The parameter modification of the initial finite element model (FEM) to match its modal data with the experimental ones requires the modal sensitivity matrix. There are two cases in which this method can't be applied successfully; the deficiency of the necessary modal information and the ill-conditioning of the modal sensitivity matrix. In this research, a novel concept that introduces the feedback loop from the sensors to the exciter of the conventional modal test setup is proposed. The research is focused on the ill-conditioning problem. Ill-conditioning happens by the similar modal sensitivities of some parameters. The feedback loop can alter the effect of the parameter to the system response. That means the modal sensitivity of the parameters becomes different from the original ones by the feedback loop. Through the proper use of feedback loop, we can change the similar modal sensitivities of some updating parameters and consequently update the system parameters successfully, which is impossible with the conventional open loop approach because of the ill-conditioned sensitivity matrix.
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