Self noise reduction in acoustic measurements with a particle velocity sensor by means of a cross correlation technique

The Microflown is a thermal acoustic sensor which does not measure sound pressure but the accompanying particle velocity (see [1-5]). This particle velocity is deduced from a temperature difference between two heated wires. A drawback is the sensor’s lower signal-to-noise (S/N-) ratio at higher frequencies compared to pressure microphones. A method is presented to reduce the noise by utilisation of cross- instead of auto-correlation spectra of two Microflowns. Dependent on the number of data points used, improvements of the signal-to-noise-ratio as high as 30 dB have be attained. The bandwidth in which the sensor’s noise characteristics are comparable to those of current microphones, thus increases from about 2 to 10 kHz.