Since the whole object under investigation will resonate at very specific frequencies, i.e mechanical resonances, air-gaps and other coupling issues do not preclude obtaining vibrational information, which can be directly related to mechanical properties. Three different techniques will be described, along with specific applications for each: Resonant Ultrasound Spectroscopy (small solids of regular shape), Acoustic Resonance Spectroscopy (large, complex, multi-component objects) and Swept-Frequency Acoustic Interferometry (liquids).
