Patent ID: 8902507

Claim:
A man-made composite material, wherein the man-made composite material has a thickness and is divided into a plurality of regions; an electromagnetic wave is incident on a first surface of the man-made composite material and exits from a second surface of the man-made composite material opposite to the first surface; an i th region is one of the plurality of regions, and i is a positive integer and selected from a group consisted of 1, 2, 3, . . . , etc.; an intersection between the i th region and the first surface is a bottom surface of the i th region, an intersection between the i th region and the second surface is a top surface of the i th region; a line connecting a radiation source to a point on the bottom surface of the i th region and a line perpendicular to the man-made composite material form an angle θ therebetween, which uniquely corresponds to a curved surface in the i th region, the curved surface to which the angle θ uniquely corresponds is sandwiched between the bottom surface and the top surface of the i th region, a set of points on the bottom surface of the i th region that have the same angle θ forms a boundary of the curved surface to which the angle θ uniquely corresponds; each point on the curved surface to which the angle θ uniquely corresponds has a same refractive index; the curved surface to which the angle θ uniquely corresponds has a generatrix which extends along a direction of the thickness of the man-made composite material and between the bottom surface and the top surface of the i th region, the curved surface to which the angle θ uniquely corresponds is formed by rotating the generatrix about the line perpendicular to the man-made composite material; and refractive indices of each of the regions decrease gradually as the angle θ increases.