Abstract: A sounder device includes a piezoelectric resonant transducer, an amplifier and a coupling transformer to drive the transducer, an electronic signal produced to provide an input signal to the amplifier, and in which the electronic signal producer includes at least two lower frequency oscillators, a logical “OR” circuit having inputs from each of the lower frequency pulse oscillators, a resonant frequency pulse oscillator having a higher frequency near the resonant frequency of the transducer, a logical “AND” circuit having a first input connected to the output of the logical “OR” circuit, a second input connected to the output of the resonant frequency oscillator, and having an output connected to the amplifier input.

Abstract: A filter cartridge has a tubular filter element made from a porous, flexible sheet forming an annular succession of pleats having axial ridges, in the form of vanes all curved in a same circumferential direction, each vane comprising an upper face and a lower face. The lower face and upper face of each vane has lines of least resistance forming hinges, enabling the curvature of the vanes to be better controlled.