Hollow sphere transducer

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... 

Meyer Jr. R, Weitzing H, Xu Q, Zhang Q, Newnham RE, Cochran JK (1994) Lead Zirconate titanate hollow-sphere transducers. J Am Ceram Soc 77 1669-1672 Motchany AI, Chvanski PP (2001) Crystal growth of an a-quartz like piezoelectric material, berlinite. Ann Chim Sci Mat 26 199-208... 

In fact, solid materials with such low acoustic impedance are extremely rare. For the acoustic matching layer of an airborne ultrasonic transducer, non-woven fabrics made of polymer or polymer materials packed in small hollow glass spheres are generally used. 

---