Photoacoustic Leak Testing

Leak testing is a critical manufacturing quality control process. Unintended leaks in pressurized or evacuated containers may be detrimental to consumers, manufacturers, and/or the environment. This paper describes a leak detection and localization technique based on photoacoustic sounds produced by scanning a carbon dioxide laser over leaks emitting a photoactive tracer gas, sulfur hexaflouride. Photoacoustic signals are recorded in a bandwidth from 3 up to 110 kHz by multiple microphones. From these recorded signals, the presence or absence of a leak may be deduced by comparison with background noise levels. 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 ±1 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 twelve signal frequencies.