Ultrasonically modified nonlinear dielectric spectra for liquids

Acoustic waves can modify the dielectric spectra of a material by modulating its complex permittivity. This effect has been widely used in acousto-optic modulation devices to modulate light. Previously, we have shown the possibility for ultrasound to modify microwave electric signals inside a material using nonlinear vector network analyzer measurements. Our experiment consists of a liquid channel above an electric co-planar waveguide. An ultrasonic transducer acoustically excites the liquid, modulating its permittivity. We then measured the nonlinear dielectric spectra of the liquid at the sum and difference of the electric and acoustic frequencies. Using finite element models of the electrical properties of our system, we can de-embed our data and obtain the nonlinear contributions to the permittivity. Here, we present preliminary results for several different liquids, each showing a distinct nonlinear spectrum. Through these measurements, we aim to quantify the electrostrictive properties of fluids and detect intermolecular species and interactions through their nonlinear spectra.