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

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 d h g h 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.

Piezoelectric performances of undoped (K,Na)NbO3 ceramics and crystals for transducers applications

“…This behavior might be explained by the large grain dimensions or the poor grain boundary quality. As expected and already established in other studies [15], the acoustical impedance (Z) and the longitudinal acoustic sound velocity (v l ) are a function of density. Further investigations are needed to distinguish whether the large grain size or whether the degraded grain boundary is responsible of the dielectric and mechanical losses.…”

Study of the role of porosity on the functional properties of (Ba,Sr)TiO 3 ceramics

“…for acoustic impedance adjustment, for permittivity reduction and increase tunability by local field concentration [25,26]. Other use of porous ceramics can be realized by embedding functional groups or other phases into the pores to extend multifunctionality for applications in catalysis and adsorbent supports [27], sensors [28][29][30][31], piezoelectric transducers [32] or multiferroic-based multistate memory devices [33,34] achievement of closed porosity are necessary. On the other hand, there is a high interest in the study of porous ceramics for understanding the role of accidental porosity on its own functional properties, which is inherent in any process of sintering.…”

Dual-frequency transducer for nonlinear contrast agent imaging

“…The backing was made of porous unpoled lead zirconate titanate (PZT) based on Ferroperm Pz37 composition (meggitt a/s) [19]. This porous material offers several advantages for transducer properties (in particular for the center element) [20].…”