Abstract: In the manufacture of wave filters, such as FM filters, polarized piezoelectrically responsive wafers are provided, temporarily, on the active regions thereof, with a removable material. Subsequent to the encapsulation of the wafer by a protective but porous coating, the filter is heated and the removable material sublimates through the porous coating establishing a wafer surface substantially free of residual impurities and leaving an uninterrupted cavity between the wafer and the coating in the active regions. The preferred sublimatable material is paradichlorobenzene.

Abstract: A piezoelectric ignition system for a plurality of gas burners includes an elongated adjustably mounted flash tube of high temperature resistant dielectric material mounted adjacent each burner. A pair of electrodes are mounted on each flash tube in spaced-apart relationship to define spark gaps, and are electrically connected in series with one another across opposite sides of a single piezoelectric voltage source. The system is adapted to accommodate heavier and lighter than air combustible gases.

Abstract: A seven character segment display assembly with each assembly including a rotatable drum carrying a character display adapted to be viewed at a window of a stationary mask. The drum includes a permanent magnet which is adapted to be attracted by the poles of a stationary wire coil wound as a bifilar center tapped winding on a core. The control circuit provides a D. C. voltage to the center tap of the coil. The circuit includes first and second invertors having outputs connected to the opposite ends of the coil. The output of the first invertor is connected to the input of the second invertor. A decoder generating logic signal pulses has an output connected to the input of the first invertor.