Flexible piezoelectric composites

Sa-Gong G, Safari A, Jang SJ, Newnham RE (1986) Poling flexible piezoelectric composites. Ferroelectrics Lett 5 131-142... 

As discussed previously, many materials are piezoelectric without being ferroelectric, quartz being a prime example (see Figure 23.14). But since ferroelectrics are also piezoelectric and since the piezoelectric property is stronger in some of these ferroelectrics such as barium titanate, PZT, and PLZT, these materials are primarily used as piezoelectrics. Composites of PZT imbedded in polymers are used to make flexible transducers that can be curved to suit the application. 

The coupling between the phases is no longer electrical but mechanical via the elastic constants and 2- Thus, combining a phase 1, which is non-piezoelectric and flexible and a phase 2, which is piezoelectric and rigid, the composite is still piezoelectric (d PP = d2), but the coefficient g PP can be specifically increased by minimizing the denominator of g PP. These special properties of piezoelectric composites, prepared from PZT and a polymer, have been taken advantage of in various apphcations (medical and sonar imaging, for example). 

Ferroelectric Ceramic—Polymer Composites. The motivation for the development of composite ferroelectric materials arose from the need for a combination of desirable properties that often caimot be obtained in single-phase materials. For example, in an electromechanical transducer, the piezoelectric sensitivity might be maximized and the density minimized to obtain a good acoustic matching with water, and the transducer made mechanically flexible to conform to a curved surface (see COMPOSITE MATERIALS, CERAMiC-MATRix). 

New possibilities exist for the development of piezoelectric devices using so-called 1-3 composites. These consist of an array of piezoelectric pillars embedded in a pliable material providing a transducer in the form of a flexible sheet (Fig. 7.5) which can be moulded to fit the shape of a reactor. A particular advantage of such a system is that the emitting face is a combination of ceramic and plastic and can provide much better acoustic transmission into aqueous systems. 

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