Calibration of a micromachined particle velocity microphone in a standing wave tube using a LDA photon-correlation technique

Abstract

In this paper, a new method of calibrating an acoustic particle velocity sensor using laser Doppler anemometry (LDA) is discussed. The results were compared and were in good agreement with the results obtained by conventional methods, where the sensitivity of the microflown is obtained with the use of a reference microphone and a standing wave tube. The LDA signal generated by the acoustic particle motion was analysed using the photon-correlation method, where the signal is considered to consist of a series of discrete photon events. The photon-correlation system is used to measure particle velocity amplitude next to the microflown particle velocity sensor in a standing wave. Measurements are performed for frequencies between 250 Hz and 4 kHz and velocities between 5 mm s−1 and 25 mm s−1 (root-mean-square (rms) values) which are equivalent to sound fields of 100 and 114 dB SPL in free field. From the output voltage of the probe microflown and the LDA-derived particle velocity in a standing wave, the sensitivity of the microflown is obtained. The two different calibration methods are in good agreement showing a discrepancy of 1 dB for the frequency range of 250 Hz–4 kHz.

Full bandwidth calibration procedure for acoustic probes containing a pressure and particle velocity sensor

“…Non-ideal behavior, such as damping due to viscous and thermal effects and non-ideal reflection of the rigid termination, can be neglected. 8 The relation between pressure p͑x͒ and particle velocity u͑x͒ at an arbitrary location in the tube is given by…”

“…The solution is to create an environment where the acoustic impedance is known. The calibration technique used so far was based on a standing wave tube, 7,8 which could only be used for low frequencies. Recently a high frequency approach was introduced by Jacobsen and Jaud based on a spherical source.…”

An integrated three-dimensional sound-intensity probe

“…For a particle velocity sensor there is no straightforward reference sensor available, so a workaround must be used. A method to calibrate the sensor with a reference particle velocity sensor is described in [40], but this requires expensive equipment and a delicate setup. In certain situations there is a well defined relation with sound pressure however, and reference sound pressure sensors are fully available.…”

Study and development of an in situ acoustic absorption measurement method

“…The impedance of a piston-on-a-sphere is given by [48,88]: . Although the description of the impedance of the spherical sound source is rather complicated, quantitatively, the outcome is similar to that of a monopole.…”

“…Laser Doppler anemometers [88] and microphones can be used as reference, of which the latter are more often used because they are generally available in acoustic labs. An example of such an environment is a standing wave tube where plane waves propagate in one dimension below the tube's cut-off frequency [88,89].…”