Understanding the Performance of Microwave Hydration Assessment with Layered Planar Models

Microwave hydration monitoring has been tested experimentally in volunteer studies with at least two prototype systems. However, there are differences between the systems both in terms of technical design, but also in the use of either the transmission loss or the time-of-flight differences to estimate the hydration status of the volunteer. In this work, a simplified planar model is used to estimate the best case sensitivity of microwave hydration monitoring to changes in the hydration status. Using this model, a change of 0.5 dB in transmission amplitude and a 0.89 % to 0.99 % change in time-of-arrival is calculated for muscle permittivity changes caused by each 1 % of dehydration, which correlates well with the literature. These results suggest that also simplified, planar models are useful for understanding microwave transmission through the arm.