Abstract: A method of joining two sheets each comprising a metallic foil and heat-sealable material comprises applying heat and pressure to squeeze the heat-sealable material away from a region between the foils so as to provide electrical contact, either directly or by way of an inserted filament, between the foils.

Abstract: An electro viscous vibrator comprises a double-headed dumb-bell shaped piston, of which the two heads are each axially movable within a separate cylindrical chamber, and a pair of concentric annular electroviscous valves in each chamber surrounding the piston head contained therein. Each pair of valves is preferably constituted by an annular electrode assembly disposed between the wall of the respective chamber, and the associated piston head, each valve of the pair being constituted by one of the two annular gaps thus formed between the chamber wall and the electrode assembly and between the electrode assembly and the piston head, suitable electrodes being located on the electrode assembly.