Celerity and thickness measurements by ultrasound in protons exchange membranes

Acoustic measurements of protonic membranes thicknesses are performed by using Insertion/Substitution technique. Ultrasound celerity in this material is firstly determined from time domain analysis of the received signal of a thick membrane. This celerity is then used to measure the different thickness of the samples from frequency analysis. Indeed, the ratio between the reference and transmitted spectra shows resonances due to the multiple transit echoes in the layer. The measurements on the dry membranes give a celerity of 1240 m/s. The measurements on fully hydrated membranes show an increased thickness of 10 - 15 %. This latter has to be compared to the typical swelling of 10 % reported in literature.