Photoacoustic detection and localization of small gas leaks

Abstract

Leak detection and localization are critical manufacturing quality-control processes. Many industrial and domestic machines use or convey pressurized gases or liquids. Unintended leaks from machine components may be detrimental to consumers, manufacturers, and the environment. This paper describes a leak detection technique based on photoacoustic sounds produced by the interaction of a carbon dioxide (CO2) laser tuned to 10.6 micrometers and a photoactive tracer gas, sulfur hexaflouride (SF6), emitted by calibrated leak sources. Acoustic signals generated by a high-speed scan of the laser beam through the cloud of tracer gas formed near the leak are recorded in a bandwidth from 3 to 52 kHz by multiple microphones. From the recorded signals, the presence or absence of a leak may be deduced by comparison with the background noise level at the signal frequencies, which occur at the harmonics of the scan rate. When a leak is present, its location is determined from a simple model of the acoustic environment and matched field processing (MFP). Current results show that a gas leak of 1 cm3 per day can be detected and localized to within +/- 3 mm in a few seconds using four microphones, placed 0.41 m from the leak location, and an incoherent average of the MFP ambiguity surfaces at eight signal frequencies. Comparisons of the Bartlett and minimum-variance-distortionless matched field processors are also presented.

<title>A new approach to photoacoustic measurements</title>

“…Photoacoustic detection and localization of gas leaks in open air was presented by Yönak and Dowling. 12,13 They were able to detect and localize tracer gas leaks (sulfur hexafluoride) with intensity flow of 1 cm 3 per day. In the experiments they used an array of 4 microphones in a single row (B&K model 4136, 1/4"), located 0.41 m from simulated leak.…”

Non-line-of-sight sound source localization using matched-field processing

“…In applications of photoacoustic detection and localization of gas leaks, 7,8 MFP was utilized in an environment where sound arrived from both direct and reflected paths. In ongoing efforts on acoustic localization in urban environments, [9][10][11] MFP and time reversal focusing have been utilized along with finite-difference time-domain (FDTD) modeling of a complex urban environment to localize single acoustic pulse sources.…”

Shallow Water Waveguide Influences on Time Reversing Array Retrofocusing

“…In particular, active TRA systems may facilitate moderate range (tens of kilometers) underwater communication through unknown acoustic environments. Novel uses of time-reversal concepts are also occurring in other areas of acoustics Roux et al, 1999;Yönak and Dowling, 1999).…”

“…In particular, active TRA systems may facilitate moderate range (tens of kilometers) underwater communication through unknown acoustic environments. Novel uses of time-reversal concepts are also occurring in other areas of acoustics Roux et al, 1999;Yönak and Dowling, 1999).The dimensions, field amplitude, and temporal decay of the retrofocus produced by a narrow-band TRA are deter-■'Author to whom correspondence should be addressed. Electronic mail: drd@engin.umich.edu mined by the signal frequency, the source-array geometry, and the acoustic environment.…”