| 摘要 |
A touch-sensitive key has a radiation propagating prism or plate 2 between a radiation source 1 and a radiation detector 6. The radiation is propagated from the upper side 3 of the prism or plate 2 so that it reaches and activates the detector 6 via a side surface 5 when the upper surface 3 is touched. External radiation 9 can freely enter the prism or plate and leave via the side surface, but this radiation is not able to activate the detector. In an embodiment (figure 1) the detector 6 is situated at a distance from the side surface 5 so that it cannot be reached by the external radiation. In an alternative embodiment (figure 2) external radiation 18 is subjected to a number of reflections inside the prism or plate 2a and upon each reflection part of the radiation is transmitted through the surface 17 in question to be absorbed in a substrate layer 19. <IMAGE> |
