Normal Incidence Impedance Measurement at Elevated Temperatures

An impedance tube, with an associated data analysis method, was developed that allowed the measurement of impedance of acoustic samples at elevated temperatures. The traditional two-microphone impedance tube method was combined with a finite element model that transfers impedance from a transition plane to the sample across a known temperature profile within the impedance tube. This impedance measurement method was validated at room temperature by comparing the results with predicted impedance from empirically based impedance models and with impedance measurements in a standard traversing microphone impedance tube. Impedance for four samples was measured at elevated temperatures, and the results were compared to room temperature measurements. For two of the samples, the impedances measured at elevated temperatures were compared to the results of extensions of room temperature empirical models, confirming the trend of the results of the elevated temperature measurements. Finally, this work examined uncertainty in measured impedance due to uncertainty in the definition of the temperature profile in the air within the impedance tube. © 2011 by the author(s).