35 research outputs found
Calibration of a micromachined particle velocity microphone in a standing wave tube using a LDA photon-correlation technique
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
Measurement of absorption with a p-u sound intensity probe in an impedance tube
An alternative method of measuring the normal-incidence sound absorption of a sample of material in an impedance tube is examined. The method is based on measurement of the sound pressure and the normal component of the particle velocity using a "p-u" sound intensity probe. This technique is compared with the traditional, well-established "transfer function method" based on two pressure microphones. The results suggest that the new method can be as accurate as the established method, but whereas the influence of transducer mismatch on the transfer function method can be eliminated using a simple "sensor-switching technique," the method based on a p-u intensity probe relies on accurate calibration of the probe
Statistically optimized near field acoustic holography using an array of pressure-velocity probes
Taenia solium Cysticercosis, Irian Jaya, Indonesia
Centers for Disease Control and Prevention, Toni, Wandra ; Akira, Ito ; Hiroshi, Yamasaki ; Thomas, Suroso ; Sri S. Margono, Emerging Infectious Diseases, 9(7), 2003, 884-885.
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Exploring the use of the microflown
This thesis discussed several acoustical measurement techniques based on the application of a relatively new acoustical particle velocity sensor
Acoustic holography with incoherent sources
In near field acoustic holography the sound field is scanned near the surface of the vibrating object; from these measurements the vibration of the structure can be calculated. In the case of correlated sources one reference signal is sufficient. When incoherent sources are present the separation of the different sound fields is difficult. Using, instead of a pressure microphone, a particle velocity sensor from which the particle velocity vector is calculated the incoherent sound fields can be separated