Innovations for tomography

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The development of a handy X-ray tomograph achieved second place in the Hugo Geiger prize. The work that achieved the third place deals with a terahertz measuring system for spectral tomography that also measures how much radiation penetrates the object or is being reflected by it.

Image: Stefan Hebele (left) and Anika Brahm
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Is the component ok or have errors been made during production? Are the inner structures built up as intended? This can be examined with an X-ray tomograph: it takes numerous X-ray images and combines them into cross-sections. This way, one gets a three dimensional model of the component without having to destroy it. Currently these apparatuses usually weigh uo to several tons, with even the lightest ones still weighing approximately 50 kilograms. During the work on his Diploma thesis at the Development Center for X-Ray Technology EZRT of the Fraunhofer Institute for Integrated Circuits IIS in Erlangen, Stefan Hebele developed a micro CT scanner that, weighing in at 19 kilograms, weighs approximately as much as a crate of beer bottles. At 350 by 300 by 230 millimeters, its dimensions are even smaller - the dimensions correspond more to a small postal package. »It is the first computer tomograph that, according to occupational safety law, may be carried by a single person, without reservation,« says Hebele, who achieved second place in the Hugo Geiger Prizes.

The operation could not be simpler: turn it on, connect a USB cable, open the cover, put the sample in it – and let‘s start. »The device is so handy that it can also be used for mobile applications. For example, it would be possible to offer mobile services. Instead of sending out samples of new materials or prototypes, companies could then simply have the service provider come on-site with its device. The results are available more quickly and it is more likely that confidentiality will be maintained than would be the case if the sample is sent out,« says Hebele. The price is yet another advantage: costing € 55,000, the X-ray tomograph is far less costly than its multi-ton colleagues that can be had for prices that start well above € 100,000. Almost any samples that do not exceed a size of four by four by four centimeters can be examined.

Simultaneous measurement of transmission and reflection

Anika Brahm from the Fraunhofer Institute for Applied Optics and Precision Engineering IOF in Jena, Germany achieved 3rd place. In her Master‘s thesis, she, too, was working on a type of tomography and developed a terahertz measuring system that makes it possible to determine transmitted and reflected light in a single measuring sweep. »Terahertz radiation is in the frequency range between infrared and microwave radiation and can penetrate materials such as wood, textiles and plastics,« she explains. Current processes irradiate the components, packages or other objects and measure how much radiation penetrates the object or how much is being reflected by it. Both methods contain identical information, but not all materials can be examined equally well with one of the versions. For example, metals do not allow terahertz pulses to penetrate them, but layers affixed to them can be examined by means of reflection. »Since we are able to utilize transmission as well as reflection with the measuring system we developed, we are more flexible in the examination,« says Anika Brahm. One more innovation: not only does the system help to find structural defects or other material defects, but it also examines the characteristic frequency spectrum. Such a spectrum tells the researchers what kind of material they are dealing with – for example, they are able to detect explosives in packages this way. Brahm summarizes: »Since the machine determines the spectral information in three dimensions for the first time, we are able to state exactly what kind of material is located where.«