Broadband RF impedance spectroscopy in micromachined microfluidic channels

Impedance spectroscopy in the radio frequency range from 100 MHz to 20 GHz can reveal the dielectric relaxations of biological and chemical solutions. S-parameters for a coplanar waveguide are derived. To perform these measurements, a coplanar waveguide device was fabricated on a conventional FR-4 substrate for fluid interrogation. The microfluidic channel was formed by milling conventional waveguides and laser-cutting channels in the dielectric substrate. Measurements using this device were performed on standards: deionized water, isopropyl alcohol, and air. These measurements were compared to those taken with a conventional dielectric probe. The results demonstrate the ability of the fabricated device to extract varying transmission parameters due to changing sample properties.