Power/Performance Bits: Oct. 3

Slowing down photonics; longer-lasting batteries; energy-harvesting roads.


Slowing down photonics
Researchers at the University of Sydney developed a chip capable of optical data into sound waves, slowing data transfer enough to process the information.

While speed is a major bonus with photonic systems, it’s not as advantageous when processing data. By turning optical signals into acoustic, data can be briefly stored and managed inside the chip for processing, retrieval and further transmission as light waves.

“The information in our chip in acoustic form travels at a velocity five orders of magnitude slower than in the optical domain,” said Birgit Stiller, research fellow at the University of Sydney. “Our system is not limited to a narrow bandwidth. So unlike previous systems this allows us to store and retrieve information at multiple wavelengths simultaneously, vastly increasing the efficiency of the device.”

This is a stylized explanation of how the chip works. 1. Photonic (light) data pulse (yellow) enters from the left. 2. A ‘write pulse’ (blue) enters from the right 3. The data and write pulses interact in the chip, producing an acoustic wave, storing the data and allowing for processing, retrieval and further transmission. 4. Another photonic read pulse (blue) enters the chip, accessing the acoustic data and transmitting the data as photonic information (yellow) to the right side of the microchip. 5. Light passes through the chip in two to three nanoseconds, depending on the length of the spiral on the chip. Information can be held on the chip for an extra 10 nanoseconds as acoustic data. (Source: Rhys Holland & Sebastian Zentilomo/University of Sydney)

“Building an acoustic buffer inside a chip improves our ability to control information by several orders of magnitude,” said Moritz Merklein, a doctoral candidate at University of Sydney. “For this to become a commercial reality, photonic data on the chip needs to be slowed down so that they can be processed, routed, stored and accessed.”

Longer-lasting batteries
Researchers at the University of Central Florida, Jilin University, and Rice University developed a much longer-lasting lithium-ion battery with a new cathode that displays excellent conductivity, is stable at high temperatures and cheap to manufacture.

The cathode is created from a thin-film alloy of nickel sulfide and iron sulfide. That combination of materials brings big advantages to their new electrode. On their own, nickel sulfide and iron sulfide each display good conductivity. Conductivity is even better when they’re combined, researchers found.

They were able to boost conductivity even more by making the cathode from a thin film of nickel sulfide-iron sulfide, then etching it to create a porous surface of microscopic nanostructures. These nanopores greatly expand the surface area available for chemical reaction.

All batteries eventually begin degrading after enough use. Quality lithium-based batteries can be drained and recharged about 300 to 500 times before they begin to lose capacity. Tests show a battery with the nickel sulfide-iron sulfide cathode, however, could be depleted and recharged more than 5,000 times before degrading.

Energy-harvesting roads
Engineers from Lancaster University propose a new form of energy harvesting: embedding materials in the road surface to generate electricity from passing traffic.

The research will focus on the development of materials like piezoelectric ceramics that when embedded in road surfaces would be able to harvest and convert vehicle vibration into electrical energy. The team is aiming for energy recovery of around one to two megawatts per kilometer under ‘normal traffic volumes, around 2,000 to 3,000 cars an hour.

This amount of energy, when stored, is the amount needed to power between 2,000 and 4,000 street lamps. As well as providing environmental benefits, the researchers argue it would also deliver significant costs savings for taxpayers.

It currently costs around 15p, or $0.20, a kilowatt hour to power a street lamp in the UK. Therefore 2,000 to 4,000 lights can cost operators – which in the UK tend to be local authorities, or the Highways Agency for motorways and trunk roads – approximately between £1,800 ($2,400) and £3,600 ($4,800) per day. Researchers say the cost of installing and operating new road energy harvesting technology would be around 20% of this cost.

“We will be developing new materials to take advantage of the piezoelectric effect where passing vehicles cause stress on the road surface, producing voltage. The materials will need to withstand high strengths, and provide a good balance between cost and the energy they produce,” said Mohamed Saafi, Professor and Chair in Structural Integrity and Materials at Lancaster.

“The system we develop will then convert this mechanical energy into electric energy to power things such as street lamps, traffic lights and electric car charging points. It could also be used to provide other smart street benefits, such as real-time traffic volume monitoring.”

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