Multi-channel ultrasonic Bessel vortex beams by spatial multiplexing metalens

Area of Science:

• Acoustic Metamaterials
• Ultrasonic Wave Manipulation
• Vortex Beam Generation

Background:

• Acoustic vortex generation is crucial for applications like underwater communication and particle manipulation.
• Current methods using phase masks are limited to single vortex beams, lacking flexibility.
• There is a need for adaptable ultrasonic vortex generation schemes.

Purpose of the Study:

• To propose a novel methodology for realizing multi-channel ultrasonic Bessel vortex beams at megahertz frequencies.
• To demonstrate independent control over topological charge and spatial orientation of multiple ultrasonic vortices.
• To enhance the functionality and adaptability of ultrasonic vortex manipulation.

Main Methods:

• Utilizing spatial multiplexing on a metalens to assign adjacent pixels for independent vortex generation.
• Designing and fabricating a four-channel metalens with a 0.2 mm pixel size.
• Experimentally measuring far-field ultrasound distributions in water.

Main Results:

• Successfully generated multi-channel ultrasonic Bessel vortex beams with independent control over topological charge and spatial orientation.
• Achieved precise control of vortex radiation direction with less than 1° error, matching simulation predictions.
• Demonstrated tunability of vortex intensity by combining multiple channels.

Conclusions:

• The proposed spatial multiplexing scheme offers a feasible and flexible methodology for generating multi-channel ultrasonic Bessel vortex beams.
• This approach significantly enhances the adaptability of ultrasonic vortex manipulation for multi-functional ultrasound devices.
• The findings open new possibilities for advanced applications in acoustics and wave-based technologies.