Browsing by Subject "Energy Harvesting"

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    Power Management Techniques for Supercapacitor Based IoT Applications
    (2018-01) Hua, Xingyi
    The emerging internet of things (IoT) technology will connect many untethered devices, e.g. sensors, RFIDs and wearable devices, to improve health lifestyle, automotive, smart buildings, etc. This thesis proposes one typical application of IoT: RFID for blood temperature monitoring. Once the blood is donated and sealed in a blood bag, it is required to be stored in a certain temperature range (+2~+6°C for red cell component) before distribution. The proposed RFID tag is intended to be attached to the blood bag and continuously monitor the environmental temperature during transportation and storage. When a reader approaches, the temperature data is read out and the tag is fully recharged wirelessly within 2 minutes. Once the blood is distributed, the tag can be reset and reused again. Such a biomedical application has a strong aversion to toxic chemicals, so a batteryless design is required for the RFID tag. A passive RFID tag, however, cannot meet the longevity requirement for the monitoring system (at least 1 week). The solution of this thesis is using a supercapacitor (supercap) instead of a battery as the power supply, which not only lacks toxic heavy metals, but also has quicker charge time (~1000x over batteries), larger operating temperature range (-40~+65°C), and nearly infinite shelf life. Although nearly perfect for this RFID application, a supercap has its own disadvantages: lower energy density (~30x smaller than batteries) and unstable output voltage. To solve the quick charging and long lasting requirements of the RFID system, and to overcome the intrinsic disadvantages of supercaps, an overall power management solution is proposed in this thesis. A reconfigurable switched-capacitor DC-DC converter is proposed to convert the unstable supercap's voltage (3.5V~0.5V) to a stable 1V output voltage efficiently to power the subsequent circuits. With the help of the 6 conversion ratios (3 step-ups, 3 step-downs), voltage protection techniques, and low power designs, the converter can extract 98% of the stored energy from the supercap, and increase initial energy by 96%. Another switched-inductor buck-boost converter is designed to harvest the ambient RF energy to charge the supercap quickly. Because of the variation of the reader distance and incident wave angle, the input power level also has large fluctuation (5uW~5mW). The harvester handles this large power range by a power estimator enhanced MPPT controller with an adaptive integration capacitor array. Also, the contradiction between low power and high tracking speed is improved by adaptive MPPT frequency.
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    Smart E-Textiles Integrated into Human Health Monitoring Systems
    (2023-06) Carlson, Sam
    E-textiles, broadly defined as any textile that has electronic capabilities, are becoming the future of portable, wearable electronics for human performance and health monitoring. There are many applications of e-textiles in the health monitoring industry, where early detection and prevention of adverse health conditions is at the forefront of concern. To illustrate the potential of e-textile monitoring in health care, two applications of health monitoring were chosen: monitoring respiratory rate and monitoring the dyadic interactions between a parent and their infant, specifically kangaroo care. As one of the primary applications examined, respiratory rate monitoring was chosen due to the documented omission of measurement for this known vital metric, which is key in detecting oncoming health decline. To address the need for better respiratory rate monitoring, an existing e-textile that was designed to monitor respiratory rate was redesigned for improved fit and accuracy. Piezoelectric energy harvesting was explored as a possible power source for using this e-textile as a completely portable device. Not only was developing an e-textile to measuring respiratory rate monitoring explored but integrating other devices into an e-textile system was demonstrated. Monitoring the dyadic interactions between a parent and their newborn infant is a complex procedure involving a variety of devices that must communicate effectively. A system that monitors the interactions between the parent and their infant was presented, and one component of the system was tested for its remote data collection capabilities. By experimenting with these two widely different health monitoring applications, the flexibility of e-textiles in both physicality and applicability was demonstrated. There is great potential for e-textiles to revolutionize health monitoring in healthcare settings and beyond, and more research and device development is required to achieve lasting positive impacts on the healthcare industry.