| 摘要 |
<p>The membrane (6) has a ring shaped fastening surface (12) concentric to a flat central surface (26). The ring shaped surface forms the radially outer edge of the membrane with the membrane also having a ring shaped connection surface (54) which connects the central surface with the edge surface. The connection surface is not flat overall and is formed by at least one ring shaped step (36,44,52). This comprises a flat annular surface (32,40,48) and a truncated cone surface step surface (30,38,46) which is connected radially inwards to the annular surface. The annular surface and the central surface lie in parallel planes with the height of each step surface measured perpendicular to the plane of the central surface being very small in relation to the width of the step.</p> |
