Design of Acoustic Bifocal Lenses Using a Fourier-Based Algorithm

Area of Science:

• Physics
• Engineering
• Acoustics

Background:

• Zone plates (ZPs) are diffractive optical elements used for focusing.
• Designing ZPs with specific multiple focal points (bifocal) presents challenges in controlling focal location and resolution.

Purpose of the Study:

• To introduce a novel design method for bifocal zone plates (ZPs).
• To achieve precise control over the locations and resolutions of multiple foci.
• To demonstrate the method's applicability in underwater ultrasonics and other fields.

Main Methods:

• Utilizing the fast Fourier transform (FFT) of a binary sequence to identify focal points.
• Employing reverse engineering with a target focusing profile.
• Applying the inverse fast Fourier transform (IFFT) to generate the binary sequence for the ZP.

Main Results:

• The FFT of the binary sequence directly indicates the main foci locations.
• The IFFT-based design method allows for flexible and powerful tailoring of bifocal ZPs.
• Absolute control over the foci locations was achieved, a key advantage over existing methods.

Conclusions:

• The developed FFT/IFFT-based design method provides a flexible and powerful tool for creating bifocal ZPs.
• This method offers unprecedented control over focal point placement and resolution.
• The technique is applicable to underwater ultrasonics and can be extended to optics and microwaves.