Classifications

• • 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

Definitions

• Artificial dielectrics are generally formed by dispersing a magnetic powder or other natural absorber in a dielectric material, such as plastics including thermoplastics and thermosets, ceramics, waxes and the like.
• the artificial dielectrics which have been formed by loading the aforementioned dielectric binders with magnetic metals, semi-conductors, ferromagnetic oxides or ferrites have very desirable magnetic and dielectric properties.
• solid ferrites i.e., ferromagnetic ferrites formed of ferric oxide and other bivalent metal oxides
• ferrites in the form of solid coatings display the higher permeabilities which are required for broad band operation.
• Such solid ferrite coatings are capable of higher permeabilities than those exhibited by the ferrite powders since the magnetic properties of ferrite decline appreciably by grinding it into powder form.
• ELM absorbing compositions of this invention it is advantageous to disperse the ELM absorber into the dielectric matrix such that dielectric matrix forms a continuous phase that maintains the particles of ELM absorber in an essentially discrete, spaced apart relationship.
• Any of a variety of conventional blending procedures for incorporating a colloidal or sub-colloidal particulate into dielectric binders are suitably employed for this purpose.
• the dielectric matrix having the ELM absorber dispersed therein is prepared by initially forming an aqueous dispersion of the ELM absorber by contacting colloidal or sub-colloidal particles of said absorber with an aqueous solution of a water-soluble surfactant or emulsifier, thereby forming the dispersion which contains from about 5 to about 70 weight percent of the absorber particles.
• aqueous dispersions of ELM absorbers are the so-called ferrofluids such as disclosed in the U.S. Patent No. 3,981,844, preferably those having an average particle diameter in the range from about 0.05 to about 0.1 micrometer.
• a water-soluble monomer such as an ethylenically unsaturated carboxylic acid or its salt such as acrylic acid or sodium acrylate; methacrylic acid, itaconic acid and maleic acid; an ethylenically unsaturated carboxamide such as acrylamide; vinyl pyrrolidone; hydroxyalkyl acrylates and meth-acrylates such as hydroxyethyl acrylate, hydroxypropyl acrylate and hydroxyethyl methacrylate; aminoalkyl esters of unsaturated acids such as 2-aminoethyl methacrylate; epoxy functional monomers such as glycidyl methacrylate; sulfoalkyl esters of unsaturated acids such as 2-sulfoethyl methacrylate; ethylenically uns
• a water-soluble monomer such as an ethylenically unsaturated carboxylic acid or its salt such as acrylic acid or sodium acrylate; methacrylic acid,
• Suitable catalysts include inorganic persulfate compounds such as sodium persulfate, potassium persulfate, ammonium persulfate; peroxides such as hydrogen peroxide, t-butyl hydroperoxide, dibenzol peroxide and dilauroyl peroxide; azo catalysts such as azobisisobutyronitrile, and other common free-radical generating compounds.
• peroxides such as hydrogen peroxide, t-butyl hydroperoxide, dibenzol peroxide and dilauroyl peroxide
• azo catalysts such as azobisisobutyronitrile, and other common free-radical generating compounds.
• free-radical generating radiation such as ultraviolet radiation, electron beam radiation and gamma radiation.
• a redox catalyst composition can be employed wherein the polymerization temperature ranges from about 25° to about 80°C.
• the monomer stream consists of 64 g of styrene, 16 g of butyl acrylate and 3 g of t-butyl hydroperoxide.
• the aqueous stream consists of 110 g of deionized water, 2.9 g of the potassium salt of a functionalized oligomer ("Polywet KX-4") and 2 g of sodium formaldehyde hydrosulfite.
• the resulting reaction mixture is stirred and maintained under nitrogen at 90°C for an additional half hour.
• the resulting 25 percent solids latex is concentrated by distillation under vacuum to a 30.3 percent solids latex (dielectric/ELM absorber) having dispersed particles with a polymeric as well as magnetic characteristic.

Landscapes

• Compositions Of Macromolecular Compounds (AREA)
• Paints Or Removers (AREA)
• Absorbent Articles And Supports Therefor (AREA)
• Shielding Devices Or Components To Electric Or Magnetic Fields (AREA)

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Citations (2)

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• 1983
  • 1983-11-07 WO PCT/US1983/001747 patent/WO1985002265A1/en active IP Right Grant
  • 1983-11-07 DE DE8383903870T patent/DE3381770D1/de not_active Expired - Fee Related
  • 1983-11-07 EP EP83903870A patent/EP0161245B1/de not_active Expired - Lifetime
  • 1983-11-07 JP JP59500081A patent/JPS61500338A/ja active Granted
  • 1983-11-07 AU AU23407/84A patent/AU562564B2/en not_active Ceased
• 1985
  • 1985-07-02 DK DK301185A patent/DK301185D0/da not_active Application Discontinuation
  • 1985-07-04 NO NO85852701A patent/NO167170C/no unknown

Patent Citations (2)

Non-Patent Citations (1)

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