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Home / Science / GPS and water do not mix. Therefore, scientists have found a new way to navigate under the sea

GPS and water do not mix. Therefore, scientists have found a new way to navigate under the sea



Nearly half a century ago, the US Department of Defense embarked on a project to precisely locate positions on the planet’s surface using satellites. What today is known as GPS has come a long way, penetrating every aspect of our daily lives, from helping city dwellers find their way through unknown roads to supply assistance. emergency services.

And even today’s most sophisticated GPS systems still cannot map a large part of the Earth: the part below the ocean, the ocean, or the river. In fact, the technology does not mix well with water, which will disrupt the radio waves GPS relies on to operate.

MIT scientists are working to create a new type of underwater GPS that can be used to better understand the mysteries between the surface and the seabed. Researchers have now revealed a device called underwater backscatter localization (UBL) that reacts to acoustic signals to provide positioning information, even when it̵

7;s stuck at depth. Ocean. All this, even without the use of batteries.

Underwater devices already exist, such as those on whales as trackers, but they often function as sound generators. The generated sound signals are blocked by a receiver, so the source of the sound can be found. Such devices require batteries to function, which means they need to be replaced regularly – and when a migratory whale wears trackers, it’s no easy task.

On the other hand, the UBL system developed by the MIT team reflects the signals, rather than emitting them. The technology is built on so-called piezoelectric materials, which create a small charge in response to vibration. This charge can be used by the device to reflect the vibration back in the direction it came from.

Thus, in the researchers’ system, a generator sends sound waves through water to a piezoelectric sensor. The acoustic signals, when they touch the device, activate the material to store charge, which is then used to reflect the waves back into the receiver. Based on the amount of time it takes the sound waves to bounce off the sensor and return, the receiver can calculate the distance to UBL.

In contrast to traditional underwater acoustic communication systems, which require each sensor to generate its own signal, backscatter nodes communicate by simply reflecting the signals, the researchers said. sound in the environment ”. “These buttons can also work by capturing energy from audio signals. So (…) UBL will allow us to build a long, scalable, cost-free underwater GPS. the battery.”

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The UBL system developed by the MIT team reflects the signals, rather than emitting them.

Photo: Reza Ghaffarivardavagh / MIT

At least, that’s the theory. In practice, the piezoelectric material is not an easy component to work with: for example, the time it takes for the piezoelectric sensor to wake up and reflect the acoustic signal is random.

To solve this problem, the scientists developed a method called frequency hopping, which involves sending an audio signal to the UBL system over a series of frequencies. Since each frequency has a different wavelength, the sound waves are reflected back in different phases. Using a mathematical theorem called the Inverse Fourier transform, the researchers can use phase patterns and time data to reconstruct the distance to the tracking device with greater accuracy.

Frequency hopping shows some promising results in deep sea environments, but shallow waters are even more problematic. Due to the short distance between the surface and the seabed, the acoustic signals bounce uncontrollably at lower depths, as if in an anechoic chamber, before they reach the receiver – potentially interfering with other sound waves are reflected in the process.

One solution involves reducing the rate at which the signal is generated by the generator, to allow the echo of each reflected sound wave to be reduced before interfering with the next sound wave. However, the slower speed might not be an option when tracking the UBL in motion: it could be that by the time the signal is reflected to the receiver, the subject has moved, completely defeating the attack score. turmeric.

Although the scientists concede that addressing these challenges will require more research, a proof of concept for this technology has been tested in shallow water and the MIT team says that the system UBL system achieve accuracy to every centimeter.

It is clear that this technology could find countless applications if it were to achieve full-scale development. It is estimated that more than 80% of the ocean floor is currently unmapped, unobserved and undiscovered; A better understanding of aquatic life can be of significant benefit to environmental research.

UBL systems can also help undersea robots operate more accurately, track underwater vehicles, and provide insights into the effects of climate change on the ocean. Worthy amount of water in the ocean has yet to be mapped and piezoelectric material could be the solution.


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