| 摘要 |
PURPOSE:To reduce multiple reflection in a lens by providing an acoustic matching layer having a thickness of 1/4 wavelength to the surface of an acoustic lens for collecting a sound wave. CONSTITUTION:The matching layer 15 having the thickness l and acoustic impedance ZM is provided to a boundary surface 5 between the acoustic lens 1 and a medium 2. The acoustic impedance Z viewing the medium 2 from the boundary surface 16 between the acoustic lens 1 and the matching layer 15 is expressed as Z=ZM(ZW+jZMtanbetal)/(ZM+jZWtanbetal), where ZW is the acoustic impedance of the medium 2 and beta is the phase constant of the matching layer 15. The reflection factor between the acoustic lens 1 and the medium 2 is zeroed when the ZM is expressed as ZM=(ZW.Z')<1/2>, where Z' is the acoustic impedance viewing the acoustic lens 1 from the boundary surface 16 and the thickness l of the matching layer 15 is taken as the 1/4 wavelength of the sound wave in the matching layer 15. |
