Wideband characteristic impedance measurement based on cylindrical wave decomposition in an impedance tube

Characteristic impedance is one of the most important parameters for evaluating acoustic materials within the acoustic materials community, particularly for porous materials. Limited by the measurement method and models, there have been few studies involving the characteristic impedance at high frequencies (above 5 kHz). This work extends a characteristic impedance measurement across a broad frequency range based on the three-microphone transfer function method. Impulse responses are measured at various circular positions. Cylindrical wave decomposition facilitates the extension of the frequency range with these impulse responses. With a theoretical air layer treated as testing material, the measurement method is validated over a wide frequency range.