Beneath the bustle of everyday life lies a hidden realm of elaborate structures, from intricate telecommunication networks to the labyrinth of subway systems and vast pipelines transporting oil and gas. Structural health monitoring (SHM) technologies play a pivotal role in ensuring the durability and safety of these essential subterranean and submerged assets.
Ultrasonic transducers are sensors that deploy high-frequency sound waves to detect flaws or subtle changes in these underground and underwater structures. Materials researchers are actively seeking next-generation solutions to surpass the constraints of traditional sensors.
Kui Yao, a Senior Principal Scientist at A*STAR’s Institute of Materials Research and Engineering (IMRE) highlighted the limitations of current technologies: “Conventional shear piezoelectric ceramic transducers contain toxic lead compositions; they are bulky, brittle and can’t conform to complex structures.” Furthermore, according to Yao, the properties of these materials degrade over time and lack the requisite reliability for use in demanding submarine settings.
Yao’s team posited that poly(L-lactic acid) (PLLA) fibres might be a superior alternative. Inherent to their molecular and crystalline structures, PLLA fibres can produce consistent pure shear mode piezoelectric responses, generating ultrasonic waves ideal for aquatic applications.
Employing a technique known as rotating electrospinning, the researchers fabricated films made from aligned PLLA fibres, which they tested extensively in both air and underwater environments. The team's findings were promising: the novel transducers demonstrated consistent sensitivity in both mediums, with a macroscopic pure shear-mode piezoelectric response over a wide frequency range of 1 to 500 kHz being markedly superior to those of traditional films with various spurious modes.
“Our polymer transducers made from aligned PLLA fibres are highly flexible and can be implemented as conformal low-profile ultrasonic generators and detectors over curved surfaces,” said Yao, considering the potential for monitoring curved underwater structures such as pipes, storage tanks and submarine hulls. By keeping an eye on structural changes, these technologies can help in realising preventive maintenance, thereby reducing the risks of catastrophic failures and the associated costs.
Moreover, because they’re biodegradable, the study reveals promising avenues for eco-friendly polymers for use in ultrasonic SHM systems. Having filed a patent for their innovation, the team is ready to take the next step towards commercialising their discovery. “Our team is improving the Technology Readiness Level (TRL) and exploring its application in real-world scenarios by licensing the technology to industry,” said Yao.
The A*STAR researchers contributing to this research are from the A*STAR’s Institute of Materials Research and Engineering (IMRE).
