Complex modal testing is employed to obtain the directional frequency responses of a four-axis active magnetic bearing system. In the test, magnetic bearings are used as exciters while the system is in operation. The directional frequency response estimates are then used to effectively identify the parameters of the active magnetic bearing system. Experimental results show that the directional frequency response function, which is properly defined in the complex domain, is a powerful tool for identification of bearing as well as modal parameters of the system.

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