Explain why ultrasound used in medical diagnosis is emitted in pulses.
Explain the principles of the detection of ultrasound waves used in medical diagnosis.
The specific acoustic impedances 
of some media are given in the table below.
The specific acoustic impedances of two media are 
and 
. The intensity reflection coefficient 
for the boundary of these two media is given by:
Calculate, to three significant figures, the fraction of the ultrasound intensity that is reflected at a boundary between air and soft tissue.
