NEAR-FIELD ELECTROMAGNETIC WAVE ABSORBER

Abstract

An absorber for electromagnetic waves in the near field, comprising at least one plastic film (10) and two linearly scratched thin metal films (11a, 11b), wherein each of the linearly scratched thin metal films (11a, 11b) has a large number of substantially parallel, intermittent, linear scratches (12a, 12b) with irregular widths and spacings in several directions, wherein one linearly scratched thin metal film (11a) has a surface resistivity of 150-300 Ω / square and the other linearly scratched thin metal film (11b) has a surface resistivity of 10-50 Ω / square.

Description

AREA OF INVENTION

[0001] The present invention relates to a near-field electromagnetic wave absorber that has a high absorption capacity for conduction noise and radiation noise in a wide frequency range from less than 1 GHz to the high single-digit GHz range, which can be used without grounding because there are essentially no frequencies at which radiation noise is maximized, and which exhibits only slight variations in noise absorption capacity between different production batches. BACKGROUND OF THE INVENTION

[0002] To prevent malfunctions and other issues caused by electromagnetic noise emanating from electronic devices in various electronic equipment and communication terminals, various electromagnetic wave absorbers have been used in practice. In this context, the inventor, in Japanese patent JP 4 685 977 B2, proposed a linearly scratched thin metal-film-plastic composite film with reduced anisotropy of electromagnetic wave absorption. This film comprises a plastic film and a single- or multi-layered thin metal film formed on at least one surface of the plastic film. The thin metal film is provided with a large number of substantially parallel, intermittent, linear scratches of irregular widths and spacing in multiple directions.Japanese patent JP 4 685 977 B2 describes how a combination of two linearly scratched thin metal foil-plastic composite films with different intersection angles of the linear scratches can efficiently absorb both electric and magnetic fields with reduced anisotropy of absorption capacity for electromagnetic waves, provided one composite film has a surface resistance of 20-377 Ω / square and the other a surface resistance of 377-10,000 Ω / square. However, Japanese patent JP 4 685 977 B2 does not include an example combining two linearly scratched thin metal foil-plastic composite films with different surface resistances and thus different degrees of linear scratch formation.

[0003] When multiple batches of thin metal foil-plastic composite films with the same surface resistivity are produced, and two thin metal foil-plastic composite films, arbitrarily selected from different batches, are laminated to create a near-field electromagnetic wave absorber, good absorption of radiation noise may not be achieved across a wide frequency range, depending on their combination. This appears to be due to the fact that (a) the thin metal foils in the linearly scratched thin metal foil-plastic composite films are extremely thin, and (b) the linear scratches are also extremely small, resulting in large inconsistencies depending on the actual production conditions, which in turn leads to large inconsistencies in product performance between production batches.

[0004] Japanese patent JP 5 203 295 B2 discloses an electromagnetic wave-absorbing film obtained by laminating a magnetic composite film comprising a magnetic thin metal film formed on at least one surface of a plastic film with a non-magnetic composite film comprising a non-magnetic thin metal film formed on at least one surface of a plastic film, wherein at least one of the magnetic thin metal film and the non-magnetic thin metal film is provided with a large number of substantially parallel, intermittent, linear scratches having irregular widths and spacings in at least one direction, wherein the linear scratches have an average width of 1-100 µm and an average spacing of 1-100 µm, wherein 90% or more of the linear scratches have widths in the range of 0.1-1,000 µm.Japanese patent JP 5 203 295 B2 describes electromagnetic wave absorbing films comprising a magnetic thin metal film with a surface resistance of 1 to 377 Ω / square and a non-magnetic thin metal film with a surface resistance of 377 to 10,000 Ω / square, exhibiting excellent absorption capacity for near-field electromagnetic wave noise.

[0005] However, it has been found that the electromagnetic wave noise absorbed in Japanese patent JP 5 203 295 B2 is so-called line noise, and that, with respect to radiation noise, it is maximized over a wide frequency range from less than 1 GHz to high single-digit GHz frequencies. Intensive research has shown that the surface resistance of 1–377 Ω / square in the linearly scratched magnetic composite film and the surface resistance of 377–10,000 Ω / square in the linearly scratched non-magnetic composite film are not well balanced, making it impossible to prevent the maximization of radiation noise over a wide frequency range. In example 1 of Japanese patent JP 5 203 295 B2, the surface resistance of the linearly scratched magnetic composite film is 30 Ω / square, while the surface resistance of the linearly scratched non-magnetic composite film is 6,000 Ω / square too high.Therefore, a ground (GND) should be connected to prevent the maximized noise from escaping when this electromagnetic wave absorbing film is used in practice for near-field noise absorption.

[0006] WO 2012 / 090586 A1 discloses a near-field electromagnetic wave absorber obtained by bonding several electromagnetic wave absorbing films, each comprising a thin metal film formed on a surface of a plastic film, wherein at least one electromagnetic wave absorbing film has a thin magnetic metal film and the thin magnetic metal film of at least one electromagnetic wave absorbing film is provided with a large number of substantially parallel, intermittent, linear scratches with irregular widths and spacings in several directions.WO 2012 / 090586 A1 describes that the linearly scratched thin metal film of each electromagnetic wave absorbing foil has a surface resistance in the range of 50-1500 Ω / square and that the near-field electromagnetic wave absorber exhibits excellent transmission noise absorption over a wide frequency range from less than 1 GHz to the high single-digit GHz range. However, it has been found that the near-field electromagnetic wave absorber described in WO 2012 / 090586 A1 has frequencies at which radiation noise is maximized. Therefore, when this near-field electromagnetic wave absorber is used in practice, a ground (GND) should be connected to prevent the leakage of maximized noise, as described in Japanese patent 5203295.

[0007] Japanese patent JP 5 559 668 B2 discloses an electromagnetic wave absorber obtained by laminating a plurality of electromagnetic wave-absorbing films over dielectric bodies in front of an electromagnetic wave reflector, each electromagnetic wave-absorbing film comprising a layer of conductive material formed on a surface of a plastic film, wherein the layer of conductive material has a surface resistance in the range of 100-1000 Ω / square. wherein the surface resistance of the conductive layer of a first electromagnetic wave-absorbing film is 100 Ω / square or more greater than that of the conductive layer of the next electromagnetic wave-absorbing film, (a) if two electromagnetic wave absorbing foils are included, the ratio of the gap between the first and second electromagnetic wave absorbing foil to the gap between the second electromagnetic wave absorbing foil and the electromagnetic wave reflector shall be 100 / 30-80 / 70, and (b) if three or more electromagnetic wave absorbing foils are included, the ratio of the gap between the first and second electromagnetic wave absorbing foils to the gap between the second and third electromagnetic wave absorbing foils shall be 100 / 30-80 / 70. the layer of conductive material of the electromagnetic wave-absorbing film is provided with a large number of essentially parallel, intermittent, linear scratches with irregular widths and spacings in several directions, and the linear scratches have widths of which 90% or more are in a range of 0.1-100 µm and on average 1-50 µm, and spacings in a range of 0.1-200 µm and on average 1-100 µm.

[0008] Japanese patent JP 5 559 668 B2 describes how, because the surface resistance of the conductive material layer of the first electromagnetic wave absorbing film is 100 Ω / square or more greater than that of the conductive material layer of the next electromagnetic wave absorbing film, an extremely higher absorption capacity for electromagnetic waves is achieved with lower anisotropy than if several electromagnetic wave absorbing films with the same surface resistance are simply laminated together.However, since this electromagnetic wave absorber has a structure in which several electromagnetic wave absorbing foils are laminated over dielectric bodies in front of the electromagnetic wave reflector (aluminum plate), it is suitable for ETC, FRID and so on, but cannot be used as a near-field electromagnetic wave absorber attached to electronic devices and the like.

[0009] Document EP 2 519 091 A1 discloses a composite electromagnetic wave absorbing film comprising several adjacent electromagnetic wave absorbing film pieces arranged on a plastic base film, each electromagnetic wave absorbing film piece being a plastic film provided with a conductive layer having a large number of substantially parallel, intermittent, linear scratches.

[0010] Document EP 3 003 002 A1 discloses a composite material for absorbing electromagnetic waves, comprising (a) a first electromagnetic wave-absorbing film comprising a plastic film and a single- or multi-layered thin metal film formed on at least one surface of the plastic film, wherein the thin metal film is provided with a large number of substantially parallel, intermittent, linear scratches of irregular widths and irregular spacing in several directions, and (b) a second electromagnetic wave-absorbing film comprising a resin or a rubber in which magnetic particles or non-magnetic, conductive particles are dispersed. SUBJECT OF THE INVENTION

[0011] Accordingly, an objective of the present invention is to provide a near-field electromagnetic wave absorber that has a high absorption capacity for line noise and radiation noise over a wide frequency range from less than 1 GHz to the high single-digit GHz range and has essentially no frequencies at which radiation noise is maximized, so that it can be used without an attached ground and exhibits only slight variations in noise absorption capacity between product lots. SUMMARY OF THE INVENTION

[0012] As a result of intensive research with regard to the above subject, the inventor has found that a near-field electromagnetic wave absorber comprising two thin metal films, each provided with a large number of essentially parallel, intermittent, linear scratches of irregular widths and spacing in several directions, exhibits improved near-field radiation noise absorption when the surface resistances of the two linearly scratched thin metal films are varied, and that, however, a combination of a linearly scratched thin metal film with a surface resistance of 20-377 Ω / square (also Ohm / square or Ω / □) and a linearly scratched thin metal film with a surface resistance of 377-10000 Ω / square, as in Japanese patent 4685977, does not have a sufficiently high absorption capacity for radiation noise in the near field over a wide frequency range from less than 1 GHz to a high single-digit GHz range.As a result of intensive research to further increase the absorption capacity of radiation noise in the near field, the inventor unexpectedly discovered that by combining a relatively high surface resistance of 150-300 Ω / square with a relatively low surface resistance of 10-50 Ω / square in a range of less than 377 Ω / square, corresponding to the low surface resistance in Japanese patent JP 4 685 977 B2, it is possible to obtain a stable near-field electromagnetic wave absorber that exhibits high absorption capacity for conduction and radiation noise over a wide frequency range from less than 1 GHz to a high single-digit GHz range and essentially has no frequencies at which radiation noise is maximized, so that it can be used without connection to a ground and only minor variations in absorption capacity occur between product batches.The present invention was completed on the basis of these findings.

[0013] The near-field electromagnetic wave absorber of the present invention comprises at least one plastic film and two linearly scratched thin metal films, each of which has a large number of substantially parallel, intermittent, linear scratches with irregular widths and spacings in several directions, one of which has a specific surface resistivity of 150-300 Ω / square and the other of which has a specific surface resistivity of 10-50 Ω / square.

[0014] In a preferred embodiment of the present invention, two plastic films, each having a linearly scratched thin metal film on one side, are glued together. In this case, preferably both linearly scratched thin metal films are glued together.

[0015] In a further preferred embodiment of the present invention, the linearly scratched thin metal films are provided on both sides of a plastic film.

[0016] The thin metal film in which linear scratches form is preferably 20-100 nm thick.

[0017] The thin metal film is preferably made of aluminum.

[0018] The linear scratches formed in the thin metal film are preferably aligned in two directions with a crossing angle of 30-90°.

[0019] Preferably, one of the linearly scratched thin metal films has a surface resistance of 150-300 Ω / square and a light transmittance of 2.5-3.5%, and the other has a surface resistance of 10-50 Ω / square and a light transmittance of 1-2.2%.

[0020] The linear scratches formed in the two thin metal films preferably have widths in the range of 0.1-100 µm and an average of 2-50 µm, and spacings in the range of 0.1-500 µm and an average of 10-100 µm. EFFECTS OF THE INVENTION

[0021] The near-field electromagnetic wave absorber of the present invention with the above characteristics has a high absorption capacity for line noise and radiation noise in a wide frequency range from less than 1 GHz to a high single-digit GHz range and can be used without the need to connect an earth connection, since there are essentially no frequencies at which radiation noise is maximized.Since one linearly scratched thin metal film has a relatively high specific surface resistivity of 150-300 Ω / square and the other linearly scratched thin metal film has a relatively low specific surface resistivity of 10-50 Ω / square, it is possible to obtain a stable near-field electromagnetic wave absorber that exhibits only minor irregularities in its noise absorption (radiation noise), even if irregularities exist between the produced linearly scratched thin metal films. The near-field electromagnetic wave absorber of the present invention, possessing such features, can be suitably attached to electronic devices in various electronic equipment and communication terminals such as personal computers, mobile phones, smartphones, and the like, to suppress electromagnetic wave noise. BRIEF DESCRIPTION OF THE DRAWINGS The Fig.Figure 1 is a cross-sectional view showing an electromagnetic wave absorbing film with a thin metal film containing linear scratches. The Fig. Figure 2 is a top view showing an example of linear scratches in a thin metal film. The Fig. 3(a) is a partial top view showing another example of linear scratches. The Fig. 3(b) is a partial top view showing another example of linear scratches. The Fig. 3(c) is a partial top view showing another example of linear scratches. The Fig. Figure 4(a) is a perspective view showing an example of devices for manufacturing an electromagnetic wave-absorbing film. The Fig. 4(b) is a top view of the device from the Fig. 4(a). The Fig. 4(c) is a section view along line AA in the Fig.4(b). The Fig. Figure 4(d) is an enlarged partial view to illustrate the principle of the formation of linear scratches inclined to the direction of movement of the film. The Fig. 4(e) is a partial top view showing the inclination angles of a pattern roller and a pressure roller to a film in the device of the Fig. 4(a) shows. The Fig. Figure 5 is a partial sectional view showing another example of devices for manufacturing an electromagnetic wave absorbing film. The Fig. Figure 6 is a perspective view showing another example of devices for manufacturing an electromagnetic wave-absorbing film. The Fig. Figure 7 is a perspective view showing another example of devices for manufacturing an electromagnetic wave absorbing film. The Fig.Figure 8 is a perspective view showing another example of devices for manufacturing an electromagnetic wave absorbing film. The Fig. 9(a) is a sectional view showing an example of the near-field electromagnetic wave absorbers of the present invention. The Fig. 9(b) is an exploded sectional view of the [unclear] in the Fig. 9(a) shown absorber for electromagnetic waves in the near field. The Fig. Figure 10 is a sectional view showing another example of the near-field electromagnetic wave absorbers of the present invention. The Fig. Figure 11(a) is a top view showing a system for evaluating the absorption capacity for conduction noise of a near-field electromagnetic wave absorber. The Fig.Figure 11(b) is a sectional view showing a system for evaluating the absorption capacity of the conduction noise of a near-field electromagnetic wave absorber. The Fig. Figure 12 is a diagram showing the ratio of the absorption capacity of the conduction noise Ploss / Pin of the test specimen from reference example 1 (comparison example 2). The Fig. 13(a) is a photograph showing the cumulative radiation noise of the test specimen from reference example 1 in a frequency range from 0.03 GHz to 3.5 GHz. The Fig. 13(b) is a photograph showing the cumulative radiation noise of the test specimen from reference example 1 in a frequency range from 3.5 GHz to 7 GHz. The Fig. Figure 14 is a diagram showing the ratio of the absorption capacity of the line noise Ploss / Pin of the test specimen from Example 1. The Fig.15(a) is a photograph showing the cumulative radiation noise of the test specimen from Example 1 in a frequency range from 0.03 GHz to 3.5 GHz. The Fig. 15(b) is a photograph showing the cumulative radiation noise of the test specimen from Example 1 in a frequency range from 3.5 GHz to 7 GHz. The Fig. Figure 16 is a photograph showing the ratio of the absorption capacity of the line noise Ploss / Pin of the test specimen from an example 2. The Fig. Figure 17 is a photograph showing the ratio of the absorption capacity of the line noise Ploss / Pin of the test specimen from an example 3. The Fig. Figure 18 is a photograph showing the ratio of the absorption capacity of the line noise Ploss / Pin of the test specimen from an example 4. The Fig.Figure 19 is a diagram showing the ratio of the absorption capacity of the conduction noise Ploss / Pin of the test specimen from a comparison example 1. The Fig. Figure 20 is a diagram showing the ratio of the absorption capacity of the conduction noise Ploss / Pin of the test specimen from a comparison example 3. The Fig. Figure 21 is a diagram showing the ratio of the absorption capacity of the conduction noise Ploss / Pin of the test specimen from a comparison example 4. The Fig. Figure 22 is a diagram showing the ratio of the absorption capacity of the conduction noise Ploss / Pin of the test specimen from a comparison example 5. The Fig. Figure 23 is a diagram showing the ratio of the absorption capacity of the conduction noise Ploss / Pin of the test specimen from a comparison example 6. The Fig.Figure 24 is a diagram showing the ratio of the absorption capacity of the conduction noise Ploss / Pin of the test specimen from a comparison example 7. The Fig. Figure 25 is a diagram showing the ratio of the absorption capacity of the conduction noise Ploss / Pin of the test specimen from a comparison example 8. The Fig. Figure 26 is a diagram showing the ratio of the absorption capacity of the conduction noise Ploss / Pin of the test specimen from a comparison example 9. The Fig. Figure 27 is a diagram showing the ratio of the absorption capacity of the conduction noise Ploss / Pin of the test specimen from a comparison example 10. The Fig. 28(a) is a photograph showing the cumulative radiation noise of a sample 1 from an example 5 in a frequency range from 0.03 GHz to 3.5 GHz. The Fig.28(b) is a photograph showing the cumulative radiation noise of sample 1 from Example 5 in a frequency range from 3.5 GHz to 7 GHz The Fig. 29(a) is a photograph showing the cumulative radiation noise of a sample 2 from Example 5 in a frequency range from 0.03 GHz to 3.5 GHz. The Fig. 29(b) is a photograph showing the cumulative radiation noise of sample 2 from example 5 in a frequency range from 3.5 GHz to 7 GHz The Fig. 30(a) is a photograph showing the cumulative radiation noise of a sample 3 from example 5 in a frequency range from 0.03 GHz to 3.5 GHz. The Fig. 30(b) is a photograph showing the cumulative radiation noise of sample 3 from example 5 in a frequency range from 3.5 GHz to 7 GHz The Fig.31(a) is a photograph showing the cumulative radiation noise of a sample 4 from example 5 in a frequency range from 0.03 GHz to 3.5 GHz. The Fig. Figure 31(b) is a photograph showing the cumulative radiation noise of sample 4 from example 5 in a frequency range from 3.5 GHz to 7 GHz. The Fig. 32(a) is a photograph showing the cumulative radiation noise of a sample 5 from Example 5 in a frequency range from 0.03 GHz to 3.5 GHz. The Fig. Figure 32(b) is a photograph showing the cumulative radiation noise of sample 5 from Example 5 in a frequency range from 3.5 GHz to 7 GHz. The Fig. 33(a) is a photograph showing the cumulative radiation noise of a sample 6 from example 5 in a frequency range from 0.03 GHz to 3.5 GHz. The Fig.Figure 33(b) is a photograph showing the cumulative radiation noise of sample 6 from example 5 in a frequency range from 3.5 GHz to 7 GHz. The Fig. 34(a) is a photograph showing the cumulative radiation noise of a sample 7 from Example 5 in a frequency range from 0.03 GHz to 3.5 GHz. The Fig. Figure 34(b) is a photograph showing the cumulative radiation noise of sample 7 from Example 5 in a frequency range from 3.5 GHz to 7 GHz. The Fig. 35(a) is a photograph showing the cumulative radiation noise of a sample 8 from Example 5 in a frequency range from 0.03 GHz to 3.5 GHz. The Fig. Figure 35(b) is a photograph showing the cumulative radiation noise of sample 8 from Example 5 in a frequency range from 3.5 GHz to 7 GHz. The Fig.36(a) is a photograph showing the cumulative radiation noise of a sample 9 from Example 5 in a frequency range from 0.03 GHz to 3.5 GHz. The Fig. Figure 36(b) is a photograph showing the cumulative radiation noise of sample 9 from Example 5 in a frequency range from 3.5 GHz to 7 GHz. The Fig. 37(a) is a photograph showing the cumulative radiation noise of a sample 10 from Example 5 in a frequency range from 0.03 GHz to 3.5 GHz. The Fig. 37(b) is a photograph showing the cumulative radiation noise of sample 10 from example 5 in a frequency range from 3.5 GHz to 7 GHz The Fig. 38(a) is a photograph showing the cumulative radiation noise of a sample 1 from a comparison example 11 in a frequency range from 0.03 GHz to 3.5 GHz. The Fig.38(b) is a photograph showing the cumulative radiation noise of sample 1 from comparison example 11 in a frequency range from 3.5 GHz to 7 GHz The Fig. 39(a) is a photograph showing the cumulative radiation noise of sample 2 from comparison example 11 in a frequency range from 0.03 GHz to 3.5 GHz. The Fig. 39(b) is a photograph showing the cumulative radiation noise of sample 2 from comparison example 11 in a frequency range from 3.5 GHz to 7 GHz The Fig. 40(a) is a photograph showing the cumulative radiation noise of a sample 3 from comparison example 11 in a frequency range from 0.03 GHz to 3.5 GHz. The Fig. 40(b) is a photograph showing the cumulative radiation noise of sample 3 from comparison example 11 in a frequency range from 3.5 GHz to 7 GHz The Fig.41(a) is a photograph showing the cumulative radiation noise of a sample 4 from comparison example 11 in a frequency range from 0.03 GHz to 3.5 GHz. The Fig. 41(b) is a photograph showing the cumulative radiation noise of sample 4 from comparison example 11 in a frequency range from 3.5 GHz to 7 GHz The Fig. 42(a) is a photograph showing the cumulative radiation noise of a sample 5 from comparison example 11 in a frequency range from 0.03 GHz to 3.5 GHz. The Fig. 42(b) is a photograph showing the cumulative radiation noise of sample 5 from comparison example 11 in a frequency range from 3.5 GHz to 7 GHz The Fig. 43(a) is a photograph showing the cumulative radiation noise of a sample 6 from comparison example 11 in a frequency range from 0.03 GHz to 3.5 GHz. The Fig.43(b) is a photograph showing the cumulative radiation noise of sample 6 from comparison example 11 in a frequency range from 3.5 GHz to 7 GHz The Fig. 44(a) is a photograph showing the cumulative radiation noise of a sample 7 from comparison example 11 in a frequency range from 0.03 GHz to 3.5 GHz. The Fig. 44(b) is a photograph showing the cumulative radiation noise of sample 7 from comparison example 11 in a frequency range from 3.5 GHz to 7 GHz The Fig. 45(a) is a photograph showing the cumulative radiation noise of a sample 8 from comparison example 11 in a frequency range from 0.03 GHz to 3.5 GHz. The Fig. 45(b) is a photograph showing the cumulative radiation noise of sample 8 from comparison example 11 in a frequency range from 3.5 GHz to 7 GHz The Fig.46(a) is a photograph showing the cumulative radiation noise of a sample 9 from comparison example 11 in a frequency range from 0.03 GHz to 3.5 GHz. The Fig. 46(b) is a photograph showing the cumulative radiation noise of sample 9 from comparison example 11 in a frequency range from 3.5 GHz to 7 GHz The Fig. 47(a) is a photograph showing the cumulative radiation noise of a sample 10 from comparison example 11 in a frequency range from 0.03 GHz to 3.5 GHz. The Fig. 47(b) is a photograph showing the cumulative radiation noise of sample 10 from comparison example 11 in a frequency range from 3.5 GHz to 7 GHz DESCRIPTION OF THE BEST EXECUTION OF THE INVENTION

[0022] The embodiments of the present invention are explained with reference to the accompanying drawings, and it should be noted that the explanations relating to one embodiment are applicable to other embodiments unless otherwise stated. Furthermore, the following explanation is not limiting, and various modifications may be made within the scope of the present invention. Electromagnetic wave absorbing film

[0023] The Fig.Figure 1 shows an example of electromagnetic wave-absorbing films that form the near-field electromagnetic wave absorber according to an embodiment of the present invention. This electromagnetic wave-absorbing film 100 (100a, 100b) consists of a plastic film 10 and a thin metal film 11 formed on one side of the plastic film 10, and the thin metal film 11 is provided with a large number of substantially parallel, interrupted, linear scratches 12 with irregular widths and spacings in several directions. (1) Plastic film

[0024] The resins forming the plastic film 10 are not particularly limited, as long as they possess sufficient strength, flexibility, and processability in addition to their insulating properties. Examples include polyesters (polyethylene terephthalate or the like), polyarylene sulfide (polyphenylene sulfide or the like), polyethersulfone, polyetheretherketones, polycarbonates, acrylic resins, polystyrenes, polyolefins (polyethylene, polypropylene, or the like), and so on. Among these, a polyethylene terephthalate (PET) film is preferred in terms of strength and cost. The thickness of the plastic film 10 can be approximately 10–100 µm, and preferably approximately 10–30 µm, to make the near-field electromagnetic wave absorber as thin as possible. (2) Thin metal film

[0025] The thin metal film 11 consists of a non-magnetic or magnetic metal. The non-magnetic metal can be aluminum, copper, silver, and so on, and the magnetic metal can be nickel, chromium, and so on. These metals can be used in their pure form or as alloys. Aluminum is preferred for cost and corrosion resistance. The thin metal film 11 can be produced by known processes such as sputtering, vacuum deposition, and so on. With regard to controlling the thickness of the thin metal film 11 and the degree of linear scratch formation, the thickness of the thin metal film 11 is preferably 20–100 nm, more preferably 30–90 nm, and most preferably 40–80 nm. (3) Linear scratches

[0026] As in the Fig. 1 and Fig.As shown in Figure 2, the thin metal film 11 of the electromagnetic wave absorbing foil 100 (100a, 100b) is provided with substantially parallel, intermittent, linear scratches 12 (12a, 12b) with irregular widths and spacings in several directions. Fig. Figure 2 shows linear scratches 12a, 12b oriented in two directions. For clarification, the depths of the linear scratches 12 are shown in the Fig.Figure 1 is exaggerated. The linear scratches 12, oriented in two directions, have different widths W and spacings I. The spacings I include both the distances parallel and those perpendicular to the linear scratches 12. The widths W and the spacings I of the linear scratches 12 are measured at an initial height of the thin metal film 11, which corresponds to the height S of the surface of the thin metal film 11 before the formation of the linear scratches. Since the linear scratches 12 have different widths W and spacings I, the electromagnetic wave-absorbing film 100 can efficiently absorb electromagnetic waves over a wide frequency range.

[0027] The widths W of the linear scratches 12 are preferably in the range of 0.1–100 µm, and particularly preferably in the range of 0.1–70 µm. The average width Wav of the linear scratches 12 is preferably 2–50 µm and particularly preferably 5–30 µm. The spacing I of the linear scratches 12 is preferably in the range of 0.1–500 µm and particularly preferably in the range of 1–400 µm. The average spacing Iav of the linear scratches 12 is preferably 10–100 µm and even more preferably 20–80 µm. Incidentally, to determine the widths W, the average width Wav, the spacing I, and the average spacing Iav of the linear scratches 12, linear scratches 12 with a small width of up to 0.1 µm are counted, unless otherwise stated below.

[0028] Since the lengths L of the linear scrapers 12 are determined by the sliding conditions (primarily by the relative velocities of the roller and the plastic film and the angle at which the plastic film wraps around the roller), they are essentially the same unless the sliding conditions are changed (essentially equal to the average length). The lengths of the linear scrapers 12 can practically range from 1 to 100 mm, but are not particularly limited.

[0029] The acute intersection angle θs (hereinafter referred to simply as the “intersection angle” unless otherwise stated) of the linear scratches 12a, 12b in two directions is preferably 30–90°, more preferably 45–90°, and most preferably 60–90°. With adapted sliding conditions (sliding direction, circumferential speed ratio, and so on) between the plastic film 10 and the pattern roll, linear scratches 12 with different intersection angles θs can be formed, as shown in the Fig. Figures 3(a) to 3(c) show that although the orientation of the linear scratches is not limited to two directions but can also include three or more directions, the formation of linear scratches in two directions is preferable when production costs and performance are fully taken into account. The linear scratches 12 consist of the Fig. 3(a) consisting of perpendicularly intersecting linear scratches 12a, 12b, in the Fig.3(b) consisting of linear scratches 12a, 12b, 12c intersecting at 60° and in the Fig. 3(c) consisting of linear scratches oriented in three directions. Device for forming linear scratches

[0030] The Fig.Figures 4(a) to 4(e) show an example of devices for forming linear scratches in a thin metal film on a plastic film in two directions. The device shown comprises (a) a spool 21 from which a plastic film 10 with a thin metal film is unwound, (b) a first pattern roll 2a inclined to the transverse direction of the plastic film 10, (c) a first pressure roll 3a arranged on the opposite side upstream of the first pattern roll 2a, (d) a second pattern roll 2b inclined opposite to the first pattern roll 2a to the transverse direction of the plastic film 10 and arranged on the same side as the first pattern roll 2a, (e) a second pressure roll 3b arranged downstream of the second pattern roll 2b on the opposite side, and (f) a reel 24 around which the plastic film 10' with a linearly scratched thin metal film is wound.Furthermore, several guide rollers 22, 23 are arranged at predetermined positions. Each pattern roller 2a, 2b is supported by a backup roller (for example, a rubber roller) 5a, 5b to prevent bending.

[0031] As in the Fig.As shown in Figure 4(c), the plastic film 10 is pressed by each pattern roller 2a, 2b because each pressure roller 3a, 3b comes into contact with the thin metal film of the plastic film 10 at a lower position than at the position where it is brought into sliding contact with each pattern roller 2a, 2b. By adjusting the height of each pressure roller 3a, 3b under this condition, the pressure of each pattern roller 2a, 2b on the thin metal film can be controlled. In particular, the lower position of each pressure roller 3a, 3b increases the pressure of each pattern roller 2a, 2b on the thin metal film of the plastic film 10, thereby forming deeper linear scratches in the thin metal film (increasing the degree of formation of linear scratches in the thin metal film).Conversely, the higher position of each pressure roller 3a, 3b reduces the pressure of each pattern roller 2a, 2b on the thin metal film of the plastic film 10, resulting in flatter linear scratches in the thin metal film of the plastic film 10 (thereby reducing the degree of formation of linear scratches in the thin metal film).

[0032] Increasing the depth of the linear scratches generally results in a smaller amount of metal remaining in the thin metal film, thus increasing the surface resistance of the linearly scratched thin metal film. Accordingly, the surface resistance of the linearly scratched thin metal film can be adjusted by changing the contact pressure of each pattern roller 2a, 2b on the thin metal film of the plastic sheet 10. Incidentally, deeper linear scratches tend to have a greater width, resulting in smaller gaps between adjacent linear scratches. The contact pressure of each pattern roller 2a, 2b on the plastic sheet 10 can be adjusted by moving each pattern roller 2a, 2b towards or away from the plastic sheet 10. This movement of each pattern roller 2a, 2b can be achieved by a drive mechanism (not shown) attached to each pattern roller 2a, 2b.

[0033] The Fig.Figure 4(d) shows the principle that linear scratches 12a are formed with an inclination relative to the direction of movement of the plastic film 10. Since the pattern roll 2a is inclined relative to the direction of movement of the plastic film 10, the direction of movement (rotation) of the fine, hard particles on the pattern roll 2a differs from the direction of movement of the plastic film 10. After a fine, hard particle at a point A on the pattern roll 2a has come into contact with the thin metal film of the plastic film 10 to form a scratch B at any given time, as represented by X, the fine, hard particle moves to a point A', and the scratch B moves to a point B' in a predetermined time interval. As the fine, hard particle moves from point A to point A', the scratch is continuously formed, resulting in a linear scratch 12a extending from point A' to point B'.

[0034] The directions and the crossing angle θs of the linear scratches 12a, 12b formed by the first and second pattern rollers 2a, 2b can be adjusted by changing the angle of each pattern roller 2a, 2b with respect to the plastic film 10 and / or the circumferential speed of each pattern roller 2a, 2b relative to the movement speed of the plastic film 10. For example, if the circumferential speed a of the pattern roller 2a increases relative to the movement speed b of the plastic film 10, the linear scratches 12a can be inclined by 45° to the direction of movement of the plastic film 10, as shown in the Fig. 4(d) represented by Y. Similarly, the circumferential speed a of the pattern roll 2a can be changed by changing the inclination angle θ2 of the pattern roll 2a to the transverse direction of the plastic film 10, as shown in the Fig.4 (e) shown. This also applies to the pattern roller 2b. Accordingly, when both pattern rollers 2a, 2b are set, the directions of the linear scratches 12a, 12b can be changed.

[0035] Since each pattern roller 2a, 2b is inclined relative to the plastic film 10, sliding with each pattern roller 2a, 2b exerts a force in a transverse direction on the plastic film 10. To prevent lateral movement of the plastic film 10, the height and / or angle of each pressure roller 3a, 3b relative to each pattern roller 2a, 2b is preferably adjusted. As in the Fig.As shown in Figure 4(e), for example, the correct setting of a crossing angle θ3 between the axis of the pattern roller 2a and the axis of the pressure roller 3a ensures such a transverse distribution of the pressure force that the transverse components are canceled out, thereby preventing lateral movement. Setting a distance between the pattern roller 2a and the pressure roller 3a also contributes to preventing lateral movement. To prevent lateral movement and breakage of the plastic film 10, the directions of rotation of the first and second pattern rollers 2a, 2b, which are inclined relative to the transverse direction of the plastic film 10, are preferably the same as the direction of movement of the plastic film 10.

[0036] To increase the pressure exerted by the pattern rollers 2a, 2b on the thin metal film of the plastic film 10, a third pressure roller 3c can be provided between the pattern rollers 2a, 2b, as shown in the Fig.Figure 5 shows that the third pressure roller 3c increases the sliding distance of the plastic film 10 proportionally to the center angle θ1, resulting in longer linear scratches 12a, 12b. Adjusting the position and inclination angle of the third pressure roller 3c helps to prevent lateral movement of the plastic film 10.

[0037] The Fig. Figure 6 shows an example of devices for forming linear scratches oriented in three directions, as in the Fig. 3(c) shown. This device differs from the one shown in the Fig.The device shown in Figures 4(a) to 4(e) is further modified by comprising a third pattern roller 2c and a third pressure roller 3d parallel to the transverse direction of the plastic film 10 downstream of the second pattern roller 2b. Although the direction of rotation of the third pattern roller 2c can be the same as or opposite to the direction of movement of the plastic film 10, it is preferably the opposite direction to effectively form linear scratches. The third pattern roller 2c, running parallel to the transverse direction, forms linear scratches 12c that are aligned with the direction of movement of the plastic film 10. The third pressure roller 3d is arranged upstream of the third pattern roller 2c, but can also be located on the downstream side. Not limited to the examples shown, the third pattern roller 2c can be arranged upstream of the first pattern roller 2a or between the first and second pattern rollers 2a, 2b.

[0038] The Fig. Figure 7 shows an example of devices for forming linear scratches oriented in four directions. This device differs from the one shown in the Fig. The device shown in Figure 6 is characterized by the inclusion of a fourth pattern roller 2d between the second pattern roller 2b and the third pattern roller 2c, and a fourth pressure roller 3e upstream of the fourth pattern roller 2d. At a slower rotational speed of the fourth pattern roller 2d, the direction (line E'F') of the linear scratches 12a' can run parallel to the transverse direction of the plastic film 10, as shown in Figure 6. Fig. 4(d) represented by Z.

[0039] The Fig. Figure 8 shows another example of devices for forming perpendicularly intersecting linear scratches, as in the Fig. 3(a) shown. This device differs from the one shown in the Fig.The device shown in sections 4(a) to 4(e) is modified by the fact that a second pattern roll 32b is arranged parallel to the transverse direction (perpendicular to the direction of movement) of the plastic film 10. Therefore, only those sections that differ from those shown in the Fig. The second pattern roller 32b differs from the second pattern roller 32b shown in Figures 4(a) to 4(e). The direction of rotation of the second pattern roller 32b can be the same as or opposite to the direction of movement of the plastic film 10. The second pressure roller 33b can also be located upstream or downstream of the second pattern roller 32b. In this device, the direction (line E'F') of the linear scratchers 12a' is aligned with the transverse direction of the plastic film 10, as shown in Figure 4(a) to 4(e). Fig. 4(d) represented by Z, and is suitable for forming perpendicularly intersecting linear scratches.

[0040] The movement speed of the plastic film 10 is preferably 5-200 m / min, and the circumferential speed of the sample roll is preferably 10-2,000 m / min. The inclination angles θ2 of the sample rolls are preferably 20° to 60°, particularly about 45°. The tension (parallel to the pressing force) of the plastic film 10 is preferably 0.05-5 kgf / cm width.

[0041] The sample roller is preferably a roller with fine particles having sharp edges and a Mohs hardness of 5 or more on its surface, for example, the diamond roller described in JP 2002-59487 A. Since the width of the linear scratches is determined by the size of the fine particles, 90% or more of the fine diamond particles preferably have a size in the range of 0.1–100 µm, particularly preferably in the range of 0.1–70 µm. The fine diamond particles are preferably applied to a surface area of ​​30% or more of the roller surface. Properties of the near-field electromagnetic wave absorber(1) Structure

[0042] As in the Fig. 9(a) and Fig.Figure 9(b) shows that the near-field electromagnetic wave absorber according to an embodiment of the present invention is obtained by bonding a first electromagnetic wave-absorbing film 100a, which has a (first) thin metal film 11a with linear scratches 12, to a second electromagnetic wave-absorbing film 100b, which has another (second) thin metal film 11b with linear scratches 12. The bonding preferably takes place with the linearly scratched thin metal films 11a, 11b on the inside, but this is not mandatory.The near-field electromagnetic wave absorber according to one embodiment of the present invention has a layered structure comprising the first electromagnetic wave-absorbing film 100a (plastic film 10a / thin metal film 11a with first linear scratches 12), an adhesive layer 20, and the second electromagnetic wave-absorbing film 100b (thin metal film 11b / plastic film 10b with second linear scratches 12). Since the thin metal films 11a and 11b face each other, the adhesive layer 20 is preferably non-conductive to prevent the thin metal films 11a and 11b from conducting. The adhesive layer 20 can be formed by applying an adhesive, but also by heat sealing or double-sided adhesive tape.

[0043] This near-field electromagnetic wave absorber can be produced by applying an adhesive 20 to a linearly scratched thin metal film 11a and then pressing both electromagnetic wave-absorbing films 100a, 100b together over the adhesive, as shown in the Fig. 9(b) shown.

[0044] If the adhesive layer 20 is very thin, the thin metal films 11a and 11b are electromagnetically coupled. In this case, it is preferred that the linear scratches 12a, 12b formed in the thin metal film 11a and the thin metal film 11b have different intersection angles θs in order to reduce the anisotropy of the absorption capacity for electromagnetic waves. The thickness of the adhesive layer 20 is preferably 1–30 µm, and more preferably 1–20 µm.

[0045] The Fig.Figure 10 shows the near-field electromagnetic wave absorber according to another embodiment of the present invention. This near-field electromagnetic wave absorber consists of a plastic film 10 and thin metal films 11a, 11b formed on both sides of the plastic film 10, and each thin metal film 11a, 11b is provided with a large number of substantially parallel, intermittent, linear scratches 12 with irregular widths and spacings in several directions. (2) Surface resistance of a linearly scratched thin metal film

[0046] It has been found that while an electromagnetic wave-absorbing film with a linearly scratched thin metal film and a near-field electromagnetic wave absorber consisting of a laminate of two such electromagnetic wave-absorbing films generally exhibit good absorption of radiation noise, significant radiation noise can escape depending on the frequency. The frequencies at which significant radiation noise escapes cannot be predicted but can only be confirmed experimentally.By laminating two identical electromagnetic wave-absorbing films, each featuring a thin metal film with varying degrees of linear scratch formation to create a near-field electromagnetic wave absorber, and by measuring the emitted radiation noise, it was found that the emitted radiation noise differs depending on the degree of linear scratch formation. It was also found that, not only because the thin metal film is extremely thin, but also because the linear scratches are extremely small, the surface resistance is uneven between production batches of near-field electromagnetic wave absorbers, and that even products with the same target degree of linear scratch formation exhibit uneven levels of emitted radiation noise.Intensive research has shown that (a) when a pair of electromagnetic wave-absorbing films have linearly scratched thin metal films with different surface resistivities, and (b) when their surface resistivities are limited in predetermined regions, radiation noise can be suppressed over a wide frequency range with small variations between production batches. The present invention was developed on the basis of these findings.

[0047] In electronic components, noise in the range of 0.03 GHz to 7 GHz generally needs to be removed. As a result of intensive research into combining the surface resistances of linearly scratched thin metal films capable of suppressing radiation noise in this range, it was found that if one linearly scratched thin metal film has a surface resistance of 150-300 Ω / square and the other has a surface resistance of 10-50 Ω / square, radiation noise in the frequency range of 0.03 GHz to 7 GHz can be suppressed, thereby reducing the inconsistency between production batches.

[0048] As described above, in an electromagnetic wave absorbing film consisting of a linearly scratched thin metal film and a near-field electromagnetic wave absorber made from a laminate of two such electromagnetic wave absorbing films, the radiation noise can be extremely high (maximized) at one or more frequencies. The maximized radiation noise should be removed at every frequency, and the maximization of the radiation noise can be practically confirmed by observing the cumulative radiation noise in a predetermined frequency range. If the cumulative radiation noise in a given frequency range is below a desired value, the radiation noise is assumed to be suppressed. Conversely, if the cumulative radiation noise exceeds the desired level, the radiation noise is assumed to be maximized at a specific frequency.Accordingly, the absorption capacity of the absorber for electromagnetic waves in the near field is evaluated based on the level of cumulative radiation noise.

[0049] In a frequency range of 0.03 GHz to 7 GHz, the desired level of cumulative radiation noise differs between a low-frequency and a high-frequency side. Here, the desired level of cumulative radiation noise is -20 dBm in the frequency range of 0.03 GHz to less than 3.5 GHz and -30 dBm in the frequency range of 3.5 GHz to 7 GHz. Consequently, if the cumulative radiation noise is -20 dBm or more in the frequency range of 0.03 GHz to less than 3.5 GHz or -30 dBm or more in the frequency range of 3.5 GHz to 7 GHz, it is assumed that the radiation noise is maximized at one or more frequencies. If the radiation noise is maximized at at least one frequency, the near-field electromagnetic wave absorber should be grounded to remove the radiation noise.

[0050] A (first) linearly scratched thin metal film 11a has a surface resistance of 150-300 Ω / square, and the other (second) linearly scratched thin metal film 11b has a surface resistance of 10-50 Ω / square. The first linearly scratched thin metal film 11a mainly absorbs conduction noise, and the second linearly scratched thin metal film 11b mainly absorbs radiation noise.

[0051] If the surface resistance of the first linearly scratched thin metal film 11a is less than 150 Ω / square, the near-field electromagnetic wave absorber cannot exhibit good conduction noise absorption. The term "good conduction noise absorption" used here means that the near-field electromagnetic wave absorber has a conduction noise absorption ratio (Ploss / Pin) that is close to that of the linearly scratched thin metal film with a surface resistance of 150–300 Ω / square in a frequency range from less than 1 GHz to a high single-digit GHz value (especially 0.1–6 GHz). Conversely, if the surface resistance of the first linearly scratched thin metal film 11a is greater than 300 Ω / square, sufficient radiation noise absorption cannot be achieved.To achieve good absorption capacity for conduction noise and radiation noise, the surface resistance of the first linearly scratched thin metal film 11a is preferably 150-210 Ω / square.

[0052] If the second linearly scratched thin metal film 11b has a surface resistivity of less than 10 Ω / square, its properties are similar to those of a thin metal film. Specifically, it exhibits high absorption of radiation noise and low absorption of conduction noise. If the second linearly scratched thin metal film 11b has a specific surface resistivity of more than 50 Ω / square, its absorption of electromagnetic waves in the near field is too low.

[0053] Since a higher surface resistance is achieved through deeper and wider linear scratches in the thin metal film (higher degree of linear scratch formation), as described above, the linear scratches formed in the thin metal film of the second electromagnetic wave-absorbing foil 100b are shallower than those formed in the thin metal film of the first electromagnetic wave-absorbing foil 100a. Accordingly, the second linearly scratched thin metal film 11b has noise-absorbing properties that are closer to those of an unscratched thin metal film than those of the first linearly scratched thin metal film 11a.

[0054] Since a greater degree of linear scratch formation in the thin metal film results in a higher surface resistance, a desired surface resistance can be achieved by adjusting the degree of linear scratch formation. Because the surface resistance tends to decrease with increasing thickness of the thin metal film, even with the same degree of linear scratch formation, the degree of linear scratch formation should be increased for a thicker metal film to obtain the desired surface resistance.

[0055] The combination of a linearly scratched thin metal film with a surface resistance of 150-300 Ω / square and a linearly scratched thin metal film with a surface resistance of 10-50 Ω / square can suppress the maximization of radiation noise in a wide frequency range from less than 1 GHz to high single-digit GHz, while maintaining good absorption capacity for conduction noise. (3) Light transmittance of a linearly scratched thin metal film

[0056] The light transmittance of the linearly scratched thin metal film increases with the degree of linear scratch formation in the thin metal film, as does the surface resistivity. Specifically, the first linearly scratched thin metal film 11a, with a surface resistivity of 150-300 Ω / square, has a light transmittance of 2.5-3.5%, and the second linearly scratched thin metal film 11b, with a surface resistivity of 10-50 Ω / square, has a light transmittance of 1-2.2%.

[0057] The present invention will be explained in more detail below using examples, without limiting it thereto. Reference example 1

[0058] A PET film with a thickness of 16 µm was vapor-deposited with aluminum in a vacuum to form a thin aluminum film with a thickness of 60 nm. Using a device with the [description of device], the aluminum was deposited in the [description of device]. Fig.In the structure shown in Figure 8, which comprises sample rolls 32a and 32b with electroplated fine diamond particles with a particle size distribution of 50–80 µm, the thin aluminum film on the plastic foil was scratched in two directions to form the electromagnetic wave-absorbing foil of Reference Example 1 with linear scratches exhibiting the properties shown below. The degree of linear scratch formation in Reference Example 1 was shown in “M1”. (Medium1) classified. Area of ​​latitudes W 0,1-50 µm, Medium Width Wave 22 µm, Area of ​​transverse distancesI 1-120 µm, Average transverse distance Iav 42 µm, Average length Lav 5 mm, and Crossing angle θs 90°.

[0059] Using an EC-80P arc resistivity / surface resistivity meter from Napson Corporation, the surface resistivity of a linearly scratched thin aluminum film was measured using a non-destructive eddy current testing method. The measurement result showed that the surface resistivity of the linearly scratched thin aluminum film was 172 Ω / square.

[0060] The electromagnetic wave-absorbing film of reference example 1, with its linearly scratched thin aluminum film, was placed in a laser transmission sensor (IB-30) available from Keyence Corporation to measure the light transmittance of the linearly scratched thin aluminum film. The result was that the light transmittance was 2.6%.

[0061] A test specimen TP1 (50 mm × 50 mm) was cut from the electromagnetic wave-absorbing foil of reference example 1. In a near-field electromagnetic wave evaluation system, comprising a 50 Ω microstrip line MSL (64.4 mm × 4.4 mm), an insulating substrate 200 supporting the microstrip line MSL, a grounded electrode 201 attached to a lower surface of the insulating substrate 200, conductor pins 202, 202 connected to both edges of the microstrip line MSL, a network analyzer NA, and coaxial cables 203, 203 connecting the network analyzer NA to the conductor pins 202, 202, as shown in the Fig. 11(a) and Fig.As shown in Figure 11(b), the test specimen TP1 was attached to the top of the insulating substrate 200 with an adhesive such that the center of the test specimen TP1 was aligned with the center of the microstrip line MSL. The reflected wave power S11 and the transmitted wave power S12 were measured with incident waves from 0.1 to 6 GHz to determine the absorption ratio of the line noise Ploss / Pin from S11 and S21. The results are shown in the Fig. 12 shown. Fig. As can be seen in Figure 12, the electromagnetic wave absorbing foil of reference example 1 has a good absorption ratio for line noise Ploss / Pin.

[0062] A test specimen TP2 (40 mm × 40 mm) cut from the electromagnetic wave-absorbing foil of reference example 1 was scanned with an EMC noise scanner (WM7400) from Morita Tech Co. Ltd. in a frequency range of 0.03 GHz to 7 GHz to measure radiation noise. Fig. 13(a) and Fig. Figure 13(b) shows the cumulative radiation noise of test specimen TP2 of reference example 1 in frequency ranges from 0.03 GHz to less than 3.5 GHz and from 3.5 GHz to 7 GHz, respectively. As can be seen from the Fig. 13(a) and Fig.As can be seen from paragraph 13(b), in a frequency range from 0.03 GHz to less than 3.5 GHz, cumulative radiation noise of -15 dBm or more, in particular -10 dBm or more, was observed in almost the entire area of ​​the test specimen TP2, and in a frequency range from 3.5 GHz to 7 GHz, cumulative radiation noise of -25 dBm or more, in particular -20 dBm or more, was observed in almost the entire area of ​​the test specimen TP2. Reference example 2

[0063] The electromagnetic wave absorbing film of reference example 2 was obtained by forming linear scratches with the properties described below in a thin aluminum film in two directions in the same way as in reference example 1, except that the pressure of the pattern rollers 32a, 32b on the plastic film in the Fig.The device shown in 8 is larger than that in reference example 1. The degree of linear scratch formation in reference example 2 was classified as "M2" (Mean 2). Area of ​​latitudes W 0,1-50 µm, Medium Width Wave 25 µm, Area of ​​transverse distances I 1-150 µm, Average transverse distance Iav 45 µm, Average length Lav 5 mm, and Crossing angle θs 90°.

[0064] The surface resistance and light transmittance of the linearly scratched thin aluminium film, measured using the same methods as in reference example 1, were 210 Ω / square and 3.2% respectively. Reference example 3

[0065] The electromagnetic wave absorbing film of reference example 3 was obtained by forming linear scratches with the properties described below in a thin aluminum film in two directions in the same way as in reference example 1, except that the pressure of the pattern rollers 32a, 32b on the plastic film in the Fig.The device shown in 8 is smaller than that in reference example 1. The degree of linear scratch formation in reference example 3 was classified as "W1" (Weak 1). Area of ​​latitudes W 0,1-30 µm, Medium Width Wave 7 µm, Area of ​​transverse distances I 15-300 µm, Average transverse distance Iav 71 µm, Average length Lav 5 mm, and Crossing angle θs 90°.

[0066] The surface resistance and light transmittance of the linearly scratched thin aluminium film, measured using the same methods as in reference example 1, were 15 Ω / square and 1.9% respectively. Reference example 4

[0067] The electromagnetic wave absorbing film of reference example 4 was obtained by forming linear scratches with the properties described below in a thin aluminum film in two directions in the same way as in reference example 1, except that the pressure of the pattern rollers 32a, 32b on the plastic film in the Fig.The device shown in 8 was made smaller than in reference example 1 and larger than in reference example 3. The degree of linear scratch formation in reference example 4 was classified as "W2" (Weak 2). Area of ​​latitudes W 0,1-50 µm, Medium Width Wave 11 µm, Area of ​​transverse distances I 10-210 µm, Average transverse distance Iav 56 µm, Average length Lav 5 mm, and Crossing angle θs 90°.

[0068] The surface resistance and light transmittance of the linearly scratched thin aluminium film, measured using the same methods as in reference example 1, were 27 Ω / square and 2.2% respectively. Reference example 5

[0069] The electromagnetic wave absorbing film of reference example 5 was obtained by forming linear scratches with the properties described below in a thin aluminum film in two directions in the same way as in reference example 1, except that the pressure of the pattern rollers 32a, 32b on the plastic film in the Fig.The device shown in 8 is larger than that in reference example 1. The degree of linear scratch formation in reference example 4 was classified as "S1" (Strong 1). Area of ​​latitudes W 0,2-70 µm, Medium Width Wave 31 µm, Area of ​​transverse distances I 0,5-100 µm, Average transverse distance Iav 37 µm, Average length Lav 5 mm, and Crossing angle θs 90°.

[0070] The surface resistance and light transmittance of the linearly scratched thin aluminium film, measured using the same methods as in reference example 1, were 624 Ω / square and 3.7% respectively. Reference example 6

[0071] The electromagnetic wave absorbing film of reference example 6 was obtained by forming linear scratches with the properties described below in a thin aluminum film in two directions in the same way as in reference example 1, except that the pressure of the pattern rollers 32a, 32b on the plastic film in the Fig.The device shown in 8 was made larger than in reference example 5. The degree of linear scratch formation in reference example 6 was classified as "S2" (Stark2). Area of ​​latitudes W 0,3-100 µm, Medium Width Wave 39 µm, Area of ​​transverse distances I 0,5-80 µm, Average transverse distance Iav 30 µm, Average length Lav 5 mm, and Crossing angle θs 90°.

[0072] The surface resistance and light transmittance of the linearly scratched thin aluminium film, measured using the same methods as in reference example 1, were 1290 Ω / square and 4.1% respectively.

[0073] With regard to the electromagnetic wave absorbing films of reference examples 1-6, the sizes of the linear scratches and the properties of the thin aluminium films with linear scratches are summarized in Table 1 below. Table 1 No. Degree of formation of linear scratches(1) Size of linear scratches (µm) (2) Features Width Distance specific resistance of the surface (Ω / square) Light transmission (%) Area Average Area Average Ref.Example 1 M1 0.1-50 22 1-120 42 172 2.6 Ref.Example 2 M2 0.1-50 25 1-150 45 210 3.2 Ref.Example 3 W1 0.1-30 7 15-300 71 15 1.9 Ref.Example 4 W2 0.1-50 11 10-210 56 27 2.2 Ref. Example 5 S1 0.2-70 31 0.5-100 37 624 3.7 Ref.Example 6 S2 0.3-100 39 0.5-80 30 1290 4.1

[0074] Note: (1) Regarding the degree of formation of linear scratches, W1 < W2 < M1 < M2 < S1 < S2 .

[0075] (2) To determine the range of widths, average width, range of spacings and average spacing of linear scratches, linear scratches with a width of up to 0.1 µm were counted. Example 1

[0076] The electromagnetic wave-absorbing foil of reference example 1 was bonded to the electromagnetic wave-absorbing foil of reference example 3, with its linearly scratched thin aluminum films inside, using a non-conductive adhesive, to create a [missing information - likely a specific type of] in the Fig. to produce the near-field electromagnetic wave absorber shown in Figure 9(a). The thickness of the adhesive layer was 5 µm. (1) Measurement of line noise

[0077] A test specimen TP1 (50 mm × 50 mm) was cut from this near-field electromagnetic wave absorber as in reference example 1 to compare its absorption ratio for line noise Ploss / Pin with that in the Fig. 11(a) and Fig. to measure the evaluation system for electromagnetic waves in the near field shown in 11(b). The results are presented in the Fig. 14 shown. As can be seen from the Fig. As can be seen in Figure 14, the near-field electromagnetic wave absorber of Example 1 had a sufficiently high absorption ratio for line noise Ploss / Pin, although somewhat less than that of the electromagnetic wave absorbing film from Reference Example 1. (2) Measurement of radiation noise

[0078] A test specimen TP2 (40 mm × 40 mm) cut from the near-field electromagnetic wave absorber of Example 1 was scanned with the EMC noise scanner (WM7400) from Morita Tech Co. Ltd. in a frequency range of 0.03 GHz to 7 GHz to measure the radiation noise. Fig. 15(a) and Fig.Figure 15(b) shows the cumulative radiation noise of the test specimen of Example 1 in frequency ranges from 0.03 GHz to less than 3.5 GHz and from 3.5 GHz to 7 GHz, respectively.

[0079] As from the Fig. As can be seen from paragraph 15(a), essentially no cumulative radiation noise of -20 dBm or more was observed in a frequency range from 0.03 GHz to less than 3.5 GHz. As can be seen from the Fig. As can be seen from paragraph 15(b), essentially no cumulative radiation noise of -30 dBm or more was observed in a frequency range from 3.5 GHz to 7 GHz. This confirms that the near-field electromagnetic wave absorber of Example 1 has excellent radiation noise absorption in a frequency range from 0.03 GHz to 7 GHz. Example 2

[0080] The electromagnetic wave absorbing film of reference example 1 was bonded to the electromagnetic wave absorbing film of reference example 4 in the same manner as in example 1 to produce a near-field electromagnetic wave absorber. Test specimens TP1 and TP2 were cut out of this near-field electromagnetic wave absorber and their absorption ratios for conduction noise (Ploss / Pin) and radiation noise were measured using the same methods as in example 1. The results are presented in the Fig. 16 or Table 2. As shown in the Fig.As can be seen in Figure 16, the near-field electromagnetic absorber of Example 2 exhibited a sufficiently high absorption ratio for line noise Ploss / Pin, although somewhat lower than that of the electromagnetic absorbing foil of Reference Example 1. Furthermore, no cumulative radiation noise of -20 dBm or more was observed in a frequency range from 0.03 GHz to less than 3.5 GHz, and no cumulative radiation noise of -30 dBm or more was observed in a frequency range from 3.5 GHz to 7 GHz. Example 3

[0081] The electromagnetic wave absorbing film of reference example 2 was bonded to the electromagnetic wave absorbing film of reference example 3 in the same manner as in example 1 to create a near-field electromagnetic wave absorber. Test specimens TP1 and TP2 were cut out of this near-field electromagnetic wave absorber to measure the absorption ratio of the conduction noise Ploss / Pin and the radiation noise using the same methods as in example 1. The results are presented in the Fig. 17 or Table 2. As shown in the Fig.As can be seen in Figure 17, the near-field electromagnetic wave absorber of Example 3 exhibited a sufficiently high absorption ratio for line noise Ploss / Pin, which, however, was somewhat lower than that of the electromagnetic wave absorbing foil of Reference Example 1. Furthermore, no cumulative radiation noise of -20 dBm or more was observed in a frequency range from 0.03 GHz to less than 3.5 GHz, and no cumulative radiation noise of -30 dBm or more was observed in a frequency range from 3.5 GHz to 7 GHz. Example 4

[0082] The electromagnetic wave absorbing film of reference example 2 was bonded to the electromagnetic wave absorbing film of reference example 4 in the same manner as in example 1 to create a near-field electromagnetic wave absorber. Test specimens TP1 and TP2 were cut out of this near-field electromagnetic wave absorber to measure the absorption ratio of the line noise (Ploss / Pin) and the radiation noise using the same methods as in example 1. The results are presented in the Fig. 18 or Table 2. As shown in the Fig.As can be seen in Figure 18, the near-field electromagnetic wave absorber of Example 4 exhibited a sufficiently high absorption ratio for line noise Ploss / Pin, which, however, was somewhat lower than that of the electromagnetic wave absorbing foil of Reference Example 1. Furthermore, no cumulative radiation noise of -20 dBm or more was observed in a frequency range from 0.03 GHz to less than 3.5 GHz, and no cumulative radiation noise of -30 dBm or more was observed in a frequency range from 3.5 GHz to 7 GHz. Comparative example 1

[0083] Test specimens TP1 and TP2, consisting solely of a PET film with a thin aluminum film 60 nm thick, as obtained in reference example 1, were measured for absorption ratios of conduction noise (ploss / pin) and radiation noise using the same methods as in example 1. The results are presented in the Fig.19 or Table 2. As shown in the Fig. As can be seen in Figure 19, the test specimen TP1 of comparison example 1 exhibits an extremely lower absorption ratio for line noise Ploss / Pin than the electromagnetic wave absorbing foil of reference example 1. Furthermore, cumulative radiation noise as high as -15 dBm or more, particularly -10 dBm or more, was observed over almost the entire area of ​​test specimen TP2 in a frequency range from 0.03 GHz to less than 3.5 GHz, and cumulative radiation noise as high as -25 dBm or more, particularly -20 dBm or more, was observed over almost the entire area of ​​test specimen TP2 in a frequency range from 3.5 GHz to 7 GHz. This confirms that test specimen TP2 of comparison example 1 emitted an extremely high level of radiation noise in a frequency range from 0.03 GHz to 7 GHz. Comparative example 2

[0084] Test specimens TP1 and TP2, consisting solely of the electromagnetic wave-absorbing foil of reference example 1, were measured with respect to the absorption ratio of the conduction noise Ploss / Pin and the radiation noise using the same methods as in example 1. The results are presented in the Fig. 12 or shown in Table 2. Incidentally, the absorption ratio for line noise Ploss / Pin of comparison example 2 was the same as in reference example 1 ( Fig.12) Furthermore, as in Comparative Example 1, in a frequency range from 0.03 GHz to below 3.5 GHz, cumulative radiation noise of -15 dBm or more, in particular -10 dBm or more, was observed in almost the entire area of ​​test specimen TP2, and in a frequency range from 3.5 GHz to 7 GHz, cumulative radiation noise of -25 dBm or more, in particular -20 dBm or more, was observed. This confirms that test specimen TP2 of Comparative Example 1 emitted an extremely high level of radiation noise in a frequency range from 0.03 GHz to 7 GHz. Comparative example 3

[0085] Test specimens TP1 and TP2, consisting solely of the electromagnetic wave-absorbing foil from reference example 3, were measured with respect to the absorption ratio of the conduction noise Ploss / Pin and the radiation noise using the same methods as in example 1. The results are presented in the Fig.20 or Table 2. As shown in the Fig. As can be seen in section 20, the test specimen TP1 of comparison example 3 exhibits a slightly lower absorption ratio for line noise P. loss / P inon the electromagnetic wave-absorbing foil of reference example 1. In a frequency range from 0.03 GHz to less than 3.5 GHz, a cumulative radiation noise of -15 dBm or more was observed only in a portion of test specimen TP2, but a cumulative radiation noise of -20 dBm to -15 dBm was observed in almost the entire area of ​​test specimen TP2. In a frequency range from 3.5 GHz to 7 GHz, a cumulative radiation noise of -25 dBm or more was observed only in a portion of test specimen TP2, but a cumulative radiation noise of -30 dBm to -25 dBm was observed in almost the entire area of ​​test specimen TP2. This confirms that test specimen TP2 of comparison example 3 emits significant radiation noise in a frequency range from 0.03 GHz to 7 GHz. Comparative example 4

[0086] Test specimens TP1 and TP2, consisting solely of the electromagnetic wave-absorbing foil from reference example 5, were measured with respect to the absorption ratio of the conduction noise Ploss / Pin and the radiation noise using the same methods as in example 1. The results are presented in the Fig. 21 or Table 2. As shown in the Fig.As can be seen from Figure 21, the test specimen TP1 of comparison example 4 exhibited a transmission noise absorption ratio Ploss / Pin comparable to that of the electromagnetic wave-absorbing foil of reference example 1. However, in a frequency range from 0.03 GHz to less than 3.5 GHz, cumulative radiation noise of -15 dBm or more, particularly -10 dBm or more, was observed over almost the entire area of ​​test specimen TP2. Similarly, in a frequency range from 3.5 GHz to 7 GHz, cumulative radiation noise of -25 dBm or more, particularly -20 dBm or more, was observed over almost the entire area of ​​test specimen TP2. This confirms that test specimen TP2 of comparison example 4 emitted extremely high levels of radiation noise in a frequency range from 0.03 GHz to 7 GHz. Comparative example 5

[0087] Two electromagnetic wave absorbing foils from reference example 1 were bonded together with their linearly scratched thin aluminum films on the inside in the same manner as in example 1 to create a near-field electromagnetic wave absorber. Test specimens TP1 and TP2 were cut out of this near-field electromagnetic wave absorber to determine the absorption ratio of the transmission noise P. loss / P in and to measure the radiation noise using the same methods as in Example 1. The results are in the Fig. 22 or shown in Table 2. As can be seen from the Fig. As can be seen in section 22, the test specimen TP1 of comparison example 5 exhibits an absorption ratio for line noise P loss / P inThe test specimen TP2 exhibits a noise level comparable to that of the electromagnetic wave-absorbing foil of Reference Example 1. However, in a frequency range from 0.03 GHz to less than 3.5 GHz, a cumulative radiation noise of -20 dBm to -15 dBm was observed over almost the entire area of ​​the specimen, although a cumulative radiation noise of -15 dBm or more was observed only in a portion of the specimen. Similarly, in a frequency range from 3.5 GHz to 7 GHz, a cumulative radiation noise of -30 dBm to -25 dBm was observed over almost the entire area of ​​the specimen, with a cumulative radiation noise of 25 dBm or more observed only in a portion of the specimen. This confirms that the specimen TP2 from Reference Example 5 emits significant radiation noise in a frequency range from 0.03 GHz to 7 GHz.This appears to be due to the fact that the two electromagnetic wave absorbing foils, which make up the near-field electromagnetic wave absorber of comparison example 5, do not sufficiently absorb the radiation noise (electromagnetic shielding). Comparative example 6

[0088] The electromagnetic wave absorbing foil of Reference Example 1 was glued onto the electromagnetic wave absorbing foil of Reference Example 5, with its linearly scratched thin aluminum films attached to the inside in the same manner as in Example 1 to create a near-field electromagnetic wave absorber. From this near-field electromagnetic wave absorber, test specimens TP1 and TP2 were cut out to measure the absorption ratio of the line noise Ploss / Pin and the radiation noise using the same methods as in Example 1. The results are presented in the Fig. 23 or shown in Table 2. As can be seen from the Fig.As can be seen in Figure 23, the test specimen TP1 of comparison example 6 exhibits a Ploss / Pin absorption ratio for line noise that is comparable to that of the electromagnetic wave-absorbing foil of reference example 1. However, in a frequency range from 0.03 GHz to less than 3.5 GHz, a cumulative radiation noise of -20 dBm to -15 dBm was observed in almost half of the test specimen TP2, although a cumulative radiation noise of -15 dBm or more was observed in only a portion of the test specimen TP2. Similarly, in a frequency range from 3.5 GHz to 7 GHz, a cumulative radiation noise of -30 dBm to -25 dBm was observed in approximately 20% of the test specimen TP2, with a cumulative radiation noise of 25 dBm or more being observed in only a portion of the test specimen TP2. This confirms that the test specimen TP2 from comparison example 6 emits significant radiation noise in a frequency range from 0.03 GHz to 7 GHz.This appears to be due to the fact that one of the electromagnetic wave absorbing films of reference examples 1 and 5, which make up the near-field electromagnetic wave absorber of comparison example 6, is unable to sufficiently absorb the radiation noise (electromagnetic shielding). Comparative example 7

[0089] Two electromagnetic wave absorbing foils from Reference Example 3 were bonded together with their linearly scratched thin aluminum films on the inside in the same manner as in Example 1 to create a near-field electromagnetic wave absorber. Test specimens TP1 and TP2 were cut out of this near-field electromagnetic wave absorber to measure the absorption ratio of the conduction noise (Ploss / Pin) and the radiation noise using the same methods as in Example 1. The results are presented in the Fig.24 or shown in Table 2. As can be seen from the Fig.As can be seen from Figure 24, the test specimen TP1 of comparison example 7 exhibited a lower absorption ratio for line noise Ploss / Pin than that of the electromagnetic wave absorbing foil of reference example 1. Furthermore, a cumulative radiation noise of -25 dBm or more was observed in a portion of test specimen TP2 in a frequency range from 3.5 GHz to 7 GHz, and a cumulative radiation noise of -30 dBm to -25 dBm was observed in approximately 15% of test specimen TP2, although a cumulative radiation noise of -20 dBm or more was not observed in a frequency range from 0.03 GHz to less than 3.5 GHz. This confirms that test specimen TP2 from comparison example 7 emits significant radiation noise in a frequency range from 0.03 GHz to 7 GHz.This appears to be due to the fact that two electromagnetic wave absorbing foils of reference example 3, which form the near-field electromagnetic wave absorber of comparison example 7, did not have sufficient absorption capacity for radiation noise. Comparative example 8

[0090] Two electromagnetic wave absorbing foils from Reference Example 4 were bonded together with their linearly scratched thin aluminum films on the inside in the same manner as in Example 1 to create a near-field electromagnetic wave absorber. Test specimens TP1 and TP2 were cut out of this near-field electromagnetic wave absorber to measure the absorption ratio for conduction noise (ploss / pin) and radiation noise using the same methods as in Example 1. The results are presented in the Fig. 25 or shown in Table 2. As can be seen from the Fig.As can be seen in Figure 25, the test specimen TP1 of comparison example 8 exhibited a slightly lower absorption ratio for line noise Ploss / Pin than that of the electromagnetic wave-absorbing foil of reference example 1. Furthermore, in a frequency range from 0.03 GHz to less than 3.5 GHz, a cumulative radiation noise of -20 dBm to -15 dBm was observed in almost the entire area of ​​test specimen TP2, although a cumulative radiation noise of -15 dBm or more was observed in only a portion of test specimen TP2. Similarly, in a frequency range from 3.5 GHz to 7 GHz, a cumulative radiation noise of -30 dBm to -25 dBm was observed in almost half of test specimen TP2, although a cumulative radiation noise of -25 dBm or more was observed in only a portion of test specimen TP2. This confirms that the test specimen TP2 of comparison example 8 emits significant radiation noise in a frequency range from 0.03 GHz to 7 GHz. Comparative example 9

[0091] The electromagnetic wave absorbing foil of reference example 3 was glued onto the electromagnetic wave absorbing foil of reference example 5, with its linearly scratched thin aluminum films attached to the inside in the same manner as in example 1, to create a near-field electromagnetic wave absorber. Test specimens TP1 and TP2 were cut out of this near-field electromagnetic wave absorber to measure the absorption ratio for line noise (ploss / pin) and radiation noise using the same methods as in example 1. The results are presented in the Fig. 26 or Table 2. As shown in the Fig.As can be seen in Figure 26, the test specimen TP1 of comparison example 9 exhibited a slightly lower absorption ratio for line noise Ploss / Pin than that of the electromagnetic wave-absorbing foil of reference example 1. Furthermore, in a frequency range from 0.03 GHz to less than 3.5 GHz, a cumulative radiation noise of -20 dBm to -15 dBm was observed in approximately 20% of test specimen TP2, although a cumulative radiation noise of -15 dBm or more was observed in only a portion of test specimen TP2. Similarly, in a frequency range from 3.5 GHz to 7 GHz, a cumulative radiation noise of -30 dBm to -25 dBm was observed in approximately 10% of test specimen TP2, although a cumulative radiation noise of 25 dBm or more was observed in only a portion of test specimen TP2. This confirms that the test specimen TP2 of comparison example 9 emits significant radiation noise in a frequency range from 0.03 GHz to 7 GHz. Comparative example 10

[0092] Two electromagnetic wave absorbing foils from Reference Example 5 were bonded together with their linearly scratched thin aluminum films on the inside in the same manner as in Example 1 to create a near-field electromagnetic wave absorber. Test specimens TP1 and TP2 were cut from this near-field electromagnetic wave absorber to measure the absorption ratio for conduction noise (Ploss / Pin) and radiation noise using the same methods as in Example 1. The results are presented in the Fig. 27 or shown in Table 2. As can be seen from the Fig.As can be seen in Figure 27, the test specimen TP1 of comparison example 10 exhibits a transmission noise absorption ratio Ploss / Pin that is comparable to that of the electromagnetic wave-absorbing foil of reference example 1. However, in a frequency range from 0.03 GHz to less than 3.5 GHz, a cumulative radiation noise of -20 dBm to -15 dBm was observed in approximately 30% of test specimen TP2, although a cumulative radiation noise of -15 dBm or more was observed in only a portion of test specimen TP2. Similarly, in a frequency range from 3.5 GHz to 7 GHz, a cumulative radiation noise of -30 dBm to -25 dBm was observed in approximately 20% of test specimen TP2, with a cumulative radiation noise of -25 dBm or more being observed in only a portion of test specimen TP2. This confirms that the test specimen TP2 of comparison example 10 emits significant radiation noise in a frequency range from 0.03 GHz to 7 GHz.

[0093] The results in Comparative Examples 5, 7, 8, and 10 show that, although a near-field electromagnetic wave absorber consists of two electromagnetic wave-absorbing films, a balanced combination of conduction noise absorption and radiation noise absorption cannot be achieved if both electromagnetic wave-absorbing films have the same surface resistance. The results in Comparative Examples 6 and 9 also show that, although a near-field electromagnetic wave absorber consists of two electromagnetic wave-absorbing films with different surface resistances, a balanced combination of conduction noise absorption and radiation noise absorption cannot be achieved if their surface resistances do not meet the requirements of the present invention.

[0094] The composition of the near-field electromagnetic wave absorbers of Examples 1-4 and Comparison Examples 1-10, as well as their absorption ratios for line noise Ploss / Pin and radiation noise, are summarized in the following Table 2. Table 2 Nr. Combination of electromagnetic wave absorbing films (degree of linear scratch formation) P loss / P in Cumulative radiation noise Example 1 Ref. Example 1(M1) Ref. Example 3(W1) Fig. 14 None Example 2 Ref. Example 1(M1) Ref. Example 4(W2) Fig. 16 None Example 3 Ref. Example 2(M2) Ref. Example 3(W1) Fig. 17 None Example 4 Ref. Example 2(M2) Ref. Example 4(W2) Fig. 18 None See example 1. Only unscratched thin aluminum film Fig. 19 Extremely large See example 2. Ref. Example 1 (M1) only Fig. 12 Extremely large See example 3. Ref. Example 3 (W1) only Fig. 20 Large See example 4. Ref. Example 5 (S1) only Fig. 21 Extremely large See example 5. Ref. Example 1(M1) Ref. Example 1(M1) Fig. 22 Large See example 6. Ref. Example 1(M1) Ref. Example 5S1 Fig. 23 Large See example 7. Ref. Example 3(W1) Ref. Example x. 3(W1) Fig. 24 Large See example 8. Ref. Example 4(W2) Ref. Example 4(W2) Fig. 25 Large See example 9. Ref. Example 3(W1) Ref. Example 5(S1) Fig. 26 Large See example 10. Ref. Example 5(S1) Ref. Example 5(S1) Fig. 27 Large Example 5

[0095] Ten electromagnetic wave absorbing foil pieces A were randomly cut from a production batch (single roll) of electromagnetic wave absorbing foil manufactured in the same manner as in Reference Example 1, exhibiting a degree of linear scratch formation of M1. Additionally, ten electromagnetic wave absorbing foil pieces B were randomly cut from a production batch (single roll) of electromagnetic wave absorbing foil manufactured in the same manner as in Reference Example 3, exhibiting a degree of linear scratch formation of W1. Each electromagnetic wave absorbing foil piece A was randomly combined with one electromagnetic wave absorbing foil piece B and bonded with a non-conductive adhesive, with their linearly scratched thin aluminum films inside, to obtain ten near-field electromagnetic wave absorber test specimens TP2.Each of the TP2 test specimens was scanned with the EMC noise scanner (WM7400) from Morita Tech Co. Ltd. in a frequency range of 0.03 GHz to 7 GHz to measure radiation noise as in reference example 1. The . Fig. 38, Fig. 39, Fig. 40, Fig. 41, Fig. 42, Fig. 43, Fig. 44, Fig. 45, Fig. 46 to Fig. Figure 47 shows the cumulative radiation noise in the ranges from 0.03 GHz to 3.5 GHz and from 3.5 GHz to 7 GHz, respectively.

[0096] As from the Fig. 28, Fig. 29, Fig. 30, Fig. 31, Fig. 32, Fig. 33, Fig. 34, Fig. 35, Fig. 36 to Fig.As can be seen in Figure 37, each near-field electromagnetic wave absorber according to the present invention, formed by bonding each electromagnetic wave absorbing film arbitrarily selected from the production lot with grade M1 linear scratch formation to an electromagnetic wave absorbing film arbitrarily selected from the production lot with grade W1 linear scratch formation, transmits only a small amount of cumulative radiation noise. This confirms that the near-field electromagnetic wave absorber of the present invention can stably suppress radiation noise with substantially no or minor irregularities in any combination of grades M1 and W1 linear scratch formation, thereby producing electromagnetic wave absorbing films with surface resistivities that meet the requirements of the present invention. Comparative example 11

[0097] Ten pieces of electromagnetic wave-absorbing foil were randomly cut from a single roll (first roll) of the electromagnetic wave-absorbing foil produced in Reference Example 1, in which the degree of linear scratch formation was M1. Ten more pieces of electromagnetic wave-absorbing foil were randomly cut from another roll (second roll) of electromagnetic wave-absorbing foil produced under the same conditions as in Reference Example 1, in which the degree of linear scratch formation was M1.Each piece of electromagnetic wave absorbing foil from the first roll was randomly combined with a piece of electromagnetic wave absorbing foil from the second roll and bonded with a non-conductive adhesive, with their linearly scratched thin aluminum films inside, to obtain ten TP2 test specimens of the near-field electromagnetic wave absorber. Each TP2 test specimen was measured for radiation noise in the same way as in Example 5. Fig. 38, Fig. 39, Fig. 40, Fig. 41, Fig. 42, Fig. 43, Fig. 44, Fig. 45, Fig. 46 to Fig. Figure 47 shows the cumulative radiation noise in the range from 0.03 GHz to 3.5 GHz and in the range from 3.5 GHz to 7 GHz, respectively.

[0098] As from the Fig.As can be seen from Figures 38-47, of the test specimens of near-field electromagnetic wave absorbers, which were produced by gluing each electromagnetic wave absorbing film, arbitrarily selected from a roll in which the degree of linear scratch formation was M1, onto an electromagnetic wave absorbing film, arbitrarily selected from another roll in which the degree of linear scratch formation was also M1, all test specimens except test specimen 8 suffered from large cumulative radiation noise, and only test specimen 8 showed good absorption capacity for radiation noise.This confirms that when two electromagnetic wave absorbing films with the appropriate degree M1 of linear scratch formation in different rolls are arbitrarily combined, most of the resulting near-field electromagnetic wave absorbers do not have satisfactory absorption capacity for radiation noise, although some of them can suppress radiation noise well.

[0099] As can be seen from Table 2, all near-field electromagnetic absorbers of comparison example 7, obtained by combining two electromagnetic absorbing films of reference example 3 (degree of linear scratch formation: W1), the near-field electromagnetic absorber of comparison example 8, obtained by combining two electromagnetic absorbing films of reference example 4 (degree of linear scratch formation: W2), and the near-field electromagnetic absorber of comparison example 10, produced by combining two electromagnetic absorbing films of reference example 5 (degree of linear scratch formation: S1), are insufficient with respect to their absorption capacity for radiation noise.This confirms that when electromagnetic wave absorbing films with the same degree of linear scratch formation (surface resistance) are combined, sufficient absorption capacity for radiation noise is not achieved, regardless of whether the degree of linear scratch formation (surface resistance) is changed. DESCRIPTION OF REFERENCE NUMBERS 1 Absorber for electromagnetic waves in the near field. 100, 100a, 100b Electromagnetic wave absorbing film. 10, 10a, 10b Plastic film. 11, 11a, 11b Thin metal film. 12, 12a, 12b, 12c, 12d Linear scratches. 2a, 2b, 2c, 2d Sample roll. 3a, 3b, 3c, 3d, 3e pressure roller. 20 adhesive layers.

Claims

[1] A near-field electromagnetic wave absorber comprising at least one plastic film (10) and two linearly scratched thin metal films (11a, 11b), wherein each of the linearly scratched thin metal films (11a, 11b) has a large number of substantially parallel, intermittent, linear scratches (12a, 12b) with irregular widths and spacings in several directions, wherein one linearly scratched thin metal film (11a) has a surface resistivity of 150-300 Ω / square and the other linearly scratched thin metal film (11b) has a surface resistivity of 10-50 Ω / square. [2] The near-field electromagnetic wave absorber according to claim 1, wherein a pair of plastic films (10) having on one side a linearly scratched thin metal film (11a, 11b) are glued together. [3] The near-field electromagnetic wave absorber according to claim 2, wherein the two linearly scratched thin metal films (11a, 11b) adhere to each other. [4] The near-field electromagnetic wave absorber according to claim 1, wherein the near-field electromagnetic wave absorber consists of a plastic film (10) and two linearly scratched thin metal films (11a, 11b) formed on both sides of the plastic film (10). [5] The near-field electromagnetic wave absorber according to claim 1, wherein both thin metal films (11a, 11b) have a thickness of 20-100 nm. [6] The near-field electromagnetic wave absorber according to claim 1, wherein the linear scratches (12a, 12b) formed in both thin metal films (11a, 11b) are aligned in two directions with a crossing angle of 30-90°. [7] The near-field electromagnetic wave absorber according to claim 1, wherein one of the linearly scratched thin metal films (11a, 11b) has a light transmittance of 2.5 to 3.5% and the other has a light transmittance of 1 to 2.2%. [8] The near-field electromagnetic wave absorber according to claim 1, wherein both thin metal films (11a, 11b) are made of aluminium. [9] The near-field electromagnetic wave absorber according to any one of claims 1 to 8, wherein the linear scratches (12a, 12b) formed in both thin metal films (11a, 11b) have a width in the range of 0.1 to 100 µm and an average of 2 to 50 µm and spacings in the range of 0.1 to 500 µm and an average of 10 to 100 µm.

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