Acoustic Impedance
The physical opposition offered by a medium to sound wave flow, defined as ratio of acoustic pressure to particle velocity.
Governing formula
Z = ρ v_sound
SI unit
Pa·s/m (Rayls)
In depth
Impedance mismatch at boundaries dictates acoustic reflection vs transmission: large impedance mismatch causes almost complete wave reflection.
Examples in the real world
Applying gel during medical ultrasound scans to eliminate air gaps and match transducer impedance with human skin.