Acoustic lens

An acoustic lens for transforming a planar acoustic wave traveling in an acoustic propagation medium into a spherical segment-shaped acoustic wave traveling in an acoustic propagation medium, and vice versa, said acoustic lens comprising:

• a biconcave lens body having a center axis and being rotationally symmetric relative to said center axis, said lens body consisting of lens material having a sound propagation speed therein which is greater than the sound propagation speed of the medium in which said planar acoustic wave travels and which is greater than the sound propagation speed of the medium in which said spherical segment-shaped acoustic wave travels;
• said lens body having a lens surface adjacent said medium in which said planar acoustic wave travels produced by rotation of a section of a straight line intersecting said center axis of said lens body at an angle;
• said lens body having a lens surface adjacent said medium in which said spherical segment-shaped wave travels produced by rotation of a section of an ellipse, said ellipse having major and minor half-axes intersecting said center axis of said lens body at respective angles;
• and
• said angle between said straight line and said center axis of said lens body, and said angle between said major half-axis of said ellipse and said center axis of said lens body, being selected for causing a planar or spherical segment-shaped wave entering into said lens body to propagate in said lens body as a conical wave having an aperture angle equal to twice said angle at which said minor half-axis of said ellipse intersects said center axis of said lens body.