Hemispheric lens array configured in electronic circuits (University of Illinois, Urbana)
Engineers at University of Illinois in Urbana designed a new type of digital camera lens based on the multiple-lens design found in the eyes of bees and dragonflies. The team led by Illinois engineering professor John Rogers, with colleagues from the U.S., Korea, Singapore, and China published their findings in this week’s issue of the journal Nature (paid subscription required).
Eyes in insects and other arthropods — invertebrate animals with external skeletons including spiders and crustaceans — link together arrays of smaller eyes, each with its own lens and light-sensitive receptor. These collections of small eyes in a hemispheric shape work together to provide arthropods a wide 180-degree angle view, with depth of field and visual acuity not found in man-made cameras.
To design a camera lens with these capabilities, Rogers and colleagues had to start almost from scratch with new materials and fabrication methods. Current camera lenses, for example, are made with glass lenses and detectors built on planar surfaces with silicon carge-couple device (CCD) chips that do not bend or flex. “Full 180 degree fields of view with zero aberrations,” says Rogers, “can only be accomplished with image sensors that adopt hemispherical layouts, much different than the planar CCD chips found in commercial cameras.”
The fabrication process for this new type of lens began with electronics, detectors and lens arrays formed on flat surfaces, using advanced methods from the semiconductor industry. The lens sheet, however, was built on a flexible polymer material similar to a contact lens, with the electronics and detectors bonded together. “To realize this outcome,” says co-author Jianliang Xiao, an engineering professor at Universiy of Colorado in Boulder, “we used soft, rubbery optics bonded to detectors/electronics in mesh layouts that can be stretched and deformed, reversibly and without damage.”
Under pneumatic pressure, the array of lenses formed into a hemisphere, following a precise, pre-determined shape, where the coupled microlenses and detectors maintain their relative position as the hemisphere shape forms. However, the spaces between the microlenses stretched to allow the flat planar surface to form into a hemisphere. The filaments providing the electrical connections formed into tiny springs during the stretching process.
Tests of the device and quantitative ray-tracing simulations show each microlens in the array produces a small image of the viewed object based on the properties of the lens and viewing angle. The individual detectors, however, responds only if a portion of the image formed by its associated microlens overlaps the active viewed area. When stimulated this way, the detectors produce a sampled image of the object that can be reconstructed with models of the optics.
The Rogers Lab at University of Illinois studies the intersection of materials and electronics, particularly soft and flexible materials that can take shapes and perform functions from biology. Rogers is also an entrepreneur, founding a company to commercialize research from his Ph.D. studies.
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