EP0900458B1 - Panneaux absorbant les ondes electromagnetiques et materiaux destines a ces derniers - Google Patents

Panneaux absorbant les ondes electromagnetiques et materiaux destines a ces derniers Download PDF

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Publication number
EP0900458B1
EP0900458B1 EP98901750A EP98901750A EP0900458B1 EP 0900458 B1 EP0900458 B1 EP 0900458B1 EP 98901750 A EP98901750 A EP 98901750A EP 98901750 A EP98901750 A EP 98901750A EP 0900458 B1 EP0900458 B1 EP 0900458B1
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EP
European Patent Office
Prior art keywords
layer
electromagnetic wave
absorber
dielectric constant
ferrite
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EP98901750A
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German (de)
English (en)
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EP0900458A1 (fr
Inventor
Vikram Joshi
Kenichi Kimura
Carlos A. Paz De Araujo
Hiroshi Kiyokawa
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Fujita Corp
Symetrix Corp
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Fujita Corp
Symetrix Corp
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Priority claimed from US08/782,938 external-priority patent/US5853889A/en
Priority claimed from US08/782,934 external-priority patent/US6037046A/en
Application filed by Fujita Corp, Symetrix Corp filed Critical Fujita Corp
Publication of EP0900458A1 publication Critical patent/EP0900458A1/fr
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    • E—FIXED CONSTRUCTIONS
    • E04—BUILDING
    • E04B—GENERAL BUILDING CONSTRUCTIONS; WALLS, e.g. PARTITIONS; ROOFS; FLOORS; CEILINGS; INSULATION OR OTHER PROTECTION OF BUILDINGS
    • E04B1/00—Constructions in general; Structures which are not restricted either to walls, e.g. partitions, or floors or ceilings or roofs
    • E04B1/62—Insulation or other protection; Elements or use of specified material therefor
    • E04B1/92—Protection against other undesired influences or dangers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q17/00—Devices for absorbing waves radiated from an antenna; Combinations of such devices with active antenna elements or systems
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q17/00—Devices for absorbing waves radiated from an antenna; Combinations of such devices with active antenna elements or systems
    • H01Q17/004—Devices for absorbing waves radiated from an antenna; Combinations of such devices with active antenna elements or systems using non-directional dissipative particles, e.g. ferrite powders
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q17/00—Devices for absorbing waves radiated from an antenna; Combinations of such devices with active antenna elements or systems
    • H01Q17/007—Devices for absorbing waves radiated from an antenna; Combinations of such devices with active antenna elements or systems with means for controlling the absorption
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q17/00—Devices for absorbing waves radiated from an antenna; Combinations of such devices with active antenna elements or systems
    • H01Q17/008—Devices for absorbing waves radiated from an antenna; Combinations of such devices with active antenna elements or systems with a particular shape

Definitions

  • the invention relates to panels utilized in construction of buildings for the purpose of absorbing electromagnetic waves, particularly in the frequency ranges of radio transmissions, television transmissions, and microwaves, and more particularly to such panels made up of two or more distinct materials, such as composites and multi-layered panels.
  • Wave absorption panels for use in building construction generally comprise a support layer of concrete or other basic building material, a reflective layer that is usually a metal mesh or other conductive material, an absorbing layer that typically is a ferrite, and an external layer, such as a silicate building tile, to protect the absorbing layer from environmental effects.
  • Other materials that have been used as an absorbing layer include conducting materials, such as carbon fibers, in a resin.
  • wave absorption panels The most successful materials for wave absorption panels, ferrites, are relatively heavy, must be up to a centimeter thick to be effective, and are relatively soft and therefore require an additional layer of building material, such as tiles, to protect them from the environmental effects.
  • wave absorption panels known in the art are bulky and heavy, making the structure expensive and unwieldy to employ on an entire building, are not capable of absorbing over the wide frequency range necessary to include all electromagnetic waves commonly present in a large metropolitan area, or both.
  • the frequency at which conventional ferrites absorb is in the 200-400 megahertz range, while VHF television frequencies range from about 100 to 250 megahertz and UHF television frequencies range from about 450 megahertz up to about 800 megahertz. Therefore, it would be highly desirable to have a wave absorption panel that is relatively light and thin while at the same time absorbs over a wide frequency range including up to about 800 megahertz.
  • the prior art wave absorption panels generally are useful only in the frequency range of television electromagnetic waves, which are the waves in which the problems due to reflection are most widespread.
  • problems with reflection of waves can have serious consequences in other specialized areas, such as radio LAN systems, which can lose data because of reflections, and airport radio control systems, in which clarity of signal can be a matter of life and death. It would be very desirable to have absorption panels that absorb strongly in the frequency ranges of these specialized uses.
  • US 5,296,859 describes an electromagnetic wave-absorbing apparatus having a broad-band electromagnetic wave-absorbing characteristic.
  • a first dielectric layer having low permittivity is arranged on a metallic reflector.
  • a ferrite layer is provided on which a second dielectric layer having a low permittivity is arranged.
  • a magnetic body having a low magnetic permeability is provided on the second dielectric layer.
  • the magnetic body uses materials, such as a rubber ferrite, whereas the second dielectric layer has a permittivity smaller than 70.
  • a first layer of concrete is provided on a metal plate.
  • a ferrite layer is arranged on the layer of concrete on which a second layer of concrete is provided.
  • EP 0 353 923 describes an electromagnetic wave absorber, wherein a dielectric plate is attached on a conductive plate. A flat ferrite plate is attached on the dielectric plate, thereby defining a two-layer structure of the dielectric plate and the ferrite plate.
  • US 4,012,738 describes a microwave radiation absorber for early-warning in frequency ranges of radar.
  • the absorber comprises a carbon-impregnated rubber layer and a thin layer of ferrite.
  • the ferrite layer comprises, for example, magnesium-zinc, magnesium-manganese or nickel-zinc mixed types (Ni 0.6 Zn 0.4 ) Ofe 2 O 3 .
  • the invention solves the above problems by providing multi-component absorbers that can be tuned to cover a wide frequency range, or to have superb absorption in a specific range, depending on the electromagnetic environmental problem defined by a specific construction site.
  • the tuning may be done by selecting the specific materials in a multi-layer stack, by selecting specific materials in a composite, by varying the thickness of the layers in a multi-layer stack or the thickness of a composite, by varying the amounts of each component in a composite, and by combinations of the foregoing.
  • the invention provides specific combinations of materials that lend themselves to the solution of the broad range problem, or to tuning for the solution to specific problems.
  • the invention provides a combination of a high dielectric material with a ferrite that is a highly effective absorber over a moderate range of television frequencies and can be tuned to a specific range by choosing the specific materials and by varying the thickness of each component layer.
  • a combination of a ferroelectric layer, a ferrite layer, a polymer, and a reflective metal provides excellent absorption across the entire television frequency range.
  • the combination of a first ferrite layer and a second ferrite layer can be tuned to a particular frequency with little change in the magnitude of the reflective loss as the frequency range over which the loss occurs is changed.
  • the invention provides an electromagnetic wave absorption panel for use in building construction, the absorption panel comprising: a building support element; and an absorber element supported by the support element, the absorber element comprising a first layer, a second layer, and a third layer, the first layer located closer to the point of incidence of the electromagnetic wave on the panel than the second layer, the third layer located more distant from the point of incidence of the electromagnetic wave than the second layer, the second layer comprising a high dielectric constant material, the first layer comprising a ferrite, and the third layer comprising a low dielectric constant material.
  • the low dielectric constant material comprises a polymer and the high dielectric constant material comprises a ferroelectric material.
  • the invention provides an electromagnetic wave absorption panel for use in building construction, the panel comprising: a building support element; and an absorber element supported by the support element, the absorber element comprising a first layer and a second layer, the first layer located closer to the point of incidence of the electromagnetic wave on the panel than the second layer, the first layer comprising a ferrite, and the second layer comprising a high dielectric constant material.
  • the ferrite comprises nickel-zinc ferrite and the high dielectric constant material comprises BST.
  • the absorber element further includes: a third layer located between the first layer and the second layer, the third layer comprising a polymer, and a fourth layer located between the third layer and the second layer, the fourth layer comprising LSM.
  • the absorber element further includes a third layer located farther from the point of incidence of the electromagnetic wave than the first layer, the third layer comprising a low dielectric constant material.
  • the third layer is located between the first layer and the second layer, and the panel further including a conductive reflective element located farther from the point of incidence of the electromagnetic wave than the absorber element.
  • the absorber element further includes a fourth layer comprising a dielectric material.
  • the invention provides an electromagnetic wave absorption panel for use in building construction, the panel comprising: a building support element; and an absorber element supported by the support element, the absorber element comprising a first layer and a second layer, the second layer located farther from the point of incidence of the electromagnetic wave on the panel than the first layer, the first layer comprising a ferroelectric material, and the second layer comprising a ferrite.
  • the absorber element further includes a third layer located farther from the point of incidence of the electromagnetic wave than the second layer.
  • the invention provides an electromagnetic wave absorption panel for use in building construction, the panel comprising: a building support element; and an absorber element supported by the support element, the absorber element comprising a first layer and the second layer, the second layer located farther from the point of incidence of the electromagnetic wave on the panel than the first layer, the first layer comprising a ferrite, and the second layer comprising a ferroelectric material.
  • the invention provides an electromagnetic wave absorption panel for use in building construction, the panel comprising: a building support element; and an absorber element supported by the support element, the absorber element comprising a first layer comprising a polymer and a second layer comprising a material having a higher dielectric constant than the polymer.
  • the second layer is located farther from the point of incidence of the electromagnetic wave on the panel than the first layer.
  • the first layer is located farther from the point of incidence of the electromagnetic wave than the second layer.
  • the second layer comprises a ferrite and there are n of the absorber elements, each absorber element comprising one of the first layers and one of the second layers, and where n is an integer between 2 and 100.
  • the invention provides an electromagnetic wave absorption panel for use in building construction, the panel comprising: a building support element; a reflective element supported by the support element; and an absorber element supported by the support element, the absorber element located closer to the point of incidence of the electromagnetic wave on the panel than the reflective element, the absorber element comprising a first layer comprising a ferrite and a second layer comprising a low dielectric constant material, the second layer located farther from the point of incidence of the electromagnetic wave than the first layer.
  • there are n of the absorber elements each absorber element comprising one of the first layers and one of the second layers, and n is an integer between 2 and 100.
  • the invention also provides an electromagnetic wave absorption panel for use in building construction, the panel comprising: a building support element; and an absorber element supported by the support element, the absorber element comprising a second layer comprising a high dielectric constant material, a first layer comprising a material in which the imaginary part of the permeability is greater than or equal to the real part of the permeability, and a third layer comprising a low dielectric constant material, the third layer located farther from the point of incidence of the electromagnetic wave on the panel than the second layer, the first layer located between the second layer and the third layer.
  • the second layer comprises a ferrite and the panel further includes a conductive reflective element located farther from the point of incidence of the electromagnetic wave than the absorber element.
  • the third layer comprises a polymer
  • the second layer comprises a material selected from the group consisting of ABO 3 type perovskites and layered superlattice materials.
  • the invention provides an electromagnetic wave absorption panel for use in building construction, the absorption panel capable of effective wave absorption over a range of frequencies, the absorption panel comprising a multi-component absorber element having an effective real part of the permittivity, ⁇ ' eff , and an effective real part of the permeability, ⁇ ' eff , such that ( ⁇ ' eff ⁇ ' eff ) 1 ⁇ 2 - 1/f over the range of frequencies, where f is the frequency of the incident wave.
  • the invention provides an electromagnetic wave absorption panel for use in building construction, the absorption panel capable of effective wave absorption over a range of frequencies, the absorption panel comprising a multi-component absorber element having an effective real part of the permittivity, ⁇ ' eff , that decreases with frequency.
  • the invention also solves the above problems by providing wave absorption panels including materials, such as high dielectric constant materials, ferroelectrics, conducting oxides, magnetoplumbites, garnets and signet magnetics that have never before been considered for use in such panels. These materials may be used in combination with ferrites that have previously been used with the wave absorption panels, the invention also provides a novel nickel-zinc ferrite that is particularly effective for use with the wave absorption panels, i.e. Ni 0.4 Zn 0.6 Fe 2 O 4 .
  • the invention provides an electromagnetic wave absorption panel for use in building construction, the absorption panel comprising: a building support element; and an absorber element supported by the support element, the absorber element comprising a high dielectric constant material.
  • the absorber element further comprises a ferrite and a polymer.
  • the high dielectric constant material comprises a material selected from the group consisting of ABO 3 type perovskites, layered superlattice materials, conducting oxides, and signet magnetics.
  • the high dielectric constant material comprises a material selected from the group consisting of BST, LSM, and Z x BaTiO 3 +(100% - Z) x BiFeO 3 where 100% > Z > 0%.
  • the invention provides an electromagnetic wave absorption panel for use in building construction, the absorption panel comprising: a building support element; and an absorber element supported by the support element, the absorber element comprising a ferroelectric material.
  • the absorber element further comprises a ferrite and a polymer.
  • the ferroelectric is selected from the group consisting of ABO 3 type perovskites and layered superlattice materials.
  • the ferroelectric is selected from the group consisting of barium titanate, strontium bismuth tantalate, strontium bismuth niobate, strontium bismuth titanate, strontium bismuth zirconate, and solid solutions thereof.
  • the invention provides an electromagnetic wave absorption panel for use in building construction, the absorption panel comprising: a building support element; and an absorber element supported by the support element, the absorber element comprising a composite of a polymer and a second material selected from the group consisting of: high dielectric constant materials, ferroelectrics, garnets, magnetoplumbites, and signet magnetics.
  • the second material comprises a material selected from the group consisting of nickel-zinc ferrite, BST, LSM, yttrium iron garnet, strontium bismuth tantalate, strontium bismuth niobate, strontium bismuth titanate, strontium bismuth zirconate, and solid solutions thereof.
  • the invention provides an electromagnetic wave absorption panel for use in building construction, the absorption panel comprising: a building support element; and an absorber element supported by the support element, the absorber element comprising a garnet.
  • the garnet is yttrium iron garnet.
  • the invention provides an electromagnetic wave absorption panel for use in building construction, the absorption panel comprising: a building support element; and an absorber element supported by the support element, the absorber element comprising a magnetoresistive material.
  • the magnetoresistive material is a material selected from the group consisting of La 0.67 Sr 0.33 MnO 3 , La x Ca( 1-x )MnO 3 , and La x Pb (1-x) MnO 3 , where 0 ⁇ x ⁇ 1.
  • the invention provides an electromagnetic wave absorption panel for use in building construction, the absorption panel comprising: a building support element; and an absorber element supported by the support element, the absorber element comprising Ni 0.4 Zn 0.6 Fe 2 O 4 .
  • the new materials result in panels that are lighter and less bulky than prior art panels and also absorb over wider frequency ranges.
  • analysis of how the new materials work has led to a deeper understanding of the wave absorption process.
  • the invention not only provides new multi-component structures for wave absorption panels which are lighter, less bulky, and absorb over wider frequency ranges than previous structures used for wave absorption in building construction, but a study of these structures has led to a deeper understanding of how the waves are absorbed, such as the role that dielectric constant can play in absorption panels, and it also has led to a process of designing a panel by first finding a structure that absorbs roughly in the region where absorption is desired, and then tuning the composition of the absorber to provide a dielectric constant and other parameters that will more closely correspond to a quarter-wave plate, and tuning the thickness of the materials to move the absorption band to cover the desired frequency range.
  • FIGS. 1 and 2 show a generalized wave absorption panel according to the invention.
  • a perspective, partially cut-away view is shown in FIG. 1, and a cross-sectional view is shown in FIG. 2.
  • FIGS. 1 and 2 and the other figures that depict cross-sections of an absorber 106 according to the invention do not depict actual panels or absorbers, but are simplified representations designed to more clearly depict the invention than would be possible from a drawing of an actual panel. For example, some layers are so thin as compared to other layers, that if all layers were depicted In correct relative thicknesses, many figures would be too large to fit on a single page.
  • the panel 100 includes four principal elements: a support element 102, a reflective element 104, an absorber element 106, and an external protective element 108.
  • each of elements 102, 104, 106, and 108 comprise a layer of material, with the layers substantially parallel to one another.
  • the support element 102 is made of a building structural material, such as concrete.
  • the reflective layer 104 is generally a layer of a conductive material, such as a metal. In the preferred embodiment it is a layer of iron mesh or an iron grid, 104, that is imbedded in the concrete 102 and also serves to strengthen the concrete, as is known in the concrete art. Generally, mesh 104 is buried 1 to five inches deep within concrete 102.
  • each embodiment of absorber 106 includes multi-components, either In the sense of including two distinct material components, such as a polymer and second material as in a polymer-ceramic composite, or in the sense of including two or more distinct layers of distinct materials. From the above, it should be understood that the term "multi-component" in this disclosure does not include a single chemical compound, even if the compound contains more than one element.
  • Protective element 108 is generally made of a conventional building material, such as a silicon-based tile that may also be decorative in nature as well as being resistant to weather.
  • An important feature of the invention is that in some embodiments, protective tile element 108 is optional, or from another aspect, forms part of absorber element 106. That is, some of the absorptive materials of the invention, such as the high dielectric constant materials (see below), are also ceramics or other hardened materials that are highly weather resistant.
  • Reflective element 104 is also optional. In some cases, it may be incorporated into a support element 102 that is thick enough to stop all radiation from passing through.
  • support element 102 may be the same as absorber element 106, when this element is strong enough to provide the support necessary for the wall or other structure of which it is a part.
  • absorber element 106 may be the same as absorber element 106, when this element is strong enough to provide the support necessary for the wall or other structure of which it is a part.
  • a reflective element may not be desirable if reflections are to be kept to a minimum. That is, in some cases, the ghost problem may be solvable only by not creating reflections at all.
  • the reflective element 104 is present, unless specified otherwise. Since the invention particularly involves the materials and structure of the absorptive element 106, we shall focus on this element in the remainder of this disclosure.
  • FIG. 2 and each embodiment of absorber 106 shown below the radiation 110 is incident from the left of the figure. This is important because the order of the absorptive multi-layers from the point 109 of incidence of the radiation 110 is significant to yield the optimum absorption.
  • Test panels 100 are bulky and not easy to fabricate in many different configurations. Further, it is difficult to create a test structure that will satisfactorily test the samples. This has been overcome in the present disclosure by creating a complex computer system capable of simulating various panel 100 configurations. Many actual embodiments of the panel 100 were built and compared to the results of the computer simulation system to assist in perfecting the simulation system. In the discussion below, the measurements given are from actual samples made as discussed below, unless it is specifically noted that the measurements are from the computer simulation system.
  • FIG. 3 shows a cross-sectional view of a preferred embodiment of absorber element 106A according to the invention.
  • the absorber was fabricated by a process discussed below, and mounted on a metal support in a coaxial fixture. That is, the support 102 and external tile 109 were not included because of the obvious difficulties in testing. However, since an electromagnetic wave is 100% reflected from a conductive metal layer, and since tests show that the external tile 109 does not significantly affect the absorber, the experimental results discussed herein are a good approximation to the actual panel 100.
  • Absorber element 106A includes a material 112, which is preferably a dielectric material, but also may be any of the materials in Table 1. In the embodiment of FIG. 3, any of the dielectrics indicated in Table 1 below may be used, though in this embodiment the dielectric 112 is preferably a high dielectric constant material.
  • Layer 114 is a ferrite. It may be any ferrite, though preferably it is a nickel-zinc ferrite, a copper-zinc ferrite, or a cobalt-zinc ferrite, and most preferably Ni 0.4 Zn 0.6 Fe 2 O 4 .
  • the dielectric material 112 is significantly thinner than the ferrite 114, particularly if it is a high dielectric constant material.
  • high dielectric constant material When material 112 is a high dielectric constant material it is generally, 2 to 10 times thinner, and most preferably, about 3 to 6 times thinner than the ferrite 114. In the embodiment of FIG. 3, the material 112 is farther from the reflector 104 and closer to the exterior of the panel 100. It has also been found that high dielectric constant materials are generally highly desirable in wave absorption panels, whatever their relative position with respect to other absorber materials.
  • high dielectric constant means a dielectric constant of 50 or more
  • low dielectric constant material means a material with a dielectric constant of 10 or less.
  • low dielectric constant materials may be silicon glass or a plastic, such as Teflon TM , a polycarbonate, a polyvinyl, or other polymer.
  • High dielectric material 112 may be a metal oxide that is ferroelectric at some temperature, though it may not be ferroelectric at room temperature.
  • high dielectric constant materials useful in wave absorption panels are the ABO 3 type perovskites, including dielectrics and ferroelectrics, such as barium strontium titanate (BST), barium titanate, and the layered superlattice materials, also including both dielectrics and ferroelectrics, such as strontium bismuth tantalate, strontium bismuth tantalum niobate, and barium bismuth niobate.
  • BST barium strontium titanate
  • layered superlattice materials also including both dielectrics and ferroelectrics, such as strontium bismuth tantalate, strontium bismuth tantalum niobate, and barium bismuth niobate.
  • the ABO 3 type perovskites are discussed in Franco Jona and G.
  • LSM La 1-x Sr x MnO 3
  • Fe 3 O 4 magnetoresistive materials, including some formulations of LSM, e.g.
  • La 0.67 Sr 0.33 MnO 3 as well as La x Ca (1-x) MnO 3 and La x Pb (1- x) MnO 3 , signet magnetics, such as BaTiO 3 + BiFeO 3 , magnetoplumbites, such as Ba 0.6 Fe 2 O 3 , garnets, such as yttrium iron garnet (3Y 2 O 3 .5Fe 2 O 4 or Y 6 F 10 O 24 ), and many others.
  • ⁇ and ⁇ reflect corresponding ceramic values ⁇ to wt.% of ceramics generalized, and may differ sometimes for an individual material in the given class.
  • a period in a formula separates two parts of a material that may be present in different proportions; for example, Ba 0.6 Fe 2 O 3 means a combination of 1 unit of BaO and 6 units of Fe 2 O 3 , which is conventional notation for materials such as magnetoplumbites and signet magnetics.
  • Table 1 lists "composites” as one type of dielectric. Numerous such composites are discussed below.
  • a "composite” means a material that is made up of a uniform mixture of at least two distinct materials, as for example, a ceramic powder uniformly distributed throughout a polymer.
  • FIG. 5 shows the absorption performance of three different multi-layer absorption tiles.
  • 106A made of a high dielectric constant material and a ferrite.
  • curves 117, 118, and 119 show the reflection loss in decibels (dB) as a function of frequency in gigahertz (GHz).
  • Reflection loss is the loss which is measured by comparing the amount of radiation incident on side 109 with the amount of radiation that is reflected from side 109. All curves were measured at room temperature.
  • Curve 117 is the reflection loss as a function of frequency for a tile 106A in which layer 112 is 1 millimeter (mm) of strontium tantalate (SrTa 2 O 6 ), and layer 114 is 5 mm of nickel-zinc ferrite (Ni 0.4 Zn 0.6 Fe 2 O 4 ), which is a solid solution of two ferrites: NiFe 2 O 4 and ZnFe 2 O 4 .
  • Curve 118 is the reflection loss as a function of frequency for a tile 106A in which layer 112 is 1 millimeter (mm) of strontium tantalate (SrTa 2 O 6 ), and layer 114 is 4 mm of nickel-zinc ferrite (Ni 0.4 Zn 0.6 Fe 2 O 4 ).
  • Curve 119 is the reflection loss as a function of frequency for a tile 106A in which layer 112 is 1 millimeter (mm) of strontium tantalate (SrTa 2 O 6 ), and layer 114 is 5 mm of manganese ferrite (MnFe 2 O 4 ).
  • the dielectric constant of the SrTa 2 O 6 was approximately 90 while the dielectric constant of the Ni 0.4 Zn 0.6 Fe 2 O 4 was approximately 10 (see FIG. 7).
  • a material having a reflection loss of 20dB or more of the incident radiation is considered to be a good absorber.
  • the absorption for the 1mm/5mm strontium tantalate/nickel-zinc ferrite curve 119 is within the range that it would be an acceptable absorber over a range of about 0.1 GHz to 0.3 GHz (100 megahertz to 300 megahertz. Decreasing the thickness of the nickel-zinc ferrite by one millimeter results in a tile that is an excellent absorber between about 0.25 GHz and 0.5 GHz as shown in curve 118.
  • ferrites have low dielectric constant, ⁇ ' , a low or moderate imaginary part of the permeability, ⁇ ", a low real part of the permeability, ⁇ ', and a high imaginary part of the permeability, ⁇ " .
  • the high dielectric constant/ferrite absorber can be tuned by design to cover a range of about 200 megahertz almost anywhere in the complete television frequency range, i.e. from about 0.1 GHz to about 8 GHz.
  • a wave absorber element 106B comprising a solid solution of two or more ferrites is illustrated in FIG. 4.
  • Such a solid solution by itself, has been found to be superior to a single ferrite, particularly when a specific frequency range is of critical concern.
  • the peak absorption frequency and the breadth of the absorption peak are highly dependent on the ratio of the particular ferrites in the solid solution and the thickness of the absorber. This is illustrated in FIG. 6, which shows the absorption performance of six different nickel-zinc ferrite solid solutions.
  • the chemical formula of the solid solutions and the thickness of each tile are given in Table 2. Table 2 Curve No.
  • the solid solution like the layered tile of FIG. 3, lends itself to the design of an absorption tile that absorbs over a desired frequency range.
  • the Ni 0.4 Zn 0.6 Fe 2 O 4 , Ni 0.50 Z 0.50 Fe 2 O 4 solid solutions provide a reflection loss of 20dB or greater over the entire television frequency range, with Ni 0.4 Zn 0.6 Fe 2 O 4 being particularly appropriate for VHF and Ni 0.50 Zn 0.50 Fe 2 O 4 being particularly appropriate for UHF.
  • the ability of a ferrite to function as a wave absorber is related to the permittivity and the permeability of the material as a function of frequency.
  • FIGS. 7 and 8 show the permittivity, ⁇ , and the permeability, ⁇ , respectively, for the solid solution ferrite Ni 0.4 Zn 0.6 Fe 2 O 4 .
  • ⁇ ' the real part of the permitivity, and ⁇ " the imaginary part of the permitivity, are shown as a function of frequency in gigahertz.
  • ⁇ ' the real part of the permeability (dielectric constant), and ⁇ " the imaginary part of the permeability, are shown as a function of frequency in gigahertz.
  • FIG. 9 Another way that one can "mix" ferrites to design an absorber element 106 is by fabricating multi-layer ferrite absorbers.
  • a multi-layer ferrite absorber 106C is shown in FIG. 9.
  • the absorber element 106C comprises two or more layers, 150 and 152, of ferrite materials, with layer 150 being a different ferrite than layer 152.
  • the peak absorption frequency and the breath of the absorption curve vary depending on the specific ferrite in the layers 150, 152 and the thickness of each layer.
  • the reflective loss in dB is shown as a function of frequency in GHz for five different thickness combinations of a multilayered absorber 106C fabricated of a layer 150 of manganese ferrite and a layer 152 of the nickel-zinc solid solution ferrite.
  • the thickness of each of the manganese ferrite and the nickel-zinc ferrite multi-layer combinations is given in Table 3.
  • Table 3 Curve Number MnFe 2 O 4 Thickness (mm)/Ni 0.4 Zn 0.6 Fe 2 O 4 Thickness (mm) 150 1/5 152 1.5/4.5 154 2/4 156 2.5/3.5 158 3/3
  • each of the multi-layered ferrite absorbers provides a reflection loss of greater than 20dB over a wide range that covers about 2/3 of the entire TV spectrum.
  • the curve 152 for a mufti-layer absorber combining 1.5 mm thick layer of MnFe 2 O 4 with a 4.5 mm thick layer of Ni 0.4 Zn 0.6 Fe 2 O 4 shows that this absorber 106C would be highly effective to absorb the entire VHF frequency spectrum.
  • the multi-layer absorber 106C composed of multiple ferrite layers can be designed so as to shift the frequency peak to any specific frequency over a relatively wide range of frequencies in the heart of the television spectrum, without significant change in the absolute magnitude of the reflection loss.
  • FIG. 10 shows another embodiment 106D of the absorber element 106 according to the invention.
  • This embodiment comprises a high dielectric constant material 160, a ferrite 162 and a low dielectric constant material 164.
  • the high dielectric constant material 160 is preferably a ferroelectric ceramic material such as barium titanate (BaTiO 3 ), though it may be other high dielectric constant material such as BST or other ABO 3 type perovskites, other layered superlattice materials, or signet magnetics, such as BaTiO 3 + BaFeO 3 . See United States Patent No. 5,519,234 issued to Araujo et al. on May 21, 1996 for a full description of layered superlattice materials.
  • Signet magnetics include BaTiO 3 + BaFeO 3 , BaTiO 3 + BiFeO 3 , and BaO.3BaTiO 3 .3Fe 2 O 3 .
  • Ferrite 162 is preferably Ni 0.4 Zn 0.6 Fe 2 O 4 , though it may be any of the other ferrites discussed above.
  • Low dielectric constant material 164 is preferably a polymer, such as Teflon TM , a polycarbonate or a polyvinyl such as Butvar TM , but may be other plastics or other relatively light weight low dielectric material.
  • FIG. 17 shows a computer simulation of the reflection loss in dB versus frequency in gigahertz for an absorption panel 100 having an absorber element 106D comprising 1 mm of a 50/50 solid solution of BaTiO 3 + BaO.6Fe 2 O 3 , 5 mm of Ni 0.4 Zn 0.6 Fe 2 O 4 , and 5 mm of Teflon TM .
  • This panel provides a reflective loss of approximately 30dB across the entire television frequency spectrum, which is the best reflective loss in this frequency range of any absorption panel known to date.
  • This is also an excellent absorber for airports in that it absorbs well in the frequency range of airport control systems, i.e. about 0.1 gigahertz to about 0.4 gigahertz.
  • FIG. 11 shows an alternative embodiment 106 E of the absorber element 106 in which a ferrite 166 and a high dielectric constant material 170 sandwich a polymer 168.
  • the preferred materials for this embodiment are the same as those for the embodiment of FIG. 10, except in a different order.
  • FIG. 18 shows a computer simulation of the reflective loss in dB versus frequency in GHz for an absorption panel 100 having a ferrite/polymer/high dielectric constant absorber element 106E having 5 mm of Ni 0.4 Zn 0.6 Fe 2 O 4 , 4 mm of polycarbonate, and 1 mm of 70/30 BST, i.e. Ba 0.7 Sr 0.3 TiO 3 .
  • This embodiment has excellent absorption in the 800 MHz - 900 MHz frequency range, and thus will make an excellent absorption panel when absorption in this range is critical, as for example when the electromagnetic wave that needs to be absorbed is a radio local area network (LAN) system.
  • LAN radio local area network
  • FIG. 12 shows another alternative embodiment 106F of a wave absorber element 106.
  • This embodiment comprises a polymer-ceramic composite layer 176.
  • the preferred polymer is polycarbonate or polyvinyl, though it also may be Teflon TM or any other suitable light-weight, relatively strong polymer.
  • a powdered form of any of the ceramic materials mentioned above may be embedded in the polymer.
  • Preferred ceramic materials are shown in Table 4 along with the mean values of the real and imaginary parts of the dielectric constant, ⁇ ' and ⁇ ", and the real and imaginary parts of the permeability, ⁇ ' and ⁇ "between 100 MHz and 1 GHz for each material.
  • FIG. 19 shows a computer simulation of the reflective loss in dB versus the frequency in GHz for an absorption panel 100 including a polymer-ceramic composite absorber element 106F comprising 13 mm of 50% polycarbonate and 50% (0.25BaTiO 3 + 0.75BiFeO 3 ). This shows good absorptivity in the high frequency radio spectrum.
  • FIG. 13 shows an embodiment 106G of the absorber 106 according to the invention comprising a ferrite 180 and a material 182.
  • This embodiment is the same as the embodiment of FIG. 3, except that the positions of the ferrite 180 and the material 182 with respect to the incident radiation 110 are reversed.
  • the ferrite 180 may be any of the ferrites listed in Table 1 or mentioned in the discussion of FIG. 3.
  • a nickel-zinc ferrite, and in particular Ni 0.4 Zn 0.6 Fe 2 O 4 is preferred.
  • the material 182 may be any of the materials listed in Table 1 or mentioned in the discussion of FIG. 3. Again, dielectric materials are preferred, though some of the other materials, such as LSM, in some frequency ranges give results better than the results with the dielectrics.
  • both a low or high dielectric constant material have been found to give good results, depending on the ferrite. It is noted that in situations in which the dielectric material is closer to the incident radiation 110, i.e. the embodiment of FIG. 3, a high dielectric constant material is preferred, while in the situations where the dielectric material is between the ferrite and the metal 104, such as FIG. 13, a low dielectric constant material, i.e. a material with a dielectric constant up to 10, also can provide excellent results. While materials with low dielectric constant are not good absorbers by themselves in the MHz frequency range, when used as a sandwich layer between a ferrite and the metal, they significantly improve the overall absorption performance of the system 100.
  • FIG. 20 shows a computer simulated graph of reflective loss In dB versus frequency in GHz for five different thicknesses of a ferrite/hlgh dielectric constant material wave absorber 106G comprising Nl 0.4 Zn 0.8 Fe 2 O 4 as the ferrite and BST as the dielectric 182.
  • a ferrite/hlgh dielectric constant material wave absorber 106G comprising Nl 0.4 Zn 0.8 Fe 2 O 4 as the ferrite and BST as the dielectric 182.
  • there is no reflective element 104 The thickness of the ferrite layer 180 for each curve is shown in Table 6.
  • the thickness of the dielectric 182 was sufficient so that no radiation passed through the sample, or, for computer simulation purposes, infinite. Practically, a few centimeters of most materials would result in no radiation passing through the sample.
  • the largest absorption was for an embodiment in which the ferrite 180 was 5mm in thickness and the magnetoplumbite was 5mm in thickness.
  • a fourth computer simulated graph for an embodiment 106G of a wave absorber was made for a sample in which the ferrite 180 was Ni 0.4 Zn 0.6 Fe 2 O 4 , the material 182 was aluminum oxide (Al 2 O 3 ), and a metal back plate 104 was included.
  • Aluminum oxide has a dielectric constant of about 9. This gave similar results to the curves of FIG. 20, but the lowest absorption was about -39 dB, that is, the absorption was a little larger than the absorption shown in FIG. 20, and the absorption was not as strongly dependent on thickness.
  • the largest absorption was for an embodiment in which the ferrite 180 was 5mm in thickness and the aluminum oxide was 1 mm in thickness.
  • the aluminum oxide can be made by a liquid deposition process that is in some respects simpler than the ceramic fabrication process for other dielectrics and ferrites disclosed herein, and thus, this embodiment with aluminum oxide has some advantages over the others.
  • FIGS. 14 and 15 show two other embodiments of highly tuneable absorber systems.
  • absorber 106H comprises a layer 186 of polymer and a layer 188 of another dielectric material.
  • absorber 1061 comprises a layer 190 of a dielectric material and a layer 192 of a polymer.
  • the dielectric material 188 and 190 has a higher dielectric constant than the polymer 186 and 192, respectively. While these embodiments show excellent tunability and the reflective loss is well over 20dB in some frequency ranges, none of the combinations of actual materials tried have shown as good absorption characteristics as the embodiments of FIGS. 3, 10 and 11.
  • the preferred polymer is polycarbonate or polyvinyl and the preferred dielectric material is BST, though other polymers and dielectrics also may be used.
  • the absorbers 106H and 106I are of particular importance because they are easily constructed and are relatively light.
  • FIG. 21 shows another embodiment 106J of an absorber 106 that provides good results.
  • Absorber element 106J comprise a layer 194 of a ferrite, a layer 196 of a tow dielectric constant material, and a layer 198 of a high dielectric constant material.
  • This embodiment 106J is the same as the embodiment of FIG. 11, except that it has been generalized to include any low dielectric constant material 196, not just a polymer. Silicon glass is an appropriate low dielectric constant material, while the preferred ferrites 194 and high dielectric constant material 198 are as discussed in connection with FIG. 11.
  • This embodiment 106J can be tuned to give much the same performance as the embodiment 106E of FIG. 11.
  • FIGS. 22, 23, and 24 show examples of how the teachings of the above layering principals can be extended to many-layered absorbers 106.
  • the embodiment 106K of FIG. 22 there is one ferrite layer 210 and three dielectric layers 212, 214, and 216. Any of the ferrites discussed above may be used as the ferrite 210, and any of the dielectrics discussed above may be used as the dielectrics, with the understanding that dielectric 214 is different from dielectrics 212 and 216.
  • An example of such an embodiment is an absorber 106K in which ferrite 210 is Ni 0.4 Zn 0.6 Fe 2 O 4 , dielectric 212 is a polymer, dielectric 214 is LSM, and dielectric 216 is BST.
  • FIG. 25 A graph of reflective loss in dB versus frequency in GHz as simulated by computer for various thicknesses of the materials is shown in FIG. 25.
  • the thicknesses of the materials is given in Table 7.
  • the invention contemplates that many more layers of dielectric may be used. Since the dielectric layers are relatively thin, it is relatively easy to form such multilayered panels.
  • Embodiment 106L of FIG. 23 shows an absorber 106 comprising a layer 220 of ferrite, a layer 222 of polymer, a second layer 224 of ferrite, a second layer 226 of polymer, and a third layer 228 of ferrite.
  • FIG. 26 shows a graph of reflective loss in dB versus frequency as computer simulated for an absorber 106L in which the ferrites 220, 224, and 228 were Ni 0.4 Zn 0.6 Fe 2 O 4 , and the polymers 222 and 226 was a polycarbonate with the properties shown in Table 5. The thicknesses of each layer for each curve are given in Table 8. Table 8 Curve No.
  • Embodiment 106M of FIG. 24 illustrates an absorber 106 comprising n ferrite/polymer layers, where n is greater than 1 and, preferably, 100 or less. That is, the basic absorber element embodiment 106M is a layer of ferrite 230 and a layer of polymer 231. The basic absorber element indicated by the number 1, is repeated n times as shown.
  • the ferrite may be any of the ferrites discussed above, and the polymer may be any of the polymers discussed above.
  • the ferrite and the polymer is the same in each absorber element, though the invention contemplates that one or all of the absorber elements 1 through n be made of different materials from the other elements.
  • the thicknesses of the ferrite 230 and the polymer 231 for the basic absorber element for each curve are given in Table 9.
  • This absorber 106N includes a high ⁇ "material 302 sandwiched between a high dielectric constant material 300 and a low dielectric constant material 304.
  • the high dielectric constant material is nearest the side of incidence of the radiation 110 and the low dielectric constant material is nearest to the support structure 100 and the metal reflector 104.
  • the imaginary part of the permeability, ⁇ " , of the middle layer 302 is not only high, but it is also higher than the real part of the permeability, ⁇ '.
  • the high dielectric constant material has a dielectric constant of 100 or more, and the low dielectric constant material has a dielectric constant of 5 or less.
  • an absorber structure has an effective ⁇ ' ⁇ ' that obeys equation (2) over a relatively wide frequency range, that is, if ( 3 ) ⁇ eff ⁇ eff 1 ⁇ 2 ⁇ 1 / f , or ( 4 ) n eff ⁇ 1 / f , where n eff is the effective index of refraction, for a broad range of frequencies, then this structure would be a good absorber.
  • any material or structure that has an effective ⁇ ' ⁇ 'that decreases with frequency over a frequency range, or which has an effective dielectric constant that decreases with frequency over a frequency range and has a ⁇ ' that is 1 or approximately 1 over that range will generally be a good absorber over at least a portion of that range, providing the thickness is near the thickness given by equation (1). That is, the fact that ⁇ ' is decreasing with frequency, increases the range over which the quarter wave relation (1) will be approximately true, and thus will increase the range over which the material or structure will make an effective quarter wave plate. The closer that the decline in the effective dielectric constant approaches equation (5) over this range, the broader will be the range over which the structure will make a good absorber. With this in mind, a review of FIGS. 7 and 8 suggests why nickel-zinc ferrite is a good absorber over a broad range of frequencies, particularly when it is combined with a high dielectric constant material.
  • FIGS. 7 and 8 show that over a significant range of frequencies near 200 MHz, ⁇ ' ⁇ ⁇ ' for Ni 0.4 Zn 0.6 Fe 2 O 4 , and thus ( ⁇ '/ ⁇ ') 1 ⁇ 2 is close to 1. This fact, when combined with the fact that this ferrite also satisfies the conditions of the previous paragraph, indicates why this material is a good absorber.
  • a preferred method of designing an electromagnetic wave absorption panel can be distilled.
  • the materials and relative thicknesses of the materials can also be tuned to shift the peak absorption frequency if desired, and to match impedances of adjacent layers as much as possible, and then in an iterative process, the resulting combination can again be tuned to more closely approach equation (4).
  • a powder 280 of the desired ceramic material, a polymer powder 281, and a solvent 282 that will dissolve the polymer are mixed in step 284.
  • a suitable solvent is tetrahydrofuran (THF).
  • THF tetrahydrofuran
  • the ceramic is suspended in the solution.
  • the resulting solution is mixed until it is homogeneous, and then poured into a mold in step 286.
  • the composite is then cured at a suitable temperature for a suitable time period.
  • a suitable temperature is room temperature and a suitable time period is twelve hours.
  • the polymer-ceramic composites have several advantages over conventional absorbers. They are not only light weight, but they can be easily fabricated at room temperature. They permit ease of combination of several materials with different properties, such as a ferroelectric and a ferrite, or a high dielectric constant material and a ferrite, permitting the tuning of a material for a specific reflectivity problem. Moreover, the resulting absorber 106 is relatively flexible, making handling and general construction easier.
  • a powder 290 of the ceramic material desired is placed inside a mold.
  • the mold is made of stainless steel.
  • the powder is isostatically pressed in the mold, preferably at a pressure of 50,000 pounds per square inch (PSI).
  • PSI pounds per square inch
  • the ceramic is removed from the mold and sintered, preferably at a temperature of between 900 °C and 1100 °C.
  • the sample was then further formed, if necessary, and then tested. If the test is a dielectric test, the disk-shaped sample as removed from the mold was suitable. For the magnetic tests, a hole was drilled in the samples to form them in a donut shape prior to testing.
  • a feature of the invention is that many of the layered absorbers according to the invention are much less bulky and less heavy than prior art absorbers.
  • the preferred thicknesses of the high dielectric constant materials mentioned above are two to ten times thinner than the preferred thicknesses of prior art ferrites according to the invention.
  • many of the high dielectric constant materials, such as BST are hardened ceramics that are weather resistant.
  • the outer protective tiles 109 can be eliminated or made less thick.
  • Another feature of the invention is that it has been found that the higher the dielectric constant of the material, the thinner the material may be and still provide good absorption in combination with other materials.
  • a further feature of the invention is that for the materials and structures of the invention there is a critical thickness, t c , for optimum absorption performance, and generally a range of thicknesses about this critical thickness for which there will be good absorption performance.
  • Another feature of the invention is that materials that have a dielectric constant, ⁇ ', that varies as a function of frequency will make good absorbers, particularly when combined with other materials that broaden the frequency range over which the effective dielectric constant of the materials follows the formula (3).
  • a further feature of the invention is that virtually all of the embodiments of the invention can be relatively easily tuned to a particular frequency within the television and higher frequency radio wavelengths. This can be done either by varying the components of each embodiment, varying the thickness of each component, or, when a composite or solid solution is involved, varying the amount of each component, or several of the foregoing.
  • the absorber panels of the invention lend themselves to the solution of specific electromagnetic environment problems for specific construction sites.
  • nickel-zinc ferrite is the best of the ferrites in absorption and the Ni 0.4 Zn 0.6 Fe 2 O 4 stoichiometry of this material is the most preferred. Several different stoichiometric formulations have been discussed above.
  • the nickel-zinc ferrite may also be doped, such as with magnesium or other metal, but the undoped ferrite has been found to be best in the television frequency range.
  • a further feature of the invention is that even though low dielectric constant materials are not good absorbers in the MHz frequency range, when used as a sandwich layer between a ferrite and a metal, they significantly improve the overall absorption performance of the wave absorption panel system.

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Claims (13)

  1. Panneau à absorption d'ondes électromagnétiques (100) destiné à être utilisé dans la construction de bâtiments, ledit panneau comprenant : un élément de support de construction (102); et un élément absorbeur (106) supporté par ledit élément de support, ledit panneau à absorption d'ondes étant caractérisé par le fait que ledit élément absorbeur comprend une première couche (166, 186, 210) et une deuxième couche (170, 182, 216), la première couche étant située plus près du point d'incidence de ladite onde électromagnétique sur ledit panneau que ladite deuxième couche, ladite première couche comprenant une ferrite, et ladite deuxième couche comprenant un matériau à haute constante diélectrique ayant une constante diélectrique de 50 ou plus.
  2. Panneau à absorption d'ondes électromagnétiques selon la revendication 1 et caractérisé, par ailleurs, par le fait que ledit élément absorbeur comporte une troisième couche (168, 212) située plus éloignée dudit point d'incidence de ladite onde électromagnétique que la première couche, ladite troisième couche comprenant un matériau à faible constante diélectrique ayant une constante diélectrique de 10 ou moins.
  3. Panneau à absorption d'ondes électromagnétiques selon la revendication 2 et caractérisé, par ailleurs, par le fait que ledit élément absorbeur comporte une quatrième couche (214) située entre ladite troisième couche et ladite deuxième couche, ladite quatrième couche comprenant La(1-x)SrxMnO3.
  4. Panneau à absorption d'ondes électromagnétiques selon la revendication 3 et caractérisé, par ailleurs, par le fait que ladite troisième couche est située entre ladite première couche et ladite deuxième couche.
  5. Panneau à absorption d'ondes électromagnétiques (100) destiné à être utilisé dans la construction de bâtiments, ledit panneau comprenant :
    un élément de support de construction (102) ;
    un élément réfléchissant (104) supporté par ledit élément de support ; et un élément absorbeur (106) supporté par ledit élément de support, ledit élément absorbeur étant situé plus près du point d'incidence de ladite onde électromagnétique sur ledit panneau que ledit élément réfléchissant, le panneau à absorption d'ondes étant caractérisé par le fait que ledit élément absorbeur comprend une première couche (162, 166, 220) comprenant une ferrite et une deuxième couche (164, 168, 222) comprenant un matériau à faible constante diélectrique ayant une constante diélectrique de 10 ou moins, ladite deuxième couche étant située plus éloignée dudit point d'incidence de ladite onde électromagnétique que ladite première couche et que ledit élément absorbeur comprend, par ailleurs, une troisième couche (160, 170) comprenant un matériau à haute constante diélectrique ayant une constante diélectrique de 50 ou plus.
  6. Panneau à absorption d'ondes électromagnétiques selon la revendication 5 et caractérisé, par ailleurs, par le fait qu'il y a une pluralité desdits éléments absorbeurs, chaque élément absorbeur comprenant une desdites premières couches (230) et une desdites deuxièmes couches (231).
  7. Panneau à absorption d'ondes électromagnétiques selon la revendication 6 et caractérisé, par ailleurs, par le fait qu'il y a n desdits éléments absorbeurs (160M), où n est un nombre entier entre 2 et 100.
  8. Panneau à absorption d'ondes électromagnétiques selon l'une quelconque des revendications 1 à 7, dans lequel ledit matériau à haute constante diélectrique est choisi parmi le groupe composé de matériaux super-réseau en couches, matériaux magnétiques en anneau, et Z x BaTiO3 + (100% - Z) x BiFeO3, où 100% > Z > 0%.
  9. Panneau à absorption d'ondes électromagnétiques selon l'une quelconque des revendications 1 à 8, dans lequel ledit élément absorbeur (106) comprend un matériau choisi parmi le groupe composé de grenats, matériaux magnétorésistifs, matériaux super-réseau en couches, magnétoplombites, matériaux magnétiques en anneau, La(1-x)SrxMnO3, Fe3O4 et Ni0,4Zn0,6Fe2O4.
  10. Panneau à absorption d'ondes électromagnétiques selon la revendication 9 et caractérisé, par ailleurs, par le fait que ledit matériau comprend du grenat d'yttrium et de fer.
  11. Panneau à absorption d'ondes électromagnétiques selon la revendication 9 et caractérisé, par ailleurs, par le fait que ledit matériau magnétorésistif est un matériau choisi parmi le groupe composé de La0,67Sr0,33MnO3, LaxCa(1-x)MnO3, et LaxPb(1-x)MnO3, où 0 < x < 1.
  12. Panneau à absorption d'ondes électromagnétiques selon les revendications 8 ou 9, dans lequel ledit élément absorbeur (176) comprend un composite d'un polymère et d'un matériau choisi parmi ledit groupe.
  13. Panneau à absorption d'ondes électromagnétiques selon les revendications 8 ou 9 et caractérisé, par ailleurs, par le fait que ledit matériau super-réseau en couches comprend un matériau choisi parmi le groupe composé de tantalate de strontium et bismuth, niobate de strontium et bismuth, titanate de strontium et bismuth, zirconate de strontium et bismuth, et les solutions solides de ces derniers.
EP98901750A 1997-01-13 1998-01-12 Panneaux absorbant les ondes electromagnetiques et materiaux destines a ces derniers Expired - Lifetime EP0900458B1 (fr)

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US782934 1991-10-25
US08/782,938 US5853889A (en) 1997-01-13 1997-01-13 Materials for electromagnetic wave absorption panels
US08/782,934 US6037046A (en) 1997-01-13 1997-01-13 Multi-component electromagnetic wave absorption panels
US782938 1997-01-13
PCT/US1998/000406 WO1998031072A1 (fr) 1997-01-13 1998-01-12 Panneaux absorbant les ondes electromagnetiques et materiaux destines a ces derniers

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JP4461970B2 (ja) * 2004-09-06 2010-05-12 三菱瓦斯化学株式会社 電波吸収体
ES2274674B1 (es) * 2004-12-24 2008-04-16 Micromag 2000, S.L. Absorbedor de radiacion electromagnetica basado en microhilos magneticos.
JP2006186725A (ja) * 2004-12-28 2006-07-13 Central Glass Co Ltd 電磁波吸収板
US20100166547A1 (en) * 2008-10-06 2010-07-01 Flodesign Wind Turbine Corporation Wind turbine with reduced radar signature
DE102009046752A1 (de) 2009-11-17 2011-05-26 Ed. Züblin Ag Vorrichtung zur Abschirmung und Beseitigung von Störsignalen elektromagnetischer Wellen - Bauteil mit chaotischer Bewehrung
US9505632B2 (en) 2010-09-22 2016-11-29 Skyworks Solutions, Inc. Compositions and materials for electronic applications
CN103452200A (zh) * 2012-05-30 2013-12-18 深圳市栢富电子有限公司 吸波组件及制造方法、微波暗室及建造方法
CN102904065A (zh) * 2012-10-19 2013-01-30 中兴通讯股份有限公司南京分公司 吸波装置及无线终端
CN108314866B (zh) * 2018-02-08 2020-09-25 西安理工大学 一种取向化Co2Z铁氧体-Fe2O3复合吸波材料及合成方法

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DE69836457T2 (de) 2007-09-13
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