A noninvasive, electromagnetic, epidermal sensing system for biofluid phenomena detection
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Health-care technologies for non-invasive monitoring of vital parameters like blood pressure and heart rate are widely used due to their capability to function as a point-of-care device. However, most of these devices are limited to using either optical based sensing methods, which are vulnerable to environmental optical interference and possess a limited penetration depth, or galvanic electrode transducers, which require multiple conducting nodes connected to the skin as well as prone to muscle action potential. In addition, most of these sensing systems are realized on hard electronics which lack epidermal conformance. These limitations highlight the need for developing minimally obtrusive, non-invasive, conformal diagnostic clinical devices for extracting vital signs as well as non-super cial limb hemodynamics. Technologies based on electromagnetic sensing using exible radio frequency (RF) resonators are well poised to address this need. Electromagnetic sensors can be leveraged to detect volumetric changes in layered material as changes in the re ection coe cient since dielectric variation in the near- eld electromagnetic boundary. The focus of this study was to develop a minimally obtrusive electromagnetic sensing system to non-invasively detect pulsatile blood ow from the radial artery through conformal and functional biointerface. For that purpose, a exible RF resonator with two di erent readout architectures have been developed. The sensing architectures integrate a novel RF skin patch resonator embedded with a coplanar outer loop antenna and a compact, standalone wireless readout hardware based on standing wave ratio (SWR) bridge, and directional coupler with RF gain and phase detector. The resonator itself is a copper-based open circuit planar Archimedean spiral with a rectangular cross-sectional area, chemically etched on a exible polyimide substrate. The readout hardware is developed exploiting o -the-shelf components, fabricated on the top of a rigid FR4 substrate. Under external RF stimulus, the resonator electromagnetically couples to the surrounding dielectric medium. Any change in the dielectric properties results in perturbation to this near eld coupling. This e ect can be measured through tracking the changes in re ected power and complex S11 modulation (amplitude and phase) from the resonator using the proposed hardwares. By leveraging this working principle and the dielectric characteristics of biological tissues, the experimental results from in-vitro benchtop models and human trials con rmed the ability of the sensing systems as the potential noninvasive blood ow and limb hemodynamics detector. Hence, the systems could be the alternative to the conventional, non-invasive wearable sensing with an unprecedented capability of multimodal bio uid phenomena detection within a single sensing platform.
Thesis (M.S.)-- Wichita State University, College of Engineering, Dept. of Biomedical Engineering