The present invention relates to an artificial medium and more particularly to an artificial left-handed system medium.
An artificial medium in which both an effective relative dielectric constant and an effective relative magnetic permeability are negative, what is called a “left-handed system medium” is a substance having a negative refractive index that does not exist in the natural world and shows a unique phenomenon in which a property of a wave motion is inverted to that of an ordinary substance, what is called a “right-handed system medium”. For instance, the inverted phenomenon includes a symbol (a negative refractive index) of an angle of refraction in the Snell's law, a direction of wave number vector (backward wave), the Doppler effect or the like. As an expansion of this conception, a matched zero refractive index medium in which both the effective relative dielectric constant and the effective relative magnetic permeability are zero also attracts a high attention. Thus, in various fields, studies are made for producing various kinds of highly developed devices and instruments by using characteristics of the left-handed system medium. For instance, in an optical field, studies are made for realizing a high resolution exceeding a diffraction limit for a lens by using the artificial medium. Further, in a field of microwave and millimeter-wave, studies are made for miniaturizing an antenna or achieving a high performance of an antenna by using the artificial medium.
It is known that a technique for forming the artificial left-handed system medium is roughly classified into two kinds. One of them is a technique using a transmission line and, for instance, non-patent literature 1 may be exemplified.
In this technique, an already established transmission theory and a right-handed system line realized by the theory are expanded in quality and a discrete inductor and a capacitor are inserted into the line to realize a left-handed system line. A great feature of this technique is to essentially show wide band characteristics. This technique is applied to an antenna supposed to be connected to a circuit element such as a filter or the transmission line and operates to an electromagnetic wave transmitted in space. Therefore, in this technique, it is extremely difficult to apply the transmission line type left-handed system medium to, for instance, a lens.
As compared therewith, as the left-handed system medium that can operate to the electromagnetic wave transmitted in the space, non-patent literature 2 may be exemplified.
This left-handed system medium has a structure having a split ring resonator combined with a conductor strip. Accordingly, the left-handed system medium has a restriction in principle that a conductor surface of the split ring resonator needs to be formed in parallel with the transmitting direction of an electromagnetic wave. As a result, the left-handed system medium has a demerit that production processes are extremely complicated.
As a structure of the left-handed system medium that can solve the above-described demerit and operate to the electromagnetic wave in the space, non-patent literature 3 may be exemplified. In this technique, the same patterns made of net shaped conductors are respectively arranged on front and back surfaces of a dielectric to realize the left-handed system medium.
Non-patent literature 1: C. Caloz And T. Itoh, “Novel microwave devices and structures based on transmission line approach of meta-materials” IEEE-MTT Int'l Symp., vol. 1 pp. 195-198, June 2003
Non-patent literature 2: R. A. Shelby, D. R. Smith, S. Schultz, “Experimental Verification of a Negative index of Refraction”, Science 292, pp. 77-79 2001
Non-patent literature 3: Gunnar Dolling, Christian Enkrich, Martin Wegner, Costas M. Soukoulis, Stefan Linden, OPTICS LETTERS, Vol. 31, No. 12, 2006
However, the artificial medium disclosed in the above-described non-patent literature 3 is proposed and supposed to be used in a band of light and hardly used in the field of microwave and millimeter-wave, because the artificial medium disclosed in the non-patent literature 3 has only a narrow frequency area where the left-handed system medium is obtained and has a dependence on a polarized wave. Namely, when the artificial medium is applied to, for instance, to the field of the microwave or millimeter-wave, an effective relative dielectric constant and an effective relative magnetic permeability may possibly greatly change depending on the direction of an electric field of an incident electromagnetic wave. A field to which the artificial medium having such a dependence on a polarized wave is applied is extremely limited, so that the artificial medium is hardly applied to various uses. Therefore, a conventional artificial medium has a problem that the artificial medium is not applied to the field of the microwave or millimeter-wave.
The present invention is devised by considering the above-described problems and it is an object of the present invention to provide an artificial medium having characteristics as a left-handed system medium over a wide frequency band and less dependence on a polarized wave.
According to the present invention, there is provided an artificial medium including: a dielectric layer; and first and second conductive patterns that are oppositely disposed across the dielectric layer, wherein: when an electromagnetic wave propagated in the direction of the thickness of the dielectric layer is incident, a current excited by the electromagnetic wave is increased in a prescribed operating frequency and a current loop is formed in a plane parallel to the direction of the thickness; the first and second conductive patterns including electrically conductive elements, a plurality of first grid lines extending in a first direction and a plurality of second grid lines extending in a second direction different from the first direction; and the electrically conductive elements are respectively located in areas where the first grid lines intersect the second grid lines.
According to the present invention, it is possible to provide an artificial medium having characteristics as a left-handed system medium over a wide frequency band and less dependence on a polarized wave.
The artificial medium of the present invention can be used for, for instance, a lens antenna for high frequency, a radome for an antenna, a superstrate for an antenna a micro-resonator and transmitter for communication or the like.
Now, an exemplary embodiment of the present invention will be described below by referring to the drawings.
(First Artificial Medium)
As shown in
Here, the “grid line” means a linear electric conductor arranged on the front surface (or the back surface) of the dielectric layer and having a substantially equal width. The “tile” means an electric conductor other than the “grid lines” arranged on an intersection of two “grid lines”. In this application, the “tile” is also especially referred to an electrically conductive element. Here, to arrange the tile on an intersection of a plurality of grid lines does not mean to arrange the tile on the intersection of the grid lines and the grid lines are not present under the tile. That is, the grid lines and the tiles form the virtual same plane by viewing them from the direction of the thickness of the dielectric layer 111.
The grid lines 110 include a plurality of first grid lines 110X extending substantially in a first direction (an X-direction in the drawing) and a plurality of second grid lines 110Y extending substantially in a second direction (a Y-direction in the drawing). Further, the tiles 140 are respectively arranged on intersections of the first grid lines 110X and the second grid lines 110Y.
In
Here, in
Further, in the drawing, the tile 140 has a square form, a width DX in the X-direction is equal to a width DY in the Y-direction. The tiles 140 are arranged on the front surface 112 and the back surface 114 of the dielectric layer 111. Each side of the square form of the tile 140 is substantially parallel to the extending direction of the first grid line 110X or the second grid line 110Y. Further, the tile 140 is arranged so that a center of gravity is overlapped on the intersection of the first grid line 110X and the second grid line 110Y.
The tiles 140 do not necessarily need to be arranged on all the intersections of the first grid lines 110X and the second grid lines 110Y. However, as illustrated below, the tiles 140 are more preferably arranged on all the intersections of the first grid lines 110X and the second grid lines 110Y. Further, the form of the tile 140 is not limited to the square form and various forms such as a rectangular form may be used.
Now, characteristics of the first artificial medium 100 according to the present invention which is constructed as described above will be described below by comparing them with characteristics of the artificial medium (refer it to as a “conventional artificial medium” hereinafter) described in the above-described non-patent literature 3.
Initially, the structure of the conventional artificial medium is described.
The conventional artificial medium 150 includes a dielectric layer 161 having a front surface 162 and a back surface 164. On the front surface 162 and the back surface 164 of the conventional artificial medium 150, a plurality of grid lines are formed in the shape of a matrix. Here, a matrix shaped pattern is considered to be a repeated pattern 155. The conventional artificial medium 150 does not have “tiles” as in the present invention.
The pattern 155 includes a plurality of grid lines 160X (first grid lines) extending in an X-direction in
Here, the patterns 155 of the dielectric layer 161 have the same forms by viewing from the direction of thickness (see
Now, a difference between the characteristics of the conventional artificial medium 150 and the characteristics of the first artificial medium 100 according to the present invention will be described below in accordance with the result of a simulation. The simulation is carried out by an FIT (Finite Integration Technique) method.
Parameters such as dimensions of elements respectively forming the artificial medium 100 and the artificial medium 150 used in the simulation are shown together in Table 1. In the Table 1, s designates the thickness of the dielectric layers 111 and 161 and t designates the thickness of the grid lines (and the tiles) respectively. Further, a relative magnetic permeability of the dielectric layers 111 and 161 is set to 1.0 and a relative dielectric constant is set to 3.4.
As shown in
On the other hand, in the artificial medium 100 according to the present invention, as shown in
Here, as shown in
As compared therewith, in the artificial medium 100 of the present invention, as shown in
As described above, between the artificial medium of the present invention and the conventional artificial medium, a significant difference is recognized in a frequency band where the good left-handed system medium having less transmission loss is obtained. Further, the artificial medium of the present invention has a feature that the artificial medium of the present invention is lower in its dependence on a polarized wave than the conventional artificial medium. Now, this difference will be described below.
As can be understood from
As apparent from the above-described results of the simulations, the artificial medium of the present invention has the characteristics as the left-handed system medium over a wider frequency area and less dependence on the polarized wave than the conventional artificial medium.
(Second Artificial Medium)
Now, a second artificial medium according to the present invention will be described below.
The second artificial medium 200 is basically formed like the above-described first artificial medium 100. The second artificial medium 200 according to the present invention includes a dielectric layer 211 having a front surface 212 and a back surface 214. On the front surface 212 and the back surface 214 of the dielectric layer 211, electrically conductive grid lines 210 and electrically conductive tiles 240 are formed. Here, patterns formed by the electrically conductive grid lines 210 and the electrically conductive tiles 240 are considered to be repeated patterns 205. The repeated patterns 205 formed respectively on the surfaces are substantially the same by viewing from the direction of the thickness of the dielectric layer 211. Further, the repeated patterns 205 respectively formed on the surfaces are arranged on the front surface 212 and the back surface 214 so that the repeated patterns substantially correspond mutually when the repeated patterns 205 respectively formed on the surfaces are viewed from the direction (a Z-direction in
However, in the second artificial medium 200, the orientation of the electrically conductive tiles 240 relative to the grid lines 210 is different from that in the first artificial medium 100. As shown in
In simulations, the parameters used in the Table 2 are used. s designates the thickness of the dielectric layer and t designates the thickness of the grid lines (and the tiles) respectively. Further, a relative magnetic permeability of the dielectric layer 211 is set to 1.0 and a relative dielectric constant is set to 3.4.
As apparent from the results of
In the second artificial medium 200, the good characteristics as described above are obtained owing to below-described reasons.
Ordinarily, a surge impedance Z is expressed by an equation of Z=√{square root over ( )}(μ0μr/∈0∈r). Here, μ0 designates a magnetic permeability of vacuum, μr designates a relative magnetic constant, ∈0 designates a dielectric constant of vacuum and ∈r designates a relative dielectric constant. Here, ordinarily, the relative magnetic permeability changes so as to gradually increase relative to the frequency until the relative magnetic permeability converges to 1 under a frequency area higher than a magnetic plasma frequency (a frequency in which the relative magnetic permeability is 0) from a negative value under a frequency higher than a magnetic resonance frequency Fo. Accordingly, in order to match the surge impedance Z to a surge impedance in a free space, the frequency of the effective relative dielectric constant is preferably changed so as to come close to a gradient of the effective relative magnetic permeability to the frequency as much as possible.
On the other hand, as apparent from the comparison of
Further, the second artificial medium 200 has significant characteristics in view of a design as described below.
As can be understood from the comparison of both the figures, in the second artificial medium 200, the change of the form of the tile gives a smaller influence to the effective relative dielectric constant than in the first artificial medium 100. This matter may be considered as described below.
In the case of the first artificial medium 100, opposed sides are parallel to each other in the two adjacent tiles 140. Accordingly, in this case, a large electrostatic capacity is generated between the two adjacent tiles due to an electric charge concentrated in the end parts of the tiles 140. Therefore, in the first artificial medium 100, an electric field between the tiles is apt to be large. As compared therewith, in the case of the second artificial medium 200, opposed sides are not parallel to each other in the two adjacent tiles 240. Therefore, an electric charge is hardly accumulated in the end parts of the tiles 240, so that the electrostatic capacity is small between the two adjacent tiles 240. According to such a difference between both the artificial media, a difference depending on the form as described above is supposed to appear.
In
As described above, the second artificial medium 200 can obtain a further higher matching in the wide frequency area having the plasma frequency Fp as a center than the first artificial medium. Furthermore, in the second artificial medium 200, since the influence of a dimensional factor of the tile is low, a degree of freedom in design can be more increased.
When an incident polarized wave is rotated by 90° to carry out a simulation similarly to the above-described first artificial medium, a significant dependence on the polarized wave is not recognized in the second artificial medium.
Here, in the artificial medium of the present invention, at least one electrically conductive tile is preferably provided in each grid line.
Now, reasons of the above-described matter will be described below.
For instance, an artificial medium 180 shown in
Results of a simulation of the artificial medium 180 constructed as described above are shown in
As shown in
Accordingly, from such a viewpoint, the change of the effective relative dielectric constant of the artificial medium 100 is more preferable than that of the artificial medium 180.
Such a large peak of the relative effective dielectric constant as shown in
According to the above-described things, it may be said that the intersections of the first grid lines and the second grid lines are preferably provided only on the electrically conductive tiles.
According to the above-described things, in the artificial medium of the present invention, at least one electrically conductive tile is preferably provided in each grid line.
Here, as for a method for producing the above-described artificial medium, when an actual production process is taken into consideration, the artificial medium may be preferably formed by a planar process, that is, by a method for laminating planes having characteristic patterns.
The above-described second artificial medium 200 is actually experimentally fabricated and its characteristics are evaluated. The artificial medium is formed by a below-described procedure.
Electrically conductive patterns including grid lines and tiles as shown in
The characteristics of the artificial medium are evaluated by a below-described method.
A relative dielectric constant and a relative magnetic permeability of the artificial medium are obtained in such a way as described below by using the above-described measuring device 400. Initially, by using the vector network analyzer 440, S parameters of the artificial medium 300 are measured in accordance with a free space method. Then, from the obtained result, the relative dielectric constant and the relative magnetic permeability of the artificial medium 300 are calculated by using a computational algorithm described in the following literatures (1) to (3).
The obtained results are shown in
As apparent from the drawings, also in the actually experimentally fabricated artificial medium, the same characteristics as the calculated results by the simulation are obtained. Namely, in the artificial medium according to the present invention, it is recognized that the characteristics having less loss over the wide frequency area are obtained.
The present invention is described in, detail by referring to the specific exemplary embodiment. However, it is to be understood to a person with ordinary skill in the art that various changes or modifications may be added without departing from the spirit and the scope of the present invention. This application is based on Japanese Patent Application (Japanese Patent Application No. 2008-045070) filed on Feb. 26, 2008 and the contents thereof is incorporated herein as a reference.
Number | Date | Country | Kind |
---|---|---|---|
P.2008-045070 | Feb 2008 | JP | national |
Number | Name | Date | Kind |
---|---|---|---|
7151506 | Knowles et al. | Dec 2006 | B2 |
7209083 | Fujishima et al. | Apr 2007 | B2 |
7253780 | Sievenpiper | Aug 2007 | B2 |
7705782 | Lee | Apr 2010 | B2 |
Number | Date | Country |
---|---|---|
2006-245984 | Sep 2006 | JP |
2007-256929 | Oct 2007 | JP |
Number | Date | Country | |
---|---|---|---|
20110102297 A1 | May 2011 | US |
Number | Date | Country | |
---|---|---|---|
Parent | PCT/JP2009/053459 | Feb 2009 | US |
Child | 12805946 | US |