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Delft has wanted a tram to its university for about 20 years. The catch is that the TU Delft campus is full of sensitive experiments. Trams shake the ground, and the current that powers them creates magnetic fields. Both can ruin a measurement. When the new Siemens trams were tested, they produced more vibration and more magnetic field than expected.

So the engineers redesigned the track and the power supply. The rails sit in fibre-reinforced concrete slabs, insulated with rubber, to stop vibration spreading. The power cables run between the rails, close together, instead of overhead. A current and its return path close together largely cancel each other's magnetic field. This passive system, from TU Delft and EM Power Systems, is patented and already used in Utrecht and Lund. The 2.5 km line opened on 5 October.

HS2 passes Wendover in the Chiltern Hills, a protected landscape. To hide it there, the route runs through a "green tunnel": a concrete box built in a trench, then buried so the land on top can be landscaped again.

Instead of pouring concrete on site, the box is made of 2,740 precast segments that form an "M" shape, with separate bores for each direction. The team built the 1.4 km central section as two halves, so digging, building and backfilling could happen at the same time. The halves were joined on 5 October.

Cement is made by heating limestone in a kiln to about 1,450 °C, which releases a lot of CO₂. Concrete accounts for about 7.5% of human CO₂ emissions, and cement is almost 90% of that.

Cambridge researchers noticed that steelmakers add lime to their electric arc furnaces, to pull impurities out of the molten steel. They swapped that lime for cement paste recovered from demolished concrete. It comes out of the furnace as fresh cement clinker. No kiln, and no new limestone. Start-up Reclinker has made "thousands of tonnes" at a Cardiff steelworks and raised £10m this week. It claims a 50% emissions cut at the same cost as normal cement.

Offshore wind farms are far from land, and their platforms have little space. Batteries that smooth out the wind's ups and downs usually end up onshore.

UK firm Verlume puts the battery on the seabed. Its Orah system stores 500 kWh and is built from modules. The 10-tonne enclosure is 7.2 × 2.4 × 2.4 m. It passed pressure, sealing and working tests in a hyperbaric chamber in Aberdeen, the largest vessel ever tested there. The full 85-tonne system is going to the OranjeWind farm in the Dutch North Sea.

AI data centres want to feed racks at 800 V DC (direct current), because higher voltage means less current and thinner cables. But chips need low voltage, so the power has to be stepped down near the chip. Just reaching 6 V usually takes two converters, 800 V to about 50 V and then to 6 V, before a final stage near the chip. Each one wastes energy and takes up space.

Navitas and Microchip have merged them. Their design uses 16 gallium nitride transistors stacked in pairs, switching a million times a second. Fast switching means the coils and capacitors can be smaller. The companies claim up to 96% peak efficiency and 2,100 watts per cubic inch. It will be shown at a data-centre hardware summit on 12–15 October.

To remove a dead satellite, you first need to know how it is spinning and what state it is in. Nobody can look from the ground in enough detail.

NASA's SSPICY mission (Small Spacecraft Propulsion and Inspection Capability) uses Otter, a spacecraft about the size of a washing machine built by Starfish Space. It launched on 1 October. From early 2027 it will approach up to four dead US objects in low orbit and measure their spin, orientation and surface condition. It steers itself using cameras and onboard software. Its electric thrusters sit on a robotic boom that points them where needed. NASA says it is the first time these technologies have been tested together.

A robot hand is usually stuck on the end of an arm. If it could move on its own, it could reach places the arm can't.

An ETH Zurich team gave a human-like robot hand an 80 g backpack with a battery, a motion sensor and a Raspberry Pi Zero computer. Then it trained the fingers to work as legs. The hand crawled over 14 surfaces at an average 9 cm a second. It got itself upright in 21 of 25 tries, and pushed a 41 g cube to targets up to 40 cm away 15 times in a row. The paper is a preprint and hasn't been peer-reviewed.

Tracking how a body bends usually means suits covered in rigid sensors or markers. They are bulky, and the shape they report can be off by 1–2 cm.

MIT engineers ran soft optical fibres in a zigzag through a silicone sheet. Each fibre has an LED at one end and a light detector at the other. When the sheet bends, less light gets through. One side of each fibre is roughened, so the signal also shows which way it bent. Software turns all the readings into a 3D shape, accurate to under 0.4 cm. It still works if some fibres are cut. The work is in Advanced Intelligent Systems.

A replacement heart valve doesn't grow. Children who need one often face more open-heart surgery to fit a bigger one.

Edwards Lifesciences' Autus valve, approved by the US Food and Drug Administration (FDA) on 1 October, is fitted at about 13 mm wide. Later, doctors can widen it to as much as 22 mm with a balloon passed through a blood vessel, without opening the chest. Its flaps are polymer instead of animal tissue, the first time the FDA has approved that for any use. In a trial of 62 children at 12 US hospitals, there were no deaths or strokes. Two valves have already been widened this way.