The process of acquiring the energy surrounding an energy system and converting it into usable electrical energy, i.e., power harvesting or scavenging,1 has seen a surge of interest in the last few years. This increase in research has been fostered by modern advances in wireless technology and low-power electronics, such as micro-electro-mechanical systems (MEMS). The advances have allowed numerous doors to open for power-harvesting systems in practical real world applications. The use of piezoelectric materials to capitalize on the ambient vibrations surrounding a system is one method that has seen a dramatic rise in use for power harvesting. Piezoelectric materials have a crystalline structure that provides them with the ability to transform mechanical strain energy into electrical charge and, conversely, convert an applied electrical potential into mechanical strain. This property allows these materials to absorb mechanical energy from their surroundings (usually ambient vibration) and transform it into electrical energy that can be used to power other devices. Vibration-based piezoelectricity is an attractive avenue for energy harvesting due to its robustness as well as its high power density and electromechanical coupling efficiency.
Although piezoelectric materials represent the primary method of harvesting energy, other methods exist, e.g., the use of electromagnetic devices. The piezoelectric energy harvesters are a substitute for other alternative EH technologies, such as electromagnetic or thermoelectric energy, because they provide the consistent source of energy needed. The potential of generating electricity from piezoelectric harvesters is higher than alternative EH technologies, where the components of the device are capable of delivering over 65% of their charge. Section 10.1 discusses some of the research that has been performed in the area of power harvesting and the future goals that must be achieved for power-harvesting systems to find their way into everyday use.
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