Antarctic Ocean’s briny puzzle

Antarctic Ocean’s briny puzzle


Something strange is happening in the Antarctic Ocean, which has scientists baffled. They have some theories but have been unable to nail down the cause of the problem.

The Antarctic Ocean’s surface waters have been turning salty since 2015.

Normally, ice melts in summer. The meltwater forms a layer on the surface, floating over denser saltwater below — a phenomenon known as ‘stratification’. The floating freshwater acts like a lid, preventing warmer saltwater from rising to the surface.

In winter, the freshwater would freeze again — but less and less due to global warming.

Since 2015, for reasons not well understood, the stratification is weakening, allowing more subsurface saltwater to mix with the freshwater, turning the surface water saltier.

This affects ice formation in winter — loss of cryosphere.

A group of researchers from the University of Southampton, UK, used satellite images to study ‘salinity signatures’.

They note that the rapid changes observed over the past decade contradict the conventional wisdom that global warming drives up the volumes of surface freshwater.

“This suggests that current understanding and observations may be insufficient to accurately predict future changes,” they say in a paper published in PNAS, suggesting closer monitoring.

Caroline Holmes, a polar researcher at British Antarctic Survey, pointed out to Livescience.com that the Southern Ocean below the surface is “chronically underobserved.”

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Published on July 14, 2025



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Adding salt to a heating solution

Adding salt to a heating solution


Store heat energy for months on end and draw it out when needed in the really cold months. Sounds far-fetched? Not to Dr Sandip Saha, Dr Chandramouli Subramaniam and Dr Rudrodip Majumdar, who have developed a prototype device using a salt — strontium bromide — to demonstrate that heat can be stored for long periods, much like the gas cylinders we use at home.

In cold climes, especially in the Himalayan north, wood is predominantly used as fuel for heating. Diesel as fuel is not only a pollutant but also scarcely available in these regions.

So, what is the alternative? Enter strontium bromide. “Strontium bromide stores heat much like a battery stores electric energy,” Saha, Professor, IIT-Bombay, Department of Mechanical Engineering, told businessline.

Dr Rudrodip Majumdar, Associate Professor, National Institute of Advanced Studies

Dr Rudrodip Majumdar, Associate Professor, National Institute of Advanced Studies

Thanks to its high energy density, chemical stability, non-toxicity, non-explosive nature, and environmental safety, the salt lends itself to use here, he says.

Prototype design

The team developed a prototype featuring solar thermal air collectors, which use sunlight to heat air during summer. The hot air is then used to warm a form of hydrated strontium bromide (hexahydrate). In this form, the strontium bromide crystals contain water molecules within their structure.

The salt absorbs heat energy as it undergoes a dehydration reaction — namely removal of water from the salt. “This reaction helps store the absorbed solar energy as chemical potential in the salt,” says Saha.

Now, to get heat out of the salt, all you have to do is reverse the process — pass moist air through it. In other words, when the salt is ‘rehydrated’, it releases the stored heat.

Apart from the solar thermal collectors, the device consists of a reactor chamber filled with strontium bromide, and a small air circulation system for the dehydration and rehydration cycles. The set-up is encased in a weatherproof unit designed for Himalayan conditions and is insulated using glass wool.

The storage module, points out Saha, “is about the size of two LPG cylinders we use at home. The heating can be done in sunnier regions such as Gujarat or Rajasthan and the dehydrated salt can be carted up the hills just before winter sets in”. For household use, the system would primarily consist of a reactor unit (containing the salt-silica gel), a blower, and a small control system. The heating solution lends itself to spaces of about 100 sq ft.

Cost-efficiency

The unit does not require high maintenance, the researchers say. The prototype has been used to demonstrate six charging and discharging cycles with no slip in performance. Salts such as strontium bromide are theoretically capable of about 600 cycles.

How do the costs compare with using diesel for heating? “Electricity from diesel costs us ₹50 per unit (kWh),” says Majumdar, currently Associate Professor at the National Institute of Advanced Studies. “If we add a carbon penalty, it could go up to ₹78 per unit. The thermochemical solution is expected to come at half the price.”

According to an article on the IIT-Bombay website, the study determined the thermochemical systems’ ‘levelised cost of heating’ (LCOH) — the average cost of producing usable heat over the lifetime of a heating system — to be ₹33–51 per kWh in different Himalayan cities. This makes it competitive with, or cheaper than diesel heating for daily use, especially when factoring in environmental costs. In Leh, specifically, LCOH dropped to ₹31 per kWh, the lowest among all the locations studied (Darjeeling, Shillong, Dehradun, Shimla, Jammu, Srinagar, and Manali being the rest).

Reinforcement

But the setup did come with its own problems initially. Like common table salt, strontium bromide, too, readily absorbs moisture from the air. If exposed to excessive humidity, the salt can liquefy, making it useless for repeated cycles.

Saha and his team found that mixing strontium bromide with silica gel helped in two ways: it absorbs extra moisture from the air during the hydration (discharging) phase, preventing the strontium bromide from dissolving; and, as the salt itself is not very strong structurally, silica gel provides support, allowing the salt to withstand the hundreds of cycles without degrading.

The optimal mix is 75 per cent strontium bromide and 25 per cent silica gel. This enables the salt mixture to be recycled for extended periods, potentially 8-9 years.

But why salt? Why not use solar power for heating?

Says Majumdar, “In the case of solar power for heating, batteries would be necessary to store energy captured during the day, for use at night. In colder climes, the state of charge for the batteries degrades faster and the chemical reactions that generate electricity within the battery slow down, reducing the battery’s efficiency.”

In contrast, he says, the salt-based system deals with only heat energy, without conversion to other forms. Therefore, intermediate losses, as seen with energy conversion, are avoided. Solar panels typically convert sunlight to electricity with an efficiency range of 15-22 per cent for commercially available panels.

Further, Majumdar points to the environmental impact: “While places like Ladakh have good ‘direct normal irradiance’ (DNI) for solar charging during summer, the aim is to avoid adding construction activity to already vulnerable areas. Transportation of the salt modules via existing supply routes (such as food grains or army supplies) makes it a viable solution.”

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Published on July 14, 2025



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Photonic radars — reality, hype and beyond

Photonic radars — reality, hype and beyond


Conventional radars struggle to generate high-frequency signals beyond 40 GH

Conventional radars struggle to generate high-frequency signals beyond 40 GH
| Photo Credit:
enot-poloskun

On June 29, the Defence Research and Development Organisation (DRDO) announced that it had developed a photonic radar system and was readying it for trials later this year. India will likely become the fourth country, after the US, China and Israel, to induct these radars.

While conventional radars use electronic devices (oscillators) to generate radio frequency (RF) signals, photonic radars combine two laser beams of slightly different frequencies (optical heterodyning) to generate, process, and analyse RF signals. Conventional radars find it difficult to generate high-frequency signals beyond 40 GHz. Photonic integrated circuits (PIC) can generate RF signals starting from 100 GHz and all the way to terahertz. This provides many advantages, as spelt out by DRDO.

The photonic radar’s ability to detect is significantly higher. It can, for example, call out an incoming hypersonic missile.

It generates purer signals — less of the ‘noise’ that emanates from the heat generated by electronic components — leading to sharper detection of the ‘echo’ from the target. Moreover, photonic radars can generate high bandwidth signals — the higher the bandwidth, the greater the resolution. In simple terms, you not only detect the target well, but you also ‘see’ it better.

Further, photonic radars are highly jam-resistant — photonic components are practically immune to electromagnetic jamming. Jammers send a lot of ‘noise’ or fake signals to confuse the radar, but photonic radars are not fooled. First of all, jammers typically do not send high-frequency signals. More importantly, photonic radars are capable of ‘frequency hopping’ — they keep changing their frequencies, which confuses the jammers.

Finally, photonic components do not have copper and are, hence, lighter. This is an ace up the sleeve. Imagine fitting these smaller, lighter radar systems in satellites, swarms of drones and fighter jets!

Now, if you pair photonic radars with gallium nitride (GaN) semiconductors, you will have a radar that is potent — GaN semiconductors can amplify signals efficiently, as explained in ‘Stealth technology: To see and not be seen’ (Quantum dated June 15, 2025), allowing them to travel farther and return stronger echoes.

DRDO has a working prototype, which means ‘technological readiness level’ of 6. That is heartening.

Swiping away hype

While DRDO has been measured in its announcement, social media comments show that many Indians are kvelling at the news. However, some reality checks are needed. One big challenge for India is in gaining access to PICs, since the country is not equipped to fabricate them. Moreover, ‘photonics’ call for special materials, mainly indium phosphide and silicon photonics, which are not easily available.

India will have to design the circuits and get them fabbed elsewhere — but where? The US has export restrictions. Accessing from China is, of course, out of the question. Likewise, other components like tunable lasers and modulators are tough to get. So, ‘from the working prototype to industry’ is not a short hop, but a giant leap.

Edging ahead

Photonic radars are cutting edge; other countries are honing the edge. India, with its development of photonic radars, is not leading but catching up. In these emerging technologies, no country is much ahead of the start-line. India has an opportunity to lead.

There are at least two radars on the tech treadmill that promise to be better than photonic radars.

One is the quantum radar. As the name suggests, it uses quantum technology for detection and imaging. As a 2019 article in MIT Technology Review says, the US has made some progress.

At the core of this technology is the production of a pair of entangled photons — sending one to the target and then comparing it on reflection with the second photon; the difference will tell the target’s tale: its location and how fast it is moving. This is high physics. By the looks of it, quantum radars are a long way away.

The second potential technology is the ‘terahertz radar’, which operates in the electromagnetic spectrum between microwaves and infrared light, typically 0.1-10 THz — called the ‘terahertz gap’ — where the signal oscillates a trillion times a second. The corresponding wavelength is about 0.3 mm.

Terahertz technology is not as recondite as quantum radar — quite a few countries have made some progress, though there is no record of a military deployment. The good news is that India is also in the game. The Ultrafast Terahertz Spectroscopy and Photonics Lab at the Jawaharlal Nehru Centre for Advanced Scientific Research, Bengaluru, the Terahertz Communication and Sensing Group at IIT-Roorkee, and the University of Hyderabad are keeping India in the reckoning.

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Published on July 14, 2025



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Altermagnets

Altermagnets


Researchers have discovered a rare and useful behaviour in a new class of magnetic materials called altemagnets, specifically in a compound named chromium antimonide (CrSb).

Altermagnets are magnetic materials whose surface (outside) display no magnetic properties — they won’t stick to a fridge. But the ‘insides’ have magnetic properties.

Altermagnets combine the best features of ferromagnets (like fridge magnets) and antiferromagnets (which cancel out their own magnetism). Although they show no external magnetism, their internal electron behaviour can be highly useful for advanced technologies like spintronics, which use electron spin rather than charge.

CrSb stands out for its strong magnetic order, which lasts well above room temperature, and a giant “spin-splitting” effect — over 30 times that of room temperature — making it a top candidate for practical applications.

Now, scientists at the SN Bose National Centre for Basic Sciences (SNBNCBS) have discovered a new property in CrSb called direction-dependent conduction polarity (DDCP). When current flows along the layers of the crystal, electrons carry it (n-type behaviour). But across the layers, the current is carried by holes (p-type behaviour). This switch, depending on direction, is extremely rare and challenges the conventional p-type/n-type classification of materials.

CrSb is the first altermagnet known to show this dual nature. It could allow future devices — like solar cells or thermoelectrics — to function without combining different materials or doping, making them simpler, smaller, and more efficient. Made from abundant, non-toxic elements, CrSb is also environmentally friendly. “It holds great promise for the next generation of electronic and spintronic devices,” says a press release.

Phase-changing emulsion

Researchers at the Fraunhofer Institute, Germany, have developed emulsions made of phase-changing materials (PCMs) and water, or mixtures of water and glycol for applications such as air conditioning inside buildings and cooling industrial machinery.

PCM emulsions are a mix of paraffins and water, or water-glycol, and are used primarily in the mobility sector, where the addition of glycol keeps the mixture from freezing.

The researchers used paraffins, which are dispersed or emulsified in water, or the water-glycol mixtures. Surfactants stabilise the ultrafine paraffin droplets distributed throughout the water, which lends the mixture thermal and mechanical stability.

The emulsions use the high energy density of paraffins during the phase transition from solid to liquid. Because the paraffins are emulsified in water, they can remain liquid regardless of their phase state in the emulsion that is created and can be used as heat transfer liquids in heating and cooling networks — meaning that the mixtures can be pumped through pipes. During the phase change, the PCMs absorb or release large amounts of heat even as their temperature remains constant. This allows for achieving twice the storage density of water — which is currently used as a heat carrier in conventional heating and cooling supply networks — in the PCM melting range while keeping the volume the same.

In addition to their high storage density, PCM emulsions also have a number of other advantages. Owing to the high heat storage capability of PCMs, systems that use them can be designed to take up less space.

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Published on July 14, 2025



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Time to roll out solar-roofed vehicles

Time to roll out solar-roofed vehicles


RE BOOST. An e-truck with a solar hood and photovoltaic roof, developed by Fraunhofer Institute of Germany

RE BOOST. An e-truck with a solar hood and photovoltaic roof, developed by Fraunhofer Institute of Germany

Between August 25 and 31, an interesting car race is set to take place in Australia. The racing cars will be flagged off at Adelaide in the south and they will zip 3,000 km across the country and pull up at Port Darwin in the north.

What’s interesting here is that the racing cars are solar-powered. And the race is set in peak Australian winter, under limited sunshine.

The annual Bridgestone World Solar Challenge has been around for several years, but will now see an Indian participation for the first time. A group of students from the Centre for Innovation, IIT-Madras, will race their solar-powered ‘Aagneya’ car.

The objective of the challenge is to promote solar in vehicles, but, clearly, there may never be a time when regular passenger cars are fully solar-powered — there just isn’t enough power. However, with electric vehicles growing in popularity, many have wondered about the feasibility of having a solar panel on the vehicle’s roof to generate some electricity, even if only a little, to give the batteries an extra oomph.

But technology is moving ahead of that. Today, vehicle companies are not looking at solar panels bolted to the roof; instead, the entire roof will be a solar panel. This is ‘vehicle integrated photovoltaics’ or VIPV — solar cells are directly embedded unobtrusively into surfaces like the roof, hood and side panels of the vehicle. The entire skin of the vehicle becomes a solar power generator.

“This is an emerging technology,” says Prof Y Raja Sekhar of Vellore Institute of Technology, who is one of the four authors of a study on VIPV in India, published in Energy. The study was conducted by VIT, University of Lisbon (Portugal), and Fitchner Consulting Engineers.

They ran a VIPV car for three hours, measured the generation, and concluded that it is possible to get 1,200-1,800 Whr “when driven a full day”.

Sekhar told Quantum that solar power can potentially take care of auxiliary power consumption — such as lighting and AC — reducing the load on batteries. The VIPV power can indeed charge the batteries, but that would call for some extra instrumentation, with the corresponding disadvantage of increased weight.

Work is happening globally in this area. For example, Fraunhofer Institute of Germany developed a 115 W solar hood, and a 3.2 kW PV roof on an 18-tonne e-truck. Companies like Sono Motors, Lightyear, Toyota and Mercedes are developing prototype VIPV cars.

Mercedes announced in December 2024 the invention of a solar paint “that could be seamlessly applied to the bodywork of EVs”. It said that the active photovoltaic surface can, under ideal conditions, give an extra 12,000 km a year.

“This could be a highly effective solution for increased electric range and fewer charging stops,” Mercedes said.

Challenges

VIPV is an evolving technology and there are challenges. The study points to one — a “significant drop in PV efficiency due to high module temperatures”. The authors suggest further research into active and passive module cooling techniques, perhaps with the use of phase-changing chemicals.

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Published on July 14, 2025



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