Electromechanical actuators ferroelectric ceramics

These materials have shown piezoelectric responses after appropriate poling [18]. Their piezoelectric actuation properties are typically worse than ceramic piezoelectric crystals however, they have the advantages of being lightweight, flexible, easily formed, and not brittle. Additionally, while ceramics are limited to strains on the order of 0.1%, ferroelectric polymers are capable of strains of 10% [91] and very high electromechanical coupling efficiencies [93]. 

Figure 3.10a shows the polarization arrangement in a ceramic system (note domains were not explicitly drawn in here, the arrows only represent the net polarization in each grain). The macroscopic piezoelectric effect is zero due to the cancellation of oppositely polarized grains. If the ceramic material is ferroelectric, it can be made piezoelectric by aligning the polarization of different grains using an external electric field through the domain switching process. A net polarization may be produced along the field direction as illustrated in Fig. 3.10b. As the electromechanical characteristic of piezoelectric effect is reversible, piezoelectric materials can be used for both sensing and actuation functions (see Chaps. 6 and 7).

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