Sensors have improved in terms of size, capability, and power consumption, but their deployment in remote areas is limited by battery power supplies. Using piezoelectric (PE) materials for energy scavenging is a possible way to remedy the situation. The technology developed in this work converts existing sources of nonpolluting energy (mechanical strain) from nature into electricity. The quantity of energy produced is not massive, but it can be easily generated from free sources such as vibration and electromagnetic waves.

A nanocomposite power generator.
Piezoelectric materials convert applied strain into electricity or alternatively, if current is applied, they deform. The PE materials are grown in a nanowire form, and include ZnO, GaN, AlN, and lithium niobate. They can be grown using a vapor-liquid-solid approach by embedding the PE materials in a soft matrix like a polymer in order to withstand large strains without falling apart. The advantage of this approach is that it would allow vertical growth of nanowires on a substrate directly in a device fabricating process sequence. For bulk production, chemistry- based methods can be used to produce nanowires of different size, shape, aspect ratio, etc.

Regardless of vertical or randomly oriented nanowires, a device using just bare nanowires can be brittle and therefore cannot sustain the maximum amount of strain without breaking down, thus limiting the power that can be generated. The key is not to lose the basic PE properties after embedding them in a polymer. If a polymer is chosen that has PE properties, then the resulting composite would maintain the PE properties of the original PE material while sustaining large strains.

The wires are grown on a substrate and then the array is intercalated with polyvinalydine difluoride (PVDF) using a spin-on technique. The nanowire-based PE material thus prepared can be fabricated into a suitable device that can be subjected to natural and manmade vibrations in an effort to convert the strain into electricity. This material form and approach will provide enhanced PE properties relative to the state-of-the-art while being able to take on maximum strain without breaking because of the brittle nature of the PE materials themselves.

This work was done by Meyya Meyyappan of Ames Research Center. NASA invites companies to inquire about partnering opportunities and licensing this patented technology. Contact the Ames Technology Partnerships Office at 1-855-627-2249 or ARC-TechTransfer@mail. Refer to ARC-16405-1.