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The device could help scientists explore uncharted regions of the ocean, track pollution and monitor the effects of climate change -- ScienceDaily

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Scientists estimate that over 95% of the Earth’s oceans have never been observed. That means there are fewer oceans on Earth than on the far side of the Moon or on the surface of Mars.

The high cost of powering underwater cameras for extended periods of time, either by tethering them to survey vessels or by sending vessels to recharge their batteries, is a major challenge that hinders widespread seafloor exploration.

Researchers at MIT have taken a big step towards overcoming this problem by developing a battery-free wireless underwater camera that is about 100,000 times more energy efficient than other submarine cameras. The device takes color photos even in dark underwater environments and transmits image data wirelessly through the water.

Autonomous cameras are voice activated. It converts the mechanical energy of sound waves traveling through water into electrical energy to power imaging and communication equipment. After capturing and encoding the image data, the camera uses sound waves to send the data to a receiver that reconstructs the image.

Requiring no power, the camera can run for weeks between retrievals, allowing scientists to search for new species in remote areas of the ocean. It can also be used to capture images of marine pollution and monitor the health and growth of farm-raised fish.

“Personally, one of the most exciting applications for this camera is in the context of climate monitoring. We are building climate models, but we lack data from over 95% of the ocean. could help us build more accurate climate models, allowing us to better understand how climate change will affect the underwater world,” said a professor of electrical engineering and computer science. Fadel Adib, associate professor, director of the Signal Kinetics Group at the MIT Media Lab, and senior author of the paper.

Joining Adib on the paper are co-lead authors and research assistants in the Signal Kinetics group Sayed Saad Afzal, Waleed Akbar and Osvy Rodriguez, research scientist Unsoo Ha, and former group researchers Mario Doumet and Reza Ghaffarivardavagh.thesis is Nature Communications.

No batteries required

To build a camera that can operate autonomously for long periods of time, researchers needed a device that could automatically collect energy underwater while consuming very little power.

The camera acquires energy using a transducer made of piezoelectric material placed on its outside. Piezoelectric materials generate an electrical signal when a mechanical force is applied. When a sound wave traveling through water strikes a transducer, it vibrates and converts its mechanical energy into electrical energy.

These sound waves can come from any source, including passing ships and marine life. The camera stores the energy it collects until it has enough energy to power the electronic devices that take pictures and communicate data.

To keep power consumption as low as possible, the researchers used commercially available ultra-low-power image sensors. However, these sensors can only capture grayscale images. We also had to develop a low-power flash, as most underwater environments lack a light source.

“We were trying to keep the hardware as minimal as possible, but it introduced new constraints on how we built the system, how we transmitted information, and how we reconstructed images. It took a lot of creativity to figure it out,” Adib said. Say.

I solved both problems at the same time by using red, green and blue LEDs. When the camera captures an image, the red LED lights up and the image sensor is used to capture the picture. Repeat the same process for the green and blue LEDs.

Although the images appear black and white, Akbar explains that red, green, and blue colors of light are reflected off the white areas of each photo. Combining the image data in post-processing can reconstruct a color image.

“When I was a kid, I was taught in art class that all colors can be created using three basic colors. The same rule applies to color images you see on your computer. , blue only, these three channels — to build a color image,” he says.

Data transmission with sound

Once the image data is captured, they are encoded as bits (1s and 0s) and sent to the receiver one bit at a time using a process called underwater backscattering. The receiver sends sound waves through the water to the camera, and the camera acts as a mirror reflecting those waves. The camera either reflects the waves back to the receiver or changes the mirror to an absorber so that it doesn’t reflect.

A hydrophone next to the transmitter senses whether the signal is reflected from the camera. Bit 1 if signal received, bit 0 if no signal. The system uses this binary information to reconstruct and post-process the image.

“This entire process requires only one switch to transform the device from non-reflective to reflective, consuming five orders of magnitude less power than typical underwater communication systems,” said Afzal. increase.

Researchers tested the camera in several underwater environments. One is a color image of a plastic bottle floating in a pond in New Hampshire.They were also able to take high-quality photographs of an African starfish, with small nodules along its arms clearly visible. Aponogeton Alvaceus in a dark environment for one week to monitor its growth.

Having demonstrated a working prototype, the researchers plan to extend the device to enable practical deployment in real-world settings. I want to increase my camera’s memory so that I can capture photos in real time, stream images, and shoot underwater videos.

We also want to extend the range of the camera. They managed to transmit data from a receiver he was 40 meters away, but increasing the range would allow the camera to be used in more underwater settings.

This work is supported, in part, by the Office of Naval Research, a Sloan Research Fellowship, the National Science Foundation, the MIT Media Lab, and the Doherty Chair of Marine Utilization.