Taking Underwater Communications And Power to New Depths With Light

A new algorithm optimizes the simultaneous transfer of data and power underwater

2 min read
Rays of sunlight penetrate the water beneath ripples on the surface of water
JONAS ALLERT/UNSPLASH

underwater oceanJONAS ALLERT/UNSPLASH

Scientists have made much progress in using light to transmit data in the open air, as well as to power various devices from a distance–but how to accomplish these feats underwater has been a bit murkier. However, in a new study published May 4 in IEEE Transactions on Wireless Communications, researchers have identified a new way to boost the transfer of power and data to devices underwater using light.

The ocean and other bodies of water are full of mysteries yet to be observed. Networks of underwater sensors are increasingly being deployed to gather information. Currently the most common approach for remotely transmitting signals underwater is via sound waves, which easily travel long distances through the watery depths. However, sound cannot carry nearly as much data as light can.

“Visible light communication can provide data rates at several orders of magnitude beyond the capabilities of traditional acoustic techniques and is particularly suited for emerging bandwidth-hungry underwater applications,” explains Murat Uysal, a professor with the Department of Electrical and Electronics Engineering at Ozyegin University, in Turkey.

He also notes that powering sensors and other devices underwater is another challenge, as replacing batteries in marine environments can be particularly difficult. Conveniently, any device that uses a solar panel to receive data via light signals could also be used to harvest energy simultaneously. In such a scenario, an autonomous underwater vehicle passing by a sensor could use a laser to both collect data and transfer power to the device.

Currently, the most effective method to do this is through an approach in which the power derived from the light signal is separated into Alternating Current (AC) and Direct Current (DC), whereby the AC signal is used to transmit data and the DC signal is used a power source. This is called the AC-DC separation (ADS) method.

However, some scientists, including Uysal’s team, have been trying to build upon a different approach that strategically switches between energy harvesting and data transfer as needed to optimize performance. This approach is called simultaneous lightwave information and power transfer (SLIPT). Yet, despite its sophistication, the SLIPT technique has not surpassed the traditional ADS method in terms of efficiency—until now.

In their study, Uysal and his colleagues devised a SLIPT optimization algorithm that allows energy to be more efficiently extracted from the light spectrum. Uysal notes that this allows their SLIPT method to “significantly outperform” the traditional ADS method.

“The feasibility of wireless power was already successfully demonstrated in underwater environments [using light], despite the fact that seawater conductivity, temperature, pressure, water currents, and biofouling phenomenon impose additional challenges,” says Uysal.

These examples have been largely experimental to date: For the real-world implementation of SLIPT, he says the commercialization of underwater devices capable of harvesting energy wirelessly will be necessary, as well as advances in underwater modems that can support communication using visible light. In the meantime, his team plans to explore ways of optimizing the trajectories of underwater autonomous vehicles, which could one day travel across vast areas of the world’s oceans, simultaneously collecting data from the futuristic sensors and remotely powering them using light.

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Europe Expands Virtual Borders To Thwart Migrants

Our investigation reveals that Europe is turning to remote sensing to detect seafaring migrants so African countries can pull them back

14 min read
A photo of a number of people sitting in a inflatable boat on the water with a patrol ship in the background.

Migrants in a dinghy accompanied by a Frontex vessel at the village of Skala Sikaminias, on the Greek island of Lesbos, after crossing the Aegean sea from Turkey, on 28 February 2020.

ASSOCIATED PRESS

It was after midnight in the Maltese search-and-rescue zone of the Mediterranean when a rubber boat originating from Libya carrying dozens of migrants encountered a hulking cargo ship from Madeira and a European military aircraft. The ship’s captain stopped the engines, and the aircraft flashed its lights at the rubber boat. But neither the ship nor the aircraft came to the rescue. Instead, Maltese authorities told the ship’s captain to wait for vessels from Malta to pick up the migrants. By the time those boats arrived, three migrants had drowned trying to swim to the idle ship.

The private, Malta-based vessels picked up the survivors, steamed about 237 kilometers south, and handed over the migrants to authorities in Libya, which was and is in the midst of a civil war, rather than return to Malta, 160 km away. Five more migrants died on the southward journey. By delivering the migrants there, the masters of the Maltese vessels, and perhaps the European rescue authorities involved, may have violated the international law of the sea, which requires ship masters to return people they rescue to a safe port. Instead, migrants returned to Libya over the last decade have reported enslavement, physical abuse, extortion, and murders while they try to cross the Mediterranean.

If it were legal to deliver rescued migrants to Libya, it would be as cheap as sending rescue boats a few extra kilometers south instead of east. But over the last few years, Europe’s maritime military patrols have conducted fewer and fewer sea rescue operations, while adding crewed and uncrewed aerial patrols and investing in remote-sensing technology to create expanded virtual borders to stop migrants before they get near a physical border.

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