Experimental and numerical analysis methods for improved material characterization using a standing wave impedance tube

Standing wave impedance tubes are one of the most commonly used methods to characterize the acoustic properties of materials, but they are often limited in frequency bandwidth below the plane wave propagation limit of ω = 1.84c/a, where c is the speed of sound, and a is the radius of the tube. We show that for commonly used materials, the singular values of the transfer matrices in both the fluid media as well as the test sample limit the measurement range before the plane waves begin to break down. This presentation will go through various experimental techniques and numerical analysis methods to mitigate measurement errors due to small singular values. Using these processes, we will show improved experimental results, particularly in the case where anechoic terminations are unavailable or difficult to achieve.