Nondestructive In-situ Permittivity Measurement of Liquid Within a Bottle Using an Open-Ended Microwave Waveguide

This research demonstrates an effective in-situ testing approach to measure permittivity of liquid samples within a container using microwaves. An open-ended waveguide is employed as a sensor in the experiment. This apparatus is easy-to-use because it does not require special calibration and is not limited by sample shape or dimensions. After positioning the bottle inside the open-ended waveguide and adding a layer of surrounding medium that fills the space between waveguide and the bottle, the waveguide functions as a resonant cavity. By analyzing the S-11 amplitude waveform over the frequency range from 250 to 550 MHz, the resonant frequencies can be obtained for a certain propagating mode. The measured values are found to match the theoretical ones extremely well; this result implies that the new establishment is highly precise and sensitive.