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Materials Science research is now entered a new phase where the structure and properties of materials are investigated, characterized and controlled at the nano scale. Today's portable electronics depend on batteries for power. Batteries and other traditional sources are too large, and tend to negate the size advantages of nano devices. Now researchers have demonstrated that easy-to-make, inexpensive nanowires can harvest mechanical energy, to overcome these challenges researches are finding alternative ways, and nano generator is one promising answer. A nano generator take advantage of unique coupled piezoelectric & semi conducting properties of zinc oxide nano structure (wires), which produce small electrical charges when they are flexed. By finding a way to collect electricity from multiple nano wires, the researchers took a big step toward a practical nano -scale power generator. When you walk, you generate 67 watts. Your finger movement is 0.1 watt. Your breathing is one watt. If you can convert a fraction of that, you can power a device. From the concept we've demonstrated, we can convert 17-30 percent of that energy. Consequently, researchers are developing innovative technologies to convert various forms of energy into electrical energy for low power nano devices. In this paper the piezoelectric zinc oxide nano wire arrays are used to demonstrate a novel approach for converting nano mechanical energy into electrical energy.
Nanotechnology is a field whose theme is the control of matter on an atomic and molecular scale, nanotechnology deals with structures of the size 100 nanometers or smaller. Nanotechnology is extremely diverse ranging from novel extensions of conventional device physics. Nanogenerator is a prototype nanometer-scale generator that produces continuous direct-current electricity by harvesting mechanical energy from such environmental sources as ultrasonic waves, mechanical vibration or blood flow. Based on arrays of vertically-aligned zinc oxide nano wires that move inside a novel “zig-zag” plate electrode, the nanogenerators could provide a new way to power nanoscale devices without batteries or other external power sources.
Nanogenerator is an energy harvesting device converting the external kinetic energy into an electrical energy based on the energy conversion by nano-structured piezoelectric material. Although its definition may include any types of energy harvesting devices with nano-structure converting the various types of the ambient energy, it is used in most of times to specifically indicate the kinetic energy harvesting devices utilizing nano-scaled piezoelectric material after its first introduction in 2006.
Although still in the early stage of the development, it has been regarded as a potential breakthrough toward the further miniaturization of the conventional energy harvester, possibly leading the facile integration with the other types of energy harvester converting the different types of energy and the independent operation of mobile electronic devices with the reduced concerns for the energy source, consequently.
Over the past decades, intensive research efforts have been carried out in developing energy harvesting system for portable and wireless applications. In particular, piezoelectric generator offers the most robust and simple solutions for mechanical energy harvesting. The main advantage of piezoelectric generator is its scalability. This is why the recent reports of energy harvesting from the environment using ZnO nanowire arrays have attracted great interests by scaling down the power source to nanoscale. PVDF stands for Poly (vinylidene fluoride). PVDF is a highly non -reactive, flexible, inexpensive, and leading polymer with good piezoelectric property. However, it must first be stretched and poled in a strong electrical field for its piezoelectricity. In this work, we present a direct-write technology to produce and place piezoelectric PVDF nanofibers at the same time with the in -situ poling and mechanical stretching process simultaneously as the foundation for nanogenerators .
2.2 Why nanogenerator is required?
• Materials Science research is now entered a new phase where the structure and properties of materials are investigated, characterized and controlled at the nano scale.
• Though as sophisticated as their larger counterparts, these devices are still burdened because they rely on an outside power.
• Batteries and other traditional sources are too large, and tend to negate the size advantages of nano devices.
• To overcome these challenges researches are finding alternative ways, and nano generator is one promising answer.
• A nano generator take advantage of unique coupled piezo electric & semi conducting properties of zinc oxide nano structure (wires), which produce small electrical charges when they are flexed.
• By finding a way to collect electricity from multiple nano wires, the researchers took a big step toward a practical nano-scale power generator.
3. Nanogenerator construction/ fabrication
The Nanogenerator is constructed with an electrode lowered on top of the nanowire array, leaving just enough space so that a significant number of the nanowires are free to flex within the gaps created by the tips. Moved by the mechanical energy such as waves or
vibration, the nanowires periodically contact the tips, transferring their electrical charges. By capturing the tiny amounts of current produced by hundreds of nanowires kept in motion, the generators produce a direct current output in the nano-Ampere range. The Nanogenerator could produce as much as 4 watts per cubic centimeter- based on a calculation for a single nanowire. The Nanogenerator would produce enough power to operate nanometer scale defense, environmental and biomedical applications, including biosensors implanted in the body, environmental monitors, and even nanoscale robots. April 14, 2006 issue of the journal Science, Wang’s research team announced the concept behind the nanogenerators. At the time the Nanogenerator could harvest power from just one nanowire at a time by dragging the tip of an atomic force microscope over it. Made of platinum coated silicon, the tip served as a schottky barrier, helping accumulate and preserve the electrical charge as the nanowire flexed and ensuring that the current flowed in one direction.