A noncontact method for determining surface density of nonporous materials with the limp-wall mass law

A new noncontact technique for determining the surface density or mass per unit area of nonporous, homogeneous membranes and foils of sub-wavelength thicknesses is introduced. Surface densities are determined through application of the limp-wall mass law and through-transmission ultrasonic measurements of bulk waves. The ultrasonic measurements are performed with commercially-available, broadband air-coupled ultrasonic transducers. Surface densities of aluminum foil, brass shim, and plastic sheets are typically found to be within 3% of their accepted values.