Resonant frequency and internal friction are like a fingerprint of a specimen’s material structure. Therefore the impulse excitation technique is in some cases perfectly suited to be used as a quality control tool.

Example 1: Diesel particulate filters

Diesel particulate filters (DPF) remove diesel particulate matter or soot from the exhaust gas of a diesel engine. DPF's are produced from porous ceramic honeycomb structures and very hard to measure. The problem with most measurement techniques is they damage the porous structure by applying to much force. The impulse excitation technique applies only weak forces by gently tapping the sample on measurement and is therefore perfectly suited to asses the quality of DPFs.

Example 2: foam components

The damping potential for the application of integral foam components in lightweight structures was evaluated. The damping can be increased significantly by reducing the relative density. The damping behaviour is proportional to the ratio of gas volume to the metal volume [1].

In the figure bellow we see the loss factor as a function of relative density for the first three modes of casting.


  1. A.Trepper, C. Körner, R.Singer. Structural Damping of Integral Foam Componets. Porous Metals and Metallic Foams, Procedings of the 5th Intl Conf on Porous Metals and Metallic Foams, Sept. 5-7, 2007, Montreal, pp. 43-46, 2008