Characterization of an RF resonator to measure fluid volume for biomedical applications

Abstract

Wearable technologies have gained a huge interest in recent years due its advantages in the early diagnosis of medical conditions such as heart attack and monitoring intercranial pressure. Additionally, wearable technologies are an attractive solution in the medical field due to wearable form factor and minimal required training for uses. As such, in this study we are investigating a wearable RF skin patch resonator for the measurement of fluid volume changes. Specifically, this study aims to characterize the sensitivity, dynamic range, and repeatability of the sensor response to changes in fluid volume. The wearable skin patch sensor is an open circuit resonator that is energized wirelessly via an external antenna placed within closed proximity. Once the resonator is energized via the external antenna, it develops its own electromagnetic field and measure the changes in fluid volume nearby. For this study, we used a vector network analyzer for the purpose of energizing the wearable sensor and collecting the $S_{11}$ return loss. From the VNA, we measure the resonance frequency shift in terms of frequency in MHz and amplitude in dB. In this study, the characterizations of the skin patch sensitivity and dynamic range were performed by dynamically increasing the fluid $(H_{2}0)$ volume inside a chamber and collecting the sensor response. The result of this study illustrates that the larger square planner resonators has higher dynamic range than the others sensor designs such as triangle, circle, and pentagon while measuring fluid volume changes up to 540 mL. Furthermore, the sensitivity of large square skin patch resonator was greater than 0.75 mL. In this study, we are able to characterize the sensitivity and dynamic range of the wearable skin patch sensor which will lead into future advancement and development.