AN ACTIVE ACOUSTIC GRILLAGE

WE PROPOSE HERE THE CONCEPT OF THE ACTIVE ACOUSTIC GRILLAGE; AN AIR GRILLE COATED WITH THIN ACTIVE SKIN ACTUATORS. THIS GRILLE WOULD REPLACE PASSIVE GRILLAGES COMMONLY USED TO EXCLUDE FOREIGN OBJECTS FROM FAN INLETS AND OUTLETS. ACOUSTIC CONTROL CONSIDERATIONS DEMAND THAT SUCH A GRILLAGE HAVE A CROSS-FLOW CELL SIZE SMALL COMP[ARED TO ACOUSTIC WAVELENGTH; 6 INCHES AT 2 kHz. CONVENTIONAL GRILLAGES MEET THIS REQUIREMENT. WE THUS PROPOSE THUS TO ADD ACTUATION AND CONTROL CAPABILITY TO CONVENTIONAL AIRFLOW GRILLAGE, AND TO USE THIS CAPABILITY TO PERFORM ACTIVE CONTROL OF THE ACOUSTIC EMISSION FROM FAN AIR INLETS AND OUTLETS. WE WILL DRAW ON PRIOR EXPERIENCE IN THIN-FILM ACOUSTIC ACTUATORS. SUCH ACTUATORS, BUILT OF PVDF PIEZOELECTRIC FILM AND LESS THAN 1 MM THICK, HAVE DEMONSTRATED ACTUATION CAPABILITY SUFFICIENT FOR THESE FAN NOISE PROBLEMS. AN ALTERNATIVE USE OF SUCH A GRILLAGE WOULD BE TO FULLY ENCLOSE A NOISE SOURCE (OR A QUIET AREA) WITH SUCH A GRILLAGE, THUS PREVENTING THE TRANSMISSION OF SOUND BUT PERMITTING AIR CIRCULATION.