High magnetic permeability composites containing fibers with ferrite fill
First Claim
1. A composite material having enhanced magnetic permeability comprising a non-magnetic matrix material and nonconducting fibers dispersed in said matrix material at a volume concentration less than 30% with respect to the matrix material, said fibers having an average aspect ratio of at least 20, said fibers having ferrite particulates therein at a concentration above the percolation threshold of said ferrite material in said fiber, and said fibers having longitudinal axes oriented randomly with respect to one another, so that the magnetic permeability of the composite is approximately proportional to the product of the magnetic permeability of the ferrite and the volume percent of ferrite material in the composite.
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Abstract
High magnetic permeability composites are obtained by incorporating ferrite fibers in the composites. The ferrite fibers consist of a polymer and particulate ferrite fill at a concentration above the percolation threshold for the ferrite fill in the polymer (typically greater than 30 volume percent). The aspect ratio and ferrite concentration of the fibers are selected to minimize demagnetization fields in the fibers. The fibers can be dispersed in low concentration in an unoriented fashion in the composites to impart high magnetic permeability to the composite. In other embodiments, the fibers are oriented in the composites to impart high magnetic permeability to the composite for incident radiation of a particular linear polarization.
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Citations
25 Claims
- 1. A composite material having enhanced magnetic permeability comprising a non-magnetic matrix material and nonconducting fibers dispersed in said matrix material at a volume concentration less than 30% with respect to the matrix material, said fibers having an average aspect ratio of at least 20, said fibers having ferrite particulates therein at a concentration above the percolation threshold of said ferrite material in said fiber, and said fibers having longitudinal axes oriented randomly with respect to one another, so that the magnetic permeability of the composite is approximately proportional to the product of the magnetic permeability of the ferrite and the volume percent of ferrite material in the composite.
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8. A composite material having enhanced magnetic permeability comprising:
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a non-magnetic matrix material; and non-conducting fibers dispersed in said matrix material at a volume concentration below a percolation threshold for said fibers in said matrix, said fibers having an aspect ratio of at least 50 and comprising;
a polymer material and a particulate ferrite, wherein the volume percent of the particulate ferrite in said fiber is above a percolation threshold for said ferrite in said polymer.
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9. A composite material having reduced reflectivity to electromagnetic radiation comprising:
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a low density, low dielectric constant matrix; chopped, ferrite filled fiber dispersed in said matrix, said fiber having a magnetic permeability greater than its dielectric constant; and chopped, non-magnetic, dielectric filled fiber dispersed in said matrix. - View Dependent Claims (10, 11, 12)
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- 13. An absorber for polarized electromagnetic energy in a frequency range from about 10 megahertz to about 10 GHz, said energy being incident on the absorber from free air, said absorber comprising fibers at least a portion of which includes a ferrite, longitudinal axes of said fibers being generally parallel to one another, and wherein said fibers are generally aligned with the magnetic field of said polarized electromagnetic energy and wherein said fibers comprise a polymer and from 20 to 80 volume percent particulate ferrite fill.
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20. An electromagnetic energy absorbing sheet material in which the dielectric constant presented to incident electromagnetic radiation is approximately equal to the magnetic permeability, comprising non-conducting fibers containing ferrite, said ferrite-containing fibers being oriented approximately parallel to one another, and non-conducting fibers containing a dielectric material, said dielectric material containing fibers oriented approximately parallel to one another.
- View Dependent Claims (21, 22, 23, 24, 25)
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24. The material of claim 22 wherein the dielectric fibers comprise a polymer and a particulate dielectric fill comprising from 20 to 70 percent by volume of the fiber.
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25. The material of claim 24 wherein the dielectric fill is a ferroelectric material such as lead-zirconium titanate (PZT), PbZrTiO4.
Specification