According to scientists, more than 95 percent of the oceans on Earth have never been seen.As a result, we know less about the oceans on Earth than we do about the far side of the moon or the surface of Mars. Widespread underwater exploration is hindered by the high cost of powering an underwater camera for an extended period of time, whether by tethering it to a research vessel or sending a ship to recharge its batteries.
miresearchers have made significant progress toward solving this issue by creating a battery-free, wireless underwater camera that is roughly 100,000 times more energy-efficient than other underwater cameras. Even in low-light conditions underwater, the camera captures color images and wirelessly transmits them.
Sound provides the camera’s power. To power its imaging and communications technology, it transforms mechanical energy from sound waves moving through water into electrical energy. The camera sends data to a receiver using sound waves. Once the image has been captured and encoded, the receiver puts the image back together.
Scientists can search remote areas of the ocean for new species because the camera doesn’t require a power source and can run for weeks on end before retrieval. Additionally, it could be used to take pictures of ocean pollution or track the wellbeing and development of fish raised in aquaculture farms.
“For me, the use of this camera in the context of climate monitoring is one of its most exciting applications. Over 95% of the ocean’s data is missing from the climate models we are building. With the aid of this technology, we may be able to create climate models that are more precise and comprehend the effects of climate change on the ocean environment, “explains Fadel Adib, senior author of the study and associate professor in the department of electrical engineering and computer science as well as the head of the Signal Kinetics group at the MIT Media Lab.
Co-lead authors and research assistants from the Signal Kinetics group, Sayed Saad Afzal, Waleed Akbar, and Osvy Rodriguez, research scientist Unsoo Ha, and former members of the group, Mario Doumet and Reza Ghaffarivardavagh, also collaborated on the paper with Adib. The research article appears in Nature Communications.
Eliminating batteries
For the researchers to build a camera that could run on its own for a long time, they needed a tool that could collect energy underwater and use very little power.
Transducers made of piezoelectric materials are positioned all over the camera’s exterior to collect energy. When a mechanical force is applied to piezoelectric materials, an electric signal is generated. The transducers vibrate and change the mechanical energy of a sound wave passing through the water into electrical energy when it strikes them.
The source of those sound waves could be anything, such as a passing ship or aquatic life. Until it has accumulated enough to power the electronics that take photos and transmit data, the camera stores the harvested energy.
The researchers used off-the-shelf, ultra-low-power imaging sensors to keep power usage to a minimum. These sensors, however, can only record grayscale images. They also needed to develop a low-power flash because most underwater environments are dark.
“We were attempting to minimize the hardware as much as possible, and this imposes new limitations on the way the system is constructed, information is sent, and image reconstruction is carried out. “To figure out how to do this, it took some creativity,” Adib claims.
They used red, green, and blue LEDs to simultaneously solve both issues. A red LED is shone by the camera as it takes a picture, which is then processed by image sensors. With green and blue LEDs, the same procedure is repeated.
The red, green, and blue colored lights are reflected in the white portion of each photograph, Akbar explains, despite the fact that the image appears to be black and white. The color image can be recreated by combining the image data during post-processing.
“We were taught as children in art classes that the three primary colors could be used to create any color. The same guidelines apply to color computer images. “To create color images, all we need are the three channels: red, green, and blue,” he claims.
Sound and data transmission
Using a technique known as underwater backscatter, image data is encoded as bits (1s and 0s) and sent to a receiver one bit at a time after being captured. The camera serves as a mirror to reflect the sound waves that are transmitted by the receiver through the water. Either the camera reflects the wave back to the receiver or turns its mirror into an absorber to stop reflection.
If a signal is reflected back from the camera, it is detected by a hydrophone next to the transmitter. It receives a bit-1 if there is a signal, and a bit-0 if there is no signal. This binary data is used by the system to reconstruct and edit the image.
This entire process uses five orders of magnitude less power than typical underwater communications systems, according to Afzal, because it only calls for one switch to change the device from a nonreflective state to a reflective state.
The camera was tested by the researchers in a variety of underwater settings. In one, they managed to photograph in color plastic bottles drifting in a pond in New Hampshire. Additionally, they were able to capture an African starfish in such clear detail that the tiny tubercles along its arms could be seen. The growth of an underwater plant called Aponogeton ulvaceus was tracked by taking pictures of it over the course of a week in a dark room.
The researchers intend to improve the device so it can be used in real-world settings now that they have shown a functioning prototype. They want to increase the camera’s memory so that it can take underwater videos, stream images, and take photos in real-time.
They also want to increase the camera’s field of view. Even though they could send data 40 meters away from the receiver, if they could make the range longer, the camera could be used in more underwater environments.
This study is being paid for by the National Science Foundation, MIT Media Lab, Doherty Chair in Ocean Utilization, Office of Naval Research, Sloan Research Fellowship, and Office of Naval Research.
