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Undergraduate student builds tabletop Schlieren System with help from CIS Microgrants Program
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Air is defined as "the invisible gaseous substance surrounding the earth..." What if you could picture the invisible? It is possible with a Schlieren Imaging System.

Mar. 21, 2014
Lisa Powell

Taking inspiration from a 2012 lecture on the subject given by Professor Gary Settles, who was visiting RIT from Pennsylvania State University, Chester F. Carlson Center for Imaging Science student Dan Goldberg decided to create a portable Schlieren System.

"I thought it was really cool, so at the next meeting of the SPIE Student Chapter at RIT I suggested we make one of these things that would be cool to look at and small enough to take to a classroom."

Schlieren is the German word for "streaks." When layers of air or gas differ in density from one another they become visible as transparent streaks or waves. A Schlieren System allows us to view this phenomenon.

When a ray of light hits something that has a different density than the air around it, the light will bend. This is called refraction. Think of the shimmering mirage rising up from an asphalt road on a hot day.  What looks like a pool of water in the distance is not what it appears to be, yet it is very real. The rays of light from the sky are being bent as they pass through the hot air rising from the ground.

Goldberg's Schlieren System uses a knife edge, a spherical mirror, and a light source to show such variations in atmospheric density. Adding the knife-edge to the System refines it "so you can see someone's breath or the heat coming off of someone's hand."

Because he was so inspired by the subject, Goldberg wanted to bring the concept to a wider audience, so, using a microgrant from the Carlson Center for Imaging Science, Goldberg designed a portable, 5-foot, single-mirror Schlieren System. Goldberg's faculty sponsor for the project was Dr. Dale Ewbank, who teaches microelectronic engineering at RIT.

Two of Goldberg's fellow students went to the SPIE annual conference in San Diego during the summer of 2013. At the meeting, they exhibited the compact Schlieren System; several people inquired as to how they could make such a system and show it to others. The System was also displayed at last year's Imagine RIT, and is expected to make an encore appearance at this year's event.

"The science behind this whole technique is old and has been known for a while; you don't need a high level of physics to understand it. That means it can be explained to high school students," Goldberg explains. He adds that Robert Hooke started experimenting with these systems soon after he discovered the schlieren phenomenon in the 17th century. At that time it was used to find imperfections in lenses and mirrors and that remains one of its uses today.

The system can be applied in medicine to observe how the breath produced by a cough moves through the air, or in fire science to observe the way heat comes off of burning leaves or pine cones, or simply to observe a gas leak in an enclosed space.

"It is an analog technique," explains Goldberg: an experiment performed "sort of the old-fashioned way."

After he graduates from RIT this year, Dan Goldberg plans to apply to graduate school, but his main focus is on finding a job to help him get through more school, perhaps working in computer science.

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