Frequency response functions: Validity and usefulness in nonlinear system identification

This paper considers the role of Higher Order Frequency Response Functions (HFRFs) for characterising nonlinear structures which can be represented by polynomial equations. By considering only the leading diagonals of these multi-dimensional HFRFs, simplifications are possible which allows practical procedures for experimentally measuring these, albeit they are approximations to the exact HFRFs due to the truncation of the series.