Abstract: The invention describes a tunable filter arrangement with a plurality of resonators which are coupled to one another and of which there is at least one which comprises a piezoelectric component made of a ferroelectric material and to which a DC voltage source is connected. The application of a DC voltage to the resonator renders it possible to change its electrical properties and thus the overall filter characteristic.

Abstract: A picture display device having a vacuum envelope which is provided with a transparent face plate and a display screen having a pattern of luminescent pixels, and with a rear wall, comprising electron-producing means, an addressing system arranged between said means and the face plate so as to address desired pixels, and, adjacent to the display screen, a plate of electrically insulating material provided with apertures for passing electrons, in operation a voltage difference being applied across said plate, characterized in that the surface at the electron entrance side of the apertured plate is coated with a coating of a material selected from the group comprising nonstoichiometric nitrides, borides and carbides of Al and/or Si, and amorphous Si.