Reflection and Transmission Characteristics of Granular Composite Materials Containing Flake-Shaped Metal Particle

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.