Alternatively, as shown in FIG. 6, the intermediate layer 6 shown in FIGS. 1 and 2 may be replaced with a new intermediate layer 6' comprising a uniform sheet of an elastomeric material which is conductive, e.g., a silicone rubber layer impregnated with conductive particles such as particles of carbon, silver, copper and the like (see U.S. Pat. No. 4,208,648).