Needle-like focusing and longitudinal depth imaging based on high-throughput acoustic metamaterials

Area of Science:

• Acoustic Metamaterials
• Wave Focusing and Imaging
• Applied Physics

Background:

• Traditional acoustic focusing methods produce point-like focal spots, insufficient for imaging objects with thickness.
• Existing techniques struggle to clearly image curved or complex structures due to limited focal characteristics.

Purpose of the Study:

• To propose and demonstrate a novel acoustic needle metalens (ANM) for enhanced acoustic imaging.
• To generate a non-localized, needle-like focal spot capable of imaging thicker, curved objects.

Main Methods:

• Design of an ANM using high-throughput spiral units with tailored phase distribution.
• Numerical simulations and experimental verification of the ANM's focusing properties at 8.5 kHz.
• Investigation of non-axial focusing by modifying beam trajectory equations.

Main Results:

• The ANM achieved a focal depth of 50.63 times the wavelength with high transmission (>0.9).
• Demonstrated non-axial acoustic needle focusing by adjusting parabolic accelerating beam trajectories.
• Successfully imaged curved objects with a thickness of three wavelengths, showcasing superior imaging capability.

Conclusions:

• The proposed ANM overcomes limitations of point-like focusing for improved acoustic imaging.
• This technology offers a new approach for high-resolution acoustic imaging of complex structures.
• Potential applications include microfluidic manipulation and advanced medical ultrasound imaging.