At the turn of the twentieth century, Nikola Tesla devoted his extraordinary abilities to pioneering research on radio-frequency electromagnetism, with the ultimate goal of perfecting a system for delivering electric power wirelessly over continental distances. Although Tesla's dream was not fully realized, this work led directly to the development of the radio. In recent years, there has been a proliferation of portable electronic devices, most of which rely on modern developments of radio technology to transfer data wirelessly. These devices are frequently marketed as wireless, although the consumer must still plug them into a power outlet regularly, at least to recharge their batteries. A method for supplying energy without cables, particularly if the source of wireless power and the receiving object are separated by midrange distances of at least several feet, could make these devices completely wireless.