Wireless Power Transfer for Low Power Medical Sensors

Abstract

Internet of Things (IoT) encloses the utilization of sensors, actuators and data communication technologies embedded into physical devices enabling them to be tracked, coordinated or controlled over the Internet. Medical IoT refers to the vision where several wearables, sensors and actuators are scattered inside medical facilities and can interact with every other object, system or person over the cloud. This interactive network of things targeted for medical applications, is expected to generate market opportunities for patients and businesses by offering real time patient data and remote patient monitoring. The integration of this technology depends on autonomous operation of the modules and sustainable powering of these devices which has proven to be one of its most challenging aspects.
Harvesting energy from renewable sources such as wind and solar, besides vibration and heat have been examined closely by research community over the past years. However, the limitations of these sources inside buildings, where solar and wind energy are not always sufficient, shifted the scientific and commercial focus to Wireless Power Transmission. This technology, despite its challenging nature, is becoming very popular because it overcomes the lack of different power sources inside buildings and provides user friendly powering method for battery-less sensor modules.
This thesis aims to investigate various antenna-rectifier topologies, also known as rectennas, and analyze the challenges that arise when harvesting low levels of radio frequency (RF) power. The initial part of this project focuses on the components that constitute a basic RF energy harvester. A system like this consists of an antenna which captures a fraction of the transmitted signal, attached to a rectifier which converts the RF signal into DC power. The development of analytical models and conducted lab measurements will identify the behavior of the rectifying circuit. In order to maximize the power transferred between the antenna and the rectifier, a matching infrastructure is necessary. Harvesting topologies with commercially available components and a matching network will be designed and manufactured along with custom antenna designs that match directly the input impedance of the rectifier. These novice antenna configurations decrease the size and cost of the system as well as improve the power conversion efficiency. Additionally, a power management integrated circuit will be introduced right after the rectifier to buffer the harvested DC power and provide protection for the sensor. Finally, this thesis culminates with a detailed presentation of the conducted total system experiments and future research possibilities.