Date of Award
Master of Science in Ocean Engineering
Sau-Lon James Hu
Directional radiation of underwater acoustic energy is commonly achieved by using transducer arrays containing many individual projectors arranged in a particular geometry. One method, which avoids the complexity of a large array of separate elements is to construct directional beam patterns by combining modes of vibration from a single “multimode” projector. Piezoelectric ceramics, such as lead zirconate titanate (PZT), have enabled the construction of most multimode transducers due to their ability to be fabricated into many different shapes and sizes. However, there is little evidence in the use of relaxor-based ferroelectric single crystals as a substitute for conventional piezoelectric ceramics in multimode transducers. By virtue of its superior piezoelectric material properties, relaxor-based ferroelectric single crystals offer dramatically improved bandwidth and power output at reduced size and weight compared to their polycrystalline ceramic counterparts.
This research explored the use of the ternary relaxor-based ferroelectric single crystal system lead indium niobate-lead magnesium niobate-lead titanate (PIN-PMN-PT) as the piezoelectric material in a multimode active-passive segmented cylinder transducer. The transducer design utilized the highly anisotropic structure of relaxor-based single crystals to exploit the transverse 32-mode of operation. The segmented construction included the minimum number of active elements required to perform multimode superposition with omnidirectional (monopole), dipole, and quadrupole vibration modes. The final configuration of the transducer maximized the coupling between active and passive segments and converged upon a desired center frequency that lied between the dipole and quadrupole resonances.
Two separate approaches were taken to investigate the frequency bandwidth of directional beam patterns generated from a multimode active-passive segmented cylinder transducer. The first method leveraged the finite element modeling software COMSOL Multiphysics® to model and simulate the frequency response and beam patterns of an individual segmented ring transducer. The second method involved physically constructing a transducer and conducting in-water acoustic testing at the Naval Undersea Warfare Center (NUWC) Division Newport – Dodge Pond Acoustic Measurement Facility. Classical cardioid and narrow cardioid beam patterns were selected to evaluate the ability of the transducer to generate directional responses between 10 – 50 kHz. Through in-water acoustic testing; it was shown that directional beam patterns could be well formed around 30 kHz, with modest directivity between 20 – 35 kHz. This demonstration of piezoelectric single crystals in a multimode transducer contributes to the field of underwater acoustics by addressing needs in application areas that require compact devices with the ability to form directional beam patterns over a wide frequency bandwidth.
Doyle, Ian M., "INVESTIGATION OF A MULTIMODE TRANSDUCER USING PIEZOELECTRIC SINGLE CRYSTALS" (2021). Open Access Master's Theses. Paper 2086.