By Stephen Beech
A new 3D ultrasonic imaging system can detect potentially deadly defects in all types of concrete.
The range of materials that concrete contains – such as stone, clay, chalk, slate, iron ore and sand – scatters normal sound waves, making clear imaging difficult to obtain.
Now Japanese and American scientists have teamed up to develop a system that can identify interior defects in concrete buildings and bridges without destroying their structure.
They explained that methods send sound waves into the material and capture the waves that echo back to create images of what’s inside, similar to ultrasound scans used to see inside the human body.
But, unlike human tissues, concrete contains a diversity of materials that scatter sound waves and make clear imaging difficult to obtain.
Researchers from Tohoku University in Japan, Los Alamos National Laboratory in New Mexico, and Texas A&M University have created a high-resolution 3D ultrasonic imaging system for concrete that automatically adapts to different types of structures.
Professor Yoshikazu Ohara said: “In our approach, the ultrasonic wave is broadband, using a wide range of ultrasonic frequencies rather than operating around a single, fixed frequency.
“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.”
He says that achieving high-quality imaging of concrete is complicated because waves lose intensity as they travel through concrete due to absorption or scattering.
It is hard to know which frequencies of sound waves will survive traveling through the material.
To accommodate the uncertainty, the team used two devices: one to generate a wide range of frequencies to send into the material and another – a vibrometer – to capture the outcoming waves.
The system, described in the journal Applied Physics Letters, can handle a wide range of frequencies, which means that even if ultrasonic waves are scattered by materials in the concrete, those that do make it through are still detected, regardless of what frequency they are.
Ohara, of Tohoku University, said: “No manual tuning is needed.
“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.”
Waves exiting the concrete are processed using imaging algorithms the team developed in previous work, which they adapted specifically for broadband ultrasonic data.
The result is a high-resolution 3D image of the defect and its location in the concrete.
Ohara added: “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.
“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.”
