Experimental Modal Analysis (EMA) is the classical modal testing approach that has been used in the industry since the introduction of the Fast Fourier Transform (FFT) in computer science.

The basis for modal parameter estimation in EMA is the estimation of Frequency Response Functions (FRF). The FRF is estimated in various ways as a ratio between the output (response) spectrum and the input (force) spectrum.

EMA is suitable for testing structures that can be isolated from the surroundings during the test. Isolating the structure is necessary to ensure all input supplied to the structure during testing is measured. Normally, the input is produced either by an impact hammer or a dynamic shaker.

Since all input are measured the FRF becomes a very clean function that only contains information about the structure’s dynamic behaviour. This is why the FRF has become the preferred basis for EMA modal estimation algorithms.

To estimate mode shapes and to accurately estimate closely spaced modes, it is necessary to estimate multiple FRF’s describing the input/output relation between different location on the structure. The following testing schemes are typically used:

• Single-Input Single-Output (SISO).
  A single force and response location is used. Only natural frequency and damping ratio of well-separated modes can be determined.
• Single-Input Multiple-Output (SIMO).
  A single force location and multiple response locations is used. Mode shape, natural frequency and damping ratio of well-separated modes can be determined.
• Multiple-Input Single-Output (MISO).
  Multiple force locations and a single response location is used. Mode shape, natural frequency and damping ratio of well-separated modes can be determined.
• Multiple-Input Multiple-Output (MIMO).
  Multiple force and response locations are used. Mode shape, natural frequency and damping ratio of closely spaced and repeated modes can be determined.

Test Geometry:

• Can be prepared through the Prepare Geometry Task
• Can be imported from Universal File Format (UFF/UNV), SVS Configuration File Format (CFG), AutoCAD DXF/DWG, Stereolithography File Format (STL)

Frequency Response Functions:

• Can be estimated using the internal impact testing module
• Can be imported through Universal File Format (UFF/UNV) and Dewesoft Data File Format (DXD)
• Raw input/output time domain measurements can be imported from measurement files through the Manage Measurements Task, or SVS Configuration File format. FRF’s are then estimated through the Prepare Data Task.
• DOF information can be assigned the FRF’s through the Assign DOF Information Task.

Internal Impact Testing Module:

• Require a data acquisition plugin license for one of the supported data acquisition systems
• Support data acquisition systems are:
  • National Instrument modules that can be controlled using NI-DAQmx driver
  • SINUS Messtechnik Apollo acquisition modules
  • HGL Dragonfly acquisition modules
  • Hottinger Baldwin Messtechnik (HBM) MX1601, MX840 and MGCplus devices
  • Support IEPE sensors with or without TEDS
• Seamless integration with all other tasks in ARTeMIS Modal EMA
• Module for setup of impact hammer threshold, data acquisition and windowing
• Support for H1, H2 and Hv FRF estimators
• Visual and oral guiding of measurement sequence
• Automatic measurement sequence with multiple impact rejection options
• Display of frequency domain functions: FRF’s, spectral densities, and coherence
• Display of raw time domain recordings optionally with windowing visualized

Complex Mode Indicator Function (CMIF) – Peak Picking:

• Intuitive modal parameter estimation based on peak-picking in frequency domain
• Immediate results even in case of hundreds of measurement points and modes
• Estimates natural frequencies, damping ratios and mode shapes using manual and/or automatic mode estimation
• Extremely robust being based on the Singular Value Decomposition of the matrices of the Frequency Response Functions
• Automatic correction of damping estimates in case exponential windows are used during internal impact testing

Rational Fraction Polynomial in Z domain (RFP-Z):

• Estimates global modes from stabilization diagram of modes extracted from rational polynomials
• Estimates natural frequencies, damping ratios and mode shapes using automatic mode estimation
• Cursors used to select the frequency range to use in the polynomial estimation
• Automatic correction of damping estimates in case exponential windows are used during internal impact testing
• Modal alignment diagrams of natural frequencies, damping ratios and mode shape complexity
• Validation of measured and synthesised FRF’s. Synthesised FRF’s are based on user choice of estimated modes

Mode Validation:

• Auto- and Cross Modal Assurance Criterion of estimated mode shapes
• Mode shape complexity diagram
• Overlaid- and difference animation of mode shapes
• Side-by-Side and Top-Bottom animations of mode shapes
• Import and validation of modes from third party software through Universal File Format (UFF/UNV)