Unless you’re Superman, seeing what’s inside your Christmas presents under the tree is something of a struggle. In fact, X-ray vision may not be of much use in determining whether it’ll be socks or underpants and the radiation could even damage the contents (especially if it’s a new puppy).
Fortunately, researchers at the Fraunhofer Institute for High Frequency Physics and Radar Techniques FHR, in Wachtberg, have developed a Stand Alone MilliMeter wave Imager - that’s SAMMI to you and me. Although it’s designed to be put to more serious use than taking the surprise out of Christmas Day, its technology allows users to identify what’s inside non-metallic packaging.
“The system detects wooden splinters lurking in diapers, air pockets in plastic, breaks in bars of marzipan and foreign bodies in foodstuffs. It can even detect and monitor the dehydration process in plants and how severely they have been stressed by drought,” said Dr Helmut Essen, head of the FHR’s millimetre-wave radar and high-frequency sensors department.
At a small 32 x 50 cm - the size of a compact laser printer - SAMMI is comfortable handling all nonmetallic materials in a range of applications from industrial product and quality control to analysing materials in the laboratory. It’s even sensitive enough to pick up dangerous substances like explosives in letters, making it ideal for paranoid politicians or celebrities with stalkers.
While Superman’s X-ray vision no doubt comes in handy, SAMMI’s millimetre-wave radar can pick out the smallest differences in materials - differences that are invisible to X-rays. SAMMI can differentiate between different fillings in chocolates or between rubber composites that have similar or identical absorption qualities.
Because it doesn’t use X-ray, SAMMI doesn’t produce ionising radiation, which can be harmful, and it doesn’t require the regular checks necessary with X-ray tubes (beat that, Superman).
But how does SAMMI work? Inside the system’s housing, there is a transmitting and a receiving antenna on each of two opposing rotating plates. A conveyor belt transports the sample between the antennae, while these send electromagnetic waves in a high frequency of 78 GHz. Different areas of the sample absorb the signal to different degrees, leading the varying material composition across a sample to show up in distinguishable contrast.
“Basically, we examine the scanned objects for dissimilarities,” explains Essen. The content of the sample appears in real time on the scanner’s fold-out display. If the package contains a knife, even the grain of the handle is discernible. If the handle is hollow, the millimetre-wave sensor would show that, too. The device scans an area of 30 x 30 cm in just 60 seconds.
“Our system can be operated without safety precautions or safety instructions and, since it weighs just 20 kilograms, it’s eminently portable. It can also be adjusted to various measuring frequencies,” Essen points out.
In future, the researchers aim to upgrade the system for terahertz frequencies of 2 THz. “Then we’ll be in a position not just to detect different structures but also to establish which type of plastic a product is made from,” said Dr Essen.
At present, SAMMI is only suitable for spot checks. However, the FHR researchers are working on adapting the millimetre-wave sensor for industrial assembly lines for rapid, automatic goods inspection. They envision mounting a line of sensors over the conveyor belt, so that in future, products can be scanned at a speed of up to 6 m/s. That’s a lot of Christmas presents.