An RF/microwave microfluidic sensor for miniaturized dielectric spectroscopy based on sensor transmission characteristics

This paper reports an RF/microwave microfluidic sensor for miniaturized dielectric spectroscopy. The sensor is designed to interface with CMOS-integrated electronics that provides the sensor with an excitation signal at RF/microwave frequencies and simultaneously measures its transmission characteristics in the voltage domain to extract the complex dielectric permittivity, ε_r, of the material-under-test (MUT). The sensor is based on a three-dimensional (3D), parallel-plate, capacitive structure with a floating electrode that is integrated into a microfluidic channel with 9μL-sample volume. Requiring only an S₂₁ measurement, dielectric readings by the sensor in a frequency range of 14MHz to 6.5GHz show an excellent agreement with bulk-solution reference measurements conducted with an Agilent 85070E dielectric probe. Using mixtures of 2.5% ethanol in de-ionized (DI) water and 10% isopropyl alcohol (IPA) in DI water as two different MUTs, the rms error is <; 0.5% for both the real and imaginary parts of permittivity over the full frequency range after a 7-point sensor calibration procedure.