Abstract
The development of flat acoustic lenses for different applications such as biomedical engineering is a topic of great interest. Flat lenses like Fresnel Zone Plates (FZPs) are capable of focusing energy beams without the need of concave or convex geometries, which are more difficult to manufacture. One of the possible applications of these type of lenses is tumor ablation through High Intensity Focused Ultrasound (HIFU) therapies with real time Magnetic Resonance Imaging (MRI) monitoring. In order to be MRI compatible, the FZP material cannot have electromagnetic interaction. In this work, a Phase-Reversal FZP (PR-FZP) made of Polylactic Acid (PLA) manufactured with a commercial 3D printer is proposed as a better, more efficient and MRI compatible alternative to conventional Soret FZPs. Phase-Reversal lenses, unlike traditional FZPs, take advantage of all the incident energy by adding phase compensation regions instead of pressure blocking regions. The manufactured PR-FZP achieves 21.9 dB of focal gain, which increases the gain compared to a Soret FZP of its same size by a factor of 4.0 dB. Both numerical and experimental results are presented, demonstrating the improved focusing capabilities of these types of lenses.
Highlights
One of the most important issues in the acoustics field is sound focusing due to its multiple applications
Knowing that we can extend the results obtained for electromagnetic waves to acoustic waves, an acoustic PR-Fresnel Zone Plates (FZPs) has been designed to increase the energy efficiency compared to conventional FZPs
Once the different radii are calculated using Eq 1, the FZP is obtained by alternating transparent regions with either pressure blocking (Soret FZP) or phase-reversal regions (PR-FZP)
Summary
One of the most important issues in the acoustics field is sound focusing due to its multiple applications. The geometry and efficiency in the optimal design of an acoustic lens are crucial parameters for its subsequent application to different fields. Acoustic FZPs are based on Soret type implementations, which focusing efficiency is low because half of the incident energy is reflected at the blocking regions. The acoustic PR-FZP has been manufactured using a commercial 3D printer and PLA Both numerical and experimental results indicate excellent performance, obtaining gains at the focal region above 21.9 dB. Due to it its low manufacturing cost and low weight, the designed PR-FZP offers great flexibility, becoming an appealing alternative to conventional HIFU devices
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