Impulse excitation technique
The impulse excitation technique measures:
- Resonant frequency
- Damping or internal friction
And the RFDA software calculates:
- Young's modulus
- Shear modulus
- Poisson ratio
To perform a measurement, a sample is supported in 2 points (the nodes) and gently tapped with a little hammer in the anti-node:
The vibration signal emitted by the sample is captured using a microphone and sent to the RFDA (Resonant Frequency and Damping Analysis) software. The software package uses a fast Fourier transformation to calculate an initial resonant frequency and uses this information to rebuild the vibration signal. It alters the build up vibration signal with the measured vibration signal in an iterative process until there is a match between both vibration signals. The resonant frequency displayed by the software is the resonant frequency of the rebuilt vibration signal. By doing a deeper analysis of the vibration signal, rather than just the fast Fourier transformation, the RFDA software is able to determine the resonant frequency with high accuracy.
For predefined shapes like rectangular bars, discs, rods and grinding wheels, the RFDA software is able to calculate the sample's elastic properties using the samples dimensions, weight and resonant frequency (ASTM E 1876).