The rectenna design developed at the Technical University of Madrid and MIT uses a flexible radio-frequency (RF) antenna that captures the WiFI signals as AC waveforms. This is connected to anAC-DC converter that uses molybdenum disulfide (MoS2), which at three atoms thick is one of the thinnest semiconductors in the world. When it is exposed to certain chemicals, the material’s atoms rearrange in a way that acts like a switch, forcing a phase transition from a semiconductor to a metallic material, creating a Schottky diode.
A key advantageof this thin layer is that the device can be built on a flexible substrate in a roll-to-roll process 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?” said Tomás Palacios, a professor in the Department of Electrical Engineering and Computer Science and director of the MIT/MTL Centre for Graphene Devices and 2D Systems in the Microsystems Technology Laboratories. “We have come up with a new way to power the electronics systems of the future — by harvesting Wi-Fi energy in a way that’s easily integrated in large areas — to bring intelligence to every object around us.”
The device can produce about 40 microwatts of power when exposed to the typical power levels of Wi-Fi signals (around 150 microwatts), a conversion efficiency around 30 per cent. This compares to 50 to 60 per cent silicon or gallium arsenide converters.
Another possible application is powering the data communications of implantable medical devices, said Jesús Grajal, a researcher at the Technical University of Madrid. For example, researchers are beginning to develop pills that can be swallowed by patients and stream health data back to a computer for diagnostics.
“Ideally you don’t want to use batteries to power these systems, because if they leak lithium, the patient could die,” said Grajal. “It is much better to harvest energy from the environment to power up these small labs inside the body and communicate data to external computers.”
The parasitic capacitance of the Schottky diode is an order of magnitude smaller than today’s state-of-the-art flexible rectifiers, so it is much faster at signal conversion and allows it to capture and convert up to 10GHz of wireless signals.