Date of Award

8-2022

Degree Name

Doctor of Philosophy

Department

Electrical and Computer Engineering

First Advisor

Massood Z. Atashbar, Ph.D.

Second Advisor

Bradley J. Bazuin, Ph.D.

Third Advisor

Paul D. Fleming, Ph.D.

Fourth Advisor

Binu B. Narakathu, Ph.D.

Keywords

Fabric-based sensors, flexible hybrid electronics, highly sensitive sensors, remote health monitoring, smart sensors and structures, wearable electronics

Abstract

Wearable sensing technology has recently received an increased attention in both research and commercialization phases and has moved from a vision of science fiction to reality with a wide variety of applications. This incredible growth can be attributed to several factors, such as affordability and ergonomics provided by advances in flexible electronics. The other factors that realized wearable sensing technology include a critical need for more accessible health care services experienced during the recent COVID pandemic, integration to the Internet of Things (IoT), and a growing consumer desire for health awareness. This dissertation presents the fulfillment of three main projects and focuses on the development of various sensors on flexible platforms such as fabrics and plastics using Flexible Hybrid Electronics (FHE) technology to facilitate healthcare monitoring.

In the first project, highly sensitive fabric-based pressure sensors were developed for detecting and decreasing sport-related head injuries. Many athletes, from football players to equestrians, rely on helmets (headgear) to protect their heads from impacts or falls. However, a loose or improperly fitted helmet could leave them vulnerable to traumatic brain injuries (TBIs), a leading cause of death or disability in the U.S. To monitor the helmet fit, a highly sensitive pressure sensor cap has been developed that can map pressure in real-time. When worn under a helmet, the cap could help reveal whether the helmet is a perfect fit. These pressure sensors rely on a capacitive mechanism and were fabricated by placing a novel porous polydimethylsiloxane (PDMS) layer between two fabric electrodes. The porous PDMS dielectric layer was fabricated by introducing nitric acid (HNO3) into a mixture of PDMS and sodium bicarbonate (NaHCO3, known as baking soda) to facilitate the liberation of carbon dioxide (CO2) gas, which induces the creation of porous microstructures within the PDMS dielectric layer. This porous PDMS material experiences large deformation, when compared to a solid PDMS layer, and thus increases the capacitance change, making the pressure sensors highly sensitive.

In the second project, a flexible wireless electrocardiogram (ECG) device was developed on a fabric platform for electrocardiographic examinations without the use of skin treatments or adhesive gels. In practice, this ECG device facilitates more frequent “at-home” screening of patients who are at risk of cardiovascular disease. The developed device consists of dry electrodes that were fabricated by printing a conductive carbon-PDMS composite on stretchable thermoplastic polyurethane (TPU) laminated on fabric and a flexible readout module that can be directly integrated into clothing. Even though dry electrodes do not use adhesive gel, they perform very similar to conventional wet electrodes and even better in terms of signal to noise ratio. Therefore, they are easier to apply and can potentially replace the wet electrodes.

In the third project, a flexible tunable and compact microstrip antenna with a conformal structure was developed for wearable applications. The antenna was fabricated by sandwiching a flexible polyimide substrate between two flexible copper tapes, forming the radiating patch and ground plane. Laser machining was introduced as a facile and fast method for the antenna fabrication. To meet the crucial need of miniaturization of devices in wearables, the antenna was compacted from 2.4 GHz to 900 MHz frequency, without increasing the size of the antenna. Mechanical characterization of the flexible antenna demonstrated the feasibility of the fabricated antenna to sense various bending and stretching stresses.

Access Setting

Dissertation-Open Access

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