An Overview of MIMO-FRF Excitation/Averaging Techniques

The use of controlled excitation is fundamental to the estimation of multiple input, multiple output (MIMO) frequency response function (FRF) data. The characteristics of the excitation greatly influences the quality of the resulting MIMO-FRF measurements. This paper presents an overview of the basic excitation methods, such as random, periodic random, pseudorandom, and burst random (random transient) as well as more advanced excitation methods, such as burst-cyclic random, slow random, MOOZ random, and periodic chirps. The application of these excitation methods is discussed relative to lightly or heavily damped systems, systems with small non-linearities, and peak to RMS (crest factor) as well as signal to noise ratio (SNR) issues. Experimental examples are given to demonstrate the important issues. Nomenclature Navg = Number of RMS spectral averages. Nc = Number of cyclic averages. Nd = Number of periodic delay blocks. Ni = Number of inputs. No = Number of outputs. Fmin = Minimum frequency (Hz.). Fmax = Maximum frequency (Hz.). Δ f = Frequency resolution (Hz.). T = Observation period (Sec.). 1