Piezoelectric materials comparison

In comparison to ordinary dielectrics, the permittivities of the so-called ferroelectric materials are about 103 times larger. The ferroelectric material can be transformed into a new type of material called piezoelectric material by heating the ferroelectric above its Curie temperature and then cooling it in a powerful electric field. A piezoelectric crystal changes its polarization once subjected to a mechanical strain. As a result, it can deform mechanically under an electric field or produce electric impulses as a result of mechanical impulses. Currently, piezoelectric materials are widely used as force or pressure transducers with fast response times and very sensitive output. Permittivities of common dielectric and ferroelectric materials are given in Table 1.9. 

Two common piezoelectric materials are polymers (polyvinylidene fluoride, PVDF) and c mics (lead zirconate titanate, PZT). The polymer materials are soft and flexible however have lower dielectric and piezoelectric properties than ceramics. Conventional piezoelectric ceramic materials are rigid, heavy and can only be produced in block form. Ceramic materials add additional mass and stiffiiess to the host structure, especially when working with flexible/lightweight materials. This and their fragile nature limit possibilities for wearable devices. Comparisons of several piezoelectric materials are presented in Table 1. 

Swallow L, Siores E, Luo J, Dodds D. Comparison of piezoelectric materials for use in energy harvesting applications . Proceedings of the Knowledge and Innovation Conference, Bolton, In I blishing, March 2007. 

Ballato and Gualtieri (1994) employ an intrinsic parameter Tj" (the motional time constant) to make comparisons between different piezoelectric materials. This constant is inversely proportional to the product of frequency and quality factor for the mth resonator mode. It is possible to define the motional time... 

The nature of acoustic waves generated in piezoelectric materials is determined by the piezoelectric material orientation as well as the metal electrodes configuration employed to generate the electric field that induces acoustic waves by converse piezoelectric effect. As gas sensors, the resonators are coated with layers which selectively absorb or adsorb analytes of interest and thereby induce a mass change that is then detected via a shift in the resonant frequency of the device (Kurosawa et al. 1990). The detection limits and the relative (5) mass sensitivities for different types of acoustic sensors are presented in Table 13.1. The comparison of various types of AW sensors is also presented in Table 13.2. Several books and reviews (Ballantine et al. 1997 Ippolito et al. 2009) provide a more detailed analysis of AW-based sensors operation. 

Table 13.3 Comparison of piezoelectric and related properties of several important piezoelectric materials...

Table 10.1 List of commonly known piezoelectric materials and their comparison [3].

Table 3. Comparison of Piezoelectric Properties of Some Semicrystalline Polymeric Materials...

Table 3.16 gives a generalized comparison of piezoelectric and electrostrictive materials. The piezoelectric expansion or contraction in the direction of an applied field results from alignment and stretching of dipoles in the material with the applied field. The expansion is linear and directly proportional to the magnitude and polarity of the applied field. 

The electrical and mechanical properties of piezoelectric polymers make them interesting also in the development of electroacustk or ultrasonic transducers for medical applications. Comparison of tbe representative PVDF material characteristics with a convenlional ferroelectric ceramic as PZT shows several features of piezoelectric polymers which make them attractive in transducer design (TU>le 1). 

In the case of fillers used in nanocomposites for energy harvesting, PZT (Zhang et al., 2014) or BaTiOs (Morvan et al., 2012) are primarily utilized because of their optimal piezoelectric properties. Such nanocomposites provide enhanced energyharvesting performance in comparison to both individual materials. 

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