On the validity of Wood’s law: From bubbly media to liquid foams

We report on the acoustic properties of various bubbly gels and foams in order to test the validity of Wood's law over a very wide range of gas concentration. By using a "double-syringe" technique, we obtain homogeneous mixtures of gas and liquid with controlled gas volume fractions ranging from 0 % to 100 %. The sound speed of acoustic waves propagating in these complex media is extracted from measurements performed at 20 kHz and reveals an excellent agreement with Wood's prediction. Attenuation measurements also complete the acoustic characterization of these bubbly media and foams.