Despite the abundance of ambient mechanical energy in our environment, it is often neglected and left unused. However, recent studies have demonstrated that mechanical vibrations can be harvested and used to power small wireless electronic devices, such as micro electromechanical sensors (MEMS) and actuators. Most commonly, these energy harvesters convert vibration into electrical energy by utilizing piezoelectric, electromagnetic or electrostatic effects. Recently, triboelectric based energy harvesters have shown to be among the simplest and most costeffective techniques for scavenging mechanical energy. The basis of triboelectric energy harvesters is the periodic contact and separation of two surfaces with opposite triboelectric properties which results in induced charge flow through an external load. Here, a vibration driven triboelectric nanogenerator (TENG) is fabricated and the effect of micro/nano scale surface modification is studied. The TENG produces electrical energy on the basis of periodic out-of-plane charge separation between gold and polydimethylsiloxane (PDMS) with opposite triboelectric charge polarities. By introducing micro/nano scale surface modifications to the PDMS and gold, the TENG's power output is further enhanced. This work demonstrates that the morphology of the surfaces in a TENG device is important and by increasing the effective surface area through micro/nano scale modification, the power output of the device can increase by 118%. Moreover, it is shown that unlike many TENGs proposed in the literature, the fabricated device has a high RMS open circuit voltage and short circuit current and can perform for an extended period of time.

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Piezoelectric materials are currently among the most promising building blocks for sensing, actuation and energy harvesting systems. However, these materials are limited in certain applications due to their lack of machinability as well as their inability to conform to curved surfaces. One method to mitigate this issue is through additive manufacturing (direct printing) of piezoelectric nanocomposites, where piezoelectric nanomaterials are embedded in a polymer matrix. Although significant progress has been made in this area, filler morphology, alignment and volume fraction are critical parameters that influence the electromechanical response and have not been adequately modeled. With the advent of additive manufacturing it is now possible to realize directly printed nanocomposites with tailored microstructure. The objective of this study is to develop and experimentally validate micromechanical and finite element models that allow the study of the electroelastic properties of a directly printed nanocomposite containing piezoelectric inclusions. Furthermore, the dependence of these properties on geometrical parameters such as aspect ratio and alignment of the active phase are investigated. In particular, the core focus of this work is to demonstrate how the gradual alignment of piezoelectric nanowires in the nanocomposite from randomly oriented to purely aligned can improve electroelastic properties of a printed nanocomposite. Finally, this work provides the first experimental validation of the theoretical and FEM models through measurement of the electroelastic properties of the nanocomposites containing barium titanate nanowires in a polydimethylsiloxane (PDMS) polymer matrix.

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