The piezoelectric effect is the fundamental physical principle underlying all ultrasound transducers. Certain materials (including lead zirconate titanate, or PZT) generate an electric voltage when mechanically compressed or stretched (direct piezoelectric effect), and conversely deform when an electric voltage is applied (converse piezoelectric effect). This dual property allows a transducer crystal to both transmit ultrasound pulses and detect returning echoes using the same element.