Charging cables, while a necessity, are something we’d like to never have to use again. That means batteries too. Battery technology, despite the increasing need in the auto industry, is only slowly advancing, but the results show potential. Researchers have been investing resources into annihilating cables; not long ago researchers from the University of Washington presented a system they named Power over Wi-Fi (PoWiFi). More recently, scientists from MIT and the Technical University of Madrid are looking into a new way of converting energy from Wi-Fi signals into electricity that could power electronics. Their latest study involves a new kind of rectenna: a device that converts alternative current electromagnetic waves into direct current (DC) electricity. The rectenna uses a flexible radio-frequency antenna which captures electromagnetic waves, including those carrying Wi-Fi, as alternative current (AC) waveforms. This antenna is then connected to a novel device called rectifier, for which the researchers used a two-dimensional semiconductor just three atoms thick (called molybdenum disulfide—MoS2), one of the thinnest semiconductors in the world. The AC signal travels into the semiconductor, which converts it into a DC voltage that can be used to power electronic circuits or recharge batteries. In short, this battery-free device passively captures and transforms ubiquitous Wi-Fi signals into useful DC power. Furthermore, the device is flexible and can be set up to cover very large areas. “What if we could develop electronic systems that we wrap around a bridge or cover an entire highway, or the walls of our office and bring electronic intelligence to everything around us? How do you provide energy for those electronics?” asked Tomás Palacios, a professor in the Department of Electrical Engineering and Computer Science & director of the MIT/MTL Center for Graphene Devices and 2D Systems in the Microsystems...