A pulsed ultrasonic beam of frequency 5MHz is incident normally on human skin. The skin layer is 3.0mm thick and is immediately followed by muscle that extends 25mm deeper until it meets bone. The speed of sound is 1600ms−1 in skin and 1540ms−1 in muscle.
(i) For the given frequency, calculate the wavelength of the ultrasound in (a) skin and (b) muscle.
(ii) Determine the total time interval between the emission of a pulse at the skin surface and the reception of the first echo returning from the muscle–bone interface.
(iii) If the transducer frequency is doubled while all layer thicknesses remain the same, explain quantitatively how (a) the wavelengths and (b) the echo time calculated in part (ii) would change.