We all know that battery technology has been slow to evolve, and none of the potentially revolutionary next-gen designs have panned out yet. So, why not just skip the battery entirely? Researchers from MIT have developed a 2D material that can harvest energy from Wi-Fi signals to directly power small electronics. The team envisions smart home devices that run forever and buildings with smart walls that generate their own power.
The device created by MIT scientists is a rectenna, which isn’t a new idea. Rectennas contain an electrical component known as a rectifier, which converts AC input into DC power. Traditionally, rectennas use silicon or gallium arsenide — they’re bulky and solid. The MIT version is flexible and only a few atoms thick. That makes it possible to integrate a rectenna into almost anything.
To build this new type of rectenna, MIT turned to a material called molybdenum disulfide (MoS2). It’s only three atoms thick, making it one of the thinnest semiconductors on the planet. That’s not the only thing that makes it special, though. When exposed to certain chemical compounds, molybdenum disulfide undergoes a phase transition from semiconductor to metallic material. That creates what’s known a junction between a semiconductor and a metal, known as a Schottky diode.
Through laboratory testing, the team discovered that the Schottky diode in this material is exceptionally efficient and minimizes resistance. That reduced a property of circuits called parasitic capacitance, allowing the rectenna to convert up to 10GHz of wireless signals. That means it could harvest power from the ambient signals of Wi-Fi, Bluetooth, and a large chunk of the cellular spectrum.
Currently, the larger rigid rectennas from years past are more efficient, capable of converting about half of the electromagnetic energy into DC power. However, you can’t build those into small electronic devices very easily, and they’re expensive. While the 2D material from MIT is just 30 percent efficient, it takes up almost no space and costs a fraction as much to produce.
This material won’t be able to meek your smartphone running just yet — in the lab, researchers can extract 40 microwatts from Wi-Fi at typical power levels. This is enough to light an LED or run a low-power system-on-a-chip. That’s why it may be ideal for smart home and “internet of things” hardware. The team also speculates implantable medical devices could use the new rectennas to generate power rather than relying on batteries that need to be replaced surgically every few years.
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