FEM-Based Design of Mass-Spring Acoustic Matching Layers for Ultra-High-Frequency Ultrasonic Transducers with...

Area of Science:

• Materials Science and Engineering
• Acoustics and Ultrasonics
• Non-Destructive Testing

Background:

• High-frequency ultrasonic transducers are crucial for non-destructive evaluation (NDE) due to their high spatial resolution.
• Effective focusing and efficient acoustic transmission remain significant challenges for ultra-high-frequency (UHF) transducers.

Purpose of the Study:

• To design and evaluate a mass-spring acoustic matching layer for a 100 MHz LiNbO3 piezoelectric transducer.
• To address challenges in focusing and acoustic transmission for UHF ultrasonic applications.

Main Methods:

• A mass-spring matching layer (0.25 μm Au/2.5 μm Parylene-C) was designed for a concave LiNbO3 transducer.
• COMSOL Multiphysics 6.1 was used for coupled-physics modeling (solid mechanics, electrostatics, acoustics).
• Frequency sweeps (50-150 MHz) and focal plane pressure analysis were performed.

Main Results:

• The mass-spring layer operates within a deposition-friendly thickness range, unlike conventional quarter-wavelength layers.
• Focal length (~1.02 mm) and beamwidth are primarily governed by aperture diffraction, with minimal change from the matching layer.
• The mass-spring matching layer achieved 1.5 times greater acoustic pressure amplitude compared to a quarter-wavelength layer at 100 MHz.

Conclusions:

• The proposed mass-spring acoustic matching layer effectively enhances focal pressure for UHF ultrasonic transducers.
• This design provides a theoretical foundation for utilizing UHF ultrasound in detecting extremely small defects.
• The study demonstrates a practical approach for fabricating matching layers on curved substrates.