Acoustic impedance converter
Convert acoustic impedance between rayls and SI units, and see how much sound bounces off a boundary with water.
That's 1.01× as hard as water, while muscle is 1.13× higher. At a boundary with water, about 0% of the sound reflects.
What it means
How much reflects?
Reflection figures are for a boundary with water, at normal incidence. Soft tissue is close enough to water to use the same numbers.
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Your impedance in every unit
Learn
Three things worth knowing
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Air reflects 99.9% of it
The mismatch between tissue and air is so large that essentially nothing crosses. A thin film of gel removes the gap and lets the sound in.
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Named after Rayleigh
The rayl honors Lord Rayleigh, whose Theory of Sound set out the whole framework. One rayl is a pascal-second per meter.
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Bone is the hard case
Bone is five times the impedance of tissue, so a third of the sound reflects at the surface and the rest scatters. That is why ultrasound cannot see through the skull.
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Background
About acoustic impedance
Acoustic impedance is density times the speed of sound in a material. Sound passes happily between materials that share it and reflects where they differ — which is the entire basis of ultrasound imaging.
Air is 0.0004 MRayl and tissue 1.6, so almost all the sound bounces off an air gap. That is why the gel exists.