Nearly half a century ago, the United States Department of Defense began work on a project to locate space on the planet’s surface using satellites.
What is now known as GPS has come a long way, penetrating every aspect of our daily lives, from strolling through unknown streets to emergency services.
And yet even the most sophisticated GPS systems today are not yet able to map a huge part of the Earth: the one under the oceans, seas or rivers. That’s because technology doesn’t mix well with water, which breaks down radio waves on which GPS is based to work.
Scientists at MIT have been looking for ways to create a new type of underwater GPS that could be used to better understand the mysteries between the surface and the seabed.
researchers they revealed a device called Underwater Backscatter Localization (UBL), which reacts to acoustic signals to provide positioning information, even when trapped in the ocean depths. All this without using even a battery.
The device that resists water forever
Underwater devices already exist, for example to be mounted as trackers, but they usually act as sound emitters.
The acoustic signals produced are intercepted by a receiver which in turn can detect the origin of the sound. Such devices require battery operation, which means that they must be replaced regularly.
But the UBL system developed by the MIT team reflects and does not emit signals.
The technology is based on so-called piezoelectric materials, which produce a small electrical charge in response to vibration. This electric charge can be used by the device to reflect the vibration back in the direction it came from.
Therefore, in the researchers’ system, a transmitter sends sound waves through water to a piezoelectric sensor. Acoustic signals, when they strike the device, trigger the material to store an electrical charge, which is then used to reflect a wave back to a receiver.
The receiver can calculate the distance to the UBL based on how long the sound wave is reflected and returned.
“Unlike traditional underwater acoustic communication systems, which require each sensor to generate its own signals, backscatter nodes communicate by simply reflecting acoustic signals in the environment,” said the researchers.
“These nodes can also be powered by harvesting energy from acoustic signals. Thus, UBL would allow us to build a long-lasting, scalable, battery-free underwater GPS. ”
There are still steps to take to get to know underwater
This is the theory. In practice, piezoelectric materials are not an easy component to use. For example, the time required for a piezoelectric sensor to “wake up” and reflect an audible signal is random.
To solve this problem, scientists have developed a method called frequency hopping, which involves sending sound signals to the UBL system over a range of frequencies.
Because each frequency has a different wavelength, the reflected sound waves return to different phases.
The frequency jump showed some promising results in deep environments, but shallow waters proved to be more problematic.
Due to the short distance between the surface and the seabed, the beeps twist uncontrollably back and forth to shallower depths before they reach the receiver.
While scientists have acknowledged that addressing these challenges would require further research, evidence of the concept for the technology has already been tested in shallow water, and the MIT team said the UBL system has achieved centimeter accuracy.
It is clear that technology could find countless applications if it ever reached a large-scale development.
It is estimated that more than 80% of the ocean floor is currently unmapped, unobserved and unexplored. A better understanding of underwater life could bring significant benefits to environmental research.
UBL systems could also help submarine robots work more accurately, track underwater vehicles and provide information on the impact of climate change on the ocean.