Measurements of nonlinear electric–acoustic interactions in liquids

Electric and acoustic waves can interact nonlinearly inside a fluid medium. These interactions can create a heterodyned signal consisting of both sum and difference frequency products of the electric and acoustic frequencies. Here, we present direct measurements of nonlinear mixing products produced by interacting electric and acoustic waves inside of various fluids. The experiment consisted of a fluid channel that was in direct contact with an electrically conductive co-planar wave guide (CPW). An acoustic signal was applied to the channel via a transducer mounted above it, and simultaneously an electric signal was applied along the CPW from a vector network analyzer (VNA). The resulting signal was then measured with VNA set to frequency offset mode to capture the sum electric-acoustic mixing product. Results are presented for various organic solvents and salt solutions, each showing a different characteristic nonlinear response. This metrology allows for direct probing of non-linear effects in electrici–acoustic systems and could lead to the development of new spectroscopic methods for characterizing chemicals and solutions.