Broadband Electrical Determination of Liquid Mixing Ratios for Microfluidics

The paper shows a microwave method to determine mixing ratio of fluids in a microfluidic channel. The method uses modified Bruggeman formula that is fitted over a broad range of frequencies. The extraction of mixing ratio is based solely on the measurement results without any reference to EM simulation, which alleviates the requirements for chip fabrication accuracy. The procedure was tested with three lengths of microfluidic channels over CPW lines, and the mixing error was determined to be less than 5% error for at least 1.5 GHz frequency range. For some frequencies the maximum error drops to below 3%.