Microscopic lipid tubules with an average aspect ratio (length/diameter) of approximately 12 were metallized electrolessly with copper or nickel-over-copper, and mixed with vinyl to make foot-square composite dielectric panels. As loadings increased the metal tubule composites displayed an onset of electrical percolation with accompanying sharp increases in real and imaginary permittivities. Gravity-induced settling of the tubules while the vinyl was drying increased true loading density at percolation threshold for nickel/copper tubules to ∼12 vol %. This threshold was at a significantly lower loading density than that previously measured for percolation by composites containing spherical conducting particles. Qualitatively, the shape of the composite permittivity versus loading density curves followed predictions by the effective-mean field theory for conducting stick composites. Changes in permittivity of the vinyl panels were observed for several days after fabrication, and were apparently associated with solvent evaporation from the matrix.

Measurements have been made of the dielectric response of distributions of metallized fibers aligned in epoxy matrices for different loading fractions and fiber lengths. These have been shown to be in reasonable agreement with a simple independent particle theory. Use of the theory allows classification of fiber dielectric behavior by fiber conductivity and a characteristic length. Some aggregation of the fibers has been observed, even at relatively low loading densities. Computer simulation suggests enhanced dielectric constants of the composites for a moderate range of separations where the fibers are offset about 75% of their lengths with respect to each other and are closer than about 10 radii. This effect may be significant for aligned fibers which tend to aggregate in the magnetic field with separations and offsets within this range. The resulting composites are rugged and easily machined, and with less than 5% fiber weight loading have large, highly anisotropic dielectric constants of 60 or more at microwave frequencies in the X band. In conjunction with their (predicted) broadband performance characteristics such media should prove useful for a variety of applications.

Composites have been formed of Cycom, nickel-coated graphite fibers, aligned at concentrations of up to 6 weight percent in polymer matrices. Dielectric constants up to approximately 70 have been measured for these samples at x band frequencies. The results have been compared with a single non-interacting particle theory.

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