EP0900458B1 - Electromagnetic wave absorption panels and materials for same - Google Patents
Electromagnetic wave absorption panels and materials for same Download PDFInfo
- 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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- European Patent Office
- Prior art keywords
- layer
- electromagnetic wave
- absorber
- dielectric constant
- ferrite
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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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
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- 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
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- 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
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- 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
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- 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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Description
- 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.
- For many years it has been recognized that reflection of electromagnetic waves from buildings and other structures causes problems, such as ghosts in television reception and static and noise in radio reception. This is a particularly significant problem in densely populated high technology societies, such as the large cities of the United States, Europe and Japan. In Japan, for example, in large cities a broadcast television electromagnetic impact statement is required before a large building may be constructed, and construction codes may require that buildings be constructed to avoid reflections of electromagnetic waves in the frequency range of radio, television and some microwaves, i.e. between 80 to 2400 megahertz. Transmission of electromagnetic waves through many building materials also has in some situations created problems of secrecy. For these reasons, extensive research has been performed to find building materials that will absorb electromagnetic radiation. See, for example, Investigation on Oblique Incident Characteristics of Ferrite Absorbing Panels For TV Ghost Suppression, Hironobu Ito et al. Japan Broadcasting Corporation et al. (about 1994). 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.
- Since nearly all matter has a characteristic frequency at which it absorbs radiation, it is relatively easy to find a material that will absorb electromagnetic radiation over some narrow frequency ranges. For example, ferrites typically have an absorption peak roughly between 200 megahertz to 400 megahertz. It is much more difficult, if not impossible, to find a material that will absorb over a broad frequency range of several thousand megahertz, or even just a few hundred megahertz. Thus, multilayered structures comprising combinations of ferrites, conducting fibers in a resin, and other similar structures have been tried as wave absorbers.
- It is known to use a quarter-wave plate to provide an electromagnetic wave absorber. In such an absorber, a thickness of material equal to one-quarter of a wavelength is placed in front of a 100% reflector, such as a metal layer. This absorption principal has not, up to now, been applied in attempting to make absorption panels for buildings because waves in the television frequency range are many meters long. Thus, such an absorber that is a few meters long would be excessively thick for use in a building.
- 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. Thus, 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. Moreover, 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. However, 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.
- It has also been found that, in practice, due to the proximity to electromagnetic wave sources of a narrow frequency, many construction sites have a negative impact on the electromagnetic environment only in a narrow frequency range. This range cannot be predicted in advance of knowing the location of a building to be constructed. Therefore, it would be highly useful to have an absorber panel and process of fabrication of absorber panels that are easily tuned to a specific frequency.
- 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. On the first dielectric layer, a ferrite layer is provided on which a second dielectric layer having a low permittivity is arranged. On the second dielectric layer, a magnetic body having a low magnetic permeability is provided. The magnetic body uses materials, such as a rubber ferrite, whereas the second dielectric layer has a permittivity smaller than 70.
- T. Takizawa, IEEE Transaction on Broadcasting, Vol. BC-. 25, No. 4, December 1979, pages 143 to 146 describes a panel for reducing ghost interference of buildings. 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.
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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 (Ni0.6Zn0.4) Ofe2O3.
- It is the object of the present invention to provide an broad-band electromagnetic wave absorption panel for use in buildings which can be easily tuned to a specific frequency.
- This object is solved by an electromagnetic wave absorption panel according to
claims - 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. For example, 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. As another example, a combination of a ferroelectric layer, a ferrite layer, a polymer, and a reflective metal provides excellent absorption across the entire television frequency range. As a further example, 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. Preferably, the low dielectric constant material comprises a polymer and the high dielectric constant material comprises a ferroelectric material.
- In another aspect, 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. Preferably, the ferrite comprises nickel-zinc ferrite and the high dielectric constant material comprises BST. Preferably, 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. Preferably, 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. Preferably, 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. Preferably, the absorber element further includes a fourth layer comprising a dielectric material.
- In another aspect 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. Preferably, the absorber element further includes a third layer located farther from the point of incidence of the electromagnetic wave than the second layer.
- In a further aspect 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.
- In yet another aspect 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. Preferably, the second layer is located farther from the point of incidence of the electromagnetic wave on the panel than the first layer. Alternatively, the first layer is located farther from the point of incidence of the electromagnetic wave than the second layer. Preferably, 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.
- In still another aspect 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. Preferably, 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. Preferably, 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. Preferably, the third layer comprises a polymer, and the second layer comprises a material selected from the group consisting of ABO3 type perovskites and layered superlattice materials.
- In addition, 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, ε'eff, and an effective real part of the permeability, µ'eff, such that (ε'eff µ'eff)½ - 1/f over the range of frequencies, where f is the frequency of the incident wave.
- In a further aspect 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, ε'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. Ni0.4Zn0.6Fe2O4.
- 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. Preferably, the absorber element further comprises a ferrite and a polymer. Preferably, the high dielectric constant material comprises a material selected from the group consisting of ABO3 type perovskites, layered superlattice materials, conducting oxides, and signet magnetics. Preferably, the high dielectric constant material comprises a material selected from the group consisting of BST, LSM, and Z x BaTiO3 +(100% - Z) x BiFeO3 where 100% > Z > 0%.
- In another aspect, 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. Preferably, the absorber element further comprises a ferrite and a polymer. Preferably, the ferroelectric is selected from the group consisting of ABO3 type perovskites and layered superlattice materials. Preferably, 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.
- In still another aspect, 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. Preferably, 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.
- In still another aspect 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. Preferably, the garnet is yttrium iron garnet.
- In still another aspect 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. Preferably, the magnetoresistive material is a material selected from the group consisting of La0.67Sr0.33MnO3, LaxCa(1-x)MnO3, and LaxPb(1-x)MnO3, where 0 < x < 1.
- In yet a further aspect, 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 Ni0.4Zn0.6Fe2O4.
- The new materials result in panels that are lighter and less bulky than prior art panels and also absorb over wider frequency ranges. In addition, 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. Numerous other features, objects and advantages of the invention will become apparent from the following description when read in conjunction with the accompanying drawings.
- FIG. 1 shows a perspective, partially cut-away view of a generalized wave absorption panel according to the invention;
- FIG. 2 shows a cross sectional view of the wave absorption panel according to the invention taken through the line 2-2 of FIG. 1;
- FIG. 3 shows a cross-sectional view of a preferred embodiment of the wave absorbing layer of the panel of FIG. 1;
- FIG. 4 shows a cross-sectional view of an alternative preferred embodiment of the wave absorbing layer of the panel of FIG. 1;
- FIG. 5 shows reflection loss vs. frequency curves for three different high dielectric constant/ferrite wave absorption tiles according to the invention;
- FIG. 6 shows reflection loss vs. frequency curves for six different nickel-zinc ferrite solid solutions;
- FIG. 7 shows the real and Imaginary parts of the permittivity as a function of frequency for the ferrite Ni0.4Zn0.6Fe2O4;
- FIG. 8 shows the real and imaginary parts of the permeability as a function of frequency for the ferrite Ni0.4Zn0.6Fe2O4;
- FIGS. 9 through 15 show cross-sectional views of alternative preferred embodiments of the wave absorbing layer of the panel of FIG. 1;
- FIG. 16 shows reflection loss vs. frequency curves for five different thickness combinations of a multilayered wave absorber fabricated of a layer of manganese ferrite and a layer of nickel-zinc solid solution ferrite;
- FIG. 17 shows a computer simulation of the reflection loss versus frequency for an absorption panel comprising 1 mm of a 50/50 solid solution of BaTiO3 + BaFeO3, 5 mm of Ni0.4Zn0.6Fe2O4, and 5 mm of Teflon™;
- FIG. 18 shows a computer simulation of the reflective loss versus frequency for an absorption panel comprising a ferrite/polymer/high dielectric constant absorption layer having 5 mm of Ni0.4Zn0.6Fe2O4, 4 mm of polycarbonate, and 1 mm of 70/30 BST;
- FIG. 19 shows a computer simulation of the reflective loss versus frequency for an absorption panel including a polymer-ceramic composite absorption layer comprising 13 mm of 50% polycarbonate and 50% (BaTiO3 + 4BiFeO3);
- FIG. 20 shows a computer simulated graph of reflective loss versus frequency for a ferrite/high dielectric constant wave absorber comprising Ni0.4Zn0.6Fe2O4 as the ferrite and BST as the dielectric 182 and having no reflective layer;
- FIGS. 21 through 24 show cross-sectional views of alternative preferred embodiments of the wave absorbing layer of the panel of FIG. 1;
- FIG. 25 shows a computer simulated graph of reflective loss versus frequency for various thicknesses of a ferrite/polymer/LSM/high dielectric constant absorber;
- FIG. 26 shows a computer simulated graph of reflective loss versus frequency for various thicknesses of a multi-layer ferrite/ polymer absorber;
- FIG. 27 shows a computer simulated graph of reflective loss versus frequency for an absorber having 50 ferrite/polymer layers for various thicknesses of the ferrite/polymer combination;
- FIG. 28 shows a flow chart of the process of making a polymer-ceramic composite material according to the invention;
- FIG. 29 shows a flow chart of the process of making a ceramic material according to the invention; and
- FIG. 30 shows a cross-sectional view of an alternative preferred embodiment of the wave absorbing layer of the panel of FIG. 1.
- 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. First of all, it should be understood that 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. Thepanel 100 includes four principal elements: asupport element 102, areflective element 104, anabsorber element 106, and an externalprotective element 108. Preferably, each ofelements support element 102 is made of a building structural material, such as concrete. Thereflective 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 withinconcrete 102. Since the electromagnetic waves that are to be absorbed are of the order of a meter to hundreds of meters in length, they "see" the mesh as essentially solid and are reflected. Theabsorber element 106 is shown only generally in FIGS. 1 and 2. The preferred embodiments of thislayer 106 will be described in detail below. As will be seen, each embodiment ofabsorber 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 ofabsorber 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 asupport element 102 that is thick enough to stop all radiation from passing through. In certain cases,support element 102 may be the same asabsorber 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. Although the preferred embodiments will generally be on concrete or other buildings in whichreflective element 104 is an integral part, in some applications, 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. In the embodiments discussed below, thereflective element 104 is present, unless specified otherwise. Since the invention particularly involves the materials and structure of theabsorptive element 106, we shall focus on this element in the remainder of this disclosure. In FIG. 2 and each embodiment ofabsorber 106 shown below, theradiation 110 is incident from the left of the figure. This is important because the order of the absorptive multi-layers from thepoint 109 of incidence of theradiation 110 is significant to yield the optimum absorption. - The fact that it is difficult to build and test
absorber panels 100 has been a significant obstacle to progress in this art.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 simulatingvarious panel 100 configurations. Many actual embodiments of thepanel 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. In the actual fabrication and testing ofabsorber 106, both for theembodiment 106A of FIG. 3 and the other actually fabricated embodiments discussed below, the absorber was fabricated by a process discussed below, and mounted on a metal support in a coaxial fixture. That is, thesupport 102 andexternal 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 theexternal tile 109 does not significantly affect the absorber, the experimental results discussed herein are a good approximation to theactual panel 100.Absorber element 106A includes amaterial 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 Ni0.4Zn0.6Fe2O4. Preferably thedielectric material 112 is significantly thinner than theferrite 114, particularly if it is a high dielectric constant material. Whenmaterial 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 theferrite 114. In the embodiment of FIG. 3, thematerial 112 is farther from thereflector 104 and closer to the exterior of thepanel 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. In this disclosure "high dielectric constant" means a dielectric constant of 50 or more, and "low dielectric constant material" means a material with a dielectric constant of 10 or less. Preferably, low dielectric constant materials may be silicon glass or a plastic, such as Teflon™, a polycarbonate, a polyvinyl, or other polymer. Aluminum oxide also may be used. Highdielectric material 112 may be a metal oxide that is ferroelectric at some temperature, though it may not be ferroelectric at room temperature. Examples of high dielectric constant materials useful in wave absorption panels are the ABO3 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. The ABO3 type perovskites are discussed in Franco Jona and G. Shirane, Ferroelectric Crystals, Dover Publications, New York, pp.108 et seq. The layered superlattice materials are discussed in United States Patent No. 5,519,234 issued May 21, 1996. Other materials that may be layered with theferrite 114 include conducting oxides such as La1-xSrxMnO3 (LSM) and Fe3O4, magnetoresistive materials, including some formulations of LSM, e.g. La0.67Sr0.33MnO3, as well as LaxCa(1-x)MnO3 and LaxPb(1- x)MnO3, signet magnetics, such as BaTiO3 + BiFeO3, magnetoplumbites, such as Ba0.6Fe2O3, garnets, such as yttrium iron garnet (3Y2O3.5Fe2O4 or Y6F10O24), and many others. - A summary of the various classes of materials that can be used as in the embodiment of FIG. 3, as well as all other embodiments of the invention disclosed herein is given in Table 1. It should be understood that the characteristics are
Table 1 Materials Class Examples of Materials in Class General Characteristics of Materials in Class Conducting oxides LSM high ε', high ε", very low µ Magnetoresistive materials La0.67Sr0.33MnO3, LaxCa(1-x)MnO3, LaxPb(1-x)MnO3, moderate ε', high ε" Miscellaneous Dielectrics Silicon glass, Al2O3 low to moderate ε', low ε", µ = 1 ABO3 type dielectrics BST high ε', low ε", µ=1 Layered superlattice material dielectrics BaBi2Nb2O9, high ε', low ε", µ = 1 Polymer dielectrics Polycarbonates, Teflon, Polyvinyls low ε', low ε", µ = 1 ABO3 type Ferroelectrics BaTiO3 high ε', moderate ε", µ = 1 Layered superlattice material ferroelectrics SrBi2Ta2O9 high ε', moderate ε", µ = 1 Magnetoplumbites Ba0.6 Fe2O3 moderate ε, high µ', low µ" Signet magnetics SaTiO3 + BiFeO3, high ε', moderate ε", BaTiO3 + BaFeO3, low µ (<1GHz) BaO.3 BaTiO3.3Fe2O3 moderate µ (>1GHz) Miscellaneous ceramics (generally dielectrics) SrTa2O6 high ε', low ε" , µ = 1 Ferrites NixZn(1-x)Fe2O4, low µ', high µ", low ε CuxZn(1-x)Fe2O4, CoxZn(1-x)Fe2O4. MnxZn(1-x)Fe2O4 Garnets Y3Fe5O12 moderate ε', ε", µ' and µ" Polymer-ceramic composites Above polymers combined with most above materials very light weight, ε and µ reflect corresponding ceramic values ∝ to wt.% of ceramics - FIG. 5 shows the absorption performance of three different multi-layer absorption tiles. 106A made of a high dielectric constant material and a ferrite. Each of
curves side 109 with the amount of radiation that is reflected fromside 109. All curves were measured at room temperature.Curve 117 is the reflection loss as a function of frequency for atile 106A in whichlayer 112 is 1 millimeter (mm) of strontium tantalate (SrTa2O6), andlayer 114 is 5 mm of nickel-zinc ferrite (Ni0.4Zn0.6Fe2O4), which is a solid solution of two ferrites: NiFe2O4 and ZnFe2O4. Curve 118 is the reflection loss as a function of frequency for atile 106A in whichlayer 112 is 1 millimeter (mm) of strontium tantalate (SrTa2O6), andlayer 114 is 4 mm of nickel-zinc ferrite (Ni0.4Zn0.6Fe2O4).Curve 119 is the reflection loss as a function of frequency for atile 106A in whichlayer 112 is 1 millimeter (mm) of strontium tantalate (SrTa2O6), andlayer 114 is 5 mm of manganese ferrite (MnFe2O4). The dielectric constant of the SrTa2O6 was approximately 90 while the dielectric constant of the Ni0.4Zn0.6Fe2O4 was approximately 10 (see FIG. 7). Generally, in the field of wave absorption panels, a material having a reflection loss of 20dB or more of the incident radiation is considered to be a good absorber. Twenty dB absorption is a reduction that is large enough to make a significant difference in the electromagnetic impact of a building, since it is enough reduction that state-of-the-art electronic circuits can filter unwanted reflections. 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 incurve 118. Changing the ferrite to a manganese ferrite results in a tile that is an excellent absorber in the range between about 0.5 GHz and 0.65 GHz. This would be an excellent choice for a building the electromagnetic impact statement of which showed that absorption in this range was critical. Generally, ferrites have low dielectric constant, ε' , a low or moderate imaginary part of the permeability, ε", a low real part of the permeability, µ', and a high imaginary part of the permeability, µ" . - Perhaps the most important fact that can be drawn from the curves of FIG. 5 is that the absorption peak frequency and the width of the absorption peak are strongly affected by small changes in thickness and by changes in materials. Thus, 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. Solid Solution Thickness 131 Ni0.4Zn0.6Fe2O4 6 mm 133 Ni0.35Zn0.65Fe2O4 7 mm 135 Ni0.50Zn0.50Fe2O4 4 mm 137 Ni0.4Fe2O4 9 mm 138 Ni0.3Zn0.7Fe2O4 10 mm 139 Ni0.25Zn0.75Fe2O4 10 mm - From the results shown in FIG. 6, it is evident that 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. Together, the Ni0.4Zn0.6Fe2O4, Ni0.50Z0.50Fe2O4 solid solutions provide a reflection loss of 20dB or greater over the entire television frequency range, with Ni0.4Zn0.6Fe2O4 being particularly appropriate for VHF and Ni0.50Zn0.50Fe2O4 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. In this disclosure, when we refer to the "permittivity" we mean a parameter that is in units corresponding to the dielectric constant. That is the real part of the "permittivity" is identical to the dielectric constant. FIGS. 7 and 8 show the permittivity, ε, and the permeability, µ, respectively, for the solid solution ferrite Ni0.4Zn0.6Fe2O4. In FIG. 7, ε', the real part of the permitivity, and ε", the imaginary part of the permitivity, are shown as a function of frequency in gigahertz. In FIG. 8, µ', the real part of the permeability (dielectric constant), and µ", the imaginary part of the permeability, are shown as a function of frequency in gigahertz. This curve is quite instructive. In most materials, the imaginary part of the permitivity, ε", and the imaginary part of the permeability, µ", are much smaller than the real parts of the corresponding parameters. However, in the nickel-zinc ferrite the imaginary part of the permeability, µ", is larger than the real part of the permeability, µ'. The imaginary part of the permeability, µ", is unusually high in this ferrite.
- Another way that one can "mix" ferrites to design an
absorber element 106 is by fabricating multi-layer ferrite absorbers. Such amulti-layer ferrite absorber 106C is shown in FIG. 9. In this embodiment of the invention, theabsorber element 106C comprises two or more layers, 150 and 152, of ferrite materials, withlayer 150 being a different ferrite thanlayer 152. Again, the peak absorption frequency and the breath of the absorption curve vary depending on the specific ferrite in thelayers multilayered absorber 106C fabricated of alayer 150 of manganese ferrite and alayer 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 - Viewed individually, 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. For example the
curve 152 for a mufti-layer absorber combining 1.5 mm thick layer of MnFe2O4 with a 4.5 mm thick layer of Ni0.4Zn0.6Fe2O4 shows that thisabsorber 106C would be highly effective to absorb the entire VHF frequency spectrum. Viewed as a group, it is evident from the results shown in FIG. 16 that themulti-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 theabsorber element 106 according to the invention. This embodiment comprises a high dielectricconstant material 160, aferrite 162 and a low dielectricconstant material 164. The high dielectricconstant material 160 is preferably a ferroelectric ceramic material such as barium titanate (BaTiO3), though it may be other high dielectric constant material such as BST or other ABO3 type perovskites, other layered superlattice materials, or signet magnetics, such as BaTiO3 + BaFeO3. 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 BaTiO3 + BaFeO3, BaTiO3 + BiFeO3, and BaO.3BaTiO3.3Fe2O3. Ferrite 162 is preferably Ni0.4Zn0.6Fe2O4, though it may be any of the other ferrites discussed above. Low dielectricconstant material 164 is preferably a polymer, such as Teflon™, a polycarbonate or a polyvinyl such as Butvar™, 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 anabsorber element 106D comprising 1 mm of a 50/50 solid solution of BaTiO3 + BaO.6Fe2O3, 5 mm of Ni0.4Zn0.6Fe2O4, and 5 mm of Teflon™. 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 theabsorber element 106 in which aferrite 166 and a high dielectricconstant material 170 sandwich apolymer 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 anabsorption panel 100 having a ferrite/polymer/high dielectricconstant absorber element 106E having 5 mm of Ni0.4Zn0.6Fe2O4, 4 mm of polycarbonate, and 1 mm of 70/30 BST, i.e. Ba0.7Sr0.3TiO3. 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. - FIG. 12 shows another
alternative embodiment 106F of awave 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™ 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, ε' and ε", and the real and imaginary parts of the permeability, µ' and µ"between 100 MHz and 1 GHz for each material.Table 4 Material ε' ε" µ' µ" 20% BaTiO3 + 80 % BiFeO 340 1 1.0 0.1 40% BaTiO3 + 60% BiFeO3 90 8 1.1 0.1 50% BaTiO3 + 50 % BiFeO 3100 10 1.2 0.1 60% BaTiO3 + 40 % BiFeO 3200 32 80% BaTiO3 + 20 % BiFeO 3300 30 1.2 0.1 60% BaTiO3 + 40% BiFeO3 + 1%Ni 48 4 1.3 0.1 60% BaTiO3 + 40% BiFeO3 + 4% Ni 53 5 1.3 0.1 4Ba0.3TiO2.3Fe2O3 3.6 negligible 1.0 0.1 BaTiO3 + SiFeO3 + Bi4Ti3O12 180 10 1.0 0.1 Fe2O4 400 300 1.5 0.5 Ba-Ferrite (BaO.6Fe2O3) 35 5 1.3 0.2 Ba- Ferrite + BaTiO 360 30 1.3 0.2 LSM 250 250 Strontium bismuth tantalate 65 0.6 1.0 0.1 Silicon Ferrite 10 1 1 20 - Experimental data for the preferred polycarbonate polymer and composites of some of the ceramic materials of Table 4 with the polycarbonate polymer are shown in Table 5. Again the mean values of the real and imaginary parts of the dielectric constant, ε' and ε", and the real and imaginary parts of the permeability, µ' and µ"between 100 MHz and 1 GHz are given for the polymer and for each composite material.
Table 5 Material Ceramic wt. % ε' ε" µ' µ" Polymer 0 2.1 0.01 1.0 0.01 BaTiO3.BiFeO3 20 3.2 0.05 1.0 0.01 BaTiO3.BiFeO3 40 4.2 0.1 1.0 0.01 BaTiO3.BiFeO3 50 4.4 0.1 1.0 0.01 BaTiO3.BiFeO3 75 6.5 0.3 1.0 0.01 4BaO.3TiO2.3Fe2O3 40 4.0 0.08 1.0 0.01 Fe2O3 40 6.0 0.8 1.0 0.01 Ba- Ferrite 40 4.0 0.2 1.0 0.01 BST (BaxSr(1-x)TiO3) 40 7.0 0.05 1.0 0.01 - 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-ceramiccomposite absorber element 106F comprising 13 mm of 50% polycarbonate and 50% (0.25BaTiO3 + 0.75BiFeO3). This shows good absorptivity in the high frequency radio spectrum. - FIG. 13 shows an
embodiment 106G of theabsorber 106 according to the invention comprising aferrite 180 and amaterial 182. This embodiment is the same as the embodiment of FIG. 3, except that the positions of theferrite 180 and the material 182 with respect to theincident radiation 110 are reversed. Theferrite 180 may be any of the ferrites listed in Table 1 or mentioned in the discussion of FIG. 3. For the television applications, a nickel-zinc ferrite, and in particular Ni0.4Zn0.6Fe2O4, is preferred. Thematerial 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. In this embodiment 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 theincident 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 themetal 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 thesystem 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 Nl0.4Zn0.8Fe2O4 as the ferrite and BST as the dielectric 182. In this particular embodiment, there is noreflective element 104. The thickness of theferrite 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. Since no radiation passes through the sample, it is either absorbed or reflected, and thus, the reflective loss again is a suitable measure of the absorptive properties as before.Table 6 Curve Number Thickness In mm 200 3 201 4 202 5 203 6 204 7 wave absorber element 106G appears to be even more important if there is noreflective element 104. Another computer simulated graph for anembodiment 106G of a wave absorber was made for a sample in which theferrite 180 was Ni0.4Zn0.6Fe2O4, thematerial 182 was LSM, and a metal backplate 104 was included. This gave similar results to the curves of FIG. 20, but the absorption was about 32 dB, and the absorption was not as strongly dependent on thickness. The largest absorption was for an embodiment In which theferrite 180 was 5mm in thickness and the LSM was 5mm in thickness. A further computer simulated graph for anembodiment 106G of a wave absorber was made for a sample in which theferrite 180 was Ni0.4Zn0.6Fe2O4, thematerial 182 was a magnetoplumbite, Ba4Ti3Fe6O19, and a metal backplate 104 was included. This gave similar results to the curves of FIG. 20, but the lowest absorption was about -29 dB, and the absorption was not as strongly dependent on thickness. The largest absorption was for an embodiment in which theferrite 180 was 5mm in thickness and the magnetoplumbite was 5mm in thickness. A fourth computer simulated graph for anembodiment 106G of a wave absorber was made for a sample in which theferrite 180 was Ni0.4Zn0.6Fe2O4, thematerial 182 was aluminum oxide (Al2O3), and a metal backplate 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 theferrite 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. In FIG. 14
absorber 106H comprises alayer 186 of polymer and alayer 188 of another dielectric material. In FIG. 15,absorber 1061 comprises alayer 190 of a dielectric material and alayer 192 of a polymer. Preferably, in each of the embodiments thedielectric material polymer absorbers 106H and 106I are of particular importance because they are easily constructed and are relatively light. - FIG. 21 shows another
embodiment 106J of anabsorber 106 that provides good results.Absorber element 106J comprise alayer 194 of a ferrite, alayer 196 of a tow dielectric constant material, and alayer 198 of a high dielectric constant material. Thisembodiment 106J is the same as the embodiment of FIG. 11, except that it has been generalized to include any low dielectricconstant material 196, not just a polymer. Silicon glass is an appropriate low dielectric constant material, while thepreferred ferrites 194 and high dielectricconstant material 198 are as discussed in connection with FIG. 11. Thisembodiment 106J can be tuned to give much the same performance as theembodiment 106E of FIG. 11. Computer simulated reflective loss curves have been run for anabsorber 106J in which theferrite 194 was Ni0.4Zn0.6Fe2O4, dielectric 196 was silicon glass, and dielectric 198 was BST. The best absorption was for anabsorber 106J in whichlayer 194 was 5 mm thick,layer 196 was 4mm thick, andlayer 198 was 1 mm thick. The reflective loss was above 20dB for the entire TV spectrum for this absorber, with a peak absorption of near 35dB. - FIGS. 22, 23, and 24 show examples of how the teachings of the above layering principals can be extended to many-layered
absorbers 106. In theembodiment 106K of FIG. 22, there is oneferrite layer 210 and threedielectric layers ferrite 210, and any of the dielectrics discussed above may be used as the dielectrics, with the understanding that dielectric 214 is different fromdielectrics Table.7 Curve No. Ferrite Thickness in mm Polymer Thickness in mm LSM Thickness in mm BST Thickness in mm 250 5 2 2 1 252 4 2 2 2 254 5 3 3 1 256 5 2 2 1 258 4 2 2 2 - 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 anabsorber 106 comprising alayer 220 of ferrite, alayer 222 of polymer, asecond layer 224 of ferrite, asecond layer 226 of polymer, and athird layer 228 of ferrite. Again, any ferrite or polymer discussed above may be used. FIG. 26 shows a graph of reflective loss in dB versus frequency as computer simulated for anabsorber 106L in which theferrites polymers Table 8 Curve No. 1 st Ferrite Thickness 1st Polymer Thickness 2nd Ferrite Thickness 2nd Polymer Thickness 3rd Ferrite Thickness 260 2 2 2 2 2 262 2 2 1 3 2 264 2 3 1 3 1 266 1 3 2 3 1 268 2 3 1 2 2 -
Embodiment 106M of FIG. 24 illustrates anabsorber 106 comprising n ferrite/polymer layers, where n is greater than 1 and, preferably, 100 or less. That is, the basicabsorber element embodiment 106M is a layer offerrite 230 and a layer ofpolymer 231. The basic absorber element indicated by thenumber 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. Preferably, the ferrite and the polymer is the same in each absorber element, though the invention contemplates that one or all of theabsorber elements 1 through n be made of different materials from the other elements. FIG. 27 shows a graph of reflective loss in dB versus frequency as computer simulated for an absorber 106M in which theferrites 230 were Ni0.4Zn0.6Fe2O4, thepolymers 231 were a polycarbonate with the properties shown in Table 5, and n = 50. The thicknesses of theferrite 230 and thepolymer 231 for the basic absorber element for each curve are given in Table 9.Table 9 Curve No. Ferrite Thickness in µ m Polymer Thickness in µ m 270 100 100 272 200 200 274 100 50 276 95 100 278 105 100 - An analysis of all the results discussed above indicates that perhaps the
best absorber 106 is anembodiment 106N shown in FIG. 30. Thisabsorber 106N includes a high µ"material 302 sandwiched between a high dielectricconstant material 300 and a low dielectricconstant material 304. Preferably the high dielectric constant material is nearest the side of incidence of theradiation 110 and the low dielectric constant material is nearest to thesupport structure 100 and themetal reflector 104. Preferably, the imaginary part of the permeability, µ", of themiddle layer 302 is not only high, but it is also higher than the real part of the permeability, µ'. Preferably, 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. - The above advances in the art are based on empirical results. Generally, it is understood by the inventors that the good results for some materials, such as the ferrites, is due to the high µ" of these materials. However, it is difficult to find an explanation of many good results obtained, particularly since many of the materials used do not have any readily identifiable property that accounts for the results. A careful analysis has been made of the above-disclosed results and the properties of the materials, and it is now understood that some of the good absorption properties are related to the principal of the quarter-wave plate. In a quarter-wave plate absorber, a thickness of material equal to one-quarter of a wavelength is placed in front of a 100% reflector, such as a metal layer. That is, this absorption principal is effective only for a thickness given by
where λeff = N(ε'µ') ½ and λ is the wavelength of the incident wave. At first glance, it would not appear that this could apply to the relatively broad absorptions discussed above, since the materials used are much thinner than a quarter of a typical television frequency wavelength, andequation 1 can be true only for an extremely narrow range of wavelengths. However, in high dielectric constant materials, the wavelength of a wave of a given frequency is much shorter than it is in air. Moreover, if for acertain absorber 106 structure, ε'µ' is a function of frequency such that:
where f is the frequency of the wave of wavelength λ, then the structure will be a good absorber over the entire frequency range for which equation (2) is true. If an absorber structure has an effective ε'µ' that obeys equation (2) over a relatively wide frequency range, that is, if
where neff is the effective index of refraction, for a broad range of frequencies, then this structure would be a good absorber. Looking at tables 4 and 5 above, we see that for many of the materials of the invention µ'eff = 1 or is very close to one. Structures made of several of these materials will also have µ'eff = 1, or close to it. Structures made of these materials and for which
over a specified frequency range will be good absorbers over that frequency range. - From the above, it can be seen that any material or structure that has an effective ε'µ'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 µ' 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 ε' 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.
- A further factor that is important in providing good absorption is impedance matching of adjacent layers. That is, that the impedance of adjacent layers should be approximately equal. In terms of the layer closest to the exterior surface of
panel 100 this means that the impedance should be 1 or close to 1, since the impedance of air is 1. If the impedance of adjacent layers is very different, then an electromagnetic wave will tend to be reflected at the interface of the two layers, and the inner layer will not participate significantly in the absorption. Impedance is defined as z = ([µ'- iµ"]/[ε'- iε"])½. While this is a complex expression, the behavior of which is difficult to see intuitively, it can be simplified somewhat by realizing that ε" and µ" are essentially losses, and thus (µ'/ε')½ is the principal parameter that needs to be matched. The impedance of air is 1. FIGS. 7 and 8 show that over a significant range of frequencies near 200 MHz, µ' ≈ ε' for Ni0.4Zn0.6Fe2O4, and thus (µ'/ε')½ 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. - From the above, a preferred method of designing an electromagnetic wave absorption panel can be distilled. First a combination of materials is found that has an index of refraction that decreases with frequency and absorbs well over a frequency range in the vicinity of the frequency range desired to be absorbed. Then, the combination is tuned so that its index of refraction more closely approaches the ideal equation (4), which broadens the absorption range. 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).
- It has been found that materials with a decreasing effective dielectric constant in particular are very effective as a front layer, i.e. the layer closer to the
incident radiation 110, in improving the wave absorption characteristics of a multi-layer absorber system. - In the above discussion, many of the embodiments included a polymer-ceramic composition. A flow chart of the process of making these compositions is shown in FIG. 28. First a
powder 280 of the desired ceramic material, apolymer powder 281, and a solvent 282 that will dissolve the polymer are mixed instep 284. For example, if the polymer is Butvar™, then a suitable solvent is tetrahydrofuran (THF). The ceramic is suspended in the solution. The resulting solution is mixed until it is homogeneous, and then poured into a mold instep 286. The composite is then cured at a suitable temperature for a suitable time period. For example, for Butvar™ a suitable temperature is room temperature and a suitable time period is twelve hours. - From the above it can be seen that 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. - Many of the dielectrics, ferroelectrics, ferrites, etc. used in the
absorbers 106 according to the invention are ceramics. All of these ceramics were made by the process illustrated in the flow chart of FIG. 29. In step 291 apowder 290 of the ceramic material desired is placed inside a mold. Preferably the mold is made of stainless steel. Instep 292 the powder is isostatically pressed in the mold, preferably at a pressure of 50,000 pounds per square inch (PSI). Then, instep 296, 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. For example, 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. Moreover, many of the high dielectric constant materials, such as BST are hardened ceramics that are weather resistant. Thus, 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, tc, 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, ε', 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. Thus, the absorber panels of the invention lend themselves to the solution of specific electromagnetic environment problems for specific construction sites.
- Another feature of the invention is that the nickel-zinc ferrite is the best of the ferrites in absorption and the Ni0.4Zn0.6Fe2O4 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.
Claims (13)
- An electromagnetic wave absorption panel (100) for use in building construction, said panel comprising: a building support element (102); and an absorber element (106) supported by said support element, said wave absorption panel characterized in that said absorber element comprises a first layer (166, 186, 210) and a second layer (170, 182, 216), said first layer being located closer to the point of incidence of said electromagnetic wave on said panel than said second layer, said first layer comprising a ferrite, and said second layer comprising a high dielectric constant material having a dielectric constant of 50 or more.
- An electromagnetic wave absorption panel as in Claim 1 and further characterized in that said absorber element includes a third layer (168, 212) located farther from said point of incidence of said electromagnetic wave than said first layer, said third layer comprising a low dielectric constant material having a dielectric constant of 10 or less.
- An electromagnetic wave absorption panel as in claim 2 and further characterized in that said absorber element includes a fourth layer (214) located between said third layer and said second layer, said fourth layer comprising La(1-x)SrxMnO3.
- An electromagnetic wave absorption panel as in claim 3 and further characterized in that said third layer is located between said first layer and said second layer.
- An electromagnetic wave absorption panel (100) for use in building construction, said panel comprising:a building support element (102) ;a reflective element (104) supported by said support element; and an absorber element (106) supported by said support element, said absorber element located closer to the point of incidence of said electromagnetic wave on said panel than said reflective element, said wave absorption panel characterized in that said absorber element comprises a first layer (162, 166, 220) comprising a ferrite and a second layer (164, 168, 222) comprising a low dielectric constant material having a dielectric constant of 10 or less, said second layer located farther from said point of incidence of said electromagnetic wave than said first layer and that said absorber element further comprises a third layer (160, 170) comprising a high dielectric constant material having a dielectric constant of 50 or more.
- An electromagnetic wave absorption panel as in claim 5 and further characterized in that there are a plurality of said absorber elements, each absorber element comprising one of said first layers (230) and one of said second layers (231).
- An electromagnetic wave absorption panel as in Claim 6 and further characterized in that there are n of said absorber elements (160M), where n is an integer between 2 and 100.
- An electromagnetic wave absorption panel according to any one of claims 1 to 7, wherein said high dielectric constant material is selected from the group consisting of layered superlattice materials, signet magnetics, and Z x BaTiO3 +(100% - Z) x BiFeO3 where 100% > Z > 0%.
- An electromagnetic wave absorption panel according to any one of claims 1 to 8, wherein said absorber element (106) comprises a material selected from the group consisting of a garnets, magnetoresistive materials, layered superlattice materials, magnetoplumbites, signet magnetics, La(1-x)SrxMnO3, Fe3O4 and Ni0.4Zn0.6Fe2O4.
- An electromagnetic wave absorption panel as in claim 9 and further characterized in that said material comprises yttrium iron garnet.
- An electromagnetic wave absorption panel as in claim 9 and further characterized in that said magnetoresistive material is a material selected from the group consisting of La0.67Sr0.33MnO3, LaxCa(1-x)MnO3, and LaxPb(1-x)MnO3, where 0 < x <1.
- An electromagnetic wave absorption panel as in claims 8 or 9 wherein said absorber element (176) comprises a composite of a polymer and a material selected from said group.
- An electromagnetic wave absorption panel as in claims 8 or 9 and further characterized in that said layered superlattice material comprises a material selected from the group consisting of strontium bismuth tantalate, strontium bismuth niobate, strontium bismuth titanate, strontium bismuth zirconate, and solid solutions thereof.
Applications Claiming Priority (5)
Application Number | Priority Date | Filing Date | Title |
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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 |
US782938 | 1997-01-13 | ||
US08/782,934 US6037046A (en) | 1997-01-13 | 1997-01-13 | Multi-component electromagnetic wave absorption panels |
PCT/US1998/000406 WO1998031072A1 (en) | 1997-01-13 | 1998-01-12 | Electromagnetic wave absorption panels and materials for same |
Publications (2)
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EP0900458A1 EP0900458A1 (en) | 1999-03-10 |
EP0900458B1 true EP0900458B1 (en) | 2006-11-22 |
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EP98901750A Expired - Lifetime EP0900458B1 (en) | 1997-01-13 | 1998-01-12 | Electromagnetic wave absorption panels and materials for same |
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EP (1) | EP0900458B1 (en) |
JP (1) | JP3852619B2 (en) |
KR (1) | KR20000064579A (en) |
CN (1) | CN1128485C (en) |
DE (1) | DE69836457T2 (en) |
WO (1) | WO1998031072A1 (en) |
Families Citing this family (11)
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JP2002314285A (en) * | 2001-04-18 | 2002-10-25 | Fujita Corp | Electromagnetic wave absorber |
US7864095B2 (en) | 2004-02-27 | 2011-01-04 | Mitsubishi Gas Chemical Company, Inc. | Wave absorber and manufacturing method of wave absorber |
JP4461970B2 (en) * | 2004-09-06 | 2010-05-12 | 三菱瓦斯化学株式会社 | Radio wave absorber |
ES2274674B1 (en) * | 2004-12-24 | 2008-04-16 | Micromag 2000, S.L. | ELECTROMAGNETIC RADIATION ABSORBER BASED ON MAGNETIC MICROWAVES. |
JP2006186725A (en) * | 2004-12-28 | 2006-07-13 | Central Glass Co Ltd | Electromagnetic wave absorbing board |
JP2012508339A (en) * | 2008-10-06 | 2012-04-05 | フロデザイン ウィンド タービン コーポレーション | Wind turbine with reduced radar signature |
DE102009046752A1 (en) | 2009-11-17 | 2011-05-26 | Ed. Züblin Ag | Prefabricated device for eliminating or reducing reflected signals from electromagnetic wave i.e. radar wave, has three dimensional randomly formed grid intermediate layer absorbing partially defused electromagnetic wave to be reflected |
US9505632B2 (en) | 2010-09-22 | 2016-11-29 | Skyworks Solutions, Inc. | Compositions and materials for electronic applications |
CN103452200A (en) * | 2012-05-30 | 2013-12-18 | 深圳市栢富电子有限公司 | Wave absorbing assembly and manufacturing method and microwave unreflected chamber and construction method |
CN102904065A (en) * | 2012-10-19 | 2013-01-30 | 中兴通讯股份有限公司南京分公司 | Wave absorbing device and wireless terminal |
CN108314866B (en) * | 2018-02-08 | 2020-09-25 | 西安理工大学 | Oriented Co2Z ferrite-Fe2O3Composite wave-absorbing material and synthetic method |
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NL112646C (en) * | 1958-12-04 | |||
US4012738A (en) * | 1961-01-31 | 1977-03-15 | The United States Of America As Represented By The Secretary Of The Navy | Combined layers in a microwave radiation absorber |
JPS51163498U (en) * | 1976-06-09 | 1976-12-27 | ||
JP2510880B2 (en) * | 1988-07-26 | 1996-06-26 | ティーディーケイ株式会社 | Multilayer type electromagnetic wave absorber and anechoic chamber consisting of the electromagnetic wave absorber |
FR2665296B1 (en) * | 1990-07-27 | 1993-12-17 | Ferdy Mayer | BROADBAND HIGH FREQUENCY ABSORBENT STRUCTURES. |
FR2666439B1 (en) * | 1990-08-30 | 1994-03-18 | Commissariat A Energie Atomique | ABSORBENT SCREEN BASED ON ELECTRONIC CONDUCTIVE POLYMER. |
JPH04354103A (en) * | 1991-05-31 | 1992-12-08 | Yoshiyuki Naito | Wideband radio wave absorbing device |
JPH08204379A (en) * | 1995-01-24 | 1996-08-09 | Mitsubishi Cable Ind Ltd | Radio wave absorber |
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1998
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- 1998-01-12 DE DE69836457T patent/DE69836457T2/en not_active Expired - Fee Related
- 1998-01-12 CN CN98800025A patent/CN1128485C/en not_active Expired - Fee Related
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DE69836457T2 (en) | 2007-09-13 |
JP3852619B2 (en) | 2006-12-06 |
WO1998031072A1 (en) | 1998-07-16 |
CN1128485C (en) | 2003-11-19 |
JP2000507400A (en) | 2000-06-13 |
DE69836457D1 (en) | 2007-01-04 |
CN1216166A (en) | 1999-05-05 |
KR20000064579A (en) | 2000-11-06 |
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