When infrared laser light is emitted against a surface, some of the invisible light penetrates the material, and here a small part of it is reflected differently by the material components. The reflected light is collected in a computer and analyzed. The result is an image that shows the internal structure of the material, similar to when reflected ultrasound creates the image of a fetus in an ultrasound scan of a pregnant woman.
The unique thing about OCT is that you can get a 3D image with a relatively good resolution – down to a few micrometers – without coming into contact with the subject.
The OCT for eye exams was developed back in the 1990s, and the technology is still drawing the most attention in the medical context. The technology can also be used to diagnose skin cancer.
The OCT also has great potential in industry – and with a grant of just over DKK 1 million from the Danish Maritime Fund, Christian Rosenberg Petersen is currently developing a compact, portable OCT system for inspecting ship colors.
“When everything is put together, we have to take measurements on a ship. With the robot arm, we can scan a relatively large area, which is only limited by the range of the robot of 85 cm. For example, we can see whether the paint contains small bubbles, whether there are problems with adhesion, or whether there is initial rust formation underneath, ”says Christian Rosenberg Petersen.
Can lead to better coatings
The project was called SHIP-COAT (underground, high-resolution, inspection of colors and coatings using non-destructive laser tomography). The portable measuring device should be ready for field tests in February 2021.
Until then, the measurements will be carried out in the laboratory under the observation of researchers from DTU Chemical Engineering. The CoaST research center (The Hempel Foundation Coatings Science and Technology Center) is located here. The aim of the research center is to develop permanent and sustainable colors – or coatings, as they are called in the industry.
OCT can be used both when developing coatings and later when the coatings are worn out.
“In connection with the development of a coating, for example, it will be possible to check the properties of the coating during a test process. As soon as the coating has been put on the market and used on ships, the quality can be continuously checked through inspections based on OCT, ”says Christian Rosenberg Petersen.
His vision is that the SHIP-COAT project can lead to better, greener marine coatings, and he also emphasizes that the technology can be used for much more than just coatings. Only the imagination is limited:
"I hope that more people outside of the medical community will become aware of optical coherence tomography and develop entirely new applications that we haven't even considered."