Acoustic resonance spectroscopy of soft solids.

An acoustic resonance apparatus for probing mechanical properties of materials with soft to moderate hardness (elastic modulus <5 GPa) is described. The technique employs stereo phono-needle transducers suitable for measurements in the range from 40 Hz to 40 kHz which are very weakly perturbing to the sample and have polarized excitation and detection. Identification of the normal modes is facilitated by the polarization information, and the technique is applicable to materials ranging from soft elastomers to hard plastics. The experimental setup is described in detail, and the utility of the technique is showcased in three example applications.