Acoustic wave propagation in a sensor port: Experimental measurements and analytical model predictions

In this paper, results from an experimental study on pressure fluctuations in a sensor port are presented. The sensor ports are attached to a large flat plate over which plane acoustic waves propagate. In addition, an analytical model is developed by solving the acoustic wave equation subject to rigid and pressure release boundary conditions. The experimental data is used as input to the model from one end of the sensor port in order to predict the pressure fluctuations at the other end of the sensor port. Two sensor ports are used; a short and a long one. The short sensor port resonates at 1000 Hz, whereas the long sensor port resonates at 245 Hz. The acoustic source generates harmonic and random plane acoustic waves, which can be modeled easily. Pressure fluctuation measurements are made both on the plate surface and inside the sensor ports for various plane wave inputs; harmonic and random. Power spectra, sound pressure levels and transfer functions are then obtained at the various microphone locations. The experimental results for the short sensor port show an amplification factor of 45 between the inlet and the rigid end of the sensor port at a frequency of 1000 Hz. For the long sensor port, the amplification is nearly 50 at a frequency of 245 Hz, with lower amplifications at higher frequencies. Using the measured power spectrum at the rigid end of the sensor port for a random plane wave input, the absorption coefficient is calculated using the half-power law. Using this absorption coefficient in our analytical model, predictions were made at both ends of the sensor port using experimental data as input. The model predictions for both sensor ports are in good agreement with experimental data.