Tests on the vibro-acoustic behaviour of a brushless DC-motor

In the design of rotating electrical machines, the vibro-acoustic behaviour becomes an important criterion. In an electrical machine, electromagnetica lly induced forces may cause vibrations of for instance, the stator. These vibrations may radiate annoying acoustic energy, especially at resonances o f the stator assembly. This paper describes some techniques to analyse the vibro-acoustic behaviour of a (brushless DC-) motor. However; the technique is quite general and cart be used for all types of electrical machines. Th e "inverse-frequency-response-function" technique (IFRF) allows the identif ication of the actual vibration behaviour of the motor frame from the measu rement of the acoustic field around the motor. Experimental modal analysis yields the resonant behaviour of the motor: A combination of both technique s indicates the critical resonances, causing the undesired acoustic emissio ns. This may lead to an improved, quieter design of the electrical motor.