Capturing the Shear and Secondary Compression Waves: High-Frame-Rate Ultrasound Imaging in Saturated Foams.

We experimentally observe the shear and secondary compression waves inside soft porous water-saturated melamine foams by high-frame-rate ultrasound imaging. Both wave speeds are supported by the weak frame of the foam. The first and second compression waves show opposite polarity, as predicted by Biot theory. Our experiments have direct implications for medical imaging: melamine foams exhibit a similar microstructure as lung tissue. In the future, combined shear wave and slow compression wave imaging might provide new means of distinguishing malignant and healthy pulmonary tissue.