If impedance difference between two media is zero, reflection is which of the following?

If impedance difference between two media is zero, reflection is which of the following?

• A. None
• B. Small
• C. Moderate
• D. Large

Answer: (A)

When two media have identical acoustic impedance, there is no reflection at their boundary. The pressure reflection coefficient is (Z2 − Z1)/(Z2 + Z1); if Z2 equals Z1, the numerator is zero and the reflected wave has zero amplitude. That means all energy is transmitted into the second medium (the wave may change speed or wavelength to match the new medium, but there’s no echo). In ultrasound terms, no impedance difference yields no boundary echo. If there were any difference, some reflection would occur, with the amount increasing as the impedance difference grows.

When two media have identical acoustic impedance, there is no reflection at their boundary. The pressure reflection coefficient is (Z2 − Z1)/(Z2 + Z1); if Z2 equals Z1, the numerator is zero and the reflected wave has zero amplitude. That means all energy is transmitted into the second medium (the wave may change speed or wavelength to match the new medium, but there’s no echo). In ultrasound terms, no impedance difference yields no boundary echo. If there were any difference, some reflection would occur, with the amount increasing as the impedance difference grows.