Pyroelectric effect
A lot of heat energy is lost to the environment by various devices ranging from computers to cars to long-distance electric transmission lines. Heat can be converted to electricity using the pyroelectric effect. This effect was first observed by the Greek philosopher Theophrastus when a gemstone tourmaline produced static electricity and attracted bits of straw when heated. This is because heating and cooling rearrange the molecular structure of certain materials, including tourmaline, and create an imbalance of electrons which result in the generation of electric current.
A device called pyroelectric nanogenerator has been designed to harvest waste heat to produce electricity by researchers of Georgia Tech. The research group applied this ancient principle to make a nanogenerator (NG) that could take advantage of time-dependent temperature change of a heat source to generate electricity.
Researchers used nanowires out of zinc oxide in an array of short lengths standing on end and demonstrated a device that produces electricity when heated or cooled. The nanogenerators can even produce power as temperatures fluctuate from day to night.
The researchers claim that this new type of NG can be the basis for self-powered nanotechnology that harvests thermal energy from the time-dependent temperature fluctuation in our environment for applications such as wireless sensors, temperature imaging, medical diagnostics and personal microelectronics.
Uses of nanogenerator
Pyroelectrictricity can play key role in consumer electronics and recovering this heat in the form of pyroelectric energy may bring about a new era of "tiny energy." Pyroelectric nanogenerators could be extremely useful for powering specific tasks in biological applications, medicine and nanotechnology, particularly in space because they perform well in low temperatures.
Ukrainian and American effort
A joint team of Ukrainian and American scientists has also demonstrated this novel pyroelectric method to power tiny devices using waste heat. Using tiny structures called ferroelectric nanowires an electrical current can be generated in response to any change in the ambient temperature, harvesting otherwise wasted energy from thermal fluctuations.
Pyroelectric properties
In the pyroelectric properties of ferroelectric nanowires the pyroelectric coefficient corresponds to the radius of the wire and its coupling. The smaller the wire radius, the more the pyroelectric coefficient diverges until a critical radius at which the response changes to paraelectric (above the Curie temperature). This so-called "size effect" could be used to tune the phase transition temperatures in ferroelectric nanostructures, thus enabling a system with a large, tunable, pyroelectric response.
In theory, the use of rectifying contacts could enable the polarized ferroelectric nanowire to generate a giant, pyroelectric, direct current and voltage in response to temperature fluctuations that could be harvested and detected using a bolometric detector. Such a nanoscale device would not contain any moving parts and could be suitable for long-term operation in ambient applications such as in-vitro biological systems and outer space.
The researchers believe that these little nanogenerators would have very high efficiency at low temperatures, decreasing at warmer temperatures.
Wake Forest University effort on Power Felt
Wake Forest University scientists have developed a technology called Power Felt composed of carbon nanotubes, a thermoelectric device that converts body heat into an electrical current.
Power Felt is composed of tiny carbon nanotubes locked up in flexible plastic fibers and made to feel like fabric. The technology uses temperature differences, say for instance, room temperature versus body temperature to create a charge.
Uses Power Felt
Potential uses for Power Felt include lining automobile seats to boost battery power and service electrical needs, insulating pipes or collecting heat under roof tiles to lower gas or electric bills, lining clothing or sports equipment to monitor performance, or wrapping IV or wound sites to better track patients' medical needs. It can be used as an emergency kit, wrapped around a flashlight, powering a weather radio, charging a prepaid cell phone and can provide relief during power outages or accidents. 72 stacked layers in the fabric yielded about 140 nanowatts of power and the addition of more nanotube layers can make them even thinner to boost the power output.
According to researchers it is even possible to make a jacket with a completely thermoelectric inside liner that gathers warmth from body heat, while the exterior remains cold from the outside temperature and can potentially power an iPod.


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