|Fig. 1: Five modules necessary for self-sufficient nano systems. (Source: V. Chen)|
Nanotechnologies represent the understanding, engineering, and manipulation of materials at approximately 1 to 100 nanometers.  At this scale, materials have unique properties that have contributed significantly to the fields of electronics, the military, medicine, and consumer products. Nanotechnologies exist in many products that typical consumers might use quite frequently and without realizing it - from sunscreens and cosmetics to coatings on eyewear.  In more recent research developments, nanotechnologies have been implemented in medical systems with applications as drug delivery modules and biosensors. 
With innovation at so many scales, there is a need for new energy systems at each of those scales. Recently, the energy crisis has called for new, sustainable forms of energy that will continue to support rapid rates of innovation. Despite significant strides in the fields of larger-scale solar, geothermal, nuclear, wind, and hydrogen energy as alternative energy sources, we still face many uncertainties related to potential nanotechnologies. These devices typically require power sources within the milliwatt range to operate.  As displayed in Fig1, energy harvesting from the environment is one of the core features of a functional, self-sufficient nanosystem.
One particular technology that offers potential for powering nanodevices is piezoelectricity. This is a method in which mechanical energy can be harvested and converted into a power source. In the context of the human body, activity can be converted into electrical energy - perfect in the context of nano-scaled biosystems.
|Table 1: Mechanical energy derived from various bodily functions and the theoretical conversion to electrical energy that could be generated via piezoelectricity. |
In one model of the nanogenerator mechanism, piezoelectric potential is created from nanowires strained externally.  Using thousands of nanowire, a gentle straining produced an output of 1.2 volts, capable of powering an LED display. 
Piezoelectric materials (ZnO, PZT) present unique properties in their internal crystal array structures.  Upon external disturbance, such as a vibration or mechanical wave, a voltage drop occurs because the internal atoms may not be symmetrically aligned.  These unique characteristics, shared across all piezoelectric materials, allow for the generation of electricity throuhg mechanical stress.
Piezoelectric nanogenerators could convert mechanical energy into electrical energy for self-powered nano-systems through a variety of methods. Some potential applications for this energy source could include body/muscle movement, blood pressure, vibration energy (acoustic/ultrasonic waves), hydraulic energy, or dynamic fluids. 
The future of integrated nanodevices exists as self-sufficient nanosystems. Advancements in nano generation via piezoelectricity are a promising solution to a problem that will help us sense, control, communicate, and actuate responses in nanosystems.
© Vincent Chen. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
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