Abstract: A piezoelectric transducer in the form of a spheroidal cap comprises a mosaic of individual piezoceramic elements having a height of 3 to 10 mms and a lateral extension that does not substantially exceed the height there being gaps between the piezoceramic elements which are filled with an electrically insulating material having a modulus of elasticity which is smaller by at least one order of magnitude than that of the ceramic material, with the rise of the spheroidal cap amounting to at least 5 cms and the apex angle of the corresponding spherical sector amounting to at least 60.degree..

Abstract: A piezoelectric transducer for destruction of concretions inside the body. The transducer essentially comprises a spheroidal cap having piezoelectric ceramic elements situated at its radially inner front side. To prevent overpressure pulses radiated at the front side of the transducer being followed by underpressure pulse reflected from the rear side of the cap, the cap is produced from metal, preferably from a copper alloy. The impact wave resistances of the cap metal and of the ceramic material should largely correspond. Furthermore, the rear-side surface of the rear wall of the cap is so shaped geometrically and/or provided with a coating, that the sonic waves reflected therefrom are no longer focussed.

Abstract: A sound deadening system is provided, comprising a laminate of a covering stratum of closed-cell soft foam having a bulk density of less than about 50 kp/m.sup.3, and a core stratum having cavities and joined to the covering stratum at locations spaced from one another by a distance less than about 10 times the thickness of the covering stratum, the total area of the joinders between the covering stratum and the core stratum being less than about 2/3 of the covering stratum area. The core stratum may have a honeycomb structure, such as expanded sheet metal, a closed-cell soft foam possibly in granular form, etc. The laminate may include additionally an additional covering stratum on the other side of the core stratum or even multiple layers of alternating covering and core strata. A paper sheet may be provided on the last core stratum for cementing to a surface. Reinforcements can be provided embedded in or on the back of the core stratum, e.g. a metal sheet.