Broadband Ultrasonic Imaging Reveals Defects in Concrete of Various Mixes

Concrete structures, such as roads and bridges, require nondestructive testing to detect possible internal defects without causing damage. Most methods send sound waves into the material and capture returning echoes to create internal images, similar to medical ultrasounds.

But unlike human tissue, concrete contains a mix of materials—stone, clay, chalk, slate, iron ore, and sand—that scatter sound waves, making clear imaging difficult.

In an article in the January 2026 issue of Applied Physics Letters, researchers from Tohoku University (Sendai, Japan), Los Alamos National Laboratory, and Texas A&M University developed a high-resolution 3D ultrasonic imaging system for concrete that automatically adapts to various structural types.

“In our approach, the ultrasonic wave is broadband, using a wide range of ultrasonic frequencies rather than operating around a single, fixed frequency,” author Yoshikazu Ohara said. “The receiver is capable of accepting an even broader range of frequencies. By automatically adapting the frequency to the material, our system improves the contrast between defects and background material in concrete.”

Achieving high-quality imaging is challenging because sound waves lose intensity as they travel through concrete due to absorption and scattering, making it difficult to predict which frequencies will persist.

To address this, the team used two devices: one to generate a wide range of frequencies and another—a vibrometer—to capture the outgoing waves. Because the system can handle a wide range of frequencies, it can detect whatever signals make it through the material.

“No manual tuning is needed,” Ohara said. “As the concrete filters out certain frequencies, the laser Doppler vibrometer simply captures whatever frequencies remain. Unlike conventional systems, we don’t have to swap transducers or adjust the frequency beforehand. The system adapts automatically.”

The exiting waves are processed using imaging algorithms adapted for broadband ultrasonic data, producing a high-resolution 3D image of discontinuities and their location.

“For a repair planner or field technician, this provides concrete information: how deep the defect is from the surface, how large it is, and how it extends in three dimensions,” Ohara said. “This makes it possible to plan repairs more efficiently. The method gives a clear 3D map of internal damage that can be directly used for maintenance and repair decisions.”

The published article is available at https://doi.org/10.1063/5.0291949.