Rapid identification of candidate materials for tonpilz head-mass design

Optimum performance of a tonpilz transducer head-mass section is often achieved when the mass is minimized and the stiffness is maximized. High stiffness keeps head-mass modes away from the band of interest with minimal material; low mass maximizes the motor section aspect ratio and reduces the stored energy in the head-mass, raising the electromechanical coupling coefficient. Therefore, the material selected for the head-mass construction plays an integral role in transducer performance. In the practical design of tonpilz radiating heads, a tool which can rapidly identify the materials best suited for a given design is desirable. The figure of merit, Eρ3, has traditionally been used. This figure of merit, however, is based on thin-plate approximations. Most actual tonpilz head-masses require thick-plate theory for accurate analysis. In this paper, the authors use a numerical routine to rapidly assess the thick-plate behavior of various materials and rank their suitability for a given head-mass geometry. These results are corroborated with finite element modeling. Finally, the thick-plate ranking scheme is compared to the traditional figure of merit. The results of this comparison challenge established assumptions about the best materials for head-mass design and identify ceramic materials as strong candidates for future designs.