Underwater “GPS” to Use Sound as a Power Source

GPS technology has become an essential ally for any trip. At least on the surface of the Earth. Because if we talk about the underwater world, the rules change substantially. The problem lies in the fact that the radio waves of this satellite technology degrade rapidly underwater. If you want to travel along the bottom of the Mediterranean, you’d be better off resorting to sound waves, i.e., sonar. At present, however, there is another pitfall to contend with: the emission of sound waves requires a lot of energy. That is not a drawback when dealing with a submarine, but if it is a device for tracking a shark or a whale, batteries are required. These creatures spend months at sea, making replacement difficult. MIT has been thinking about the problem and seems to have found the solution: using the sound waves themselves as energy sources.

Enter UBL

The American researchers have dubbed this tech as UBL, which stands for Underwater Backscatter Localization. Although the name sounds complicated, the concept is relatively simple. What it does is harness the impact of sound waves on a piezoelectric mechanism instead of using batteries. As a reminder, piezoelectricity is electricity generation by mechanical pressure on specific materials such as quartz. MIT’s UBL is a prototype underwater tracker that could technically operate indefinitely.

The device essentially absorbs some of the sound wave energy from the underwater environment onto the piezoelectric mechanism while deflecting the rest as an acoustic signal. A receiver then translates this sequence —this is the “backscatter” part— into a binary code. Thus, the UBL emits responses to the acoustic pulses that provide information about the water’s salinity and temperature. It will also pinpoint a sea creature’s exact location and even the effects of climate change on the underwater environment.

Ocean echoes 

Although the technology holds great promise, it faces several challenges. Chief among them are echoes. This is because acoustic signals travel to the receiver, but also the seabed and the surface, bouncing back and forth. This is not a significant problem in deep waters since it is sufficient to use waves at various frequencies, a technique known as frequency hopping. However, in shallow waters, the waves’ echo is multiplied by bouncing against the bottom and the surface. MIT engineers have chosen to modulate the sound waves by reducing the signals’ frequency or bit rate to solve this. With this approach, no new signals are emitted until the previous one has faded away.

The only problem with this approach is that moving objects require a higher bit rate to be monitored. If the sound waves are spaced too far apart, the object will have already changed its position. Finding the right balance point between water depth, sound frequencies, and the tracked objects’ movement is now the main focus of research.

Such developments are crucial because, as the researchers point out, the surface of the Moon is better known than the seafloor. One of the reasons is that driverless rovers cannot be sent out for long periods, as they would go astray. And, speaking of rovers, we recommend this article on underwater robots inspired by sea creatures. 

Source: MIT