
The key to this discovery is a new method of wirelessly transmitting power, dubbed “mid-field powering.” As the name implies, mid-field power transfer uses radio waves that sit between near-field (tens of gigahertz) and far-field (tens of megahertz). Near-field radiation can penetrate human flesh, but can only effectively transfer power over a short distance (millimeters). Far-field waves can transfer power over longer distances, but are unfortunately scattered or absorbed by human skin. To create mid-field waves, Poon created a patterned antenna (pictured below) that generates special near-field waves. When these special waves hit the skin, they turn into mid-field waves that can then penetrate a few more centimeters of flesh. (For more on how wireless power transfer actually works, read our explainer.)
Read more of this article at - http://www.extremetech.com/extreme/182686-here-come-the-rice-grain-sized-brain-implants-stanford-discovers-way-of-beaming-power-to-microimplants-deep-inside-your-body