Determination of surface density of nonporous membranes with ultrasonic immersion measurements

The surface density of nonporous membranes is estimated with a conventional ultrasonic immersion measurement system without need for a priori information about the membrane such as wave speed, density, thickness or impedance under most testing conditions. The derivation, theoretical limitations and practical restrictions of the technique are discussed. The broadband nature of the measurement allows the surface density values to be estimated at multiple discrete frequencies within the useful bandwidth of the transducer. In experimentation, the technique was used to measure surface densities in a range of 0.044–0.328 kg/m2. All calculated surface densities are within 5% or less of their nominal values with an average percent difference of 1.7%.