Radio wave control element

Abstract

The present invention addresses the problem of providing a radio wave control element that consumes little power required to control radio waves. The present invention addresses the problem by having a first electrode, a liquid crystal composition layer, and a second electrode in this order, at least one of the first electrode and the second electrode having a metasurface structure, and further having a temperature adjustment mechanism for heating and cooling the liquid crystal composition layer, the solid-liquid crystal phase transition temperature of the liquid crystal composition layer being 40 DEG C or higher.

Description

Technical Field

[0001] This invention relates to an electromagnetic wave control element using a metasurface structure and a liquid crystal layer. Background Technology

[0002] High-frequency radio waves (millimeter waves, terahertz waves) required for high-capacity wireless communication have high propagation characteristics. Therefore, in order to transmit radio waves to the target location, a reflector that bends the radio waves in any direction is needed.

[0003] However, for example, the direction of electromagnetic wave reflection by a conventional reflector is constant, and the reflection direction is a normal reflection where the angle of incidence and the angle of exit are equal. Therefore, in a conventional reflector, the range of changes in the direction of electromagnetic wave propagation is greatly limited, making it difficult to transmit electromagnetic waves to the desired location.

[0004] To solve this problem, a radio wave control element that arbitrarily controls the direction of the radio waves is used.

[0005] As such radio wave control elements, there are known elements that use ICs (Integrated Circuits) to adjust the phase within the reflecting surface to reflect radio waves toward the target direction.

[0006] However, radio wave control components using ICs have the problem of high power consumption.

[0007] In contrast, as a low-power radio wave control element, a radio wave control element using liquid crystal is known. This radio wave control element adjusts the orientation state of the liquid crystal by applying a voltage to the liquid crystal layer sandwiched between electrodes, thereby adjusting the phase distribution within the reflective surface and reflecting radio waves in the target direction.

[0008] As an example, Patent Document 1 describes an electromagnetic wave control element (tunable LC device) comprising: a first substrate; a first reflector located on the first substrate and including a first electrode layer; a liquid crystal layer (LC layer) located on the first reflector; a second reflector located on the liquid crystal layer and including a second electrode layer; and a second substrate located on the second reflector, wherein the liquid crystal layer can be adjusted by applying an electrical signal to at least one of the first or second electrode layers.

[0009] Previous technical documents Patent documents Patent Document 1: Japanese Patent Publication No. 2023-513660 Summary of the Invention

[0010] The technical problem to be solved by the invention The radio wave control element described in Patent Document 1 uses a metasurface structure formed by arranging liquid crystal layers and conductive microstructures.

[0011] In this radio wave control element, each microstructure serves as an electrode, and by adjusting the voltage applied to each electrode, the orientation of the liquid crystal compound in the region corresponding to each electrode is adjusted. This, in turn, adjusts the phase distribution within the reflective surface, enabling the reflection of radio waves towards the target direction.

[0012] Using this liquid crystal-based radio wave control element, the direction of radio wave propagation can be controlled to the target direction with less power consumption than the radio wave control element using IC mentioned above.

[0013] However, in existing liquid crystal-based radio wave control elements, power consumption remains relatively high because a constant power supply is required during operation. Therefore, improvements are needed to further reduce power consumption.

[0014] The purpose of this invention is to solve the problems of the prior art and to provide a radio wave control element that uses a metasurface structure and a liquid crystal layer to control the direction of radio wave propagation and consumes less power to control the radio waves.

[0015] means for solving technical problems To address this issue, the present invention has the following structure.

[0016] [1] An electromagnetic wave control element, comprising, in sequence, a first electrode, a liquid crystal composition layer, and a second electrode, wherein, At least one of the first electrode and the second electrode has a metasurface structure composed of multiple arranged microstructures. The radio wave control element also has a temperature regulation mechanism for heating and cooling the liquid crystal composition layer. The solid-liquid phase transition temperature of the liquid crystal composition layer is above 40°C.

[0017] [2] According to the radio wave control element described in [1], wherein, In X-ray diffraction spectra measured at temperatures below 40°C, The liquid crystal composition layer can have peak values ​​in the range of diffraction angles below 15°.

[0018] [3] According to the radio wave control element described in [1] or [2], wherein, The liquid crystal composition layer contains a dichroic substance.

[0019] [4] According to the radio wave control element described in [3], wherein, The content of dichroic material is 30% or more by mass relative to the total mass of the liquid crystal composition layer.

[0020] Invention Effects According to the radio wave control element of the present invention, the direction of radio wave travel can be controlled with less power consumption. Attached Figure Description

[0021] Figure 1 This is a diagram that conceptually illustrates an example of the radio wave control element of the present invention.

[0022] Figure 2 This is a diagram that conceptually illustrates an example of the use of the radio wave control element of the present invention.

[0023] Figure 3 It is a conceptual representation Figure 1 A three-dimensional view of the metasurface structure of the radio wave control element shown.

[0024] Figure 4 This is a conceptual diagram illustrating the function of the radio wave control element of this invention.

[0025] Figure 5 This is a conceptual diagram illustrating the function of the radio wave control element of this invention. Detailed Implementation

[0026] Hereinafter, the radio wave control element of the present invention will be described in detail based on the preferred embodiment shown in the accompanying drawings.

[0027] In this specification, the numerical range represented by “~” indicates the range included by the values ​​recorded before and after “~” as the lower and upper limits.

[0028] In this specification, "same" includes the range of errors generally permissible in the technical field.

[0029] The figures shown below are conceptual diagrams illustrating the radio wave control element of the present invention. Therefore, the shape, size, thickness, and positional relationship of each component may not necessarily match the actual dimensions.

[0030] Figure 1 The present invention is conceptually represented as an example of an electromagnetic wave control element (electromagnetic wave control element).

[0031] The radio wave control element 10 of the present invention is a reflective radio wave control element that uses a reflective metasurface structure and a liquid crystal layer to control the travel direction of radio waves (electromagnetic waves) to a target direction.

[0032] As an example, this radio wave control element of the present invention is used in indoor and outdoor radio wave communications, and is employed in active antennas and beam steering devices that can switch the direction of radio wave travel for transmission.

[0033] As an example, the radio wave control element 10 of the present invention acts on radio waves with frequencies of 0.007 to 0.3 THz and reflects the radio waves in a desired direction. That is, the radio wave control element of the present invention reflects radio waves with wavelengths of 1 to 43 mm in a desired direction.

[0034] Preferably, the radio wave control element 10 of the present invention reflects radio waves with a frequency of 0.1 to 0.3 THz, i.e. radio waves with a wavelength of 1 to 3 mm, in the desired direction.

[0035] like Figure 1 As shown, the radio wave control element 10 of the present invention has, from the bottom down, a first electrode layer 26, a liquid crystal composition layer 20, and a metasurface structure 12.

[0036] The metasurface structure 12 is formed by microstructures 14 arranged in two dimensions on the support 16 to form a resonator. Furthermore, a liquid crystal composition layer 20 is disposed on the support 24.

[0037] Furthermore, the first electrode layer 26 is configured to cover the entire surface of the support 24 opposite to the liquid crystal composition layer 20.

[0038] Furthermore, in the radio wave control element 10 of the present invention, a temperature adjustment mechanism 30 is provided on the lower surface side of the first electrode layer 26. The temperature adjustment mechanism 30 heats and cools the liquid crystal composition layer 20.

[0039] The temperature control mechanism 30 in the figure heats the liquid crystal composition layer 20 by heating the first electrode layer 26 and cools the liquid crystal composition layer 20 by cooling the first electrode layer 26.

[0040] In addition, in the radio wave control element 10, the temperature adjustment mechanism 30 is bonded to the first electrode layer 26, the first electrode layer 26 is bonded to the support 24, and the liquid crystal composition layer 20 is bonded to the support 16 (metasurface structure 12) as needed using an adhesive (adhesive, bonding agent).

[0041] There are no limitations on the adhesive method. Various methods that can transmit the radio waves targeted by the radio wave control element 10, such as OCA (Optical Clear Adhesive), can be used.

[0042] As an example, Figure 1 In the radio wave control element 10 shown, the microstructure 14 is formed of a conductive material and also serves as an electrode forming an electrode pair with the first electrode layer 26. Furthermore, a power supply 28 for applying a voltage between the microstructure 14 and the first electrode layer 26 is connected to each microstructure 14.

[0043] Furthermore, there are no restrictions on the power source 28; any known AC power source can be used as long as it can supply the required power.

[0044] As described above, the radio wave control element 10 is a reflective radio wave control element that uses a reflective metasurface structure and a liquid crystal composition layer to control the travel direction of radio waves (electromagnetic waves) to a target direction.

[0045] As an example, such as Figure 2 As conceptually shown, this radio wave control element 10 is used in a radio wave reflecting device RD (active antenna). Specifically, the radio wave reflecting device RD uses the radio wave control element 10 to switch the reflection direction of a high-direction radio wave RW radiated by an antenna ANT located behind a building BL to a direction toward region AR1 in front of the building BL, which is shadowed when viewed from the antenna ANT, and a direction toward region AR2, which is different from region AR1.

[0046] For example, if users utilizing wireless communication are mostly located in area AR1 during the day and in area AR2 at night, the areas where users are concentrated sometimes change according to the time of day. In this case, the radio wave reflecting device RD changes the area supplied with the radio wave RW by changing the reflection direction of the radio wave RW according to the time of day.

[0047] In the radio wave control element 10 of the present invention, the liquid crystal composition layer 20 undergoes a phase change by heating. It is solid (glass state) at room temperature, and transforms into a liquid crystal phase when heated. In the state of transformation into the liquid crystal phase, the orientation direction of the liquid crystal compound LC in the liquid crystal composition layer 20 can be changed by supplying power from the power source 28 to the microstructure 14, i.e., by applying a voltage between the microstructure 14 and the first electrode layer 26.

[0048] Furthermore, if the liquid crystal composition layer 20 is cooled to return to room temperature while the orientation of the liquid crystal compound LC is maintained by continuously applying voltage, the orientation state of the liquid crystal compound LC will be maintained and the liquid crystal composition layer 20 will be solidified even after the voltage is stopped.

[0049] The temperature control mechanism 30 is used for heating and cooling of the liquid crystal composition layer 20.

[0050] As described above, by supplying electricity to each microstructure 14 while it is heated, a voltage is applied to the liquid crystal composition layer 20 between the microstructure 14 and the first electrode layer 26, causing a change in the orientation state of the liquid crystal compound LC. Furthermore, by adjusting the electricity supplied to each microstructure 14, the voltage applied to the region of the liquid crystal composition layer 20 corresponding to the microstructure 14 can be adjusted, thereby adjusting the orientation of the liquid crystal compound LC between the microstructure 14 and the first electrode layer 26.

[0051] As an example, in a heated state, i.e., in the liquid crystal phase state, and in a state without applied voltage, the liquid crystal compound LC of the liquid crystal composition layer 20 is as described later. Figure 5 As conceptually shown in the upper layer, it is oriented in a direction parallel to the main surface of the liquid crystal composition layer 20. Furthermore, the main surface of the liquid crystal composition layer 20 refers to the XY plane, which will be described later.

[0052] In the following description, this orientation state will also be referred to as "horizontal orientation".

[0053] If a voltage is applied to the liquid crystal composition layer 20 while it is heated, then as Figure 5 Conceptually shown in the second layer from the top, the liquid crystal compound LC in the region corresponding to the microstructure 14 changes its orientation state according to the intensity of the applied voltage and tilts relative to the thickness direction of the liquid crystal composition layer 20. In this example, the liquid crystal compound LC is oriented to the maximum extent along the thickness direction of the liquid crystal composition layer 20. Furthermore, the thickness direction of the liquid crystal composition layer 20 is the Z direction, described later.

[0054] In the following description, this orientation state will also be referred to as "vertical orientation".

[0055] In addition, the thickness direction refers to the stacking direction of the first electrode layer 26, the support 24, the liquid crystal composition layer 20 and the support 16.

[0056] Furthermore, the main surface is the largest surface of the sheet (film, plate, layer), which is usually the two sides in the thickness direction of the sheet.

[0057] Furthermore, the normal direction refers to the direction that is orthogonal to the main surface.

[0058] As mentioned above, Figure 1 The radio wave control element 10 shown utilizes a reflective metasurface structure.

[0059] like Figure 3 As conceptually illustrated, in the metasurface structure 12 of the example figure, the microstructure 14 is, for example, a flat plate structure with a rectangular planar shape, aligned with its two sides in the X and Y directions orthogonal to each other, and arranged in two dimensions along the X and Y directions. Furthermore, the planar shape refers to the shape when viewed from a direction orthogonal to the main surface of the plate; in this example, it is the shape when viewed from a direction orthogonal to the main surface of the support 16.

[0060] In the metasurface structure 12, the unit cell UC (unit cell UC) of the metasurface structure is constituted by a single microstructure 14 and the surrounding space extending from the middle between it and the adjacent microstructures 14 (see reference). Figure 3 and Figure 5 ).

[0061] If an electromagnetic wave is incident on the electromagnetic wave control element 10 of the present invention having this structure, the electromagnetic wave is modulated in phase by the resonance of the microstructure 14 (cell) when it passes through the transmissive metasurface structure 12, and then modulated in phase by the transmissive liquid crystal composition layer 20.

[0062] The radio waves are then reflected by the first electrode layer 26, which also serves as a reflector.

[0063] The electromagnetic wave reflected by the first electrode layer 26 is transmitted through the liquid crystal composition layer 20 again and its phase is modulated. It is then modulated by the metasurface structure 12 and emitted from the electromagnetic wave control element 10 as a reflected electromagnetic wave.

[0064] Here, as described above, the orientation state, i.e., the refractive index, of the liquid crystal compound LC in the liquid crystal composition layer 20 varies depending on the voltage applied to each microstructure 14 under heated conditions.

[0065] That is, the effective refractive index for electromagnetic waves changes as the orientation state of the liquid crystal compound (LC) changes.

[0066] When no voltage is applied to the liquid crystal composition layer 20, the liquid crystal compound LC in the liquid crystal composition layer 20 is, for example, horizontally aligned.

[0067] As described above, if a voltage is applied to the liquid crystal composition layer 20 under heating conditions, the liquid crystal compound LC in the region corresponding to the microstructure 14 tilts and aligns relative to the main surface of the liquid crystal composition layer 20 according to the magnitude of the applied voltage.

[0068] Furthermore, if the liquid crystal composition layer 20 returns to room temperature while maintaining the orientation state of the liquid crystal compound LC, that is, while a voltage is applied, it returns to a solid state, and the orientation of the liquid crystal compound LC is maintained even when the voltage is stopped.

[0069] In the radio wave control element 10, the greater the voltage applied to the liquid crystal composition layer 20, the closer the liquid crystal compound LC is to vertical alignment, and the refractive index of the liquid crystal composition layer 20 in that region changes from the state before the voltage was applied. That is, in the liquid crystal composition layer 20, the refractive index of the corresponding region can be changed according to the voltage applied to each microstructure 14, thus imparting a phase difference to the transmitted radio wave.

[0070] exist Figure 4 In this context, as conceptually shown by the incident direction IN and the exit direction OUT, the overall direction of travel of a radio wave RW can be considered as the normal direction relative to the straight line connecting the wavefronts of multiple radio waves RW.

[0071] Consider a scenario in the radio wave control element 10 where, for example, the phase delay of a radio wave RW incident on and reflected to each of a plurality of one-dimensionally arranged unit cells UC gradually increases from the unit cell UC on the right side of the figure toward the unit cell UC on the left side of the figure. In this case, even if the straight line connecting the wavefronts of the individual incident radio waves RWs is parallel to the reflecting surface, the straight line connecting the wavefronts of the individual radio waves RWs reflected in each unit cell UC will be inclined relative to the reflecting surface. That is, the travel direction of the radio wave RW emitted from the reflecting surface, i.e., the emission direction OUT, only changes by an angle θ relative to the incident direction IN of the radio wave RW.

[0072] Thus, by controlling the phase delay amount by performing phase modulation on each unit cell UC, the travel direction of the radio wave RW can be controlled.

[0073] That is, in the radio wave control element 10, by adjusting the power supplied to each microstructure 14, adjusting the voltage applied to the corresponding region, and adjusting the orientation of the liquid crystal compound in the liquid crystal composition layer 20, regions with different refractive indices can be generated in the surface direction of the liquid crystal composition layer 20.

[0074] Therefore, incident electromagnetic waves can be reflected in a direction different from that of specular reflection. For example, when electromagnetic waves are incident from the normal direction of the liquid crystal composition layer 20, the electromagnetic waves are reflected in a direction inclined relative to the normal direction, rather than being reflected in the normal direction.

[0075] Furthermore, by changing the power supplied to each microstructure 14 to change the voltage applied to the corresponding region of the liquid crystal composition layer 20, the orientation state, i.e., refractive index, i.e., phase of the liquid crystal compound at each position in the planar direction can be adjusted to switch the reflection direction of the incident electromagnetic wave.

[0076] As described above, the radio wave control element 10 of the present invention is an active radio wave control element that can change the reflection direction of the incident radio wave by adjusting the power supplied to each microstructure 14.

[0077] In the radio wave control element 10 of the present invention, similar to the known metasurface structure, the metasurface structure 12 is formed by arranging microstructures 14 as microstructures in two dimensions on the support 16.

[0078] As described above, in the metasurface structure 12 of the example figure, the microstructures 14 have a rectangular planar shape and are arranged in two dimensions at equal intervals in the X and Y directions that are orthogonal to each other.

[0079] There are no limitations on the support 16. As long as it can support the microstructure 14 and transmit radio waves of the frequency targeted by the radio wave control element 10, such as radio waves of 0.007 to 0.3 THz, various known sheet materials can be used.

[0080] As an example, the support 16 may include a metal substrate having an oxide insulating layer such as a silicon substrate containing silicon oxide, a support made of oxides such as silicon oxide, a support made of semiconductors such as germanium and chalcogenide glass, a polyacrylic resin film such as polymethyl methacrylate, a cellulose resin film such as cellulose triacetate, a cyclic olefin polymer film (e.g., manufactured by JSR Corporation under the trade name "ARTON" and manufactured by Zeon Corporation under the trade name "ZEONOR"), a polyethylene terephthalate (PET) film, a polycarbonate film, and a polyvinyl chloride film, a liquid crystal polymer (LCP) film, and a glass plate, etc.

[0081] The thickness of the support 16 is not limited, as long as it can support the microstructure 14 and achieve sufficient transmittance to the radio waves that are to be targeted, and the thickness can be appropriately set according to the material in which the support 16 is formed, and can obtain sufficient strength according to the purpose of the radio wave control element 10.

[0082] Furthermore, in the radio wave control element 10 of the present invention, the metasurface structure 12 is not limited to having a support 16.

[0083] That is, if possible, the radio wave control element of the present invention can form a metasurface structure 12 by directly arranging microstructures 14 on the surface of the liquid crystal composition layer 20.

[0084] Microstructures 14 are arranged on one surface of the support 16, thereby forming a metasurface structure 12.

[0085] The metasurface structure 12 is a structure formed by separating microstructures 14 and arranging them in two dimensions on a plane. It is basically composed of the arrangement of unit cells formed by a microstructure 14 and the space surrounding the microstructure 14.

[0086] In the radio wave control element 10 of the present invention, the metasurface structure is basically a known metasurface structure (metamaterial). Therefore, in the radio wave control element 10 of the present invention, various known metasurface structures can be utilized.

[0087] That is, in this invention, there are no limitations on the shape and forming material of the microstructure 14, the arrangement of the microstructure 14, and the spacing (pitch) of the microstructure 14.

[0088] Furthermore, the reflection characteristics of the radio waves targeted by the radio wave control element 10 according to the present invention can be designed using known methods. As an example, the amplitude and phase of the radio waves reflected by the microstructure 14 used can be calculated using commercially available simulation software, and the arrangement of the microstructure 14 can be set in such a way as to achieve the distribution of the target phase modulation amount (refractive index).

[0089] As an example, the radio wave control element 10 of the present invention targets radio waves with a frequency of 0.007 to 0.3 THz, preferably 0.1 to 0.3 THz.

[0090] Therefore, in the metasurface structure 12, the microstructure 14 is selected in such a way as to impart a desired phase difference to the radio wave of that frequency, and the arrangement of the microstructure is then set.

[0091] The metasurface structure 12 is essentially composed of a unit cell formed by a microstructure 14 and the space surrounding the microstructure 14. The metasurface structure 12 modulates the phase of the incident electromagnetic wave by means of the resonance of the microstructure 14 through the arrangement of the unit cells.

[0092] Furthermore, in the radio wave control element 10 of the present invention, the number of microstructures 14 in a unit cell is essentially one, but the present invention is not limited thereto. That is, in the radio wave control element of the present invention, a unit cell may have multiple microstructures 14 as needed, depending on the target optical characteristics, the size of the microstructures 14, the forming material and shape, and the size of the unit cell. In this case, a unit cell may have different microstructures 14. However, when a unit cell has multiple microstructures 14, the phase modulation amount in the space where each microstructure of the unit cell is located is basically equal.

[0093] In the radio wave control element 10 of the present invention, there is no limitation on the material used to form the microstructure 14 constituting the metasurface structure 12, and various materials used as microstructures in known metasurface structures can be used.

[0094] Metals and dielectrics can be used as materials for forming the microstructure 14. In the case of metals, copper, gold, and silver are preferred from the viewpoint of low optical loss. Furthermore, composites composed of metal particles and binders, as well as oxide semiconductors, can also be used as materials for forming the microstructure 14. On the other hand, in the case of dielectrics, silicon, titanium oxide, and germanium are preferred from the viewpoint of high refractive index and the ability to perform large phase modulation.

[0095] In addition, such as Figure 1 As shown, when the microstructure 14 also serves as an electrode in an electrode pair with the first electrode layer 26, the microstructure 14 is formed of a conductor.

[0096] Similarly, the shape of the microstructure 14 constituting the metasurface structure 12 is not limited, and various shapes used as microstructures in known metasurface structures can be utilized.

[0097] Examples include: cross-shaped solids that intersect cuboids, cuboid-shaped solids, cylindrical solids, V-shaped solids such as those with cuboids connected at the ends as shown in Japanese Patent Application Publication No. 2018-046395, approximately H-shaped solids such as H-beams, and approximately C-shaped solids such as C-channels.

[0098] Furthermore, as shown in Japanese Patent Application Publication No. 2018-046395, V-shaped solids and cross-shaped solids can be formed by adjusting the angle between two cuboids to create various shapes.

[0099] In addition, it is also possible to utilize, for example, “Appl.Sci.2018,8(9),1689;https: / / doi.org / 10.3390 / app8091689” Figure 5 The solid shown has a base shape, etc.

[0100] In the metasurface structure 12, such microstructures 14 can be used individually or in multiple forms simultaneously. Furthermore, as... Figure 3 As shown, the same microstructures 14 can be arranged in the same orientation, or in different orientations, or a mixture of the same orientation and different orientations can exist.

[0101] In the example shown, as a preferred embodiment, in the metasurface structure 12, identical microstructures 14 having all the same structure are arranged in two dimensions with the same orientation and at equal intervals along the mutually orthogonal X and Y directions.

[0102] However, the present invention is not limited thereto. As described above, multiple microstructures can be used simultaneously, and the arrangement and spacing of the microstructures 14 can also be different in the surface direction of the support 16.

[0103] In particular, considering the controllability of the reflection direction of electromagnetic waves in the state of liquid crystal compound LC orientation caused by applying a voltage to liquid crystal composition layer 20, it is preferable that the metasurface structure 12 uses all identical microstructures 14. Moreover, it is more preferable that the identical microstructures 14 of the metasurface structure 12 are arranged in the same orientation and at equal intervals in two dimensions, and even more preferably arranged at equal intervals in two dimensions in orthogonal X and Y directions.

[0104] in addition, Figure 1 In the radio wave control element 10 shown, there is one metasurface structure 12, but the present invention is not limited to this.

[0105] That is, in the radio wave control element of the present invention, the first electrode layer 26 side can also be a metasurface structure. In other words, the radio wave control element of the present invention can have two metasurface structures separated by a liquid crystal composition layer. In this case, the two metasurface structures can be the same object or different objects. Furthermore, the two metasurface structures can be metasurface structures made of the same material that are staggered in position from the microstructures.

[0106] The liquid crystal composition layer 20 is a layer formed by aligning a liquid crystal compound LC in a specified state. It is solid (glass state) at room temperature, but transforms into a liquid crystal phase when heated. The orientation of the liquid crystal compound LC can be changed by applying a voltage. Preferably, the liquid crystal composition layer 20 transforms from a solid phase to a nematic phase when heated.

[0107] Therefore, in the liquid crystal composition layer 20, when the phase has transformed into a liquid crystal phase by heating, as described above, by applying a voltage between the microstructure 14 and the first electrode layer 26, the orientation state of the liquid crystal compound LC changes according to the power supplied to each microstructure 14. In the liquid crystal composition layer 20, the orientation state of the liquid crystal compound LC is horizontal in a stable state. The higher the applied voltage, the more tilted it is relative to the main surface of the liquid crystal composition layer 20, and thus the closer it is to a vertical orientation.

[0108] Furthermore, the liquid crystal compound LC is cooled while maintaining its orientation under applied voltage. If it returns to room temperature, it reverts to a solid state while maintaining its orientation. In this state, the liquid crystal composition layer 20 maintains the orientation of the liquid crystal compound as it was under applied voltage even if the applied voltage is stopped.

[0109] That is, the radio wave control element 10 of the present invention adjusts the orientation of the liquid crystal compound LC by heating and applying voltage, and then cools it back to room temperature (below the phase transition temperature) while the voltage is applied. Thus, even if the power supply is stopped thereafter, the orientation of the liquid crystal compound LC can be maintained. Therefore, even if the voltage is not subsequently applied to the liquid crystal composition layer 20, the radio wave control element 10 can control the reflection direction of the incident radio wave to the desired direction.

[0110] Therefore, the radio wave control element 10 according to the present invention can significantly suppress the power consumption for radio wave control.

[0111] Furthermore, by heating the device from a state where the reflection direction of the radio wave is controlled in a certain direction, supplying electricity to each microstructure 14 again to change the orientation of the liquid crystal compound LC, and then cooling it, the reflection direction of the incident radio wave can be changed, and the radio wave can be controlled to other desired directions. That is, as described above, the radio wave control element 10 of the present invention is an active radio wave control element in which the reflection direction (control direction) of the radio wave can be arbitrarily changed.

[0112] Furthermore, in the liquid crystal composition layer 20 of the radio wave control element 10 in the example figure, the orientation of the liquid crystal compound LC is horizontal in a stable state.

[0113] Therefore, if the power supply is stopped while the liquid crystal compound (LC) is heated above the phase transition temperature, the LC will revert to horizontal orientation.

[0114] In this invention, the liquid crystal composition layer 20 is a layer with a solid-liquid phase transition temperature of 40°C or higher, preferably a solid-nematic phase transition temperature of 40°C or higher.

[0115] When the solid-liquid phase transition temperature of the liquid crystal composition layer 20 is below 40°C, a phase transition can occur even at temperatures close to room temperature, altering the orientation of the liquid crystal compound LC. That is, when the solid-liquid phase transition temperature of the liquid crystal composition layer 20 is below 40°C, if the voltage applied to the liquid crystal composition layer 20 is stopped after cooling, the orientation of the liquid crystal compound LC will revert to a horizontal orientation. Therefore, when the solid-liquid phase transition temperature of the liquid crystal composition layer 20 is below 40°C, in order to perform radio wave control, similar to the conventional radio wave control element described in Patent Document 1, a voltage needs to be continuously applied, resulting in increased power consumption.

[0116] The solid-liquid phase transition temperature of the liquid crystal composition layer 20 is preferably 50°C or higher, more preferably 60°C or higher, and even more preferably 80°C or higher.

[0117] Furthermore, there is essentially no upper limit to the solid-liquid phase transition temperature of the liquid crystal composition layer 20. However, considering the heating energy required to induce the phase transition of the liquid crystal composition layer 20, the prevention of damage to other components due to heat, and the prevention of thermal expansion, the phase transition temperature is preferably 120°C or lower.

[0118] Furthermore, in the radio wave control element of the present invention, as an example, the solid-to-liquid phase transition temperature of the liquid crystal composition layer 20 is determined by observing the liquid crystal composition forming the liquid crystal composition layer 20 using a polarized light microscope. That is, while observing with a polarized light microscope, the liquid crystal composition forming the liquid crystal composition layer 20 is heated to a temperature at which it becomes a liquid crystal phase, and then, while cooling it down, the temperature at which it transforms from the liquid crystal phase to another phase such as a crystalline phase is measured.

[0119] Alternatively, the support 16 or support 24 can be peeled off to expose the liquid crystal composition layer 20, and a sample of the liquid crystal composition layer 20 can be taken by scraping or other methods. Using this sample, the solid-liquid crystal phase transition temperature of the liquid crystal composition layer 20 can be determined by the methods described above. Furthermore, the solid-liquid crystal phase transition temperature can also be determined by thermal analysis such as differential scanning calorimetry (DSC) and thermogravimetric analysis (TG). Moreover, the solid-liquid crystal phase transition temperature can be determined by identifying the phase using X-ray diffraction (XRD).

[0120] Furthermore, there is no limitation on the thickness of the liquid crystal composition layer 20, as long as the thickness that imparts the required phase difference to the radio waves is appropriately set according to the forming material of the liquid crystal composition layer 20.

[0121] In this invention, the liquid crystal composition layer 20 can be formed, for example, on the surface of the alignment film described later, by a known method corresponding to the liquid crystal compound or the like used.

[0122] Furthermore, the liquid crystal composition layer 20 will be described in detail later.

[0123] In the radio wave control element 10, a liquid crystal composition layer 20 is formed on the support 24.

[0124] Support 24 is basically the same as support 16 mentioned above.

[0125] Here, the support 24 used to form the liquid crystal composition layer 20 can be the same support as the support 16 described above, and the surface of the substrate on which the liquid crystal composition layer 20 is formed has an alignment film for aligning the liquid crystal compound LC to a predetermined state.

[0126] The alignment film can utilize various known alignment films. Examples include a triboelectric film composed of organic compounds such as polymers, an inclined vapor-deposited film of inorganic compounds, a film with microgrooves, and a film formed by accumulating organic compounds such as ω-trisanoic acid, dioctadecylmethylammonium chloride, and methyl stearate using the Langmuir-Blodgett (LB) process.

[0127] Furthermore, as an alignment film, it is also possible to produce a so-called photoalignment film by irradiating polarized or unpolarized light onto a raw material with photoalignability.

[0128] These orientation films can be formed using known methods corresponding to the forming material of the host.

[0129] The entire surface of the support 24 on the side opposite to the liquid crystal composition layer 20 is covered by the first electrode layer 26.

[0130] The first electrode layer 26 is an electrode that changes the orientation of the liquid crystal compound LC in the liquid crystal composition layer 20, and as described above, it also functions as a reflective layer that reflects electromagnetic waves incident from the metasurface structure 12 side.

[0131] The first electrode layer 26 is not limited; as long as it has sufficient conductivity and can reflect electromagnetic waves that are to be targeted, it can be a sheet made of various known materials.

[0132] As an example of the first electrode layer 26, examples include metal layers such as copper, aluminum, gold, and silver; inorganic conductive materials such as ITO (indium tin oxide); organic conductive materials such as polythiophene, represented by PEDOT (poly(3,4-ethylenedioxythiophene)); and graphene. Inorganic conductive materials, organic conductive materials, and graphene are transparent to visible light, but they function as reflective layers for electromagnetic waves of the aforementioned frequencies.

[0133] There is no limitation on the thickness of the first electrode layer 26, as long as the thickness is appropriately set according to the forming material of the first electrode layer 26 to reflect the electromagnetic waves to the target with the required reflectivity.

[0134] As described above, the radio wave control element 10 is provided with a temperature regulation mechanism 30 on the lower surface side of the first electrode layer 26.

[0135] The temperature control mechanism 30 heats and cools the liquid crystal composition layer 20 by heating the first electrode layer 26 and cooling the liquid crystal composition layer 20 by cooling the first electrode layer 26.

[0136] In the radio wave control element 10 shown in the figure, the liquid crystal composition layer 20 is heated by the temperature adjustment mechanism 30, so that the liquid crystal composition layer 20 is transformed from a solid (solid phase) into a liquid crystal phase.

[0137] Furthermore, after adjusting the orientation of the liquid crystal compound LC in the liquid crystal phase state, the liquid crystal composition layer 20 is cooled by the temperature adjustment mechanism 30, thereby restoring the liquid crystal composition layer 20 to a solid state. As described above, the radio wave control element 10 of the present invention can maintain the orientation state of the liquid crystal compound LC even when the voltage applied to the microstructure 14 is stopped in this state, and can reduce the power consumption of radio wave control.

[0138] In the radio wave control element 10 of the present invention, the temperature adjustment mechanism 30 is provided not only with a heating mechanism for converting the liquid crystal composition layer 20 into a liquid crystal phase, but also with a cooling mechanism for cooling the liquid crystal composition layer 20, thereby rapidly cooling it after controlling the orientation of the liquid crystal compound. This prevents the liquid crystal composition layer 20 from unnecessarily crystallizing due to cooling, and allows the solidified liquid crystal composition layer 20 to be preferably in a state where it has a peak value in the X-ray diffraction spectrum described later in the range of diffraction angles below 15°.

[0139] The temperature regulating mechanism 30 is not limited and can utilize various temperature regulating mechanisms that use known heating and cooling mechanisms.

[0140] As examples of heating mechanisms, methods that involve direct or indirect contact with a warm medium such as warm water, radiant heating using heaters employing Joule heating-based resistance heating, warm air heating, and heating using Peltier elements are all exemplified.

[0141] As a cooling mechanism, examples include methods that allow refrigerants such as cold water to come into direct or indirect contact, cooling using Peltier elements, and cooling based on cold air.

[0142] Multiple heating and cooling mechanisms can be used in combination.

[0143] In addition, in the example shown, the temperature of the liquid crystal composition layer 20 is adjusted by adjusting the temperature of the first electrode layer 26, but the present invention is not limited thereto.

[0144] For example, the temperature of the liquid crystal composition layer 20 can be adjusted by regulating the temperature of the microstructures 14 and / or the support 16 of the metasurface structure 12. Alternatively, the liquid crystal composition layer 20 can be directly heated and cooled.

[0145] Furthermore, as shown in the example figure, when the liquid crystal composition is heated and cooled indirectly, heating can be performed at different locations using the first electrode layer 26 and cooling can be performed using the metasurface structure 12.

[0146] The following is for reference. Figure 5 The conceptual diagram illustrates the function of the radio wave control element 10 of the present invention.

[0147] In addition, Figure 5 In order to simplify the accompanying drawings and clearly illustrate the function of the radio wave control element 10 of the present invention, only the microstructure 14 (metasurface structure 12), the liquid crystal composition layer 20, the first electrode layer 26, and the power supply 28 are shown in the figures. Furthermore, in Figure 5 In the diagram, the dashed lines represent the unit cells (unit cells UC) corresponding to each microstructure 14.

[0148] As described above, in the radio wave control element 10, under steady-state conditions, such as Figure 5 As shown in the upper layer, the liquid crystal compound LC of the liquid crystal composition layer 20 is horizontally oriented (approximately horizontally oriented).

[0149] In this state, heating of the liquid crystal composition layer 20 begins via the temperature control mechanism 30. If heating of the liquid crystal composition layer 20 begins and the temperature exceeds the transition temperature, the liquid crystal composition layer 20 transitions from a solid to a liquid crystal phase. In this state, the power supply 28 is off. When the liquid crystal composition layer 20 is in the state of being transformed into a liquid crystal phase, the power supply 28 is turned on to supply power to the microstructure 14, which functions as the first electrode, thereby applying a voltage to the liquid crystal composition layer 20.

[0150] Therefore, as Figure 5 As shown in the second layer from the top, the liquid crystal composition layer 20 changes the orientation state of the liquid crystal compound LC according to the power supplied to each microstructure 14, i.e., the applied voltage. In the example shown, the cell on the right side of the figure has the highest applied voltage, and the liquid crystal compound LC is in a vertical orientation state. Furthermore, the cell on the left side of the figure remains horizontally oriented with almost no applied voltage. Moreover, in the cell in the very center of the figure, an intermediate potential is applied, and the liquid crystal compound LC is in an orientation state that is between horizontal and vertical orientation.

[0151] If the orientation state of the liquid crystal compound LC is stable, then as Figure 5 As shown in the third layer from the top, the liquid crystal composition layer 20 is cooled by the temperature regulation mechanism 30 while the power supply 28 is kept in the driving state (on).

[0152] When the temperature of the liquid crystal composition layer 20 is at room temperature (below the transition temperature), such as Figure 5 As shown in the lower layer, the driving of the power supply 28 is turned off, and the applied voltage is stopped. As described above, in this state, even without applying voltage, the orientation of the liquid crystal compound LC remains the same as in the state where voltage was applied. In addition, the temperature adjustment mechanism 30 essentially turns off when the temperature reaches room temperature, but performs temperature control as needed to maintain room temperature.

[0153] Therefore, if radio wave RW is incident in this state, then as previously referenced... Figure 4 As explained, the incident radio wave RW is given a phase corresponding to the orientation state of the liquid crystal compound LC corresponding to the applied voltage, and the reflection direction is controlled so that it is reflected in a predetermined direction.

[0154] Therefore, the radio wave control element 10 according to the present invention can significantly suppress the power consumption for radio wave control.

[0155] Furthermore, from Figure 5 As shown on the right, the liquid crystal composition layer 20 is heated again, and then electricity is supplied to each microstructure 14 again to adjust the orientation of the liquid crystal compound LC. After cooling, the reflection direction of the incident radio wave RW can be changed, thereby controlling the travel direction of the radio wave RW to other desired directions.

[0156] As described above, in the radio wave control element 10 of the present invention, the liquid crystal composition layer 20 is solid at room temperature, and the solid-liquid phase transition temperature is 40°C or higher, preferably the solid-nematic phase transition temperature is 40°C or higher.

[0157] Here, the preferred method for the radio wave control element of the present invention is to have a peak value in the X-ray diffraction spectrum (XRD spectrum) of the liquid crystal composition layer 20 measured at a temperature below 40°C, which is within the range of a diffraction angle of 15° or less.

[0158] The liquid crystal composition layer 20 with such XRD spectrum peaks has a high degree of orientation (=Δn), which can appropriately control radio waves with frequencies of 0.007 to 0.3 THz.

[0159] In the XRD spectrum, peaks in the range of diffraction angles below 15° indicate the presence of periodic structures such as crystalline and smectic phases in the liquid crystal composition layer 20.

[0160] If the liquid crystal composition layer 20, which transforms into a liquid crystal phase (nematic phase) at a temperature above 40°C, is cooled to room temperature from a temperature above the solid-liquid crystal phase transition temperature, a glass state is formed in which the molecular fluctuations of the liquid crystal phase are frozen. However, by mixing periodic structures such as crystalline phase and smectic phase in the glass state, an electromagnetic wave control element 10 with high orientation can be obtained.

[0161] It is known that phases of higher order than nematic phases, namely crystalline and smectic phases, typically have higher orientation degrees. Therefore, it is assumed that the liquid crystal composition layer 20 exhibits high orientation degrees due to the presence of such higher-order phases mixed in the glass state.

[0162] If the orientation degree of the liquid crystal composition layer 20 is high, the refractive index anisotropy (Δn) can be increased. Δn increases with the greater anisotropy (inherent birefringence) of the molecules contained in the liquid crystal composition layer 20, but the higher the orientation degree, which represents the degree of alignment of the molecules in a certain direction, the greater Δn.

[0163] Typically, nematic liquid crystals and glass forms obtained by cooling and fixing nematic liquid crystals exhibit an alignment degree of approximately 0.6 to 0.85. On the other hand, smectic liquid crystals and crystalline phases, which are higher-order phases, exhibit an alignment degree higher than 0.85.

[0164] It is believed that by having this higher-order phase mixed in the glass state, the orientation degree of the liquid crystal composition layer 20 becomes higher than 0.85.

[0165] The glass state formed by cooling and immobilizing the liquid crystal phase does not have a periodic structure, so periodicity is usually not observed. In the XRD spectrum, broad peaks (diffuse peaks) caused by the average intermolecular distance are observed.

[0166] On the other hand, higher-order phases such as crystalline and smectic phases typically form periodic structures such as layered structures, and peaks corresponding to the length of these layers are observed in XRD spectra. Typically, the width of the diffuse peaks observed in nematic phases and the glassy state is greater than 15°. The length of the layer is the interval of the periodic structure, also known as the period length.

[0167] That is, in XRD spectra, peaks at angles below 15° indicate higher-order phases with periodic structures, such as crystalline and smectic phases.

[0168] As an example, the XRD of the liquid crystal composition layer 20 can be measured simply by using the liquid crystal composition that forms the liquid crystal composition layer 20.

[0169] For example, a film is made by dissolving the liquid crystal composition forming the liquid crystal composition layer 20 in a solvent and spin-coating it onto a conventional alignment film such as a polyimide that has undergone a rubbing treatment.

[0170] The film is heated to a temperature above 40°C, which is the same temperature process used in actual applications in radio wave control devices, and after forming a liquid crystal phase with LC orientation of the liquid crystal compound in the liquid crystal composition, it is cooled to below 40°C (below the transition temperature), thereby obtaining a sample of liquid crystal composition layer 20 in which the liquid crystal composition is immobilized. Using this sample, the XRD of the liquid crystal composition layer is measured as shown below.

[0171] Alternatively, the support 16 or support 24 can be peeled off to expose the liquid crystal composition layer 20, and the liquid crystal composition layer 20 can be sampled by scraping or other methods. The sample is then processed in the same way as the liquid crystal composition to obtain a sample of the liquid crystal composition layer 20.

[0172] Next, the XRD spectrum was measured using the in-plane method. Furthermore, this measurement was performed while the liquid crystal composition layer was held at a temperature below 40°C.

[0173] Hereinafter, X-ray diffraction analysis using the in-plane method will also be referred to as "in-plane XRD". In-plane XRD is performed by irradiating the sample surface with X-rays using a thin-film X-ray diffraction device under the following conditions.

[0174] (condition) • Use a Cu ray source (CuKα, output 45kV, 200mA) • X-ray incident angle 0.2° • Optical system used: Parallel optical system (CBO (Cross Beam Optics)) (PB (Parallel Beam)) • 0.2mm incident slit, 0.5deg (degree) parallel slit in-plane PSC, 10mm long-side limiting slit • Light-receiving slit on the receiving side: 20mm; Light-receiving parallel slit in-plane PSA (Parallel Slit Analyzer): 0.5deg • Detector: HyPix3000 (0D mode) manufactured by Rigaku Corporation. ·2θχ / Scan conditions: Set the range of 1–40 degrees to 0.008 degrees / step and 2.0 degrees / minute (min). · Scan conditions: Set the range of -120 to 120 degrees to 0.5 degrees / step and 9.6 degrees / minute. The above conditions are the set values ​​for a thin-film X-ray diffraction apparatus. Known apparatuses can be used as thin-film X-ray diffraction apparatuses. As an example of a thin-film X-ray diffraction apparatus, the SmartLab manufactured by Rigaku Corporation can be cited.

[0175] The sample was positioned on an X-ray diffraction apparatus with the long axis (orientation axis) of the liquid crystal compound LC aligned parallel to the incident X-rays. The azimuth angle at this point ( Set it to 0°.

[0176] The orientation axis direction is determined as follows.

[0177] Perform in-plane XRD (2θχ / (Scanning) to observe the periodic structure along the orientation axis. This is achieved by calibrating the observed peaks at a 0.5° scale. The direction of the orientation axis is defined as the direction orthogonal to the orientation within the substrate plane where the peak intensity is maximized.

[0178] For azimuth ( In-plane XRD (2θχ / ) was performed in the range of 0° to 90°, with a scale of 0.5°. (Scan), by performing a scan on the observed peak values. Scan to determine the orientation of the substrate plane where the peak intensity is greatest.

[0179] Perform in-plane XRD (2θχ / ) in the direction where the peak intensity is maximized. (Scanning), thus obtaining the XRD spectrum. The diffraction angle θ is 2θχ / (the diffraction angle of the in-plane XRD). The diffraction angle 2θχ / in the scan .

[0180] Here, in the XRD spectrum, the portion of the peak intensity that is more than 80% higher than the baseline intensity is considered the peak value. The baseline intensity is defined using a well-known method.

[0181] Additionally, peak intensity is measured in cps (counts per second).

[0182] In addition, peak intensity is the difference between baseline intensity and peak intensity.

[0183] In the radio wave control element 10 of the present invention, when the liquid crystal composition layer 20 is in a state below 40°C, the peak value of the XRD spectrum of the liquid crystal composition layer 20 measured in this way preferably exists in the range of diffraction angle below 15°.

[0184] As described above, peaks within a diffraction angle range of 15° or less indicate the presence of higher-order phases with periodic structures, such as crystalline and smectic phases. The peaks are preferably located within a diffraction angle range of 1° to 15°, more preferably within a diffraction angle range of 1.5° to 15°, and even more preferably within a diffraction angle range of 1.8° to 15°.

[0185] Here, after applying a voltage to the liquid crystal composition layer 20 to orient the liquid crystal compound LC, and then cooling it to room temperature (phase transition temperature) and solidifying it, the amount and state of higher-order phases with periodic structures, such as crystalline phases and smectic phases, existing in the liquid crystal composition layer 20 at temperatures below 40°C, vary depending on the time it takes to return to room temperature.

[0186] Specifically, in order to properly form a higher-order phase periodic structure, improve the orientation degree of the liquid crystal composition layer 20 and increase the refractive index anisotropy (Δn), after applying a voltage to the liquid crystal composition layer 20 to orient the liquid crystal compound LC, it is necessary to rapidly cool it to room temperature.

[0187] As described above, in the radio wave control element 10 of the present invention, the temperature adjustment mechanism 30 heats and cools the liquid crystal composition layer 20, and in addition to the heating mechanism, it also has a cooling mechanism.

[0188] In the radio wave control element 10 of the present invention, the temperature adjustment mechanism 30 for adjusting the temperature of the liquid crystal composition layer 20 has a cooling mechanism (cooling function), thereby enabling rapid cooling to room temperature after the liquid crystal compound LC is oriented by applying voltage to the liquid crystal composition layer 20.

[0189] Therefore, the radio wave control element 10 of the present invention can stably improve the orientation degree (=Δn) of the liquid crystal composition layer 20 during radio wave control. According to this radio wave control element 10 of the present invention, radio waves with a frequency of 0.007 to 0.3 THz can be stably and appropriately controlled.

[0190] In this invention, from the viewpoint of further improving the degree of orientation, in the liquid crystal composition layer 20, a periodic structure corresponding to at least one peak with a diffraction angle of 15° or less is formed. The half-peak width of the peak in the scan is preferably less than 30°, more preferably 3° to 23°, and even more preferably 3° to 20°.

[0191] As we all know, The scanning results indicate the direction and extent of the distribution of the measured periodic structures. Therefore, the narrower the half-width at half-maximum (WHM) of the peak, the more the measured periodic structures exist in the same direction, i.e., the higher the orientation.

[0192] The half-peak width of the peak can be obtained by fitting the observed peak value with the Gaussian function.

[0193] Furthermore, the liquid crystal composition layer 20 only needs to have a periodic structure corresponding to at least one peak with a diffraction angle of 15° or less. The half-width at half-maximum (WHM) of the peaks in the scan should be less than 30°, but it is preferable to have a periodic structure corresponding to peaks less than 15°. The half-peak width of the peaks in the scan was less than 30°.

[0194] In this invention, the peak value A is preferably observed in the liquid crystal composition layer 20 in a direction outside the range of ±5° in a direction orthogonal to the orientation axis of the liquid crystal composition orientation direction. That is, it is preferably observed in the azimuth angle. Peak A was observed within a range of ±85°.

[0195] The orientation of the liquid crystal composition layer 20 (sample) can be confirmed by the following methods.

[0196] With the liquid crystal composition layer 20 inserted into the light source side of an optical microscope (manufactured by Nikon Corporation, ECLIPSE E600 POL), the sample was placed on the sample stage, and the absorbance of the sample was measured using a multi-channel spectrometer (manufactured by Ocean Optics, Inc., QE65000), and the degree of orientation was calculated using the following formula.

[0197] Orientation degree: S = [(Az0 / Ay0) - 1] / [(Az0 / Ay0) + 2] Az0: Absorbance of the sample for polarized light along the absorption axis Ay0: Absorbance of the sample for polarized light along the transmission axis When the sample does not absorb visible light, the orientation can be confirmed using the same method through infrared spectroscopy.

[0198] Regarding the peak value of the wavenumber of vibrations originating from the orientation axis direction of the molecule, the peak intensity of polarized light relative to the orientation axis direction is set as Az0, and the peak intensity of polarized light relative to the direction orthogonal to it is set as Ay0, and the degree of orientation can be calculated by the above formula.

[0199] In the radio wave control element 10 of the present invention, there is no limitation on the liquid crystal compound constituting the liquid crystal composition layer 20. Therefore, either low-molecular-weight liquid crystal compounds or high-molecular-weight liquid crystal compounds can be used.

[0200] "Low-molecular-weight liquid crystal compounds" refer to liquid crystal compounds that do not have repeating units in their chemical structure. "High-molecular-weight liquid crystal compounds" refer to liquid crystal compounds that have repeating units in their chemical structure.

[0201] Examples of low-molecular-weight liquid crystal compounds include those described in Japanese Patent Application Publication No. 2013-228706. Examples of high-molecular-weight liquid crystal compounds include those described in Japanese Patent Application Publication No. 2011-237513.

[0202] The liquid crystal compound is preferably a thermotropic liquid crystal, capable of displaying either a nematic phase or a smectic phase, but preferably at least a nematic phase. As described above, the temperature range for displaying the nematic phase is 40°C or higher.

[0203] To prevent polymerization, the liquid crystal compound preferably does not contain polymerizable groups. Furthermore, to prevent a decrease in voltage retention, the liquid crystal compound preferably does not contain ionic components. Moreover, from the viewpoint of maintaining a constant response speed, a lower liquid crystal viscosity is preferred; therefore, low-molecular-weight liquid crystal compounds are preferred over high-molecular-weight liquid crystal compounds.

[0204] The content of liquid crystal compound in the liquid crystal composition layer 20 is preferably 30% by mass or more, and more preferably 50% by mass or more.

[0205] In the radio wave control element 10 of the present invention, the liquid crystal composition layer 20 preferably contains a dichroic material in addition to the liquid crystal compound.

[0206] By including a dichroic material in the liquid crystal composition layer 20, the Δn of the liquid crystal composition layer 20 during radio wave control can be increased more appropriately.

[0207] In this invention, there are no particular limitations on dichroic substances.

[0208] Dichroism refers to substances that exhibit dichroism, which means that the absorbance varies depending on the polarization direction.

[0209] That is, examples of dichroic substances include visible light absorbing substances (dichroic pigments), luminescent substances (fluorescent substances, phosphorescent substances), ultraviolet light absorbing substances, infrared light absorbing substances, nonlinear optical substances, carbon nanotubes, inorganic substances (such as quantum rods), etc., and conventionally known dichroic substances (dichroic pigments) can be used.

[0210] Specifically, examples include paragraphs

[0067] to

[0071] of Japanese Patent Application Publication No. 2013-228706, paragraphs

[0008] to

[0026] of Japanese Patent Application Publication No. 2013-227532, paragraphs

[0008] to

[0015] of Japanese Patent Application Publication No. 2013-209367, paragraphs

[0045] to

[0058] of Japanese Patent Application Publication No. 2013-14883, and Japanese Patent Application Publication No. 2013-10 Paragraphs

[0012] to

[0029] of Japanese Patent Application Publication No. 9090, paragraphs

[0009] to

[0017] of Japanese Patent Application Publication No. 2013-101328, paragraphs

[0051] to

[0065] of Japanese Patent Application Publication No. 2013-37353, paragraphs

[0049] to

[0073] of Japanese Patent Application Publication No. 2012-63387, and paragraphs

[0016] to

[0018] of Japanese Patent Application Publication No. Hei 11-305036. Japanese Patent Application Publication No. 2001-133630, paragraphs

[0009] to

[0011] ; Japanese Patent Application Publication No. 2011-215337, paragraphs

[0030] to

[0169] ; Japanese Patent Application Publication No. 2010-106242, paragraphs

[0021] to

[0075] ; Japanese Patent Application Publication No. 2010-215846, paragraphs

[0011] to

[0025] ; Japanese Patent Application Publication No. 2011-048311, paragraphs

[0009] to [001 ... The compounds described in paragraphs

[017] to

[0069] , paragraphs

[0013] to

[0133] of Japanese Patent Application Publication No. 2011-213610, paragraphs

[0074] to

[0246] of Japanese Patent Application Publication No. 2011-237513, paragraphs

[0005] to

[0041] of International Publication No. 2016 / 060173, and paragraphs

[0008] to

[0062] of International Publication No. 2016 / 136561.

[0211] Furthermore, materials with liquid crystal properties are preferred for dichroic materials.

[0212] As a dichroic substance, a dichroic azo dye compound is preferred.

[0213] Dichroic azo dye compounds are azo dye compounds whose absorbance varies depending on the direction. Dichroic azo dye compounds may or may not exhibit liquid crystal properties. When dichroic azo dye compounds exhibit liquid crystal properties, they can exhibit either nematic or smectic properties.

[0214] The content of dichroic material in the liquid crystal composition layer 20 is not limited, but is preferably 30% by mass or more.

[0215] By setting the content of dichroic material in the liquid crystal composition layer 20 to 30% by mass or more, the Δn of the liquid crystal composition layer 20 during radio wave control can be increased more appropriately.

[0216] The content of the dichroic substance in the liquid crystal composition layer 20 is more preferably 40% by mass or more, and even more preferably 50% by mass or more. When the dichroic substance exhibits liquid crystal properties, liquid crystal compounds other than the dichroic substance may not be included, and Δn can be increased by the dichroic substance; therefore, the content is more preferably 80% by mass or more.

[0217] The radio wave control element of the present invention has been described in detail above. However, the present invention is not limited to the above examples. Various improvements and modifications can be made without departing from the spirit of the present invention.

[0218] For example, Figure 1 The radio wave control element 10 of the present invention shown holds the liquid crystal composition layer 20 by a support 16 and a support 24, and a microstructure 14 (second electrode) and a first electrode layer 26 are provided on the side of the support opposite to the liquid crystal composition layer 20, but the present invention is not limited thereto.

[0219] As an example, the radio wave control element of the present invention can be structured as follows: as described in B.Kang, et al, SID 2023DIGEST (2023) p.993, microstructures are arranged in a two-dimensional arrangement on two supports, with the microstructures facing the liquid crystal composition layer, and the liquid crystal composition layer is held between the two supports.

[0220] In this structure, a planar electrode layer can be disposed on a support instead of a microstructure. Alternatively, one microstructure (electrode) can be positioned opposite the liquid crystal composition layer, while another microstructure is disposed on the opposite side of the support relative to the liquid crystal composition layer, instead of having both microstructures (electrodes) opposite the liquid crystal composition layer.

[0221] Example The present invention will now be described in further detail based on embodiments.

[0222] The materials, amounts, proportions, processing contents, and processing steps shown in the following embodiments can be appropriately modified without departing from the spirit of the invention. Therefore, the scope of the invention should not be interpreted as limited by the embodiments shown below.

[0223] [Preparation of Liquid Crystal Compositions] <Liquid Crystal Compounds> The following compound 1 was prepared as a liquid crystal compound.

[0224] Compound 1 [Chemical Formula 1] <Dichromatic substances> As dichroic substances, the following compounds 2-1 and 2-2 were prepared.

[0225] Compound 2-1 [Chemical Formula 2] Compound 2-2 [Chemical Formula 3] The above-mentioned compound 1, compound 2-1 and compound 2-2 and liquid crystal compound A (manufactured by DIC Corporation, RDP-A3123) were mixed to form the composition shown in Table 1 below, thereby preparing liquid crystal compositions corresponding to Examples 1 to 5 and Comparative Example 1.

[0226] <Determination of Solid-Liquid Crystal Phase Transition Temperature> The prepared liquid crystal composition was placed on a hot stage. The liquid crystal composition on the hot stage was observed using a polarizing microscope.

[0227] After heating the liquid crystal composition to a temperature that becomes a liquid crystal phase, the temperature at which it transforms from the liquid crystal phase into crystals was observed while cooling it down (this was set as the solid-liquid crystal phase transition temperature).

[0228] As a result, the solid-liquid phase transition temperatures of the liquid crystal compositions corresponding to Examples 1-5 were all above 40°C, while the solid-liquid phase transition temperature of the liquid crystal composition corresponding to Comparative Example 1 (compound A was 100% by mass) was below 40°C. The results are also recorded in Table 1.

[0229] [Fabrication of Liquid Crystal Composite Layer] A polyimide resin (manufactured by Hitachi Chemical Co., Ltd., LX-1400) with a thickness of about 30 nm was coated on a 3 cm square quartz glass substrate as an alignment film, and a friction treatment was performed (rotation speed 1000 rpm, moving speed 20 mm / s, 1 reciprocating motion).

[0230] On this alignment film, a solution of liquid crystal composition dissolved in chloroform solvent with a solid component concentration of 1% by mass was cast, and a sample with a film thickness of 90 nm was obtained by spin coating.

[0231] After heating to above the nematic phase transition temperature to achieve the same temperature process as in actual use in radio wave control elements, forming the nematic phase oriented in the liquid crystal composition, the mixture is cooled to room temperature, thereby obtaining liquid crystal composition layers oriented to correspond to Examples 1-5 and Comparative Example 1 (see Table 1).

[0232] <Determination of X-ray Diffraction> The prepared liquid crystal composition layer was measured by X-ray diffraction (XRD) using the method described above.

[0233] In XRD spectra, samples with peaks observed below 15° are designated as A, and samples without peaks observed below 15° are designated as B.

[0234] <Determination of Orientation> The orientation degree of the prepared liquid crystal composition layer was measured using the method described above.

[0235] Samples with an orientation degree higher than 0.85 are designated as A, and samples with an orientation degree lower than 0.85 are designated as B.

[0236] <Determination of Refractive Index Anisotropy (Δn)> Regarding the liquid crystal composition layer produced, the refractive index anisotropy Δn at 30 GHz was measured using the method described in Applied Optics, Vol. 44, No. 7, p1150 (2005).

[0237] Regarding the refractive index anisotropy Δn, a liquid crystal composition was filled and aligned within a variable short-circuit waveguide. An electromagnetic wave of 30 GHz was input into the waveguide, and the amplitude ratio of the reflected wave to the incident wave was measured. Measurements were performed by varying the orientation of the static magnetic field and the length of the short-circuit, and the refractive indices ne and no were determined. For the refractive index anisotropy (Δn@30 GHz), calculations were performed based on ne-no.

[0238] Samples with Δn greater than or equal to 0.40 are designated as A, samples with Δn less than 0.40 but greater than or equal to 0.25 are designated as B, samples with Δn less than 0.25 but greater than or equal to 0.20 are designated as C, and samples with Δn less than 0.20 are designated as D.

[0239] The results are shown in Table 1 below.

[0240] [Fabrication of radio wave control components] Using the liquid crystal composition layer, the radio wave control elements of Examples 1 to 5 and Comparative Example 1 were fabricated by the method described in B.Kang, et al, SID 2023 DIGEST (2023) p.993.

[0241] The radio wave control element has a metasurface structure consisting of microstructures arranged in two-dimensionally at equal intervals in the orthogonal XY directions.

[0242] Furthermore, the radio wave control element has a structure in which the microstructures are held toward the liquid crystal composition layer by two supports with microstructures formed on one side. In addition, the supports are made of glass plates.

[0243] Furthermore, each of the microstructures constituting the electrode pair was connected to an AC power source.

[0244] In this radio wave control element, a temperature regulation mechanism is installed in integral contact with the surface of a support. The temperature regulation mechanism uses a Peltier element.

[0245] <Evaluation of Orientation Maintenance> The manufactured radio wave control element is heated to a temperature above the liquid crystal phase transition temperature of the liquid crystal composition layer using a temperature regulation mechanism.

[0246] Next, while maintaining the temperature, an equal amount of bias voltage is applied to each microstructure to change the orientation state of the liquid crystal compound.

[0247] Then, the liquid crystal composition was cooled to room temperature (20°C) while the driving voltage was applied, the power supply from the power source was stopped, and the voltage applied to the liquid crystal composition layer was stopped.

[0248] At this time, before the bias voltage was applied and heated to a temperature above the liquid crystal phase transition temperature, during the applied state and after cooling and stopping the application, the reflected radio waves from the radio wave control element were measured using the method described in B.Kang, et al, SID 2023 DIGEST (2023) p.994, with the help of a horn antenna connected to a network analyzer.

[0249] Based on the measured reflected electromagnetic waves, the sample whose reflected electromagnetic wave characteristics are maintained after cooling and stopping the application of voltage, i.e., the sample that maintains the orientation state of the liquid crystal compound, is designated as A, and the sample whose reflected electromagnetic wave characteristics are relaxed after not maintaining the application of voltage, i.e., the orientation state of the liquid crystal compound, is designated as B.

[0250] The results are shown in Table 1 below.

[0251] [Table 1]

[0252] As shown in Table 1, the radio wave control element of the present invention, which has a liquid crystal phase transition temperature of 40°C or higher for the liquid crystal composition layer, can maintain the orientation state of the liquid crystal compound in the liquid crystal composition layer even after the liquid crystal compound is oriented by heating and applying voltage to the liquid crystal composition layer, and then cooling and stopping the application of voltage.

[0253] That is, according to the radio wave control element of the present invention, after the liquid crystal compound is oriented by heating and applying voltage, and then cooled, the direction of travel of the radio wave can be controlled to the target direction even without applying voltage. Therefore, the radio wave control element according to the present invention can reduce the power consumption required to control the radio wave.

[0254] <Evaluation of Frequency Variableness (Tuning Ability)> The manufactured radio wave control element is heated to a temperature above the liquid crystal phase transition temperature of the liquid crystal composition layer using a temperature regulation mechanism.

[0255] Next, while maintaining the temperature, an equal amount of bias voltage is applied to each microstructure to change the orientation state of the liquid crystal compound.

[0256] Then, the liquid crystal composition was cooled to room temperature (20°C) while the driving voltage was applied, the power supply from the power source was stopped, and the voltage applied to the liquid crystal composition layer was stopped.

[0257] This operation was performed by varying the bias voltage between 0 and 25V, and the frequency variability (tunability) of each radio wave control element was measured using a horn antenna connected to a network analyzer, according to the method described in B. Kang, et al, SID 2023 DIGEST (2023) p.994.

[0258] As a result, the frequency variability of the radio wave control element in Embodiment 5 was the highest, followed by the radio wave control element in Embodiment 4, then Embodiments 2 and 3, and finally Embodiment 1 was the lowest. The difference between Embodiment 2 and Embodiment 3 was small, but Embodiment 3 was higher.

[0259] The results show that the larger Δn is, the higher the frequency variability of the radio wave control element, meaning a wider range of achievable characteristic variations. Higher frequency variability also means a wider frequency range for the radio waves controlled by the element. Furthermore, higher frequency variability allows for a wider range of movable phases, thus expanding the range of reflection angles.

[0260] Industrial availability It can be preferably used in active antennas, beam steering devices, etc., in radio wave communication, etc.

[0261] Symbol Explanation 10 - Radio wave control element, 12 - Metasurface structure, 14 - Microstructure, 16, 24 - Support, 20 - Liquid crystal composition layer, 26 - First electrode layer, 28 - Power supply, 30 - Temperature regulation mechanism, LC - Liquid crystal compound, ANT - Antenna, AR1, AR2 - Region, BL - Building, RD - Radio wave reflection device, RW - Radio wave.

Claims

1. A radio wave control element, comprising, in sequence, a first electrode, a liquid crystal composition layer, and a second electrode, wherein, At least one of the first electrode and the second electrode has a metasurface structure formed by arranging a plurality of microstructures. The radio wave control element also has a temperature regulation mechanism for heating and cooling the liquid crystal composition layer. The solid-liquid phase transition temperature of the liquid crystal composition layer is above 40°C.

2. The radio wave control element according to claim 1, wherein, In X-ray diffraction spectra measured at temperatures below 40°C, The liquid crystal composition layer is capable of having a peak value in the range of diffraction angles below 15°.

3. The radio wave control element according to claim 1 or 2, wherein, The liquid crystal composition layer contains a dichroic substance.

4. The radio wave control element according to claim 3, wherein, The content of the dichroic substance is 30% or more by mass relative to the total mass of the liquid crystal composition layer.

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