Piezoelectric composite

The integration of piezoelectric materials into composites allows for the improvement of constitutive properties as well as of failure behavior and consequently for an extension of the application spectrum. So this chapter is concerned with the conception and modeling of such piezoelectric composites for structural apphcations. For the prediction of the effective composite properties, different methodologies of micro-electromechanics are investigated and vahdated through experiments and finite element analyses. 

Aim of this paragraph is a short description of the very wide material gronp -piezoelectric composites - with the special attention to the hydrophone apphcations. Non-homogeneous stmctures are often called piezoelectric composites if at least one of the phases is piezoelectric. Two or even more phases joined together are involved in the composite structure. Quality of the mutual joints between phases involved is the most important material issue today (chemistry, physics, material research etc.). 

For the composite stmcture it is not important whether the phases are different materials or the same materials with just different ciystallographic orientation. Basically, there are two distinct possibilities  

Composites are being designed specifically for mar different applications (Das-Gupta 1994 Newnham 1986 Safari 1994 Tressler et al. 1999) 

Among the many factors designed for the particular composite application following quantities should be pointed out 

Composites must be designed with respect to the specific application needs, which could be represented by not just one parameter. Several parameters could compete in the composite s figure of merit (FOM). 

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R. Y. Ting, "Evaluation of New Piezoelectric Composite Materials for Hydrophone AppUcations," presented at the Bernard Jaffe Memorial Colloquium, American Ceramics Society, 86 Meeting, Pittsburgh, 1984. 

CH2—CI2—) —(—CF2— CFH—) (39). Ceramic crystals have a higher piezoelectric efficiency. Their high acoustic impedance compared to body tissues necessitates impedance matching layers between the piezoelectric and the tissue. These layers are similar in function to the antireflective coatings on a lens. Polymer piezoelectric materials possess a more favorable impedance relative to body tissues but have poorer performance characteristics. Newer transducer materials are piezoelectric composites containing ceramic crystals embedded in a polymer matrix (see Composite materials, polymer-MATRIX Piezoelectrics). 

Finally, metallic fibers find some limited applications as reinforcement in composites. They are generally not desirable due to their inherently high densities and because they present difficulties in coupling to the matrix. Nonetheless, tungsten fibers are used in metal-matrix composites, as are steel fibers in cement composites. There is increasing interest in shape memory alloy filaments, such as Ti-Ni (Nitanol) for use in piezoelectric composites. We will discuss shape-memory alloys and nonstructural composites in later chapters of the text. 

Viart, N., Richard-Plouet, M., Muller, D. and Pourroy, G., Synthesis and characterization of Co/ZnO nanocomposites towards new perspectives offered by metal/piezoelectric composite materials , I ll in Solid Films, 2003 437 1-9. 

Bowen, L.J., et al. (1993) Injection moulded fine-scale piezoelectric composite transducer. 1993 IEEE Ultrasonics Symposium, pp. 499-503. 

The following discussion should be supplemented by reference to the article by T.R. Gururaja el al. [4], one of the contributing authors being R.E. Newnham, a pioneer in the field of piezoelectric composites. 

MAJOR PRODUCT APPLICATIONS thermistors, capacitors, optics, ferroelectric ceramics, filler for ferroelectric polymers, pyro and piezoelectric composites... 

J. Qiu, J. Tani and T. Takagi, An intelligent Piezoelectric Composite Material without Bending Deformation, Journal of Technical Physics, 35(1-2), 99-107, 1994. 

There are numerous manufacturing techniques tested and reported already for the piezoelectric composites and new techniques are being further developed (Safari 1994)... 

Another example of the piezoelectric composite stmctures either with 3-0 or 3-1 connectivity is the miniature piezoelectric hollow sphere transducer (Alkoy et al. 1997 Fernandez et al. 1996 Meyer et al. 1994). Technique allowing for the manufacturing of the extremely small thin-walled bubbles (1-6 mm in diameter and 80 xm wall thickness) from PZT slurry has been developed. Such bubbles could be electroded and poled either radially (3-0 coimectivity) or cylindrically (3-1 connectivity) if the hole is drilled through the bubble (Fig. 7.30). Composite stracture vibrates in radial (breathing) or in thickness mode. Effective hydrostatic piezoelectric coefficient as well as significantly enhanced with... 

Gururaja TR, Schultze WA, Cross LE, Newnham RE, Auld BA, Wang YJ (1985a) Piezoelectric composite materials for ultrasonic transducer applications. Part 1 Resonant modes of vibration of PZT Rod-polymer composites. IEEE Trans Sonics Ultrason SU-32 481-498 Gururaja TR, Schultze WA, Cross LE, Newnham RE (1985b) Piezoelectric composite materials for ultrasonic transducer applications. Part II Evaluation of ultrasonic medical applications. IEEE Trans Sonics Ultrason SU-32 499 513... 

Haun MJ, Moses P, Gururaja TR, Schulze WA, Newnham RE (1983) Transversely reinforced 1-3 and 1-3-0 piezoelectric composites. Eerroelectrics 49 259-264 HaunMJ, EurmanE, Jang SJ, McKinstry HA, Cross LE( 1987) Thermodynamic theory of PbTiOs. J Appl Phys 62 3331 3338... 

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

Shown in Fig. 3.16 is a 1-3 piezoelectric composite with PZT ceramic rods embedded in a polymer resin. This structure is now widely used in medical ultrasonic transducers because the polymer helps reducing the acoustic impedance mismatch between human body and the PZT so that energy transmission becomes more efHcient. The load on the polymer phase can be transferred to the ceramic so that the effective load on the ceramic is enhanced, which produces higher electric signal when it is used as stress sensor. This composite structure also gives a much higher figure of merit for hydrophone applications [18],... 

There are many other multifunctional materials being created, for example, piezoelectric-piezomagnetic composite, magnetoelectric-piezoelectric composite, etc. They can respond to several different types of external fields and perform multiple functions. 

Xu, Q.C. Yoshikawa, S. Belck, J.R. Newnham, R.E. Piezoelectric Composites with High Sensitivity and High Capacitance for Use at High Pressures. IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, Vol. 38, No. 6 (1991), pp. 634-639... 

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