Microwave-induced-acoustic sensing of alcohol in water

The high deviation in the absorption of electromagnetic energy in water and alcohol at lower regions of the microwave frequency spectrum allowed microwave induced pressure fluctuations to be implemented as a means of detecting methanol within water. Spectral thermal measurements across 0.9 GHz to 5 GHz were used to verify the absorption differences, the subsequent data indicating twin maxima in methanol where only a single maxima would be expected due to a single relaxation time. The pressure measurements used moderate power, long duration, sample excitation as an alternative to the high power short duration systems that have been previously described. The technique was successfully implemented using a modified domestic microwave oven and minimal signal processing to obtain a detection accuracy of better than 10% with water/methanol concentrations