A Non-invasive Wearable Readout System for Bio-fluid Phenomena Detection

This work presents a preliminary evaluation of a complete wearable radiofrequency (RF, 40 MHz bandwidth) readout device for a novel electromagnetic skin patch sensor to monitor health parameters associated with shifts in biofluid volume. The skin patch sensor consists of a continuous trace of copper configured into a square planar spiral surrounded by an embedded coplanar outer loop antenna. When an incident RF wave from the loop antenna impinges upon the planar spiral, the coupled system exhibits a multiband resonant response. The readout system connected to the sensor comprises of an RF signal generator, resistive reflectometer, RF power detector, and a microcontroller unit with an inbuilt 10-bit ADC and a blue-tooth transceiver. During continuous wave sweeping, the recorded response from the sensor was transmitted wirelessly to the host computer for further post-processing and data interpretation. Results: Experimental results demonstrated that the developed prototype could successfully detect resonant frequency of an NFC tag-based fixed resonator and a fluid volume shift of 0 to 600 mL in an in-vitro beaker study using the multiband planar spiral skin patch sensor. The outcomes were further validated against the similar findings from a commercial benchtop vector network analyzer (VNA). Conclusion: This RF readout device provides a wearable alternative to current methods for analyzing the resonant response from the sensor system under different dielectric conditions for biomedical applications including measurement of limb hemodynamics, detect changes in intracranial and ventricular stroke volume, and cardiac function.