The field of power harvesting has experienced significant growth over the past few years due to the ever-increasing desire to produce portable and wireless electronics with extended lifespans. Current portable and wireless devices must be designed to include electrochemical batteries as the power source. The use of batteries can be troublesome due to their limited lifespan, thus necessitating their periodic replacement. In the case of wireless sensors that are to be placed in remote locations, the sensor must be easily accessible or of a disposable nature to allow the device to function over extended periods of time. Energy scavenging devices are designed to capture the ambient energy surrounding the electronics and convert it into usable electrical energy. The concept of power harvesting works towards developing self-powered devices that do not require replaceable power supplies. A number of sources of harvestable ambient energy exist, including waste heat, vibration, electromagnetic waves, wind, flowing water, and solar energy. While each of these sources of energy can be effectively used to power remote sensors, the structural and biological communities have placed an emphasis on scavenging vibrational energy with piezoelectric materials. This article will review recent literature in the field of power harvesting and present the current state of power harvesting in its drive to create completely self-powered devices.

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A review of power harvesting using piezoelectric materials (2003–2006)

Power consumption is forecast by the International Technology Roadmap of Semiconductors (ITRS) to pose long-term technical challenges for the semiconductor industry. The purpose of this paper is threefold: (1) to provide an overview of strategies for powering MEMS via non-regenerative and regenerative power supplies; (2) to review the fundamentals of piezoelectric energy harvesting, along with recent advancements, and (3) to discuss future trends and applications for piezoelectric energy harvesting technology. The paper concludes with a discussion of research needs that are critical for the enhancement of piezoelectric energy harvesting devices.

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Powering MEMS portable devices—a review of non-regenerative and regenerative power supply systems with special emphasis on piezoelectric energy harvesting systems

Thin film piezoelectric materials offer a number of advantages in microelectromechanical systems (MEMS), due to the large motions that can be generated, often with low hysteresis, the high available energy densities, as well as high sensitivity sensors with wide dynamic ranges, and low power requirements This paper reviews the literature in this field, with an emphasis on the factors that impact the magnitude of the available piezoelectric response For non-ferroelectric piezoelectrics such as ZnO and AlN, the importance of film orientation is discussed The high available electrical resistivity in AlN, its compatibility with CMOS processing, and its high frequency constant make it especially attractive in resonator applications The higher piezoelectric response available in ferroelectric films enables lower voltage operation of actuators, as well as high sensitivity sensors Among ferroelectric films, the majority of the MEMS sensors and actuators developed have utilized lead zirconate titanate (PZT) films as the transducer Randomly oriented PZT films show piezoelectric e(31, f) coefficients of about - 7 C/m(2) at the morphotropic phase boundary In PZT films, orientation, composition, grain size, defect chemistry, and mechanical boundary conditions all impact the observed piezoelectric coefficients The highest achievable piezoelectric responses can be observed in {001} oriented rhombohedrally-distorted perovskites For a variety of such films, e(31,f) coefficients of - 12 to - 27 C/m(2) have been reported

Thin Film Piezoelectrics for MEMS

The vast reduction in the size and power consumption of sensors and CMOS circuitry has led to a focused research effort on the on-board power sources which can replace the batteries. The concern with batteries has been that they must always be charged before use. Similarly, the sensors and data acquisition components in distributed networks require centralized energy sources for their operation. In some applications such as sensors for structural health monitoring in remote locations, geographically inaccessible temperature or humidity sensors, the battery charging or replacement operations can be tedious and expensive. Logically, the emphasis in such cases has been on developing the on-site generators that can transform any available form of energy at the location into electrical energy. Piezoelectric energy harvesting has emerged as one of the prime methods for transforming mechanical energy into electric energy. This review article provides a comprehensive coverage of the recent developments in the area of piezoelectric energy harvesting using low profile transducers and provides the results for various energy harvesting prototype devices. A brief discussion is also presented on the selection of the piezoelectric materials for on and off resonance applications. Analytical models reported in literature to describe the efficiency and power magnitude of the energy harvesting process are analyzed.

Advances in energy harvesting using low profile piezoelectric transducers

Hydrokinetic energy conversion systems and assessment of horizontal and vertical axis turbines for river and tidal applications: A technology status review

The Energy Harvesting Eel (Eel) is a new device that uses piezoelectric polymers to convert the mechanical flow energy, available in oceans and rivers, to electrical power. Eel generators make use of the regular trail of traveling vortices behind a bluff body to strain the piezoelectric elements; the resulting undulating motion resembles that of a natural eel swimming. Internal batteries are used to store the surplus energy generated by the Eel for later use by a small, unattended sensor or robot. Because of the properties of commercially available piezoelectric polymers, Eels will be relatively inexpensive and are easily scaleable in size and have the capacity to generate from milli-watts to many watts depending on system size and flow velocity of the local environment. A practical Eel structure has been developed that uses the commercially available piezoelectric polymer, PVDF. Future Eels may use more efficient electrostrictive polymer. Every aspect of the system from the interactions between the hydrodynamics of the water flow and structural elements of the Eel, through the mechanical energy input to the piezoelectric material, and finally the electric power output delivered through an optimized resonant circuit has been modeled and tested. The complete Eel system, complete with a generation and storage system, has been demonstrated in a wave tank. Future work on the Eel will focus on developing and then deploying a small, lightweight, one-watt power generation unit, initially in an estuary and then subsequently in the ocean. Such Eels will have the ability to recharge batteries or capacitors of a distributed robotic group, or remote sensor array, thus extending the mission life indefinitely in regions containing flowing water.

S.A. Kammann

Papers

The Energy Harvesting Eel: a small subsurface ocean/river power generator