Acoustic impedance is a measure of how much sound pressure is generated by a sound wave when it encounters a material. It is defined as the ratio of sound pressure to particle velocity in a medium. This property helps determine how sound waves will behave when they pass from one material to another, such as from air into water or through different tissues in the human body. The formula for acoustic impedance is given by Z = ρ × c, where Z is the acoustic impedance, ρ is the density of the medium, and c is the speed of sound in that medium. Understanding acoustic impedance is essential in fields like ultrasound imaging and acoustics, as it influences sound transmission and reflection at boundaries between different materials.