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Energy harvesting (or energy scavenging) technology captures unused ambient energy, such as vibration, strain, light, temperature gradients, temperature variations, gas flow energy, and liquid flow energy, and converts it into usable electrical energy. Even though advances have been made, the batteries that power portable microelectronics and wireless devices provide only a finite amount of power. Energy harvesting is a perfect solution for the problem of finite battery power for various low-power applications, providing sustained, cost-effective, and environmentally friendlier sources of power. Unconventional methods for waste-energy harvesting and scavenging are being explored to provide sustained power to these micro- and nanodevices. Efforts are being made to garner electric power from mechanical vibrations, light, spatial variations, and temporal temperature variations. Another potential source for low-power electronics is the thermal- and mechanical-waste energy of asphalt pavement, especially via pyroelectricity. However, this potential has not yet been extensively explored. An exception is Israel's current large-scale effort to pave kilometers of roads with a specially designed series of piezoelectric modules in the pavement. Pyroelectric materials are able to convert most of the electromagnetic radiation's spectrum (ultraviolet, IR, microwave, x rays, and terahertz) energy into electrical energy; that is, they transform photons to phonons and then to electrons.5 Since it follows that these materials can be exploited for conversion of thermal energy to electricity, they have been investigated recently for energy harvesting via pyroelectric linear and nonlinear properties. One key advantage of pyroelectrics over thermoelectrics is the stability of many pyroelectric materials at up to 1200 °C or more, which enables energy harvesting from high-temperature sources, thereby increasing thermodynamic efficiency. It is noteworthy that annually more than 100 TJ of low-grade waste heat (10 °C to 250 °C) is discharged by industries worldwide, such as electric power stations, glass manufacturers, petrochemical plants, pulp and paper mills, steel and other foundries, and the automobile industry. In the United States in 2009, around 55% of the energy generated from all of the sources was lost as waste heat.6 Technology to recover this low-grade waste heat or convert into usable electricity could save industrial sectors billions of dollars annually and reduce greenhouse gases. Pyroelectric electric generators (PEGs) can play a significant role in such technology. This chapter presents a review of PEGs with discussions on linear and nonlinear energy harvesting processes, thermodynamics of pyroelectrics, and an investigation of important pyroelectric materials with modeling of numerically simulated results for energy conversion.
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