This underwater camera works wirelessly without batteries

Enlarge / MIT engineers have built a wireless, battery-less underwater camera that could help scientists explore unknown regions of the ocean, track pollution or monitor the effects of climate change. Adam Glanzman

MIT engineers have built a wireless, battery-less underwater camera that can harvest power on its own while consuming very little power, according to a new paper in the journal Nature Communications. The system can take color photos of distant submerged objects, even in dark environments, and transmit the data wirelessly for real-time monitoring of underwater environments, aiding in the discovery of new rare species, or monitoring ocean currents , pollution or commercial and military operations.

We already have a variety of methods for taking underwater images, but according to the authors, "most oceanic and marine organisms have yet to be observed." This is partly because most existing methods require tethering to ships, underwater drones or power plants for power and communication. Methods that do not use a connection must incorporate battery power, which limits their lifespan. While it is in principle possible to harvest energy from ocean waves, underwater currents or even sunlight, adding the necessary equipment to do so would result in an underwater camera much bulkier and more expensive.

The MIT team therefore set out to develop a solution for a wireless and battery-free imaging method. The design goal was to minimize the hardware needed as much as possible. Since they wanted to keep power consumption to a minimum, for example, the MIT team used inexpensive off-the-shelf imaging sensors. The trade-off is that these sensors only produce grayscale images. The team also needed to develop a low-power flash, as most underwater environments don't get much natural light.

Enlarge / Overview of how the underwater backscatter imaging system works. SS Afzal et al., 2022

The solution to both challenges turned out to incorporate red, green and blue LEDs. The camera uses the red LED for in-situ illumination and captures that image with its sensors, then repeats the process with the green and blue LEDs. The image may appear black and white, according to the authors, but all three colors of light from the LEDs are reflected in the white portion of each image. Thus, a color image can be reconstructed during post-processing.

“When we were kids in art class, we were taught that we could create any color using three basic colors,” says co-author Fadel Adib. "The same rules apply to color images that we see on our computers. We just need red, green and blue, those three channels, to build color images."

Instead of a battery, the sensor relies on piezo-acoustic backscatter for ultra-low-power communication after image data has been encoded into bits. This method does not need to generate its own acoustic signal (as with sonar, for example), relying instead on modulating the reflections of incident underwater sounds to transmit the data one bit at a time. These data are picked up by a remote receiver capable of recovering the modulated patterns, and the binary information is then used to reconstruct the image. The authors estimate that their underwater camera is about 100,000 times more energy efficient than its counterparts, and could run for weeks.

Naturally, the team built a proof-of-concept prototype and ran tests to demonstrate that their method worked. For example, they pictured pollution (in the form of...