Frequency selective transmissive dielectric filter

Abstract

To provide a frequency selective transmissive filter that achieves excellent selective transparency relative to an electromagnetic wave of a desired specific frequency.SOLUTION: A frequency selective transmissive dielectric filter 10 includes a first dielectric layer 11 and a laminate 12 disposed on both surfaces of the first dielectric layer 11. A laminate 12 is formed by laminating a lamination unit in which a second dielectric layer 12a and a sub-wavelength grating layer 12b are overlapped in N layers (where N is an integer) with the sub-wavelength grating layer 12b of the lamination unit being the first dielectric layer 11 side.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a frequency selective transmissive dielectric filter.

Background Art

[0002] In 5G communication technology (28 GHz) and in-vehicle millimeter-wave radar (18 - 110 GHz), millimeter waves of a specific frequency are used as electromagnetic waves, and it is essential to remove noise etc. when using such millimeter waves of a specific frequency. As a filter that removes noise etc. and transmits only millimeter waves of a specific frequency, that is, a filter for reflecting or absorbing unnecessary electromagnetic waves, technologies such as a filter using a frequency selective surface (FSS) are known. For example, 5G communication technology is generally used in combination with existing wireless communication technologies such as LTE and Wi-Fi, and noise generated by these existing wireless communications can couple to the 5G communication circuit and cause communication failures. Therefore, for example, in an example of FSS for 5G communication technology, it is designed to block electromagnetic waves of a specific frequency (for example, the 2.4 GHz and 5.3 GHz bands of Wi-Fi signals) using a metasurface composed of a metal material (Non-Patent Document 1). Also, for example, in-vehicle millimeter-wave radar has conventionally used electromagnetic waves of different bands (for example, 77 GHz for forward monitoring and 24 GHz for peripheral monitoring) according to its purpose, so a filter that specifically transmits only desired electromagnetic waves has been required. Therefore, for example, in an example of FSS for in-vehicle millimeter-wave radar, by periodically forming a fine shape smaller than the wavelength on a metal material, electromagnetic waves of one frequency (for example, 24 GHz) are reflected and electromagnetic waves of the other frequency (for example, 77 GHz) can be selectively transmitted (or vice versa) (Non-Patent Document 2). Such FSS is designed based on knowledge of antennas, radio wave engineering, and millimeter-wave metasurfaces, and is composed of a metal pattern as described above.

Prior Art Documents

Non-Patent Documents

[0003] [Non-Patent Document 1] M.R.Chaharmir et.al., “Design of Dual-Band Frequency Selective Surfaces to Block Wi-Fi Using Printable Electronics Technology”, 17th International Symposium on Antenna Technology and Applied Electromagnetics(ANTEM), 2016 [Non-Patent Document 2] B.Schoenlinner et.al., “Compact Multibeam Dual-Frequency (24 and 77 GHz) Imaging Antenna for Automotive Radars”, 33RD EUROPEAN MICROWAVE CONFERENCE, VOLS 1-3, CONFERENCE PROCEEDINGS, Page785-788, 2003 [Summary of the Invention] [Problems to be Solved by the Invention]

[0004] The FSS used in 5G communication technology as described above is a so-called band-stop filter that selectively reflects (blocks) electromagnetic waves in the GHz band frequencies (2.4 GHz and 5.3 GHz bands). In addition, the FSS for in-vehicle millimeter-wave radars as described above has a wide frequency passband (bandwidth), and there are restrictions on the control of frequency selectivity.

[0005] An object of the present invention is to provide a new frequency selective transmission filter that can achieve excellent selective transmission for electromagnetic waves of a desired specific frequency. [Means for Solving the Problems]

[0006] As a result of intensive studies to solve the above problems, the present inventors have found that, by using a dielectric material, a structure in which a first dielectric layer having a high refractive index is used as a defect layer, and a stacked structure of a second dielectric layer and a sub-wavelength grating layer is stacked on top and bottom thereof in a desired number of stages (one or more stages) is used as a basic structure, and by controlling the thickness of the first dielectric layer and the second dielectric layer, the pitch or thickness of the sub-wavelength grating layer, etc., a frequency selective transmissive filter that selectively transmits electromagnetic waves of a desired specific frequency with high efficiency can be realized. The present invention has been further studied based on these findings and has been completed.

[0007] That is, the above problems of the present invention have been solved by the following means. 〔1〕 A frequency selective transmissive dielectric filter having a first dielectric layer and a laminate disposed on both surfaces of the first dielectric layer, wherein the laminate is formed by stacking N layers (where N is a natural number) of a stacking unit formed by overlapping a second dielectric layer and a sub-wavelength grating layer with the sub-wavelength grating layer of the stacking unit facing the first dielectric layer side. 〔2〕 The frequency selective transmissive dielectric filter according to 〔1〕, wherein the thickness of the first dielectric layer is 0.1 to 14.0 mm. 〔3〕 The frequency selective transmissive dielectric filter according to 〔1〕 or 〔2〕, wherein the first dielectric layer, the second dielectric layer, and the sub-wavelength grating layer are made of the same material. 〔4〕 The frequency selective transmissive dielectric filter according to any one of 〔1〕 to 〔3〕, wherein the thicknesses of the first dielectric layer, the second dielectric layer, and the sub-wavelength grating layer, or the pitch of the sub-wavelength grating layer continuously changes from one end to the other end of the frequency selective transmissive dielectric filter. 〔5〕 The frequency selective transmissive dielectric filter according to any one of 〔1〕 to 〔3〕, wherein the thicknesses of the first dielectric layer, the second dielectric layer, and the sub-wavelength grating layer, or the pitch of the sub-wavelength grating layer changes stepwise from one end to the other end of the frequency selective transmissive dielectric filter. 〔6〕 A frequency-selective transmissive dielectric filter array formed by arranging a plurality of the frequency-selective transmissive dielectric filters according to any one of [1] to [5] above. 〔7〕 A method for manufacturing a frequency-selective transmissive dielectric filter, including obtaining the frequency-selective transmissive dielectric filter according to any one of [1] to [5] above by forming the first dielectric layer, the second dielectric layer, and the sub-wavelength grating layer with a 3D ceramic printer. 〔8〕 The method for manufacturing a frequency-selective transmissive dielectric filter according to [7] above, wherein the first dielectric layer, the second dielectric layer, and the sub-wavelength grating layer are formed of the same material.

Advantages of the Invention

[0008] The frequency-selective transmissive dielectric filter of the present invention can function as a frequency-selective transmissive filter that selectively transmits electromagnetic waves of a desired specific frequency with high efficiency.

Brief Description of the Drawings

[0009]

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Embodiments for Carrying Out the Invention

[0010] Preferred embodiments of the present invention will be described, but the present invention is not limited to the following embodiments except as defined by the present invention.

[0011] In this specification, the "electromagnetic wave in the millimeter wave band" means an electromagnetic wave having a frequency of 0.3 to 400 GHz.

[0012] [Frequency Selective Transmissive Dielectric Filter] The frequency-selective transmissive dielectric filter of the present invention (hereinafter, also referred to as "the filter of the present invention") has a first dielectric layer and laminates disposed on both surfaces of the first dielectric layer. The laminate is formed by stacking a stacking unit in which a second dielectric layer and a sub-wavelength grating layer are overlapped, with the sub-wavelength grating layer of the stacking unit facing the first dielectric layer side, and stacking N layers (stacking the stacking unit N stages, where N is a natural number). In the filter of the present invention, the number of stages (N) of the stacking unit disposed on one surface side of the first dielectric layer is the same as the number of stages (N) of the stacking unit disposed on the other surface side. By having the above structure, the filter of the present invention can selectively transmit electromagnetic waves of a desired specific frequency with high efficiency. When the filter of the present invention is composed of a first dielectric layer "D", a second dielectric layer "H", and a sub-wavelength grating layer "L", and the number of stacked layers of the stacking unit is "N" and the stacking unit is "HL" or "LH", the structure of the filter of the present invention is expressed as "[(HL)×N]D[(LH)×N]".

[0013] When the filter of the present invention is a narrow-band filter (narrow-band band-pass filter), in the electromagnetic wave transmission spectrum with the vertical axis being the transmittance and the horizontal axis being the wavelength, it is preferable that the full width at half maximum is within the range of "transmission peak wavelength ± (1% of the transmission peak wavelength) or less", more preferably within the range of "transmission peak wavelength ± (0.5% of the transmission peak wavelength) or less", and even more preferably within the range of "transmission peak wavelength ± (0.1% of the transmission peak wavelength) or less". For example, when the transmission peak wavelength is 800 μm, the range of "transmission peak wavelength ± (1% of the transmission peak wavelength) or less" is the range of 792 to 808 μm. The "full width at half maximum" means, in the electromagnetic wave transmission spectrum, the difference between the wavelength on the long wavelength side and the wavelength on the short wavelength side corresponding to a transmittance of 50% when the transmittance at the transmission peak wavelength is set to 100%. When the filter of the present invention is a narrowband filter, in the electromagnetic wave transmission spectrum with the vertical axis representing the transmittance and the horizontal axis representing the frequency, the bandwidth (GHz) is preferably within the range of "transmission peak frequency ± (1% of the transmission peak frequency) or less", more preferably within the range of "transmission peak frequency ± (0.5% of the transmission peak frequency) or less", and even more preferably within the range of "transmission peak frequency ± (0.1% of the transmission peak frequency) or less". For example, when the transmission peak frequency is 100 GHz, the range of "transmission peak frequency ± (1% of the transmission peak frequency) or less" is the range of 99 to 101 GHz. Note that the "bandwidth" means the bandwidth when the transmittance becomes 50% in the electromagnetic wave transmission spectrum with the transmittance at the transmission peak frequency being 100%.

[0014] Figure 1(A) shows an example of an embodiment of the filter of the present invention. The filter 10 of the present invention shown in Figure 1(A) has a first dielectric layer 11, and a laminate 12 is disposed so as to sandwich the first dielectric layer 11 from above and below. The laminate 12 is formed by alternately stacking a second dielectric layer 12a and a sub-wavelength grating layer 12b, and the sub-wavelength grating layer 12b is disposed on the side of the first dielectric layer 11. In the present invention, a two-layer stacked structure formed by overlapping one layer of the second dielectric layer 12a and one layer of the sub-wavelength grating layer 12b is referred to as a "stacking unit" (therefore, in the present invention, when referring to a "stacking unit formed by overlapping a second dielectric layer and a sub-wavelength grating layer", it means a stacked structure composed of two layers obtained by overlapping one layer each of the second dielectric layer and the sub-wavelength grating layer). The laminate 12 shown in Figure 1(A) has a structure in which two stacking units are overlapped. That is, the number of stacked layers N (the number of repetitions of the stacking unit) of the stacking unit is 2. Note that in Figure 1(A), the structure of the sub-wavelength grating layer 12b is shown in a simplified manner. Actually, as shown as an example in Figure 1(B), the sub-wavelength grating layer 12b has a sub-wavelength grating structure. In the example shown in Figure 1(B), a plurality of regular square columnar (width: w, height: h) patterns 12b1 are arranged at regular intervals in the x-axis direction and the y-axis direction (with a x , a y as the period). Details of each of these layers will be described later.

[0015] The frequency (band) of the electromagnetic wave selectively transmitted by the filter of the present invention is not particularly limited and can be appropriately set according to the use of the filter of the present invention. By controlling the size, pitch, etc. of the first dielectric layer, the second dielectric layer, and the sub-wavelength grating layer, for example, the transmission frequency can be controlled between 3.5 and 400 GHz, may be controlled between 3.6 and 300 GHz, or may be controlled between 3.7 and 200 GHz.

[0016] Hereinafter, each component of the filter of the present invention will be described below.

[0017] (First dielectric layer) The filter of the present invention has a first dielectric layer. In the first dielectric layer, the laminate provided on both of its surfaces (in the z-axis direction shown in Fig. 1(A)) acts as a reflector, so that the electromagnetic wave incident on the first dielectric layer is repeatedly multiply reflected and only a specific wavelength is transmitted. There is no particular limitation on the material of the first dielectric layer, and a known dielectric can be used. Among them, it is preferable to use a high dielectric. Examples of the high dielectric include ceramics such as silicon, alumina, zirconia, silicon carbide, aluminum nitride, silicon nitride, yttria, barium titanate, and compounds containing the ceramics.

[0018] The thickness of the first dielectric layer (thickness in the z-axis direction shown in Fig. 1(A)) can be appropriately set according to the purpose. From the viewpoint of controlling the filter of the present invention to selectively transmit electromagnetic waves in a specific millimeter wave band, the thickness of the first dielectric layer is preferably 0.1 to 14.0 mm, more preferably 0.13 to 13.7 mm, and even more preferably 0.2 to 13.3 mm.

[0019] (Laminate) The filter of the present invention has a laminated structure in which N layers (N stages) of a laminated unit formed by overlapping a second dielectric layer and a sub-wavelength grating layer are stacked. As described above, the laminate functions as a reflector and reflects or absorbs electromagnetic waves other than the target transmission frequency. In the laminate, the sub-wavelength grating layer constituting the outermost layer of the laminate is arranged in contact with the first dielectric layer. The number of stacked layers N of the stacked unit (the number of repetitions of the stacked unit) is a natural number (1 or more), and from the viewpoint of making the filter of the present invention a narrower-band band-pass filter, it is preferably 2 or more, and more preferably 3 or more. There is no particular limitation on the upper limit of the number of stacked layers N, but from the viewpoint of avoiding thick film formation, it is usually 100 or less, may be 50 or less, may be 20 or less, or may be 10 or less.

[0020] It is preferable that the plurality of second dielectric layers constituting the laminate have the same thickness as each other on the same straight line in the thickness direction (the z-axis direction shown in FIG. 1(A)). Also, it is preferable that the plurality of sub-wavelength grating layers constituting the laminate have the same thickness as each other on the same straight line in the thickness direction (the z-axis direction shown in FIG. 1(A)). That is, it is preferable that the thicknesses of the plurality of second dielectric layers constituting the laminate are constant on the same straight line in the thickness direction, and it is also preferable that the thicknesses of the plurality of sub-wavelength grating layers constituting the laminate are constant on the same straight line in the thickness direction. Note that having the same thickness means that the thicknesses are substantially the same. That is, there may be variations in thickness as long as the effects of the present invention are not impaired. For example, if the thicknesses of each of the plurality of second dielectric layers are all within the range of the arithmetic mean value of the thicknesses of the plurality of second dielectric layers ±10% (preferably within the range of the arithmetic mean value ±5%, more preferably within the range of the arithmetic mean value ±2%), then on the same straight line in the thickness direction, it can be evaluated that the thicknesses of each of the plurality of second dielectric layers are the same as each other. This is the same for the plurality of sub-wavelength grating layers. In addition, when the filter of the present invention is controlled so as to transmit only electromagnetic waves of a specific frequency as a whole (when the entire filter is controlled to have the same transmission characteristics), for each of the layers constituting the filter of the present invention, it is preferable that the thickness of the entire layer is uniform (the thickness error is small). Similarly to the above, for each of the layers, even when there is some variation in the thickness of the entire layer (there is variation in the thickness in the z-axis direction at each point on the xy-plane shown in Fig. 1(A)), if the degree of the variation is within the range of the average of the thickness of the entire layer in each layer ±10% (preferably within the range of the average of the thickness ±5%, more preferably within the range of the average of the thickness ±2%), the thickness of the entire layer can be evaluated as being uniform. The average of the thickness of the entire layer in each layer can be calculated as the arithmetic mean value of 16 randomly measured thicknesses (the thickness in the stacking direction, the thickness in the z-axis direction shown in Fig. 1(A)).

[0021] -Second dielectric layer- The second dielectric layer is preferably thinner than the first dielectric layer, and more preferably about half or less in thickness. As the material (constituting material) of the second dielectric layer, the dielectrics described for the first dielectric layer can be used, and it is preferable that the constituting material of the second dielectric layer is the same as the constituting material of the first dielectric layer. The thickness of the second dielectric layer (the thickness in the z-axis direction shown in Fig. 1(A)) can be appropriately determined according to the thickness of the first dielectric layer, the thickness of the sub-wavelength grating layer, the number of stacked layers N of the stacking unit, etc., and also according to the frequency to be transmitted.

[0022] -Sub-wavelength grating layer- The sub-wavelength grating layer is a layer having a sub-wavelength grating structure. As shown as an example in Fig. 1(B), the sub-wavelength grating layer 12b is a layer in which a plurality of patterns 12b1 are arranged in alignment. By controlling the pitch etc. of the sub-wavelength grating structure, the sub-wavelength grating layer can be made to have a desired refractive index (effective refractive index). As the constituting material of the sub-wavelength grating layer (the constituting material of the pattern), the dielectrics described for the first dielectric layer can be used, and it is preferable that it is the same constituting material as the constituting material of the first dielectric layer. Note that the effective refractive index of the sub-wavelength grating layer is usually lower than the refractive indices of the first dielectric layer and the second dielectric layer. In particular, when each layer is made of the same material, the effective refractive index of the sub-wavelength grating layer is an average value depending on the volume occupancy ratio of each pattern and the material of the gap between each pattern (for example, air). Therefore, the refractive indices of the first dielectric layer and the second dielectric layer are higher than the effective refractive index of the sub-wavelength grating layer.

[0023] In FIG. 1(B), the pattern 12b1 shows a square columnar structure. However, the shape of the pattern of the sub-wavelength grating layer in the filter of the present invention is not particularly limited. For example, the shape on the xy-axis plane (the cross-sectional shape when the pattern is cut by the xy-axis plane) may be circular, elliptical, triangular, quadrilateral (square, rectangle, etc.), or polygonal. Also, the shape on the xz-axis plane or the yz-axis plane may be circular, elliptical, quadrilateral (square, rectangle, etc.), or polygonal. That is, for example, in addition to the square columnar shape shown in FIG. 1(B), it may be cylindrical, conical, elliptical cylindrical, elliptical conical, triangular columnar, triangular pyramidal, cross-shaped, polygonal columnar, polygonal pyramidal, spherical, substantially spherical, etc. Also, the pattern may be an island structure, or its inverted structure or lattice structure. In the case of an inverted structure or lattice structure, the shape of the cavity is regarded as the shape of the "pattern".

[0024] The frequency of the electromagnetic wave selectively transmitted by the filter of the present invention can also be controlled by the period of the pattern. FIG. 2 shows an end view (cross-sectional view) when the sub-wavelength grating layer 12b shown in FIG. 1(B) is cut by the xy-axis plane, and the end face shape of the pattern 12b1 is square. Here, the period is the size of one structural pattern unit constituting a plurality of patterns 12b1. Period a y with respect to period a x the value of (a x / a y ), or period a x with respect to period a y the value of (a y / a x) is not particularly limited and can be appropriately set to selectively transmit electromagnetic waves of the target frequency. From the viewpoints of the manufacture of the sub-wavelength grating layer and physical stability, each value (a x / a y 、a y / a x ) is preferably from 0.6 to 3.7, more preferably from 0.7 to 3.6, and even more preferably from 0.8 to 3.5.

[0025] The period a x 、a y is appropriately controlled by the width of the pattern (the width in the x-axis direction and the width in the y-axis direction). For example, a x can be set to 1 to 10 times the width in the x-axis direction, may be 1 to 9 times, or may be 1 to 7 times. Also, a y can be set to 1 to 10 times the width in the y-axis direction, may be 1 to 9 times, or may be 1 to 7 times. Note that a x is not 1 time the width in the x-axis direction, and a y is not 1 time the width in the y-axis direction (in this case, it does not become a sub-wavelength grating). Therefore, the lower limit values in the above preferred multiple ranges are all preferably 1.1, more preferably 1.2, and even more preferably 1.3. The height of the pattern is synonymous with the thickness of the sub-wavelength grating layer.

[0026] The constituent materials of the respective layers constituting the filter of the present invention may be different materials, but are preferably all the same material. By adopting such a configuration, for example, even if the usage environment (e.g., temperature, pressure, etc.) of the filter of the present invention changes, it is difficult for strain, change in refractive index, etc. to occur between the layers. Therefore, the filter of the present invention can be accurately designed and can be used even in an environment with drastic temperature changes or in a harsh environment such as outer space. In addition, by using the same material, it can be manufactured at low cost when manufacturing with a 3D ceramic printer.

[0027] In the filter of the present invention, the first dielectric layer and the second dielectric layer can also be layers having a sub-wavelength grating structure. Even when the first dielectric layer and the second dielectric layer have a sub-wavelength grating structure, the refractive indices of the first dielectric layer and the second dielectric layer are usually controlled to be higher than the effective refractive index of the sub-wavelength grating layer. As an example of the filter of the present invention as described above, FIG. 3 shows a longitudinal sectional view of a filter 10 of the present invention in which a first dielectric layer 11 and a second dielectric layer 12a have a sub-wavelength grating structure.

[0028] The filter of the present invention may have layers other than the first dielectric layer, the second dielectric layer, and the sub-wavelength grating layer. For example, the filter 10 of the present invention shown in FIG. 3 has a substrate 13 on the bottom surface. Also, for example, it may have a blocking portion that covers the side surface of the layer. Further, for example, in the form of FIG. 1(A), a sub-wavelength grating layer 12b may be further provided on the outermost second dielectric layer 12a.

[0029] Since the filter of the present invention can be manufactured using a technique such as a 3D ceramic printer as described later, for example, the thickness of each layer and the pitch of the sub-wavelength grating layer can be continuously varied within the same filter. As an example of such a filter, the filter of the present invention can be a linear variable filter in which the thickness of each layer and the pitch of the sub-wavelength grating layer continuously change from one end to the other end of the filter of the present invention (in the x-axis direction and / or the y-axis direction shown in FIG. 1(A)). In an example of the linear variable filter shown in FIG. 4, the thickness of each layer continuously linearly changes from one end to the other end of the filter 10 of the present invention. By making it such a linear variable filter, the frequency of the electromagnetic wave transmitted through the filter can be designed to continuously change in the x-axis direction and / or the y-axis direction.

[0030] In addition, the filter of the present invention can also vary, for example, the thickness of each layer and the pitch of the sub-wavelength grating layer stepwise within the same filter. As an example of such a filter, the filter of the present invention can be a filter in which the thickness of each layer and the pitch of the sub-wavelength grating layer change stepwise from one end to the other end of the filter of the present invention (in the x-axis direction and / or the y-axis direction shown in FIG. 1(A)). FIG. 5 shows a top view of a filter in which the filter 10 of the present invention is divided into three sections in the x-axis direction and three sections in the y-axis direction (S1 to S9). In an example of the filter of the present invention shown in FIG. 5, it is shown that the frequencies of the electromagnetic waves transmitted respectively are different by the shades of the colors shown for each section. FIG. 6 shows a longitudinal end view when the filter of the present invention shown in FIG. 5 is cut in the z-axis direction on the dashed-dotted line. FIG. 6 schematically shows a longitudinal end view of a filter in which sections S1 to S3 are provided in the filter 10 of the present invention. In an example shown in FIG. 6, the thickness of each layer is different for each section. In the case of such a configuration, from the viewpoint of regularly changing the selectively transmitted wavelength, it is preferable that the materials constituting each layer are the same material. Note that, in the example shown in FIG. 6, there is no partition provided at the boundary between each section, but it is also possible to adopt a form in which a partition is provided at the boundary between each section.

[0031] [Frequency Selective Transmission Dielectric Filter Array] A plurality of the filters of the present invention can be arranged to form a frequency selective transmissive dielectric filter array. Fig. 7 schematically shows a top view of a frequency selective transmissive dielectric filter array formed by arranging the filters (10a, 10b, 10c) of the present invention for selectively transmitting electromagnetic waves of different frequencies. Examples of each filter of the present invention constituting such a filter array include filters of the present invention having different thicknesses for each layer, filters having different materials for each layer, filters having different pitches of sub-wavelength grating layers, etc. Further, each filter of the present invention constituting the filter array may be a filter in which the thickness of each layer and the pitch of the sub-wavelength grating layer are continuously or stepwise varied within the same filter as shown in Figs. 4 and 6. By adjusting each of the filters of the present invention constituting the filter array as described above, an array that selectively transmits electromagnetic waves of different frequencies for each filter can be obtained. In the frequency selective transmissive dielectric filter array shown in Fig. 7, the filters of the present invention are arranged with gaps therebetween, but they can also be arranged so that the filters are in contact with each other without gaps. Note that a filter array arranged such that the filters are in contact with each other as described above exhibits substantially the same effects as the filter of the present invention shown in Figs. 5 and 6. Therefore, in such a case, the names "filter" and "filter array" do not substantially distinguish them, and the filter of the present invention shown in Figs. 5 and 6 can also be regarded as the above filter array.

[0032] [Method for manufacturing frequency selective transmissive dielectric filter] The manufacturing method of the filter of the present invention is not particularly limited. For example, the filter of the present invention can be manufactured by using a 3D ceramic printer. Since the aforementioned FSS (FSS for 5G communication technology and FSS for in-vehicle millimeter-wave radar) is usually created by vapor-depositing metal or the like, it is difficult to form a layer with a thickness of several tens of μm. In contrast, with a 3D ceramic printer, each layer can be made into a layer with a thickness of several tens of μm, and the layer can also be formed into a laminated structure. Further, according to a 3D ceramic printer, a sub-wavelength structure with a desired effective refractive index can be designed and manufactured relatively easily. Furthermore, by using the same constituent material for each layer constituting the filter of the present invention, it is also possible to manufacture the aforementioned linear variable filter, a filter in which the frequency of the electromagnetic wave transmitted through each section is different, and the like. As a manufacturing method using a 3D ceramic printer, a method applicable to a 3D ceramic printer such as a binder jet method or a stereolithography method can be selected. In addition, as a manufacturing method other than the manufacturing method using the above 3D ceramic printer, for example, a plate material in which holes of a sub-wavelength structure are formed on a ceramic substrate is used as a sub-wavelength grating layer, and the filter of the present invention can also be manufactured by combining and laminating it with a plate material in which such holes are not formed.

[0033] The filter of the present invention can be used, for example, in 6G communication, space communication, use in harsh environment applications, game devices, etc., in addition to the above-mentioned 5G communication and in-vehicle millimeter-wave radar. Since the filter of the present invention uses a dielectric as a constituent material, a material having a melting point much higher than that of metal can be selected, and it can be used even in a high-temperature environment. Furthermore, by manufacturing the filter of the present invention from the same material, even when subjected to thermal expansion due to a large temperature difference such as in outer space, no difference in the linear expansion coefficient occurs for each layer, so strain and the like are less likely to occur in the filter of the present invention. Also, in order to reduce the delay of wireless communication, it is assumed that electromagnetic waves with higher frequencies (higher frequencies than Wi-Fi and Bluetooth) are used. It is considered that game devices and the like equipped with the filter of the present invention in combination for such wireless communication are less affected by noise and the like.

Examples

[0034] The present invention will be described in more detail based on examples. The present invention is not construed as being limited to the following examples except as defined in the present invention.

[0035] <Calculation of Transmission Characteristics of Each Filter> In the examples, the transmission characteristics of each frequency-selective transmission dielectric filter assumed can be calculated by simulation using the RCWA (Rigorous Coupled-Wave Analysis) method. For this simulation, DiffractMOD manufactured by Synopsys was used as numerical calculation software. The set values in the simulation are as per the following simulation conditions and the parameters of each filter shown in each experimental example. In the above simulation, the incident light is TE polarized (the electric field of the incident light is parallel to the x-axis direction). - Simulation Conditions - · Wavelength resolution: 0.001 μm · Harmonics: 2

[0036] (Experimental Example 1) Regarding a frequency-selective transmission dielectric filter having a first dielectric layer and a laminate arranged on both surfaces of the first dielectric layer, and the laminate being formed by stacking N layers with a stacking unit formed by overlapping a second dielectric layer and a sub-wavelength grating layer with the sub-wavelength grating layer of the stacking unit facing the first dielectric layer side, the design parameters were set as follows so that the transmission peak frequency of the electromagnetic wave passing through the frequency-selective transmission dielectric filter would be around 32 GHz. Furthermore, for filters 1-1 to 1-4 with the number of stacked layers N being 1 to 4, the transmittance of the electromagnetic wave for each filter was calculated by the above simulation. Note that the constituent materials of all layers were the same dielectric (alumina (Al2O3)). The results are shown in Table 1 and FIG. 8 below. - Design Parameters - Refractive index of the first and second dielectric layers: 3.0 Refractive index of the sub-wavelength grating layer: 2.23 Thickness of the first dielectric layer: 1400 μm Thickness of the second dielectric layer: 700 μm Shape of the pattern: Regular quadrangular prism Height of the pattern: 940 μm Width of the pattern: 470 μm Period of the pattern (a x 、a y ): 940 μm

[0037]

Table 1

[0038] As shown in Table 1 and Fig. 8, it was shown that by controlling the above various parameters, a band-pass filter having frequency-selective transmissivity with a peak frequency of the transmitted electromagnetic wave of about 32 GHz can be formed. Further, the filter with the stacking number N = 1 (Filter 1-1) is a broad band-pass filter with a wide full width at half maximum of the transmission peak and a wide frequency bandwidth, while by setting the stacking number N to 2 or more, a narrow band-pass filter with a narrow bandwidth can be formed, and it was shown that by further increasing the stacking number, it can be controlled to a narrow band-pass filter with an even narrower bandwidth (Filters 1-2 to 1-4).

[0039] (Experimental Example 2) The transmittance of the electromagnetic wave for each filter was calculated by the above simulation in the same manner as in Experimental Example 1, except that the design parameters were set as follows so that the peak frequency of the electromagnetic wave transmitted through the frequency-selective transmissive dielectric filter was around 400 GHz. The results are shown in Table 2 and Fig. 9 below. - Design parameters - Refractive index of the first and second dielectric layers: 3.0 Refractive index of the sub-wavelength grating layer: 2.23 Thickness of the first dielectric layer: 110 μm Thickness of the second dielectric layer: 55 μm Shape of the pattern: Regular quadrangular prism Height of the pattern: 75 μm Width of pattern: 37.5 μm Period of pattern (a x 、a y ): 75 μm

[0040]

Table 2

[0041] As shown in Table 2 and Figure 9, by controlling the above various parameters, it was shown that a band-pass filter having frequency-selective transmissivity with a transmission peak frequency of the transmitted electromagnetic wave of about 400 GHz can be formed. Further, the filter with the number of laminations N being 1 (Filter 2-1) is a broad band-pass filter with a wide full width at half maximum of the transmission peak and a wide frequency bandwidth, whereas by setting the number of laminations N to 2 or more, a narrow band-pass filter with a narrow bandwidth can be formed, and it was shown that by further stacking the number of laminations, it can be controlled to a narrow band-pass filter with an even narrower bandwidth (Filters 2-2 to 2-4).

[0042] (Experimental Example 3) The transmittance of the electromagnetic wave for each filter was calculated by the above simulation in the same manner as in Experimental Example 1 except that the design parameters were set as follows so that the transmission peak frequency of the electromagnetic wave passing through the frequency-selective transmissive dielectric filter is around 3.5 GHz. The results are shown in Table 3 and Figure 10 below. - Design parameters - Refractive index of the first and second dielectric layers: 3.0 Refractive index of the sub-wavelength grating layer: 2.23 Thickness of the first dielectric layer: 12600 μm Thickness of the second dielectric layer: 6300 μm Shape of the pattern: Regular square prism Height of the pattern: 8400 μm Width of the pattern: 4200 μm Period of the pattern (a x 、a y ): 8400 μm

[0043]

Table 3

[0044] As shown in Table 3 and FIG. 10, it was shown that by controlling the above various parameters, a band-pass filter having frequency-selective transmissivity with a transmission peak frequency of the transmitted electromagnetic wave of about 3.5 GHz can be formed. Further, the filter with the number of layers N being 1 (filter 3-1) is a broad band-pass filter with a wide full width at half maximum of the peak and a wide frequency bandwidth, while by setting the number of layers N to 2 or more, a narrow-band filter with a narrow bandwidth can be formed, and it was shown that by further stacking the number of layers, it can be controlled to a narrow-band filter with an even narrower bandwidth (filters 3-2 to 3-4).

[0045] (Experimental Example 4) Regarding the filter 1-3 (number of layers N = 3) in Experimental Example 1, the period of the pattern of the sub-wavelength grating layer was set as follows according to the following design parameters, and the period (a y ) in the x-axis direction with respect to the period (a x ) in the y-axis direction (a x / a y ) was changed to be 0.8 to 3.5. Except for this, the transmittance of the electromagnetic wave for each filter was calculated by the above simulation in the same manner as in Experimental Example 1. The electric field E was in the x-axis direction as shown in FIG. 2. The results are shown in Table 4 below and FIG. 11. -Design Parameters- Pattern period (a x ) : 752 to 3290 μm Pattern period (a y ) : 940 μm

[0046]

Table 4

[0047] As is clear from Table 4 and FIG. 11 above, it was shown that even when the thicknesses of the filter or each layer are the same, the transmission peak wavelength and the transmission peak frequency can be controlled by adjusting the period of the pattern.

[0048] Therefore, it was shown that the filter of the present invention can be made into a frequency selective transmission dielectric filter that can selectively transmit electromagnetic waves having a desired specific frequency by adjusting the above parameters.

Explanation of Reference Numerals

[0049] 10, 10a, 10b, 10c Frequency selective transmission dielectric filter 11 First dielectric layer 12 Laminate 12a Second dielectric layer 12b Sub-wavelength grating layer 12b1 Pattern 13 Substrate 20 Frequency selective transmission dielectric filter array S1~S3 Sections 1 to 3

Claims

1. It has a first dielectric layer and laminates disposed on both surfaces of the first dielectric layer, wherein the laminate is formed by stacking N (where N is a natural number) laminate units each formed by overlapping a second dielectric layer and a sub-wavelength grating layer with the sub-wavelength grating layer of the laminate unit facing the first dielectric layer side. A frequency selective transmissive dielectric filter.

2. The frequency selective transmissive dielectric filter according to Claim 1, wherein the thickness of the first dielectric layer is 0.1 to 14.0 mm.

3. The frequency selective transmissive dielectric filter according to Claim 2, wherein the first dielectric layer, the second dielectric layer, and the sub-wavelength grating layer are made of the same material.

4. The frequency selective transmissive dielectric filter according to Claim 3, wherein the thicknesses of the first dielectric layer, the second dielectric layer, and the sub-wavelength grating layer, or the pitch of the sub-wavelength grating layer continuously changes from one end to the other end of the frequency selective transmissive dielectric filter.

5. The frequency selective transmissive dielectric filter according to Claim 3, wherein the thicknesses of the first dielectric layer, the second dielectric layer, and the sub-wavelength grating layer, or the pitch of the sub-wavelength grating layer changes stepwise from one end to the other end of the frequency selective transmissive dielectric filter.

6. A frequency selective transmissive dielectric filter array formed by arranging a plurality of the frequency selective transmissive dielectric filters according to any one of Claims 1 to 5.

7. A method for manufacturing a frequency selective transmissive dielectric filter, including manufacturing the frequency selective transmissive dielectric filter according to any one of Claims 1 to 5 by forming the first dielectric layer, the second dielectric layer, and the sub-wavelength grating layer with a 3D ceramic printer.

8. The method for manufacturing a frequency selective transmissive dielectric filter according to Claim 7, wherein the first dielectric layer, the second dielectric layer, and the sub-wavelength grating layer are formed of the same material.

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