Measurement of the dielectric constants of metallic nanoparticles embedded in a paraffin rod at microwave frequencies

A cylindrical rod composed of a uniform mixture of metallic nanoparticles and alumina powder dissolved in paraffin was inserted in the center of a cylindrical microwave cavity. The real and imaginary parts of the complex dielectric constant of metallic nanoparticles at various microwave frequencies of the TM₀₁₀ mode can be determined from the resonant frequency and quality factor, respectively, of the transmission resonance spectrum. This method involves the protection of the sample from adsorbed moisture and prevents the rod from filling with air, thus making the experimental values more accurately and stably determined than they are by the dielectric double-cavity method. The real parts of the dielectric constants of metallic nanoparticles are negative and their magnitudes decrease as the particle size decreases. This finding is consistent with theory, which states that conduction becomes weaker as the particle size is reduced.