Shanky Saxena - Design and Development of MEMS based Guided Beam Type Piezoelectric Energy Harvester (Energy Systems in Electrical Engineering)

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In the current race of miniaturization of microelectronic circuits and systems, the power required by these systems particularly by the Wireless Sensor Networks (WSNs) has reduced to a very low level. WSNs consist of many Mobile sensor nodes (MSNs) which are driven by miniaturized lithium-ion batteries that are exhaustible and replacement is not feasible at remote locations. Energy harvesting provides an unending power source that is adequate to power these sensor nodes specifically for remote area applications. Energy harvester can convert freely available ambient energy into electrical energy to provide an endless source of power for MSNs. In Microelectromechanical system (MEMS) based energy harvesters, electrical and mechanical components are integrated into a single device, making them tiny and compact which is suitable for remote area applications. MEMS-based piezoelectric vibration energy harvesters are a preferred choice because of their simplicity in design, operation, and compatibility with fabrication technology. The realization of cantilever-based piezoelectric energy harvesters has always been challenging because great care is required to develop and characterize each unit process leading to the technology development for the fabrication of a specific device.

This monograph is focused on MEMS-based piezoelectric vibration energy harvesters. State of the art technologies have been reviewed to understand the available technologies suitable for vibration energy harvesting. Analytical equations governing the device key parameters have been introduced in the initial portion of the monograph. Simulation steps have been presented using snapshots and results have been depicted by graphs making it easy to comprehend. In the later section of the monograph, a detailed fabrication process on the development of micromachining processes based on both wet and dry etching techniques has been discussed. Elaborate structural, material, morphological, topological, dynamic, and electrical characterization of the device has been presented. In the last section, a real-time practical application is selected, and a piezoelectric energy harvester is designed which is suitable to operate in the desired environment.

My compliments to the authors for putting together this valuable contribution in the form of a monograph which would be of interest and use to graduate students and researchers alike.

The internet of things (IoT) is a network embedded with sensors, software and other technologies that allow to transmit and receive data. Increased use of sensors in IoT imposes a challenge to power these sensors operating at remote locations. The use of Lithium-ion batteries is not sustainable as they are not environment friendly and requires timely replacement. Energy harvesting is a technology that converts freely available ambient energy into electrical energy. Vibration energy harvesting is preferred because vibrations of different amplitude and frequency are freely available in the environment. Piezoelectric type vibration energy harvesters are prominently used due to their simple operation and compatibility with MEMS fabrication technology. Cantilever structure fixed from one end and free from the other are widely used to realize a Piezoelectric vibration energy harvester.

In this monograph, a fixed-fixed or guided beam Piezoelectric Vibration Energy Harvester has been designed, fabricated and tested for low-frequency operation. Device design has been done ensuring low-frequency operation, stable and reliable device operation and higher potential generation. Single beam, Cantilever array and guided beam structures have been designed and investigated using FEM. Fabrication technology is one of the most significant steps in the realization of a device. Guided two-beam and four-beam piezoelectric energy harvester devices have been fabricated. In both of these devices, a combination of wet and dry bulk micromachining techniques has been utilized. Aqueous TMAH etching for wet bulk micromachining, RIE (reactive ion etching) and DRIE (deep reactive ion etching) for dry bulk micromachining processes have been used.