ultrasound; longitudinal wave with frequency greater than 20 kHz

piezoelectric effect; ultrasound transducer as a device that emits and receives ultrasound

ultrasound A-scan and B-scan

acoustic impedance of a medium;
\(Z = ρc \)

reflection of ultrasound at a boundary;
\(\dfrac{I_r}{I_0} = \dfrac{(Z_2 - Z_1)^2}{(Z_2 + Z_1)^2}\)

impedance (acoustic) matching; special gel used in ultrasound scanning

Doppler effect in ultrasound; speed of blood in the patient;
\(\dfrac{Δf}{f} = \dfrac{2v\cos{θ}}{c}\) for determining the speed v of blood.