Charge Your Cellphone By Talking

Imagine a self-powered cellphone that charges by the pressure waves formed when you talk or walk. Researchers have found a certain type of piezoelectric material that can covert energy at a 100 percent increase when manufactured at a very small size (specifically 21 nanometers in thickness). This suggests that disturbances in the form of sound waves could be harvested for powering nanodevices and microdevices of the future.

Here's how it works. Piezoelectrics are (usually) crystal or ceramic materials that generate voltage when a form of mechanical stress is applied (think car cigarette lighters). It's an old technology now powering dance floors in Europe. Combine piezoelectrics with the strange, infinitessimally small nanoworld, where many materials change their properties dramatically (gold turns red, toxic, and liquid at room temperature; opaque materials like copper become transparent; insulators like silicon become conductors). Piezoelectric materials at 21-nm thick turn into power-harvesting titans.

The findings could have potentially profound effects for low-powered electronic devices like cell phones and laptops. Many contain nano-sized components (1 nanometer equals one-billionth of a meter). All need a lot of recharging. But pressure-senstitive, self-powered piezoelectrics could harness energy from the sound waves in your speech or your walk. Free of charge takes on a whole new meaning.

The research is published in Physical Review B, the scientific journal of the American Physical Society.

Julia Whitty is Mother Jones' environmental correspondent, lecturer, and 2008 winner of the PEN USA Literary Award, the Kiriyama Prize and the John Burroughs Medal.