Lenses and ultrasonic imaging

The processes of image formation by acoustic lenses are discussed. First, the process of refraction in lens materials, which are relatively thin compared to the wavelength of sound, is commented upon. Some experimental results for lucite wedges are presented, and it is shown that spatial modulation of the refracted beam occurs because of thickness-related transmission effects. The progress in theoretical aspects of lens design is discussed by reference to work relating to single refracting surfaces, Luneberg lenses, two and multiple layer lenses and multiple element lenses. Some commentary is given on insertion losses and diffraction related effects. One possible effect of turbulence is discussed.