What caught our attention outside the world of oil and gas this month
Low-power transistors could replace batteries
Engineers at the University of Cambridge have developed a new type of ultralow power transistors which could function for months – even years – without a battery by “scavenging” energy from their environment.
Using a similar principle to a computer’s sleep mode, the new transistor harnesses a tiny “leakage” of electrical current, known as a near-off-state current, for its operations. This leak, is a characteristic of all transistors, but this is the first time that it has been effectively captured and used functionally.
The results, reported in the journal Science, open up new avenues for system design for the Internet of Things, wearable tech and other devices.
The transistors can be produced at low temperatures and can be printed on almost any material, from glass and plastic to polyester and paper. They are based on a unique geometry which uses a 'non-desirable' characteristic, namely the point of contact between the metal and semiconducting components of a transistor, a so-called 'Schottky barrier.'
Professor Arokia Nathan of Cambridge's Department of Engineering, the paper's co-author commented that: “We've found that these Schottky barriers, which most engineers try to avoid, actually have the ideal characteristics for the type of ultralow power applications.”
The design also achieves a very high level of gain, or signal amplification. The transistor's operating voltage is less than a volt, with power consumption below a billionth of a watt.
“If we were to draw energy from a typical AA battery based on this design, it would last for a billion years,” explained the paper's first author Dr Sungsik Lee, also of the Department of Engineering.
Not a day goes by without news of a new application for wonder-material graphene. This month, researchers at the Center for Multidimensional Carbon Materials (CMCM), part of the Institute for Basic Science (IBS), published a study examining how coating glass with graphene can help protect it from corrosion.
Because glass has a high degree of both corrosion and chemical resistance, it is the primary packaging material for preserving medicines and chemicals. However, over time at high humidity and pH, some glass types corrode.
Corroded glass loses its transparency and its strength is reduced. Although there are different types of glass, ordinary glazing and containers are made of silicon dioxide (SiO2), sodium oxide (Na2O) along with minor additives. Glass corrosion begins with the adsorption of water on the glass surface. Hydrogen ions from water then diffuse into the glass and exchange with the sodium ions present on the glass surface. The pH of the water near the glass surface increases, allowing the silicate structure to dissolve.
Graphene’s chemical inertness, thinness, and high transparency makes it a promising coating material. Its also provides a chemical barrier, in that it blocks helium atoms from penetrating through the material.
IBS scientists grew graphene on copper using a technique previously invented by Prof. Rodney S. Ruoff and collaborators, and transferred either one or two atom-thick layers of graphene onto both sides of rectangular pieces of glass. The effectiveness of the coating was the tested by water immersion.
After 120 days of immersion in water at 60°C, uncoated samples had “significantly increased in surface roughness and defects, and reduced in fracture strength.” Yet both the single and double-layer graphene-coated glass had essentially no change in both fracture strength and surface roughness.
Prof. Ruoff, director of the CMCM and Professor at the Ulsan National Institute of Science and Technology (UNIST) commented that: “In the future, when it is possible to produce larger and yet higher-quality graphene sheets and to optimize the transfer on glass, it seems reasonably likely that graphene coating on glass will be used on an industrial scale.”
The use of graphene coating is also being explored as a protective layer for other materials requiring resistance to corrosion, oxidation, friction, bacterial infection and electromagnetic radiation.
New research from MIT has suggested the use of ambient vibrations to monitor structural integrity.
A study recently published in the Mechanical Systems and Signal Processing journal, used the university’s Green Building – a 21-storey research building – in the campus as a test bed for predicting structural integrity. The team fitted the site with 36 accelerometers which record vibrations and movements on selected floors, from the building’s foundation to its roof.
They also built a computer simulation of the building, including information such as wall density and the strength of various structural elements. This allowed them to predict how the building might behave when subject to certain stresses.
“These sensors represent an embedded nervous system,” commented says Oral Buyukozturk, a professor in MIT’s Department of Civil and Environmental Engineering (CEE). “The challenge is to extract vital signs from the sensors’ data and link them to health characteristics of a building, which has been a challenge in the engineering community.”
Data from the accelerometers could then be fed into this model. During the search for features which would produce viable information on integrity the team also developed a new method with the seismic interferometry concept that describes how a vibration’s pattern changes as it travels from the ground level to the roof.
Such a model could be useful in future structural integrity and building monitoring systems.
“I would envision that, in the future, such a monitoring system will be instrumented on all our buildings, city-wide,” lead author Hao Sun said. “Outfitted with sensors and central processing algorithms, those buildings will become intelligent, and will feel their own health in real time and possibly be resilient to extreme events.”
“The broader implication is, after an event like an earthquake, we would see immediately the changes of these features, and if and where there is damage in the system,” Buyukozturk added. “This provides continuous monitoring and a database that would be like a health book for the building.”
Sweaty robot stays cool
A paper presented at the IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS) this month outlined a system for efficient robot cooling – pumping cold water through their porous bone structures.
Kengoro, a humanoid robot developed by the University of Tokyo’s JSK Lab, is designed to be able to replicate the human body in a number of energy-intensive tasks. In examining ways to keep the system cool, researchers decided to experiment by using the frame of the robot itself as a delivery mechanism for coolant.
Kengoro’s main skeletal structure is built from laser-sintered aluminium powder. By adjusting the density of the laser during the fabrication process, the team could make different pieces of the structure more or less permeable to liquids, allowing water to be directed through the skeleton.
Further adjustments of density enabled the water to seep through into more porous sections on the outer surface of the components. As it reaches these areas, it evaporates, mimicking the cooling effect of sweat in the human body.
More porous components are then used in motor sections which require the most cooling – e.g. arm or knee joints.
Currently, Kengoro requires about a cup of deionised water per day to maintain efficiency, or more if it is performing particularly intensive tasks. However, tests have suggested that the system is better than traditional water cooling, and three times better than air cooling alone – although not quite as efficient as a radiator.
Nevertheless, the concept opens up new possibilities for mechanical cooling in other sectors – provided operators can handle sweaty machines.
MIT researchers have been experimenting with synthetic rubber “fur” which could be used to create wetsuits that keep divers warmer for longer.
Mimicking the fur of beavers, otters and other mammals, the rubber fabric uses tiny individual “hairs” to trap warm bubbles of air when plunged into liquids.
“We are particularly interested in wetsuits for surfing, where the athlete moves frequently between air and water environments,” says Anette (Peko) Hosoi, a professor of mechanical engineering and associate head of the department at MIT. “We can control the length, spacing, and arrangement of hairs, which allows us to design textures to match certain dive speeds and maximize the wetsuit's dry region.”
The pelts were created by graduate student Alice Nasto, who created several molds by laser-cutting thousands of tiny holes in acrylic blocks. With each mold, she used a software program to alter the size and spacing of individual hairs. These were then filled with a soft casting rubber (polydimethylsiloxane or PDMS), and were removed once they had cured.
In their experiments, the researchers mounted each hairy surface to a vertical, motorised stage, with the hairs facing outward. These surfaces were then dunked in silicone oil allowing them to observe the air pockets which formed.
MIT noted that: “The researchers could see within the hairs a clear boundary between liquid and air, with air forming a thicker layer in hairs closer to the surface, and progressively thinning out with depth. Among the various surfaces, they found that those with denser fur that were plunged at higher speeds generally retained a thicker layer of air within their hairs.”
This also allowed the creation of a mathematical model which could predict each fur’s ability to trap air.
“We found that the weight of the water is pushing air in, but the viscosity of the liquid is resisting flow (through the tubes),” Hosoi added. “The water sticks to these hairs, which prevents water from penetrating all the way to their base.”
In addition to diver’s wetsuits, these materials – and the mathematical model behind them – could have a number of applications in industrial coatings and fabrication techniques.