ultrasound

• any frequency above the upper limits of human hearing
• when passed betwean materials, some wave is reflected and some is transmitted ( and refracted)

  partial reflection
• medical imagery

  • waves can pass through body.
  • when they reach a boundary between two materials ( such as womb and babies skin ) some wave is reflected back
• industrial imaging

  • to find flaws in pipes
  • if crack - some waves reflected back and detected