CIE A Level Physics (9702) exams from 2022

Revision Notes

24.1.1 The Piezoelectric Transducer

The Piezoelectric Transducer

  • The piezoelectric effect is defined as:

The ability of particular materials to generate a potential difference (p.d.) by transferring mechanical energy to electrical energy

  • A transducer is any device that converts energy from one form to another

 

Piezoelectric Crystals

  • At the heart of a piezoelectric transducer is a piezoelectric crystal
  • Piezoelectric crystals are materials which produce a p.d. when they are deformed
    • This deformation can be by compression or stretching
  • If a p.d. is applied to a piezoelectric crystal, then it deforms, and if the p.d. is reversed, then it expands
    • If this is an alternating p.d. then the crystal will vibrate at the same frequency as the alternating voltage
    • Crystals must be cut to a certain size in order to induce resonance

 

  • One of the most common piezoelectric crystals is quartz, which is made from a lattice of silicon dioxide atoms
    • When the lattice is distorted, the structure becomes charged creating an electric field and, as a result, an electric current
    • If an electric current is applied to the crystal, then this causes the shape of the lattice to alternate which produces a sound wave
    • Due to the conventional direction of electric current, it will flow from the positive to negative region of the crystal

Applications of the Piezoelectric Transducer

  • Microphone
    • A piezoelectric microphone detects pressure variations in sound waves
    • These can then be converted to an electrical signal for processing
  • Ultrasound
    • In a piezoelectric transducer, an alternating p.d. is applied to produce ultrasound waves and sent into the patient’s body
    • The returning ultrasound waves induce a p.d. in the transducer for analysis by a healthcare professional

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