Deep-Subwavelength-Optimized Holey-Structured Metamaterial Lens for Nonlinear Air-Coupled Ultrasonic Imaging

Area of Science:

• Materials Science
• Acoustics
• Non-Destructive Testing

Background:

• Traditional ultrasonic non-destructive testing (NDT) requires liquid coupling, limiting its application.
• Air-coupled NDT offers non-contact inspection but suffers from low signal efficiency due to impedance mismatch.
• Existing air-coupled methods struggle with signal amplitude, hindering defect detection.

Purpose of the Study:

• To design a metamaterial lens for improved air-coupled acousto-ultrasonic imaging.
• To address the signal inefficiency and enhance damage detection capabilities in air-coupled NDT.
• To demonstrate the lens's effectiveness on various materials and defect types.

Main Methods:

• A holey-structured metamaterial lens with a feature size of λ/14 was designed.
• The lens geometry was optimized to match Fabry-Perot resonance modes for improved acoustic impedance.
• Transmission tests and air-coupled inspections were performed on fabricated lenses and material samples.

Main Results:

• The metamaterial lens increased signal amplitude by 11 dB at its design frequencies.
• Improved damage imaging sensitivity and resolution were observed in air-coupled inspections.
• The lens effectively enhanced defect detection on aluminum and carbon-fiber-reinforced polymer (CFRP) samples.

Conclusions:

• The developed holey-structured metamaterial lens significantly enhances air-coupled ultrasonic NDT.
• This technology offers a promising solution for sensitive and high-resolution damage detection in complex components.
• The metamaterial lens facilitates efficient non-contact inspection across diverse materials.