Chennai: In a breakthrough research, Indian Institute of Technology-Madras (IIT-M) and University of Nairobi researchers have used metamaterials to improve detection of defects in large structures by guided wave ultrasound.
The results of this collaborative work have been recently published in the international reputed peer-reviewed journal AIP Advances.
The paper has been co-authored by Prof Prabhu Rajagopal, Department of Mechanical Engineering, IIT-M and his collaborators at the University of Nairobi–Dr Michael Gatari and Mr John Birir, a PhD student they jointly guide as part of a ‘Joint Degree Programme.’
“This work has much promise for remote inspection in industry and biomedicine,” the researchers wrote in their recent paper. With this knowledge, the team was expanding the concept to detect different sizes and geometries of defects.
A release IIT-M said that many engineering structures including buildings, pipelines and rails, among others, require periodic testing to prevent catastrophic failures that could occur due to corrosion, impact, and strain.
It said high frequency sound waves that travel in the bulk (bulk ultrasound) were widely used for non-invasive and non-destructive testing of structural materials.
However, conventional bulk ultrasonic inspection was tedious and time-consuming as it involves point-by-point assessment of structures and this was especially challenging in large scale assets.
Although ultrasound guided by features such as plates, bars, wires, pipes etc. was an attractive alternative, such ‘guided ultrasound’ was limited by resolution due to the relatively lower frequencies used, the release said.
Addressing this pressing challenge, IIT-M and University of Nairobi researchers have used metamaterials to improve detection of defects in large structures by guided wave ultrasound.
Prof Prabhu Rajagopal said use of ultrasound scans in medical diagnostics was well-known and the principle remains the same for structural monitoring.
“In conventional bulk ultrasound-based testing, the sound waves are sent into the sample, say pipe or pillar, perpendicular to the item, and a detector calculates the time interval between the transmission and reception of the sound waves that are either transmitted or reflected”, he said.
Sound waves travel at a uniform speed if the object was defect-free, but defects impede or deflect sound waves, which results in delays in reception.
Conventional ultrasound-based testing must be made at multiple regions of the test material and was cumbersome to be used with large objects such as train tracks, oil pipelines and reinforcing structures of tall buildings, among others.
“This is where Guided Wave Testing (GWT) helps. In GWT, the sound waves are sent along the length of the structure rather than into the structure. This allows the waves to travel long distances. GWT has poorer resolution than conventional ultrasound-based testing due to diffraction limitations”, he said.
Thus, guided waves were only a long-range screening tool and must be used in conjunction with a testing tool with better resolution for accurate detection of defects.