US Patent 8243258 Lithographic apparatus having acoustic resonator

A lithographic apparatus may be provided with an acoustic resonator to dampen an acoustic vibration in the lithographic apparatus. The acoustic resonator may include a Helmholtz resonator. The helmholz resonator may be provided with an active element to provide active damping and/or altering a spring characteristic of the mass spring assembly formed by the resonator. The resonator may be provided at a slit in a shield between the patterning device stage and the projection system to suppress transfer of acoustical vibrations, caused by e.g. a movement of the patterning device stage, to the projection system.