A team of researchers from Korea and the U.S. has developed a novel metamaterial that can convert linear vibration mode ultrasound waves into circular vibration mode ultrasound waves, which can detect internal fractures in various directions within a structure. The research was published in Nature Communications.
Ultrasound waves are widely used for non-destructive testing of structures, such as welds and plates, to find defects that could compromise their integrity. However, conventional ultrasound waves have a limitation: they cannot detect defects that are parallel to the direction of the linear vibration. This means that some hidden structural faults could go unnoticed and cause serious damage.
To overcome this challenge, the researchers designed a metamaterial that can transform the linear vibration mode ultrasound waves into circular vibration mode ultrasound waves, which can probe defects in any direction. The metamaterial consists of a three-dimensional microstructure with cylindrical holes that act as resonators. The metamaterial can achieve perfect polarization conversion from linear to circular by satisfying a coupled resonance theory.
The researchers demonstrated the effectiveness of the metamaterial by conducting ultrasonic experiments on aluminum plates with different types of defects, such as cracks, holes, and notches. They found that the metamaterial-enhanced circular vibration mode ultrasound waves could detect the defects with high sensitivity and accuracy, regardless of their orientation.
The researchers believe that their metamaterial could have various applications in the fields of engineering, medicine, and materials science, where ultrasound imaging and sensing are essential. For example, the metamaterial could be used to inspect bridges, pipelines, aircraft, and spacecraft for hidden structural faults, or to diagnose diseases and injuries in soft tissues and organs.
The following table summarizes the main features and advantages of the metamaterial compared to conventional ultrasound waves:
| Feature | Conventional ultrasound waves | Metamaterial-enhanced ultrasound waves |
|---|---|---|
| Vibration mode | Linear | Circular |
| Defect detection | Limited by orientation | Independent of orientation |
| Sensitivity | Low | High |
| Accuracy | Low | High |
| Application | Restricted | Diverse |
