Characterization of ion-track membranes by non-contact ultrasonic magnitude and phase spectroscopy

A novel non-contact and air-coupled ultrasonic technique to characterize ion-track membranes (ITM) is described and tested. It is based on the application of Fourier spectral analysis to ultrasound pulses transmitted through ITM, thus both magnitude and phase of the transmission coefficient (TC) are obtained. It takes advantage of the fact that ITM offer two rather decoupled paths to ultrasound propagation: the solid foil and the pore space. As propagation in the pore space can provide significant information about the pores, a procedure is developed to distinguish between these two contributions. This procedure is applied to TC measurements performed on a set of membranes specially produced and characterized for this purpose and having different pore density, pore size, and pore tilting angle. Influence of such membrane properties on ultrasound propagation in the pore space is analyzed.