The μ-flown: a novel device for measuring acoustic flows

Abstract

An acoustic wave consists of two elements, the acoustic pressure and the acouslic flow. Up to now one has to measure the pressure and calculale the flow to determine the acoustic flow, so it would be convenient to have a sensor Ibat is able to measure acoustic flows. At the University of Twente a novel device has been de ~eloped which fulfils this need. In this p~per a short introduction to Ihe governing priaciples of this dynamic flow sen~or, the fabrication process, the electronics and some of its interesting applications will be presented. This micromachined device measuring acoastie flows is called the microflown or ~-flown.

Laser method of sound emission control from vibrating surfaces of noise road barriers

“…Intensity sound probes [2][3][4][5][6][7], their arrays and based on them near-field acoustic cameras [8], acoustic holography [9][10][11], or beamforming [12][13][14] are examples of such methods. Each of them can be also adapted as complementary tool for presented method verification.…”

Study and development of an in situ acoustic absorption measurement method

“…However, this probe is rather large, it is susceptible to wind, and there are limitations at high frequencies. In 1994, a sensor called the Microflown was invented, which can directly measure acoustic particle velocity in a small spot (approximately 3 mm x 1 mm x 0.5 mm) compared to the wavelength of audible frequencies [14,15]. This sensor was commercialised in 1997.…”

“…Although the history of sound pressure microphones goes back to 1876, it was not until 1994 before a convenient particle velocity sensor called the Microflown was invented [14,15]. It provides a direct measurement of the acoustic particle velocity and it can be regarded as a point sensor, due to its sub-millimetre dimensions; much smaller than the wavelength of most frequencies of interest [15].…”

“…It provides a direct measurement of the acoustic particle velocity and it can be regarded as a point sensor, due to its sub-millimetre dimensions; much smaller than the wavelength of most frequencies of interest [15]. Microflowns are usually combined with a conventional microphone in a so-called PU probe; where P stands for sound pressure and U for acoustic particle velocity.…”

“…The absorption coefficient can be defined as the ratio of absorbed to ingoing intensity: (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17) Often, a reflecting rigid surface is present behind the sample. Without transmission through the sample, absorption can directly be calculated from the reflection coefficient.…”