Engineers in Netherlands Optimize Micro Designs to Study Solar Flares

These tiny spacers are a critical component in a gamma ray imaging device that will be used by NASA to study solar flares.

For researchers in the Laboratory for Micro Engineering at Delft University of Technology in The Netherlands, the term "it's a small world" has a very special meaning. That's because this group of engineering professionals works in a world where very small parts must be created to do very big jobs.

In the world of micro engineering it is not unusual to be confronted with designs which must be accurate to within a few micrometers or even nanometers.

The Delft group has worked extensively with both the European Space Agency and NASA to design critical, highly sensitive components. Recently, Associate Professor Peter V. Pistecky, in cooperation with NASA, utilized Algor design and analysis software in the development of a unique and innovative gamma ray detection device. The device will be used in future space-based research of solar flares.

Seeing the Unseen

The visible part of a solar flare can tell scientists a lot about its behavior and causes, but it is not the complete picture. Solar flares emit gamma rays, which can provide additional information about their behavior. Unfortunately, it is impossible to create an image of gamma rays using conventional, photographic means.

Mr. Pistecky and his associates developed the Gamma Ray Imaging Device (called GRID) in cooperation with scientists from the Laboratory for Astronomy and Solar Physics at the NASA Goddard Space Flight Center. The GRID measures certain components of gamma ray images by passing them through two sets of tiny slits placed at each end of an assembly resembling a conventional telescope.

The images are focused through the slits to detectors. Data from the detectors are fed to a computer which creates a precise image of the gamma ray emissions of a solar flare. The challenge facing Mr. Pistecky was to create patterns of tiny slits with a high level of accuracy that could withstand the rigors of being launched into space.

Algor software was used to analyze the deflection of the flexible spacer when the island spacers on each side are compressed. A deflection contour is depicted.

Tiny Design Parameters

"We determined that the finest pattern of slits should be 50 micrometers wide at a pitch of 100 micrometers," says Mr. Pistecky. "The position accuracy had to be on the order of a few micrometers within an area 130 millimeters square. It was obvious from the beginning that these slit patterns could not be created by known machining technologies. A number of designs were considered including a stack of 1,300 long thin tungsten blades with small spacers between them to create the slits," continues Mr. Pistecky, "However, the necessary accuracy could not be obtained. After exploring a variety of configurations using Algor design and analysis software, the solution turned out to be a series of spacers that act like springs. Algor analysis showed that this design provided the necessary accuracy for the tiny slits, while allowing the blades to move slightly in order to withstand temperature changes and loads such as those experienced at liftoff."

The final configuration, optimized with Algor software, consists of two "island" spacers with a flexible spacer between them. The blades are placed between the spacers, then the tiny assembly is compressed, causing the flexible spacer to deflect. This reduces the distance between the island spacers by a few micrometers, increasing the accuracy of the spaces between the blades. The final assembly is created by placing groups of these tiny spacer/blade assemblies at intervals of three millimeters using precision reference frames.

Peter V. Pistecky (left) and his associates Henk van der Wulp and Frans van Rongen in the clean room after assembling the GRID spacer. The spacer assembly measures 13 x 13 centimeters and contains 1,300 blades held in place by 14,300 tiny spacers.

Deflection Analysis Critical

"The deflection of the flexible spacer was a critical part of the Algor analysis," says Mr. Pistecky, "The accuracy required was measured in tens of nanometers. The spacer model was built using plate elements. The displacement, forced by the island spacers, was modeled with displacement boundary elements. In addition to displacement data, this technique also allowed us to determine the spring stiffness of the spacer package."

More Realistic Model Based on Etching Results

"The spacers are made of a rolled material 100 micrometers thick, then etched to a thickness within two micrometers of the specifications," says Mr. Pistecky, "The results of the etching process provided the necessary input for another, even more precise, Algor model of the 'real-world'. We found, for example, that the etched spacer has a nonuniform thickness distribution of between 38 and 45 micrometers in an ellipse-shaped distribution. Even these small differences were implemented in the final Algor model.

"A total of 14,300 spacers were manufactured," continues Mr. Pistecky, "Then, high precision electric discharge machining was used to create the reference frames. The final assembly of the slit patterns was performed in a clean room environment. Our real-world tests show that the final slit pattern assembly behaves according to the Algor analysis prediction."

About Algor

"The most important feature of Algor software is its user friendliness," says Mr. Pistecky, "I use Algor in my courses to explain the basic problems of stress and strain in mechanical parts. I also use the software's design capabilities to build solid models of parts for courses in micro engineering. I capture the screen pictures with Pizazz Plus and print them directly to transparencies. With the Supercap utility I can even add motion to the models. This improves the students' understanding of the problems a great deal.

"I have attended three Algor courses in Pittsburgh and every one was money well spent. I cannot imagine a faster way to become familiar with all aspects of design optimization and analysis. Last but not least," continues Mr. Pistecky, "I want to mention the outstanding service we have received from the people at Algor. Sometimes I feel like Pittsburgh is closer to Delft than some Dutch cities just a few miles away!"

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