In this case, the modal characteristics of a Printed Circuit Board (PCB) is acquired by performing experimental modal analysis. A hammer impact test is carried out with a single teardrop uni-axial accelerometer to study the modal behavior. The roving excitation method helps users completely avoid the mass loading effect that might be introduced with a roving response procedure. Since the PCB is lightweight, the selected hammer and sensor were chosen because they weigh considerably lesser than the board itself. To excite the higher frequency modes, a hard tip is chosen. The hammer impact test module of the EDM Modal suite assists in executing this test.

Operating Deflection Shape (ODS) Analysis helps users understand the dynamics of the unit under test by animating the test structure’s vibration. As the term suggests, the structure’s deformation during operating conditions is visualized. This aids in understanding the forced response of the test unit.

Modal testing and analysis are important processes that improve the design of a product. Therefore, it is crucial to ensure testing is carried out with optimal settings. The Shaped Random and Burst Shaped Random output excitation introduced by Crystal Instruments provides unique advantages such as a better estimation of the quality factor, damping and FRF amplitude. This indicates that the obtained modal parameters are more accurate. A modal test is carried out to examine the data to see the improvement in the results with these newly introduced techniques when compared to the conventional shaker excitation signals. The green curve shows the FRF obtained using the Shaped Random excitation and the blue curve shows the FRF obtained using the white noise excitation. As illustrated, the advantages of shaped peaks using the newly introduced approach leads to more accurate estimations of the quality factor, damping and FRF amplitude as discussed in the forthcoming sections.

Analyzing the modal parameters of a structure is crucial in optimizing the mechanical properties of the test object. The natural frequencies, damping and mode shapes of the unit under test help in adjusting the design of the test structure which ultimately improves the structural behavior of the test unit.

The latest 8.1 release of the Crystal Instrument’s EDM Modal software features multi-Resolution spectrum technology implemented into the MIMO FRF testing suite. Multiple passes of FFT yield a much finer resolution in the lower frequency region. This provides the advantage of a better estimation of the quality factor (or damping) and the amplitude of the frequency response functions at the resonant frequencies.

Studying the modal properties of the structure under test is important to optimize the design of the test structure and to improve the NVH characteristics. Finite Element Analysis is widely used to obtain the mechanical properties of different objects. However, it is not only difficult to replicate the exact environmental constraints and boundary conditions but also challenging to obtain the damping ratios of the different modes. Experimental modal analysis not only helps in solving these issues but can also help in validating the results of the finite element model.

Roving excitation or response? Uni-ax or Tri-ax? SIMO or MIMO?

A modal impact hammer test is broadly classified between two types: roving hammer and roving response. Each method has its own pros and cons.