A technique for measuring velocity and attenuation of ultrasound in liquid foams

► We present a new setup for measuring the ultrasonic transmission through liquid foams. ► Broadband measurements of velocity and attenuation are possible (60–600kHz). ► It is shown that the acoustic properties of liquid foams depend on bubble sizes. ► This work is a first step for acoustic spectroscopy of liquid foams. We describe an experimental setup specifically designed for measuring the ultrasonic transmission through liquid foams, over a broad range of frequencies (60–600kHz). The question of determining the ultrasonic properties of the foam (density, phase velocity and attenuation) from the transmission measurements is addressed. An inversion method is proposed, tested on synthetic data, and applied to a liquid foam at different times during the coarsening. The ultrasonic velocity and attenuation are found to be very sensitive to the foam bubble sizes, suggesting that a spectroscopy technique could be developed for liquid foams.