Cellphones charged by voice sound waves. Drug delivery systems enabled by minute body movements. Military equipment powered by the motion of soldiers walking? Self-powered devices like these are now one step closer to reality thanks to a Texas A&M professor’s discovery that when certain piezoelectric materials are produced at the nanoscale – specifically at about 21 nanometers in thickness – they double their ability to convert mechanical energy into electrical energy. Conversely, when these piezoelectric materials are produced in sizes larger or smaller than about 20 to 23 nanometers, they lose substantial amounts of this energy-converting ability, says Tahir Cagin, the nanotechnology specialist who made the discovery, together with partners at the University of Houston. A pioneer in power harvesting – a field aimed at creating self-energized devices that don’t need power supplies replaced or recharged – Cagin has detailed his findings in a fall 2008 article in Physical Review B, published by the American Physical Society. As reported, the science of piezoelectrics is central to Cagin’s work.
Discovered by French scientists in the 1880s, piezoelectric materials – usually crystals or ceramics – generate voltage when a form of mechanical pressure is applied. Employed in World War I sonar devices, the technology is hardly new. Piezo materials are routinely used today in microphones, quartz watches, cigarette lighters and even in a handful of European nightclubs where dance floors have been built to transform energy from footsteps into lighting power and in a Hong Kong gym where exercisers’ energy is helping to power both lights and music. If the technology isn’t new, however, Cagin’s approach to it is. His focus is specifically on nano-sized piezoelectric materials. “When materials are brought down to the nanoscale dimension, their properties for some performance characteristics dramatically change,” says the past recipient of the Foresight Nanotech Institute’s prestigious Feynman Prize in Nanotechnology.
This finding and the knowledge that nanoscale materials are more “pliable and susceptible to change from their surrounding environment” have confirmed Cagin’s belief that miniscule changes in motion, presure and sound can be used to trigger nanoscale piezoelectric devices capable of powering everything from the delivery of drugs to the human body to the collection and conversion of sound vibrations into energy for cellphones, PDAs, laptops, mp3 players and an almost endless list of other low-powered electronic devices. “Even the disturbances in the form of sound waves such as pressure waves in gases, liquids and solids may be harvested for powering nano- and micro devices of the future if these materials are processed and manufactured appropriately for this purpose,” Cagin notes.