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How do the direct and converse piezoelectric effects differ?

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Figure 1: Ferroelectric properties of barium titanate (BaTiO3). (Left) Above 120° C the structure of the BaTiO3 crystal is cubic, and there is no net polarization of charge; (right) below 120° C the structure changes to tetragonal, shifting the relative positions of the ions and causing a concentration of positive and negative charges toward opposite ends of the crystal. — capacitor dielectric and piezoelectric ceramics Figure 1: Ferroelectric properties of barium titanate (BaTiO₃). (Left) Above 120° C the structure of the BaTiO₃ crystal is cubic, and there is no net polarization of charge; (right) below 120° C the structure changes to tetragonal, shifting the relative positions of the ions and causing a concentration of positive and negative charges toward opposite ends of the crystal.

The direct and converse piezoelectric effects represent two reciprocal ways that certain materials, such as specific piezoelectric ceramics, interact with mechanical and electrical forces.12

Direct Piezoelectric Effect: This occurs when a material is subjected to mechanical stress, such as bending, twisting, or squeezing. This physical pressure causes a displacement of ions within the crystal lattice, resulting in the generation of an electric voltage or polarization across the material. This effect is commonly utilized in devices like gas igniters, microphones, and pressure sensors.314
Converse Piezoelectric Effect: This is the reciprocal process, occurring when an external electric field is applied to the material. The field induces a physical distortion or change in the material's dimensions, known as strain. This effect is essential for applications requiring precise mechanical movement or vibration, such as in ultrasound generation, precision positioners, and electronic oscillators.321

In essence, the direct effect converts mechanical energy into electrical energy, while the converse effect converts electrical energy into mechanical energy.32