MIT invention uses ultrasound to shake drinking water out of the air, even in dry regions

Researchers at MIT have developed a device that collects moisture from the air and turns it into drinking water within minutes. The team hopes that the technology could eventually be used to provide clean water to communities where natural sources are scarce.

Atmospheric water harvesting (AWH) systems work by drawing moisture from the air and condensing it into liquid water. This typically involves cooling humid air or using sponge-like materials called "sorbents" that absorb water vapor, which is then released and condensed into droplets.

The challenge is that AWH devices typically rely on the sun to evaporate water from the sorbent, which can take several hours or even days. This limits their usefulness in dry, resource-stressed environments including regions where there is no salt water to desalinate.

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MIT's new device, however, uses ultrasonic waves (ultrasound) to shake moisture loose from the sorbent. The released moisture then drains through small nozzles at the base of the device, where it can be collected and used.

According to the researchers, their ultrasonic prototype is 45 times more efficient at extracting captured water compared to evaporation alone. They detailed their findings in a paper published Nov. 18 in the journal Nature Communications.

"People have been looking for ways to harvest water from the atmosphere, which could be a big source of water particularly for desert regions and places where there is not even saltwater to desalinate," study co-author Svetlana Boriskina, a principal research scientist at MIT, said in a statement. "Now we have a way to recover water quickly and efficiently."

Drinking water — from days to minutes

MIT's approach uses ultrasound — sound waves that travel at frequencies above 20 kilohertz, beyond the range of human hearing — to liberate moisture from the sorbent.

The heart of the AWH device is a flat ceramic ring that vibrates when voltage is applied. Researchers found that high-frequency pulses were ideal for breaking the weak bonds between the absorbed water and the material surface.

"It's like the water is dancing with the waves, and this targeted disturbance creates momentum that releases the water molecules, and we can see them shake out in droplets," lead study author and MIT graduate student, Ikra Iftekhar Shuvo, said in the statement.

The researchers tested the device by placing quarter-sized samples of sorbent material in a humidity chamber set to different levels. When the samples were saturated, they were placed on the ultrasonic actuator and vibrated at high frequency. In each case, the device shook the samples dry in just a few minutes.

A potential challenge is that the new device needs a power source, unlike AWH systems that use sunlight alone. The researchers suggest that their device could be paired with a small solar cell that also acts as a sensor to detect when the sorbent is full. This could trigger a release cycle that would allow the system to collect and release water multiple times a day.

The team envisions a compact household setup that combines a fast-absorbing material with an ultrasonic actuator, each about the size of a window, that vibrates to release the trapped water.

"The beauty of this device is that it’s completely complementary and can be an add-on to almost any sorbent material," said Boriskina. "It's all about how much water you can extract per day. With ultrasound, we can recover water quickly, and cycle again and again. That can add up to a lot per day."