Imagine a world where electronic devices work without batteries. Researchers at MIT have developed a fully flexible device that converts wifi signals into electricity, potentially powering smartphones, wearables, and medical sensors.
This device, known as a rectenna, features a flexible radio-frequency (RF) antenna that captures electromagnetic waves, including wifi, and converts them into AC signals. These signals then pass through an ultra-thin, two-dimensional semiconductor, transforming into DC voltage to power circuits or recharge batteries.
Unlike traditional rectennas that use rigid materials, this innovation is flexible and can be mass-produced using roll-to-roll fabrication, covering large surfaces like buildings or highways. According to MIT professor Tomás Palacios, this technology could integrate electronic intelligence into everyday structures.
Early applications include wearable technology, implantable medical devices, and the internet of things. The researchers’ prototype generates around 40 microwatts of power from wifi signals, sufficient to power small electronics like LEDs or microchips.
One promising medical application is battery-free ingestible sensors, which can transmit health data without the risk of lithium leakage from batteries. Researcher Jesús Grajal highlights the safety benefits of harvesting energy from the environment for these devices.
Traditional rectennas rely on silicon or gallium arsenide, which are expensive and rigid. Previous flexible rectennas could not capture high-frequency signals like wifi. To solve this, researchers used molybdenum disulfide (MoS₂), an ultra-thin semiconductor. By inducing a phase transition, they created a Schottky diode, optimizing energy conversion efficiency.
The MoS₂ rectifier reduces parasitic capacitance, enhancing speed and enabling efficient wifi signal conversion at frequencies up to 10 gigahertz. This advancement allows it to cover wireless standards like wifi, Bluetooth, and LTE.
The current device achieves up to 40% power conversion efficiency, with typical wifi power levels reaching 30%. While silicon-based rectennas still outperform it at 50-60%, this new approach is a step toward efficient, flexible energy harvesting.
Harvard physicist Philip Kim praises the breakthrough, noting its potential for utilizing ambient radio-frequency energy. The MIT-led team, including researchers from Madrid, Boston University, and the Army Research Laboratory, plans to refine the system for greater efficiency.
The project was supported by MIT International Science and Technology Initiatives, the Army Research Laboratory, the National Science Foundation, and the Air Force Office of Scientific Research.
