When blinking numbers are displayed on an LCD, the common signal is the need for resetting. However, at the laboratory of Zong Lin Wang at Georgia Tech, the blinking indicates 5-years of successful research. Electronic devices are powered through nanoscale generators which produce mechanical energy directly from the environment via the use of tiny nano-wires.

Mechanical energy can be extracted using nano-generators, which produce energy from our heart beat, fingers, rustling of a shirt, vibration of large machines or simply walking with your shoes. These nano-generators will certainly not be able to generate high volume of energy, but they might be used to provide energy for micro-scale and nano-scale devices or even to recharge an iPod.

The nano-generators which have been developed by Wang adopt the piezoelectric effect present in crystalline materials like zinc oxide. This type of materials releases an electric charge when the structure is compressed or flexed. Binding together millions of nano-scale zinc oxide wires can produce a more constant charge. The team was able to develop a system which generated 3 volts – around 300 nano-amps.

At the Georgia Tech, laboratory Zhong Lin Wang and his team has after 5 years of research developed a blinking LCD signal which can produce electricity to power typical electronic devices through the use of nano-scale generators. These generators produce electricity from the mechanical energy present in the environment.

The architecture has significantly been simplified. This has made the system better and enabling more nanowires to be combined. The electricity output through these changes has increased tremendously. It can even power LCDs & laser diodes. Wang who is a Regents’ Professor In Georgia Tech’s School of Materials Science and Engineering claims that if this rate of improvement is sustained the technology will soon be able to power healthcare devices, environmental monitoring and personal electronics.

In the Journal Nano letters, a recent improvement in the development of nanogenerators was reported – Related to the simplistic way to produce these diminutive generators -. Moreover, the Nature Communication says that this type of progress is encouraged by the Defense Advanced Research Project Agency (DARPA) of U.S Department of Energy, National Science Foundation and U.S Air Force.

Wang said that the main aim is to power tiny devices used in health care, or personal electronics and environmental monitoring. Developing smart solution to power these devices is important.

The first zinc oxide nanogenerators had a dozen of nanowires that were placed on a rigid substrate covered with metal electrode. However, the more recent technology integrates nanowires into the polymer, so that electricity can be generated by simple flexing the material. Irrespective of the configuration, the nanowire arrays had to be assembled in a complex way.

In a more recent paper, Wang and his team of scientists, Yan Zhang, Youfan Hu, Guang Zhu, Chen Xu and Zetang Li came up with a simpler way to create the nano-generator. They created arrays of nanowires in a conical shape. The wires that had been created were then cut from the substrate and dropped into an alcohol solution.

The solution that had the nanowires was afterward dripped onto the thin metal electrode as well as on a flexible polymer film. The alcohol was given some time; so that it could dry, afterward additional layers were added. Several layers of the nanowire were added to create a composition, which Wang thinks can be used at the industrial level in the future.

If these small nanowire sandwiches are flexed, enough electricity to power a commercial display (that of a pocket calculator) was generated. The nanowire sandwiches are of rectangular size of 2 cm by 1.5 cm.

According to Wang, soon nanogenerators will be able to create self-powered systems, like for example a system which monitors the presence of toxic gas in the environment, and thereafter produces warning signs. Such a system would be construed with the use of capacitors, for energy storage, until the energy would be enough to power additional features. For instance, simple pressing your two fingers on a nanogenerator can currently power a liquid-crystal display.

Nevertheless, the energy output by the actual nanogenerators is significantly below that of cardiac peacemakers and iPods. According to Wang, it might be possible to reach those levels within 3 to 5 years. Besides, the nanogenerators that the team has just developed are 100 times stronger than the one they created a year ago.

A Second Advancement

In October, 2010, members of the team, Wang, Sheng Xu and Benjamin J. Hansen said that there were alternative ways to create these piezoelectric nanowires. Lead zirconate titanate (also called PZT) can also be used. This was reported in the Journal Nature Communication, it was also mentioned that this material is used by industries. However, there is a hitch, the material is difficult to work with as it requires an extremely high temperature ranging up to 650 degrees celsius.

However, Wang’s team did once again produce extraordinary results. They were able to grow a vertically-aligned single-crystal nanowire array of PZT with the use of different non-conductive and conductive substrates. A process called the hydrothermal decomposition was used, which was performed at merely 230 degrees Celsius.

The circuit was changed by going from alternative current (AC) to direct current (DC). These PZT nanogenerators were afterward used to provide electricity to power a commercial laser diode. The research added another material which can now be used to produce Wang’s nanogenerators. Although that PZT isn’t as effective as zinc oxide, it provides an additional source of material to generate power.

A Third Advancement

Wang and his group members Sihong Wang, Guang Zhu and Rusen Yang published another report in Nano letters showing a third way to increase the efficiency of nanogenerators. The method is called the ‘scalable sweeping printing’. The process consisted of two steps:

1. Sending Vertically-aligned Zinc oxide nanowires, which was received by polymer substrate to create horizontal arrays.

2. Then parallel strips of electrodes are applied to bind the nanowires.

The use of a single layer, gave an open-circuit of 2.03 volts. The highest output generated was nearly of a density of 11 milliwatts per cm3.

Wang said that the progresses in nanogenerators have improved tremendously, since they started to work on it in 2005. In the near future, these tiny generators can be able to power small systems. He also said that he expects to see this technology in use by general devices in the upcoming 5 years.

Source: Physorg and Nano Letters

© Jimmy Eriksson for Renewable Power News, 2010. | Permalink | No comment

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