Stainless steel fiber ͑SSF͒/poly͑vinylidene fluoride͒ composite is prepared via simple blending and hot pressing route. The dependence of the dielectric properties of the composite on both volume fraction of the fillers and frequency is investigated. The percolation threshold of the composite, 9.4 vol % ͑0.094 volume fraction͒, is much lower than that of the common two phase metal particle-polymer composite. A dielectric constant of 427 is observed at 50 Hz with 10 vol % of SSF. Large enhancements of the ac conductivity and loss tangent are also observed near the percolation threshold. The dielectric properties are explained by percolation theory while the dielectric anomalies are attributed to the high slenderness ratio of the SSF fillers.

Through the use of polyethylenes with different crystallinities as matrices, the effects of the matrix crystallinity on the percolation threshold and dielectric behavior of percolative composites have been investigated. The results suggest that the percolation threshold is negatively related to the matrix crystallinity, whereas the enhancement of the dielectric constant is positively related to the matrix crystallinity. A two-dimensional diagram is proposed to illustrate such relationships. In addition, it has been found that the insulator-conductor transition is much flatter in low-crystallinity-matrix-based composites, and this may be favorable for preparing threshold composites with a high dielectric constant and a low loss tangent.