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.