How Airborne Ultrasound Seal Inspection Works

Airborne ultrasound seal inspection works by transmitting a focused, high-frequency sound wave from one side of a seal to a receiver on the other side. A well-bonded seal transmits sound consistently; a fold, air gap, inclusion, or unbonded layer reflects sound instead of transmitting it, producing a measurably weaker signal at that exact location.

What's the physical principle at work?

Sound behaves very differently crossing a solid, well-bonded interface than it does crossing a gap of air. The effect is similar to how a double-paned window blocks sound: a continuous, properly sealed pane transmits far less noise than one with a gap in it. In a package seal, the "gap" is exactly the kind of defect that matters — an inclusion, a fold, a channel, or an area that never reached bonding temperature.

What does the signal actually tell you?

Every scan produces a quantitative signal value, not just a visual impression. A strong, uniform signal across the seal indicates consistent bonding; a weak or highly variable signal marks delamination, incomplete sealing, wrinkles, channels, or foreign-material inclusions. Because the output is a number, not a judgment call, it can be logged, trended, and used to set statistically defensible accept/reject thresholds — something no visual method can offer.

What are L-Scan and C-Scan?

TThese are the two ways the signal is captured. An L-Scan is a single linear pass along the seal, producing a line graph of signal strength — fast enough for 100% in-line inspection as the seal passes through the sensor. A C-Scan moves the sensor in both directions across the seal, building a full two-dimensional "Opto-Acoustic" image of the entire seal area, typically used offline for deeper characterization, defect-location mapping, and process troubleshooting.

Why does this work even on materials visual inspection can't handle?

Because the measurement depends on acoustic transmission, not surface appearance, it works regardless of a material's color, opacity, or print — which is exactly where visual inspection struggles most. It also responds distinctly to porous, fibrous materials like Tyvek: an under-sealed Tyvek seal leaves more fiber structure intact, scattering more sound and producing a noisier signal, while an over-sealed, crystallized Tyvek seal becomes acoustically more uniform, producing an unusually smooth, high signal. Both conditions are visible to ultrasound and invisible, or nearly invisible, to the eye.

Does material thickness confuse the measurement?

Only modestly. Signal strength is driven far more by whether layers are properly bonded than by minor thickness variation, which is part of why the same underlying method works across such a wide range of film, foil, paper, and nonwoven combinations without being recalibrated for every thickness change.