ELECTRICALLY CONTROLLABLE FILTER DEVICE

摘要

The present invention relates to an electrically controllable filter device comprising an electrode structure which induces a filter for waves within a given wavelength range. The electrode structure is so formed that it within the given wavelength range acts as a filter merely upon electrical feeding whereas it in the absence of electrical feeding has no filtering effect. Furthermore, the electrode structure is so arranged that the filter depending on how the electrode structure is fed can be tuned to a number of different discrete frequencies.