MIT battery-free wireless camera captures the unexplored ocean

MIT Battery-free wireless underwater camera

MIT engineers have designed a battery-free, wireless underwater camera to capture unexplored parts of the ocean, which is more than 95 percent of its total. The costs of powering an underwater camera for a long time by connecting it to a vessel or sending a ship to recharge its batteries would be high. Thus, MIT engineers came up with a wireless undersea camera powered by sound waves that can run for weeks in the most remote parts of the sea. After capturing and encoding image data, the autonomous camera also uses sound waves to transmit data to a receiver that reconstructs the image.

The device can be used as a tool for scientists to investigate unknown aquatic regions, track pollution, and observe the effects of climate change. According to their site, this device is roughly 100,000 times more energy-efficient than other undersea cameras. It can take color photos, also in the deepest and darkest environments, and transmits image data wirelessly through the water. To achieve that, it converts mechanical energy from sound waves traveling through water into electrical energy that powers its imaging and communications equipment.

‘One of the most exciting applications of this camera for me personally is in the context of climate monitoring. We are building climate models, but we are missing data from over 95 percent of the ocean. This technology could help us build more accurate climate models and better understand how climate change impacts the underwater world,’ says Fadel Adib, associate professor in the Department of Electrical Engineering and Computer Science and director of the Signal Kinetics group in the MIT Media Lab, and senior author of a new paper on the system.

all images by MIT (Massachusetts Institute of Technology)

shooting a low-energy colored image

To achieve a long period of operation, the new MIT camera (see more here) uses micro energy harvesting techniques utilizing piezoelectric elements to produce its own energy autonomously. The camera gains energy using transducers that are placed around its exterior. When a sound wave (from a passing ship or marine life) traveling through the water hits the transducers, they vibrate and convert that mechanical energy into electrical energy. The camera saves harvested energy until it has enough to power the electronics that take photos and communicate data. Thanks to ultra-low-power imaging sensors, it keeps its power consumption as low as possible. However, these sensors can only capture grayscale images. To reconstruct the colored image of the subject and to enable visibility in low-light environments, a low-power flash is needed as well. To capture a colored image, the device uses three different LEDs (a red, a green, and a blue one). The camera shoots a grayscale image while flashing the red LED; then, it repeats the same process with the other LEDs. When the image data are combined in post-processing, the color image can be reconstructed.

‘When we were kids in art class, we were taught that we could make all colors using three basic colors. The same rules follow for color images we see on our computers. We just need red, green, and blue — these three channels — to construct color images,’ says Akbar from the research team.

Sending data with sound

In order to transmit the image, a transceiver sends sound signals to the camera through the water column.

A component in the camera reacts to the sound waves by either reflecting or absorbing the received signal. These reflections or absorptions can be understood as digital 1’s or 0’s. The transceiver taking track of the reflection pattern can reconstruct the digital image.‘This whole process, since it just requires a single switch to convert the device from a nonreflective state to a reflective state, consumes five orders of magnitude less power than typical underwater communications systems,’ mentions Akbar from the team.

So far, the researchers have tested the camera in different underwater environments, capturing from plastic bottles to starfishes. The device was also effective at repeatedly imaging the underwater plant Aponogeton ulvaceus in a dark environment over the course of a week to monitor its growth. To further enhance the camera’s performance, they plan to increase its memory so it can capture photos in real-time, stream images, or even shoot underwater videos. They also want to extend the camera’s range, transmitting data up to 40 meters to the receiver. Pushing that range wider would enable the camera to be used in more underwater settings.

‘This will open up great opportunities for research both in low-power IoT devices as well as underwater monitoring and research,’ says Haitham Al-Hassanieh, an assistant professor of electrical and computer engineering at the University of Illinois Urbana-Champaign, who was not involved with this research.