Ultrasound propagation in the micropores of track membranes

Abstract

Air-coupled and high-frequency ultrasonic spectroscopy is used to study ultrasound transmission through track membranes (TMs). Observed behavior, anomalous compared to that observed for other membranes, suggests independent ultrasound propagation through the pores. This is proved experimentally by studying frequency dependence of some acoustical parameters and by closing the pore aperture at the TM surface. This changes boundary conditions so that such wave is inhibited. Ultrasound propagation in such small pores opens up a new way to investigate gas behavior under rarefied conditions and provides a new technique to characterize TMs.

Micro- and nanoporous materials produced using accelerated heavy ion beams

“…The thickness of the membranes is 10 and 12 µm, respectively. The first membrane was prepared for experiments on the propagation of ultrasonic waves through a porous medium [10]. The second one is a conventional microfiltration TM used, for instance, for purifying drinking water [6].…”

Ultrasound attenuation in cylindrical micro-pores: Nondestructive porometry of ion-track membranes

“…Gómez et al [8] show that the theory given by (1) describes quite well the ultrasound transmission through the nonporous foils used to produce itMs. it also describes quite accurately transmission through itMs with sealed pores.…”

“…nevertheless, recent works ( [8], [9]) showed that this assumption is not applicable to itMs. the transmission of airborne ultrasound pulses through these membranes and the influence of pore diameter and boundary conditions (open-and sealed-pore conditions) at the membrane surface were studied [8], and revealed that ultrasound transmission through itMs is the result of two decoupled contributions: transmission through the solid and transmission through the pores. subsequently, a procedure was developed to separate these two contributions [9].…”

“…in addition, the solid frame or porous skeleton may also be rather complex: it may contain fibers, grains or particles and aggregates of them, cracks, and microcracks, and so forth. finally, these problems are especially significant when pore dimensions are in the micrometer scale where the macroscopic description of the fluid may become questionable: both pore diameter and wavelength may become comparable to the mean free path of the fluid molecules [8], [9]. this case has been excluded from the analytical solutions conventionally proposed for sound propagation in narrow ducts [12], [13].…”

“…theoretical Background for ultrasound Propagation in Porous Media sound propagation in fluid-saturated porous media is described by Biot's theory [7], [8]. this theory predicts the simultaneous propagation of two different longitudinal waves (the fast and the slow compressional waves).…”