Oral: Measuring nonlinear mixing of microwaves and ultrasound in liquids

Acoustic waves modulate the permittivity and conductivity of a medium and therefore modulate electric waves also present in that medium. This modulation can be detected by the nonlinear mixing products produced at the sum and difference frequencies of the electric and acoustic waves. Here, we present a method of measuring these mixing products directly using a vector network analyzer at microwave electric and ultrasonic acoustic frequencies. Our experiment used a fluid channel in direct contact with an electric coplanar wave guide. We introduced acoustic waves from above with an ultrasonic transducer and applied an electrical signal to the coplanar waveguide. We then measured the acoustically modified electric signal with a vector network analyzer set to frequency offset mode to isolate the mixing products of the electric and acoustic waves. The results we present are for various organic solvents, each showing a different nonlinear response. This metrology allows for simultaneous measurement of acoustic stimulus to electric response and could be developed into a new spectroscopic method for characterizing chemicals and solutions.