Multimode Tonpilz transducer is well-known for providing a wider bandwidth than a single-mode transducer. In this paper, a new structure of the head mass of a multimode Tonpilz transducer was designed to further widen the bandwidth. The mechanical quality factor of a Tonpilz transducer is in inverse proportion to the weight of the head mass. Making the cavity inside the head mass will surely lead to a lighter head mass, which can lead to a lower mechanical quality factor thus a wider bandwidth. Through finite element analyses, the cross-coupled effects of the void head mass structure on the transducer performance were analyzed. Then the functional forms of the performance were derived in relation to the head mass structure and were inserted into the genetic algorithm to achieve the widest possible bandwidth. The structure of the tail mass was also optimized using the same method to match the new head mass. Further, it was shown that the matching layer on top of the head mass could be safely eliminated without affecting the performance of the transducer due to the low mechanical quality factor.
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