State what is meant by the specific acoustic impedance of a medium.
The intensity reflection coefficient 
is given by the expression
Explain the meanings of the symbols , 
and 
in this expression.
A parallel beam of ultrasound has intensity 
as it enters a muscle. The beam passes through a thickness of 
of muscle before being incident on the boundary with a bone, as shown in the figure below.
The intensity of the ultrasound beam as it passes into the bone is 
.
Some data for muscle and bone are given in the table below.
Calculate the ratio 
.
