Finite element modelling of dense and porous piezoceramic disc hydrophones R. Ramesh * , H. Kara, C.R. Bowen Materials Research Centre, Department of Engineering and Applied Sciences, University of Bath, Bath BA2 7AY, UK Received 10 February 2004; received in revised form 30 April 2004; accepted 1 May 2004 Available online 7 June 2004 Abstract The acoustic characteristics of dense and porous piezoceramic disc hydrophones have been studied by finite element modelling (FEM). The FEM results are validated initially by an analytical model for a simple disc of dense piezoceramic material and then it is extended to a porous piezoceramic disc replicating a foam-reticulated sample. Axisymmetric model was used for dense piezoceramic hydrophone due its regular geometric shape. 3-dimensional model was used for the porous piezoceramics, since the unit cell model is inadequate to fully represent transducers of finite lateral dimensions. The porous PZT discs have been synthesised by foam-retic- ulation technique. The electrical impedance and the receiving sensitivity of the hydrophones in water are evaluated in the frequency range 10–100 kHz. The model results are compared with the experimental data. The receiving sensitivity of piezocomposite hy- drophones is found to be reasonably constant over the frequency range studied. The sharp resonance peaks observed for the dense piezoceramic hydrophone has broadened to a large extent for porous piezoceramic hydrophones, indicating higher losses. The flat frequency response suggests that the 3–3 piezocomposites are useful for wide-band hydrophone applications. Ó 2004 Elsevier B.V. All rights reserved. PACS: 43.38.Fx Keywords: Piezoceramics; Piezocomposites; Porous structures; Modelling; Hydrophones; Underwater acoustics 1. Introduction Piezocomposite materials have drawn considerable attention in recent years due to their application in ultrasonic and underwater transducers [1,2]. Piezocom- posites have higher electromechanical coupling coeffi- cient, lower acoustic impedance and higher hydrostatic coefficients compared to the conventional Lead Zirco- nate Titanate (PZT) materials. Further, by changing the ceramic/polymer volume fractions, the material param- eters of a composite transducer can be altered to meet specific requirements [3]. Although piezocomposite of various connectivities do exist [4], only composites with 1–3, 2–2 and 3–3 connectivities have been found to be more useful for transducer applications [5–7]. 1–3 piezocomposites have been studied extensively and various modelling and experimental studies have been reported in literature [8,9]. Although, 1–3 com- posites are highly useful for transducer applications, their production is tedious and expensive [5]. 3–3 pi- ezocomposites prove to be an alternative, with compa- rable material properties and relatively simpler method of synthesis [10]. 3–3 piezocomposites in the form of porous PZT materials show considerably improved transducer characteristics. Experimental studies on porous piezoelectric structures indicate that they have high hydrostatic figure-of-merit [10] and high receiving sensitivity [11,12]. However, their depth-handling capa- bility and the stability to hydrostatic pressure have yet to be proved. The mechanical strength of the transducer can be improved by filling with a polymer as second phase. In certain cases, depending on the method of syn- thesis, the 3–3 piezocomposites are found to coexist with 0–3 composites for intermediate ceramic volume frac- tions. The material properties of these composites with mixed connectivities can be evaluated using theoretical models [13,14]. Some theoretical models have been * Corresponding author. NPOL, Thrikkakara, Cochin 682 021, India. E-mail address: ramesh_rmani@hotmail.com (R. Ramesh). 0041-624X/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.ultras.2004.05.001 Ultrasonics 43 (2005) 173–181 www.elsevier.com/locate/ultras