JP6333122B2 - Metal slit array - Google Patents

Description

  The present invention relates to a metal slit array that functions as a metamaterial in which microcoils are loaded in parallel plates.

  Beserago has shown that negative refraction occurs when light enters a medium with both negative dielectric constant and magnetic permeability, and an artificial structure with negative permeability and dielectric constant has been proposed. This artificial structure in which the magnetic permeability and dielectric constant are negative consists of an assembly of structures that are sufficiently larger than atoms and smaller than the light wavelength scale, and is called a metamaterial. When a metamaterial that is a negative refraction medium is used, a complete lens having a planar structure can be created. With a perfect lens, it is possible to observe even fine objects exceeding the diffraction limit, and it is possible to faithfully reproduce the near field (evanescent wave).

  The metamaterial can be applied to a lens for terahertz electromagnetic waves that has recently attracted attention. The terahertz electromagnetic wave is an electromagnetic wave having a frequency of 0.1 to 10 THz (wavelength of 30 μm to 3000 μm), and the wavelength is substantially coincident with the far infrared to millimeter wave region, and is sandwiched between “light” and “millimeter wave”. Exists in the frequency domain. For this reason, terahertz electromagnetic waves have both the ability to distinguish at high spatial resolution like light and the ability to transmit substances similar to millimeter waves. The terahertz wave band has been an undeveloped electromagnetic wave so far, and its application to characterization of materials by time-domain spectroscopy, imaging and tomography utilizing the characteristics of electromagnetic waves in this frequency band has been studied. Generation of terahertz electromagnetic waves has both material permeability and straightness, so that safe and innovative imaging instead of X-rays and ultra-high speed wireless communication of several hundred Gbps can be realized.

In particular, terahertz imaging has a great appeal as one of safe, secure, and highly accurate visualization techniques that replace X-rays. It has been reported that terahertz nano-imaging by near-field that broke through the diffraction limit and resolution of 400 nm (1 wavelength / 540) at 1.4 THz can be obtained. Imaging at 0.3 THz using a resonant tunneling diode has also been reported. The metamaterial can be designed with a negative refractive index n = −1, and the near-field light that is an evanescent component is restored at a remote location, and there is a possibility that a flat lens that exceeds the diffraction limit can be realized.
As an example of such a metamaterial, unit cells composed of split ring resonators having a negative magnetic permeability, which are a combination of two large and small rings having cuts, and metal wires having a negative dielectric constant are arranged in a matrix. Metamaterials are known (see Patent Document 1). In this case, the cut positions of the large and small rings are, for example, opposite positions, but are not limited thereto. Negative refraction can be realized by arranging the unit cells along one axis so as to have a gradient refractive index.
By the way, it is known that a metal parallel plate in which metal plates are arranged in parallel with a predetermined distance therebetween exhibits a negative dielectric constant at a frequency equal to or lower than a cutoff frequency. In addition, it is known that dielectric resonators exhibit negative permeability near the resonance frequency. Therefore, as shown in Non-Patent Document 1, a disk-shaped dielectric resonator is loaded in a metal parallel plate, and a negative dielectric constant is realized by the metal parallel plate and a negative permeability is realized by the dielectric resonator. To do. Thereby, in a metal parallel plate loaded with a disk-shaped dielectric resonator, negative refraction is realized at a predetermined frequency, and TE mode electromagnetic waves propagate.

JP 2011-254482 A

IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 55, NO. 6, JUNE 2007 P.1280-1287 Tetsuya Ueda and 2 others "

Just as a dielectric resonator exhibits a negative permeability at the resonance frequency, a split ring resonator also exhibits a negative permeability near the resonance frequency. And realizing the metamaterial by the unit cell which consists of a split ring resonator and a metal wire was performed. Moreover, combining a metal parallel plate and a dielectric resonator has been performed.
An object of the present invention is to realize a metamaterial by a metal slit array in which microcoils that have not been realized in the past are loaded in parallel plates.

To achieve the above object, the invention according to claim 1 is an upper wall made of a metal flat plate and a metal flat plate arranged to face the upper wall with a predetermined interval. A unit array consisting of a parallel flat plate formed of a lower wall and a microcoil loaded in the parallel flat plate is provided, and a plurality of the unit arrays are arranged at predetermined intervals in the same plane to form a metal slit array. The main feature is that the magnetic permeability of the microcoil is negative at the frequency of the terahertz wave band where the dielectric constant of the parallel plate exhibits a negative dielectric constant.
The invention according to claim 2 is the invention according to claim 1, wherein the length of one side of the upper wall and the lower wall is about 0.06λ to about 0.00 when the wavelength of the frequency is λ. The main feature is that it is 07λ.

According to the first and second aspects of the present invention, a metal flat plate upper wall, and a metal flat plate lower wall arranged to face the upper wall with a predetermined interval, A unit array is constituted by a parallel plate composed of the above and a microcoil loaded in the parallel plate, and a plurality of the unit arrays are arranged at a predetermined interval on the same plane to constitute a metal slit array. Since the magnetic permeability of the microcoil is negative at the frequency of the terahertz wave band where the dielectric constant of the parallel plate exhibits a negative dielectric constant, the metal slit array functions as a metamaterial.
Thereby, the metal slit array concerning this invention can implement | achieve a negative refractive index.

It is a perspective view which shows the structure of the unit array of 1st Example of this invention which comprises the metal slit array of this invention. It is a front view which shows the structure of the microcoil which comprises the unit array of 1st Example of this invention. It is a side view which shows the structure of the microcoil which comprises the unit array of 1st Example of this invention. It is a graph which shows an example of the analysis parameter of the unit array of 1st Example of this invention. It is a figure which shows the frequency characteristic of the transmitted power of the unit array of 1st Example of this invention. It is a figure which shows the frequency characteristic of the refractive index of the unit array of 1st Example of this invention. It is a figure which shows the frequency characteristic of the dielectric constant of the unit array of 1st Example of this invention. It is a figure which shows the frequency characteristic of the magnetic permeability of the unit array of 1st Example of this invention. It is a figure which shows the wave number with respect to the frequency of the unit array of 1st Example of this invention. It is a figure which shows the structure of the prism using the metal slit array which consists of a unit array of 1st Example of this invention. It is a figure which shows the structure of the metal slit array which consists of a unit array of 1st Example of this invention. It is a graph which shows an example of the analysis parameter of the prism using the metal slit array which consists of a unit array of 1st Example of this invention. It is a figure which shows the propagation characteristic according to frequency of the prism using the metal slit array which consists of a unit array of 1st Example of this invention. It is a figure which shows the propagation characteristic according to frequency of the prism using the metal slit array which consists of a unit array of 1st Example of this invention. It is a figure which shows the propagation characteristic according to frequency of the prism using the metal slit array which consists of a unit array of 1st Example of this invention. It is a figure which shows the propagation characteristic according to frequency of the prism using the metal slit array which consists of a unit array of 1st Example of this invention. It is a figure which shows the propagation characteristic according to frequency of the prism using the metal slit array which consists of a unit array of 1st Example of this invention. It is a figure which shows the propagation characteristic according to frequency of the prism using the metal slit array which consists of a unit array of 1st Example of this invention. It is a graph which shows an example of the analysis parameter of the unit array of 2nd Example of this invention. It is a figure which shows the frequency characteristic of the transmitted power of the unit array of 2nd Example of this invention. It is a figure which shows the frequency characteristic of the refractive index of the unit array of 2nd Example of this invention. It is a figure which shows the frequency characteristic of the dielectric constant of the unit array of 2nd Example of this invention. It is a figure which shows the frequency characteristic of the magnetic permeability of the unit array of 2nd Example of this invention. It is a figure which shows the wave number with respect to the frequency of the unit array of 2nd Example of this invention. It is a graph which shows an example of the analysis parameter of the prism using the metal slit array which consists of a unit array of 2nd Example of this invention. It is a figure which shows the propagation characteristic according to frequency of the prism using the metal slit array which consists of a unit array of 2nd Example of this invention. It is a figure which shows the propagation characteristic according to frequency of the prism using the metal slit array which consists of a unit array of 2nd Example of this invention. It is a figure which shows the propagation characteristic according to frequency of the prism using the metal slit array which consists of a unit array of 2nd Example of this invention. It is a graph which shows an example of the analysis parameter of the unit array of 3rd Example of this invention. It is a figure which shows the frequency characteristic of the transmitted power of the unit array of 3rd Example of this invention. It is a figure which shows the frequency characteristic of the refractive index of the unit array of 3rd Example of this invention. It is a figure which shows the frequency characteristic of the dielectric constant of the unit array of 3rd Example of this invention. It is a figure which shows the frequency characteristic of the magnetic permeability of the unit array of 3rd Example of this invention. It is a figure which shows the wave number with respect to the frequency of the unit array of 3rd Example of this invention. It is a figure which expands and shows the frequency characteristic of the transmitted power of the unit array of 3rd Example of this invention. It is a graph which shows an example of the analysis parameter of the prism using the metal slit array which consists of a unit array of 3rd Example of this invention. It is a figure which shows the propagation characteristic according to frequency of the prism using the metal slit array which consists of a unit array of 3rd Example of this invention. It is a figure which shows the propagation characteristic according to frequency of the prism using the metal slit array which consists of a unit array of 3rd Example of this invention. It is a figure which shows the propagation characteristic according to frequency of the prism using the metal slit array which consists of a unit array of 3rd Example of this invention. It is a figure which shows the propagation characteristic according to frequency of the prism using the metal slit array which consists of a unit array of 3rd Example of this invention. It is a figure which shows the propagation characteristic according to frequency of the prism using the metal slit array which consists of a unit array of 3rd Example of this invention. It is a figure which shows the propagation characteristic according to frequency of the prism using the metal slit array which consists of a unit array of 3rd Example of this invention. It is a figure which shows the propagation characteristic according to frequency of the prism using the metal slit array which consists of a unit array of 3rd Example of this invention. It is a figure which shows the propagation characteristic according to frequency of the prism using the metal slit array which consists of a unit array of 3rd Example of this invention. It is a figure which shows the propagation characteristic according to frequency of the prism using the metal slit array which consists of a unit array of 3rd Example of this invention. It is a figure which shows the propagation characteristic according to frequency of the prism using the metal slit array which consists of a unit array of 3rd Example of this invention.

FIG. 1 is a perspective view showing the configuration of the unit array of the first embodiment of the present invention constituting the metal slit array of the present invention, and FIG. 1 is a front view showing the configuration of the microcoil constituting the unit array of the first embodiment of the present invention. The figure is shown in FIG. 2A and the side view is shown in FIG. 2B.
The unit array 1 of the first embodiment of the present invention constituting the metal slit array of the present invention shown in these drawings is made of metal disposed on the surface of the upper wall of the periodic boundary wall 13 having a rectangular cross section as shown in the figure. It has a parallel flat plate made up of a rectangular upper wall metal plate 11 and a metal rectangular lower wall metal plate 12 arranged on the surface of the lower wall. The upper wall metal plate 11 and the lower wall metal plate 12 face each other with an interval (height) h to form a parallel plate, and the parallel plate forms a wave guide. One metal microcoil 10 is disposed between the upper wall metal plate 11 and the lower wall metal plate 12. In the unit array 1 of the first embodiment, as shown in FIG. 1, the horizontal axis is the z-axis, and the width direction axis of the upper wall metal plate 11 and the lower wall metal plate 12 is the x-axis. In addition, the axis in the height direction of the parallel plate is set as the y-axis while being orthogonal to the z-axis. An electromagnetic wave incident on the unit array 1 of the first embodiment, for example, a terahertz electromagnetic wave, has an electric field component E in the x-axis direction, a magnetic field component H in the y-axis direction, and a traveling direction k in the z-axis direction. Has been.

In the unit array 1 of the first embodiment according to the present invention, the upper wall metal plate 11 and the lower wall metal plate 12 have the same size, and the width in the x-axis direction is Px, as shown in FIG. The length in the z-axis direction is Pz, the thickness is t, and the height of the parallel plate (the interval in the y-axis direction between the upper wall metal plate 11 and the lower wall metal plate 12) is h.
In the unit array 1, a periodic boundary wall 13 having a structure corresponding to one waveguide constituted by the xz plane of the upper wall and the lower wall and the yz plane of the left wall and the right wall shown by hatching. And a metal slit array can be designed with an analysis model of the unit array 1 extracted by one. In addition, the parallel flat plate which consists of the upper wall metal plate 11 and the lower wall metal plate 12 in the unit array 1 comes to show a negative dielectric constant in the frequency below a cut-off frequency.

  As shown in FIGS. 2A and 2B, the spiral microcoil 10 loaded between the upper wall metal plate 11 and the lower wall metal plate 12 has a thin metal wire having a diameter r3 and an outer diameter r2 (inner diameter is smaller). It is created by spirally winding at an interval of pitch p so as to be r1). The height of the microcoil 10 is the same as the height h of the parallel plate. When the microcoil 10 resonates, the microcoil 10 exhibits a negative magnetic permeability. Therefore, the unit array 1 of the first embodiment is arranged with a predetermined period in the y-axis direction and the x-axis direction, that is, a large number of unit arrays 1 are periodically arranged in a plane that is the xy plane, thereby generating a predetermined terahertz wave. A metal slit array that exhibits a negative refractive index in the band can be constructed. Thereby, a prism, a lens, etc. which exhibit the negative refractive index used for a terahertz wave band by a metal slit array can be constituted.

  FIG. 3 shows an example of analysis parameters when the unit array 1 of the first embodiment according to the present invention is applied to the terahertz wave band. In this case, the target frequency for obtaining a negative refractive index is 0.3 THz. In the analysis parameters in the analysis shown in FIG. 3, the Px of the upper wall metal plate 11 and the lower wall metal plate 12 is about 62 μm, Pz is also about 62 μm, and the parallel plate interval (height) h is about 159.5 μm. It is said. In this case, the cutoff frequency fc in vacuum of the waveguide made of parallel plates is about 0.97 THz. Further, the thickness t of the upper wall metal plate 11 and the lower wall metal plate 12 is about 0.25 μm. Furthermore, the diameter r3 of the fine metal wire constituting the spiral microcoil 10 is about 10 μm, the inner diameter r1 around which the fine metal wire is wound is about 30 μm, and the outer diameter r2 is about 50 μm.

  In the unit array 1 of the first embodiment having such analysis parameters, the electric field component E is in the width (x-axis) direction and the magnetic field component H is in the height (y-axis) direction, and the length (z-axis) direction. When a TE mode incident wave traveling in the direction is input, the frequency characteristics of the transmission coefficient S21 of the transmitted wave that propagates through the unit array 1 in the z-axis direction and the reflection coefficient S11 of the reflected wave to be reflected are obtained. Analyzed. Analysis was performed using finite element method electromagnetic simulator ANSYS HFSS Ver.14.1.1. Referring to the frequency characteristics of the transmitted power in FIG. 4 as an analysis result, the transmission coefficient S21 indicated by the broken line is about 80% or more at about 0.27 THz and about 0.75 THz lower than the cutoff frequency fc, and the unit array 1 The TE mode incident wave is almost transmitted, but the reflection coefficient S11 indicated by the solid line is almost 100% when the frequency is less than 0.75 THz between 0.1 THz and 1 THz excluding the predetermined range centered on the above frequency. Almost everything is reflected. Further, the transmission coefficient S21 is about 5% to about 20% at frequencies up to 1.0 THz exceeding 0.75 THz.

FIG. 5 shows the analysis result of the frequency characteristics of the refractive index n of the unit array 1 when the analysis parameters are used. Referring to FIG. 5, the real part (Re (n)) of the refractive index n indicated by the solid line is almost 0 from 0.2 THz to about 0.25 THz, and rapidly increases at about 0.25 THz and about 0.25 THz. It is positive of about +10 to +11 in the range of about 0.27 THz. Then, it suddenly drops at about 0.27 THz and becomes negative -11. When it exceeds about 0.27 THz, it approaches 0 and becomes 0 at about 0.3 THz. It becomes almost 0 at about 0.3 THz to 0.35 THz.
The imaginary part (Im (n)) of the refractive index n indicated by the broken line is about +10 positive at 0.2 THz, and rapidly rises to about +25 positive at about 0.25 THz. If it exceeds about 0.25 THz, it will drop rapidly and will be zero at about 0.27 THz. And it is 0 from about 0.27 THz to about 0.3 THz, and becomes positive from 0 to +3 when it exceeds about 0.3 THz.
That is, it can be seen that the unit array 1 has a negative refractive index n in the frequency range from about 0.27 THz to about 0.3 THz.

FIG. 6 shows the analysis result of the frequency characteristics of the relative permittivity ε of the unit array 1 when the analysis parameters are used. Referring to FIG. 6, the real part (Re (ε)) of the relative permittivity ε shown by the solid line is about −290 negative at about 0.2 THz and gradually increases as the frequency increases, but about −400 at about 0.25 THz. It falls rapidly to the negative of. And if it exceeds about 0.25 THz, it will rise rapidly and will be 0 in about 0.27 THz. Above about 0.27 THz, it falls to a negative value of about -80, and the negative value is almost maintained up to about 0.35 THz.
The imaginary part (Im (ε)) of the relative dielectric constant ε indicated by a broken line is 0 from 0.2 THz to 0.25 THz, and increases rapidly at about 0.25 THz to become about +200 positive. If it exceeds about 0.25 THz, it will drop rapidly and will be zero at about 0.27 THz. And it becomes 0 from about 0.27 THz to about 0.35 THz.
That is, it can be seen that the unit array 1 has a negative dielectric constant ε in the frequency range from about 0.27 THz to about 0.3 THz.

FIG. 7 shows the analysis result of the frequency characteristics of the relative permeability μ of the unit array 1 when the analysis parameters are set. Referring to FIG. 7, the real part (Re (μ)) of the relative permeability μ indicated by the solid line is positive from 0 to about +1 from about 0.2 THz to about 0.27 THz, but exceeds about 0.27 THz. Then it drops rapidly and becomes negative about -23. And when it exceeds about 0.27 THz, it will rise rapidly and will be set to 0, and the value of 0 is substantially maintained to about 0.35 THz.
The imaginary part (Im (μ)) of the relative permeability μ indicated by the broken line is 0 from 0.2 THz to 0.25 THz, and slightly decreases at about 0.25 THz and becomes negative of about −1. If it exceeds about 0.25 THz, it will fall slowly, but will fall rapidly about 0.27 THz and will become negative of about -12. And when it exceeds about 0.27 THz, it will rise rapidly and will be set to 0, and the value of 0 is substantially maintained to about 0.35 THz.
That is, it can be seen that the unit array 1 has a negative relative permeability μ at about 0.27 THz.

FIG. 8 shows the analysis result of the wave number with respect to the frequency of the unit array 1 when the analysis parameters are used. Referring to FIG. 8, the wave number becomes 0 from 0.2 THz to 0.25 THz, and when it exceeds about 0.25 THz, the wave number rapidly rises to about 62, and this wave number is maintained until about 0.27 THz. Is done. When it exceeds about 0.27 THz, the wave number drops rapidly and becomes zero at about 0.3 THz.
That is, it can be seen that the unit array 1 can increase the resolution at about 0.25 THz to about 0.27 THz.

Next, the configuration of the prism 20 using the unit array 1 of the first embodiment according to the present invention is shown in FIG. 9A, the outline of the configuration of this prism 20 is shown in FIG. 9B, and the analysis parameters of this prism 20 are shown in FIG. 9C. Shown in
As shown in FIG. 9A, the prism 20 includes a waveguide 23, a second region 22, a metal slit array 2, and a first region 21. The waveguide 23, the second region 22, and the first region 21 are dielectrics having a relative dielectric constant εr of about 20. A waveguide 23 is impedance-matched and connected to one surface of the rectangular parallelepiped second region 22, and a terahertz wave incident wave is incident on the second region 22 via the waveguide 23 and propagates in the second region 22. To go. One surface of the metal slit array 2 is connected to the surface of the second region 22 facing the incident surface, and an incident wave propagated through the second region 22 is incident on the metal slit array 2. As shown in FIG. 9B, the metal slit array 2 has a surface facing one surface as a slope, the width of one surface is a, the length from the first surface to the slope is b, and the shorter one from the first surface to the slope. Is d. In this case, the angle θ formed with the normal line 21 a on the slope of the metal slit array 2 is the incident angle to the metal slit array 2. As shown in FIG. 9B, the metal slit array 2 is configured by arranging the unit arrays 1 at predetermined intervals c in the row direction and the column direction. Then, by reducing the number of unit arrays 1 to be arranged in the row direction from the bottom to the top, a metal slit array 2 having a surface facing one surface as a slope is formed.

  FIG. 9C shows analysis parameters when the target frequency for obtaining a negative refractive index in this prism 20 is 0.3 THz. In the analysis parameters shown in FIG. 9C, the incident angle θ is 45 °, the width a of the metal slit array 2 is 310 μm, the longer length b from one surface to the inclined surface is 325 μm, the shorter length d is 46 μm, A predetermined interval c in which the unit arrays 1 are arranged in the row direction and the column direction is 62 μm, and the length of the second region 22 is 400 μm. In this analysis parameter, the unit array 1 is dimensioned so that a maximum of five unit arrays 1 can be arranged in the row direction. Here, as an example of the number of unit arrays 1 arranged, about 200 unit arrays 1 shown in FIG. 1 are arranged in the x-axis direction shown in FIG. 1, and about 50 unit arrays 1 are arranged in the y-axis direction. Thus, an array group composed of 200 * 50 unit arrays 1 arranged on one plane of the xy plane is configured, and a metal slit array is configured by arranging about 10 groups in the z-axis direction. Can be considered. In the metal slit array having such a configuration, the number of unit arrays 1 is too large, and the time for analysis becomes enormous. Further, the number of unit arrays 1 to be arranged is not limited to the above-described number, and it is conceivable that the number of unit arrays 1 is greatly decreased or greatly increased. Therefore, the analysis parameters are set so that the number of unit arrays 1 is a number that does not require an enormous analysis time. Even if the analysis is performed with the number of unit arrays 1 reduced, the analysis result is almost the same as the analysis result when the number of unit arrays 1 is large.

The propagation characteristics of the terahertz wave in the prism 20 using the metal slit array 2 composed of the unit array 1 of the first embodiment was analyzed using the finite element method electromagnetic field simulator ANSYS HFSS Ver.14.1.1. The analysis results are shown in FIGS. 10A to 10F. 10A, the frequency of the incident terahertz wave is 275 GHz, the frequency of the incident terahertz wave in FIG. 10B is 280 GHz, the frequency of the incident terahertz wave in FIG. 10C is 285 GHz, and the incident terahertz wave in FIG. The frequency of the wave is 290 GHz, the frequency of the terahertz wave incident in FIG. 10E is 300 GHz, and the frequency of the terahertz wave incident in FIG. 10F is 400 GHz.
10A to 10F, the incident angle θ is 45 °, and when the angle of the outgoing terahertz wave is a clockwise angle from the normal line 21a, a positive refractive index is obtained as shown in FIG. 9A. When the angle of the outgoing terahertz wave is an angle counterclockwise from the normal line 21a, the refractive index is negative as shown in FIG. 9A. Referring to FIGS. 10A to 10F, in the propagation characteristics of FIGS. 10A to 10E, the angle of the outgoing terahertz wave is counterclockwise with respect to the normal line 21a. Therefore, in the frequency band of 275 GHz to 300 GHz, the prism is used. It can be seen that 20 exhibits a negative refractive index. Further, in the propagation characteristics shown in FIG. 10F, it can be seen that the angle of the outgoing terahertz wave is not counterclockwise from the normal line 21a, and the prism 20 does not exhibit a negative refractive index at 400 GHz.

  Next, a unit array according to the second embodiment of the present invention will be described. The unit array of the second embodiment is the same as that of the unit array 1 of the first embodiment shown in FIG. 1, and the analysis parameters are different from those of the unit array 1 of the first embodiment. Here, the description of the configuration of the unit array of the second embodiment is omitted. An example of analysis parameters when the unit array of the second embodiment is applied to the terahertz wave band is shown in FIG. In this case, the target frequency for obtaining a negative refractive index is 0.3 THz. As shown in FIG. 11, the analysis parameters for the analysis are as follows: Px of the upper wall metal plate 11 and lower wall metal plate 12 is about 74 μm, Pz is about 60 μm, and the parallel plate interval (height) h is about 159. .5 μm. In this case, the cutoff frequency fc in vacuum of the waveguide made of parallel plates is about 0.97 THz. Further, the thickness t of the upper wall metal plate 11 and the lower wall metal plate 12 is about 0.25 μm. Furthermore, the diameter r3 of the fine metal wire constituting the spiral microcoil 10 is about 10 μm, the inner diameter r1 around which the fine metal wire is wound is about 30 μm, and the outer diameter r2 is about 50 μm.

  In the unit array of the second embodiment having such analysis parameters, the electric field component E is in the width (x-axis) direction, and the magnetic field component H is in the height (y-axis) direction so as to be in the length (z-axis) direction. When a traveling TE mode incident wave is input, a transmission coefficient S21 of the transmitted wave that is output by propagating the unit array of the second embodiment in the z-axis direction and a reflection coefficient S11 of the reflected wave to be reflected The frequency characteristics were analyzed. Analysis was performed using finite element method electromagnetic simulator ANSYS HFSS Ver.14.1.1. Referring to the frequency characteristic of the transmitted power in FIG. 12 as the analysis result, the transmission coefficient S21 indicated by the broken line is almost 100% at about 0.255 THz lower than the cutoff frequency fc, and the unit array of the second embodiment is TE. The incident wave in the mode is almost transmitted, but in the range of 0.2 THz to 0.3 THz excluding a predetermined range centered on the above frequency, the reflection coefficient S11 indicated by the solid line is almost 100%, and almost all of them are transmitted. Reflected.

FIG. 13 shows the analysis result of the frequency characteristics of the refractive index n of the unit array of the second embodiment when the analysis parameters are used. Referring to FIG. 13, the real part (Re (n)) of the refractive index n indicated by the solid line is almost 0 from 0.2 THz to about 0.237 THz. Then, it falls rapidly at about 0.237 THz and becomes negative about -0.004 to -0.012 in the range of about 0.237 THz to about 0.263 THz, but about 0.259 THz to about 0.00 in this range. It becomes positive of about +0.007 in the range of 260 THz. Then, it rapidly rises at about 0.263 THz and becomes positive of +0.04, and becomes 0 at about 0.271 THz to about 0.3 THz.
The imaginary part (Im (n))) of the refractive index n indicated by the broken line becomes a positive value of about +0.01 at 0.2 THz, and rapidly rises to a positive value of about +0.032 at about 0.237 THz. If it exceeds about 0.237 THz, it will fall rapidly and will be set to 0 in about 0.252 THz. And it becomes 0 from about 0.252 THz to about 0.272 THz, and when it exceeds about 0.272 THz, it becomes positive of 0- + 0.03.
That is, the unit array of the second embodiment has a negative refractive index n in the frequency range from about 0.237 THz to about 0.259 THz and the frequency range from about 0.260 THz to about 0.263 THz. Recognize.

FIG. 14 shows the analysis result of the frequency characteristics of the relative permittivity ε of the unit array of the second embodiment when the analysis parameters are set. Referring to FIG. 14, the real part (Re (ε)) of the relative permittivity ε shown by the solid line becomes negative at about −0.23 at about 0.2 THz and gradually increases as the frequency increases, but at about 0.238 THz about It falls rapidly to a negative of -0.5. And if it exceeds about 0.238 THz, it will rise rapidly and will be 0 in about 0.253 THz. When it exceeds about 0.253 THz, it falls to a negative value of about -0.9, and the negative value is substantially maintained up to about 0.3 THz.
The imaginary part (Im (ε)) of the relative dielectric constant ε indicated by the broken line becomes 0 from 0.2 THz to 0.238 THz, and rapidly decreases at about 0.238 THz and becomes negative about −0.18. If it exceeds about 0.238 THz, it will rise rapidly and will be zero at about 0.253 THz. And it becomes 0 from about 0.253 THz to about 0.3 THz.
That is, it can be seen that the unit array of the second embodiment has a negative relative dielectric constant ε in a frequency range from about 0.2 THz to about 0.3 THz excluding about 0.253 THz.

FIG. 15 shows the analysis result of the frequency characteristics of the relative permeability μ of the unit array of the second embodiment when the analysis parameters are used. Referring to FIG. 15, the real part (Re (μ)) of the relative permeability μ indicated by the solid line is positive from 0 to about +0.003 from about 0.2 THz to about 0.253 Hz, but about 0.253 THz. If it exceeds, it will fall rapidly and become negative of about -0.018. And when it exceeds about 0.253 THz, it rises rapidly and becomes 0, and the value of 0 is substantially maintained up to about 0.3 THz.
The imaginary part (Im (μ)) of the relative magnetic permeability μ indicated by the broken line is 0 from 0.2 THz to 0.237 THz, increases slightly at about 0.237 THz, and becomes positive of about +0.001. When it exceeds about 0.237 THz, it rises slowly, but rises rapidly at about 0.254 THz and becomes positive of about +0.013. And when it exceeds about 0.254 THz, it will fall rapidly and will be set to 0, and the value of 0 is substantially maintained to about 0.3 THz.
That is, it can be seen that the unit array of the second embodiment has a negative relative permeability μ at about 0.253 THz.

FIG. 16 shows the analysis result of the wave number with respect to the frequency of the unit array of the second embodiment when the analysis parameters are used. Referring to FIG. 16, the wave number is 0 from 0.2 THz to 0.24 THz, and when it exceeds about 0.24 THz, the wave number increases rapidly to about 61. This wave number is maintained until about 0.257 THz. Is done. When it exceeds about 0.257 THz, the wave number drops rapidly and becomes zero at about 0.275 THz.
That is, it can be seen that the resolution of the unit array of the second embodiment can be increased at about 0.24 THz to about 0.275 THz.

Next, the prism 30 using the unit array of the second embodiment according to the present invention includes a metal slit array 3 using the unit array of the second embodiment instead of the unit array 1 of the first embodiment. The configuration of the prism 30 is the same as that of the prism 20 shown in FIG. 9A, and the configuration of the metal slit array 3 is the same as that of the metal slit array 2 shown in FIG. 9B. Therefore, the description of the prism 30 and the metal slit array 3 is omitted.
FIG. 17 shows analysis parameters when the target frequency for obtaining a negative refractive index in the prism 30 is 0.3 THz. In the analysis parameters shown in FIG. 17, the incident angle θ is 39 °, the width a of the metal slit array 2 is 370 μm, the longer length b from one surface to the inclined surface is 320.7 μm, and the shorter length d is 45 μm, a predetermined interval c in which the unit arrays of the second embodiment are arranged in the row direction and the column direction is 62 μm, and the length s of the second region 22 is 400 μm. In this analysis parameter, the reason why the maximum number of unit arrays of the second embodiment can be arranged in the row direction is as described above.

The propagation characteristics of the terahertz wave in the prism 30 using the metal slit array 3 composed of the unit array of the second embodiment was analyzed using a finite element method electromagnetic field simulator ANSYS HFSS Ver.14.1.1. The analysis results are shown in FIGS. 18A to 18C. 18A, the frequency of the incident terahertz wave is 270 GHz, the frequency of the incident terahertz wave in FIG. 18B is 275 GHz, and the frequency of the incident terahertz wave in FIG. 18C is 280 GHz.
18A to 18C, the incident angle θ is 39 °, and when the angle of the outgoing terahertz wave is a clockwise angle from the normal line 31a, the refractive index becomes positive and the outgoing terahertz is When the wave angle is counterclockwise from the normal 31a, the refractive index is negative. Referring to FIGS. 18A to 18C, in the propagation characteristics of FIGS. 18A to 18C, the angle of the outgoing terahertz wave is counterclockwise from the normal line 31a. Therefore, the prism is used in the frequency band of 270 GHz to 280 GHz. It can be seen that 30 exhibits a negative refractive index.

  Furthermore, a unit array of the third embodiment according to the present invention will be described. The unit array of the third embodiment is the same as the configuration of the unit array 1 of the first embodiment shown in FIG. 1, and the unit array 1 of the first embodiment and the unit array of the second embodiment and the analysis parameters are the same. Have been made different. Here, the description of the configuration of the unit array of the third embodiment is omitted. An example of analysis parameters when the unit array of the third embodiment is applied to the terahertz wave band is shown in FIG. In this case, the target frequency for obtaining a negative refractive index is 0.3 THz. As shown in FIG. 19, the analysis parameters for the analysis are as follows: Px of the upper wall metal plate 11 and lower wall metal plate 12 is about 69.1 μm, Pz is about 56 μm, and the interval (height) h between the parallel plates is It is about 148.8 μm. In this case, the cut-off frequency fc in the vacuum of the waveguide made of parallel plates is about 1.01 THz. Further, the thickness t of the upper wall metal plate 11 and the lower wall metal plate 12 is about 0.25 μm. Furthermore, the diameter r3 of the fine metal wire constituting the spiral microcoil 10 is about 9.4 μm, the inner diameter r1 around which the fine metal wire is wound is about 28 μm, and the outer diameter r2 is about 46.8 μm.

  In the unit array of the third embodiment having such analysis parameters, the electric field component E is in the width (x-axis) direction, and the magnetic field component H is in the height (y-axis) direction so as to be in the length (z-axis) direction. When a traveling TE mode incident wave is input, the transmission coefficient S21 of the transmitted wave that is output by propagating the unit array of the third embodiment in the z-axis direction and the reflection coefficient S11 of the reflected wave to be reflected The frequency characteristics were analyzed. Analysis was performed using finite element method electromagnetic simulator ANSYS HFSS Ver.14.1.1. Referring to the frequency characteristic of the transmitted power in FIG. 20 as an analysis result, the transmission coefficient S21 indicated by the broken line is almost 100% at about 0.27 THz and about 0.79 THz which are lower than the cut-off frequency fc. The TE-mode incident wave is almost transmitted through the unit array of FIG. 1, but the reflection coefficient S11 indicated by the solid line is almost 100% at 0.2 THz to 1.0 THz excluding a predetermined range centered on the above frequency. And almost everything will be reflected.

FIG. 21 shows the analysis result of the frequency characteristics of the refractive index n of the unit array of the third embodiment when the analysis parameters are used. Referring to FIG. 21, the real part (Re (n)) of the refractive index n indicated by the solid line is almost 0 from 0.2 THz to about 0.205 THz. And it falls rapidly at about 0.205 THz and becomes negative about -4 to -12 in the range of about 0.205 THz to about 0.265 THz, but in the range of about 0.255 THz to about 0.260 THz in this range. It becomes positive of about +6 to +7. Then, it rapidly rises at about 0.265 THz and becomes positive +4, and becomes 0 at about 0.28 THz to about 0.4 THz.
The imaginary part (Im (n)) of the refractive index n indicated by the broken line is about +10 positive at 0.2 THz, and rapidly rises to about +28 positive at about 0.205 THz. If it exceeds about 0.205 THz, it will fall rapidly and will be set to 0 in about 0.24 THz. And it is 0 from about 0.24 THz to about 0.28 THz, and becomes positive from 0 to +9 when it exceeds about 0.28 THz.
That is, the unit array of the third embodiment may have a negative refractive index n in a frequency range from about 0.205 THz to about 0.25 THz and a frequency range from about 0.26 THz to about 0.265 THz. Recognize.

FIG. 22 shows the analysis result of the frequency characteristics of the relative permittivity ε of the unit array of the third example when the analysis parameters are set. Referring to FIG. 22, the real part (Re (ε)) of the relative permittivity ε shown by the solid line becomes negative at about −310 at about 0.2 THz and gradually increases as the frequency increases, but about −550 at about 0.255 THz. It falls rapidly to the negative of. And if it exceeds about 0.255 THz, it will rise rapidly and will be 0 in about 0.27 THz. Above about 0.27 THz, it falls to a negative value of about -100, and the negative value is almost maintained up to about 0.35 THz.
The imaginary part (Im (ε)) of the relative dielectric constant ε indicated by the broken line is 0 from 0.2 THz to 0.255 THz, and rapidly decreases at about 0.255 THz and becomes negative about −210. If it exceeds about 0.255 THz, it will fall rapidly and will be set to 0 in about 0.27 THz. And it becomes 0 from about 0.27 THz to about 0.35 THz.
That is, it can be seen that the unit array of the third example has a negative dielectric constant ε in a frequency range from about 0.2 THz to about 0.35 THz except about 0.27 THz.

FIG. 23 shows the analysis result of the frequency characteristics of the relative permeability μ of the unit array of the third embodiment when the analysis parameters are used. Referring to FIG. 23, the real part (Re (μ)) of the relative permeability μ indicated by the solid line is positive from 0 to about +1.5 from about 0.2 THz to about 0.273 Hz, but is about 0.273 THz. If it exceeds, it will fall rapidly and become negative about -1.9. And when it exceeds about 0.273 THz, it will rise rapidly and will be set to 0, and the value of 0 is substantially maintained to about 0.35 THz.
The imaginary part (Im (μ)) of the relative magnetic permeability μ indicated by a broken line is 0 from 0.2 THz to 0.251 THz, and increases slightly at about 0.251 THz and becomes positive of about +0.7. When it exceeds about 0.251 THz, it rises slowly, but at about 0.272 THz, it rises rapidly and becomes positive of about +4.6. And when it exceeds about 0.272 THz, it will fall rapidly and will be set to 0, and the value of substantially 0 will be substantially maintained to about 0.35 THz.
That is, it can be seen that the unit array of the third example has a negative relative permeability μ at about 0.273 THz.

FIG. 24 shows the analysis result of the wave number with respect to the frequency of the unit array of the third embodiment when the analysis parameters are set. Referring to FIG. 24, the wave number is 0 from 0.2 THz to 0.252 THz, and when it exceeds about 0.252 THz, the wave number rapidly rises to about 62, and this wave number is maintained until about 0.273 THz. Is done. When it exceeds about 0.273 THz, the wave number drops rapidly and becomes zero at about 0.294 THz.
That is, it can be seen that the unit array of the third embodiment can increase the resolution at about 0.252 THz to about 0.294 THz.

  FIG. 25 shows only a part of the frequency band in the frequency characteristic of the transmitted power of the unit array of the third embodiment when the analysis parameters are used. Referring to the analysis result of FIG. 25, at about 0.272 THz lower than the cut-off frequency fc, the transmission coefficient S21 indicated by the broken line is about 96%, and the TE mode incident wave is substantially transmitted through the unit array of the third embodiment. To come. The transmission coefficient S21 is about 10% at about 0.27 THz, and rapidly increases to about 96% at about 0.272 THz. Further, it can be seen that the transmission coefficient S21 is about 10% at about 0.2745 THz, and rapidly decreases from about 96% of about 0.272 THz.

Next, the prism 60 using the unit array of the third embodiment according to the present invention includes a metal slit array 6 using the unit array of the third embodiment instead of the unit array 1 of the first embodiment. The configuration of the prism 60 is the same as that of the prism 20 shown in FIG. 9A, and the configuration of the metal slit array 6 is the same as that of the metal slit array 2 shown in FIG. 9B. Therefore, the description of the prism 60 and the metal slit array 6 is omitted.
FIG. 26 shows analysis parameters when the target frequency for obtaining a negative refractive index in the prism 60 is 0.3 THz. In the analysis parameters shown in FIG. 26, the incident angle θ is 39 °, the width a of the metal slit array 2 is 345.5 μm, the longer length b from one surface to the inclined surface is 289.6 μm, and the shorter length thereof. d is 37.5 μm, the predetermined interval c in which the unit arrays of the third embodiment are arranged in the row direction and the column direction is 62 μm, and the length s of the second region 22 is 373.3 μm. In this analysis parameter, the reason why the maximum unit array of the third embodiment can be arranged in the row direction is as described above.

  The propagation characteristics of the terahertz wave in the prism 60 using the metal slit array 6 composed of the unit array of the third embodiment was analyzed using a finite element method electromagnetic field simulator ANSYS HFSS Ver.14.1.1. The analysis results are shown in FIGS. 27A to 27J. The frequency of the incident terahertz wave in FIG. 27A is 280 GHz, the frequency of the incident terahertz wave in FIG. 27B is 290 GHz, the frequency of the incident terahertz wave in FIG. 27C is 300 GHz, and the incident terahertz wave in FIG. The frequency of the wave is 310 GHz, the frequency of the terahertz wave incident in FIG. 27E is 320 GHz, the frequency of the terahertz wave incident in FIG. 27F is 350 GHz, and the frequency of the terahertz wave incident in FIG. 27G is 400 GHz. The frequency of the incident terahertz wave in FIG. 27H is 600 GHz, the frequency of the incident terahertz wave in FIG. 27I is 800 GHz, and the frequency of the incident terahertz wave in FIG. 27J is 1000 GHz. There.

  27A to 27J, the incident angle θ is 39 °, and when the angle of the outgoing terahertz wave is a clockwise angle from the normal 61a, the refractive index becomes positive and the outgoing terahertz is When the wave angle is counterclockwise from the normal 61a, the refractive index is negative. Referring to FIGS. 27A to 27J, in the propagation characteristics of FIGS. 27B to 27D, the angle of the outgoing terahertz wave is counterclockwise from the normal line 61a, so that the prism is used in the frequency band of 290 GHz to 310 GHz. It can be seen that 60 exhibits a negative refractive index. 27E to 27J, the angle of the outgoing terahertz wave is not counterclockwise from the normal line 21a, and the prism 60 does not exhibit a negative refractive index at 320 GHz to 400 GHz. I understand. In the propagation characteristic shown in FIG. 27C with a frequency of 300 GHz, a negative refraction angle of about 25 degrees is obtained, and the prism 60 has a negative refraction index n = −3 based on the relationship between the refraction angle and the refraction index. 0.0.

The metal slit array of the present invention described above realizes a negative dielectric constant with a parallel plate in a cut-off state in a unit array, and realizes a negative magnetic permeability by resonance of a microcoil, thereby providing a negative in the terahertz wave band. It functions as a metamaterial that exhibits a dielectric constant and a negative magnetic permeability. That is, the magnetic permeability by the microcoil is negative at the frequency of the terahertz wave band where the dielectric constant by the parallel plate exhibits a negative dielectric constant. The metal slit array in this case is sufficiently large with respect to the wavelength of the terahertz wave band to be used, and has an infinite periodic structure in the x-axis direction and the y-axis direction when the traveling direction of the incident wave is the z-axis. In this infinite periodic structure, for example, several tens to several hundreds of unit arrays are arranged in the x-axis direction shown in FIG. 1, and several tens to several hundreds of unit arrays are arranged in the y-axis direction. To do. As a result, an array group consisting of hundreds to tens of thousands of unit arrays arranged on one plane of the xy plane is formed, and the array group is arranged by arranging several to several tens of groups in the z-axis direction. A slit array can be constructed. In this case, the unit arrays are stacked vertically. In this case, the upper wall metal plate and the lower wall metal plate adjacent to the upper wall metal plate (the lower wall metal plate and the lower wall metal plate are adjacent thereto). It is preferable that the upper wall metal plate of the unit array to be formed of a single metal plate having a double thickness. Here, if the thickness of the upper wall metal plate and the lower wall metal plate is t, the thickness of one metal plate is 2t. Furthermore, in the unit array of each embodiment, one microcoil was loaded, but the upper wall in the form of an elongated flat plate made of metal and the metal arranged to face the upper wall with a predetermined interval. It is also possible to provide a parallel flat plate formed of a bottom wall made of an elongated flat plate, and load a plurality of microcoils in a single row in the parallel flat plate.
By using the metal slit array according to the present invention described above, a planar lens or prism that exhibits a negative refractive index in the terahertz wave band can be realized.

1 Unit Array 2 Metal Slit Array 3 Metal Slit Array 6 Metal Slit Array 10 Micro Coil 11 Upper Wall Metal Plate 12 Lower Wall Metal Plate 13 Periodic Boundary Wall 20 Prism 21 First Region 21a Normal 22 Second Region 23 Waveguide 30 Prism 31a Normal 60 Prism 61a Normal

Claims (2)

A parallel plate comprising an upper wall made of a metal flat plate and a lower plate made of a metal flat plate arranged so as to face the upper wall at a predetermined interval, and loaded in the parallel plate A unit array of microcoils
A plurality of the unit arrays are arranged at predetermined intervals in the same plane to form a metal slit array.
A metal slit array, wherein a magnetic permeability of the microcoil is negative at a frequency in a terahertz wave band where a dielectric constant of the parallel plate exhibits a negative dielectric constant.   2. The length of one side of the upper wall and the lower wall is about 0.06λ to about 0.07λ, where λ is a wavelength of the frequency of the terahertz wave band. Metal slit array.