At the Massachusetts Institute of Technology, engineers have built a wireless camera that does not require a battery to operate underwater. The necessity arose when scientists wanted to observe life under the oceans. They realized they knew less about earth’s oceans than the surface of Mars or the far side of the moon.
An underwater camera must remain tethered to a research vessel for receiving power or sent to a ship periodically to recharge its batteries. This limitation is a big challenge, preventing easy and widespread explorations underwater.
MIT engineers took up the challenge of overcoming the problem. They came up with a camera that does not require batteries, works underwater, and transmits wirelessly. Compared to other underwater cameras, the new camera is more than 1000,000 times more energy-efficient. The device even takes color photos, transmitting them wirelessly through the water.
Sound powers the new autonomous camera—converting the mechanical energy of sound waves into electrical energy for powering its imaging and communications circuitry. After capturing the image, the camera encodes the data and uses underwater waves to transmit it to a receiver for reconstructing the image.
As the camera does not need a rechargeable power source, it can run for a long time before retrieval. This enables scientists to explore remote areas under the ocean. The camera is helpful in capturing images of ocean pollution and monitoring the health and growth of fish.
For a camera that can operate autonomously underwater for long periods, engineers required a mechanism for harvesting underwater energy by itself while using up very little power internally.
The camera uses transducers made of piezoelectric materials that the engineers placed around its exterior. The transducers produce an electrical signal when sound waves hit them. The sound waves may come from any source, such as from marine life or a passing ship. The camera then stores the energy it has harvested, until it has enough for powering its electronics.
The camera has ultra-low-power imaging sensors to keep its power consumption at the lowest possible levels—but these sensors capture only gray-scale images. Moreover, underwater environments are mostly dark, so the camera also needs a low-power flash.
MIT engineers solved both problems simultaneously by using three LEDs of red, blue, and green colors. For capturing an image, the camera first uses the red LED, then repeats the process with a blue LED, and finally with the green LED.
Although each image is black and white, the white part of each photo has the reflection of its respective colored light. Combining the image data during post-processing reconstructs the color image.
The engineers use an underwater backscatter process to transmit the captured image data after encoding it as bits. A nearby receiver transmits sound waves through the water to the camera, reflecting it back just as a mirror would. The camera can choose to either reflect the sound back to the receiver or act as an absorber and not reflect it.
The transmitter has a hydrophone next to it. If it senses a reflected signal from the camera, it treats it as a bit 1. If there is no signal, then it is a bit 0. The receiver uses this binary information for communicating with the camera.
