Section 2: Physics of Ultrasound

Further Reading (Olympus Technical Note)
The boundary between two materials of different acoustic impedances is
called an acoustic interface. When sound strikes an acoustic interface at
normal incidence, some amount of sound energy is reflected and some
amount is transmitted across the boundary. The dB loss of energy on
transmitting a signal from medium 1 into medium 2 is given by:
dB loss of transmission = 10 log 10 [ 4Z 1 Z 2 / (Z 1 +Z 2 ) 2 ]
The dB loss of energy of the echo signal in medium 1 reflecting from an
interface boundary with medium 2 is given by:
dB loss of Reflection = 10 log 10 [ (Z 1 -Z 2 ) 2 / (Z 1 +Z 2 ) 2 ]