diameters. Also, as shown in FIG. 5 (e), even if the plurality of dielectric waveguides have different cross-sectional shapes (for example, one has a circular outer edge and the other has an elliptical outer edge). good. That is, the diameter and the cross section of each of the plurality of dielectric waveguides can be set to an appropriate size and shape according to the wavelength of the electromagnetic wave transmitted by each.

Further, as shown in FIG. 6, instead of covering the entire dielectric waveguide 10 with the foamed resin material 20, a connector portion for connecting the dielectric waveguides with each other and a predetermined dielectric waveguide 10 are used. Only a portion that may come in contact with another member, such as a support portion for holding at a height, may be covered with the foamed resin material 20. That is, the foamed resin material 20 may be provided over a predetermined length (distance) in the longitudinal direction of the dielectric waveguide 10, and may be provided at a plurality of places.

In addition, the foaming ratio of the foamed resin material 20 may be changed between a region close to the contact surface in contact with the dielectric waveguide 10 (i.e., inside) and a region far from the contact surface (i.e., outer). For example, as shown in FIG. 7, the area from the area close to the contact surface with the dielectric waveguide 10 of the foamed resin material 20 to the area far from is divided into areas A1 to A4, and each area advances as areas A1, A2, A3 and A4. The foaming rate of the area may be reduced stepwise. According to this configuration, in the inner region near the contact surface with the dielectric waveguide 10, the effect of confining the electromagnetic wave is enhanced by relatively increasing the foaming ratio, and in the outer region far from the contact surface with the dielectric waveguide 10. The rigidity of the cable can be increased by relatively reducing the foaming rate.

As described above, in the electromagnetic wave transmission cable 100 of the present embodiment, the surface of the dielectric waveguide 10 is covered with the foamed resin material 20. The foamed resin material 20 contains a large amount of air, and the average refractive index is smaller than the refractive index of the dielectric waveguide 10. According to this configuration, even when another object such as a metal or a human body is in contact with the outer surface of the electromagnetic wave transmission cable 100, it is possible to maintain the electromagnetic wave confinement effect in the dielectric waveguide 10. Become.

Further, in the electromagnetic wave transmission cable 100 of the present embodiment, the dielectric waveguide 10 is made of PTFE or e-PTFE. Since the expanded porous resin (e-PTFE) used in the present embodiment has a characteristic micro nodule and a fine fiber structure in the extending direction, a low refractive index medium (average Can act as a low rate medium).

The porosity (proportion of the porous portion in the resin) of the drawn porous resin can be selected between 30 and 90% according to the application, but in order to coat the outside with the foamed resin material 20 as in this embodiment, The refractive index difference with the foamed resin material 20 is required. In order to suppress the transmission loss of electromagnetic waves, a refractive index difference of at least about 0.01 is required, and the desirable porosity obtained therefrom is 70% or less. Therefore, the optimum range of the porosity of the stretched porous resin in the dielectric waveguide 10 of the present embodiment is 30 to 70%.

FIG. 8 is a view schematically showing the configuration of the electromagnetic wave transmission cable 200 of the present embodiment. The electromagnetic wave transmission cable 200 includes a dielectric waveguide 10 made of a dielectric such as resin, a foamed resin material 20 covering the outer surface of the dielectric waveguide 10, and a metal film 30 coating the outer surface of the foamed resin material 20. And. The dielectric waveguide 10 is a waveguide for transmitting the electromagnetic wave EW.

FIG. 9 is a cross-sectional view of the electromagnetic wave transmission cable 200 along the longitudinal direction. Similar to the dielectric waveguide 10 and the foamed resin material 20, the metal film 30 has a rotationally symmetric shape around the central axis CA. The metal film 30 extends in the longitudinal direction of the dielectric waveguide 10, and the outer surface of the foamed resin material 20 covering the dielectric waveguide 10 so as to surround the outer periphery of the foamed resin material 20 about the central axis CA. Is further coated. Although FIG. 8 shows the case where the outer edge of the cross section of the metal film 30 in the direction perpendicular to the central axis CA is circular, it may be oval, elliptical, rectangular or the like. The outer edge of the cross section of the metal film 30 may have the same shape as the outer edge of the cross section of the dielectric waveguide 10 or the foamed resin material 20, or may have a different shape. That is, the metal film 30 may have a shape that covers the foamed resin material 20.

The dielectric waveguide 10 of the present embodiment is made of e-PTFE (expanded polytetrafluoroethylene) which is expanded by drawing PTFE (polytetrafluoroethylene), which is a fluorocarbon resin, to have continuous porosity, and fixed by firing. It consists of The dielectric waveguide 10 has a refractive index of about 1.1 to 1.2, and has a diameter of about 0.6 mm (the diameter of the cross section in the direction perpendicular to the central axis CA) shorter than the wavelength of the electromagnetic wave EW .

The foamed resin material 20 of the present embodiment is composed of expanded polystyrene with an expansion ratio of about 30 times (about 3% of the bulk density). The foamed resin material 20 has a refractive index (a refractive index close to 1, for example, 1.016) lower than that of the dielectric waveguide 10.

The foamed resin material 20 can be obtained by, for example, inserting the dielectric waveguide 10 inside the foamed resin having a hollow shape, winding the foamed resin around the dielectric waveguide 10, or the like. It is formed on the outer peripheral surface.

The metal film 30 is made of, for example, a metal having a relatively high conductivity such as gold, silver, copper or the like. The metal film 30 is formed on the outer surface of the foamed resin material 20 and has a thickness of about 1 μm or more. The metal film 30 can be formed, for example, by a method of forming a metal film directly on the surface of the foamed resin material 20, or a sheet with a metal film having a metal film formed beforehand on the surface of a dielectric sheet. It is manufactured by the method of winding so that it may face the side of.

The outer peripheral portion of the metal film 30 is covered with a protective film (not shown) made of a dielectric or the like. This protective film has only a protective function and does not contribute to electromagnetic wave transmission. For example, when the metal film 30 is produced by a method of winding the metal film-covered sheet around the foamed resin material 20, the dielectric sheet can be used as a protective film as it is without peeling off.

Thus, in the electromagnetic wave transmission cable 200 of the present embodiment, the metal film 30 is formed to further cover the outer surface of the foamed resin material 20 covering the dielectric waveguide 10. The effect of the metal film 30 will be described with reference to FIGS. 10 and 11.

FIG. 10 is a graph showing the relationship between the diameter of the dielectric waveguide and the transmission loss according to the presence or absence of the outer coating.

In the case where the dielectric waveguide alone is not provided with the outer coating, the transmission loss decreases as the diameter of the dielectric waveguide becomes smaller (the dielectric waveguide becomes thinner), as shown by a broken line in FIG.

When the dielectric waveguide is coated with the foamed resin, as shown by the alternate long and short dash line in FIG. 10, the outer coating is formed in the range where the diameter of the dielectric waveguide is more than a certain extent (about 0.7 mm to 1 mm in FIG. 10). The transmission loss is lower as compared to the case where it is not provided (shown by a broken line), and the transmission loss decreases as the diameter of the dielectric waveguide becomes smaller. However, when the diameter of the dielectric waveguide becomes smaller than a certain value (0.6 mm), the transmission loss is deteriorated to the extent that transmission can not be performed (shown as unmeasurable in FIG. 10).

On the other hand, when the outer surface of the foamed resin covering the dielectric waveguide is further covered with a metal film, transmission loss is reduced in proportion to the diameter of the dielectric waveguide, as shown by a solid line in FIG. Even in the range in which the diameter of the dielectric waveguide is smaller than a certain value (0.6 mm), the deterioration of the transmission loss to the extent that transmission can not be performed does not occur.

FIG. 11 is a graph showing the relationship between the diameter of the dielectric waveguide and the effective refractive index according to the presence or absence of the outer coating. The effective refractive index indicates the average refractive index of the medium contributing to the electromagnetic wave transmission, and is a parameter that characterizes the transmission state of the electromagnetic wave.

When the dielectric waveguide is coated with the foamed resin, as shown by the alternate long and short dash line in FIG. 11, as the diameter of the dielectric waveguide becomes smaller (the dielectric waveguide becomes thinner), the effective refractive index is Asymptotically to the refractive index (1.016). This indicates that the propagation medium of the electromagnetic wave is changed from the dielectric to the foamed resin as the diameter of the dielectric waveguide becomes smaller. In transmission using a foamed resin as a propagation medium, confinement of electromagnetic waves is unstable, and eventually transmission can not be performed.

On the other hand, when the outer surface of the foamed resin is covered with a metal film, as shown by a solid line in FIG. 11, the effective refractive index does not gradually approach the refractive index of the foamed resin, and the diameter of the dielectric waveguide is small. The effective refractive index also decreases as This indicates that the electromagnetic wave propagation medium is not changed to the foamed resin, and the electromagnetic wave is stably transmitted in the dielectric portion of the dielectric waveguide.

As described above, in the electromagnetic wave transmission cable 200 according to the present embodiment, the outer coating of the dielectric waveguide 10 is a double structure of the foamed resin material 20 and the metal film 30, so that the transmission occurs when covered only with the foamed resin. Loss reduction can be suppressed. That is, when the dielectric waveguide is coated only with the foamed resin, the electromagnetic wave is below the lower limit of the transmission loss determined by the physical properties of the dielectric waveguide and the foamed resin (for example, the effective refractive index is less than the refractive index of the foamed resin) Can not be transmitted. However, by further covering the foamed resin material 20 with the metal film as in the present embodiment, it is possible to realize the transmission loss equal to or lower than the lower limit value (the lower limit value of the transmission loss in the case of covering only with the foamed resin). .

Further, in the electromagnetic wave transmission cable 200 of the present embodiment, the metal film 30 functions as a shield against electromagnetic waves (noises) from the outside. Therefore, since the dielectric waveguide 10 is shielded from the outside, stable electromagnetic wave transmission becomes possible.

Further, as compared with the case where the dielectric waveguide is covered with only the foamed resin, the thickness of the entire covering portion can be reduced, so that miniaturization can be achieved.

The embodiment of the present invention is not limited to the one shown in the above example. For example, in the said Example, the example which the foamed resin material 20 was comprised from expanded polystyrene was demonstrated. However, the material of the foamed resin material 20 is not limited to this, and it may be made of a foamed resin material having an average attenuation rate of 0.1 cm ⁻¹ or less. For example, the foamed resin material 20 may be made of foamed polyurethane, foamed polyolefin, foamed polyolefin (foamed polyethylene, foamed polypropylene), foamed polytetrafluoroethylene (PTFE) or the like. That is, the foamed resin material 20 may be made of foamed resin of the same material as the dielectric waveguide 10.

Further, in the above embodiment, as a material for forming the dielectric waveguide 10, an example is used in which e-PTFE obtained by further stretching and forming a PTFE material to give continuous porosity, and further sintering and fixing it. Explained. However, such materials do not necessarily have to be sintered and fixed because they have low loss transmission performance even before sintering and fixing. That is, the dielectric waveguide 10 may be made of a dielectric material having expanded porosity.

Further, in the above embodiment, the case where the foamed resin material 20 is made of foamed polystyrene and the refractive index to an electromagnetic wave of 0.1 to 0.5 THz is about 1.1 has been described as an example. However, the average refractive index of the foamed resin material 20 is not limited to this. It is desirable that the foaming rate of the foamed resin material 20 is high because a low refractive index produces a confinement effect of electromagnetic waves, but if the foaming rate is too high, it becomes too soft and difficult to handle. Therefore, it is desirable that the foamed resin material 20 is foamed to such an extent that the average refractive index in the bulk state is less than 1.2.

In the first embodiment, the case where the diameter of the dielectric waveguide 10 is 0.8 mm to 1 mm has been described as an example, but the size of the diameter is not limited to this. However, in order to enable transmission with little loss, the dielectric waveguide 10 may be formed to have a diameter equal to or less than the wavelength of the electromagnetic wave EW, preferably equal to or less than a half wavelength.

In the second embodiment, the dielectric waveguide 10 is covered with the foamed resin material 20, and the outer surface of the foamed resin material 20 is covered with the metal film 30. However, air may be sandwiched between the dielectric waveguide 10 and the metal film 30 instead of the foamed resin material 20. For example, the foamed resin material 20 may not be uniformly provided between the dielectric waveguide 10 and the metal film 30, but the foamed resin material 20 may be partially provided. According to such a configuration, it is possible to make the average refractive index close to one.

In the second embodiment, the case where the entire outer surface of the foamed resin material 20 is covered with the metal film 30 has been described. However, the metal film 30 may be patterned to partially cover the outer surface of the foamed resin material 20 as long as the distance is equal to or less than the wavelength of the electromagnetic wave EW. The patterning of the metal film may be configured, for example, by a method of winding a metal thin wire or a method of covering a net like a mesh shield. The patterning of the metal film may be configured by forming a wire grid or a metamaterial structure using a mask at the time of film formation.

Further, in the second embodiment, by adjusting the structures and materials of the dielectric waveguide 10 and the metal film 30, it is possible to reduce the necessary thickness of the foamed resin material 20.

In the second embodiment, the metal film 30 is made of metal such as gold, silver or copper. However, the metal film 30 may be made of aluminum or alloy. Alternatively, a dielectric film may be used in place of the metal film 30 as an outer film for covering the foamed resin material 20. For example, if the dielectric film has a refractive index of about 1.4 or more, the refractive index difference at the interface can be sufficiently secured.

In addition, the electromagnetic wave transmission cable of this embodiment is, for example, a cable for large capacity high speed information communication for in-vehicle use as a substitute for a car information harness such as a car, a data center for large capacity communication required for large capacity communication, etc. It can be used as a cable.

DESCRIPTION OF REFERENCE NUMERALS 10 dielectric waveguide 20 foamed resin material 30 metal film 100 200 electromagnetic wave transmission cable 11 to 13 dielectric waveguide

Claims

One or more dielectric waveguides made of a dielectric and transmitting electromagnetic waves;
A foamed resin material provided along the longitudinal direction of the one or more dielectric waveguides and covering the outer peripheral surface of the one or more dielectric waveguides;
The electromagnetic wave transmission cable characterized by having.
The electromagnetic wave transmission cable according to claim 1, wherein the one or more dielectric waveguides are made of a dielectric including a material having expanded porosity.
The outer diameter of each of the one or more dielectric waveguides is less than the length represented by the wavelength of the electromagnetic wave to be transmitted × the refractive index of the dielectric, according to claim 1 or 2. Electromagnetic transmission cable.
4. The foamed resin material according to claim 1, wherein the foaming ratio is different between an area close to a contact surface in contact with the outer peripheral surface of the one or more dielectric waveguides and an area far from the contact surface. The electromagnetic wave transmission cable as described in any one of the above.
5. The electromagnetic wave transmission cable according to claim 4, wherein the foamed resin material decreases in foaming ratio as it goes away from the area near the contact surface.
The electromagnetic wave transmission cable according to any one of claims 1 to 5, wherein the foamed resin material has a convex structure on an inner surface in contact with the one or more dielectric waveguides.
The foamed resin material according to any one of claims 1 to 6, wherein the foamed resin material has a convex structure on the outer surface opposite to the inner surface in contact with the one or more dielectric waveguides. Electromagnetic transmission cable.
The electromagnetic wave transmission according to any one of claims 1 to 7, further comprising an outer coating that covers the outer surface of the foamed resin material along the longitudinal direction of the one or more dielectric waveguides. cable.
The electromagnetic wave transmission cable according to claim 8, wherein the outer coating is a metal film.
The electromagnetic wave transmission cable according to claim 8, wherein the outer coating is a dielectric film.
The electromagnetic wave transmission cable according to any one of claims 8 to 10, further comprising a protective film which covers the outer surface of the outer coating along the longitudinal direction of the dielectric waveguide.
The electromagnetic wave transmission cable according to claim 11, wherein the protective film is made of a material including a dielectric material.
The foam resin material covers the outer surface of the one or more dielectric waveguides at a plurality of locations in the longitudinal direction of the one or more dielectric waveguides. The electromagnetic wave transmission cable as described in 1.
The electromagnetic wave transmission cable according to any one of claims 1 to 13, wherein the foamed resin material is made of any of foamed polystyrene, foamed polyurethane, foamed polyolefin, and foamed polytetrafluoroethylene.
The electromagnetic wave transmission cable according to any one of claims 1 to 14, wherein the foamed resin material is formed of a foamed resin of the same material as the dielectric.
The electromagnetic wave transmission cable according to any one of claims 1 to 15, wherein the electromagnetic wave has a frequency of 30 to 100,000 GHz.
The electromagnetic wave transmission cable according to any one of claims 1 to 16, wherein an average refractive index to the electromagnetic wave of the foamed resin material is 1 or more and 1.2 or less.
The thickness of the portion covering the one or more dielectric waveguides of the foamed resin material is characterized by being equal to or more than the length of the wavelength of the electromagnetic wave × the average refractive index of the foamed resin material. The electromagnetic wave transmission cable according to any one of claims 1 to 17.
The electromagnetic wave transmission cable according to any one of claims 1 to 18, wherein an average attenuation factor of the foamed resin material to the electromagnetic wave is 0.1 cm -1 or less.