A reading plate has an array of holes in its surface. Rounded ends of rods project selectively through these holes by the action of a set of bimorphous piezoelectric reeds, on which they rest perpendicularly. Each reed is connected to a source of electric voltage which can assume two distinct values...http://www.google.co.uk/patents/US4044350?utm_source=gb-gplus-sharePatent US4044350 - Electromechanical transducer for relief display panel
