© De Luca and Fedullo(Left) The design for trapping sunlight using two elliptical mirrors, with M1 collecting sunlight and M2 (the zozzaroid) focusing sunlight back to the vertex of M1 and into the blackbody. (Right) The mirrors used in a scheme for steam generation. Image credit: De Luca and Fedullo.
In the Greek legend of Dionysius' ear, Dionysius made a cave shaped like an ellipse in order to hear the words whispered by a prisoner in one of the foci of the cave. Some science museums today feature a similar exhibit, where two people at opposite ends of a room can whisper into giant ellipses and distinctly hear each others' words. This sort of cave, called Dionysius' ear, has also inspired the design of a new sunlight trap proposed by physicists Roberto De Luca and Aniello Fedullo, both of the University of Salerno in Italy.
As the scientists explain in a study to be published in the
European Journal of Physics, their sunlight trapping system is the optical equivalent of acoustical Dionysius' ear. The design consists of two parabolic mirrors arranged face-to-face. Sunlight first hits the larger mirror and reflects to the smaller mirror placed a short distance away. Then the light from the smaller mirror reflects back, this time being focused into the vertex of the larger mirror. By confining sunlight into this small region, scientists can ideally trap solar radiation. The sunlight is stored in a blackbody, which consists of a cavity with perfectly reflecting inner walls.
"Through a sunlight trap system, solar radiation is first concentrated in a small region of space and then sent into a blackbody, where it can be stored (not for an arbitrary long time, though) for a variety of uses," De Luca told PhysOrg.com. "For example, after having trapped sunlight in a cavity with perfectly reflecting inner walls, what we call a blackbody, one can think of heating water enclosed in a container placed inside the cavity itself. Other uses of this concept are also conceivable."
