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(a) Schematic diagram of the AM structure in coiling up space. Brass plate with width and length immersed in air. (b) The effective medium (width, cm) characterized by the relative effective refractive index and effective acoustic impedance . (c) The real part (red circles) and imaginary part (red dots) of , and the power transmission (blue lines) as a function of frequency.
(a) The relative effective refractive index, , as a function of the size of the AM structure . (b) The distribution in the direction perpendicular to the lens axis. The line and points refer to the desired and effective for different sizes of the AM units. (c) The required size distribution of AM units in the direction for the desired . (d) The relative effective acoustic impedance, , and the fitted one for different sizes of the AM units.
Pressure field amplitude pattern (arbitrary units) for (a) free space, (b) the idealized GRIN lens, and (c) the designed lens. Pressure field phase pattern for (d) free space, (e) the idealized GIRN lens, and for (f) the designed lens. (g) Closer view of the upper part of the designed lens. Pressure amplitude distribution along a line passing through the focal spot (h) in the propagation direction (shown as line “1” in (c)) and (i) in a direction transverse to the propagation direction (shown as line “2” in (c)).
The real and imaginary parts of (a) and (b) as a function of the channel width . Pressure field (c) amplitude (arbitrary units) and (d) phase pattern for the designed lens with . Pressure amplitude distribution along (e) line “1” and (f) line “2” shown in (c).
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