PhysicsCode 9702
Production and use of ultrasound
What this topic asks you to be able to do
- understand that applying a p.d. across a piezo-electric crystal makes it change shape, and that changing its shape makes the crystal generate an e.m.f.
- understand how a piezoelectric transducer creates ultrasound waves and detects them
- understand how ultrasound pulses reflected at the boundaries between tissues can give diagnostic information about internal structures
- define a medium's specific acoustic impedance as Z = ρc, in which c stands for the speed of sound within that medium
- use IR / I0 = (Z₁ – Z₂)² / (Z₁ + Z₂)² in order to get the intensity reflection coefficient across a boundary joining two media
- recall I = I₀e–μx and use it to work out how ultrasound is attenuated as it passes through matter