Explosive detection devices are currently installed at hundreds of thousands of locations worldwide from battlefields in Afghanistan to terminals in airports. It is reasonable to expect that demand for such devices will continue to be high for the foreseeable future. However, the unfortunate dilemma pervading current manufacturing methods for detection devices is that the devices with the highest levels of sensitivity come at extremely high expense. The most sensitive sensors currently available are based on ion mobility spectrometers (IMS) which work by ionising the molecules in an air sample and then measuring how quickly they move through a drift tube. While this methodology provides accurate measurements, the equipment is very difficult to construct and is very expensive. In an area like explosives detection where lives are at risk it is simply not suitable to accept a lower level of functionality for a more appealing price.
Photo: Georgia Tech
A solution to this problem of price vs. quality has been tackled by a team of scientists at the Georgia State Institute. Lead by Dr. Krishna Naishadham, the team have developed a cheap inkjet printable ammonia sensor (ammonia is a key ingredient in many explosive devices). The sensor is manufactured by printing carbon nanotubes on paper (or substrate with similar properties such as polyethylene terephthalate). The ink (which contains an emulsion of silver nanoparticles) is deposited and subsequently treated with ultrasonic waves which ensure that the silver nanoparticles are dispersed evenly throughout the solution. The ink then sets, forming microscopic cylindrical nanotubes which can then be coated with a conductive polymer which attracts ammonia and provides a very accurate measurement of ammonia content in a given air space. These nanotubes can also be formed into RF circuits, antennae and more, meaning the device can be manufactured with the inbuilt functionality of data transmission. This wireless communication allows for operating personnel to remain at a safe distance until safety is confirmed. Components can be formed out of flexible organic materials such as liquid crystal polymer which gives the device increased benefits of robustness and water resistance. Due to the low power requirements, solar cells or thin-film printed batteries will be a sufficient energy source which makes implementation much simpler. The fact that components are printed also means maximum flexibility in terms of where the device can be placed. While this product is currently still a prototype, the prospect of a flexible, cheaply manufactured wireless explosives detection device remains extremely attractive for security in the future.
Tim Phillips, Catenary Solutions
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