Polarised piezoelectric ceramic crystal - has varying polarisation applied to give required characteristics for varying focal length of mirror

摘要

In the process for polarising a piezoelectric ceramic crystal (1), a block of dielectric constant equal to that of the crystal is placed in contact with the upper surface of the crystal. An electrode layer (2) is formed on the under surface of the crystal. The dielectric block, which is a solid of revolution, is stepped, being thickest at its centre, and thinnest at the edges. Three separate conductive layers (7, 8, 9) are applied to the steps of the block, so as to form capacitors with the lower conductive layer. A voltage is applied between the upper and lower conductive layers to create inhomogeneous polarisation in the piezoelectric crystal. The crystal is used for electrically controlled, variable focus mirrors.