@article{ruiz_ridder_fan_gong_li_mills_cobarrubias_strohmaier_jur_lach_2021, title={Self-Powered Cardiac Monitoring: Maintaining Vigilance With Multi-Modal Harvesting and E-Textiles}, volume={21}, ISSN={["1558-1748"]}, DOI={10.1109/JSEN.2020.3017706}, abstractNote={Remote patient monitoring has emerged from the intersection of engineering and medicine. Advances in sensors, circuits and systems have made possible the implementation of small, wearable devices capable of collecting and streaming data for long periods of time to help physicians track diseases and detect conditions in a non-intrusive manner. Cardiac monitoring comprises many of these applications, with the need to capture transient cardiac events motivating the adoption of wearable monitors in standard clinical practice. However, user burden and battery life limit the duration of monitoring or require heavy duty cycling, thus preventing the adoption of these technologies for use cases that require long-term vigilant monitoring, in which the sensor system cannot miss a critical cardiac event. To overcome these challenges, this paper introduces a self-powered system for uninterrupted vigilant cardiac and activity monitoring that senses and streams electrocardiogram (ECG) and motion data continuously to a smartphone while consuming only $683~\mu \text{W}$ on average. To achieve self-powered operation under environmental and wearability constraints, the system incorporates an energy combining technique to support multi-modal energy harvesting from indoor solar and thermoelectric energy. A custom ECG shirt made of a knitted compression fabric with embedded dry electrodes addresses issues of user comfort, skin irritation and motion artifacts. Vigilant Atrial Fibrillation (AF) monitoring is used as an example case study, analyzing sampling frequency and bit-depth quantization and their correlation to vigilant, self-powered operation. The integrated system demonstrates an important step forward for remote patient monitoring beyond the clinic.}, number={2}, journal={IEEE SENSORS JOURNAL}, author={Ruiz, Luis Javier Lopez and Ridder, Matthew and Fan, Dawei and Gong, Jiaqi and Li, Braden Max and Mills, Amanda C. and Cobarrubias, Elizabeth and Strohmaier, Jason and Jur, Jesse S. and Lach, John}, year={2021}, month={Jan}, pages={2263–2276} }
 @article{dieffenderfer_goodell_mills_mcknight_yao_lin_beppler_bent_lee_misra_et al._2016, title={Low-Power Wearable Systems for Continuous Monitoring of Environment and Health for Chronic Respiratory Disease}, volume={20}, ISSN={2168-2194 2168-2208}, url={http://dx.doi.org/10.1109/JBHI.2016.2573286}, DOI={10.1109/jbhi.2016.2573286}, abstractNote={We present our efforts toward enabling a wearable sensor system that allows for the correlation of individual environmental exposures with physiologic and subsequent adverse health responses. This system will permit a better understanding of the impact of increased ozone levels and other pollutants on chronic asthma conditions. We discuss the inefficiency of existing commercial off-the-shelf components to achieve continuous monitoring and our system-level and nano-enabled efforts toward improving the wearability and power consumption. Our system consists of a wristband, a chest patch, and a handheld spirometer. We describe our preliminary efforts to achieve a submilliwatt system ultimately powered by the energy harvested from thermal radiation and motion of the body with the primary contributions being an ultralow-power ozone sensor, an volatile organic compounds sensor, spirometer, and the integration of these and other sensors in a multimodal sensing platform. The measured environmental parameters include ambient ozone concentration, temperature, and relative humidity. Our array of sensors also assesses heart rate via photoplethysmography and electrocardiography, respiratory rate via photoplethysmography, skin impedance, three-axis acceleration, wheezing via a microphone, and expiratory airflow. The sensors on the wristband, chest patch, and spirometer consume 0.83, 0.96, and 0.01 mW, respectively. The data from each sensor are continually streamed to a peripheral data aggregation device and are subsequently transferred to a dedicated server for cloud storage. Future work includes reducing the power consumption of the system-on-chip including radio to reduce the entirety of each described system in the submilliwatt range.}, number={5}, journal={IEEE Journal of Biomedical and Health Informatics}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Dieffenderfer, James and Goodell, Henry and Mills, Steven and McKnight, Michael and Yao, Shanshan and Lin, Feiyan and Beppler, Eric and Bent, Brinnae and Lee, Bongmook and Misra, Veena and et al.}, year={2016}, month={Sep}, pages={1251–1264} }