Energy harvesting is an energy-to-energy conversion technology involving processes that generate electrical energy from other sources of energy such as mechanical, thermal, chemical, solar, and radio frequency. Use of mechanical and solar energy represents the most developed technologies and offers solutions over a broad range of energy levels. Solar cells are used to power wrist watches, calculators, and road signs, whereas mechanical-energy harvesting solutions based on piezoelectric transducers are being used to harvest energy from sources such as vibration or shock loading. Radio-frequency-based harvesters, for example, are finding use in converting ambient electromagnetic energy to power sensor nodes. Conversion of thermal gradients to electrical energy is another promising technology.

This book is restricted to the generation of small amounts of electrical energy on a local scale and for conversion of mechanical potential and kinetic energy to electrical energy. Persons interested in learning more about the fundamental concepts of energy harvesting will find the treatment of relevant topics readable with little prerequisite requirement of engineering topics. This book will be of particular interest to application engineers from diverse disciplines and industries. It provides a fundamental view of the scope of the energy-harvesting technology as well as the trade-offs and limitations for practical systems.

The book will be of interest to those who want to know the potentials as well as shortcomings of energy-harvesting technologies. It is particularly useful for energy-harvesting system design because it provides a systematic approach to: selection of the proper transduction mechanisms, methods of interfacing with a host system, and electrical energy collection and conditioning options.

The book is divided into five chapters. Chapter 1 briefly describes the various energy-conversion processes currently being used in the generation of electrical energy from sources such as solar, radio frequency, thermoelectric, and energy from human activity.

Chapter 2 describes the three primary types of transducers typically used for converting mechanical energy to electrical energy, that is, piezoelectric, electromagnetic, and electrostatic. Magnetostrictive-based transducers are also briefly introduced.

Chapter 3 presents an in-depth analysis of the interfacing mechanisms used for coupling the host system to the energy harvester for effective transfer of mechanical kinetic and/or potential energy to the transducer.

Chapter 4 addresses collection and conditioning circuits needed to extract the generated electrical energy for delivery to a load. The theme of chapters 2, 3, and 4 shows the connection between the three components of an energy-harvesting system, namely, the host interfacing mechanism, the transducer, and the collection and conditioning circuit.

In addition to the design of efficient energy harvesters, this book also discusses how certain types of energy harvesters can be configured to provide self-powered sensing capabilities. Additional circuitry not requiring any external power may also provide further enhancement by including logic functionality. Case studies with particular emphasis on shock-loading-based energy harvesting and sensory applications are presented in Chapter 5.

An extensive list of references is provided to direct the reader to appropriate literature for more in-depth material not covered in the book.

We thank James Harrington, SPIE Tutorial Text Series Editor, for encouraging us to write the book and Tim Lamkins, SPIE Press Manager, for his editorial suggestions and support. We very much appreciate the effort, patience, and guidance provided by Nicole Harris, our editor at SPIE.