Interactions of Electromagnetic Radiation with Electrolytes at High to Ultra-High Frequencies

Abstract

At frequencies above one megahertz, the behaviour of electrolytic solutions changes from an ionic conductor to a lossy dielectric. High frequency conductance measurements of aqueous electrolytes (Na₂SO₄ and KCl) have been made by continuous wave and pulse admittance methods, in cells with immersed, shiny Pt electrodes to study this transition. Peak conductance frequencies as a function of concentration did not conform to the classical circuit representation of a resistance and capacitance. Measured phase angles indicate that relatively concentrated electrolytes (0.001 ? 1 M) exhibit inductance due to electromagnetic and perhaps mass (inertial) effects. Modelling was possible with a constant value of the inductance, L, and capacitance, C, using a simple RLC equivalent circuit. Ion and solvent perturbations in high frequency electrical fields first are discussed in terms of a damped harmonic oscillator model, whose macroscopic response is self-consistent and equivalent mathematically to RLC network. However, it is improbable that mass effects are sufficiently large to explain the majority of the inductance, which arises primarily from the transmission of energy through the solution. Obviously, the skin effects found in electrolytes will be distinct from those for metallic conductors.