Acoustic Detection of Gas Ingress in Vacuum Systems via Frequency Shift Using Marker Gases

Description / Abstract (EN) Abstract This work discloses a method for detecting gas ingress and leakage in vacuum or pressurized systems based on the analysis of naturally generated acoustic signals produced by gas flow through a leakage or non-tightness. The method relies on the observation of shifts in characteristic acoustic frequencies when the gas environment in the vicinity of the leakage is altered. A marker gas or gas mixture with acoustic properties significantly different from those of ambient air—such as speed of sound, density, or molecular mass (e.g., carbon dioxide, helium, methane, sulfur hexafluoride, or other suitable gases)—is introduced locally or by placing the object under test into a controlled gas atmosphere. The resulting change in gas composition modifies the propagation conditions of sound within the leakage, leading to measurable shifts in the generated acoustic and/or ultrasonic frequency components. These frequency shifts are detected using a broadband microphone or acoustic sensor and analyzed in the frequency domain. The method does not require the injection of artificial acoustic excitation and relies solely on the sound naturally generated by the gas flow through the leakage itself. Observable frequency shifts may occur in both the audible and ultrasonic ranges, typically from approximately 1 kHz up to at least 200 kHz, depending on leakage geometry, flow conditions, gas properties, and sensing equipment. The analysis may be performed on individual spectral components, selected frequency bands, or a portion of the generated spectrum, including optional synchronous modulation of marker gas concentration to improve detection reliability. The method can be applied for localized leak searching via directed marker gas exposure as well as for integral testing by immersing the object or system in a marker gas environment. It is applicable to vacuum systems, sealed enclosures, pipelines, technological equipment, and other systems requiring leakage or gas ingress detection, including cases where visual access is impossible. This publication is intended as an open and defensive disclosure to establish prior art and prevent exclusive patenting of the described method.