Measurement of the microwave absorption for small samples in a coaxial line

Microwave absorption measurements in terms of power loss per unit volume of very small liquid and solid samples (0.003-2.6 μL) contained in capillaries inserted across the dielectric of a coaxial line have been made between 2 and 26.5 GHz. This perturbation technique makes it possible to measure small differences in the absorption of the samples in a swept fashion. The measured value of the microwave absorption of heavy and light water is within 10% of the value calculated from published values of the dielectric constant at all frequencies up to the highest frequency measured and within 5% at frequencies (<20 GHz) where the effects of the impedence mismatch caused by the sample are minimal. The measured differences in the Debye relaxation times of light and heavy water agrees with published values to even better accuracies owing to the similarities in the dielectric constants and thus similarities in the mismatch in the coax caused by the sample