What happens to reflections as impedance mismatch between media increases?

• A. Increases
• B. Decreases
• C. Remains the same
• D. Varies with frequency

Answer: (A)

When two media have different acoustic impedances, more of the ultrasound energy is reflected at their boundary. The reflected amplitude is proportional to the difference between the impedances relative to their sum, so as the mismatch grows, the reflection becomes stronger. In energy terms, the reflected energy fraction rises with mismatch and can approach all of the incident energy if the mismatch is very large. If the impedances are equal, there would be no reflection. So, increasing impedance mismatch leads to greater reflections.