Variable-frequency polarization of a piezoelectric actuator

A piezoelectric actuator (2, fig 1) for a fuel injection valve (1, fig 1) has an actuator body (23, fig 1) that comprises a plurality of ceramic layers (26, 27, fig 1) and a plurality of electrode layers (28, 29, fig 1) disposed between the ceramic layers (26, 27, fig 1). The domain structures in the ceramic layers are formed by variable frequency polarization, which may be effected in three intervals T1, T2, T3. Upon the transition to a subsequent interval of the variable frequency polarization, the frequency f of the polarizing voltage is reduced and the amplitude of the polarizing voltage is increased.