Abstract: Foil includes a first etch-resistant layer which at least partially covers the neighboring layer and has a weight per unit area of 0.5-20 g/m.sup.2, a first aluminum or aluminum alloy layer having a thickness of about 30 .mu.m to 150 .mu.m, a dielectric layer of plastic having a thickness of about 5 to 100 .mu.m, a second aluminum or aluminum alloy layer having a thickness of about 30 .mu.m to 150 .mu.m, and a second etch-resistant layer which at least partially covers the neighboring layer and has a weight per unit area of 0.5 to 20 g/m.sup.2.

Abstract: To adapt the frequency band of oscillating circuits with frequencies greater than the set frequency, made from a metal-plastic-metal sandwich foil useful as an identification label and manufactured from rolls (1) of sandwich foil connected to each other by at least one plastic film, the oscillating circuits are conveyed almost continuously through two frequency-measuring cells (5,6) between which is located a reduction unit (7). After comparison of the set value and actual value, the frequency band of an oscillating circuit is adapted by reduction of the capacitor part of the oscillating circuit by means of the reduction unit (7), which is controlled by the correction unit (8).

Abstract: A metal strip is used for elements in a regenerative heat exchanger employed for the exchange of latent and sensible heat from a warm outgoing air stream to a cold ingoing air stream. The strip is placed alternatingly in the form of flat and corrugated sheets to form flow channels for the warm and cold air. The metal strip, for example, an aluminum foil, is coated or laminated at least on one side with a paper-like hydrophillic material. The hydrophillic layer comprises a mixture of cellulose fibers and fibers with olefin hydrocarbons as basis. Furthermore, fungicides can be added to the mixture.