Why a physical part
Software cannot know the wall thickness.
The wall sits between the heart and every microphone on the skin. Its effect appears in the recording, so the insert measures it there and divides it out.
Why it is not a model
One division, no training set.
A learned correction would need paired recordings and imaging from thousands of patients, and its errors would be hard to attribute. This is arithmetic, and it can be checked with a calculator.
Where it is now
Rev D
Printed, hand fitted, workable. More than 100 people have handled it.
Bench
Simulation and bench evidence, 111 recordings. The study has not started.
Tooling
Not paid for, and not dated. What exists is a printed part and a method.