EP0380267B1 - Mikrowellen-Absorbermaterial, das nadelförmige magnetische Metallfasern enthält - Google Patents

Mikrowellen-Absorbermaterial, das nadelförmige magnetische Metallfasern enthält Download PDF

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Publication number
EP0380267B1
EP0380267B1 EP19900300632 EP90300632A EP0380267B1 EP 0380267 B1 EP0380267 B1 EP 0380267B1 EP 19900300632 EP19900300632 EP 19900300632 EP 90300632 A EP90300632 A EP 90300632A EP 0380267 B1 EP0380267 B1 EP 0380267B1
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Prior art keywords
absorber
filaments
conductor
binder
microns
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Expired - Lifetime
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EP19900300632
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English (en)
French (fr)
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EP0380267A1 (de
Inventor
Charles E. Iii C/O Minnesota Mining Boyer
Eric J. C/O Minnesota Mining Borchers
Richard J. C/O Minnesota Mining Kuo
Charles D. C/O Minnesota Mining Hoyle
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3M Co
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Minnesota Mining and Manufacturing Co
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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
    • H01Q17/005—Devices for absorbing waves radiated from an antenna; Combinations of such devices with active antenna elements or systems using woven or wound filaments; impregnated nets or clothes

Definitions

  • This invention involves electromagnetic radiation absorbers which comprise magnetic metallic filaments embedded in dielectric binders.
  • Electromagnetic radiation absorbers typically are non-conductive composites of one or more kinds of dissipative particles dispersed through dielectric binder materials.
  • the absorption performance of the composite absorber depends predominantly on the electromagnetic interactions of the individual particles with each other and with the binder.
  • U.S. Patent 4,538,151 discloses an absorber comprising a mixture of: metal or alloy fibers having high electric conductivity, a length from 0.1mm (100 microns) to 50mm and a length to diameter ratio ("aspect ratio") larger than 10; ferrite or a ferromagnetic material; a high molecular weight synthetic resin; and, optionally, carbon black.
  • whiskers if monocrystalline in structure, or acicular filaments if polycrystalline.
  • the paints are typically dispersions of the metal/binder composites.
  • U.S. Patent 4,606,848 (Bond) teaches a paint comprising stainless steel, carbon, or graphite fibers in polyurethane, alkyd, or epoxy binders.
  • the fibers range in length from 10 micron to 3 cm (30,000 micron) as the diameter ranges from 0.01 micron to 30 micron, thus the aspect ratio is a constant 1000.
  • the invention is a non-conductive microwave radiation absorber, comprising acicular magnetic metallic filaments with an average length of about 10 microns or less, a diameter of about 0.1 micron or more, and aspect ratios between 10:1 and 50:1.
  • the filaments are dispersed in a dielectric binder.
  • An absorbing paint may be formed by dispersing the filaments into a base liquid, such as by dissolving the filament/binder dispersion in the base liquid.
  • the absorber or the paint may be applied to a conductor such as a metal foil, plate or wire.
  • Figures 1-4 are graphs of the real and imaginary parts of the permittivity and permeability of four embodiments of the invention, as a function of incident radiation frequency.
  • Figure 5 is a graph of the predicted absorption response of one embodiment of the invention, and of the actual absorption response of another embodiment of the invention, as a function of incident radiation frequency.
  • Figure 6 is a cross sectional view of another embodiment of the invention.
  • One embodiment of the invention is a non-conductive composite absorber having at least two major components.
  • the first component is acicular magnetic metallic polycrystalline filaments (or simply "filaments") having an average length of less than about 10 micron, a diameter greater than about 0.1 micron, and length to diameter ratios ("aspect ratios") between 10:1 and 50:1.
  • the second component is dielectric binder in which the filaments are dispersed, and which contributes to the absorption performance of the composite absorber.
  • Another embodiment of the invention is an absorbing paint for direct application to either a conductive or insulating surface.
  • This embodiment may be made by dispersing either the filaments themselves into a base liquid, or by forming a pigment comprising the composite absorber and dissolving the pigment in a base liquid. In either case the paint must remain non-conductive. For this reason, dissolving the composite absorber pigment is preferred, as the dielectric binder substantially surrounds the filaments and prevents them from electrical contact with each other. If an absorber is used as a pigment, a polymeric binder material is preferred for ease of preparation and use, although the choice of binder depends on the choice of base liquid.
  • Another embodiment of the invention includes a conductor adjacent the composite absorber.
  • the conductor may be an object which the absorber is designed to shield, or it may be a conductive layer intended to promote microwave absorption.
  • the composite should be in a form which has a thickness in the direction of radiation propagation greater than about one-fortieth (2.5 percent) of the wavelength to be absorbed.
  • the composites of this invention absorb radiation over a broad incident frequency range in the microwave region of approximately 2 to 20GHz, implying a thickness greater than about 0.0375 cm.
  • impedance matching of the absorber to the incident medium is preferred but not required.
  • the match is done by a material having permeability and permittivity values that minimize reflection of microwaves at the surface of incidence.
  • a layer of such impedance matching material is added to the absorber or dried absorbing paint, and the dimensions, weight, etc. of the layer are considered in the complete design.
  • All the embodiments employ magnetic metallic polycrystalline filaments.
  • Presently available filaments typically range in length from 50-500 microns and in diameter from 0.1 to 0.5 microns; to preserve the filament shape, the aspect ratios generally are maintained between 500:1 to 1000:1.
  • These filaments can be shortened for use in the invention by milling and grinding. The average sizes of the filaments may be determined from individual measurements performed with a scanning electron microscope.
  • the reduction in length of the magnetic metallic filaments broadens the absorption performance of the composite material in which they are embedded.
  • Long filaments produce only narrowband absorption response because of their conductivity, although it is generally stronger than that of, for example, the carbonyl iron spheres known in the art, due to the dipole moments of the filaments.
  • the shortened, low aspect ratio magnetic metallic filaments used in the present invention produce effective and versatile absorbers, exhibiting strong absorption magnitude over a broad frequency range. We believe at this time that the dissipative performance of the filaments is due in part to the magnetic and metallic natures of the filaments, in addition to their length and aspect ratio.
  • the inventive absorber has a reduced volume loading factor (absorbing particle volume as a percentage of total absorber volume), which leads to a reduction in weight of the final product.
  • volume loading factors for composites based on carbonyl iron microspheres typically range from 40 to 65 percent.
  • the volume loading may be as low as 25 to 35 percent with no decrease in absorption performance.
  • the reduced acceptable volume loading factor also helps ensure that the composite absorber is an insulator, i.e., it has a high bulk resistivity, despite the conductivity of the individual filaments. If the bulk resistivity is too low, the composite absorber effectively becomes a conductive sheet, which reflects microwaves instead of absorbing them.
  • the resistivity of iron for example, is about 10 ⁇ 5 ohm-cm at room temperature. Insulators typically have bulk resistivities of 1012 ohm-cm or more. Samples of the invention with 25 percent volume loading of iron filaments have measured bulk resistivity of approximately 1.5x1013 ohm-cm at room temperature, indicating an insulator.
  • filaments may be used in the invention.
  • Iron, nickel, and cobalt filaments are suitable, as are their alloys.
  • iron-nickel, nickel-manganese, and iron-chromium alloys are acceptable, if they form acicular magnetic metallic polycrystalline filaments of the proper size.
  • More than one type of filament may be used in a single absorber, and other absorbing materials (e.g., carbonyl iron) may be added to the composite material to tailor the absorption versus frequency characteristics to a particular application.
  • the dielectric binder may be ceramic, polymeric, or elastomeric. Ceramic binders are preferred for applications requiring exposure to high temperatures, while polymeric and elastomeric binders are preferred for their flexibility and lightness.
  • polymeric binders are suitable, including polyethylenes, polypropylenes, polymethylmethacrylates, urethanes, cellulose acetates, epoxies, and polytetrafluoroethylene (PTFE).
  • the polymeric binder may be a thermosetting polymer, a thermoplastic polymer, or a conformable polymer which changes shape to assume a final applied configuration.
  • a heat-shrinkable binder may be formed from cross-linked or oriented crystallizable materials such as polyethylene, polypropylene, and polyvinylchloride; or from amorphous materials such as silicones, polyacrylates, and polystyrenes.
  • Solvent-shrinkable or mechanically stretchable binders may be elastomers such as natural rubbers or synthetic rubbers such as reactive diene polymers; suitable solvents are aromatic and aliphatic hydrocarbons. Specific examples of such materials are taught in U.S. Patent No. 4,814,546 (Whitney et al.).
  • Suitable elastomeric binders are natural rubbers and synthetic rubbers, such as the polychloroprene rubbers known by the trade name "NEOPRENE.”
  • the binder may be homogenous, or a matrix of interentangled fibrils, such as the PTFE matrix taught in U.S. Patent 4,153,661 (Ree et al.).
  • An electrical conductor with a microwave absorbing coating may be made by extruding a composite absorber onto the conductor.
  • Many polymeric binders are suitable for extrusion, especially polyvinylchlorides, polyamides, and polyurethanes.
  • the conductor may be a wire, cable, or conductive plate.
  • binder depends on the final absorption versus frequency characteristics desired and the physical application required.
  • the choice of binder also dictates the procedure and materials required to assemble the composite absorber, paint, or coated conductor. The basic procedures are illustrated by the following examples.
  • A-D Four samples of the invention, labeled A-D, were prepared, differing only in the lengths of filaments produced.
  • 100 parts by weight of commercially available iron filaments typically 50-200 microns in length and 0.1 to 0.5 microns in diameter, were wetted with methylethylketone and pulverized to shorter lengths in a high speed blade mixer for one hour. After the shortened filaments settled, the excess solvent was decanted away.
  • the filaments were milled again, in methylethylketone with 800 grams of 1.3 millimeter diameter steel balls at 1500 revolutions per minute in a sand mill supplied by Igarashi Kikai Seizo Company Ltd. Each of the four samples was milled for a different amount of time. The milling times were: Sample A, 15 minutes; Sample B, 30 minutes; Sample C, 60 minutes; and Sample D, 120 minutes.
  • the distributions of filament length in microns as a percentage of total filaments measured for each sample is shown in Table 1. The percentages do not add to 100 due to rounding. Approximately 150 filaments were measured for each sample.
  • the longest length, average length, average diameter, and aspect ratio of the samples are shown in Table II, the first three measured in microns.
  • the average length calculation used the average length of each size range, weighted by the percentage distribution in each size range.
  • the diameters of the filaments were essentially unchanged by the milling, i.e., they ranged from 0.1 to 0.5 microns. Because Table 1 shows that substantially all of the filaments in the samples have lengths of 10 microns or less, the diameter range of 0.1 to 0.5 microns implies that the filaments in each sample have aspect ratios between 20:1 and 50:1. The preferred aspect ratio range is 10:1 to 25:1, using the average length and diameter values of Table 2.
  • a paint containing the milled filaments was made from two major components.
  • the first component was (by weight) 198.0 parts of methylethylketone, 50.0 parts of toluol, 43.6 parts of a polyurethane ("ESTANE” type 5703 supplied by B.F. Goodrich Company), and 2.5 parts of a suitable dispersing agent ("GAFAC” type RE-610 supplied by GAF Corporation). This component was stirred until the polyurethane dissolved.
  • the second component was (by weight) 100 parts of the shortened iron filament samples, 2.7 parts of diphenylmethane diisocyanate, and 1.8 parts of propylene glycol methylether acetate. The two components were mixed in a blade mixer to form a homogeneous paint. Each mixture was degassed and cast onto a flat surface, then allowed to dry in air to remove the volatile vehicle chemicals.
  • the resulting radiation absorber was machined into circular toroidal ("donut-shaped") samples for coaxial microwave absorption measurements.
  • the inner and outer diameters of the sample were 3.5 ⁇ 0.0076mm and 7.0 ⁇ 0.0076mm, respectively.
  • Each sample was placed, at a position known to ⁇ 0.1mm, in a 6cm long coaxial airline connected to a Hewlett-Packard Model 8510A precision microwave measurement system.
  • the substrates used had a permittivity of 2.58 and a permeability of 1.00.
  • Figures 1-4 show that filament length strongly affects both the real and imaginary parts of permittivity.
  • the real part of the permittivity decreases significantly faster than the imaginary part, thus the ratio of the imaginary part to the real part (a measure of the absorption ability of the composite) increases with decreasing filament length.
  • the effect of the varying filament length on the measured absorber permeability is generally weak, but in Sample D the imaginary part of the permeability shows a significant decrease compared to that of Samples A-C, especially at low frequencies. For this reason, Sample C (average filament length about 5 microns) is preferred, although each of the samples is an acceptable microwave absorber.
  • a stock formulation containing iron filaments was made as follows. First, 52.49 grams of synthetic rubber ("NEOPRENE” type W as supplied by E.I. du Pont de Nemours Company) was banded on a two roll rubber mill and mixed for five minutes to reach an elastic phase. Then 0.52 grams benzothiazyl disulfide, 13.12 grams stearic acid, and 2.62 grams white mineral oil were added, and mixing continued for another five minutes. After 147.38 grams of commercial length iron filaments were added, mixing continued until the average length of the filaments was approximately 6.5 microns and the average diameter approximately 0.26 microns, for an aspect ratio of 25:1.
  • a curing accelerator comprising 0.26 grams hexamethylenetetramine, 0.26 grams tetramethylthiuram disulfide, and 0.52 grams polyethylene glycol.
  • the accelerator was mixed into the iron filament/binder mixture to produce the stock formulation.
  • the volume loading of the filaments into the binder was determined to be 35%.
  • the stock formulation was kept below 30°C.
  • a thin calipered sheet of the stock formulation was dissolved in a base mixture of equal parts butylacetate and toluene, followed by agitation for two hours. This formed a paint designated Sample E.
  • a 16.5cm square aluminum plate was repeatedly sprayed with thin coats of the paint, allowing typically 15 to 30 minutes drying time between each spraying. To keep the solid content of the paint at approximately 15% by volume, the same butylacetate/toluene base mixture was thinned into the paint as needed. Once a final sprayed thickness of about 1mm was reached, the coat was allowed to dry and cure at room temperature for three days.
  • the coated aluminum plate was mounted in a measurement chamber with microwave radiation normally incident on the coated side. Actual measurements of the transmission and reflection coefficients were used to calculate the predicted absorption for transverse magnetic (TM) radiation incident upon the plate at a 65° angle from normal, as a function of incident frequency. The predicted results are graphed in Figure 5 and show the desired broad and strong absorption response, at least 10dB over a 13 GHz range from 6 to 19 GHz and at least 20dB over a 3dB wide range from 10.5 to 13.5 GHz.
  • TM transverse magnetic
  • a paint designated Sample F was made by the same procedures as for Sample E above with the following ingredients: "NEOPRENE" Type W, 69.99 grams; benzothiazyl disulfide, 0.70 gram; stearic acid, 17.50 grams; white mineral oil, 3.50 grams; iron filaments, 196.50 grams; hexamethylenetetramine, 0.35 gram; tetramethylthiuram disulfide, 0.35 gram; polyethylene glycol, 0.70 gram. The volume loading of the iron filaments was 25%. After painting the conductive plate, actual measurements were made of the absorption coefficient for TM radiation incident upon the plate at a 65° angle from normal, as a function of incident frequency.
  • results are also graphed in Figure 5 and confirm the desired broad and strong absorption response, at least 10dB over a 11 GHz range from 5 to 16 GHz, at least 20dB over a 3.5dB wide range from 9 to 12.5 GHz, and at least 30dB over a 1 dB wide range from 10.6 to 11.6 GHz.
  • the construction shown schematically in Figure 6 was made as follows. Iron filaments 43 were dispersed in a 1.2mm thick calipered sheet 42 made from the stock formulation which was used to form Sample E of Example 2. A conductive layer 48 of aluminum, vapor coated on one side of a polyester support sheet 46, was adhered to sheet 42 with an ethylene acrylic acid (EAA) type internal adhesive 44 between the polyester support sheet 46 and the stock formulation 42. This produced a radiation absorber/conductive metal layer construction, sometimes known as a Dallenbach construction.
  • EAA ethylene acrylic acid
  • the absorbing composite may be coated directly on the conductive layer without any internal adhesive at all.
  • an absorbing paint could be made and applied to a suitable conductive layer, as in Example 2.
  • an impedance matching layer 56 is preferred but not required.
  • Suitable materials for this layer include polymeric materials with high volumes of trapped air, such as air-filled glass microbubbles embedded in the binder materials described above.
  • An absorber comprising iron filaments in a matrix of interentangled polytetrafluoroethylene (PTFE) fibrils was made according to the process of U.S. Patent 4,153,661 (Ree et al.).
  • a water-logged paste of 10.0 grams of iron filaments and 4 cc of an aqueous PTFE dispersion (5.757 grams of PTFE particles) was intensively mixed at about 75°C, biaxial calendered at about 75°C, and dried at about 75°C.
  • the lengths of the filaments were reduced by the mixing and calendering steps to an estimated range of 1 to 10 microns.
  • the volume loading of the whiskers in the total volume of the absorber was calculated to be 32.7 percent.

Claims (23)

  1. Mikrowellenstrahlen-Isolationsabsorbermaterial, welches nadelförmige magnetische Metallfasern aufweist, die eine durchschnittliche Lange von etwa 10 Mikron oder weniger aufweisen, Durchmesser von etwa 0,1 Mikron oder darüber und Längenverhältnisse zwischen 50:1 und 10:1, dispergiert in einem Dielektrizitätsbinder.
  2. Absorbermaterial nach Anspruch 1, dadurch gekennzeichnet, daß die Fasern eine durchschnittliche Länge von etwa 5 Mikron aufweisen.
  3. Absorbermaterial nach Anspruch 1, dadurch gekennzeichnet, daß die Fasern Längenverhältnisse zwischen 25:1 und 10:1 aufweisen.
  4. Absorbermaterial nach Anspruch 1, dadurch gekennzeichnet, daß die magnetischen Metallfasern aus einer Gruppe ausgewählt werden, die Eisen, Nickel, Kobalt sowie deren Legierungen aufweist.
  5. Absorbermaterial nach Anspruch 1, dadurch gekennzeichnet, daß der Dielektrizitätsbinder einen keramischen Werkstoff darstellt.
  6. Absorbermaterial nach Anspruch 1, dadurch gekennzeichnet, daß der Dielektrizitätsbinder ein Polymerisat darstellt.
  7. Absorbermaterial nach Anspruch 6, dadurch gekennzeichnet, daß der Polymerisatbinder ein Polymerisat aufweist, das aus einer Gruppe ausgewählt wird, die hitzehärtbare Polymere und thermoplastische Polymere umfaßt.
  8. Absorbermaterial nach Anspruch 6, dadurch gekennzeichnet, daß der Polymerisatbinder ein Polymerisat aufweist, das aus einer Gruppe ausgewählt wird, die Polyethylene, Polypropylene, Polymethacrylate, Urethane, Celluloseacetate und Polytetrafluorethylene umfaßt.
  9. Absorbermaterial nach Anspruch 6, dadurch gekennzeichnet, daß der Polymerisatbinder ein Polymerisat aufweist, das aus einer Gruppe ausgewählt wird, die wärmeschrumpfbare Polymere, lösungsschrumpfbare Polymere und mechanisch dehnbare Polymere umfaßt.
  10. Absorbermaterial nach Anspruch 1, dadurch gekennzeichnet, daß der Dielektrizitätsbinder ein Elastomer darstellt.
  11. Absorbermaterial nach Anspruch 1, dadurch gekennzeichnet, daß die Raumbelastung der Fasern bei 35 Prozent oder darunter liegt.
  12. Kombination des Absorbermaterials nach Anspruch 1 und einem in der Impedanz übereinstimmenden Material.
  13. Mikrowellenstrahlenabsorbierende Farbe, folgendes umfassend:
    (a) ein Pigment, welches das Absorbermaterial aus Anspruch 1 aufweist, und
    (b) eine Basisflüssigkeit, in welcher das Pigment gelöst wird.
  14. Farbe nach Anspruch 13, dadurch gekennzeichnet, daß es sich bei der Basisflüssigkeit um eine Mischung aus Butylacetat und Toluol handelt.
  15. Leiter, der mit dem Absorbermaterial aus Anspruch 1 beschichtet ist.
  16. Beschichteter Leiter nach Anspruch 15, dadurch gekennzeichnet, daß das Absorbermaterial und der Leiter in einer geschichteten Lage aneinandergeheftet werden.
  17. Leiter nach Anspruch 16, ferner eine Schicht mit übereinstimmender Impedanz umfassend.
  18. Verfahren zur Herstellung eines Mikrowellenstrahlen-Isolationsmaterials, dadurch gekennzeichnet, daß das Verfahren die folgenden Schritte umfaßt:
    (a) Bildung von nadelförmigen magnetischen Metallfasern mit einer durchschnittlichen Länge von 10 Mikron oder weniger, Durchmessern von 0,1 Mikron oder darüber und mit Längenverhältnissen zwischen 50:1 und 10:1;
    (b) Dispersion der Fasern aus Schritt (a) in einem Dielektrizitätsbinder.
  19. Verfahren nach Anspruch 18, ferner den folgenden Schritt umfassend:
       (c) Lösen des Ergebnisses von Schritt (b) in einer Basisflüssigkeit.
  20. Verfahren nach Anspruch 18, ferner den folgenden Schritt umfassend:
       (c) Auftragen des Ergebnisses von Schritt (b) auf einen Leiter.
  21. Verfahren nach Anspruch 20, dadurch gekennzeichnet, daß der Schritt (d) die Verwendung eines Klebstoffs umfaßt, zur Klebeverbindung des Ergebnisses von Schritt (b) an den Leiter.
  22. Verfahren nach Anspruch 20, dadurch gekennzeichnet, daß der Schritt (d) das Extrudieren des Ergebnisses von Schritt (b) auf den Leiter umfaßt.
  23. Verfahren nach Anspruch 18, ferner den folgenden Schritt umfassend:
       (e) Zufuhr eines in der Impedanz übereinstimmenden Materials zu dem Ergebnis von Schritt (b).
EP19900300632 1989-01-26 1990-01-22 Mikrowellen-Absorbermaterial, das nadelförmige magnetische Metallfasern enthält Expired - Lifetime EP0380267B1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US30242789A 1989-01-26 1989-01-26
US302427 1989-01-26

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EP0380267B1 true EP0380267B1 (de) 1993-10-27

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EP (1) EP0380267B1 (de)
JP (1) JPH02235396A (de)
AU (1) AU615817B2 (de)
CA (1) CA2005198A1 (de)
DE (1) DE69004109T2 (de)

Families Citing this family (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5275880A (en) * 1989-05-17 1994-01-04 Minnesota Mining And Manufacturing Company Microwave absorber for direct surface application
IT1230281B (it) * 1989-06-15 1991-10-18 Sits Soc It Telecom Siemens Procedimento per la realizzazione di assorbitori per campi elettromagnetici.
US4972058A (en) * 1989-12-07 1990-11-20 E. I. Du Pont De Nemours And Company Surface heating food wrap with variable microwave transmission
JPH0935927A (ja) * 1995-07-20 1997-02-07 Tokin Corp 複合磁性体及びそれを用いた電磁干渉抑制体
DE19756620A1 (de) 1997-12-19 1999-06-24 Bosch Gmbh Robert Verfahren zur Herstellung eines Absorbermaterials
ES2274674B1 (es) * 2004-12-24 2008-04-16 Micromag 2000, S.L. Absorbedor de radiacion electromagnetica basado en microhilos magneticos.
DE102007011590B4 (de) * 2007-03-08 2008-12-04 Genesis Adaptive Systeme Deutschland Gmbh Materialverbund für die EMV-Abschirmung
CN105670370B (zh) * 2016-01-04 2017-11-03 北京环境特性研究所 一种毛条型宽频隐身材料
CN110854545B (zh) * 2019-10-29 2021-03-16 南京邮电大学 一种基于水银热胀冷缩调控的频带转移吸波器

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Publication number Priority date Publication date Assignee Title
US4538151A (en) * 1982-03-31 1985-08-27 Nippon Electric Co., Ltd. Electro-magnetic wave absorbing material
US4507224A (en) * 1982-12-03 1985-03-26 Agency Of Industrial Science & Technology Ceramics containing fibers of silicon carbide
JPS61500338A (ja) * 1983-11-07 1986-02-27 ザ　ダウ　ケミカル　カンパニ− 低密度の電磁放射線吸収性組成物
US4606848A (en) * 1984-08-14 1986-08-19 The United States Of America As Represented By The Secretary Of The Army Radar attenuating paint
EP0278458A3 (de) * 1987-02-10 1989-12-06 Buchtal Gesellschaft mit beschränkter Haftung Plattenförmiges, Elektrisch leitendes unglasiertes keramisches Element

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DE69004109D1 (de) 1993-12-02
CA2005198A1 (en) 1990-07-26
JPH02235396A (ja) 1990-09-18
AU615817B2 (en) 1991-10-10
DE69004109T2 (de) 1994-05-11
EP0380267A1 (de) 1990-08-01
AU4708889A (en) 1990-08-02

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