Radio wave control element

Abstract

Provided is a radio wave control element capable of suppressing the generation of excess noise light in a visible light region and an infrared light region. A radio wave control element having a first electrode, a liquid crystal composition layer, and a second electrode in this order, the thickness of the liquid crystal composition layer being 4 [mu] m or more, and the cumulative absorbance (Q) represented by formula (1) in the wavelength range of 350-1000 nm in the absorption spectrum of a chloroform solution of the liquid crystal composition constituting the liquid crystal composition layer being 10000 L * g <-1 > * cm <-1 > or more. .

Description

Technical Field

[0001] This invention relates to an electromagnetic wave control element. Background Technology

[0002] High-frequency radio waves (millimeter waves, terahertz waves) required for high-capacity wireless communication have high linearity. Therefore, radio wave control elements are needed to bend the direction of radio wave propagation into arbitrary directions.

[0003] However, for example, the reflection direction of radio waves by a typical reflector is constant, and the reflection direction is a normal reflection with the incident angle and the exit angle being equal. Therefore, the range of changing the direction of radio wave travel is greatly limited, and there is a problem that it is difficult to transmit radio waves to the desired location.

[0004] In contrast, an electromagnetic wave control element is proposed, which is configured as a structure in which a liquid crystal layer is disposed between a metasurface structure made of conductors and conductors (electrodes). By changing the voltage applied between the two conductors, the refractive index of the liquid crystal layer is changed, thereby changing the directivity of the electromagnetic wave.

[0005] Patent Document 1 discloses a wave control element that uses a liquid crystal medium, and the liquid crystal medium is a specified multicolor compound.

[0006] Previous technical documents Patent documents Patent Document 1: Japanese Patent No. 7101619 Summary of the Invention

[0007] The technical problem to be solved by the invention However, the radio wave control element is conceived for use near sensors that detect visible light and / or infrared (IR), such as image sensors for image recognition and temperature sensors. It is known that when these sensors detect (measure) visible light and infrared (IR), if reflected, scattered, or diffracted visible light and / or infrared (IR) is incident through the conductor of the radio wave control element, it becomes noise, contributing to a decrease in detection accuracy (measurement accuracy).

[0008] In view of the above, the objective of the present invention is to provide an electromagnetic wave control element capable of suppressing the generation of excess noise light in the visible light region and the infrared light region.

[0009] means for solving technical problems In order to solve the above-mentioned problems, the inventors conducted in-depth research and discovered that the following structure can solve the problems.

[0010] [1] An electromagnetic wave control element, comprising, in sequence, a first electrode, a liquid crystal composition layer, and a second electrode, wherein, The thickness of the liquid crystal composition layer is 4 μm or more. The cumulative absorbance Q of the chloroform solution of the liquid crystal composition constituting the liquid crystal composition layer, expressed by formula (1), in the wavelength range of 350–1000 nm in the absorption spectrum is 10000 L·g. -1 ·cm -1 above.

[0011] [Formula 1] In equation (1), Q represents the cumulative absorbance (L·g). -1 ·cm -1 D represents the mass concentration of the liquid crystal composition in the chloroform solution (g·L). -1 L represents the optical path length (cm) of the cuvette used in the absorption spectrum determination, and Abs(λ) represents the absorbance at wavelength λ (nm).

[0012] [2] According to the radio wave control element described in [1], wherein, The liquid crystal composition layer comprises a liquid crystal compound and a dichroic pigment.

[0013] [3] According to the radio wave control element described in [1] or [2], wherein, At least one of the first electrode and the second electrode is composed of a plurality of microstructures arranged together.

[0014] Invention Effects According to the present invention, an electromagnetic wave control element capable of suppressing the generation of excess noise light in the visible light region and the infrared light region can be provided. Attached Figure Description

[0015] Figure 1 This is a diagram illustrating an example of the use of a radio wave control element.

[0016] Figure 2 This is a diagram illustrating an example of a metasurface structure used in radio wave control elements.

[0017] Figure 3 This diagram illustrates the mechanism by which the emission direction of radio waves is altered in radio wave control elements.

[0018] Figure 4 This is a diagram that conceptually represents an example of a radio wave control element.

[0019] Figure 5 This is a diagram that conceptually represents an example of a liquid crystal alignment pattern in a radio wave control element.

[0020] Figure 6 It is a graph showing the relationship between the applied voltage and the amount of phase delay of the radio wave.

[0021] Figure 7 This is a diagram that conceptually represents another example of a radio wave control element.

[0022] Figure 8 This is a diagram that conceptually represents another example of a radio wave control element. Detailed Implementation

[0023] The present invention will now be described in detail.

[0024] The following description of the constituent elements is based on a representative embodiment of the present invention, but the present invention is not limited to this embodiment.

[0025] In addition, in this specification, the numerical range indicated by “~” represents the range including the values ​​recorded before and after “~” as the lower and upper limits.

[0026] Furthermore, in this specification, "parallel" and "orthogonal" refer to the range of parallel ±5° and the range of orthogonal ±5°, respectively, rather than representing parallel and orthogonal in a strict sense.

[0027] Furthermore, in this specification, each component may be described using a single equivalent substance or in combination of two or more substances. In cases where two or more substances are used in combination for each component, unless otherwise specified, the content of that component refers to the total content of the combined substances.

[0028] Unless otherwise specified, the bonding direction of the divalent groups (e.g., -CO-O-, etc.) described in this specification is not limited. For example, in the case where Y is -CO-O- in a compound represented by the formula "XYZ", the compound can be either "XO-CO-Z" or "X-CO-OZ".

[0029] [Radio wave control components] The radio wave control element of the present invention sequentially comprises a first electrode, a liquid crystal composition layer, and a second electrode, wherein, The thickness of the liquid crystal composition layer is 4 μm or more. The cumulative absorbance Q of the chloroform solution of the liquid crystal composition constituting the liquid crystal composition layer, expressed by formula (1), in the wavelength range of 350–1000 nm in the absorption spectrum is 10000 L·g. -1 ·cm -1 above.

[0030] The radio wave control element of the present invention operates on radio waves (electromagnetic waves). Examples of radio waves include those with frequencies of 1 GHz to 1000 GHz and wavelengths of 300 μm to 30 cm. Radio waves in this frequency band are also referred to as high-frequency radio waves (centimeter waves, millimeter waves, terahertz waves), which are capable of high-capacity wireless communication and have high linearity.

[0031] In the radio wave control element of the present invention, by applying a voltage between the first electrode and the second electrode, the orientation state of the liquid crystal compound contained in the liquid crystal composition layer is controlled, and the refractive index anisotropy of the liquid crystal composition layer is adjusted, thereby enabling the adjustment of the propagation direction of the radio wave.

[0032] The following description uses accompanying drawings to illustrate specific examples of radio wave control elements.

[0033] exist Figure 1 The radio wave reflecting device 2 shown uses the radio wave control element 10, which is based on the technology of this invention. The radio wave reflecting device 2 is capable of reflecting radio waves RW, which have high directivity, radiated from the antenna ANT located behind the building BL, toward the area AR1 in front of the building BL, which is shadowed when viewed from the antenna ANT.

[0034] Furthermore, the radio wave reflecting device 2 can change the reflection direction of the radio wave RW in different directions in multiple regions AR1 and AR2. For example, if users utilizing wireless communication are mostly located in region AR1 during the daytime and mostly in region AR2 during the nighttime, the areas where users are concentrated sometimes change according to the time of day. In this case, the radio wave reflecting device 2 can change the area supplying the radio wave RW by changing the reflection direction of the radio wave RW according to the time of day.

[0035] like Figure 2 As shown, the radio wave control element 10 is a reflective radio wave control element having a metasurface structure 12 and reflecting the travel direction of the radio wave RW in the desired direction.

[0036] The metasurface structure 12 is a structure utilizing metamaterials. Metamaterials are artificial materials that exhibit properties not found in natural materials, such as a negative refractive index for electromagnetic waves. The electromagnetic wave control element 10 is a structure formed by arranging multiple unit cells UC in a two-dimensional manner. The two-dimensional plane formed by the arrangement of multiple unit cells UC becomes the reflecting surface of the electromagnetic wave RW. Each unit cell UC contains a microstructure 14 as a metamaterial, which constitutes the smallest unit on the reflecting surface capable of dynamically changing the phase of the electromagnetic wave RW. As an example, the microstructure 14 is made of metal. The microstructure 14 is on the order of the wavelength of the incident electromagnetic wave RW and functions as a resonator that resonates through interaction with the incident electromagnetic wave RW. Electrically, the microstructure 14 can be considered, for example, equivalent to a resonant circuit in which an alternating current resonates by connecting a coil and a capacitor in series. Through the resonance of the microstructure 14, the phase of the incident electromagnetic wave RW changes. Furthermore, by dynamically changing the resonance conditions of the microstructure 14 through various methods, the phase delay of the radio wave RW can also be controlled.

[0037] The radio wave control element 10 primarily operates on radio waves with frequencies ranging from 1 GHz to 1000 GHz (1 THz). Therefore, in the radio wave control element 10, the metasurface structure 12 is configured to operate on radio waves with frequencies ranging from 1 GHz to 1000 GHz. For example, the wavelength of radio waves with frequencies ranging from 1 GHz to 1000 GHz is 300 μm to 30 cm, and the size of the microstructure 14 constituting the metasurface structure 12 is approximately half the wavelength. By setting the size of the microstructure 14 to be below the wavelength of the radio wave RW, the microstructure 14 resonates through the transmitted radio wave RW, functioning as a phase modulation element that modulates the phase of the radio wave RW.

[0038] exist Figure 3 In the example shown by the incident direction IN and the exit direction OUT, the overall travel direction of the radio wave RW can be considered as the normal direction relative to the straight line connecting the wavefronts of the multiple radio waves RW. Furthermore, consider the case in the radio wave control element 10 where, for example, the phase delay of the radio wave RW incident on and reflected to each of the multiple one-dimensionally arranged unit cells UC gradually increases from the right-hand unit cell UC towards the left-hand unit cell UC. In this way, even when the straight line connecting the wavefronts of the individual incident radio waves RW is parallel to the reflecting surface, the straight line connecting the wavefronts of the individual radio waves RW reflected in each unit cell UC will be tilted relative to the reflecting surface. That is, the travel direction of the radio wave RW emitted from the reflecting surface, i.e., the exit direction OUT, only changes by an angle θ relative to the incident direction IN of the radio wave RW. Thus, by controlling the phase delay for each unit cell UC, the travel direction of the radio wave RW can be controlled.

[0039] As a result, in a conventional reflector, the direction of travel of the radio wave RW can only be changed to the direction of positive reflection, while the radio wave reflecting device 2, by using the metasurface structure 12, can change the direction of travel of the radio wave RW to a direction other than positive reflection. Furthermore, by dynamically changing the phase retardation in each unit cell UC, the direction of travel of the radio wave RW can be dynamically changed.

[0040] As an example, such as Figure 4 As conceptually shown, the radio wave control element 10 uses a liquid crystal composition layer 20 as a means to dynamically change the resonance conditions of the microstructures 14 of the metasurface structure 12. The radio wave control element 10, from bottom to top, includes a second electrode 26, a liquid crystal composition layer 20, and a metasurface structure 12. The liquid crystal composition layer 20 is disposed on a support 24. Furthermore, the second electrode 26 is configured to cover the entire surface of the support 24 opposite to the liquid crystal composition layer 20. The metasurface structure 12 is disposed on the surface of the support 16 opposite to the liquid crystal composition layer 20.

[0041] Furthermore, in Figure 4 In the example shown, the liquid crystal composition layer 20 contains a crystalline dichroic pigment LC as a liquid crystal compound. Because the liquid crystal composition layer 20 contains the crystalline dichroic pigment LC, the cumulative absorbance Q, expressed by formula (1) described later, in the absorption spectrum of the chloroform solution constituting the liquid crystal composition layer within the wavelength range of 350–1000 nm is 10000 L·g. -1 ·cm -1 That's all. This point will be discussed in more detail later.

[0042] Each unit cell UC comprises a microstructure 14, a liquid crystal composition layer 20, and a second electrode 26. The microstructure 14 is provided individually for each unit cell UC. The support 16, liquid crystal composition layer 20, support 24, and second electrode 26 are not independent structures for each unit cell UC, but are integrally formed with regions corresponding to multiple unit cells UC.

[0043] In the radio wave control element 10, the second electrode 26 and the support 24, and the liquid crystal composition layer 20 and the support 16 are bonded together using an adhesive as needed. There are no limitations on the bonding method; various methods using OCA (Optical Clear Adhesive) that can transmit the radio waves targeted by the radio wave control element 10, or known methods that can transmit the radio waves targeted by the radio wave control element 10, can be used.

[0044] As an example, the microstructure 14 is formed of a conductive material and also serves as an electrode that forms an electrode pair with the second electrode 26.

[0045] Furthermore, a power supply 28 for applying a voltage between the microstructure 14 and the second electrode 26 is connected to each microstructure 14. Therefore, the magnitude of the voltage applied to each unit cell UC can be controlled. The second electrode 26 is a common electrode shared by all unit cells UC, while each microstructure 14 of each unit cell UC functions as an individual electrode. The second electrode 26, functioning as a common electrode, is an example of the "second electrode" according to the technology of this invention, while the individual electrode also used by the microstructure 14 is an example of the "first electrode." The microstructure 14 as the first electrode and the second electrode 26 as the second electrode are an example of an "electrode pair for applying voltage."

[0046] There is no particular limitation on the voltage application mechanism that applies voltage to each microstructure 14, for example, TFT (thin film transistor).

[0047] The radio wave control element 10 is a reflective type, and the second electrode 26 also serves as a reflective layer for the reflected radio wave RW.

[0048] The orientation state (hereinafter also referred to as orientation pattern) of the liquid crystal composition layer 20 is changed by applying a voltage. Hereinafter, an example of driving (changing) the orientation state of the liquid crystal dichroic pigment LC by applying a voltage is shown. The arrangement direction of the microstructures 14 of each unit cell UC is a direction orthogonal to the thickness direction (Z direction in the figure) of the liquid crystal composition layer 20 (X direction or Y direction in the figure). Here, the microstructures 14 and the second electrode 26 are disposed on opposite sides of the thickness direction of the liquid crystal composition layer 20. By supplying power from the power source 28, a voltage is applied between the microstructures 14 of each unit cell UC and the second electrode 26. By applying the voltage, an electric field is generated in the thickness direction of the liquid crystal composition layer 20, thereby changing the orientation state of the liquid crystal dichroic pigment LC of each unit cell UC. Furthermore, by adjusting the voltage applied to each unit cell UC, the orientation state of the liquid crystal dichroic pigment LC of each unit cell UC can be adjusted.

[0049] like Figure 5 As shown, the cross-section of the liquid crystal dichroic pigment LC is approximately elliptical with a major axis and a minor axis. As an example, when no voltage is applied between the microstructure 14, which functions as an electrode pair, and the second electrode 26, no electric field is generated in the liquid crystal composition layer 20. In this state, as... Figure 5As conceptually shown in the preceding paragraph, the liquid crystal dichroic pigment LC is oriented with its long axis along the thickness direction of the liquid crystal composition layer 20. In the following description, this orientation is also referred to as "vertical orientation".

[0050] If a voltage is applied between the microstructure 14 and the second electrode 26 from this state, an electric field is generated in the liquid crystal composition layer 20, thereby changing the orientation state of the crystalline dichroic pigment LC. Specifically, as... Figure 5 As conceptually shown in the lower paragraph, the orientation state of the crystalline dichroic pigment LC in the region corresponding to the microstructure 14 changes according to the magnitude of the applied voltage, tilting relative to the thickness direction of the liquid crystal composition layer 20. Figure 5 In the example shown in the lower paragraph, the tilt angle of the liquid crystal dichroic pigment LC is maximized. In the maximized tilt angle state, the liquid crystal dichroic pigment LC is oriented with its long axis perpendicular to the thickness direction of the liquid crystal composition layer 20. In the following description, the orientation state with the tilt angle maximized is also referred to as "horizontal orientation".

[0051] The greater the tilt of the crystalline dichroic pigment LC, that is, the closer the long axis of the crystalline dichroic pigment LC is to the main surface direction of the liquid crystal composition layer 20 (in Figure 5 The greater the angle (X-direction or Y-direction) of the liquid crystal composition layer 20, the higher its refractive index. Conversely, the smaller the tilt of the crystalline dichroic pigment LC, i.e., the closer the long axis of the crystalline dichroic pigment LC is to the thickness direction of the liquid crystal composition layer 20 (Z-direction in the figure), the smaller the refractive index of the liquid crystal composition layer 20. Through such changes in the refractive index of the liquid crystal composition layer 20 in each unit cell UC, the resonance condition of the microstructure 14 changes, and the phase retardation of the incident electromagnetic wave RW changes. In this example, Figure 5 The phase delay of the lower segment of the unit cell UC is compared to Figure 5 The upper segment of the unit cell has a large UC.

[0052] That is, in the liquid crystal composition layer 20 surrounding the microstructure 14 located in each unit cell UC, if the orientation state of the crystalline dichroic pigment LC changes, the refractive index of the liquid crystal composition layer 20 for transmitting the electromagnetic wave RW through each unit cell UC changes. Furthermore, since the refractive index is positively correlated with the dielectric constant, the resonant condition of the microstructure 14, which functions as a resonator, changes due to the change in the refractive index of the liquid crystal composition layer 20. This change in the resonant condition of the microstructure 14 manifests as a change in the phase retardation of the electromagnetic wave RW. Therefore, by changing the refractive index of the liquid crystal composition layer 20, the phase retardation of the electromagnetic wave RW can be changed. Moreover, the change in the refractive index of the liquid crystal composition layer 20 itself also causes a change in the phase retardation of the electromagnetic wave RW. The refractive index of the liquid crystal composition layer 20 in each unit cell UC changes according to the voltage V applied to each unit cell UC; therefore, as an example, the relationship between voltage V and the phase retardation of the electromagnetic wave RW is as follows: Figure 6 As shown.

[0053] The method of driving the orientation state of a crystalline dichroic pigment LC by applying a voltage is not limited to the methods described above, and various methods can be used. For example, ECB (Electrically Controlled Birefringence), VA (Vertical Aligned), IPS (In-Plane Switching), TN (Twisted Nematic), and PASCAL methods can be used. Furthermore, methods characterized by high-speed response can include polymer-dispersed liquid crystal methods, phase-separated liquid crystal methods, strong dielectric liquid crystal methods, anti-strong dielectric liquid crystal methods, and blue phase liquid crystal methods.

[0054] like Figure 3As shown, if an electromagnetic wave RW is incident on the electromagnetic wave control element 10 from the microstructure 14 side, the electromagnetic wave RW sequentially passes through the microstructure 14 and the liquid crystal composition layer 20. Furthermore, the electromagnetic wave RW is reflected at the second electrode 26, which also acts as a reflective layer, and again sequentially passes through the liquid crystal composition layer 20 and the microstructure 14 before exiting the electromagnetic wave control element 10. The electromagnetic wave RW is reflected through this incident / exit path. In the incident / exit path, for the electromagnetic wave RW that passes through each unit cell UC, phase modulation is generated due to the resonance of the microstructure 14 and phase modulation is generated due to the transmission of the liquid crystal composition layer 20. More specifically, in each unit cell UC, the resonance condition of the microstructure 14 is determined according to the refractive index of the liquid crystal composition layer 20, and phase modulation of the electromagnetic wave RW is generated through resonance corresponding to this condition. Furthermore, phase modulation of the electromagnetic wave RW corresponding to the magnitude of the refractive index of the liquid crystal composition layer 20 is also generated.

[0055] according to Figure 6 The relationship shown is that the applied voltage V controls the phase delay of the radio wave RW by a certain amount per unit cell UC, thereby controlling the reflection direction of the radio wave RW reflected in the radio wave control element 10.

[0056] Also Figure 3 As shown, in a conventional reflector, the direction of travel of the radio wave RW can only be changed to the direction of positive reflection. However, in the radio wave control element 10, by using the metasurface structure 12, the direction of travel of the radio wave RW can be changed to a direction other than positive reflection. Furthermore, by dynamically changing the phase delay in each unit cell UC, the direction of travel of the radio wave RW can be dynamically changed.

[0057] Furthermore, the control of the direction of travel of the radio wave RW emitted from the radio wave control element 10, in addition to, Figure 3 As shown in the example, in addition to controlling the reflected radio wave RW to travel in one direction as a whole, various other examples are considered. For example, the radio wave RW emitted from the radio wave control element 10 can be focused toward a certain focal point or diverge in the opposite direction. The direction of travel of the emitted radio wave RW can be controlled by adjusting the voltage applied to each unit cell UC to adjust the amount of phase delay of the radio wave RW in each unit cell UC.

[0058] For example, consider the following situation: Figure 3As shown, in the case of multiple unit cells UC arranged in one direction, the phase retardation of the central unit cell UC is increased, while the phase retardation is decreased towards both sides. In this case, if the wavefronts of the radio waves RW transmitted through each unit cell UC form a V-shape, the emitted radio waves RW can be focused. Conversely, consider the case where the phase retardation of the central unit cell UC is decreased, while the phase retardation is increased towards both sides. In this case, if the wavefronts of the radio waves RW transmitted through each unit cell UC form a mountain shape (inverted V-shape), the emitted radio waves RW can be diverged. The degree of focusing and divergence can also be adjusted by controlling the phase retardation of the radio waves RW transmitted through each unit cell UC by adjusting the magnitude of the applied voltage.

[0059] Similar to known metasurface structures, the metasurface structure 12 is formed by arranging microstructures 14 as metamaterials in two dimensions on a support 16. In the metasurface structure 12 illustrated in the figure, as... Figure 2 As shown, the microstructures 14 are arranged in two dimensions at equal intervals in the X and Y directions, which are orthogonal to each other. Furthermore, in this metasurface structure 12, for example, all the microstructures 14 are identical.

[0060] The support 16 is not limited; any known sheet material can be used as long as it can support the microstructure 14 and transmit radio waves RW with a frequency of 1 to 1000 GHz targeted by the radio wave control element 10. Examples of supports 16 include metal substrates with oxide insulating layers such as silicon substrates containing silicon oxide, supports made of oxides such as silicon oxide, supports made of semiconductors such as germanium and chalcogenide glass, polyacrylic resin films such as polymethyl methacrylate, cellulose resin films such as cellulose triacetate, cyclic olefin polymer films (e.g., those manufactured under the trade name "ARTON" by JSR Corporation, and those manufactured under the trade name "ZEONOR" by Zeon Corporation), polyethylene terephthalate (PET) films, polycarbonate films, and polyvinyl chloride films, as well as glass plates.

[0061] There are no restrictions on the thickness of the support 16, as long as it can support the microstructure 14 and achieve sufficient transmittance for radio waves RW with frequencies of 1 to 1000 GHz, and thus achieve sufficient strength depending on the application of the radio wave control element 10. The thickness of the support 16 can be appropriately set according to the forming material of the support 16 to meet these conditions.

[0062] Furthermore, in the radio wave control element 10 according to the technology of this invention, the support 16 is not a necessary structure for the metasurface structure 12, and the support 16 may be omitted. For example, if possible, the metasurface structure 12 can be formed by directly arranging microstructures 14 on the surface of the liquid crystal composition layer 20. Or, as... Figure 7 Like the radio wave control element 10b shown, the metasurface structure 12 (microstructure 14) can also be formed on the side of the liquid crystal composition layer 20 of the support 16.

[0063] As described above, the metasurface structure 12 is a structure formed by separating and arranging the microstructures 14, which are metamaterials, in a two-dimensional plane. More specifically, it is basically composed of the arrangement of unit cells UC, which are units of a microstructure 14 and the space surrounding the microstructure 14.

[0064] In the radio wave control element 10 according to the technology of the present invention, the morphology of the metasurface structure is substantially the same as that of known metasurface structures. Therefore, various known metasurface structures can be utilized in the radio wave control element 10 according to the technology of the present invention.

[0065] That is, in the technology of the present invention, there are no limitations on the shape and forming material of the microstructure 14, the arrangement of the microstructure 14, and the spacing of the microstructure 14. Furthermore, the metasurface structure 12 can be designed using known methods based on the wavelength of the radio wave RW controlled by the radio wave control element 10 and the target reflection characteristics (e.g., the range of controllable reflection directions). For example, the amplitude and phase of the radio wave RW reflected by the microstructure 14 can be calculated using commercially available simulation software, and the arrangement of the microstructure 14 can be set in a manner that becomes the distribution of the target phase modulation amount. Regarding phase modulation, in the case of using the liquid crystal composition layer 20 as in this example, it is generated based on the refractive index and the interaction between the refractive index and the microstructure 14, and the phase modulation amount is determined based on the resonance characteristics of the microstructure 14, which change according to the refractive index.

[0066] The radio wave control element 10 according to the present invention controls radio waves RW with frequencies ranging from 1 to 1000 GHz. Therefore, in the metasurface structure 12, a microstructure 14 is selected to impart a desired phase difference to the radio waves RW at that frequency, and the arrangement of the microstructures is then determined. Specifically, when the radio waves RW with frequencies ranging from 1 to 1000 GHz are controlled, the wavelength range of the radio waves RW is approximately 300 μm to 30 cm; therefore, the size of the microstructure 14 is also selected to be within this wavelength range.

[0067] While the number of microstructures 14 in a unit cell UC is generally one, the present invention is not limited to this. That is, in the radio wave control element involved in the present invention, a unit cell UC can have multiple microstructures 14 as needed, depending on the reflection characteristics, the size of the microstructures 14, the forming material and shape, and the size of the unit cell UC. In this case, a unit cell UC can have different microstructures 14. However, the unit cell UC is the smallest unit capable of dynamically changing the phase of the radio wave RW; therefore, even when a unit cell UC has multiple microstructures 14, the phase modulation amount is determined for each unit cell UC.

[0068] Furthermore, the material used to form the microstructure 14 is not limited, and various materials known for their use as microstructures in metasurface structures can be used. Examples of materials for forming the microstructure 14 include metals and dielectrics. In the case of metals, copper, gold, and silver are preferred examples 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 examples considering their high refractive index and ability to increase phase modulation. Additionally, as... Figure 4 As shown, when the microstructure 14 also serves as an electrode in an electrode pair with the second electrode 26, the microstructure 14 is formed of a conductor.

[0069] Similarly, the shape of the microstructure 14 is not limited, and various shapes used as microstructures in known metasurface structures can be utilized. Examples include: a cross-shaped solid where cuboids intersect; a cuboid shape; a cylindrical shape; a V-shaped solid where cuboids are connected at the ends, as shown in Japanese Patent Application Publication No. 2018-046395; a roughly H-shaped solid, such as an H-beam; and a roughly C-shaped solid, such as a C-channel. Furthermore, as shown in Japanese Patent Application Publication No. 2018-046395, the V-shaped solid and the cross-shaped solid can utilize various shapes by adjusting the angle formed by two cuboids. In addition, shapes such as those described in "Appl.Sci.2018,8(9),1689;https: / / doi.org / 10.3390 / app8091689" can also be used. Figure 5 The solid shown has a base shape, etc.

[0070] In the metasurface structure 12, the microstructures 14 can be of the same type, or multiple types of microstructures 14 can be used in combination. Furthermore, the same microstructures 14 can be arranged in the same orientation or in different orientations in the XY plane. Also, microstructures 14 with the same orientation and microstructures 14 with different orientations can coexist. However, in the radio wave control element 10 according to the technology of this invention, it is preferable to use only one type of microstructure 14, and to arrange all microstructures 14 in the same orientation.

[0071] And, as Figure 3 As shown, a preferred embodiment of the metasurface structure 12 is a two-dimensional arrangement of identical microstructures 14, all having the same structure, at equal intervals in the orthogonal X and Y directions. However, the invention is not limited to this; as described above, various microstructures can be used together, and the spacing and arrangement of the microstructures 14 can differ in the planar direction of the support 16. However, considering the controllability of the reflection direction of the electromagnetic wave RW when a voltage is applied to the liquid crystal composition layer 20, it is preferable to use identical microstructures 14 for the metasurface structure 12. Furthermore, it is more preferable that the spacing between the microstructures 14 is equal, and even more preferable that they are equally spaced in both the orthogonal X and Y directions.

[0072] The liquid crystal composition layer 20 is a layer formed by aligning a liquid crystal dichroic pigment LC in a predetermined state. As described above, the orientation state of the liquid crystal dichroic pigment LC changes when a voltage is applied.

[0073] Figure 4 In the illustrated liquid crystal composition layer 20, the crystalline dichroic pigment LC is vertically oriented when no voltage is applied. If a voltage is applied to the liquid crystal composition layer 20, the crystalline dichroic pigment LC is oriented at an angle relative to the thickness direction, depending on the voltage, and may at most become horizontally oriented. Furthermore, in the radio wave control element 10, the orientation of the crystalline dichroic pigment LC is not limited to changing from vertical to horizontal or vice versa; it can also change from an angle relative to the thickness direction to a horizontal or vertical orientation, or from a horizontal or vertical orientation to an angle relative to the thickness direction, or even change from an angle relative to the thickness direction to a state where the orientation is tilted relative to the thickness direction.

[0074] Furthermore, the liquid crystal composition layer 20 may be formed on the surface of the alignment film described later, for example, by a known method.

[0075] In the radio wave control element 10, a liquid crystal composition layer 20 is formed on a support 24. The support 24 is substantially the same as the support 16 described above.

[0076] Here, the support 24 forming the liquid crystal composition layer 20 can also use the aforementioned support 16 as the main body, and the surface of the main body on which the liquid crystal composition layer 20 is formed has an alignment film for aligning the crystalline dichroic pigment LC to a predetermined state. Various known alignment films can be used. Examples include a rubbing film made of organic compounds such as polymers, a tilted 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 based on the Langmuir-Blodgett process (LB). Furthermore, as an alignment film, a so-called photo-aligned film can also be formed by irradiating polarized or unpolarized light onto a raw material with photo-orientation properties. These alignment films can be formed using known methods corresponding to the forming material of the main body.

[0077] Alternatively, an alignment film may be formed on the support 16 supporting the microstructure 14, and a liquid crystal composition layer 20 may be formed on the alignment film.

[0078] The liquid crystal composition containing a liquid crystal compound (liquid crystal dichroic pigment LC) used to form the liquid crystal composition layer 20 will be described later.

[0079] The entire surface of the support 24 forming the liquid crystal composition layer 20, opposite to the liquid crystal composition layer 20, is covered by the second electrode 26. The second electrode 26 is an electrode that alters the orientation of the crystalline dichroic pigment LC in the liquid crystal composition layer 20, and as described above, it also functions as a reflective layer for reflecting radio waves RW with frequencies of 1 to 1000 GHz incident from the metasurface structure 12 side. Furthermore, in Figure 4 In the example shown, the second electrode 26 is configured to be disposed between the support 24 and the liquid crystal composition layer 20, but it is not limited to this configuration. Figure 7 As shown in the radio wave control element 10b, the second electrode 26 can be disposed on the surface of the support 24 on the side of the liquid crystal composition layer 20. Additionally, in Figure 7 In the example shown, the second electrode 26 is also composed of a metasurface structure with multiple microstructures. That is, Figure 7 The example shown is an example where both the first and second electrodes are composed of a metasurface structure with multiple microstructures.

[0080] The second electrode 26 is not limited; as long as it has sufficient conductivity and can reflect electromagnetic waves RW, it can be made of a sheet of various known materials.

[0081] As an example of the second electrode 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.

[0082] There is no limitation on the thickness of the second electrode 26, as long as the thickness is appropriately set according to the forming material of the second electrode 26 to reflect the electromagnetic waves to the target with the required reflectivity.

[0083] Furthermore, in Figure 4 In the example shown, the second electrode 26 is configured as a uniform sheet-like layer covering the entire main surface of the support 24, but it is not limited to this, such as... Figure 7 Like the radio wave control element 10b shown, the second electrode 26 can also be a metasurface structure composed of multiple microstructures arranged together.

[0084] As described above, the radio wave control element 10 according to the present invention is a reflective radio wave control element having a metasurface structure 12 and a liquid crystal composition layer 20. In the radio wave control element 10, by supplying power to each microstructure 14, the orientation state of the crystalline dichroic pigment LC in the corresponding region of the liquid crystal composition layer 20 is changed, forming regions with different refractive indices according to each unit cell UC, thereby reflecting the radio wave RW in the desired direction. Furthermore, by changing the power supplied to each microstructure 14, i.e., the voltage applied to the liquid crystal composition layer 20, the reflection direction of the incident radio wave RW can be switched.

[0085] In this invention, the thickness of the liquid crystal composition layer 20 in the radio wave control element 10 is 4 μm or more, and the cumulative absorbance Q, expressed by the following formula (1), in the absorption spectrum of the chloroform solution of the liquid crystal composition constituting the liquid crystal composition layer 20 within the wavelength range of 350 to 1000 nm is 10000 L·g. -1 ·cm -1 above.

[0086] [Formula 2] In equation (1), Q represents the cumulative absorbance (L·g). -1 ·cm -1 D represents the mass concentration of the liquid crystal composition in the chloroform solution (g·L). -1L represents the optical path length (cm) of the cuvette used in the absorption spectrum determination, and Abs(λ) represents the absorbance at wavelength λ (nm). In addition, the definite integral in equation (1) represents the value obtained by numerically integrating the absorbance measured at 1nm intervals within the wavelength range of 350 to 1000 nm.

[0087] As described above, the radio wave control element 10 is a component for controlling the travel direction of high-frequency radio waves from 1 to 1000 GHz. The microstructure 14 and the second electrode 26 used in the radio wave control element 10 are capable of reflecting, scattering, and diffracting visible light and / or infrared light (IR).

[0088] However, as mentioned above, the radio wave control element is envisioned for use near sensors that detect visible light and / or infrared light, such as image sensors for image recognition and temperature sensors. For example, in the case of a wireless communication device integrated with an LED lighting device, the brightness distribution of the LED can sometimes be disturbed due to reflections from the radio wave control element. In this case, it is known that when sensors such as image sensors for image recognition and temperature sensors detect (measure) visible light and infrared light, if the visible light and / or infrared light that is reflected, scattered, or diffracted is incident through the fine structure of the radio wave control element and / or the second electrode (conductor), it becomes noise, causing a decrease in detection accuracy (measurement accuracy).

[0089] In contrast, the radio wave control element 10 of the present invention has a liquid crystal composition layer 20 with a thickness of 4 μm or more, and the liquid crystal composition layer 20 has a cumulative absorbance Q of 10000 L·g in the wavelength range of 350 to 1000 nm. -1 ·cm -1 Furthermore, it exhibits high light absorption characteristics in the visible to infrared light region. The radio wave control element 10 of the present invention, by giving the liquid crystal composition layer 20, disposed near the microstructure 14 that reflects, scatters, and diffracts visible and / or infrared light, and the second electrode 26, high light absorption characteristics, can reduce the reflected, scattered, and diffracted visible and / or infrared light that becomes unwanted noise light through the microstructure 14 and the second electrode 26. Therefore, when the radio wave control element 10 is used near sensors that detect visible and / or infrared light, such as image sensors for image recognition and temperature sensors, noise from these sensors can be reduced.

[0090] In the radio wave control element 10, the reflectivity, as measured below, is preferably less than 3%, more preferably less than 1%.

[0091] Specifically, a halogen lamp (350–1100 nm light source) is used as the light source, and the light is irradiated towards the sample surface at a 45-degree angle relative to the sample surface. Figure 4In the middle, arrow I0), detects the light reflected and scattered from the surface's normal direction ( Figure 4 (See arrow I1 in the image) and measure the amount of reflected light. The measuring instrument can use the TOPCON CORPORATION SR-3 spectroradiometer. Furthermore, a standard reflector made of barium sulfate (BaSO4) is used as a reference for measuring reflectivity, and the ratio of the amount of reflected light measured with the standard reflector is taken as the reflectivity.

[0092] From the viewpoint of reducing visible light and / or infrared light that is reflected, scattered, or diffracted as excess noise light, the thickness of the liquid crystal composition layer 20 is preferably 4 μm or more, and more preferably 10 μm or more.

[0093] On the other hand, there is no upper limit to the thickness of the liquid crystal composition layer 20, as long as the thickness is appropriately set according to the forming material of the liquid crystal composition layer 20 to impart the required phase difference to the radio wave RW. The thickness of the liquid crystal composition layer 20 is preferably 200 μm or less, more preferably 150 μm or less, and even more preferably 100 μm or less. This is preferred from the viewpoint that by setting the thickness of the liquid crystal composition layer 20 to 200 μm or less, the switching of the reflection direction of the radio wave RW can be performed more quickly.

[0094] Furthermore, the refractive index anisotropy Δn of the liquid crystal composition layer 20 relative to the radio wave is not limited, but a larger value is preferred. Here, in the reflective radio wave control element 10 of this example, the refractive index anisotropy Δn of the liquid crystal composition layer 20 relative to the radio wave 100 GHz is preferably 0.35 or more. This is preferred from the viewpoint that by setting the refractive index anisotropy Δn of the liquid crystal composition layer 20 relative to the radio wave 100 GHz to 0.35 or more, the liquid crystal composition layer 20 can be made thinner, which allows for faster switching of the reflection direction of the radio wave RW.

[0095] In the radio wave control element 10 of the present invention, the cumulative absorbance Q, expressed by the above formula (1), is set to be 10000 L·g in the absorption spectrum of the chloroform solution of the liquid crystal composition constituting the liquid crystal composition layer 20 within the wavelength range of 350 to 1000 nm. -1 ·cm -1 In the above structure, the liquid crystal composition constituting the liquid crystal composition layer 20 preferably contains at least one dichroic pigment.

[0096] Hereinafter, the cumulative absorbance Q, which is a characteristic point of the present invention, will be described in detail, and then the components contained in the liquid crystal composition constituting the liquid crystal composition layer 20 (hereinafter also simply referred to as "liquid crystal composition") will be described in detail.

[0097] The cumulative absorbance Q of the chloroform solution of the liquid crystal composition in the absorption spectrum within the wavelength range of 350–1000 nm, as expressed by the above formula (1), is 10000 L·g. -1 ·cm -1 above.

[0098] The cumulative absorbance Q is an indicator of the light absorption characteristics of a liquid crystal composition in the wavelength range of 350 to 1000 nm. A high cumulative absorbance Q value indicates excellent absorption characteristics. As described above, by improving the absorption characteristics of the liquid crystal composition layer disposed near the microstructure and / or the second electrode (conductor), visible light and / or infrared light that becomes noise light due to reflection, scattering, and diffraction by the microstructure and / or the second electrode (conductor) can be reduced.

[0099] Furthermore, as another effect, it is known that the refractive index of a material is related to its light absorption characteristics. The inventors have discovered that by adjusting the cumulative absorbance Q of the liquid crystal composition within a specified range, the refractive index anisotropy for radio waves becomes very large. In particular, it has been found that by improving the absorption characteristics in the wavelength range of 350–1000 nm, the refractive index in the radio wave region can be increased, thereby increasing the refractive index anisotropy for radio waves.

[0100] From the viewpoint of reducing visible light and / or infrared light that becomes noise, the cumulative absorbance Q is preferably 12000 L·g. -1 ·cm -1 The above, more preferably 15000 L·g -1 ·cm -1 The above is further preferred to be 20000 L·g -1 ·cm -1 above.

[0101] There is no particular upper limit to the cumulative absorbance Q, but it is usually 50,000 L·g. -1 ·cm -1 The following is more typically 40,000 L·g -1 ·cm -1 The following is typically 30,000 L·g -1 ·cm -1 the following.

[0102] The cumulative absorbance Q is calculated using the above formula (1).

[0103] In the determination of cumulative absorbance Q, commercially available devices can be used, such as the UV-3100PC spectrophotometer manufactured by SHIMADZUCORPORATION. In the determination of cumulative absorbance Q, a chloroform solution containing a specified amount of the liquid crystal composition is filled into a cuvette of a specified optical path length, and the measurement is performed.

[0104] Furthermore, when measuring the cumulative absorbance Q from the liquid crystal composition layer of the radio wave control element, the radio wave control element is disassembled, the liquid crystal composition is collected from the liquid crystal composition layer, and a chloroform solution containing a specified amount of the liquid crystal composition is filled into a colorimetric cell of a specified optical path length for measurement.

[0105] <Dichroic Pigment> Dichroic pigments are substances that exhibit dichroism, which means that the absorbance varies depending on the polarization direction.

[0106] As a dichroic pigment, the optimal type of dichroic pigment is appropriately selected in a manner that satisfies the aforementioned cumulative absorbance Q range. A single dichroic pigment may be used, or two or more may be used in combination. Preferably, the liquid crystal composition contains two or more dichroic pigments. When the liquid crystal composition contains two or more dichroic pigments, it is preferable to contain two to four dichroic pigments, and more preferably two to three dichroic pigments.

[0107] Dichroic pigments preferably exhibit liquid crystal properties. That is, liquid crystal dichroic pigments are preferred. Furthermore, exhibiting liquid crystal properties means that, when the temperature is changed, the compound has the property of displaying a liquid crystal phase (intermediate phase) between a crystalline phase (low-temperature side) and an isotropic phase (high-temperature side). As a specific observation method, by observing the compound under a polarizing microscope while heating or cooling it, the optical anisotropy and fluidity originating from the liquid crystal phase can be confirmed.

[0108] From the viewpoint of achieving better results with the present invention, the preferred dichroic pigment is a compound represented by formula (X).

[0109] [Chemical Formula 1] In equation (X), R 1 and R 2 Each of the following can be independently represented as a straight-chain or branched hydrocarbon group having 1 to 10 carbon atoms. The hydrocarbon group may contain oxygen, nitrogen, or sulfur atoms.

[0110] The number of carbon atoms in the above-mentioned hydrocarbon group is 1 to 10, and from the viewpoint of better effect of the present invention, it is preferably 1 to 8, and more preferably 2 to 6.

[0111] The aforementioned hydrocarbon group is either straight-chain or branched, preferably straight-chain.

[0112] The hydrocarbons mentioned above can be saturated hydrocarbon groups or unsaturated hydrocarbon groups.

[0113] The aforementioned hydrocarbon group may contain oxygen, nitrogen, or sulfur atoms. The aforementioned hydrocarbon group may contain multiple atoms selected from the group consisting of oxygen, nitrogen, and sulfur atoms.

[0114] For example, the aforementioned hydrocarbon group may contain -O-, -S-, -CO-, -CS-, -CO-O-, or -CO-NR between carbon-carbon atoms or at the end. 10 -、-NR 10 - or groups formed by combining them.

[0115] R 10 It represents a hydrogen atom or an alkyl group.

[0116] Preferably, the hydrocarbon group can contain -O-, -S-, -CO-, CS-, -CO-O-, or -CO-NR between carbon-carbon atoms or at the end. 10 -、-NR 10 - or alkyl groups that combine them.

[0117] R 1 and R 2 They can bond with each other to form a ring. The formed ring can be an aliphatic ring or an aromatic ring.

[0118] A and B independently represent divalent aromatic cyclic groups.

[0119] Examples of divalent aromatic cyclic groups include divalent aromatic hydrocarbon cyclic groups or divalent aromatic heterocyclic groups.

[0120] A divalent aromatic hydrocarbon cyclic group is a group formed by removing two hydrogen atoms from an aromatic hydrocarbon ring. The aforementioned aromatic hydrocarbon ring can be a monocyclic or fused ring. Examples of such aromatic hydrocarbon rings include benzene rings, naphthalene rings, anthracene rings, pyrene rings, phenanthrene rings, and fluorene rings.

[0121] A divalent aromatic heterocyclic group is a group formed by removing two hydrogen atoms from an aromatic heterocycle. The aforementioned aromatic heterocycle can be a monocyclic or a fused ring. Examples of aromatic heterocycles include pyridine rings, pyrimidine rings, pyridazine rings, pyrazine rings, triazine rings (e.g., 1,2,3-triazine rings, 1,2,4-triazine rings, and 1,3,5-triazine rings), tetraazine rings (e.g., 1,2,4,5-tetraazine rings), quinoxaline rings, pyrrole rings, furan rings, thiophene rings, imidazole rings, oxazole rings, thiazole rings, benzopyrrole rings, benzofuran rings, benzothiophene rings, benzoimidazolium rings, benzoxazole rings, benzothiazole rings, benzoxazole rings, naphthopyrrole rings, naphthofuran rings, naphthothiophene rings, naphthoimidazolium rings, naphthooxazole rings, pyrroloimidazolium rings (e.g., 5H-pyrrolo[1,2-a]imidazolium rings), imidazoxazole rings (e.g., imidazo[2,1-b]oxazole rings), and thieno[2,1-b]oxazole rings. 3-d]thiazole ring, benzothiadiazole ring, benzodithiophene ring (e.g., benzo[1,2-b:4,5-b']dithiophene ring, thieno[3,2-b]thiophene ring, thiazo[5,4-d]thiazo[2,3-b:6,7-b']thiophene ring, naphtho[2,3-b:6,7-b']thiophene ring, benzo[3,2-b]thiophene ring, thiazo[5,4-d]thiazo[5,4-d]thiazo[5,4-b ... [Dithiophene ring, naphtho[2,1-b:6,5-b']dithiophene ring, naphtho[1,2-b:5,6-b']dithiophene ring and 1,8-dithiabicyclopentane[b,g]naphthylene ring, etc.), benzothiophene and benzothiophene ring, dithiophene[3,2-b:2',3'-d]thiophene ring and 3,4,7,8-tetrathiabicyclopentane[a,e]cyclopentadiene ring.

[0122] L represents a single bond, -CR=CR-, -C≡C-, -CR=N-, or -N=N-.

[0123] R can independently represent a hydrogen atom, a halogen atom, or an alkyl group having 1 to 6 carbon atoms.

[0124] n represents an integer from 1 to 3. When n is 2 or 3, there are multiple A and L that can be the same or different.

[0125] R 3 It represents a hydrogen atom or a substituent.

[0126] There are no particular restrictions on the types of substituents, such as halogen atoms (e.g., fluorine, chlorine, bromine, and iodine atoms), hydrocarbon groups (alkyl (including cycloalkyl, bicycloalkyl, and tricycloalkyl), alkenyl (including cycloalkenyl and bicycloalkenyl), alkynyl, and aryl), heterocyclic groups, cyano, isothiocyanate groups, nitro, alkoxy, aryloxy, silyl, silanoxy, heterocyclic, acyloxy, carbamoyloxy, alkoxycarbonyloxy, and aryloxycarbonyl. alkyl oxy, primary amino, secondary or tertiary amino (including aniline), alkyl thio, aryl thio, heterocyclic thio, alkyl or aryl sulfinyl, alkyl or aryl sulfonyl, acyl, aryloxy carbonyl, alkoxy carbonyl, aryl or heterocyclic azo, imide, phosphin, oxophosphin, oxophosphinyloxy, oxophosphinylamino, phosphonyl, carboxyl, phosphate, sulfonic acid, hydroxyl, thiol, amide, carbamoyl, urea, borate, and groups formed by combining them.

[0127] Preferably, the substituents are alkyl, alkoxy, cyano, or isothiocyanate groups that may contain oxygen, nitrogen, or sulfur atoms. The alkyl group may contain oxygen, nitrogen, or sulfur atoms. For example, the alkyl and alkoxy groups may contain -O-, -S-, -CO-, -CS-, -CO-O-, or -CO-NR between carbon atoms. 10 -、-NR 10 - or groups formed by combining them. R 10 It represents a hydrogen atom or an alkyl group.

[0128] The aforementioned alkyl and alkoxy groups may include multiple -O-, -S-, -CO-, -CS-, -CO-O-, -CO-NR 10 -、-NR 10 - or groups formed by combining them.

[0129] There is no particular limitation on the number of carbon atoms in the alkyl and alkoxy groups mentioned above, but it is preferably 1 to 10, and more preferably 1 to 6.

[0130] R represents a hydrogen atom or an alkyl group.

[0131] The total content of dichroic pigments in the liquid crystal composition is 30% by mass or more relative to the total mass of the liquid crystal composition. Furthermore, when the liquid crystal composition contains only one dichroic pigment, the total content of the dichroic pigment is equivalent to the content of that single dichroic pigment relative to the total mass of the liquid crystal composition. And, when the liquid crystal composition contains two or more dichroic pigments, the total content of the dichroic pigments is equivalent to the combined amount of those two or more dichroic pigments.

[0132] In liquid crystal composition layers formed from liquid crystal compositions, a state with high refractive index anisotropy for electromagnetic waves can be obtained. The exact reason for this is not yet clear, but it is speculated that by increasing the total content of dichroic pigments in the liquid crystal composition layer, the interaction between the dichroic pigments is increased, thereby increasing the orientational order of the absorption axes caused by the absorption framework in the dichroic pigments. As a result, the absorption anisotropy of the dichroic pigments increases with the increase in refractive index anisotropy at wavelengths longer than the absorption wavelength.

[0133] Furthermore, the total content of dichroic pigments in the liquid crystal composition is preferably 50% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more, relative to the total mass of the liquid crystal composition. There is no particular upper limit, and examples include 100% by mass or less.

[0134] <Light Absorber> In addition to, or in place of, dichroic pigments, liquid crystal compositions may also contain light-absorbing materials.

[0135] Examples of light-absorbing materials include anthraquinone-based, quinoline-based, perylene-based, pyrrole methine (PM)-based, rhodamine (RH)-based, boron dipyrromethene (BODIPY)-based, and squarine (SQ)-based materials. For example, commercially available products such as FDB-007 (trade name, a cyanine dye manufactured by YAMADACHEMICAL CO.,LTD.) can also be used. Furthermore, tetraaza porphyrin (TAP)-based, squarine-based, and cyanine (CY)-based materials can also be cited. Furthermore, commercially available products such as PD-311S (trade name, tetrazaporphyrin dye, manufactured by Yamamoto Chemical Co., Ltd.) and FDG-006 (trade name, tetrazaporphyrin dye, manufactured by YAMADA CHEMICAL CO.,LTD.) can also be used.

[0136] <Other Ingredients> The liquid crystal composition may contain other components besides the dichroic pigments described above. Examples of such other components include liquid crystal compounds. In cases where the dichroic pigments do not exhibit liquid crystal properties, the liquid crystal composition comprises both a dichroic pigment and a liquid crystal compound.

[0137] For example, the liquid crystal composition preferably contains an azo compound, and the liquid crystal compound is preferably a liquid crystal compound having an azo structure. By including an azo compound in the liquid crystal composition, the Δn (birefringence) of the liquid crystal composition layer can be increased. Therefore, in order to impart the desired refractive index, i.e., the desired phase difference, to the radio wave, the required thickness of the liquid crystal composition layer can be made thinner. By making the liquid crystal composition layer thinner, the orientation of the liquid crystal compound changes more rapidly when the applied voltage is changed. As a result, the response speed to changes in the voltage applied to the liquid crystal composition layer can be accelerated, and the switching of the travel direction of the incident radio wave can be performed in a shorter time.

[0138] As an azo compound, there are no particular restrictions as long as it contains an azo structure (-N=N-). There are no particular restrictions on the number of azo structures azo compound can possess, as long as it is 1 or more, preferably 2 or more. There is no particular upper limit to the number of azo structures, but it is more common to find 5 or fewer, and even more common to find 3 or fewer.

[0139] The azo compound can be a liquid crystal compound or a non-liquid crystal compound, but is preferably a liquid crystal compound. That is, the azo compound is preferably a liquid crystal compound having an azo structure.

[0140] As an azo compound, the compound represented by formula (1) is preferred.

[0141] [Chemical Formula 2] In equation (1), Ar 1 This represents an aromatic ring with a valence of (m1+1).

[0142] The aromatic ring with the (m1+1) valence mentioned above can be a monocyclic ring or a fused ring with two or more rings. Alternatively, the aromatic ring can be a ring formed by multiple monocyclic rings bonded together by single bonds (e.g., biphenyl ring, terphenyl ring).

[0143] Examples of aromatic rings with the aforementioned (m1+1) valence include aromatic hydrocarbon rings or aromatic heterocycles.

[0144] Examples of aromatic hydrocarbon rings include benzene rings, naphthalene rings, anthracene rings, fluorene rings, biphenyl rings, and anthracene rings. Among these, benzene rings are preferred.

[0145] Examples of aromatic heterocycles include pyridine rings, thiophene rings, quinoline rings, isoquinoline rings, and thiazole rings.

[0146] For example, when m1 is 1, Ar 1 This indicates a divalent aromatic ring.

[0147] In equation (1), Ar 2 Aromatic rings with a valence of (m2+2).

[0148] The aromatic ring with the (m2+1) valence mentioned above can be a monocyclic ring or a fused ring with two or more rings. Alternatively, the aromatic ring can be a ring formed by multiple monocyclic rings bonded together by single bonds (e.g., biphenyl ring, terphenyl ring).

[0149] As an aromatic ring with the aforementioned (m2+1) valence, examples include aromatic hydrocarbon rings or aromatic heterocycles.

[0150] Examples of aromatic hydrocarbon rings include benzene rings, naphthalene rings, anthracene rings, fluorene rings, biphenyl rings, and anthracene rings. Among these, benzene rings are preferred.

[0151] Examples of aromatic heterocycles include pyridine rings, thiophene rings, quinoline rings, isoquinoline rings, and thiazole rings.

[0152] For example, when m2 is 1, Ar 2 This indicates a trivalent aromatic ring.

[0153] In equation (1), Ar 3 The aromatic ring represents the (m3+1) valence.

[0154] The aromatic ring with the (m3+1) valence mentioned above can be a monocyclic ring or a fused ring with two or more rings. Alternatively, the aromatic ring can be a ring formed by multiple monocyclic rings bonded together by single bonds (e.g., biphenyl ring, terphenyl ring).

[0155] As an aromatic ring with the aforementioned (m3+1) valence, examples include aromatic hydrocarbon rings or aromatic heterocycles.

[0156] Examples of aromatic hydrocarbon rings include benzene rings, naphthalene rings, anthracene rings, fluorene rings, biphenyl rings, and anthracene rings. Among these, benzene rings are preferred.

[0157] Examples of aromatic heterocycles include pyridine rings, thiophene rings, quinoline rings, isoquinoline rings, and thiazole rings.

[0158] For example, when m3 is 1, Ar 3 This indicates a divalent aromatic ring.

[0159] In equation (1), R 1 R 2 and R 3 Substituents are represented independently.

[0160] When m1≥2, multiple R 1 Multiple Rs can be the same or different. When m² ≥ 2, multiple Rs... 2 Multiple Rs can be the same or different, provided that m³ ≥ 2. 3 They can be the same or different.

[0161] The aforementioned substituents are monovalent substituents, and examples include alkyl, alkenyl, aralkyl, aryl, heterocyclic, halogen, cyano, nitro, mercapto, hydroxyl, alkoxy, aryloxy, alkylthio, arylthio, acyloxy, amino, alkylamino, dialkylamino, carboxamide, sulfonamide, aminosulfonylamino, oxycarbonylamino, oxysulfonylamino, urea, thiourea, acyl, oxycarbonyl, carbamoyl, sulfonyl, sulfinyl, aminosulfonyl, carboxyl (including salts), sulfonyl (including salts), and groups formed by combining these groups. These groups can be further substituted by these groups.

[0162] In equation (1), m1, m2 and m3 each independently represent integers from 0 to 5. m1 is preferably 1 to 3, m2 is preferably 0 to 1, and m3 is preferably 1 to 3.

[0163] In formula (1), n1 represents an integer from 1 to 4, preferably from 1 to 3, and more preferably from 2 to 3.

[0164] Furthermore, the liquid crystal composition preferably contains no solvent. "Substantially contains no solvent" means that the solvent content is 5% by mass or less relative to the total mass of the liquid crystal composition, preferably 1% by mass or less.

[0165] <Liquid Crystal Composition> The liquid crystal composition is a composition that displays liquid crystal properties. For example, when the liquid crystal composition contains a dichroic pigment, the liquid crystal composition is capable of displaying liquid crystal properties.

[0166] The liquid crystal composition preferably displays a nematic phase over the entire temperature range of 10 to 50°C. Furthermore, the liquid crystal composition preferably displays a nematic phase at any temperature between 50 and 150°C, and exhibits a glassy state or smectic liquid crystal properties at any temperature below 50°C.

[0167] Here, the radio wave control element may have other functional layers. Alternatively, in the radio wave control element, the support body may be configured as a layer with other functions.

[0168] For example, support 16 or support 24 may contain light-absorbing material that absorbs light in any wavelength range of 350 to 1000 nm.

[0169] By configuring the support to contain light-absorbing material, it is possible to suppress light in the visible to infrared range that is reflected due to the difference in refractive index between the support and the liquid crystal composition layer 20.

[0170] Examples of light-absorbing materials include anthraquinone-based, quinoline-based, perylene-based, pyrrole methine (PM)-based, rhodamine (RH)-based, boron dipyrromethene (BODIPY)-based, and squarine (SQ)-based materials. For example, commercially available products such as FDB-007 (trade name, a cyanine dye manufactured by YAMADACHEMICAL CO.,LTD.) can also be used. Furthermore, tetraaza porphyrin (TAP)-based, squarine-based, and cyanine (CY)-based materials can also be cited. Furthermore, commercially available products such as PD-311S (trade name, tetrazaporphyrin dye, manufactured by Yamamoto Chemical Co., Ltd.) and FDG-006 (trade name, tetrazaporphyrin dye, manufactured by YAMADA CHEMICAL CO.,LTD.) can also be used.

[0171] Alternatively, the support may not contain a light-absorbing material, but may have a layer containing a light-absorbing material outside the support. Furthermore, the support containing the light absorber or the layer containing the light-absorbing material may not be in contact with the liquid crystal composition layer.

[0172] Furthermore, the support may contain ultraviolet-absorbing materials that absorb ultraviolet light.

[0173] Fluorescence caused by ultraviolet light is generated in liquid crystal compositions or other components. It is detected by various sensors in the same way as reflected light from visible and infrared light, and may be a cause of noise.

[0174] In contrast, by designing a structure in which the support contains ultraviolet-absorbing material, it is possible to suppress the generation of fluorescence caused by ultraviolet light.

[0175] Examples of hindered phenolic compounds, benzophenone compounds, benzotriazole compounds, salicylates, benzophenone compounds, cyanoacrylates, and nickel complex salts are examples of hindered phenolic compounds. Examples of hindered phenolic compounds include 2,6-di-tert-butyl-p-cresol, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], N,N'-hexamethylenebis(3,5-di-tert-butyl-4-hydroxycinnamoamide), 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene, and tris-(3,5-di-tert-butyl-4-hydroxybenzyl)-isocyanurate. Examples of benzotriazole compounds include 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, 2,2-methylenebis(4-(1,1,3,3-tetramethylbutyl)-6-(2H-benzotriazole-2-yl)phenol), 2,4-bis(n-octylthio)-6-(4-hydroxy-3,5-di-tert-butylaniline)-1,3,5-triazine, triethylene glycol-bis[3-(3-tert-butyl-5-methyl-4-hydroxyphenyl)propionate], N,N'-hexamethylenebis( Examples of UV inhibitors include 3,5-di-tert-butyl-4-hydroxycinnamoamide, 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene, 2-(2'-hydroxy-3',5'-di-tert-butylphenyl)-5-chlorobenzotriazole, 2-(2'-hydroxy-3',5'-di-tert-pentylphenyl)-5-chlorobenzotriazole, 2,6-di-tert-butyl-p-cresol, and pentaerythritol ester-tetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]. The amount of these UV inhibitors added in the entire film, by mass percentage, is preferably 1 ppm to 1.0%, more preferably 10 to 1000 ppm.

[0176] Alternatively, the support may not contain ultraviolet-absorbing material, but may have a layer containing ultraviolet-absorbing material outside the support. Furthermore, the support containing ultraviolet absorber or the layer containing ultraviolet-absorbing material may not be in contact with the liquid crystal composition layer.

[0177] And, as Figure 8 Like the radio wave control element 10c shown, a planarization layer 36 may also be present between the liquid crystal composition layer 20 and the metasurface structure 12 (microstructure 14).

[0178] If the microstructure 14 comes into contact with the liquid crystal composition layer 20, light will be reflected at the interface between the microstructure 14 and the liquid crystal composition layer 20, which may be detected by various sensors and become a source of noise. This reflection is caused not only by the difference in refractive index between the microstructure 14 and the liquid crystal composition layer 20, but also by a step difference mainly occurring at the ends of the microstructure 14.

[0179] In contrast, by providing a structure in which a planarization layer 36 is provided between the liquid crystal composition layer 20 and the microstructure 14, reflected light in the range of visible light to infrared light can be suppressed.

[0180] Examples of planarization layers 36 include saturated or unsaturated polyester resins, (meth)acrylic resins, urethane acrylate resins, polyester acrylate resins, polyurethane acrylate resins, epoxy acrylate resins, urethane resins, epoxy resins, vinyl resins, polycarbonate resins, cellulose resins, acetal resins, polyethylene resins, polystyrene resins, polyamide resins, polyimide resins, melamine resins, phenolic resins, and silicone resins. Furthermore, polymers that can be included in the curable composition layer, such as adhesive polymers and polymerizable compounds, can be used. The organic film used in the planarization layer is preferred because it contains heterocyclic compounds, which can prevent corrosion of the metal pattern of the microstructure. The organic film used in the planarization layer may contain a single heterocyclic compound or two or more heterocyclic compounds. It may also contain other components besides the aforementioned polymers and heterocyclic compounds (e.g., surfactants).

[0181] Furthermore, the radio wave control element can have a temperature adjustment component that adjusts the temperature of the liquid crystal composition layer. In this case, the orientation state of the liquid crystal compound in the liquid crystal composition layer can be fixed. This method will be described in detail below.

[0182] Regarding the temperature adjustment component, its structure is not particularly limited as long as it is a component that adjusts the temperature of the liquid crystal composition layer 20. The placement of the temperature adjustment component is also unrestricted, as long as it can adjust the temperature of the liquid crystal composition layer 20. The temperature adjustment component can be arranged in a layered manner between any of the components constituting the radio wave control element, or it can be placed outside the radio wave control element.

[0183] Furthermore, the temperature adjustment component may include a heating device for increasing the temperature of the liquid crystal composition layer 20 and a cooling device for decreasing the temperature of the liquid crystal composition layer 20.

[0184] The steps for fixing the orientation state of the liquid crystal compound in the liquid crystal composition layer 20 using an electromagnetic control element with a temperature adjustment component are as follows. Furthermore, the liquid crystal compound included in the liquid crystal composition layer 20 is a compound that exhibits liquid crystal properties when heated by the temperature adjustment component. Specifically, a composition that exhibits a nematic phase at any temperature between 50 and 150°C and exhibits a glassy state or a smectic phase at any temperature below 50°C is preferably used.

[0185] First, in the radio wave control element, the liquid crystal composition layer 20 is heated by a temperature adjustment component and transformed into a liquid crystal phase. Next, while maintaining the heating process, a voltage is applied between the second electrode 26 and the microstructure 14 to control the orientation direction of the liquid crystal compound. At this time, the voltage applied per unit cell UC can be varied to create different orientation states of the liquid crystal compound. Afterward, if the heating and heating processes are stopped, the orientation state of the liquid crystal compound is fixed below the liquid crystal phase transition temperature. That is, the orientation state of the liquid crystal compound can be maintained even without applying a voltage.

[0186] Furthermore, depending on the type of liquid crystal compound used, a state with higher orientation can be generated in the radio wave control element. For example, when the liquid crystal compound displays a nematic phase and a higher-order liquid crystal phase such as a smectic phase, the higher-order liquid crystal phase can be fixed by rapidly cooling the radio wave control element using a temperature adjustment component.

[0187] Furthermore, in the radio wave control element, there may be a layer between the first electrode and the second electrode that does not change its refractive index due to voltage, or there may be a gap between one of the first electrode and the second electrode and the liquid crystal composition layer.

[0188] The layer whose refractive index does not change due to voltage is preferably a dielectric, and there are no particular restrictions on the material, as long as it has sufficient transmittance to radio waves (RW). Examples include semiconductors such as silicon, silicon oxide, germanium, and chalcogenide glasses; polyacrylic resins such as polymethyl methacrylate; cellulose resins such as cellulose triacetate; cyclic olefin polymers; polyethylene terephthalate (PET); polycarbonate and polyvinyl chloride resins; and glass.

[0189] Furthermore, the alignment film used to align the aforementioned liquid crystal dichroic pigment LC to a specified state can be set as a layer that does not produce a change in refractive index.

[0190] There is no particular limitation on the thickness of the layer that does not produce a change in refractive index, but it is preferably the same thickness as the liquid crystal composition layer 20. The difference between the thickness of the layer that does not produce a change in refractive index and the thickness of the liquid crystal composition layer 20 is preferably 100 μm or less, and more preferably 50 μm or less.

[0191] If a layer that does not produce a change in refractive index is disposed between the second electrode 26 and the microstructure 14, the distance between the electrodes can be increased. With this structure, electromagnetic wave loss can be suppressed while maintaining a high response speed of the electromagnetic wave control element 10. The position of the driving electrode for applying voltage to the liquid crystal composition layer is not particularly limited, but the electrode can also be the second electrode 26 and the microstructure 14. Furthermore, in order to effectively apply voltage to the liquid crystal composition layer, the electrode can be disposed between the layer that does not produce a change in refractive index and the liquid crystal composition layer. A high-resistance electrode can be used in this case to minimize the impact on electromagnetic waves. Furthermore, in order to drive via a lateral electric field, the electrode can be disposed such that the liquid crystal composition layer is sandwiched in the horizontal direction.

[0192] Furthermore, the material constituting the layer that does not produce a change in refractive index is not particularly limited in terms of dielectric constant relative to the applied voltage. As with the case where the second electrode 26 of the radio wave control element 10 and the microstructure 14 are electrodes, when the liquid crystal composition layer and the layer that does not produce a change in refractive index are arranged in series between opposing surface electrodes, a higher dielectric constant of the layer that does not produce a change in refractive index is more effective in increasing the electric field on the liquid crystal composition layer, and is therefore preferred. Furthermore, when the electrodes are arranged such that the liquid crystal composition layer is sandwiched in the horizontal direction for driving by a lateral electric field, a lower dielectric constant of the layer that does not produce a change in refractive index is more effective in increasing the electric field on the liquid crystal composition layer, and is therefore preferred. Moreover, the layer that does not produce a change in refractive index can be patterned in the in-plane direction or the thickness direction, thereby allowing the radio wave control amount to be adjusted by adjusting the in-plane average effective value of the refractive index or the effective value distribution within the element.

[0193] Furthermore, the radio wave control element may have a light-shielding layer that blocks at least a portion of light in the wavelength range of 250 to 1000 nm.

[0194] There are no particular restrictions on the location of the light-shielding layer in the radio wave control element, but it is preferably located on the side where external light is incident on the liquid crystal composition layer. By having a light-shielding layer in the radio wave control element, light that can be absorbed by the dichroic pigment can be prevented from reaching the dichroic pigment, thereby suppressing the decomposition of the dichroic pigment.

[0195] Example The present invention will now be described in further detail based on embodiments. 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 present invention should not be interpreted limitedly by the embodiments shown below.

[0196] <Dichroic Pigment> The following compounds 1-1 to 1-4 were prepared as dichroic pigments.

[0197] [Chemical Formula 3] In addition, Table 1 shows the cumulative absorbance Q of compounds 1-1 to 1-4, measured using the same procedure as for the cumulative absorbance Q of the liquid crystal composition. For the cumulative absorbance Q of compounds 1-1 to 1-4, D in formula (1) is replaced with the mass concentration (g·L) of any of the compounds 1-1 to 1-4 in a chloroform solution. -1 The cumulative absorbance Q of the liquid crystal composition was measured using the same procedure as that used for liquid crystal compositions.

[0198] [Table 1]

[0199] Next, the above compounds 1-1 to 1-4, liquid crystal compound A (RDP-94990 manufactured by DIC Corporation) and liquid crystal compound B (RDP-A3123 manufactured by DIC Corporation) were mixed to form the composition shown in Table 2 below, thereby preparing the composition.

[0200] In addition, in Table 2, the "Component 1 (%)" and "Component 2 (%)" columns indicate the types of each component used and the mass content (mass %) of each component relative to the total mass of the composition. Furthermore, in Table 2, liquid crystal compound A represents liquid crystal A, and liquid crystal compound B represents liquid crystal B. Also, in Table 2, "Cumulative Absorbance Q" refers to the measured value of the aforementioned cumulative absorbance Q.

[0201] [Table 2]

[0202] [Example 1-1] The method described in B. Kang, et al, SID 2023 DIGEST (2023) p. 993 was used to produce the following: Figure 7 The device shown is a radio wave control element consisting of a support, a microstructure (second electrode), a liquid crystal composition layer, a microstructure (first electrode), and a support.

[0203] Two supports were constructed using glass with a thickness of 500 μm. Furthermore, the microstructures serving as the first and second electrodes were constructed using 1.45 mm diameter circular copper with a thickness of 600 nm.

[0204] The liquid crystal composition layer is formed using composition A. The thickness is set to 200 μm.

[0205] [Examples 1-2] A liquid crystal composition layer was formed using composition B, and a radio wave control element was fabricated in the same manner as in Example 1.

[0206] [Comparative Example 1-1] A liquid crystal composition layer was formed using composition C, and a radio wave control element was fabricated in the same manner as in Example 1.

[0207] [Comparative Examples 1-2] A liquid crystal composition layer was formed using composition D, and a radio wave control element was fabricated in the same manner as in Example 1.

[0208] [Examples 2-1 to 2-2, Comparative Examples 2-1 to 2-2] The thickness of the liquid crystal composition layer was set to 10 μm. Otherwise, radio wave control elements were fabricated in the same manner as in Examples 1-1 to 1-2 and Comparative Examples 1-1 to 1-2.

[0209] [Examples 3-1 to 3-2, Comparative Examples 3-1 to 3-2] The thickness of the liquid crystal composition layer was set to 500 μm. Otherwise, radio wave control elements were fabricated in the same manner as in Examples 1-1 to 1-2 and Comparative Examples 1-1 to 1-2.

[0210] [Examples 4-1 to 4-2, Comparative Examples 4-1 to 4-2] The thickness of the liquid crystal composition layer was set to 4 μm. Otherwise, radio wave control elements were fabricated in the same manner as in Examples 1-1 to 1-2 and Comparative Examples 1-1 to 1-2.

[0211] [Examples 5-1 to 5-2, Comparative Examples 5-1 to 5-2] The thickness of the liquid crystal composition layer was set to 8 μm. Otherwise, radio wave control elements were fabricated in the same manner as in Examples 1-1 to 1-2 and Comparative Examples 1-1 to 1-2.

[0212] <Evaluation> (Reflectivity) The reflectivity of the radio wave control elements of the manufactured embodiments and comparative examples was measured as follows.

[0213] Specifically, a halogen lamp (350–1100 nm) was used as the light source, illuminating the sample surface at a 45-degree angle relative to it. The light reflected and scattered from the surface's normal direction was detected, and the amount of reflected light was measured. A TOPCON CORPORATION SR-3 spectroradiometer was used as the measuring instrument. Furthermore, a standard reflector plate made of barium sulfate (BaSO4) was used as a reference for measuring reflectivity, and the ratio of the amount of reflected light measured using the standard reflector plate was taken as the reflectivity.

[0214] The reflectance measurements were evaluated based on the following criteria.

[0215] • A: Reflectivity less than 1% • B: Reflectivity ≥ 1% and < 3% • C: Reflectivity is 3% or higher and less than 5% • D: Reflectivity is above 5% The results are shown in Table 3.

[0216] [Table 3]

[0217] As shown in Table 3, the embodiments of the present invention have lower reflectivity compared to the comparative examples. Therefore, it can be seen that the embodiments of the present invention can suppress the generation of excess noise light in the visible light and infrared light regions.

[0218] Furthermore, as can be seen from the comparison of the embodiments, the thickness of the liquid crystal composition layer is preferably 10 μm or more.

[0219] As can be seen from the above, the present invention has significant effects.

[0220] Symbol Explanation 2-Electronic wave reflecting device; 10, 10b, 10c-Electronic wave control element; 12-Metasurface structure; 14-Microstructure; 16, 24-Support; 20-Liquid crystal composition layer; 26-Second electrode; 28-Power supply; 36-Planarization layer; ANT-Antenna; AR1, AR2-Region; BL-Building; LC-Liquid crystal dichroic pigment; RW-Electronic wave; UC-Unit cell.

Claims

1. A radio wave control element, comprising, in sequence, a first electrode, a liquid crystal composition layer, and a second electrode, wherein, The thickness of the liquid crystal composition layer is 4 μm or more. The cumulative absorbance Q of the chloroform solution of the liquid crystal composition constituting the liquid crystal composition layer, expressed by formula (1), in the wavelength range of 350–1000 nm in the absorption spectrum is 10000 L·g. -1 ·cm -1 above, In equation (1), Q represents the cumulative absorbance, and the unit of the cumulative absorbance is L·g. -1 ·cm -1 D represents the mass concentration of the liquid crystal composition in the chloroform solution, and the unit of the mass concentration is g·L. -1 L represents the optical path length of the cuvette used in the measurement of the absorption spectrum, and the unit of the optical path length is cm. Abs(λ) represents the absorbance at wavelength λ, and the unit of wavelength λ is nm.

2. The radio wave control element according to claim 1, wherein, The liquid crystal composition layer comprises a liquid crystal compound and a dichroic pigment.

3. The radio wave control element according to claim 1 or 2, wherein, At least one of the first electrode and the second electrode is composed of a plurality of microstructures arranged together.

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