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High Power Evaluation of Textured Piezoelectric Ceramics for SONAR Projectors
Restricted (Penn State Only)
Shankar, Arjun K
Master of Science
Date of Defense:
August 31, 2017
Richard Joseph Meyer Jr., Thesis Advisor
Russell Charles Burkhardt, Committee Member
Stephen Thompson, Committee Member
Daniel C Brown Jr., Committee Member
Textured ceramics of the relaxor ferroelectric [(1-x)Pb(Mg1/3Nb2/3)-O3-xPbTiO3] (PMN-PT or PMNT) have shown piezoelectric properties suitable for high power SONAR projectors. The piezoelectric coefficient (d33>800pm/V), the electromechanical coupling coefficient (k33>0.80), and the mechanical quality factor (Qm>90) in various forms of PMN-PT showcase the potential for these textured ceramics to be implemented in a high power, broad bandwidth acoustic projector. This work attempted to devise a set of experiments to quickly characterize the electromechanical performance of these materials in relevant devices in order to provide feedback to both the material developers and the user community. In this effort, the performance of textured PMNT and Manganese doped PMNT (Mn:PMNT) was compared to conventional lead zirconate titanate (PZT) ceramics. Two primary transducer designs were investigated: the Langevin sandwich and the Tonpilz. Modeling was first carried out through the GiD-ATILA finite element software package to predict the transducer behavior in air and in water. Transducers were then fabricated using piezoelectric rings of dimensions specified by the modeling results. The Langevin sandwich transducers underwent a a series of preload and temperature tests, monitoring key electromechanical properties over a range of preload stresses and temperatures. Results from this experiment showed significantly reduced d33 (660pC/N for PMNT and 410pC/N for Mn:PMNT), lower k33 (0.38 for PMNT and <0.35 for Mn:PMNT), and increased resonance frequency shifts as a function of stress (>6% for PMNT and Mn:PMNT at 25MPa) compared to the modeling results. Tonpilz transducers were fabricated and tested in air and in water using the anechoic test facility and high pressure test facility at the Applied Research Laboratory (ARL) at Pennsylvania State University. Small signal measurements in air showed similar poor electromechanical material properties for PMNT and Mn:PMNT as the sandwich transducers. Linearity and harmonic distortion measurements in water revealed reduced source levels, increased harmonic distortion, and unstable behavior at high drive levels both on and off resonance for PMNT and Mn:PMNT compared to modeled results. Isothermal measurements were made at 50 deg C and source levels were monitored as a function of duty cycle. PZT4 and PZT8 showed source levels greater than 5dB higher compared to PMNT and Mn:PMNT for all duty cycles measured. The primary cause for lower than expected performance from textured PMNT can be traced back to the increased PT composition and reduced texture fraction in the material (30% and 85%, respectively). This elevated PT concentration resulted in increased thermal instability at lower temperatures, resulting in domain reconfiguration and poorer electromechanical properties at the operating temperatures for these experiments. The reduced texture fraction decreased the piezoelectric response in PMNT, causing reductions in the expected source levels produced from the devices. The results found from this work suggest modifications need to be made to the PT composition and texture fraction in the textured materials in order to unlock the true potential for use in high power SONAR projectors. Despite these results, the method used to rapidly fabricate, test, and evaluate the performance of these SONAR projectors could be directly used to carry out similar device evaluations for different piezoelectric materials, providing rapid feedback to the material developers in order to optimize material properties for future studies of textured piezoelectric ceramics.
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