Modal Assurance Criterion

This article reviews the using of the original Modal Assurance Criterion (MAC). The Modal Assurance Criterion is a statistical indicator that is most sensitive to large differences and relatively insensitive to small differences in the mode shapes. This yields a good statistic indicator and a degree of consistency between mode shapes. The MAC considers only modal shapes which mean that a separate frequency comparison must be used in conjunction with the MAC values to determine the correlated mode pairs. The MAC is often to used to pair modes shapes derived from analytical models with those obtained experimentally. It is easy to apply and does not require an estimate of the system matrices. It is bounded between 0 and 1, with 1 indicating fully consistent mode shapes. It can only indicate consistency and does not indicate validity or orthogonality. A value near 0 indicates that the modes are not consistent.