JP2018064203A - Active element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve transmission wave propagation control with only one metamaterial layer.SOLUTION: A split ring resonator 3 includes: a ring portion 4 made of metal and having an annular shape in plan view; a first dividing portion 5 which is a gap provided in the ring portion 4; and a field effect transistor 6 in which a source S is connected to one end of the ring portion 4 divided by the first dividing portion 5 and a drain D is connected to the other end of the ring portion 4 opposed to the one end with the first dividing portion 5 interposed therebetween.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a metamaterial active element using a split ring resonator.

  Millimeter waves and terahertz waves with sub-millimeter wavelengths are expected to be applied to imaging and radar technology due to their transparency and high resolution. In imaging and radar technology, a technique for controlling the propagation direction of electromagnetic waves in an arbitrary direction or condensing light at an arbitrary point is required. There is a phased array antenna technique as a technique for controlling the propagation of electromagnetic waves. However, in the millimeter wave and terahertz wave bands, which are super high frequency bands, the loss in the feeding network to the arrayed antenna is very large. For example, when a 4 × 4 planar array antenna is used at a frequency of 100 GHz or more, a loss of 10 dB or more occurs (see Non-Patent Document 1).

  Further, in controlling the near electromagnetic field distribution such as condensing, an unnecessary radiation component becomes large if the resolution of wavefront formation of the electromagnetic wave is about half a wavelength. Therefore, a transmission wavefront control technique using a metamaterial technique in a spatial system has been proposed as a technique for dynamically controlling the propagation direction and focal length of an electromagnetic wave in a super-high frequency band at high speed and low loss (Non-patent Document 2). reference).

  For example, in the technology disclosed in Non-Patent Document 2, using a split ring resonator used as a unit cell of a metamaterial device, the resonant frequency is shifted by changing the capacitance component of the split portion of the split ring resonator, By making the frequency region away from the resonance frequency the operating frequency, a transmission phase shift amount distribution is formed with low loss, and the wavefront of the electromagnetic wave transmitted through the metamaterial device is controlled.

  FIG. 13A to FIG. 13C are diagrams illustrating the concept of wavefront control of electromagnetic waves disclosed in Non-Patent Document 2. 13A to 13C, x, y, and z represent coordinate axes, H represents a magnetic field direction, E represents an electric field direction, and k represents a wave number direction. As shown in FIG. 13A, the metamaterial device 100 is formed by periodically forming split ring resonators 102 (unit cells) in an array on a dielectric substrate 101.

  FIG. 13B shows the structure of a conventional typical split ring resonator 102. The split ring resonator 102 includes a ring part 103 made of metal and a split part 104 that is a gap provided in the ring part 103. An electromotive force is excited in the dividing unit 104 by an incident electromagnetic wave having an electric field component in the y-axis direction parallel to the dividing unit 104, and a circulating current is generated. This circulating current becomes maximum at the LC resonance frequency determined by the capacitive component and the inductive component derived from the dividing unit 104 and the ring unit 103.

  When the resonance frequency is shifted by changing the dimension W of the dividing unit 104, the larger the dimension W of the dividing unit 104 is, the smaller the capacitance component is, so that the resonance frequency becomes higher and the electromotive force excited by the incident electromagnetic wave. Will grow. On the other hand, when the dimension W of the dividing portion 104 is small, the capacitance component is large, so that the resonance frequency is low and the electromotive force excited by the incident electromagnetic wave is small.

  That is, the split ring resonator having a smaller capacitive component of the split unit 104 has a higher resonance frequency, a higher resonance peak intensity (resonance strength), and a lower electromagnetic wave transmittance. Therefore, by changing the setting of the capacitance component of the dividing unit 104 of each divided ring resonator 102, for example, a transmission phase shift amount characteristic as shown in FIG. 13C can be realized.

Here, when the transmission phase shift amount distribution in the metamaterial device plane is φ (x, y), the propagation direction (deflection angle) θ [rad] and the focal length f ₀ [m] of the electromagnetic wave are expressed by the following equations. The controllable range of the deflection angle and the focal length is determined by the transmission phase shift control amount.

  In equations (1) and (2), λ is the wavelength of the incident electromagnetic wave. If a transmission phase control amount of 2π [rad] can be realized, it is possible to form an arbitrary wavefront of electromagnetic waves that pass through the metamaterial device.

W. Shin, et al., “A 108-112 GHz 4 × 4 Wafer-Scale Phased Array Transmitter with High-Efficiency On-Chip Antennas”, IEEE JOURNAL OF SOLID-STATE CIRCUITS, Vol.48, No.9, pp .2041-2055, 2013 D. Kitayama, et al., “Laminated metamaterial flat lens at millimeter-wave frequencies”, OPTICS EXPRESS, Vol.23, No.18, pp.23348-23356, 2015

  As described above, it is desired to realize a phase control amount of 2π [rad] in the method of controlling transmitted wave propagation by distributing the transmitted phase shift amount in the metamaterial device plane. However, since the phase change amount of the scattered wave with respect to the direct wave is in principle within a range of ± π / 2 [rad], it is difficult to realize a phase control amount of 2π [rad] with one layer of metamaterial. is there. Therefore, in order to freely control the focus and propagation direction (deflection angle) of the transmitted wave according to the characteristics of the transmitted phase shift amount distribution, the metamaterial layer needs to be multilayered. However, since multi-layering has a problem that disadvantages occur in terms of cost, size, and mounting, a technique for controlling the focus and propagation direction (deflection angle) of the transmitted wave with only one metamaterial layer is required.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an active element capable of realizing transmitted wave propagation control with only one metamaterial layer.

An active element of the present invention includes a ring-shaped ring portion made of metal in a plan view, a first divided portion which is a gap provided in the ring portion, and one end of the ring portion divided by the first divided portion. And a transistor having a drain connected to the other end of the ring portion opposed to the one end with the first divided portion interposed therebetween.
In addition, one configuration example of the active element according to the present embodiment further includes a second divided portion that is another gap provided in the ring portion.

Further, in one configuration example of the active element of the present embodiment, a structure including the ring portion, the first divided portion, and the transistor is used as a unit cell, and a plurality of the unit cells are arranged in an array. The operation state of the transistor is set for each unit cell so as to have a desired transmission characteristic with respect to an incident electromagnetic wave.
Further, one configuration example of the active element according to the present embodiment has a structure including the ring portion, the first divided portion, the transistor, and the second divided portion as a unit cell, and a plurality of the unit cells are arranged in an array. The operation state of the transistor is set for each unit cell so that the unit cell has a desired transmission characteristic with respect to incident electromagnetic waves.

Further, the active element of the present embodiment includes a ring-shaped ring portion made of metal in a plan view, a first divided portion that is a gap provided in the ring portion, and the ring portion divided by the first divided portion. A variable capacitance element having a first electrode connected to one end of the ring portion and a second electrode connected to the other end of the ring portion facing the one end with the first divided portion interposed therebetween. To do.
In addition, one configuration example of the active element according to the present embodiment further includes a second divided portion that is another gap provided in the ring portion.

Further, in one configuration example of the active element of the present embodiment, a plurality of unit cells are arranged in the form of a unit cell having a structure including the ring part, the first division part, and the variable capacitance element, and the unit The cell is characterized in that the capacity of the variable capacitance element is set for each unit cell so as to have a desired transmission characteristic with respect to an incident electromagnetic wave.
Further, one configuration example of the active element according to the present embodiment is a unit cell having a structure including the ring portion, the first division portion, the variable capacitance element, and the second division portion, and the unit cell is arranged in an array. The unit cell is configured such that the capacity of the variable capacitance element is set for each unit cell so that the unit cell has a desired transmission characteristic with respect to incident electromagnetic waves.

  According to the present invention, by connecting a transistor to the first divided portion, which is a gap provided in the ring portion, it is possible to control the transmittance of the active element with respect to incident electromagnetic waves in the state of operation of the transistor. It is possible to control the focal point and propagation direction (deflection angle) of the transmitted wave with only one metamaterial layer without making the material layer multi-layered.

  In the present invention, the transmittance of the active element with respect to incident electromagnetic waves can be controlled by increasing or decreasing the capacity of the variable capacitance element by connecting the variable capacitance element to the first divided portion that is a gap provided in the ring portion. It is possible to control the focal point and propagation direction of the transmitted wave with only one metamaterial layer.

  Further, in the present invention, by providing the ring portion with the second divided portion that is a gap different from the first divided portion, the intensity ratio between the case of transmitting the incident electromagnetic wave and the case of blocking the incident electromagnetic wave is increased. And the performance of the active device can be improved.

It is a figure explaining the concept of the transmitted wave propagation control of this invention. It is a figure explaining an example of the plane structure of the split ring resonator which concerns on the 1st Embodiment of this invention. It is a figure which shows the gate size dependence of the equivalent circuit at the time of ON / OFF of the field effect transistor which concerns on the 1st Embodiment of this invention, and the source-drain resistance of the field effect transistor, and the source-drain parasitic capacitance. . When the field effect transistor functions as an ideal switch in the first embodiment of the present invention, the field effect transistor is divided into incident electromagnetic waves when the source-drain resistance is large and the source-drain resistance is small. It is a figure which shows the frequency dependence of the transmittance | permeability of a ring resonator. It is a figure explaining the desirable characteristic of the transmittance | permeability of the split ring resonator at the time of ON of the field effect transistor in the 1st Embodiment of this invention, and the transmittance | permeability of the split ring resonator at the time of OFF. It is a figure explaining an example of the planar structure of the split ring resonator which concerns on the 2nd Embodiment of this invention. When the field effect transistor functions as an ideal switch in the second embodiment of the present invention, the field effect transistor is divided into incident electromagnetic waves when the source-drain resistance is large and the source-drain resistance is small. It is a figure which shows the frequency dependence of the transmittance | permeability of a ring resonator. It is a figure explaining the desirable characteristic of the transmittance | permeability of the split ring resonator at the time of ON of the field effect transistor in the 2nd Embodiment of this invention, and the transmittance | permeability of the split ring resonator at the time of OFF. It is a figure explaining an example of the planar structure of the split ring resonator which concerns on the 3rd Embodiment of this invention. It is a figure explaining the transmittance | permeability characteristic of the split ring resonator at the time of increase / decrease of the variable capacitance element in the 3rd Embodiment of this invention. It is a figure explaining an example of the planar structure of the split ring resonator which concerns on the 4th Embodiment of this invention. It is a figure explaining the transmittance | permeability characteristic of the split ring resonator at the time of increase / decrease in the variable capacitance element in the 4th Embodiment of this invention. It is a figure explaining the concept of the wavefront control of the conventional electromagnetic waves.

[Principle of the Invention]
FIG. 1A and FIG. 1B are diagrams for explaining the concept of transmitted wave propagation control of the present invention. 13A to 13C, x, y, and z represent coordinate axes, H represents a magnetic field direction, E represents an electric field direction, and k represents a wave number direction. In the present invention, in the metamaterial active element plane (in the xy plane of FIG. 1A), the transmission wave propagation is controlled not by the transmission phase shift amount distribution but by the transmission intensity distribution. Also in the present invention, the metamaterial active element 1 has a structure in which split ring resonators 3 (unit cells) are periodically formed in an array on a dielectric substrate 2.

In the present invention, the transmission intensity distribution is formed and controlled by connecting a field effect transistor to the divided portion of each divided ring resonator 3 and changing the resistance of the divided portion.
As the structure of the split ring resonator 3, a structure in which a field effect transistor is connected to a first split portion that is a gap provided in a metal ring portion, and a second split portion that is another gap are provided. There is a structure.

  In the split ring resonator 3 formed on the dielectric substrate 2, by turning on the field effect transistor of the split ring resonator 3 arranged in a region where it is desired to transmit incident electromagnetic waves, for example, FIG. A transmission intensity distribution as shown in FIG. As an example of forming the transmission intensity distribution, for example, the field effect is such that only the region in the metamaterial active element surface where the distance to the focal point is 2nπ (n = 0, 1, 2,...) Becomes the transmission region. There are a method of turning on a transistor, a method of turning on a field effect transistor so that only a region in a metamaterial active element surface where a wavefront inclined in a direction to be deflected is formed becomes a transmission region.

In the present invention, a flat active element capable of realizing the following effects can be realized by producing a metal pattern.
(I) In the present invention, the propagation direction (deflection angle) and focal length of the transmitted wave can be dynamically controlled by only one metamaterial layer (layer in which the split ring resonators 3 are arranged in an array), and the transmission The metamaterial layer does not need to be multi-layered so that the control amount of the phase shift amount is 2π.

(II) In the present invention, the transmittance with respect to the incident electromagnetic wave can be controlled near the LC resonance frequency of the split ring resonator 3 by making the resistance component of the split portion of the split ring resonator 3 variable.

(III) In the first divided portion of the split ring resonator 3, if the parasitic capacitance of the field effect transistor realized by the semiconductor process is larger than the capacitance component of the gap formed by the metal pattern, the circulating current is excited. The intensity of LC resonance is weakened, and the intensity ratio of transmitted waves is reduced. On the other hand, by introducing a structure in which a second divided portion different from the first divided portion is introduced, even if the parasitic capacitance of the field effect transistor is large, the metal pattern that forms the path of the circular current is increased. Since the asymmetry is not lost, the transmitted wave intensity ratio can be increased.

(IV) In the present invention, when the metamaterial active element 1 is used as a condenser lens, the focal length of the lens can be dynamically controlled by only one metamaterial layer. For example, the position according to the formula (3) so that only the region in the metamaterial active element surface where the distance to the focal point is 2nπ is set as the transmission region, that is, ± x _n (n = 0, 1, 2, ..)) Is turned on and the field effect transistors of the other divided ring resonators 3 are turned off, so that the metamaterial active element 1 is used as a condenser lens. The focal length of the lens at this time is f ₀ .

  Here, λ represents the wavelength of the transmitted wave. A position where the distance to the focal point is 2nπ ± π / 2 may be set as the transmission region.

(V) Further, in the present invention, when the metamaterial active element 1 is used as a deflection lens, it is possible to dynamically control the propagation direction (deflection angle) of the transmitted wave with only one metamaterial layer. For example, by turning on the field effect transistor of the split ring resonator 3 at an interval d according to the equation (4) to form a transmission region having an intermittent arrangement, the transmission wave is deflected in the direction of ± θ [rad]. be able to.

[First Embodiment]
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 2A shows an example of a planar structure of the split ring resonator 3 that is a unit cell of the metamaterial active element according to the present embodiment. The split ring resonator 3 according to the present embodiment includes a ring-shaped ring portion 4 made of a metal in a plan view, a first split portion 5 that is a gap provided in the ring portion 4, and a first split portion 5. A source S is connected to one end of the divided ring portion 4, and a field effect transistor 6 having a drain D connected to the other end of the ring portion 4 opposite to the one end with the first divided portion 5 interposed therebetween. The As shown in FIG. 1A, a plurality of split ring resonators 3 are formed in an array on the dielectric substrate 2.

  2A schematically shows the structure of the split ring resonator 33, but the manufacturing process for forming the field effect transistor 6 to be connected to the metal pattern on the dielectric substrate 2 is a well-known technique. Therefore, detailed description is omitted.

  When an electromagnetic wave is incident perpendicularly to the surface on which the split ring resonator 3 is formed, the circular current I is excited and formed by the capacitive component C formed by the first split portion 5 and the ring portion 4. LC resonance occurs at the LC resonance frequency determined by the inductive component L. This resonance is indicated by a broken line 20 in FIG. 2B in which the split ring resonator 3 is a surface parallel to the external electric scene (the Ek plane in FIG. 1A) and divides the path of the circulating current I into two. This is because of the asymmetric structure with respect to the surface). When the dimension W1 of the first divided portion 5 is small, that is, when the capacitance component C is large, the asymmetry is lost and the LC resonance intensity is small. .

  In the present embodiment, a field effect transistor 6 is provided in the first split section 5 of the split ring resonator 3, and the resistance component of the first split section 5 is controlled to change the intensity of the LC resonance, thereby transmitting the transmitted wave. Control strength. For example, the source S of the field effect transistor 6 is connected to one end of the ring portion 4 divided by the first dividing portion 5 as described above, and the ring portion 4 facing the one end with the first dividing portion 5 interposed therebetween. Since the drain D of the field effect transistor 6 is connected to the other end of the transistor and a voltage is applied to the gate G of the field effect transistor 6, an inversion layer is formed in the channel, and the resistance between the source and the drain is reduced. 1 division | segmentation part 5 short-circuits.

FIG. 3A shows an equivalent circuit when the field effect transistor 6 is ON, and FIG. 3B shows an equivalent circuit when the field effect transistor 6 is OFF. When the field effect transistor 6 is added to the first division portion 5, as shown in FIG. 2B, the dimension of the first division portion 5 is apparently smaller than the original mechanical dimension W1. That is, the field effect transistor 6 functions as a capacitor C _SD when OFF (FIG. 3A) and functions as a resistor R _{SD — on} when ON (FIG. 3B).

FIG. 3C shows the gate size dependence of the source-drain resistance R _SD — _on and the source-drain parasitic capacitance C _SD of the field effect transistor 6. The horizontal axis of FIG. 3C is the gate width of the field effect transistor 6 or the reciprocal of the gate length. As shown in FIG. 3C, for example, when the gate width of the field effect transistor 6 increases or the gate length decreases, the source-drain resistance R _SD — _on decreases, and the source-drain parasitic capacitance C _SD gets bigger. That is, the source-drain resistance R _SD — _on and the source-drain parasitic capacitance C _SD are in a trade-off relationship. As the source-drain parasitic capacitance C _SD is larger, the asymmetry of the path of the circulating current I is lost and the strength of the LC resonance is reduced.

FIG. 4A shows the frequency of transmittance of the split ring resonator 3 with respect to incident electromagnetic waves when the field effect transistor 6 functions as an ideal switch (R _{SD — on} = 0Ω, C _SD = 0 pF). Indicates dependency. 4A, T _ONa indicates the transmittance of the split ring resonator 3 when the field effect transistor 6 is ON, and T _OFFa indicates the transmittance of the split ring resonator 3 when the field effect transistor 6 is OFF. Yes.

When the field effect transistor 6 is turned ON and the first dividing unit 5 is short-circuited, the LC resonance intensity is reduced. Therefore, when the frequency of the incident electromagnetic wave is near the LC resonance frequency f _LC or the resonance frequency f _LC , the field effect The transmittance of the split ring resonator 3 with respect to incident electromagnetic waves can be controlled by the gate voltage applied to the transistor 6.

On the other hand, when the source-drain resistance R _SD — _on of the field effect transistor 6 increases, the transmittance of the split ring resonator 3 when the field effect transistor 6 is ON is transmitted as indicated by T _ONb in FIG. It deteriorates with respect to the ideal value T _{ONa of the} rate, and the transmission loss when ON is increased. Further, when the source-drain resistance R _SD — _on increases, the transmittance T _OFFb of the split ring resonator 3 when the field effect transistor 6 is OFF becomes larger than the ideal value T _OFFa of the transmittance, and the _resistance against incident electromagnetic waves is increased. The blocking characteristics are slightly deteriorated.

Here, when the field effect transistor 6 having a small source-drain resistance R _SD — _on is used, the source-drain parasitic capacitance C _{SD of the} field effect transistor 6 is determined from the trade-off relationship described in FIG. growing. Since the source-drain parasitic capacitance _CSD increases the capacitance component in the first division section 5 of the split ring resonator 3, the LC resonance intensity when the field effect transistor 6 is OFF is reduced. That is, as shown in FIG. 4C, the transmittance T _OFFc of the split ring resonator 3 when the field effect transistor 6 is OFF becomes very large with respect to the ideal value T _{OFFa of the} transmittance. Even if is turned OFF, the incident electromagnetic wave cannot be blocked.

The source of the field effect transistor 6 - drain resistance R _SD _ _on small, source - if drain parasitic capacitance C _SD is large, the split ring resonator 3 when ON of the field effect transistor 6 transmittance T _ONC of The deterioration is slight even compared with the ideal value T _ONa of the transmittance.

Figure 4 (A) As apparent from the description of to FIG 4 (C), the source of the field effect transistor 6 - drain parasitic capacitance C _SD and source during ON of the field effect transistor 6 - drain resistance R _SD _ _on from among the trade-off relationship, the ratio T _ON / T _oFF between the transmittance T _oFF of split ring resonator 3 when the transmittance T _ON and oFF of the split ring resonator 3 when ON of the field effect transistor 6 LC The value of the source-drain resistance R _SD — _on needs to be selected so as to increase in the vicinity of the resonance frequency f _LC (FIG. 5). Needless to say, the value of the source-drain resistance R _SD — _on can be adjusted by the gate size of the field effect transistor 6.

  As described above, in the present embodiment, the metamaterial active element in which the split ring resonators 3 capable of controlling the transmittance of electromagnetic waves are arranged in an array is used, and the distance to the focal point is 2nπ or 2nπ ± π / 2. Only the region in the metamaterial active element surface as described above is a transmission region, so that the focus can be dynamically controlled. Further, by forming a transmittance distribution such that the wave front of the electromagnetic wave is inclined, the transmitted wave propagation direction (deflection angle) can be dynamically controlled. If the technique of the present embodiment is applied to, for example, imaging or radar, measurement time can be shortened.

  When the focus or wavefront is actually controlled, the voltage applied to the source S, drain D, and gate G of the field effect transistor 6 of each split ring resonator 3 of the metamaterial active element is controlled by a control means (not shown). Thus, the ON / OFF of the field effect transistor 6 may be controlled for each split ring resonator 3 (for each unit cell) so as to have a desired transmission characteristic with respect to the incident electromagnetic wave.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. FIG. 6A shows an example of a planar structure of the split ring resonator 3 that is a unit cell of the metamaterial active element according to the present embodiment. The split ring resonator 3 according to the present embodiment includes a ring-shaped ring portion 4 made of a metal in a plan view, a first split portion 5 that is a gap provided in the ring portion 4, and a first split portion 5. A field effect transistor 6 having a source S connected to one end of the divided ring portion 4 and a drain D connected to the other end of the ring portion 4 facing the one end with the first divided portion 5 in between; 4 and a second dividing section 7 which is another gap provided in the area 4. Similar to the first embodiment, the metamaterial active element is formed by forming a plurality of split ring resonators 3 in FIG. 6A in an array on a dielectric substrate.

This embodiment realizes a larger T _ON / T _OFF ratio than the first embodiment. When the field effect transistor 6 is added to the first dividing unit 5, as shown in FIG. 2B of the first embodiment and FIG. 6B of the present embodiment, the first dividing unit 5 The dimension is apparently smaller than the original mechanical dimension W1.

On the other hand, in the present embodiment, the source-drain parasitic capacitance C _SD of the field effect transistor 6 is added to the first division unit 5, and the size of the first division unit 5 is effectively reduced. Even so, since the asymmetry of the path of the circulating current I is maintained by the introduction of the second dividing section 7, the LC resonance intensity when the field effect transistor 6 is OFF is larger than that of the first embodiment. Become.

In the case of the split ring resonator 3 of the present embodiment, when the field effect transistor 6 is turned on and the first split section 5 is short-circuited, the LC determined by the capacitance C _s generated by the newly introduced second split section 7. Resonance occurs at the resonance frequency. When the field effect transistor 6 is OFF, the LC resonance frequency is determined by the source-drain parasitic capacitance C _SD and the capacitance C _s . FIG. 7A shows the transmittance of the split ring resonator 3 of the present embodiment with respect to incident electromagnetic waves when the field effect transistor 6 functions as an ideal switch (R _{SD — on} = 0Ω, C _SD = 0 pF). The frequency dependence of is shown.

In FIG. 7A, T _ONa indicates the transmittance of the split ring resonator 3 when the field effect transistor 6 is ON, and T _OFFa indicates the transmittance of the split ring resonator 3 when the field effect transistor 6 is OFF. As described above, the LC resonance frequency f _LC1 when OFF is determined by 1 / {(1 / C _s ) + (1 / C _SD )}, and the LC resonance frequency f _LC2 when ON is determined by the capacitance C _s . As described above, when an ideal switch is used, LC resonance frequencies f _LC1 and f _LC2 that are different depending on whether the switch is ON or OFF are shown, and the incident electromagnetic wave is divided in the vicinity of the LC resonance frequencies f _LC1 and f _LC2. The transmittance of the ring resonator 3 can be controlled.

On the other hand, when the source-drain resistance R _SD — _on of the field effect transistor 6 increases, the transmittance of the split ring resonator 3 when the field effect transistor 6 is ON is transmitted as indicated by T _ONb in FIG. 7B. It deteriorates with respect to the ideal value T _{ONa of the} rate, and the transmittance change becomes small. When the source-drain resistance R _SD — _on is large, the degradation of the transmittance T _OFFb of the split ring resonator 3 when the field effect transistor 6 is OFF is slight compared with the ideal value T _OFFa of the transmittance. is there.

Here, when the field-effect transistor 6 having a small source-drain resistance R _SD — _on is used, the source-drain parasitic capacitance C _SD of the field-effect transistor 6 is compared with the capacitance C _s generated by the second dividing unit 7. Even when the field effect transistor 6 is in an OFF state, the LC resonance frequency is determined by the capacitance C _s , and the transmittance of the split ring resonator 3 at the OFF time is T _{OFFc in} FIG. _7C. As shown by, the transmittance deteriorates with respect to the ideal value T _OFFa , and the transmittance change becomes small.

Figure 7 (A) As apparent from the description of to FIG 7 (C), the source of the ON time of the field effect transistor 6 - capacitance formed by the drain resistance R _SD _ _on the second divided portion 7 C _s from among the trade-off relationship, the ratio T _ON / T _oFF between the transmittance T _oFF of split ring resonator 3 when the transmittance T _ON and oFF of the split ring resonator 3 when ON of the field effect transistor 6 LC The value of the source-drain resistance R _SD — _on needs to be selected so as to increase in the vicinity of the resonance frequency f _LC1 (FIG. 8).

Thus, in the present embodiment, the intensity of LC resonance when the field effect transistor 6 is OFF can be increased, and a larger T _ON / T _OFF ratio can be realized as compared with the first _embodiment. Therefore, the intensity ratio between the transmitted wave passing through the transmission region (the region where the split ring resonator 3 where the field effect transistor 6 is ON) and the electromagnetic wave leaking from the region other than the transmission region is increased. Can do.

  Also in the present embodiment, when the focus and wavefront are actually controlled, the source S, drain D, and gate of the field effect transistor 6 of each split ring resonator 3 of the metamaterial active element are controlled by a control means (not shown). By controlling the voltage applied to G, ON / OFF of the field effect transistor 6 may be controlled for each split ring resonator 3 so as to have a desired transmission characteristic with respect to incident electromagnetic waves.

In the present embodiment, when the capacitance C _s generated by the first dividing unit 5 and the capacitance C _s generated by the second dividing unit 7 are different (for example, the dimension W1 of the first dividing unit 5 and the second dividing unit). 7 may be the same case), but either case is acceptable.

In the present embodiment, the case where the frequency of the incident electromagnetic wave is the LC resonance frequency f _LC1 or the vicinity of the LC resonance frequency f _LC1 is mainly described. However, in addition to the electromagnetic wave in such a frequency range, the frequency The electromagnetic wave having the LC resonance frequency f _LC2 or the vicinity of the LC resonance frequency f _LC2 may be used as the incident electromagnetic wave. According to the present embodiment, the transmission characteristics for electromagnetic waves can be greatly changed at the LC resonance frequencies f _LC1 and f _LC2 , so that different transmission wave propagation control can be performed for electromagnetic waves having different frequencies.

  In the first and second embodiments, the example in which the operation state of the field effect transistor 6 is controlled to either ON or OFF is described. However, the present invention is not limited to this. Control may be performed so that the state is a complete intermediate region between ON and OFF.

[Third Embodiment]
In the first embodiment, the field effect transistor is used as the element provided in the first division section. However, the present invention is not limited to this, and a variable capacitance element may be used. FIG. 9 is a diagram for explaining an example of the planar structure of the split ring resonator according to the present embodiment. The same components as those in FIG. In the split ring resonator 3 of the present embodiment, the first electrode E1 is connected to one end of the ring part 4, the first split part 5, and the ring part 4 divided by the first split part 5, The variable capacitance element 8 includes a second electrode E2 connected to the other end of the ring portion 4 facing the one end with the first division portion 5 interposed therebetween. Similar to the first embodiment, the metamaterial active element is obtained by forming a plurality of split ring resonators 3 of FIG. 9 in an array on a dielectric substrate.

The variable capacitance element 8 is an element in which the capacitance between the electrodes E1 and E2 changes according to the voltage applied to the control terminal E3.
Therefore, when the capacitance of the variable capacitance element 8 is increased, transmittance characteristics (for example, T _{UP in} FIG. 10) corresponding to the case where the field effect transistor 6 is turned on in the first embodiment can be obtained. When the capacitance of the capacitive element 8 is decreased, a transmittance characteristic (for example, T _{DOWN in} FIG. 10) corresponding to the case where the field effect transistor 6 is turned off can be obtained.

When the capacitance generated by the first dividing unit 5 is C, the capacitance when the variable capacitance element 8 is increased is C _UP , and the capacitance when the variable capacitance element 8 is decreased is C _DOWN , the LC resonance frequency f _LC1 of FIG. C + C _DOWN ), and the LC resonance frequency f _{LC2 in} FIG. 10 is determined by (C + C _UP ).

[Fourth Embodiment]
Also in the second embodiment, a variable capacitance element may be used instead of the field effect transistor. FIG. 11 is a diagram for explaining an example of the planar structure of the split ring resonator according to the present embodiment. The same components as those in FIG. 6A are denoted by the same reference numerals. The split ring resonator 3 according to the present embodiment includes a ring part 4, a first split part 5, a second split part 7, and a variable capacitance element 8. Similar to the first embodiment, the metamaterial active element is obtained by forming a plurality of split ring resonators 3 of FIG. 11 in an array on a dielectric substrate.

The variable capacitance element 8 is as described in the third embodiment. When the capacitance of the variable capacitance element 8 is increased in the present embodiment, transmittance characteristics (for example, T _{UP in} FIG. 12) corresponding to the case where the field effect transistor 6 is turned on in the second embodiment can be obtained. If the capacitance of the variable capacitance element 8 is reduced, a transmittance characteristic (for example, T _{DOWN in} FIG. 12) corresponding to the case where the field effect transistor 6 is turned off can be obtained.

The capacitance generated by the first dividing unit 5 is C, the capacitance generated by the second dividing unit 7 is C _s , the capacitance when the variable capacitance element 8 is increased, C _UP , and the capacitance when the variable capacitance element 8 is decreased is C _DOWN. Then, the LC resonance frequency f _LC1 in FIG. 12 is determined by 1 / {(1 / C _s ) + (1 / (C + C _DOWN ))}, and the LC resonance frequency f _{LC2 in} FIG. 12 is 1 / {(1 / C _s ) + (1 / (C + C _UP ))}.

In the third and fourth embodiments, as in the second embodiment, in addition to the electromagnetic wave whose frequency is near the LC resonance frequency f _LC1 or the LC resonance frequency f _LC1 , the frequency is LC resonance. An electromagnetic wave in the vicinity of the frequency f _LC2 or the LC resonance frequency f _LC2 may be used as an incident electromagnetic wave, and different transmitted wave propagation control may be performed on electromagnetic waves having different frequencies.

  In the third and fourth embodiments, when the focus and wavefront are actually controlled, the control terminal E3 of the variable capacitance element 8 of each split ring resonator 3 of the metamaterial active element is controlled by a control means (not shown). By controlling the voltage applied to, the capacitance of the variable capacitance element 8 may be controlled for each split ring resonator 3 so as to have a desired transmission characteristic for incident electromagnetic waves.

In the first to fourth embodiments, all the patterns of the ring portions 4 constituting each divided ring resonator 3 may be the same, or the pattern of the ring portions 4 may be changed in the metamaterial active element plane. . By changing the pattern of the ring portion 4, the capacitance C which are suitable for the desired transmitted wave propagation control, it is possible to set the C _s.

  The present invention can be applied to a metamaterial element using a split ring resonator.

  DESCRIPTION OF SYMBOLS 1 ... Metamaterial active element, 2 ... Dielectric substrate, 3 ... Split ring resonator, 4 ... Ring part, 5 ... 1st division part, 6 ... Field effect transistor, 7 ... 2nd division part, 8 ... Variable Capacitance element.

Claims (8)

A ring-shaped ring portion made of metal in plan view,
A first divided portion which is a gap provided in the ring portion;
A transistor having a source connected to one end of the ring portion divided by the first divided portion and a drain connected to the other end of the ring portion facing the one end across the first divided portion. An active element comprising: The active device of claim 1, wherein
Furthermore, the active element characterized by including the 2nd division part which is another gap provided in the said ring part. The active device of claim 1, wherein
A structure composed of the ring part, the first divided part, and the transistor is used as a unit cell, and a plurality of unit cells are arranged in an array,
An active element, wherein the operation state of the transistor is set for each unit cell so that the unit cell has a desired transmission characteristic with respect to incident electromagnetic waves. The active device according to claim 2, wherein
A structure composed of the ring part, the first divided part, the transistor, and the second divided part is used as a unit cell, and a plurality of unit cells are arranged in an array,
An active element, wherein the operation state of the transistor is set for each unit cell so that the unit cell has a desired transmission characteristic with respect to incident electromagnetic waves. A ring-shaped ring portion made of metal in plan view,
A first divided portion which is a gap provided in the ring portion;
A first electrode is connected to one end of the ring portion divided by the first divided portion, and a second electrode is connected to the other end of the ring portion facing the one end across the first divided portion. An active element comprising a connected variable capacitance element. The active device according to claim 5, wherein
Furthermore, the active element characterized by including the 2nd division part which is another gap provided in the said ring part. The active device according to claim 5, wherein
A structure composed of the ring part, the first divided part and the variable capacitance element is used as a unit cell, and a plurality of unit cells are arranged in an array,
An active element, wherein the unit cell has a capacity of each variable cell so that the unit cell has a desired transmission characteristic with respect to an incident electromagnetic wave. The active device according to claim 6, wherein
A structure composed of the ring part, the first divided part, the variable capacitance element, and the second divided part is used as a unit cell, and a plurality of the unit cells are arranged in an array,
An active element, wherein the unit cell has a capacity of each variable cell so that the unit cell has a desired transmission characteristic with respect to an incident electromagnetic wave.