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Ultrasound-excited thermography

Ultrasound-excited thermography

A component is mechanically excited with ultrasound. Friction in microcracks or defects generates heat, which is made visible by infrared. Ideal for detecting microcracks, delaminations, or adhesive failures.

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What is ultrasound-excited thermography?

In ultrasound-excited thermography, high-power ultrasound is introduced into the test object — typically in the range of 15 to 50 kHz. At defect locations (e.g., crack edges or poorly bonded layers), the vibrational energy is converted into thermal energy — depending on the defect type, through friction (hysteresis), material damping, or the thermoelastic effect.

The resulting heat signal is recorded by an IR camera. A Fourier transformation then generates a phase image that visually highlights the defects — independent of surface structure, material emissivity, or environmental influences.

Benefits

Defect-selective. Heat is preferably generated at real faults.

Very quick – only seconds per contact point.

High sensitivity even subsurface.

Robust against emissivity and surface gloss.

Can be automated using portal or robot systems and delivers reproducible results.

Applications

Microcracks and fatigue cracks in metals/castings

Delaminations in CFRP/GFRP, Sandwich, GLARE

Glue failure and kissing bonds

welding/spot seam inspection, spot weld screening

Gears, axles, sheets, die-cast parts

Test setup – movement & excitation

Note: Ultrasound-excited thermography is statically operated. There are two types of stimulation: Lock-In and Pulsed.

Select excitation

Lock-In
Pulsed
-reset
LockIn Curve
In lock-in mode, the component is excited with sinusoidally modulated ultrasound power. The IR camera records synchronously with the modulation, so each image corresponds to a defined excitation state. Fourier analysis of the sequence calculates the phase and amplitude of the temperature signal for each pixel. Phase images suppress drift, surface structure, and emissivity variations; amplitude images show the response strength. When the frequency is chosen close to a resonance mode, the local vibration amplitude increases and defects become more pronounced. A prerequisite is reproducible coupling of the sonotrode with defined contact pressure.

Typical applications

  • Microcracks and fatigue cracks in metals and castings
  • Delaminations in CFRP/GFRP, GLARE®, sandwich structures
  • Kissing bonds and adhesion defects in bonded joints
  • Spot weld and seam weld inspection
  • Structural components in aerospace, automotive, and energy sectors

Advantages
Depth-selective and robust defect detection with high SNR through synchronized phase/amplitude evaluation under reproducible coupling conditions.

Pulsed curve
In pulse mode, short ultrasound bursts are coupled into the component. The IR camera records a sequence before, during, and after each burst. The thermal transient reveals defects, since friction and damping there are immediately converted into heat. Evaluation uses time contrast or difference images; TSR smooths the response. With a burst sequence, an FFT can additionally provide phase and amplitude images. Burst duration and duty cycle limit the heat input. Frequencies near resonance modes enhance the response. Multiple identical bursts increase the SNR. Reproducible coupling and synchronous triggering are essential.

Typical applications

  • Fast scanning of contact points in series production
  • Crack screening in gears, shafts, and sheets
  • Debonds in adhesive and sandwich structures
  • Impact damage in composite components

Advantages
Very short inspection times per contact point with high defect contrast in the transient response, while maintaining controlled heat input.

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Whether feasibility studies, series tests or individual part analyses

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Still unclear whether we can test your product?

In a short initial consultation, we will explain how we can provide you with useful support with thermography — clearly, transparently and without obligation.

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FAQ

Our frequently asked questions — answered quickly and easily.

All questions/answers

Can the system be automated?

For which materials is the method suitable?

What differentiates the method from other thermography techniques?

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