The operational principle of SAM is that a transducer is affixed to an acoustic lens. This lens, in turn, is linked to the object through liquid (distilled water). The acoustic lens often features a sapphire delay line: its transducer-side is flat, while the opposite end boasts a spherical curvature. This design enables the ultrasonic waves generated by the transducer to be focused, leveraging the significant difference in sound velocity between the coupling medium and the delay line to achieve this effect.
The method assesses the echoes produced by the contrast in acoustic impedance (Z) between different materials. Acoustic impedance is calculated using the formula Z = ρ x c, where ρ represents the density of the medium and c denotes the speed of sound within that medium.