There exist numerous low-frequency excitation sources, such as walking, breathing, and ocean waves, capable of providing viable amounts of mechanical energy to power many critical devices, including pacemakers, cell phones, MEMS devices, wireless sensors, and actuators. Harvesting significant energy levels from such sources can only be achieved through the design of devices capable of performing effective energy transfer mechanisms over low frequencies. In this chapter, two concepts of efficient low-frequency piezoelectric energy harvesters are presented, namely, variable-shaped piezoelectric energy harvesters and piezomagnetoelastic energy harvesters. Linear and nonlinear electromechanical models are developed and validated in this chapter. The results show that the quadratic shape can yield up to two times the energy harvested by a rectangular one. It is also demonstrated that depending on the available excitation frequency, an enhanced energy harvester can be tuned and optimized by changing the length of the piezoelectric material or by changing the distance between the two tip magnets.
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Harvesting energy from wasted mechanical energy has been the topic of several investigations in the past decade (Sodano, Park, & Inman, 2004; Anton & Sodano, 2007; Erturk, 2009; Karami, 2011; Abdelkefi, 2012). The ultimate goal of designing and fabricating these harvesters is to replace small batteries that have finite life span or would require expensive and difficult replacement. They are also used to operate self-powered devices including wireless and structural health monitoring sensors, cameras, pacemakers, data transmitters, and medical implants (Roundy & Wright, 2005; Clair, Bibo, Sennakesavababu, & Daqaq, 2010; Karami & Inman, 2012; Abdelkefi & Ghommem, 2013). These harvesters can be deployed in different locations including structure’s surface, cell phones, pacemakers, buildings, bridges, etc. Different transduction mechanisms have been used, such as electrostatic (Anton & Sodano, 2007), electromagnetic (Arnold, 2007; Karami, 2011), and piezoelectric (Sodano et al., 2004; Erturk, 2009). Because of its ease of application, non-reliance on external input voltage, and its suitability for designing small energy harvesters, the piezoelectric option has flourished in most of the recent investigations.