Over the past decade, wearables have become pervasive in our lives. Healthcare wearables like a smartwatch continuously monitor personal health status and provide personalized feedback to motivate progress towards medically recommended goals. While present set of on-body electronics empowers users to visualize health status outside of clinic spaces, its traditionally rigid and bulky form factor limit comfortable wear time particularly during exercise or sleep. The mechanical mismatch between the device and the skin concentrates stress at the wear location and generates feelings of discomfort. Miniaturized and soft sensors that conform with human skin will minimize this mechanical mismatch and enable more intimate and comfortable device-skin interface. My thesis presents new skin-interfaced devices for personal dosimetry and photoplethysmogram (PPG) fabricated in mm-scale and flexible form factors. Battery is generally the bottleneck for further reduction of bulk and weight in developing portable electronics. This work focuses on investigating low-power optoelectronic approaches for continuous and wireless sensing using off-the-shelf photodiodes, supercapacitors, and RF-harvesting antennas. The results report the development and field test of a battery-free UV dosimeter as small as 8mm in diameter and weighing ~55mg. In addition, I demonstrate an LED-less and flexible PPG sensor designed to utilize ambient lights, from the sun or indoor lighting, as a passive illumination source for detection of heart rate. The average power consumption of an LED-less PPG is as low as <500 mW, and when it is integrated with a small battery (Ø 9.5mm) of capacity 11mAh it can offer continuous operation up to 3 days. Investigations in flexible and miniaturized, low-power wearables ultimately aim to increase societal participation in effortless and long-term monitoring of health status like UV exposures and heart rate.

Creator

• Heo, Seung Yun

DOI

• https://doi.org/10.21985/n2-5jre-dc70

Subject

• Biomedical engineering
• Engineering

Language

• en

Alternate Identifier

• etdadmin_upload_858088
• http://dissertations.umi.com/northwestern:15834

Date created

• 2021-01-01

Resource type

• Dissertation

Rights statement

• In Copyright