According to scientists’ estimates, more than 95 percent of Earth’s oceans have never been observed, meaning we see less of our planet’s oceans than we do of the far side of the moon or the surface of Mars. One of the great challenges hindering extensive undersea exploration is the high cost of powering an underwater camera for extended periods of time. Doing so now requires tethering it to a research vessel or sending a ship out frequently to recharge its batteries.
Engineers at MIT have taken a major step toward overcoming this problem by developing an ultra-efficient battery-free wireless underwater camera. In fact, it is about 100,000 times more energy efficient than other underwater cameras. Even in dark underwater environments, the device can take color photos and transmit image data wirelessly through the water.
What makes this autonomous camera particularly unique is that it is powered by sound. It converts the mechanical energy of sound waves traveling through the water into electrical energy to power its imaging and communication equipment. After capturing and encoding the image data, the camera also uses sound waves to transmit the data to a receiver that can reconstruct the image.
Because it does not require power, the camera can operate continuously for weeks before being retrieved, which will allow scientists to search for new species in remote areas of the ocean. It can also be used to capture images of marine pollution or to monitor the health and growth of fish kept in aquaculture farms.
Sensors made of piezoelectric material are placed on the outside of the camera and are used to capture energy. The piezoelectric material generates an electrical signal when it is subjected to a mechanical force. When sound waves passing through the water touch the sensor, they vibrate and the mechanical energy is converted into electrical energy. These sound waves may come from any source, such as a passing ship or marine life. The camera stores the harvested energy until it accumulates enough to power the electronics that take the pictures and communicate the data.
To keep power consumption as low as possible, engineers use off-the-shelf ultra-low power imaging sensors. However, these sensors can only capture grayscale images. And, because most underwater environments lack a light source, they also needed to develop a low-power flash. They solved both problems using red, green, and blue LEDs. When the camera captures an image, it illuminates a red LED and then uses the image sensor to take the photo. It repeats the same process with green and blue LEDs.
