Which act as acoustic barriers, leading to the use of gel on the skin to improve transmission?

Which act as acoustic barriers, leading to the use of gel on the skin to improve transmission?

• A. Water acts
• B. Metals act
• C. Air and other gases act
• D. Bones act

Answer: (C)

Air pockets at the skin surface act as a strong barrier to ultrasound because air has a very different acoustic impedance than soft tissue, so most of the sound is reflected and little penetrates. The gel used on the skin fills in those gaps and provides a medium with an impedance closer to tissue, which reduces reflections and allows the sound waves to enter the body more effectively. This is why gel is essential for good transmission. Metals or bones create impedance mismatches that also reflect or scatter waves, and water isn’t the barrier here—it’s a good transmitter, but gel is preferred on the skin to maintain constant contact and displace air.

Air pockets at the skin surface act as a strong barrier to ultrasound because air has a very different acoustic impedance than soft tissue, so most of the sound is reflected and little penetrates. The gel used on the skin fills in those gaps and provides a medium with an impedance closer to tissue, which reduces reflections and allows the sound waves to enter the body more effectively. This is why gel is essential for good transmission. Metals or bones create impedance mismatches that also reflect or scatter waves, and water isn’t the barrier here—it’s a good transmitter, but gel is preferred on the skin to maintain constant contact and displace air.