Multiobjective Optimization of an Underwater Acoustic Projector with Porous Piezocomposite Active Element Nasedkin A.V. Southern Federal University Rostov-on-Don, Russia Liu J.-C. National Taiwan Ocean University Keelung, Taiwan Shevtsova M.S. Southern Scientific Center of Russian Academy of Sciences Rostov-on-Don, Russia Chang S.-H., Wu J.-K. National Kaohsiung Marine University Kaohsiung, Taiwan Abstract—this paper concerns a multiobjective optimization problem for an underwater ultrasonic transducer based on the porous piezoelectric ceramics. The number of the design variables was decreased using the obtained dependences for the effective characteristics of PZT material on porosity. The optimization problem based on the Pareto-frontier calculation has been solved using the live-link of finite-element (FE) package Comsol Multiphysics with MATLAB. Keywords—piezoelectric composite materials, acoustic transducer, sund pressure level (SPL), transmitting current response (TCR), multiobjective optimization, Pareto-frontier I. INTRODUCTION Nowadays there is a variety of applications for porous piezoceramic materials used as active parts in ultrasonic transducers, hydrophones and other piezoelectric devices. The rise of the number of investigations, referred to a development of the effective structures for porous PZT-based acoustic transducers, depends on a high piezoelectric sensitivity of such materials, extended frequency bandwidth and better matching to the acoustic medium. The purpose of the presented work is to develop the methods for synthesizing the optimal structures of underwater transducers. On the base of previously developed numerical method for determining the effective moduli of porous PZT materials [4, 5], the structural optimization problem has been formulated and solved for a multilayered acoustic projector. In order to effectively fulfill its purpose the underwater acoustic transducer should meet such requirements as: high sensitivity; ability to take high mechanical load and hydrostatic pressure; durability. But one of the most significant challenges in creating the optimal designs of powerful acoustic transducers is the problem of impedance matching. The use of intermediate layers allows to overcome this difficulty. However in case of active element made of dense piezoelectric ceramics a number of layers are needed; and this involves big energy losses of the whole structure. The effective method for getting over this challenge is the use of porous piezoelectric ceramics. This allows to reduce the number of intermediate layers and provides the better acoustic agreement between the transducer and the medium simultaneously. Various experimental [1, 2] and theoretical [3, 12] investigations show, that porous piezoelectric ceramics may significantly improve the desired properties of a transducer and expand the use of piezoelectric materials. In previous works [4, 5] it was investigated how the properties of piezoelectric materials depend on porosity for the ceramics of different connectivity and ferroelectric hardness. Such dependencies have been obtained for the full set of material constants. Presented research is devoted to the structural optimization of a multilayered transducer with the porous PZT active element. All the material parameters of an active layer are expressed via the value of porosity. Previously obtained dependencies allowed to sufficiently decrease a number of the design variables. For an underwater acoustic projector consisted of five layers: acoustic window, matching, piezoelectric, backing plate and protective foam layers (Fig. 1), we formulated the coupled problem of acoustics and electric elasticity in axial- symmetric statement. An averaged sound pressure level (SPL), transmitting current response (TCR) and the mean-square value of the SPL irregularity in frequency range from 100 to 400 kHz were used as the optimized objectives. A calculation of the Pareto frontier was performed in the seven-dimensional space of design variables: porosity of a PZT layer, Young's modules, densities and Poisson's ratios of an acoustic window and matching layer. The coupled problem was numerically implemented by the live-link of the finite-element (FE) package Comsol Multiphysics with MATLAB.