AKUSTISK RIKTNINGSOMVANDLARE INNEFATTANDE EN ELEKTRETFOLIE, SOM HAR EN METALLYTA OCH SOM STRECKER SIG OVER EN MOTELEKTRODPLATTA, SOM HAR EN METALLYTA

摘要

An electret transducer comprises an electrostatically charged electret foil (10) superimposed directly over a selectively metalized rough surface (16) of a backplate (18). Selective metalization is realized by depositing a thin metal layer (20), the contour of which is defined by a predetermined relationship, over the rough surface (16). The sensitivity of the electret transducer at any point thereon is directly proportional to the width of the metal layer on the backplate. The response characteristic of the electret transducer comprises a main lobe and a plurality of sidelobes below a preselected threshold.