Acoustic Fresnel lenses with extraordinary transmission

TLDR: In this paper, the authors investigated numerically and experimentally highly efficient acoustic lenses based on the principle of extraordinary acoustic transmission, which can transmit up to 83% of the incident energy and generate sharp focusing with very high amplification.

Abstract: We investigate numerically and experimentally highly efficient acoustic lenses based on the principle of extraordinary acoustic transmission. We study circular, flat lenses composed of perforated air channels. The geometry is similar to binary Fresnel lenses, and the lenses exploit several resonance mechanisms to enhance the transmission, such as Fabry–Perot resonances in the channels and cavity resonances on the lens surface. The proposed lenses are able to transmit up to 83% of the incident energy and generate sharp focusing with very high amplification (up to 16 dB experimentally). Furthermore, the resulting lenses are thinner than other designs providing similar performance, making them ideal candidates for application in acoustic imaging and medical diagnostics.

Figures

FIG. 3. Schematic diagram of the experimental setup and acquisition system.

FIG. 1. (a) Lens A is composed of a circular plate with five axisymmetric air channels. xf is the focal length and r2 to r5 denote the central radius of the channels (r1 ¼ 0 is the radius of the central channel). The panel on the right shows in detail the geometry of the air channels in the axial plane. (b) Lens B is identical to Lens A, but concentric rings are added on both sides of the lens. The panel on the right shows the geometry of the cavities formed by the rings in the axial plane. (c) and (d) are pictures of the 3D printed Lens A and Lens B, respectively.

FIG. 4. Simulated (left panels) and experimental (right panels) intensity fields obtained with (a) Lens A and (b) Lens B. The dashed rectangle on the left figures represents the area in which the experimental field was measured. (c) and (d) represent the intensity fields along the x and y axis at focus obtained with Lens A. (e) and (f) represent the same quantities than (c) and (d) but obtained with lens B. x¼ 0 indicates the right edge of the lens.

FIG. 2. (a) Modulus and (b) phase of the transmission coefficient of the first Bloch mode of a periodic grating of SCs (solid lines) and CCs (dashed lines) with grating period b. (c) Intensity amplification of Lens A as a function of frequency and h0. (d) Amplification of Lens B as a function of frequency and d=k0.