Reflection is greatest when there is a very large difference in impedance between media. Which option best describes this condition?

Reflection is greatest when there is a very large difference in impedance between media. Which option best describes this condition?

• A. Very Large Impedance Difference
• B. Identical Impedances
• C. Small Impedance Difference
• D. Moderate Impedance Difference

Answer: (A)

Reflection strength at a boundary scales with how different the media’s acoustic impedances are. Acoustic impedance Z is the product of density and sound speed, and the amplitude of the reflected wave is governed by the mismatch term (Z2 − Z1)/(Z2 + Z1). When the difference between Z2 and Z1 is very large, this ratio approaches 1 in magnitude, so most of the incident energy is reflected back and you get a strong echo. If the impedances are the same, the ratio is zero and there’s essentially no reflection; with small or moderate differences, only a portion reflects, producing weaker echoes. So the condition described is a very large impedance difference. This is why interfaces like air-tissue or bone-tissue surfaces generate pronounced reflections.

Reflection strength at a boundary scales with how different the media’s acoustic impedances are. Acoustic impedance Z is the product of density and sound speed, and the amplitude of the reflected wave is governed by the mismatch term (Z2 − Z1)/(Z2 + Z1). When the difference between Z2 and Z1 is very large, this ratio approaches 1 in magnitude, so most of the incident energy is reflected back and you get a strong echo. If the impedances are the same, the ratio is zero and there’s essentially no reflection; with small or moderate differences, only a portion reflects, producing weaker echoes. So the condition described is a very large impedance difference. This is why interfaces like air-tissue or bone-tissue surfaces generate pronounced reflections.