Article

Fabrication, modelling and use of porous ceramics for ultrasonic transducer applications

Journal of Electroceramics (Impact Factor: 1.42). 08/2007; 19(1):127-139. DOI: 10.1007/s10832-007-9117-3

ABSTRACT Porous ceramics are of interest for ultrasonic transducer applications. Porosity allows to decrease acoustical impedance,
thus improving transfer of acoustical energy to water or biological tissues. For underwater applications, the dhgh figure of merit can also be improved as compared to dense materials. In the case of high frequency transducers, namely for
high resolution medical imaging, thick film technology can be used. The active films are generally porous and this porosity
must be controlled. An unpoled porous PZT substrate is also shown to be an interesting solution since it can be used in a
screen-printing process and as a backing for the transducer. This paper describes the fabrication process to obtain such materials,
presents microstructure analysis as well as functional properties of materials. Modelling is also performed and results are
compared to measurements. Finally, transducer issues are addressed through modelling and design of several configurations.
The key parameters are identified and their effect on transducer performance is discussed. A comparison with dense materials
is performed and results are discussed to highlight in which cases porous piezoceramics can improve transducer performance,
and improvements are quantified.

0 Bookmarks
 · 
59 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: Porous lead zirconate titanate (PZT) ceramics with interconnected pores were fabricated by using a novel tert-butyl alcohol (TBA)-based gel-casting method. The resultant samples were sintered at different temperatures and subsequently characterized in terms of both microstructure and piezoelectric properties to study effects of sintering behavior. Both microstructure and piezoelectric properties exhibited obvious dependence on sintering temperature. It was noted that porosity and grain size played dominant roles in determining the magnitudes of dielectric constant (ɛ) and piezoelectric constant d33, respectively. With the increase of sintering temperature, the porosity declined and the grain size increased which exerted opposite influences on piezoelectric properties mainly via ɛ and d33. Since anti-interference ability of the ceramic correlates linearly with ɛ, it is possible to adjust sintering temperature to tailor porosity and pore morphology in order to achieve optimum piezoelectric properties as well as relatively high anti-interference ability.
    Ceramics International 03/2010; 36(2):549-554. · 2.09 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In previous work, screen-printing technology was used to elaborate an integrated piezoelectric structure on a porous substrate [1]. The substrate was chosen to withstand the film sintering temperature which was lowered at 800degC thanks to the addition of PGO to a PZT composition. The acoustical impedance of this substrate is very close to that of the deposited piezoelectric thick film, making it an adequate backing to deliver a short pulse-echo response, but the resonance frequency is lowered. Intermediate functional layers were necessary between the substrate and the piezoelectric layer. The transducer based on a porous PZT structure including a dense barrier layer and a gold rear electrode is used as a reference device. Here, another set of materials is considered as possible candidate to fulfill both functions of substrate and backing: porous alumina associated with a dense alumina barrier layer and platinum rear electrode. Since the thicknesses of these layers is not negligible compared to the wavelength of the first thickness mode of the piezoelectric layer, they have a relatively strong influence on the electro- acoustic response. The input acoustic impedance of this stack must be controlled very precisely in order to make it an adequate backing The damping of the backing is optimized to deliver a relatively short pulse-echo response, without excessive lowering of the resonance frequency. The piezoelectric thick film on alumina substrate has similar properties to the one on porous PZT. A mean thickness around 30 micrometers and a thickness coupling factor around 40% were obtained in both cases. As a result of the damping, the structure resonates at 40 MHz, the anti-resonance of the piezoelectric thick film alone being around 65 MHz. Pulse-echo measurements allows comparison of the performance of the two devices in terms of sensitivity, axial resolution and bandwidth. The results are compared and discussed, showing that the sensitivity/bandwidth trade-offs of - the two transducers are significantly different.
    Proceedings of the IEEE Ultrasonics Symposium 01/2007;
  • [Show abstract] [Hide abstract]
    ABSTRACT: The properties of 0.65Pb(Mg1/3Nb2/3)O3--0.35PbTiO3 (0.65PMN--0.35PT) thick films were studied for high-frequency piezoelectric transducer applications. The films were prepared by screen-printing a thick-film paste on platinized alumina substrates and subsequent sintering at 950 °C. The effective thickness-coupling factor of these films was close to 48%, which is comparable with bulk ceramics having the same compositions. Furthermore, simulations of two configurations representing one element of a high-frequency linear-array transducer (30 MHz) suggests that 0.65PMN--0.35PT thick-films in 50 Ω electrical matching environment improves the performance in comparison with standard Pb(Zr,Ti)O3 (PZT) compositions.
    Japanese Journal of Applied Physics 05/2013; 52(5):5502-. · 1.06 Impact Factor