Infographics / Ultrasound Physics

Transducer construction and the piezoelectric effect

Cross-section through one transducer element, drawn back to front. From the rear: a backing / damping block, a thin metal electrode, the piezoelectric crystal (PZT) whose thickness sets the resonant frequency, a second front electrode, and a quarter-wavelength matching layer that couples energy into the tissue on the right. Emitted ultrasound propagates into soft tissue. Captions note that resonant frequency equals c divided by twice the crystal thickness (thicker crystal gives lower frequency), that the backing block shortens the pulse to give wider bandwidth and better axial resolution, that the quarter-wave matching layer maximises energy transfer, and that the piezoelectric effect converts voltage to vibration and back.