GODA Kazuya

The reflection and transmission characteristics of granular composite materials containing Cu or Ag-coated Cu flake-shaped particles were investigated by measurement in free space and by calculation based on transmission line theory. The negative permittivity spectra, which characterized the permittivity properties of metals, were observed in the Cu and Ag-coated Cu flake composites with particle contents above the percolation threshold Φc. For the Cu and Ag-coated Cu flake composites below Φc. the measured absolute values of the reflection coefficient |Γ| and the transmission coefficient ITI increased and decreased with increasing frequency, respectively. The Ag-coated Cu flake composite aboveりcexhibited metallic reflection and transmission characteristics with |Γ| > 0.9 and ITI < 0.1; these characteristics of the Ag-coated Cu flake composite agreed with the calculated results based on transmission line theory. Meanwhile, the measured values of |Γ| and ITI for the Cu flake composites above Φc tended to deviate from the theoretical values due to changes in electrical conductivity.

We evaluated the reflection and transmission characteristics in the microwave region of metal granular composite materials containing flaky Cu particles, flaky Ag-coated Cu particles, and acicular FeCo nanoparticles as anisotropic shape particles. In the flaky Cu particle composite and the flaky Ag-coated Cu particle composite, a significant jump of the ac conductivity σ with the particle content was observed at the percolation threshold φc at 4 and 3 vol.%, respectively; the σ of composites with particle content above φc showed a value above 10-1 S/cm. The 6 vol.% flaky Ag-coated Cu particle composite exhibited metallic reflection and transmission properties. On the other hand, the 6 vol.% flaky Cu particle composite showed a tendency for the transmission coefficient to decrease and the reflection coefficient to increase with increasing frequency. For the acicular FeCo nanoparticle composites, the electrical conductivity was low and the permeability was not affected by eddy currents even in the GHz range. The 49.9 vol.% acicular FeCo nanoparticle composite exhibited the frequency dispersion of permeability by magnetic resonance at several GHz, and the 10 vol.% composite showed slight absorption above 10 GHz.