Moving Components in Miniature

There is a special place in the ID building at Ruhr University Bochum: the clean
There is a special place in the ID building at Ruhr University Bochum: the cleanroom. This is where the movable systems are manufactured. RUB, Kramer
Electromagnetic engines can’t be reduced to just any size. It takes clever engineering tricks to generate active movement in miniature format. Researchers in Bochum are constantly coming up with new technologies.

Over the years, a great many technical components have been shrunk in size. But miniaturization reaches its limits when tiny systems are supposed to move actively, because conventional electromagnetic motors become inefficient when reduced to miniature format. Researchers from the Chair of Microsystems Technology at Ruhr University Bochum, Germany, have therefore come up with clever tricks to set them in motion. Their systems are driven by electrostatic force. Applications range from measuring instruments for basic research on living cells to the construction of compact radar systems. The Ruhr University Bochum’s science magazine Rubin has published an

Methods from chip production

Using standard methods from microchip production, Professor Martin Hoffmann’s team in Bochum produces mini actuators consisting, for example, of a silicon substrate and water spheres. By applying a voltage to them, the researchers ensure that an electrostatic force sends the droplets rolling.

"There’s nothing special about making the water droplets move," says Martin Hoffmann. "It has been done for a long time. Our aim is to use the droplets as rollers to transport or precisely align tiny objects." The engineers from Bochum have already shown that the principle is feasible. They created a rolling mini table by attaching a square plate to four drops of water. "We have to apply a water-repellent layer to the underside of the plate to prevent it from getting wet," explains Hoffmann. "Only the four corners have areas where the water adheres to the plate." This is how the rollers are mounted on the plate.

Tiny zoom lens in the pipeline

Backed by the German Research Foundation, Hoffmann’s group now plans to refine this concept. One of their goals is to create a three-dimensional system in which the droplets move through a kind of high-bay warehouse. This would allow them to build a tiny zoom lens in which the droplet would be the lens that could be deformed and moved into different positions.

Moving systems can also be produced entirely from silicon structures with no liquids whatsoever. Martin Hoffman explains the process in a detailed article in the science magazine Rubin, the "In motion" edition. His team uses the technology, for example, to develop a compact radar antenna without a large dish and to build a system that can be used to analyze the behavior of living cells under pressure.