What Is Active Thermography? And Why Should Manufacturers Care?
If you work in composites manufacturing, you've almost certainly heard the phrase 'non-destructive testing' and there's a decent chance it makes you think of ultrasonic probes and a specialist who arrives at the end of the build to tell you whether your part is good or scrap.
Here at Bullfrog, we have a different approach to NDT inspections.
Let's start with the basics
Thermography, in its simplest form, is the measurement of thermal radiation. Objects emit thermal radiation as a function of their temperature. And an infrared camera captures spatial variations in that emission as a thermal image, warmer areas and cooler areas rendered in contrasting tones according to the chosen display palette.
Passive thermography uses this as-is. A camera is pointed at a component, and the natural thermal state of the surface is captured, no external energy input is applied. This is useful in some situations but limited for structural inspection.
Active thermography adds an energy input from an excitation source. You deliberately stimulate the surface, typically thermally and the camera tracks how that energy propagates through the material over time.
What Defects Actually Look Like in Thermal Data
Sound material conducts heat predictably. A defect such as a delamination, a void, a dis-bond, an inclusion disrupts that conduction. Different defects produce different thermal signatures depending on how they interact with heat flow, impeding it, accelerating it, or scattering it, but all produce a detectable departure from the response of sound surrounding material.
On a thermal image, defects appear as areas that cool more slowly, heat more quickly, or otherwise behave differently from the surrounding material. With the right excitation source, camera and right parameters you can resolve features just a few millimetres across, beneath the surface of a composite layup.
In Bullfrog's system, the excitation source heats the surface in a controlled pulse. The camera captures a sequence of thermal frames, and image processing algorithms analyse the transient response not just a single snapshot, but the full story of how heat moves through the part.
Why In-Process Inspection Changes Everything
Most NDT methods were designed for end-of-line inspection. You build the part, cure it, finish it then check whether it's acceptable. Ultrasonics, for example, typically needs a completed, cured component. The probe needs good acoustic coupling to the surface, which usually means a gel, water immersion, or at minimum a well-prepared flat face. UT requires sequential, localised scanning with physical contact rather than full-field, non-contact imaging.
Active thermography doesn't need coupling. There is no contact with the part, no coupling medium, and no surface preparation requirement. The excitation source and camera operate at a standoff distance.
The non-contact nature of the technique means inspection is not confined to finished components, it can, in principle, be applied at intermediate stages of the build process, such as between debulk cycles or following ply drops, where contact-based methods would be impractical.
That's not a subtle difference. That's a fundamentally different relationship with quality.
How It Compares to Ultrasonics
Ultrasonics is a mature, well-validated technique and absolutely has its place, particularly for thick laminates and for detailed characterisation of known defect locations. We're not here to dismiss or replace it.
But for in-process inspection of composite layups, the practical comparison looks like this:
Ultrasonics requires contact or immersion, a fully cured part in most configurations, specialist setup, and localised scanning passes. In manual and semi-automated configurations, it is slow, technique-dependent, and usually not practical mid-build.
Active thermography is non-contact, provides full-field imaging in a single acquisition, and can be deployed within a manufacturing environment by personnel trained in the technique rather than requiring specialist NDT resource for every inspection.
For manufacturing environments where cycle time matters and defects introduced mid-layup are the biggest quality risk, that second column is a much better fit.
What Bullfrog Does Specifically
Bullfrog's system is designed to sit in your manufacturing environment, not in a metrology lab. The hardware is robust, portable, and built around the realities of a composites shop floor: limited space, moving parts, variable lighting, time pressure.
The software handles the image processing, anomaly detection, and reporting, thus, giving engineers a clear, interpretable output rather than raw thermal data that requires specialist interpretation. The goal is to make high-quality in-process inspection accessible to the people who are building the parts.
It's not about replacing your NDT team or replacing final end-of-line inspection. It's about giving your manufacturing engineers a tool they can use, at the point where it makes the most difference.
