The evolution of wireless sensor networks (WSNs) underpins the Internet of Things (IoT). The potential of such a wirelessly connected world spans a wide range of applications, including transportation, home automation, healthcare, smart environments, and many more. Although the performance of WSNs is both pervasive and self-organizing, the widespread deployment of sensor nodes for wireless communication is restricted by the lack of alternative energy sources to power the continuous operation of the sensor nodes. The need to replace and recharge batteries is the greatest weakness of WSNs and requires extensive system maintenance. Electromagnetic energy harvesting based on Faraday's law of induction is a smart method of generating electrical energy from the mechanical energy of ambient vibration sources. Macro/mesoscale techniques have emerged over the years and offer attractive solutions to the hazards of batteries. However, there remain major challenges that restrict the implementation of these harvester systems at the micro-scale, including low transduction, limited operational bandwidth, and inefficient power conversion.
The primary objective of this project is to develop a new class of highly efficient, miniaturized, integrated, wideband micro-power energy harvesters fabricated using CMOS processing technology. Novel device concepts and innovative material advancements will be explored to overcome the fundamental limitations of harvester performance under realistic operating conditions. The work focuses on enabling self-powered, sensor-driven health and environment monitoring applications that will lead to an "Ambient Assisted Living" scenario. Therefore, the expected outcomes are to contribute to advancing the state-of-the-art in the areas of materials integration, microelectromechanical systems, and power management electronics which underpin the future growth of the overall ICT sector.
An advanced two-stage tuning approach has been proposed to enable reliable and efficient microgenerators in scavenging energy from low-frequency vibrations. Based on the thoroughly analyzed performance, the proposed approach shows potential advantages over the conventional methods to overcome fundamental limitations of MEMS energy harvesting from ambient vibrations. Employing the two-stage tuning transducers into electromagnetic energy harvesters is capable of maintaining a large tuning range with high reliability, and then making the microgenerators more efficient in scavenging kinetic energy from low-frequency vibrations. To validate the innovative proof-of-concept, a MEMS prototype was designed and fabricated by SOI-MUMPS processing with a device layer thickness of 25 µm and an active dimension of 4 mm x 5 mm. This standard microfabrication process is compatible with CMOS technology in integrating the ASIC power management unit into the energy harvesting system. Experimental measurement of the device has been conducted to verify the performance of the two-stage tuning mechanism in comparison with the analytical results.
Internet of Things (IoT) is regarded among the fastest growing technological platforms in the coming decades. These advanced systems enable intelligent decision-making for a smart environment around human beings. However, the technological limitations of batteries for powering IoT have led to research into harvesting alternative ambient energy sources, such as mechanical vibrations due to its widespread abundance in nature. Lately, Mechanical Energy Harvesting (MEH) devices have stimulated a lot of research efforts, however, without any major breakthrough in the outcome due to unfavorable scaling effects in the power-density. In this project, we aim to challenge the fundamental limitations of highly miniaturized MEH devices. We propose a solution that involves significant innovation in device physics, engineering of proficient device designs, next-generation material development for ultra-sophisticated microfabrication, and circuit design. Towards achieving the goal of delivering a realistic solution for powering IoT-based applications, we focus on addressing four critical challenges as follows. (i) Developing highly anisotropic, nano-structured, micro-patterns of exchange-coupled permanent magnets with high energy product. (ii) Significant increase in the electromagnetic (EM) coupling in a novel MEMS topology-critical to high-performance MEMS EM-MEH devices. (iii) Optimized design of MEMS device incorporating nonlinear oscillation to simultaneously increase the overall power-density and the operational bandwidth, for efficient operation under low-amplitude external vibrations. (iv) Development of high-efficiency power management IC, including an integrated energy storage unit, which is designed for low-voltage sources to overcome the essential impediments in EM transduction at the micro-scale.