For continuously gathering information on ocean conditions, one thing that’s been proposed is a network of sensors that would transmit data from the sea floor. Changing their batteries, however, could be quite challenging. That’s where a new MIT system is designed to come in.
Created by a team led by Asst. Prof. Fadel Adib, the setup consists of two main parts: a battery-less seabed sensor, and a surface-located transmitter/receiver. The latter is battery-powered, and could be put on a boat, an anchored buoy, or the shore.
At regular intervals, the transmitter sends an acoustic wave down through the water, to the sensor. That wave causes piezoelectric material within the sensor to vibrate, generating a weak electrical current. The sensor then utilizes that current to reflect a modified acoustic signal back up to the receiver – it’s similar to the fashion in which existing RFID (radio frequency identification) labels work.
That signal actually consists of some acoustic waves, and some gaps between them in which no wave is reflected. Because the receiver interprets the waves and gaps as 1s and 0s, the sensor is thus able to transmit oceanographic data in the form of binary code.
In water-tank tests, the “Piezo-Acoustic Backscatter System” has already been successfully used to transmit three kilobytes per second of accurate data, from two sensors simultaneously at a distance of 10 meters (33 ft) between sensor and receiver. That data consisted of water temperature and water pressure.
Down the road, an interconnected network of the sensors might also be used for applications such as studying climate change and tracking marine life over extended periods of time. The devices could even be placed in lakes or seas on other planets, providing longer-term monitoring than would be possible via occasional visits from spacecraft.
“How can you put a sensor under the water on Titan that lasts for long periods of time in a place that’s difficult to get energy?” says Adib. “Sensors that communicate without a battery open up possibilities for sensing in extreme environments.”