Comparison of Models for a Piezoelectric 31-Mode Segmented Cylindrical Transducer

date September 20, 2013
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Friday, September 20, 2013 4:00 p.m. in ETC 4.150

Nicholas J. Joseph
Applied Research Laboratories and Department of Mechanical Engineering
The University of Texas at Austin

Piezoelectric transducers with thin-shelled cylindrical geometry are often used to radiate axisymmetric acoustic fields underwater.  This is achieved by generating a uniform electric field across the thickness of the piezoelectric cylinder to develop circumferential strains and, consequently, uniform radial expansion.  The uniform radial expansion is known as the breathing mode and is the desired behavior of these sources.  To tune their performance in a cost-effective way, the cylinders can be constructed of alternating active (piezoelectric) and inactive (non-piezoelectric) segments along their circumference.  Existing lumped parameter models for these transducers reduce the system to a single degree of freedom using effective piezoelectric properties of the composite cylinder.  These models accurately capture the breathing motion of the cylinder but neglect other modes and overestimate the efficiency of the transducer.  Experiments show that segmented transducers may demonstrate a detrimental higher frequency resonance within the operational frequency band.  The parasitic mode associated with this resonance is shown to result from bending motion of the segments and can significantly decrease the radiated acoustic pressure.  Discussed here is the development of a multiple-degree-of-freedom lumped parameter model that captures both the breathing and bending modes of the transducer and provides a more accurate estimate of its efficiency.  Results from the multi-degree-of-freedom model are compared with those from a one-degree-of-freedom model, finite element models, and experimental data.