Vacuum Bag Leak Detection with Acoustic Cameras: Application Note

Posted by Batter Fly 20-02-2026 0 Comment(s) 629 Warmtebeeld- en akoestische camera's,

Introduction

In the composite materials manufacturing sector (aerospace, marine, automotive), the vacuum resin infusion process is critical. The presence of micro-leaks in the nylon bag compromises the structural integrity of the piece, causing porosity or dry spots. Locating these leaks in large components can be like looking for a needle in a haystack.

Acoustic cameras (or Acoustic Imagers) represent the solution of excellence, transforming the imperceptible noise of an air leak into a clear and immediate visual image.

Why Use Acoustic Technology?

Traditionally, leak detection is carried out using point-source ultrasonic devices or, worse, through human hearing and manual visual inspection. Here is why the acoustic camera is superior:

Scanning Speed: You can inspect square meters of surface in a few seconds, simply by framing the area.
Safe Distance: There is no need to physically pass over every inch of the bag; you can detect leaks even from several meters away.
Precision in Noisy Environments: Thanks to beamforming and frequency selection, the camera filters out the workshop's background noise, focusing only on the acoustic signature of the leak.
Instant Documentation: Each leak is photographed and geolocated on the part, facilitating immediate repair with sealant tape (tacky tape).

The Physical Principle: Turbulence and Ultrasound

When external air is sucked into the vacuum bag through a hole (even a microscopic one), a transition from a high-pressure area to a low-pressure area is created. This transition generates turbulence.

This turbulence emits high-frequency sound waves, predominantly in the ultrasonic range (above 20 kHz). Acoustic cameras use an array of dozens of MEMS microphones to calculate the delay with which the sound hits each sensor, triangulating the exact position of the sound source.

Step-by-Step Inspection Guide

1. Preparation and Camera Setup

Frequency Configuration: Set the camera to a range between 25 kHz and 40 kHz. Vacuum leaks in nylon bags produce very "thin" and high-frequency sounds that stand out clearly from the noise of motors or fans (usually below 15 kHz).
Threshold Adjustment: Adjust the sensitivity to eliminate ambient sound reflections and isolate only the sound pressure peak of the leak.

2. Panoramic Scanning

Frame the entire component from a distance of 2-3 meters.
Move slowly along the perimeter of the bag, paying particular attention to critical areas: sealant tape joints, nylon folds (dog ears), and vacuum valve insertion points.

3. Localization and Zoom

Once an acoustic "heat spot" is identified on the screen (often represented as a colored circle), move closer to define the exact point of rupture.

Note: Sound can bounce off the metallic surfaces of the mold. If you see a suspicious signal, change the angle slightly: if the "spot" moves, it is a reflection; if it remains fixed on the bag, it is a real leak.

4. Validation and Repair

Apply light manual pressure near the detected point: if the displayed sound intensity changes, you have confirmed the position.
Proceed with sealing and immediately verify with the camera that the acoustic signal has disappeared.

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Analysis of Results

Leak Type	Visual Signal	Common Cause
Micro-hole in nylon	Small and intense point	Improper handling or dropped tools.
Leak in Tacky Tape	Diffuse signal along the edge	Dirty mold surface or tape not pressed well.
Valve Leak	Concentric circle on the flange	Worn or off-center valve gasket.

To identify micro-leaks in a vacuum bag (vacuum bagging), not all acoustic cameras are created equal. The "acoustic signature" of a vacuum leak is extremely weak and high-frequency compared to a compressed air leak.

1. Crucial Technical Specifications

Feature	Minimum Recommended Specification	Why It Matters
Number of Microphones	At least 64 (preferably 124+)	More microphones increase spatial resolution and the ability to distinguish the leak from ambient noise.
Frequency Range	2 kHz - 65 kHz (or higher)	Leaks in nylon bags often resonate between 30 and 50 kHz. A 20 kHz limit would miss the most useful signal.
Sensitivity (Threshold)	< 0.005 l/min at 5 bar / 0.5m	Must be able to detect microscopic holes (pinholes) even with low pressure differentials.
Field of View (FOV)	62° or higher	A wide FOV allows scanning large molds (aircraft wings, hulls) in a single pass.

2. Essential Software Features

Adjustable High-Pass Filter: You must be able to manually cut all frequencies below 25 kHz. In a workshop, the noise of vacuum pumps or forklifts would otherwise cover the bag's signal.
Multi-Source Detection: The camera must be able to visualize multiple leaks simultaneously on the screen, without the strongest "masking" the weaker ones.
Distance Analysis (Acoustic Autofocus): Since sound intensity drops with distance, the camera must calculate the distance from the bag to correctly estimate the magnitude of the leak.

3. Form Factor and Usability

One-Handed Operation: Fundamental to have the other hand free to apply sealant tape or move piping.
Battery Life: At least 4-5 hours of continuous use to cover the entire bag preparation cycle.
Cloud/Report Integration: The ability to generate an instant PDF proving the absence of leaks.

Conclusions

Integrating an acoustic camera into the infusion process drastically reduces setup times and minimizes the risk of costly scrap. In a sector where the cost of materials and labor is high, the ability to "see the vacuum escaping" is a fundamental competitive advantage.