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| CSIRO | SOLVE | Issue 8 | Aug 06 | |
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ARTICLE
 SENSORS: Sensory Solutions By Bianca Nogrady
The science of ‘advanced materials’ is fast opening up new industrial frontiersIn the high-speed, low-atmosphere conditions of space travel, even the most minuscule piece of dust or rock can cause serious damage to space vehicles – and repairs are obviously not simply a matter of taking the ship to a local garage for a quick touch-up. For one thing, the nearest garage is likely to be hundreds of thousands of kilometres away. For this reason CSIRO Industrial Physics (CIP) is developing materials that are able to detect when damage has occurred, assess the severity of the damage and self-repair it – without the need for human intervention. This is just one example of the potential for so-called ‘advanced materials’. Dr Don Price, chief scientist at CIP, says the most basic definition of an advanced material is anything “cleverer than a lump of concrete or a piece of timber”. Examples are an extra-durable coating to reduce wear and tear, an optical film that filters out particular light frequencies, a superconductor that can operate at higher temperatures or even a molecular-scale electronic circuit. CIP’s focus is small-scale advanced materials, and you cannot get much smaller than a SQUID, or Superconducting QUantum Interference Device. Barely the size of a fingernail, a SQUID is an extremely sensitive magnetic sensor, powerful enough to detect minute fluctuations in the magnetic field of the brain when you think. In terms of more practical uses, it can pick up the magnetic field disruptions caused by tiny pieces of metal when, for example, they are buried inside food products or other materials where they should not be. This makes SQUIDs a valuable development for the food, pharmaceutical and security industries, according to Dr Marcel Bick, science capability leader in superconducting systems and devices at CSIRO. “One obstacle for the food industry is that metal parts can break off during food processing,” Dr Bick says. “If it is packaged in aluminium foil, conventional metal detectors will have problems detecting it.” One of the initial applications for SQUIDs is detecting needles in meat. “When livestock are vaccinated, needles can break off in the meat and conventional X-ray units have difficulties seeing into meat because it is very dense,” he says. Most of CSIRO’s SQUIDs are high-temperature superconductors. They consist of a superconducting ring made from a film of ceramic material just 200 nanometres thick (a nanometre is one billionth of a metre). Compared to low-temperature superconducting devices, which must be maintained at temperatures of – 269˚C in liquid helium, CSIRO’s SQUIDs operate in the relatively high temperature medium of liquid nitrogen (– 196˚C). This makes them much more portable. They can be transported in something as small as a thermos flask containing liquid nitrogen.
The mining industry is another sector taking a close interest in SQUIDs. Some companies are already using them to search for ore bodies that conventional technologies are unable to detect. In this application, SQUIDs are being used both on the ground and in the air. “There’s a system we’ve been using which is airborne…you put the SQUID in a so-called ‘bird’ and tow it behind a plane to do mineral exploration,” says Dr Bick. “A similar approach is being looked at for use in defence to detect large objects such as submarines.” Dr Price says that in the case of SQUIDs, the advanced materials component is the high-temperature superconducting materials, but also the way these materials are processed to make them act as highly sensitive sensors. “The other aspect is if you build these into other materials to make them capable of sensing,” Dr Price says. “That’s when it becomes pretty advanced.” This ability to sense changes in the environment or within a material has clear applications in the aerospace industry. However, instead of using superconducting sensors, CIP is developing extremely small electronic sensors and mechanisms that can be built into materials. “Our work is aimed at developing sensors, sensing techniques and methods for using the data from very large numbers of sensors to diagnose and respond to a situation using a self-organisational approach,” Dr Price says. “It’s more analogous to the way a nest of ants or a swarm of bees respond to external circumstances and/or repair their nest or hive.” For example, if a space vehicle is damaged by micrometeoroids, an advanced material would be able to initiate internal self-repairs. “It’s about developing intelligence in the way materials respond to their environment to give them some of the self-repair properties that biological materials have,” Dr Price says. Advanced materials research and development also covers faster and more cost-effective production, such as the Light Metals Flagship’s research into producing advanced titanium–aluminium alloys. Dr Jawad Haidar, leader of the titanium alloys project, says this field of research could turn high-performance aerospace alloys into much more commonly used materials. “Titanium alloys have some very special properties,” Dr Haidar says. “They are very light, very strong and corrosion resistant.” However, they are extremely expensive to produce because there are multiple steps in production and significant wastage. To avoid this, CSIRO has developed a simple, direct production method that is expected to reduce costs by up to a factor of 10. Part of the challenge in producing these alloys is adding extra alloying ingredients to improve the properties of the end material. “For example, for the so-called Ti-6Al-4V alloy used in the aerospace industry, vanadium is added to make the alloy suitable for the extreme conditions,” Dr Haidar says. “The CSIRO technology is capable of making this alloy directly from low-cost chemicals containing titanium, aluminium and vanadium.” While metallurgy is not usually the province of physicists, Dr Price says physicists are well placed to contribute to the development of advanced materials. “There’s a whole branch of physics now known as condensed matter physics, which seeks to study, understand and design the physical properties of solids,” he says. “The skills that physicists bring to materials science are in measurement, theoretical physics – which seeks to explain and/or predict the physical properties of materials – and in physical methods of producing and processing materials, for example thin-film deposition.” Coatings also fall into the realm of ‘advanced materials’ and CSIRO is using thin-film deposition techniques to develop and apply coatings with dedicated properties. For example, researchers have developed a titanium nitride coating for machine tools, which is highly durable. “One application is the dies (stamps) that the Royal Australian Mint uses for making coins,” Dr Price says. “They can make many more coins before the dies have to be replaced.” Other coatings are designed to be biocompatible, meaning they can be used to coat the surface of medical implants such as artificial joints so the implants will not interact detrimentally with the body. Thin-film deposition has also allowed researchers to produce multilayered optical filters with extremely sharp and tailored filtration properties. A filter may be designed to filter out only certain spectra of light and could have applications in astronomy or the military. “You can have a filter than lets through all the light except a particular frequency of laser light, so they could be used for eye protection,” Dr Price says. Materials science also has links with the rapidly advancing field of nanotechnology, for example the production of nanoparticles with various properties that can be embedded into other materials. Work is being done to develop nanosensors that are sensitive to particular chemicals that could be used to detect even extremely low levels of toxins in the environment. Dr Price says these nanoparticles could also have electronic capabilities: “They’re developing ways of being able to mix them with inks, so that you can actually print them on substrates and build electronic circuits essentially by printing. It could pave the way for electronic circuits that would be extremely cheap to produce.” Ultimately, work on advanced materials could even lead to the development of electronic circuits built of individual molecules. Work is being done to measure the electronic properties of single molecules – a field called molecular electronics. Dr Price says that now traditional electronic circuits have reached the stage where they cannot get too much smaller, the next logical step is to go down to the level of the molecule. APPLICATION A wide range of applications are possible including self-repairing materials, detecting needles in meat, submarines in the sea and even a molecular-scale electronic circuit BENEFIT Advanced materials include fingernail-sized sensors (SQUIDs), thin-film coatings and nanoparticles with various properties For further information contact: |
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