Non-Intrusive, Wearable Sensor-Circuits for Electroencephalography and Electrocardiography Monitoring

Abstract

Wearable devices for physiological signal monitoring have attracted significant interest due to their applications in mobile health monitoring. However, many existing wearable systems remain rigid, bulky, intrusive, and susceptible to motion artifacts, and may cause skin irritation during long-term use, limiting their practical adoption. To address these challenges, this dissertation presents the development of non-intrusive, wireless sensor–circuit platforms for electrocardiogram (ECG) and electroencephalography (EEG) monitoring, jointly establishing a unified path towards the next generation of wearable devices. For ECG monitoring, a highly stretchable wireless sensor-circuit device was developed, consisting of a sensor patch and a circuit patch. The circuit patch exhibits a Young’s modulus of 0.83 MPa, comparable to that of human skin, and is capable of reliable operation under tensile strains of up to 100 % through the integration of electrical metamaterial-based interconnects (EMIs). The EMIs are realized using polymer-embedded three-dimensional helical microchannels filled with liquid metal. An ultra-soft and stretchable sensor patch based on a carbon nanotube (CNT)–polydimethylsiloxane (PDMS) and silicone oil (SO) nanocomposite was also developed and connected to the circuit patch with magnets. Using a custom wireless platform, recorded signals are transmitted to a portable device, enabling stable, wireless ECG monitoring during physical activities with minimal motion artifacts. Compared to ECG monitoring on the chest, EEG monitoring presents greater challenges due to the requirement for reliable electrical contact on the hairy scalp, necessitating a distinct sensor–circuit architecture. Accordingly, this dissertation presents the first EEG sensor–circuit device enabling non-intrusive, wireless EEG recording. The EEG sensor incorporates miniaturized stemmed micro-suction cup structures and is composed of a CNT–PDMS–SO nanocomposite with a thin silver-plated surface layer, fabricated using a novel, scalable, and cost-effective method. Gentle pressing the sensor against the scalp generates negative pressure within conical cavity arrays, enabling secure adhesion. With a trace amount of conductive gel, the sensor achieves stable electrical contact comparable to gold-standard Ag/AgCl wet gel electrodes. Custom-built amplifier and Bluetooth transmission printed circuit boards with a radio footprint of 4 mm were integrated with the sensors, enabling fully wearable and visually imperceptible EEG monitoring during daily activities.