State what the acoustic impedance of a medium means.
The data for some media are shown in Fig. 10.1. Use the information in Fig. 10.1 to calculate the density of bone.
A parallel ultrasound beam of intensity $I$ is incident normally on a boundary between two media. The media have acoustic impedances $Z_1$ and $Z_2$. The transmitted intensity is $I_T$ and the reflected intensity is $I_R$. State the relationship between $I$, $I_T$ and $I_R$.
The reflection coefficient $\alpha$ is defined by $\alpha = \frac{(Z_2 - Z_1)^2}{(Z_2 + Z_1)^2}$. Use the data in Fig. 10.1 to find the reflection coefficient $\alpha$ for the boundary between gel and soft tissue.
Use the information in Fig. 10.1 to find the reflection coefficient $\alpha$ for a boundary between air and soft tissue.
Using your answers in (b)(ii), explain why gel is applied to the skin surface during ultrasound diagnosis.