A membrane receives an incident energy signal at a first surface of the membrane. An actuating electrode, located adjacent to the membrane on a side opposite the first surface, applies an actuating pressure to the membrane if an actuating potential is applied between the actuating electrode and the membrane. A restoring electrode, located adjacent to the first surface of the membrane, applies a restoring pressure to the membrane if a restoring potential is applied between the restoring electrode and the membrane. The restoring electrode has an outer surface defining an aperture that enables the incident energy signal to pass, for example, without significant obstruction and without significant attenuation, through the restoring electrode to impinge upon the membrane, and the length of the restoring electrode is at least as great as the smallest width of the aperture.