Sara earned a doctorate in optical measurement

Published: 13 August 2013

With the help of so-called diffuse light, Sara Rosendahl in her doctoral thesis studied the properties of different surfaces. The work has two main tracks, one is about optical measurements on molded steel items and the second part is to further develop the Road eye, a project led by LTU-researcher Johan Casselgren.

Measuring surface with stereo camera

Before Sara Rosendahl began her doctoral studies at LTU and the research subject Experimental Mechanics she studied Engineering Physics at Umeå University and worked as a trainee at the company Optronic in Skellefteå. The first part of Sara's thesis aims to verify if molded steel products have been properly produced, a Vinnova project where several large engineering firms were involved. In the production process, the companies wanted to quickly measure steel products and compare them against its CAD drawing. To achieve this, Sara together with her colleague Per Bergström, presented a stereo camera stereoscopic imaging using projected fringes. By using information from the CAD drawing, they could determine the shape of the component.

To increase the accuracy of the measurements, another optical measuring method was used, digital holography, something that Per Bergström still conducts research on in conjunction with PhD-student Davood Khodadad. What Sara and Per came up with is that it is possible to use the CAD model to quickly determine the shape of a component.

Optical measurement detects moisture

The second part of the thesis is about measuring surfaces as a part ot the project Road eye at LTU's competence centre CASTT. Road eye is a sensor that can read the road surface and, for example, warn the driver of a slippery road. Sara Rosendahl developed an improved sensor with two detectors instead of one, to be able to say more about the surface being measured.

To see any improvements with the sensor that has two detectors, Sara measured the surface of sand by using diffused light. But larger sand particles did not differ significantly from smaller particles. However, there was significant differences in measurements of moist compared with dry sand, this is because optical measurements also can detect differences in the material under the studied surface. From the results, Sara developed a model that describes the moisture content of the surface. Measurements were also made on ice, and Sara could see certain tendencies to be able to distinguish between different types of ice. Further research will be conducted when it comes to measuring the ice, you want the Road eye to distinguish between more types of ice than is now the case.

The results of Sara's research on moisture measurement of a surface is something that could also be used in the production of granular material to control the material's moisture content.