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uni'wissen 01-2014_ENG

cylindrical prototype was only four centimeters wide and five centimeters long. Petsch contrib- uted a rubber-like lens that can be deformed with tiny motors, and Schuhladen designed an iris made of controllable liquids. The images taken by an image sensor equipped with the prototype were of excellent quality. “It was possible to set the sharpness and lighting according to the same principle at work in the eye – an initial success,” says Zappe. Bottles of ink and electronics are laid out on Schuhladen’s laboratory workspace. He mixes liquids and wires up circuits to create a liquid iris that opens and closes on demand. The iris is made of a clear oil and a black ink. He pours them into a chamber between two sheets of glass equipped with transparent electrical contacts. The liquids do not mix, since one of them is oil-based while the other is water-based. The ink is in a ring within the oil. The liquids stay in place even if you shake the chamber, because they have the same density. By applying an electrical voltage to the liquid on transparent electrodes, a method known as electrowetting, Schuhladen can cause the dark ring to expand and contract. The iris then allows more or less light to pass through. The challenge for Petsch is to develop a tech- nique for deforming the rubber-like lens. He applies tiny anchors to the sides of the rubber. Micromotors pull the lens apart, making it flatter. This allows Petsch to regulate the focal length in the exact same way the eye does, by changing the curvature of the lens. A stretchable lens like this can also be used to correct imaging errors like those caused by an astigmatism, since it can be bent in an irregular shape. The next step will bring the researchers even closer to their goal of imitating the human eye: They are currently working on a synthetic muscle capable of deforming the lens exactly like an eye muscle. It is made of plastic material, a so-called liquid crystal elastomer (LCE), which shortens with increasing tempera- tures. This synthetic muscle will assume the role of the micromotors. It was developed by a team at the University of Mainz that is collaborating on the project. Zappe also wants to combine the “Potential areas of application for this system we see include camera technology, medicine, and microscopy.” In analogy to the structures of the human eye, the integrated eye is composed of an iris (black), a lens (blue), and a sensor (orange). The opening of the iris and the curvature of the lens can be adjusted in the bionic imaging system – like in its model from nature. The optofluidic iris consists of an ink ring embedded in oil. When an electrical voltage is applied, the ring of ink expands: The iris closes and allows less light to pass through. The flexible plastic lens (blue) hangs on muscle-like elastomers (red) that contract when heated by a power source, causing the lens to flatten. In the human eye, the ciliary muscles (red) change the curvature of the lens. The retina (orange) receives the image information and passes it on to the brain via the optical nerve (green). In the bionic imaging system, a sensor (orange) identifies the image information and passes it on to a micro-controller (green), where it is processed to create an image. Illustration: Gisela and Erwin Sick Chair of Micro-Optics 30