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Nanogenerator: (Left, clockwise) Arrays of zinc oxide nanowires packaged in a thin polymer film generate electrical current when flexed. The nanogenerator could be embedded in clothing and used to convert the rustling of fabric into current to power portable devices such as cell phones.
Hearing aid: An array of vertically aligned piezoelectric nanowires could serve as a hearing aid. When sound waves hit them, the wires bend, generating an electrical potential. The electrical signal can then be amplified and sent directly to the auditory nerve.
Signature verification: A grid of piezoelectric wires underneath a signature pad would record the pattern of pressure applied by each person signing. Combined with a database of such patterns, the system could authenticate signatures.
Bone-loss monitor: A mesh of piezoelectric nanowires could monitor mechanical strain indicative of bone loss. Dangerous stress to the bone would generate an electrical current in the wires; this would cause the device to beam an alert signal outside the body. The sensor could be implanted in a minimally invasive procedure.
Freeing nanoelectronics from outside power sources opens up all sorts of possibilities. A nanopiezotronic hearing aid integrated with a nanogenerator might use an array of nanowires, each tuned to vibrate at a different frequency over a large range of sounds. The nanowires would convert sounds into electrical signals and process them so that they could be conveyed directly to neurons in the brain. Not only would such implanted neural prosthetics be more compact and more sensitive than traditional hearing aids, but they wouldn’t need to be removed so their batteries could be changed. Nanopiezotronic sensors might also be used to detect mechanical stresses in an airplane engine; just a few nanowire components could monitor stress, process the information, and then communicate the relevant data to an airplane’s computer. Whether in the body or in the air, nano devices would at last be set loose in the world all around us.