JP2010062471A - Method of defining dimension of conductive element and dimension of clearance between conductive elements in fss for transparent radio wave absorbers, and radio wave absorber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of defining dimension of a conductive element and a dimension of clearance between the conductive elements so as to obtain an FSS pattern which is transparent and inconspicuous. <P>SOLUTION: In the FSS for transparent radio wave absorbers, the method of defining the dimension L of a conductive element and a dimension of clearance g between the conductive elements includes the steps of: (I) performing digitalization as an inverse number of contrast to a spatial frequency f with respect to one-dimensional array along a direction of a certain FSS pattern; (II) calculating an intensity limit which can acquire a contrast sensitivity function CSF matching the RC plot group obtained in the step (I), using the contrast sensitivity function CSF; (III) creating a map indicating an intensity limit line A<SB>1</SB>which connects the plots of the same intensity LL<SB>ef</SB>on the two-dimensional coordinate which sets the dimension g as a horizontal axis and sets the dimension L as a vertical axis; and (IV) determining the dimension L and the dimension g from the map. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a transparent wave absorber, and more particularly, to an FSS structure of a transparent wave absorber.

  The remarkable progress of wireless technology in recent years has simultaneously increased the possibility of causing radio interference such as interference and interference in the wireless system. For example, in a UHF band RFID system in which an RFID tag provided in an article is recognized by a wireless device called a reader / writer, radio wave interference in an identification zone of the reader / writer is a major factor that hinders the spread.

  In order to prevent radio interference such as interference and interference in the identification zone of such a radio system, the use of a transparent radio wave absorber has been proposed.

  In general, a transparent radio wave absorber is composed of a transparent absorption layer and a transparent reflection layer that is disposed at a predetermined distance (for example, 1/4 of the wavelength) from the transparent absorption layer. In recent examples, in order to reduce the distance between the two layers, the transparent absorption layer is configured by installing a frequency selection member called FSS (Frequency Selective Surface) on a transparent substrate. The FSS has a repeated arrangement pattern of transparent conductive elements. On the other hand, a transparent reflective layer is comprised by installing a transparent reflective film in a transparent substrate.

  As is apparent from the above-described configuration, the conventional transparent radio wave absorber is configured to be in a “transparent” state as a whole. However, when the transparent electromagnetic wave absorber is actually visually confirmed, it is confirmed that only the pattern of the FSS transparent conductive element (hereinafter simply referred to as “FSS pattern”) is conspicuous. Is not completely transparent.

  Such a problem occurs because, in the conventional FSS, the transparency of the FSS pattern is designed and configured focusing on only the visible light transmittance. The human eye is sensitive to small differences in transmittance, so that a “transparent” FSS pattern is conspicuously visible in the transparent wave absorber.

  The visibility which was the case of such an FSS pattern makes the appearance of a transparent electromagnetic wave absorber worse, and becomes the cause which impairs the beauty | look.

  However, as far as the present inventors know, no transparent wave absorber having a “transparent and inconspicuous” FSS pattern has been reported so far. This is considered to be due to the fact that there is no clear index indicating the state of “transparent and inconspicuous” for the FSS pattern.

  The present invention has been made in view of such a background. In the present invention, the method for determining the dimensions of the conductive elements and the gaps thereof in order to obtain a transparent and inconspicuous FSS pattern, and the FSS pattern are conspicuous. An object of the present invention is to provide a transparent electromagnetic wave absorber that is difficult and has a good appearance.

In the present invention, in the FSS for a transparent wave absorber having a two-dimensional repeating pattern of conductive elements arranged on a transparent substrate, the dimension L of the conductive element in one direction and the dimension g of the gap between the conductive elements. A method for determining
The method is
(I) A step of digitizing a one-dimensional array of a certain FSS pattern along the one direction as a reciprocal of contrast with respect to a spatial frequency f,
(I-1) obtaining the contrast information Gf from the one-dimensional array of the FSS pattern, with the viewing distance d, the transmittance Ti of the gap portion, and the transmittance Tc of the conductive element as fixed values;
(I-2) Step of performing Fourier transform processing on the contrast information Gf to obtain spectral information Sf;
(I-3) Performing a process for obtaining an MTF response represented by the following expression (1) on the spectrum information Sf to obtain an MTF response signal; and

（Ｉ−４）前記ＭＴＦ応答信号を逆数化することにより、空間周波数ｆに対するＲＣプロット群を得るステップ、
を有する工程と、
（ＩＩ）視野角をｗ、輝度をＬｋとしたとき、以下の式（２）で表されるコントラスト感度関数ＣＳＦを用いて、

(I-4) obtaining an RC plot group with respect to the spatial frequency f by reciprocalizing the MTF response signal;
A process comprising:
(II) When the viewing angle is w and the luminance is Lk, the contrast sensitivity function CSF represented by the following formula (2) is used.

（Ｉ）で得られたＲＣプロット群に一致するコントラスト感度関数ＣＳＦが得られるような限界輝度を算出する工程であって、
（ＩＩ−１）視野角ｗを固定値として、ＲＣプロット群を構成する各プロット毎に、限界輝度ＬＬ_ｉを算出するステップ、および
（ＩＩ−２）算出された各輝度ＬＬ_ｉを用いて、以下の式（３）

A step of calculating a limiting luminance such that a contrast sensitivity function CSF matching the RC plot group obtained in (I) is obtained,
(II-1) A step of calculating a limit luminance LL _i for each plot constituting the RC plot group with a viewing angle w as a fixed value, and (II-2) using each calculated luminance LL _i , The following formula (3)

から、実効限界輝度ＬＬ_ｅｆを算出するステップ、
を有する工程と、
（ＩＩＩ）前記隙間の寸法ｇを横軸とし、前記導電性素子の寸法Ｌを縦軸とした二次元座標上に、同一の輝度ＬＬ_ｅｆのプロット同士を結んだ少なくとも一つの限界輝度線Ａ_ｉを示したマップを作成する工程であって、
前記工程（Ｉ）、工程（ＩＩ）を、前記導電性素子の寸法Ｌおよび前記導電性素子間の隙間の寸法ｇが異なる各種ＦＳＳパターンについて実施し、これにより、前記マップが作成される工程と、
（ＩＶ）前記マップから、前記導電性素子の寸法Ｌおよび前記導電性素子間の隙間の寸法ｇを定める工程であって、
（ＩＶ−１）前記マップ上に、前記透明電波吸収体が適正に作動するＦＳＳパターンの範囲Ｐを表示するステップ、
（ＩＶ−２）前記限界輝度線Ａ_ｉおよび前記範囲Ｐで囲まれた領域のうち、前記限界輝度線Ａ_ｉよりも左側の領域を選定領域として定めるステップ、および
（ＩＶ−３）得られた少なくとも一つの前記選定領域に含まれるように、前記導電性素子の寸法Ｌおよび前記導電性素子間の隙間の寸法ｇを定めるステップ、
を有する工程と、
を有することを特徴とする方法が提供される。

A step of calculating an effective limit luminance LL _ef from
A process comprising:
(III) At least one limit luminance line A _i connecting plots of the same luminance LL _ef on a two-dimensional coordinate with the dimension g of the gap as the horizontal axis and the dimension L of the conductive element as the vertical axis. The process of creating a map showing
The step (I) and the step (II) are performed on various FSS patterns having different dimensions L of the conductive elements and dimensions g of the gaps between the conductive elements, thereby creating the map. ,
(IV) determining the dimension L of the conductive element and the dimension g of the gap between the conductive elements from the map,
(IV-1) displaying a range P of the FSS pattern in which the transparent wave absorber properly operates on the map;
(IV-2) of the limit brightness lines A _i and the range surrounded by the P region, said step defining a left region as selected areas than the limit luminance lines A _i, and (IV-3) obtained Determining a dimension L of the conductive element and a dimension g of a gap between the conductive elements so as to be included in at least one of the selected regions;
A process comprising:
There is provided a method characterized by comprising:

Here, in the method according to the present invention, the step of obtaining the contrast information Gf from the one-dimensional array of the FSS pattern includes:
Converting a one-dimensional array of the FSS pattern from the viewing distance d into an FSS pattern Ga defined by an angle;
Calculating a Michelson contrast value MC represented by the following formula (4) from the transmittance Ti of the gap portion and the transmittance Tc of the conductive element;

前記ＦＳＳパターンＧａに、前記マイケルソンコントラスト値ＭＣを乗じるステップと、
により算出されても良い。

Multiplying the FSS pattern Ga by the Michelson contrast value MC;
It may be calculated by

  The Michelson contrast value MC may be in the range of 0.08 to 0.15.

  In the method according to the present invention, the selected region may be a region where a size g of the gap satisfies g ≧ 0.05 mm.

  In the method according to the present invention, the FSS pattern range P in which the transparent radio wave absorber operates properly may include the FSS pattern range when the absorption amount of the transparent radio wave absorber is 10 dB or more.

  In the method according to the present invention, the transmittance Ti of the gap portion is in the range of 0.85 to 0.90, and the transmittance Tc of the conductive element is in the range of 0.65 to 0.82. May be.

  In the method according to the present invention, the viewing distance d may be in the range of 500 mm to 1500 mm.

  In the method according to the present invention, the viewing angle w may be in the range of 20 ° to 30 °.

In the method according to the present invention, the limit luminance line A _i may be a limit luminance line when the effective limit luminance LL _ef is 100 cd / m ² or more.

  In the method according to the present invention, the FSS pattern may be constituted by a two-dimensional repetitive pattern of a conductive element having a side length L and a slit having a width g.

Alternatively, in the method according to the present invention, the FSS pattern is composed of a two-dimensional repeating pattern of a conductive element having a side length of L and an intermediate portion having a width of D,
The intermediate portion is composed of two slits each having a width g, and a second conductive element sandwiched between the two slits,
In the steps (I) to (IV), when the ratio (L / D) between the length L of one side of the conductive element and the width D of the intermediate portion is a fixed value k, the second conductive element Width M of
M = L / k-2g
And the same operation may be performed.

In the method according to the present invention, the conductive element is rectangular.
The steps (I) to (IV) may be repeated for a one-dimensional array along another direction perpendicular to the one direction.

  Alternatively, the conductive element may be square.

Further, in the present invention, a transparent radio wave absorber comprising an FSS having a two-dimensional repeating pattern of conductive elements arranged on a transparent substrate, called an FSS pattern,
When the FSS pattern is determined by the evaluation methods shown in the following (I) to (III), a transparent radio wave absorber characterized by satisfying the determination criteria shown in (IV) is provided:
(Evaluation method)
(I) The FSS pattern Ga defined by an angle is defined with an arrangement in one dimension of the FSS pattern, where the dimension of the conductive element is L, the dimension of the gap between the conductive elements is g, and the viewing distance is d = 500 mm. Converted,
From the transmittance Ti of the gap portion and the transmittance Tc of the conductive element, a Michelson contrast value MC represented by the following formula (5) is calculated,

前記ＦＳＳパターンＧａに、前記マイケルソンコントラスト値ＭＣを乗じ、
これにより、前記ＦＳＳパターンの前記一つの次元における配列から得られるコントラスト情報Ｇｆを算出し、
前記コントラスト情報Ｇｆをフーリエ変換処理した後、得られたスペクトル情報Ｓｆに対して、以下の式（６）で表されるＭＴＦ応答を求める処理を実施して、ＭＴＦ応答信号を取得し、

Multiplying the FSS pattern Ga by the Michelson contrast value MC,
Thereby, the contrast information Gf obtained from the array in the one dimension of the FSS pattern is calculated,
After performing the Fourier transform process on the contrast information Gf, the obtained spectrum information Sf is subjected to a process for obtaining an MTF response represented by the following formula (6) to obtain an MTF response signal,

さらに得られた前記ＭＴＦ応答信号を逆数化することにより、前記ＦＳＳパターンについての、空間周波数ｆに対するＲＣプロット群を得る。
（ＩＩ）視野角をｗとし、輝度をＬｋとしたとき、以下の式（７）で表されるコントラスト感度関数ＣＳＦを用いて、

Further, the obtained MTF response signal is inversed to obtain an RC plot group with respect to the spatial frequency f for the FSS pattern.
(II) When the viewing angle is w and the luminance is Lk, the contrast sensitivity function CSF represented by the following formula (7) is used.

視野角ｗ＝２０゜として、（Ｉ）で得られたＲＣプロット群に一致するコントラスト感度関数ＣＳＦが得られるような限界輝度ＬＬを算出する；この際には、
ＲＣプロット群を構成する各プロット毎に限界輝度ＬＬ_ｉを算出し、
算出された各限界輝度ＬＬ_ｉを用いて、以下の式（８）

With the viewing angle w = 20 °, a limit luminance LL is calculated so that a contrast sensitivity function CSF that matches the RC plot group obtained in (I) is obtained;
The limit luminance LL _i is calculated for each plot constituting the RC plot group,
Using each calculated limit luminance LL _i , the following equation (8)

から、実効限界輝度ＬＬ_ｅｆを算出する。
（ＩＩＩ）同様の評価を、前記一つの次元と直交する別の次元について実施する。
（ＩＶ）得られた両次元における実効限界輝度ＬＬ_ｅｆが、いずれも判断基準ＬＬ_ｅｆ≧１０００ｃｄ／ｍ^２を満足するかどうかを評価する。

From the above, the effective limit luminance LL _ef is calculated.
(III) The same evaluation is performed for another dimension orthogonal to the one dimension.
(IV) It is evaluated whether or not the obtained effective limit luminance LL _ef in both dimensions satisfies the judgment criterion LL _ef ≧ 1000 cd / m ² .

Furthermore, in the present invention, an electromagnetic wave absorber comprising a plurality of conductive elements provided on a transparent substrate with a predetermined length L and a gap g in a predetermined direction,
The length L and the interval g are in coordinates with the length L as the vertical axis and the interval g as the horizontal axis.
A lower limit line indicating a lower limit value of desired electromagnetic wave absorption;
An upper limit line indicating the upper limit of desired electromagnetic wave absorption;
A limit brightness line connecting the desired limit brightness values;
An electromagnetic wave absorber characterized by having a value within the range surrounded by.

  In the present invention, it is possible to provide a method for determining the dimensions of the conductive elements and the gaps thereof to obtain a transparent and less noticeable FSS pattern, and a transparent radio wave absorber that is less noticeable and has a good appearance. Become.

  First, in order to better understand the features of the present invention, the configuration of a conventional transparent wave absorber will be described. In FIG. 1, an example of the cross section of the conventional transparent electromagnetic wave absorber is shown. FIG. 2 shows an example of a top view of an absorption layer in a conventional transparent radio wave absorber. In both figures, it should be noted that the dimensions of some members are exaggerated and therefore these figures do not correspond to actual scales.

  The conventional transparent radio wave absorber 100 includes an absorption layer 110, a reflection layer 140, and a spacer 170 for forming a space 160 therebetween.

  The absorption layer 110 is configured by disposing an FSS (frequency selective film) 125 on the first transparent substrate 120. In addition, in the example of FIG. 1, the transparent protective layer 135 is further installed on the upper part of the FSS 125, but the installation of this transparent protective layer 135 is arbitrary. The first transparent substrate 120 (and the transparent protective layer 135) is made of a transparent material such as glass or PET (polyethylene terephthalate).

  On the other hand, the reflective layer 140 includes a second transparent substrate 150 and a transparent reflective film 145 disposed on one surface thereof. The second transparent substrate 150 is made of a transparent material such as glass or PET (polyethylene terephthalate). The transparent reflective film 145 is configured by repeatedly laminating a transparent metal thin film and a transparent oxide thin film, for example. For the transparent metal thin film, for example, silver is used, and for the transparent oxide thin film, for example, zinc oxide, indium oxide, or the like is used.

  As shown in FIG. 2, the FSS 125 is configured by disposing a regular pattern 128 of the conductive element 126 on the first transparent substrate 120. In the present application, such a regular pattern 128 of the conductive element 126 is hereinafter referred to as “FSS pattern” 128. In the example of this figure, the conductive element 126 has a square shape with one side length L, and each conductive element 126 repeats in the vertical direction (X direction) and the horizontal direction (Y direction) (5 The regular pattern 128 of the conductive element 126 is formed. The periphery of each conductive element 126 is surrounded by a gap 130 having a width of g. The conductive element 126 is made of a transparent conductive material such as ITO (indium tin oxide).

  The transparent radio wave absorber 100 configured by combining such transparent members is “transparent” as a whole. However, this “transparent” state is merely “transparent” in that the transmittance to visible light is high, and is not “transparent” to the perceptibility of the human eye. That is, when a human actually observes the radio wave absorber 100 configured as described above, the distance between the radio wave absorber and the human (hereinafter referred to as “viewing distance”), the angle at which the radio wave absorber is viewed ( Hereinafter, the FSS pattern 128 included in the radio wave absorber 100 becomes conspicuous depending on conditions such as “viewing angle” and the illuminance of the environment. This is because the human eye has the ability to perceive a small difference in transmittance, and thus distinguishes between the transmittance of the conductive element portion of the FSS pattern 128 and the transmittance of the gap portion. is there.

  Further, when the FSS pattern 128 is conspicuously visible in the transparent radio wave absorber 100 as described above, the appearance of the transparent radio wave absorber 100 is deteriorated, and the aesthetic appearance thereof is impaired.

  Therefore, in order to maintain the aesthetics of the transparent electromagnetic wave absorber, the “transparent and inconspicuous” FSS pattern is always used in the installation environment, regardless of conditions such as viewing distance, viewing angle, and environmental illumination. Need to form.

  However, as far as the present inventors know, there is an index that indicates that the FSS pattern is "transparent and inconspicuous", in other words, an index that can identify "conspicuous FSS pattern" / "inconspicuous FSS pattern". do not do. Therefore, at present, it is impossible to design and form a “transparent and inconspicuous” FSS pattern.

  As a result of promoting earnest research and development under such problems, the inventors of the present application, as will be described later, are transparent and conspicuous FSS patterns based on human perception ability, and transparent and inconspicuous FSS patterns. The index which identifies is found. It has also been found that by using such an indicator, a transparent and inconspicuous FSS pattern for a transparent radio wave absorber can be obtained.

  In general, the perceptibility of contrast inherent in a certain pattern changes according to the viewing distance d to the pattern. This is because the spatial frequency f of the pattern varies with the viewing distance d. FIG. 3 shows the concept of this spatial frequency f. In the example of this figure, a two-period striped pattern is drawn on the screen 1 and is imaged on the retina of the human eye 2. Spatial frequency is the number of repetitions per unit angle (1 °) on this retina, and f in this figure is 2 (cycles / °). Since this angle changes in inverse proportion to the viewing distance, the spatial frequency also changes accordingly. The reason why the human eye cannot distinguish fine stripes is because it has a response to this spatial frequency and the contrast of the high spatial frequency is significantly reduced. Even if the stripe pattern on the screen is the same, it depends on the viewing distance. Note that contrast is perceived as changing.

  It is known that the response of the human eye to such a spatial frequency f can be modeled by a function called MTF (Modulation transfer function) (B. Chitprasert, KR Rao, “Human Visual Weighted Progressive Image Transgression Image Transform”). ", IEEE Trans. On Comm. Vol. 38, No. 7, July, 1990: Non-Patent Document 1), the contrast of a certain pattern can be quantified.

  In addition, when such a contrast pattern forms an image on the retina, the pattern perceptibility of whether or not the pattern can be identified also has a frequency characteristic, but this frequency characteristic changes depending on the surrounding luminance, It is known that the higher the luminance, the higher the sensitivity that can be identified. Further, it is known that such a perceptible / impossible threshold value based on luminance and spatial frequency can be quantified by a function called a contrast sensitivity function CSF, as will be described later.

  The inventors of the present application combine the above two techniques related to pattern perceptibility to determine whether the target FSS pattern can be perceived by the human eye or not under certain conditions. Found that can be judged.

  That is, according to the present invention, there is a method capable of determining the length L of the conductive element of the FSS pattern and the size of the gap g between the conductive elements based on the index for determining perceivable / impossible of the FSS pattern. Provided, thereby providing a “transparent and unobtrusive” FSS pattern.

  Hereinafter, a method for determining the length L of the conductive element having such an FSS pattern and the dimension g of the gap between the conductive elements according to the present invention will be described. FIG. 4 shows a flowchart of the method according to the invention. FIG. 5 shows a top view of an example of the absorption layer of the transparent radio wave absorber according to the present invention to which such a method can be applied. The absorption layer of the transparent wave absorber according to the present invention basically has the same configuration as the conventional absorption layer 110 shown in FIG. Therefore, in FIG. 5, members corresponding to those in FIG. 2 are denoted by reference numerals with “N” added to the reference numerals in FIG. 2. For example, the absorbing layer according to the present invention is represented by 110N, the conductive element of the FSS according to the present invention is represented by 126N, and the FSS pattern is represented by 128N. The conductive element 126N has a square shape with one side length L, and the gap between the conductive elements 126N is g.

  In FIG. 5, the conductive elements 126N are arranged in 5 rows × 5 columns. However, in the actual FSS 125N, it is understood by those skilled in the art that the arrangement of the conductive elements 126N is configured by more matrices. Is obvious. In FIG. 5, the conductive element 126N has a square shape, but the conductive element 126N may have a rectangular shape.

As shown in FIG. 4, in the method of the present invention, (I) a one-dimensional array of an FSS pattern is referred to as the reciprocal of contrast with respect to the spatial frequency f (referred to as “RC plot group”; see below for details). And calculating the limit luminance LL _ef using the contrast sensitivity function CSF so that a contrast sensitivity function CSF matching the RC plot group obtained in step (I) is obtained. (S200) and (III) at least one limit brightness obtained by connecting plots of the same limit brightness LL _ef on a two-dimensional coordinate having the gap g as the horizontal axis and the length L of the conductive element as the vertical axis. comprising a step (S300) of creating a map showing the contours a _i, from the resulting map, the conductive element defines a gap g between the length L and the conductive element and the step (S400), the.

  Here, the step (I) includes obtaining the contrast information Gf from the one-dimensional array of the FSS pattern with the viewing distance d, the transmittance Ti of the transparent substrate, and the transmittance Tc of the conductive element as fixed values (S110). The obtained contrast information Gf is subjected to a Fourier transform process to obtain spectral information Sf (S120), and an MTF response is obtained from the obtained spectral information Sf to obtain an MTF response signal. A step (S130) and a step (S140) of obtaining an RC plot group for the spatial frequency f by reciprocalizing the obtained MTF response signal.

The step (II) is a step (S210) of calculating the limit luminance LL for each plot constituting the RC plot group with the viewing angle w as a fixed value, and the effective limit luminance using each limit luminance LL. Calculating LL _ef (S220).

The step (IV) includes a step (S410) of displaying the FSS pattern range P in which the transparent radio wave absorber operates properly on the map obtained in the step (III), and the limit luminance line A _i and Of the regions surrounded by the range P, a step (S420) of defining a region on the left side of the limit luminance line A _i as a selected region, and the length L of the conductive element so as to be included in at least one selected region. And a step (S430) of determining a gap g between the conductive elements.

  Hereinafter, each step will be described in detail.

(Process I)
(Step S110)
In step S110, contrast information Gf is obtained from a one-dimensional array of an FSS pattern (for example, an array in the X direction in FIG. 5).

  First, basic parameters are input and an FSS pattern is specified. Here, it should be noted that the specified FSS pattern is information of a one-dimensional array (for example, information on the X direction or the Y direction in FIG. 5).

  Basic parameters include a length L and a gap size g in one direction (for example, X direction) of a conductive element having a certain FSS pattern, a transmittance Ti of the conductive element 126N, and a transmittance of the first transparent substrate 120N. Tc and viewing distance d are included. For example, when the first transparent substrate 120N is glass or PET film and an ITO film is formed thereon, the transmittance Tc of the conductive element portion is in the range of about 0.65 to 0.82. Yes, the transmittance of the gap is in the range of about 0.85 to 0.90. On the other hand, the viewing distance d is in the range of 500 mm to 1500 mm, for example.

For example, this step 110 is
(A) Using the viewing distance d, converting the one-dimensional array information of the FSS pattern into the FSS pattern Ga defined by the angle according to the following equation (9):

（ｂ）隙間の透過率Ｔｉ、および導電性素子１２６Ｎの透過率Ｔｃから、以下の式（１０）で表されるマイケルソンコントラスト値ＭＣを算定するステップと、

(B) calculating a Michelson contrast value MC represented by the following formula (10) from the transmittance Ti of the gap and the transmittance Tc of the conductive element 126N;

（ｃ）得られたＦＳＳパターンＧａにマイケルソンコントラスト値ＭＣを乗じるステップと、
を有し、これらのステップ（ａ）〜（ｃ）を経て、コントラスト情報Ｇｆが取得されても良い。

(C) multiplying the obtained FSS pattern Ga by a Michelson contrast value MC;
The contrast information Gf may be acquired through these steps (a) to (c).

(Step S120)
Next, the obtained contrast information Gf is subjected to Fourier transform processing to obtain spectral information Sf.

  FIG. 6 shows an example of spectrum information Sf obtained by Fourier transforming the contrast information Gf. This spectrum information Sf is obtained when L = 10 mm, g = 0.2 mm, viewing distance d = 500 mm, and Michelson contrast value MC = 0.1 in the FSS pattern 128N as shown in FIG. Is the result.

(Step S130)
Next, a process for obtaining an MTF (Modulation Transfer Function) response is performed on the obtained spectrum information Sf. The spatial impulse response of the eyeball optical system is referred to as PSF (Point Spread Function), and PSF is subjected to Fourier transform, and the absolute value of this is taken as MTF. The MTF is expressed by the following formula (11) by the spatial frequency f (Non-patent Document 1).

これにより、ＦＳＳパターンのＭＴＦ応答信号が得られる。図７には、前述の図６に示したスペクトル情報Ｓｆを用いて、ＦＳＳパターンのＭＴＦ応答を求めた結果を示す。通常の場合、この処理により、図７に示すように、複数のピークを有する応答信号が得られる。

Thereby, the MTF response signal of the FSS pattern is obtained. FIG. 7 shows the result of obtaining the MTF response of the FSS pattern using the spectrum information Sf shown in FIG. In a normal case, a response signal having a plurality of peaks is obtained by this process as shown in FIG.

(Step S140)
Next, the aforementioned MTF response signal is inverted, and this numerical group is plotted against the spatial frequency f (these plot groups are hereinafter referred to as “RC plot groups”).

  Through such processing, the one-dimensional array information of a specific FSS pattern is digitized as an RC plot group indicating the reciprocal of contrast.

(Step II)
Next, the limit luminance LL _ef is obtained using the contrast sensitivity function CSF. Here, the contrast sensitivity function CSF means a frequency characteristic of perceptual sensitivity to a contrast stimulus of a certain luminance level. This is generally obtained by performing the following measurement by psychophysical experiment. First, give the subject a contrast stimulus whose luminance changes sinusoidally around the luminance level, measure the contrast of the perceptible / impossible threshold by changing the luminance level and amplitude, and take the reciprocal of it Is. (That is, the contrast sensitivity function CSF has a reciprocal dimension of contrast.)
This contrast sensitivity function CSF can be modeled by the following mathematical formula (BGJ Barten, “Evaluation of subjective image quality with the square-root integral method”, J. Opt. Spc. No. 10, Oct. 1990: see Non-Patent Document 2).

ここで、ｆは、空間周波数（サイクル／゜）、ｗは、視野角（゜）、Ｌｋは、輝度（ｃｄ／ｍ^２）である。

Here, f is a spatial frequency (cycle / °), w is a viewing angle (°), and Lk is luminance (cd / m ² ).

(Step S210)
First, in step S210, the contrast sensitivity function CSF that matches the above-described RC plot group is obtained by changing the luminance Lk with the viewing angle w (°) as a fixed value. The luminance obtained by this operation is referred to as “limit luminance” LL. The viewing angle w is, for example, in a range of 20 ° ≦ w ≦ 30 °.

  FIG. 8 shows an example in which the RC plot group described above and the contrast sensitivity function CSF obtained when the luminance Lk is changed are plotted on the same graph. In this figure, each parameter was set as follows: length L = 10 mm of conductive element, gap g = 0.2 mm, viewing distance d = 1000 mm, viewing angle w = 20 °, Michelson contrast MC = 0.1.

  In FIG. 8, plot groups indicated by black circles indicate RC plot groups, and curves B1 to B4 indicate the contrast sensitivity function CSF at each luminance Lk. From this figure, it can be seen that the locus of the contrast sensitivity function CSF changes as the luminance Lk changes. In other words, the contrast sensitivity function can be set so that the locus coincides with a certain RC value in the RC plot group.

However, the change of the locus on the high luminance side is saturated, and hardly changes at 1000 cd / m ² or more. Therefore, it is not possible to make a match above a certain RC value (this value varies depending on the spatial frequency). However, this fact does not indicate the limitations of this method, but rather provides a basis for not being able to perceive patterns under all conditions.

Actually, the closest contrast sensitivity function CSF is set for each point of the RC plot group, and thereby the limit luminance LL is calculated. Therefore, a plurality of values of the limit luminance LL exist for one RC plot group, and these are denoted as LL _i . As described above, for RC plots that cannot be matched due to saturation of CSF luminance dependence, there is no practical problem even if a large limit luminance (for example, 10000 cd / m ² ) is applied for convenience.

Such limit luminance LL _i can be obtained recursively as a so-called minimization problem, and the BFGS quasi-Newton method that allows the upper and lower limits of the variable is suitable as the method because of the feature of CSF saturated on the high luminance side. ing. However, the present invention is not limited to this, and other methods such as a genetic algorithm, a neural network, a synthesized annealing method, or a particle swarm optimization method may be used.

(Step S220)
In step S210 described above, the limit luminance LL _i is calculated.

  It should be noted that the contrast sensitivity function CSF indicates a response to a sinusoidal contrast signal and does not directly correspond to a stimulus including a harmonic. For example, as is apparent from the spectrum of FIG. 6, the spectrum information Sf of the FSS pattern has many harmonic components, and the RC plot group obtained based on the spectrum information Sf and the contrast sensitivity function CSF It cannot be compared directly with functions.

On the other hand, the energy diffused into the harmonic spectrum of the RC plot group influences the perception of contrast, like the single frequency spectrum of a sinusoidal contrast signal. Therefore, it can be considered that the contribution of the harmonic spectrum of these RC plot groups occurs when sinusoidal contrast stimuli having the frequency of each spectrum are input in parallel. Therefore, the actual limit brightness LL _ef can be obtained by combining the limit brightness LL _i of each RC plot in the RC plot group by the following equation (13).

そこで、このステップＳ２２０では、上記式（１３）を用いて、実際の限界輝度ＬＬ_ｅｆ（以下、「実効限界輝度ＬＬ_ｅｆ」という）が算定される。なお、実効限界輝度ＬＬ_ｅｆは、対象とするＦＳＳパターンが知覚可能／知覚不可能となる輝度の閾値を示していることに留意する必要がある。

Therefore, in this step S220, the actual limit luminance LL _ef (hereinafter referred to as “effective limit luminance LL _ef ”) is calculated using the above equation (13). It should be noted that the effective limit luminance LL _ef indicates a luminance threshold at which the target FSS pattern is perceptible / non-perceptible.

(Step III)
(Step S300)
Next, in step S300, the processes of step (I) and step (II) are performed for various FSS patterns having different lengths L of conductive elements and gaps g between the conductive elements. Then, using the effective limit brightness LL _ef obtained, the horizontal axis of the gap g, the length L of the conductive elements on the vertical axis and the on a two-dimensional coordinate, the plot between the same effective limit brightness LL _ef A map showing at least one connected limit luminance line A _i is created.

  FIG. 9 shows an example of a map created through steps (I) to (III). This map was obtained when the viewing distance d = 1000 mm, the viewing angle w = 20 °, and the Michelson contrast MC = 0.125 were adopted as the parameter conditions. The gap g (mm) between the conductive elements 126N was changed from 0.05 mm to 1.0 mm. Further, the length L (mm) of the conductive element 126N was changed in the range of 0 to 60 mm.

FIG. 9 shows two limit luminance lines A1 and A2. The limit brightness line A1 is obtained by connecting plots having an effective limit brightness LL _ef of 100 cd / m ² , and the limit brightness line A2 has an effective limit brightness LL _ef of 1000 cd / m 2. It is obtained by connecting the plots to be ² . As shown in this figure, the limit luminance line A _i is a straight line that rises to the right in a normal case. Note that the limit luminance lines were also calculated when the value of the effective limit luminance LL _ef exceeds 1000 cd / m ² , but these limit luminance lines may almost coincide with the limit luminance line A2 of 1000 cd / m ^2. all right. As described above, this is because the luminance dependence of the contrast sensitivity function is almost saturated at 1000 cd / m ² . Therefore, limit brightness line in the effective limit brightness _{LL ef} exceeding 1000 cd / ^{m 2} can be regarded as the effective limit brightness _{LL ef} may be replaced by limit brightness line when the 1000 cd / ^{m 2.}

Further, as is clear from the process of deriving these limit luminance lines A _i , the lower right region of the limit luminance line A1 in FIG. 9 is such an environment even in an environment where the luminance is less than 100 cd / m ^2. This means that the FSS pattern is perceived as a pattern. On the other hand, the upper left region from the limit luminance contour line A1 indicates that such an FSS pattern is not perceived by human eyes in an environment where the luminance is 100 cd / m ² or less.

Similarly, in FIG. 9, the upper left region from the limit luminance line A2 means that an FSS pattern having such a conductive element arrangement cannot be perceived in an environment where the luminance is 1000 cd / m ² or less. ing. However, as described above, the limit luminance line A2 can be applied to an environment where the effective limit luminance LL _ef exceeds 1000 cd / m ^2. It can be said that it represents a region of the FSS pattern that cannot be perceived by the human eye at any luminance.

(Process IV)
(Step S410)
Next, in step S410, the range P of the FSS pattern in which the transparent wave absorber properly operates is drawn on the map created in step (III).

  Here, such a range P may be described as a range of the FSS pattern when the absorption amount in the transparent radio wave absorber 100N is 10 dB or more (for example, the absorption amount is 10 dB or 30 dB), for example.

FIG. 10 shows a state in which such a range P is superimposed on the map shown in FIG. In this figure, a region (hatched portion) sandwiched between two broken lines P1 and P2 represents a region of an FSS pattern when the amount of absorption in the transparent radio wave absorber 100N is 10 dB or more, that is, a range P. The upper broken line P1 at this time is expressed by the following equation

Y = 39.1 * X ^0.55 (X1)

Is a curve approximated by Also, the lower broken line P2 represents the following equation

Y = 18.5 * X ^0.45 (X2)

Is a curve approximated by At this time, the distance between the reflective layer and the absorbing layer is 27.2 mm, and the sheet resistance is 120Ω.

(Step S420)
Next, in the map, a region on the left side of the limit luminance line A _i among the regions surrounded by the limit luminance line A _i and the range P is defined as a “selected region” SA _i .

This “selected area” SA _i is configured so that an FSS pattern is formed so as to enter such an area.
(1) Such an FSS pattern can be sufficiently used as an absorption layer of a transparent radio wave absorber, and (2) such an FSS pattern has an effective limit luminance LL _ef that forms a limit luminance line A _i. Less than brightness, cannot be perceived,
Represents.

The “selected area” SA _i will be specifically described with reference to FIG. FIG. 11 shows a diagram in which the horizontal axis is expanded to a range of 0 to 0.4 mm and the vertical axis is expanded to a range of 0 to 30 mm in FIG. Reference numerals in the figure such as A1, A2, P1, P2, etc. are the same as those in the case of FIG.

In FIG. 11, a portion surrounded by a thick line indicates a selection region SA1 in the luminance of effective limit luminance LL _ef ≦ 100 cd / m ² . That is, an FSS pattern having (g, L) pairs included in the selected area SA1 cannot be perceived at a luminance of less than 100 cd / m ² . Similarly, in FIG. 11, the hatched portion indicates the selected area SA2 in the luminance of the effective limit luminance LL _ef ≦ 1000 cd / m ² . Therefore, an FSS pattern having (g, L) pairs included in the selected area SA2 cannot be perceived at a luminance of less than 1000 cd / m ² .

Note that, as described above, the selection area SA2 indicated by hatching is a selection area even for the luminance of the effective limit luminance LL _ef > 1000 cd / m ² . That is, the FSS pattern having the (g, L) group included in the selected area SA2 cannot be visually recognized at any luminance.

Although not essential to the invention, the selection area may be further restricted to a region satisfying the gap g ≧ g _p. Here g _p, for example, such as the minimum feature size of the pattern processing techniques, the minimum value of the gap g defined by external factors.

FIG 12, in a case in which such a gap g ≧ _{g p} as a condition, the effective limit brightness _{LL ef} ≦ 100cd / ^{m 2} selection in the luminance region SA1 '(area in the thick line in the figure), the effective limit The selection area SA2 ′ (the hatched area in the figure) in the luminance of luminance LL _ef ≦ 1000 cd / m ² is shown.

(Step S430)
Next, in step S430, to be included in the selection region SA _i described above, the length L and gap g of the conductive elements of the FSS pattern is set. As described above, when the configuration of the FSS pattern is included in the selection area SA _i , this means that it cannot be perceived at a luminance less than the effective limit luminance LL _ef that forms the limit luminance line A _i . Therefore, this operation makes it possible to obtain a transparent and inconspicuous FSS pattern at a specific luminance (effective limit luminance).

As described above, in the present invention, by using the map showing the selected area SA _i (or SA _i ′) as shown in FIG. 11 (or FIG. 12), the target is obtained at a specific luminance (effective limit luminance). It is possible to easily determine whether the FSS pattern is perceived by the human eye. Therefore, by using the method of the present invention, it is possible to easily design or form a “transparent and inconspicuous” FSS pattern.

In the above description, in step (III), a map is formed on the two-dimensional coordinates in which the horizontal axis is represented by the gap g between the conductive elements and the vertical axis is represented by the length L of the conductive elements. An example was described. However, in the two-dimensional coordinates created in step (III), the vertical axis may be represented by the gap g between the conductive elements, and the horizontal axis may be represented by the length L of the conductive elements. In this case, the selected area SA _i defined in the step (IV) is an area below the limit luminance line A _i among the areas surrounded by the range P and the limit luminance line A _i .

  Further, in the above description, taking the FSS pattern 128N having a repeating arrangement of the conductive elements 126N as shown in FIG. 5 as an example, the length L of the conductive element that can provide a transparent and inconspicuous FSS pattern 128N, and the conductive The gap g between the elements has been described. However, the method of the present invention can also be applied to sequences other than the repetitive sequences shown in FIG.

  FIG. 13 shows an FSS pattern 228N having a repeating arrangement of conductive elements different from FIG. In the example of this figure, each conductive element 226N is separated by an intermediate portion 224N including two slits 221N, and the intermediate portion 224N includes another conductive element 229N between the two slits 221N. Including. The length of the conductive element 226N is L, the width of the slit 221N is g, and the length of the intermediate portion 224N is D (therefore, the width of the short side of another conductive element 229N is D-2g).

  The FSS pattern 228N having such a repetitive arrangement can also be evaluated in the same procedure as the FSS pattern 128N described above. However, the length of the short side of another conductive element 229N needs to be expressed using L and g. Here, by fixing the length ratio L / D to 3, the length of the short side of 229N is obtained by L / 3-2g. Similar to the FSS pattern 128N, pattern information defined by an angle can be obtained using this arrangement information, and contrast information and spectrum information can be obtained by the same method, and a similar evaluation can be performed.

  One skilled in the art can readily appreciate that this approach is also applicable to FSS patterns with other repeating sequences. For example, the length ratio L / D may not be three. Moreover, the number of the slits to be separated may be three or more. That is, in the present invention, if the shape element of the FSS pattern is uniquely determined using the parameters (L, g) and the spectrum information Sf is obtained, the same evaluation can be performed. Furthermore, the dimension of the parameter space (that is, the number of parameters) of the present method is not limited to 2, and may be 3 or more.

  Note that the analysis using the method according to the present invention as described above is carried out focusing on a one-dimensional array of FSS patterns. Therefore, when designing an actual FSS pattern, the above-described steps are also performed on a one-dimensional array of FSS patterns in another direction (for example, the Y direction in FIG. 5). From the analysis results obtained with both one-dimensional arrays, a two-dimensional array of transparent and inconspicuous FSS patterns (that is, the length of the conductive element and the width of the gap) is finally determined. However, if each conductive element 126N has a square shape and the gap 130N between the conductive elements is equal in the horizontal direction (X direction in FIG. 5) and the vertical direction (Y direction in FIG. 5), one analysis is omitted. It will be apparent to those skilled in the art that this is possible.

(Transparent wave absorber)
In another aspect of the present invention, a transparent wave absorber comprising an absorption layer having a transparent and inconspicuous FSS pattern is provided.

  FIG. 14 shows a schematic cross-sectional view of a transparent radio wave absorber according to the present invention. The radio wave absorber according to the present invention basically has the same configuration as that of the conventional absorption layer 110 shown in FIG. Therefore, in FIG. 14, members corresponding to those in FIG. 1 are denoted by reference numerals with “N” added to the reference numerals in FIG. 1. For example, the radio wave absorber according to the present invention is represented by 100N, the absorption layer according to the present invention is represented by 110N, the reflective layer is represented by 140N, and the spacer is represented by 170N. The transparent wave absorber 100N according to the present invention is different from the conventional transparent wave absorber 100 in that the arrangement pattern of the conductive elements of the FSS 125N is transparent and inconspicuous.

  It can be confirmed by the following evaluation method that the transparent wave absorber 100N according to the present invention has a transparent and inconspicuous FSS pattern.

(Evaluation methods)
(AI) The array Gr in one dimension (direction) of the FSS pattern is converted into the FSS pattern Ga defined by the angle by the following formula (14) with the viewing distance d = 500 mm.

ここで、対象次元における導電性素子の寸法をＬとし、導電性素子間の隙間の寸法をｇとする。

Here, the dimension of the conductive element in the target dimension is L, and the dimension of the gap between the conductive elements is g.

  Next, the Michelson contrast value MC represented by the following formula (15) is calculated from the transmittance Ti of the gap portion and the transmittance Tc of the conductive element.

次に、前記ＦＳＳパターンＧａに、前記マイケルソンコントラスト値ＭＣを乗じ、ＦＳＳパターンの対象次元における配列から得られるコントラスト情報Ｇｆを算出する。

Next, the FSS pattern Ga is multiplied by the Michelson contrast value MC to calculate contrast information Gf obtained from an array in the target dimension of the FSS pattern.

  Further, after the Fourier transform process is performed on the contrast information Gf, a process for obtaining an MTF response represented by the following equation (16) is performed on the obtained spectrum information Sf to obtain an MTF response signal.

さらに得られたＭＴＦ応答信号を逆数化することにより、ＦＳＳパターンについての、空間周波数ｆに対するＲＣプロット群を得る。
（Ａ−ＩＩ）視野角をｗとし、輝度をＬｋとしたとき、以下の式（１７）で表されるコントラスト感度関数ＣＳＦを用いて、

Further, by reciprocalizing the obtained MTF response signal, an RC plot group with respect to the spatial frequency f for the FSS pattern is obtained.
(A-II) When the viewing angle is w and the luminance is Lk, the contrast sensitivity function CSF represented by the following equation (17) is used.

視野角ｗ＝２０゜として、（Ａ−Ｉ）で得られたＲＣプロット群に一致するコントラスト感度関数ＣＳＦが得られるような限界輝度ＬＬ_ｅｆを算出する。この際には、ＲＣプロット群を構成する各プロット毎に限界輝度ＬＬ_ｉを算出し、算出された各限界輝度ＬＬ_ｉを用いて、以下の式（１８）
から、実効限界輝度ＬＬ_ｅｆを算出する。

With the viewing angle w = 20 °, the limit luminance LL _ef is calculated so that a contrast sensitivity function CSF that matches the RC plot group obtained in (AI) can be obtained. At this time, the limit luminance LL _i is calculated for each plot constituting the RC plot group, and the following formula (18) is used by using the calculated limit luminance LL _i.
From the above, the effective limit luminance LL _ef is calculated.

（Ａ−ＩＩＩ）同様の評価を、前記一つの次元と直交する別の次元についても実施する。さらに、両次元において得られた実効限界輝度ＬＬ_ｅｆが、いずれも判断基準ＬＬ_ｅｆ≧１０００ｃｄ／ｍ^２を満足するかどうかを評価する。

(A-III) The same evaluation is performed for another dimension orthogonal to the one dimension. Furthermore, it is evaluated whether or not the effective limit luminance LL _ef obtained in both dimensions satisfies the judgment criterion LL _ef ≧ 1000 cd / m ² .

As a result, when any effective limit luminance LL _ef satisfies the determination criterion, an FSS pattern that is not perceived, or an FSS pattern that is not perceived at virtually any luminance is formed in an environment with a luminance of 1000 cd / m ² or less. Can be judged.

  Thus, in the present invention, a transparent radio wave absorber 100N having a transparent and inconspicuous FSS pattern is obtained, and this prevents the aesthetic appearance of the transparent radio wave absorber 100N from being impaired.

  Examples of the present invention will be described below.

Example 1
The FSS pattern selection area was actually calculated by the following processes 1 to 3.

(1. Creation of a map showing the limit luminance line)
A limit luminance line map was created using a computer program capable of automatically calculating steps (I) to (III) of the method according to the present invention. FIG. 15 shows a calculation chart of the computer program used when creating such a map. Hereinafter, a method of creating a map of the limit luminance line will be described with reference to this computer program chart.

First, in step S1510, parameters for calculation are input. The specific parameters are the initial value (g ₀ , L ₀ ) of the combination of the dimension L of the conductive element and the dimension g of the gap between the conductive elements in the FSS pattern, Michelson contrast value MC, viewing distance d, and field of view. The angle w. In addition, a certain value LL ₀ (for example, LL ₀ = 1 cd / m ² ) is input as an initial value of luminance.

In this embodiment, the Michelson contrast value MC = 0.1, the viewing distance d = 500 mm, and the viewing angle w = 20 °. Moreover, the form of the FSS pattern, employing the pattern of FIG. _5, and a _{(g 0, L 0) =} (0.05mm, 6mm).

Next, in step S1520, an initial value of the contrast sensitivity function CSF is calculated using the viewing angle w and LL ₀ among the input parameters described above.

  Next, in step S1530, the pattern information Gr relating to the length is converted into the pattern information Ga relating to the angle by the above-described equation (9).

  Next, in Step S1540, the amplitude of the contrast signal of the pattern information Ga (that is, contrast information Gf) is calculated using the input Michelson contrast value MC.

  Next, in step S1550, the obtained contrast information Gf is subjected to Fourier transform processing, and spectrum information Sf is calculated.

  Next, in step S1560, an MTF response signal for the spectrum information Sf is calculated.

  Next, in step S1570, the reciprocal of the obtained MTF response signal is calculated, and an RC plot group is obtained.

Next, in step S1580~ step S1610, for each spectrum i of the resulting RC plot group, is adjusted brightness so that the contrast sensitivity function CSF is closest and RC _i at the frequency _{f i,} consequently limits Luminance LL _i is calculated. At this time, the luminance is first adjusted so that the difference between the RC value (RC ₁ ) of the _first spectrum and the contrast sensitivity function is minimized (step S1580), and the limit luminance LL ₁ at that time is calculated (step S1580). Step S1590). Similarly, the luminance is adjusted so that the difference between the RC values (RC _{2 to} RC _n ) of the second and subsequent spectra and the contrast sensitivity function is minimized, and the limit luminances LL _{2 to} LL _{n at} that time are calculated. .

Thereafter, when the limiting luminance is acquired for all the spectra of the RC plot group, the process proceeds to step S1620 by the determination step of step S1610. In step S1620, the effective limit luminance LL _ef is calculated from each limit luminance LL _i acquired in the previous step using the above-described equation (13).

  Such processing was performed for each (g, L) group. In this example, the range of g was 0.05 mm <g ≦ 1.0 mm, and the range of L was 6 mm <L ≦ 60 mm.

(2. Creating a map)
Next, a map showing the limit luminance line A _i was created by connecting lines where the effective limit luminance LL _ef is equal in the coordinates where the horizontal axis is the gap g and the vertical axis is the dimension L of the conductive element. The limit luminance line is shown for the case where the effective limit luminance LL _ef is 100 cd / m ² and 1000 cd / m ² .

(3. Calculation of selected areas)
Next, the range P of the FSS pattern in which the transparent radio wave absorber operates properly is displayed on the above-described map, and the selected area SA _i is obtained. The range P was an area where the absorption amount of the transparent radio wave absorber was 10 dB or more.

FIG. 16 shows the selected area SA obtained in the first embodiment. In FIG. 16, A1 is a limit brightness line when the effective limit brightness LL _ef is 100 cd / m ² , and A2 is a limit brightness line when the effective limit brightness LL _ef is 1000 cd / m ² . A region between P1 and P2 corresponds to the range P. Therefore, the area surrounded by the thick frame corresponds to the selected area SA1 in the environment where the effective limit luminance LL _ef is 100 cd / m ² , and the FSS pattern included in this area is in the environment where the luminance is 100 cd / m ² or less. Can't perceive. A region surrounded by diagonal lines corresponds to the selected region SA2 in an environment where the effective limit luminance LL _ef is 1000 cd / m ² , and when the FSS pattern is included in this region, the FSS is practically at any luminance. It can be said that the pattern cannot be perceived.

(Example 2)
By the same processing as in Example 1, the selection region of the FSS pattern under another condition was calculated. In this example, Michelson contrast value MC = 0.1, viewing distance d = 500 mm, and viewing angle w = 30 ° were adopted as input parameters. Other conditions are the same as those in the first embodiment.

FIG. 17 shows the selection areas SA1 and SA2 obtained in the second embodiment. In Example 2, g _p = 0.05 mm, and the selection region was calculated by adding the condition of g ≧ g _p .

(Example 3)
By the same processing as in Example 1, the selection region of the FSS pattern under another condition was calculated. In this example, Michelson contrast value MC = 0.1, viewing distance d = 1000 mm, and viewing angle w = 20 ° were adopted as input parameters. Other conditions are the same as those in the first embodiment.

FIG. 18 shows selection areas SA1 and SA2 obtained in the third embodiment. In Example 3, the selected region was calculated by setting g _p = 0.05 mm and adding the condition of g ≧ g _p .

Example 4
By the same processing as in Example 1, the selection region of the FSS pattern under another condition was calculated. In this example, Michelson contrast value MC = 0.1, viewing distance d = 1500 mm, and viewing angle w = 20 ° were adopted as input parameters. Other conditions are the same as those in the first embodiment.

FIG. 19 shows selection areas SA1 and SA2 obtained in the fourth embodiment. In Example 4, the selected region was calculated by setting g _p = 0.05 mm and adding the condition of g ≧ g _p .

(Example 5)
By the same processing as in Example 1, the selection region of the FSS pattern under another condition was calculated. In this example, Michelson contrast value MC = 0.125, viewing distance d = 500 mm, and viewing angle w = 20 ° were adopted as input parameters. Other conditions are the same as those in the first embodiment.

FIG. 20 shows selected areas SA1 and SA2 obtained in the fifth embodiment. In Example 5, g _p = 0.05 mm, and the condition of g ≧ g _p was added to calculate the selected region.

(Example 6)
By the same processing as in Example 1, the selection region of the FSS pattern under another condition was calculated. In this example, Michelson contrast value MC = 0.125, viewing distance d = 1000 mm, and viewing angle w = 20 ° were adopted as input parameters. Other conditions are the same as those in the first embodiment.

FIG. 12 described above shows the selection areas SA1 and SA2 obtained in the sixth embodiment. In Example 6, the selected region was calculated by setting g _p = 0.05 mm and adding the condition of g ≧ g _p .

(Example 7)
By the same processing as in Example 1, the selection region of the FSS pattern under another condition was calculated. In this example, Michelson contrast value MC = 0.125, viewing distance d = 1000 mm, and viewing angle w = 30 ° were adopted as input parameters. Other conditions are the same as those in the first embodiment.

FIG. 21 shows selected areas SA1 and SA2 obtained in the seventh embodiment. In Example 7, the selected region was calculated by setting g _p = 0.05 mm and adding the condition of g ≧ g _p .

(Example 8)
By the same processing as in Example 1, the selection region of the FSS pattern under another condition was calculated. In this example, Michelson contrast value MC = 0.125, viewing distance d = 1500 mm, and viewing angle w = 20 ° were adopted as input parameters. Other conditions are the same as those in the first embodiment.

FIG. 22 shows selected areas SA1 and SA2 obtained in the eighth embodiment. In Example 8, g _p = 0.05 mm, and the condition of g ≧ g _p was added to calculate the selected region.

Example 9
By the same processing as in Example 1, the selection region of the FSS pattern under another condition was calculated. In this example, Michelson contrast value MC = 0.15, viewing distance d = 500 mm, and viewing angle w = 20 ° were adopted as input parameters. Other conditions are the same as those in the first embodiment.

FIG. 23 shows selection areas SA1 and SA2 obtained in the ninth embodiment. In Example 9, the selected region was calculated by setting g _p = 0.05 mm and adding the condition of g ≧ g _p .

(Example 10)
By the same processing as in Example 1, the selection region of the FSS pattern under another condition was calculated. In this example, Michelson contrast value MC = 0.15, viewing distance d = 1000 mm, and viewing angle w = 20 ° were adopted as input parameters. Other conditions are the same as those in the first embodiment.

FIG. 24 shows selection areas SA1 and SA2 obtained in the tenth embodiment. In Example 10, g _p = 0.05 mm and the condition of g ≧ g _p was added to calculate the selected region.

(Example 11)
By the same processing as in Example 1, the selection region of the FSS pattern under another condition was calculated. In this example, Michelson contrast value MC = 0.15, viewing distance d = 1500 mm, and viewing angle w = 20 ° were adopted as input parameters. Other conditions are the same as those in the first embodiment.

FIG. 25 shows selection areas SA1 and SA2 obtained in the eleventh embodiment. In Example 11, g _p = 0.05 mm and the condition of g ≧ g _p was added to calculate the selected region.

Example 12
By the same processing as in Example 1, the selection region of the FSS pattern under another condition was calculated. However, in this example, the pattern of FIG. 13 was adopted as the form of the FSS pattern. For this reason, the ratio (L / D) of the length L of one side of the conductive element to the width D of the intermediate portion is fixed to 3, and the width M of the second conductive element is
M = L / 3-2g
The same processing as described above was performed. The initial value (g ₀ , L ₀ ) was set to (0.05 mm, 9 mm). Also, Michelson contrast value MC = 0.1, viewing distance d = 500 mm, and viewing angle w = 20 ° were adopted as input parameters. Other conditions are the same as those in the first embodiment.

FIG. 26 shows the selection areas SA1 and SA2 obtained in the twelfth embodiment. In Example 12, the selected region was calculated by setting g _p = 0.05 mm and adding the condition of g ≧ g _p .

At this time, the upper broken line P1 is a curve approximated by the following equation:

Y = 62.0 * X ^0.45 (Y1)

The lower broken line P2 is a curve approximated by the following formula:

Y = 34.0 * X ^0.46 (Y2)

The distance between the reflective layer and the absorbing layer was 25.0 mm, and the sheet resistance was 100Ω.

(Example 13)
By the same processing as in Example 12, the selection region of the FSS pattern under another condition was calculated. However, in this example, Michelson contrast value MC = 0.1, viewing distance d = 500 mm, and viewing angle w = 30 ° were adopted as input parameters. Other conditions are the same as in Example 12.

  FIG. 27 shows the selection areas SA1 and SA2 obtained in the present Example 13.

(Example 14)
By the same processing as in Example 12, the selection region of the FSS pattern under another condition was calculated. However, in this example, Michelson contrast value MC = 0.1, viewing distance d = 1000 mm, and viewing angle w = 20 ° were adopted as input parameters. Other conditions are the same as in Example 12.

  FIG. 28 shows the selection areas SA1 and SA2 obtained in the fourteenth embodiment.

(Example 15)
By the same processing as in Example 12, the selection region of the FSS pattern under another condition was calculated. However, in this example, Michelson contrast value MC = 0.1, viewing distance d = 1500 mm, and viewing angle w = 20 ° were adopted as input parameters. Other conditions are the same as in Example 12.

  FIG. 29 shows the selection areas SA1 and SA2 obtained in the fifteenth embodiment.

(Example 16)
By the same processing as in Example 12, the selection region of the FSS pattern under another condition was calculated. However, in this example, Michelson contrast value MC = 0.125, viewing distance d = 500 mm, and viewing angle w = 20 ° were adopted as input parameters. Other conditions are the same as in Example 12.

  FIG. 30 shows selection areas SA1 and SA2 obtained in the sixteenth embodiment.

(Example 17)
By the same processing as in Example 12, the selection region of the FSS pattern under another condition was calculated. However, in this example, Michelson contrast value MC = 0.125, viewing distance d = 1000 mm, and viewing angle w = 20 ° were adopted as input parameters. Other conditions are the same as in Example 12.

  FIG. 31 shows the selection areas SA1 and SA2 obtained in the seventeenth embodiment.

(Example 18)
By the same processing as in Example 12, the selection region of the FSS pattern under another condition was calculated. However, in this example, Michelson contrast value MC = 0.125, viewing distance d = 1000 mm, and viewing angle w = 30 ° were adopted as input parameters. Other conditions are the same as in Example 12.

  FIG. 32 shows selection areas SA1 and SA2 obtained in the eighteenth embodiment.

(Example 19)
By the same processing as in Example 12, the selection region of the FSS pattern under another condition was calculated. However, in this example, Michelson contrast value MC = 0.125, viewing distance d = 1500 mm, and viewing angle w = 20 ° were adopted as input parameters. Other conditions are the same as in Example 12.

  FIG. 33 shows selection areas SA1 and SA2 obtained in the nineteenth embodiment.

(Example 20)
By the same processing as in Example 12, the selection region of the FSS pattern under another condition was calculated. However, in this example, Michelson contrast value MC = 0.15, viewing distance d = 500 mm, and viewing angle w = 20 ° were adopted as input parameters. Other conditions are the same as in Example 12.

  FIG. 34 shows the selection areas SA1 and SA2 obtained in the present Example 20.

(Example 21)
By the same processing as in Example 12, the selection region of the FSS pattern under another condition was calculated. However, in this example, Michelson contrast value MC = 0.15, viewing distance d = 1000 mm, and viewing angle w = 20 ° were adopted as input parameters. Other conditions are the same as in Example 12.

  FIG. 35 shows the selection areas SA1 and SA2 obtained in Example 21.

(Example 22)
By the same processing as in Example 12, the selection region of the FSS pattern under another condition was calculated. However, in this example, Michelson contrast value MC = 0.15, viewing distance d = 1500 mm, and viewing angle w = 20 ° were adopted as input parameters. Other conditions are the same as in Example 12.

  FIG. 36 shows the selection areas SA1 and SA2 obtained in the present Example 22.

  Table 1 summarizes the types of FSS patterns (FIG. 5 or FIG. 13), parameter values, and obtained drawings that were used in obtaining the selected region in each example.

  The present invention can be applied to a transparent radio wave absorber, particularly a transparent radio wave absorber FSS structure.

It is an example of typical sectional drawing of the conventional transparent electromagnetic wave absorber. It is an example of the top view of the absorption layer of the conventional transparent electromagnetic wave absorber. It is a conceptual diagram explaining the spatial frequency f. FIG. 5 is a flow diagram illustrating an example of a method for obtaining a transparent and inconspicuous FSS pattern according to the present invention. It is an example of the top view of the absorption layer of the electromagnetic wave absorber by this invention. It is a figure showing an example of spectrum information Sf obtained after Fourier transform of contrast information Gf. It is the figure which showed the result of having calculated | required the MTF response of the FSS pattern based on the spectrum information Sf shown in FIG. It is the graph which overlapped and showed one RC plot group and the contrast sensitivity function CSF in various brightness | luminances. It is an example of the map which showed the limit luminance line _Ai . It is the figure which showed the area | region where the absorption amount of a radio wave absorber becomes 10 dB on the map of FIG. It is the graph which expanded the horizontal axis and the vertical axis | shaft of FIG. In the graph of FIG. 10 is a diagram showing a selected region plus the conditions of g ≧ g _p. It is the top view which showed another structure of the FSS pattern. It is sectional drawing which showed typically an example of the transparent electromagnetic wave absorber by this invention. 6 is a flowchart used when creating a map of limit luminance lines in Example 1. FIG. 3 is a diagram showing a selection region obtained in Example 1. It is the figure which showed the selection area | region obtained in Example 2. FIG. It is the figure which showed the selection area | region obtained in Example 3. FIG. It is the figure which showed the selection area | region obtained in Example 4. FIG. It is the figure which showed the selection area | region obtained in Example 5. FIG. It is the figure which showed the selection area | region obtained in Example 7. FIG. It is the figure which showed the selection area | region obtained in Example 8. FIG. It is the figure which showed the selection area | region obtained in Example 9. FIG. It is the figure which showed the selection area | region obtained in Example 10. FIG. It is the figure which showed the selection area | region obtained in Example 11. FIG. It is the figure which showed the selection area | region obtained in Example 12. FIG. It is the figure which showed the selection area | region obtained in Example 13. FIG. It is the figure which showed the selection area | region obtained in Example 14. FIG. It is the figure which showed the selection area | region obtained in Example 15. FIG. It is the figure which showed the selection area | region obtained in Example 16. FIG. It is the figure which showed the selection area | region obtained in Example 17. FIG. It is the figure which showed the selection area | region obtained in Example 18. FIG. It is the figure which showed the selection area | region obtained in Example 19. FIG. It is the figure which showed the selection area | region obtained in Example 20. FIG. It is the figure which showed the selection area | region obtained in Example 21. FIG. It is the figure which showed the selection area | region obtained in Example 22. FIG.

Explanation of symbols

1 Screen 2 Human Eye 100 Conventional Transparent Wave Absorber 100N Transparent Wave Absorber 110, 110N Absorption Layer 120, 120N First Transparent Substrate 125, 125N FSS of the Present Invention
126, 126N conductive element 128, 128N FSS pattern 130, 130N gap 135 protective layer 140 reflective layer 145 reflective film 150 second transparent substrate 160 space 170 spacer 221N slit 224N intermediate portion 226N conductive element 228N FSS pattern 229N another conductive Sex element.

Claims (15)

In a FSS for a transparent radio wave absorber having a two-dimensional repeating pattern of conductive elements arranged on a transparent substrate, a method of determining a dimension L of the conductive elements and a dimension g of a gap between the conductive elements in one direction. There,
The method is
(I) A step of digitizing a one-dimensional array of a certain FSS pattern along the one direction as a reciprocal of contrast with respect to a spatial frequency f,
(I-1) obtaining the contrast information Gf from the one-dimensional array of the FSS pattern, with the viewing distance d, the transmittance Ti of the gap portion, and the transmittance Tc of the conductive element as fixed values;
(I-2) Step of performing Fourier transform processing on the contrast information Gf to obtain spectral information Sf;
(I-3) Performing a process for obtaining an MTF response represented by the following expression (1) on the spectrum information Sf to obtain an MTF response signal; and

(I-4) obtaining an RC plot group with respect to the spatial frequency f by reciprocalizing the MTF response signal;
A process comprising:
(II) When the viewing angle is w and the luminance is Lk, the contrast sensitivity function CSF represented by the following formula (2) is used.

A step of calculating a limiting luminance such that a contrast sensitivity function CSF matching the RC plot group obtained in (I) is obtained,
(II-1) A step of calculating a limit luminance LL _i for each plot constituting the RC plot group with a viewing angle w as a fixed value, and (II-2) using each calculated luminance LL _i , The following formula (3)

A step of calculating an effective limit luminance LL _ef from
A process comprising:
(III) At least one limit luminance line A _i connecting plots of the same luminance LL _ef on a two-dimensional coordinate with the dimension g of the gap as the horizontal axis and the dimension L of the conductive element as the vertical axis. The process of creating a map showing
The step (I) and the step (II) are performed on various FSS patterns having different dimensions L of the conductive elements and dimensions g of the gaps between the conductive elements, thereby creating the map. ,
(IV) determining the dimension L of the conductive element and the dimension g of the gap between the conductive elements from the map,
(IV-1) displaying a range P of the FSS pattern in which the transparent wave absorber properly operates on the map;
(IV-2) of the limit brightness lines A _i and the range surrounded by the P region, said step defining a left region as selected areas than the limit luminance lines A _i, and (IV-3) obtained Determining a dimension L of the conductive element and a dimension g of a gap between the conductive elements so as to be included in at least one of the selected regions;
A process comprising:
A method characterized by comprising: The step of obtaining the contrast information Gf from the one-dimensional array of the FSS pattern includes:
Converting a one-dimensional array of the FSS pattern from the viewing distance d into an FSS pattern Ga defined by an angle;
Calculating a Michelson contrast value MC represented by the following formula (4) from the transmittance Ti of the gap portion and the transmittance Tc of the conductive element;

Multiplying the FSS pattern Ga by the Michelson contrast value MC;
The method according to claim 1, wherein the method is calculated by:   The method according to claim 2, wherein the Michelson contrast value MC is in the range of 0.08 to 0.15.   The method according to any one of claims 1 to 3, wherein the selected region is a region where a dimension g of the gap satisfies g ≧ 0.05 mm.   5. The FSS pattern range P in which the transparent radio wave absorber operates properly includes the FSS pattern range when the absorption amount of the transparent radio wave absorber is 10 dB or more. 6. The method as described in one.   The transmittance Ti of the gap portion is in the range of 0.85 to 0.90, and the transmittance Tc of the conductive element is in the range of 0.65 to 0.82. The method according to any one of 1 to 5.   The method according to claim 1, wherein the viewing distance d is in the range of 500 mm to 1500 mm.   The method according to claim 1, wherein the viewing angle w is in a range of 20 ° to 30 °. The method according to claim 1, wherein the limit luminance line A _i is a limit luminance line when the effective limit luminance LL _ef is 100 cd / m ² or more.   The said FSS pattern is comprised by the two-dimensional repeating pattern of the electroconductive element whose length of one side is L, and the slit which has the width | variety g, The one of Claim 1 thru | or 9 characterized by the above-mentioned. Method. The FSS pattern is composed of a two-dimensional repeating pattern of a conductive element having a side length of L and an intermediate portion having a width of D,
The intermediate portion is composed of two slits each having a width g, and a second conductive element sandwiched between the two slits,
In the steps (I) to (IV), when the ratio (L / D) between the length L of one side of the conductive element and the width D of the intermediate portion is a fixed value k, the second conductive element The width M of
M = L / k-2g
The method according to claim 1, wherein a similar operation is carried out. The conductive element has a rectangular shape,
12. The method according to claim 1, wherein the steps (I) to (IV) are repeated for a one-dimensional array along another direction perpendicular to the one direction. Method.   The method according to claim 1, wherein the conductive element has a square shape. A transparent wave absorber comprising an FSS having a two-dimensional repeating pattern of conductive elements disposed on a transparent substrate,
When the FSS pattern is determined by the evaluation methods shown in the following (I) to (III), the transparent radio wave absorber that satisfies the determination criteria shown in (IV):
(Evaluation method)
(I) The FSS pattern Ga defined by an angle is defined with an arrangement in one dimension of the FSS pattern, where the dimension of the conductive element is L, the dimension of the gap between the conductive elements is g, and the viewing distance is d = 500 mm. Converted,
From the transmittance Ti of the gap portion and the transmittance Tc of the conductive element, a Michelson contrast value MC represented by the following formula (5) is calculated,

Multiplying the FSS pattern Ga by the Michelson contrast value MC,
Thereby, the contrast information Gf obtained from the array in the one dimension of the FSS pattern is calculated,
After performing the Fourier transform process on the contrast information Gf, the obtained spectrum information Sf is subjected to a process for obtaining an MTF response represented by the following formula (6) to obtain an MTF response signal,

Further, the obtained MTF response signal is inversed to obtain an RC plot group with respect to the spatial frequency f for the FSS pattern.
(II) When the viewing angle is w and the luminance is Lk, the contrast sensitivity function CSF represented by the following formula (7) is used.

With the viewing angle w = 20 °, a limit luminance LL is calculated so that a contrast sensitivity function CSF that matches the RC plot group obtained in (I) is obtained;
The limit luminance LL _i is calculated for each plot constituting the RC plot group,
Using each calculated limit luminance LL _i , the following equation (8)

From the above, the effective limit luminance LL _ef is calculated.
(III) The same evaluation is performed for another dimension orthogonal to the one dimension.
(IV) It is evaluated whether or not the obtained effective limit luminance LL _ef in both dimensions satisfies the judgment criterion LL _ef ≧ 1000 cd / m ² . An electromagnetic wave absorber comprising a plurality of conductive elements provided on a transparent substrate with a predetermined length L and a gap g in a predetermined direction,
The length L and the interval g are in coordinates with the length L as the vertical axis and the interval g as the horizontal axis.
A lower limit line indicating a lower limit value of desired electromagnetic wave absorption;
An upper limit line indicating the upper limit of desired electromagnetic wave absorption;
A limit brightness line connecting the desired limit brightness values;
An electromagnetic wave absorber characterized by having a value within a range surrounded by.

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