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
The piezoelectric effect
In the piezoelectric effect, an applied voltage causes a piezo-crystal to contract or expand, and vice versa
Piezoelectric Crystals
- At the heart of a piezoelectric transducer is a piezoelectric crystal
- Piezoelectric crystals are materials which produce an e.m.f 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 the negative region of the crystal
A molecule in a quartz crystal
When the compression and stretching alternates, an alternating e.m.f. is induced
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
