High sensitivity microwave characterization of organic molecule solutions of nanoliter volume

A microwave resonator composed of a sapphire cylinder and a quartz plate with a 400 nl cavity was developed for the determination of the complex permittivity of liquids at 10 GHz. This sensor was calibrated over a wide range of values for real and imaginary parts of permittivity. The measured resonator losses induced by the liquid were found to be proportional to the dipole relaxation time of the liquid molecules, as predicted by perturbation theory. Our analysis of weight concentration and temperature dependence of the measured inverse quality factor revealed a sensitivity of about 0.1% for aqueous solutions of glucose.