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Thanks to a team of scientists from Hong Kong, it is now possible to constantly monitor the structural integrity of any object and detect damage in real time. The technology is based on a network of conductive nanocomposite materials, which are sprayed onto structures like a layer of paint. Due to its low production costs, the "sprayable" nano-tech can drastically improve safety standards of buildings, train tracks and even airplanes.
Some of the nano-scale particles utilized by the sensors were also first developed by the PolyU (Hong Kong Polytechnic University) team, headed by Professor Zhou Limin and Professor Su Zhongqing. However, the technology also requires the use of ultrasound actuators, which have long been used for similar purposes. The difference is that traditional sensors are heavy and rigid, making them viable only for testing huge structures such as bridges and dams.
Meanwhile, according to Professor Su, these sensors are both lightweight and flexible, meaning they can be installed on any object, regardless of shape or size. At the PolyU unveiling, he explained that “...due to its light weight, the novel nanocomposite sensors can be applied to moving structures like trains and airplanes. That will help to pave the way for real-time monitoring of these structures in future, increasing the safety of engineering assets and revolutionizing the traditional system maintenance philosophy.”
The idea of measuring stuctural health with ultrasound waves is nothing new. An ultrasound actuator creates GUWs (guided ultrasonic waves) and emits them at a wide array of frequencies. Sensors detect the GUWs, measure them and collect the data. If a crack or any other type of damage is present inside the structure, the waves scatter, creating an array of unique frequencies.
By comparing characteristics of the scattered GUWs, the technology can not only detect the type and location of the damage but also quantify its extent.
Sensors that are currently on the market weigh 2-4 grams each and are priced at about $10 a piece. Considering that a multitude of sensors is necessary for producing accurate measurements, the overhead costs for such a system are quite high. On the other hand, the sensors introduced by Professor Zhou Limin and Professor Su Zhongqing's team weigh a measly 0.04 grams each. Plus, their low production costs give them an estimated market price of just $0.50.
Most importantly, they are extremely flexible, which means they are universally compatible with all structure types. Furthermore, they can be sprayed directly onto objects, eliminating the time and effort constraints associated with installing conventional sensors. It is even possible to apply them to moving structures, including heavy machinery and airplanes.
Currently available sensors can measure a wide range of high GUW frequencies, which indicate large inconsistencies and cracks. But, while the new ones only detect waves up to 900kHz, they work at an ultralow magnitude. As such, even tiny, 1-2mm cracks can be picked up by the sensors.
Aside from collecting more detailed readings, the quantity of data will also be increased. This is simply due to the fact that increasing the number of sensors in a network improves overall measuring capabilities. And with sensors that are 20 times cheaper, it's probably safe to assume that engineers will be able to afford a few extras.