Helical acoustic lens
View Patent ↗A meta-material acoustic lens is based on multiple acoustic channels, having a helix shaped path arranged radially around the center. The helix pitch is a function of the helix radius. This changes the effective thickness of the lens as a function of its distance from the center of the lens. This create a phase shift gradient across the lens, which in turn changes the wavefront from one side of the lens to the other. This results with either a focusing lens, when the effective thickness decreases from center to edge of the lens, or a diverging lens when the effecting thickness decreases from center to edge of the lens.
1. An acoustic lens comprising of one or more slices wherein:
a) each slice comprises of one or more radial layers
b) each layer comprises a plurality of radially arranged helical channels,
c) each channel at each layer has an entrance port and a exit port,
d) the helix pitch p of each helical channel is a function of the radius of the layer for the helical channel,
e) if the number of slices N is larger than one then the exit port of each channel at slice I, 1≤I≤N−1 connects to the entrance port of a matched channel at slice I+1.
2. The acoustic lens of claim 1 , where the pitch p(r) is given by p(r)=α(r)/360°,
α
(
r
)
=
180
-
H
2
+
(
H
+
R
2
+
f
2
-
f
2
+
r
2
)
2
π
r
,
where H is the thickness of the lens, f is the focal length of the lens, R is radius of the lens, and r is the radius of the helical channel.
3. The acoustic lens of claim 1 where the number of slices is greater than one, at least the helixes of one slice are rotated clockwise, at least the helixes of one slice are rotated counter clockwise, and the sum complete helical turns of each channel through all slices of the lens is a whole number.
4. The acoustic lens of claim 1 where the lens is attached to the mouth side of an acoustic horn.
5. The acoustic lens and horn of claim 4 where the focal length of the acoustic lens is f,
0.5 s<f<2 s, where s is the length of the acoustic horn.