TECHNOLOGY AREAS: Materials/Processes, Sensors, Weapons

ACQUISITION PROGRAM: PMS 415 Undersea Defensive Warfare Systems: Next Generation Countermeasure

OBJECTIVE: Develop experimental methods and evaluate the linear and non-linear electromechanical properties of relaxor piezoelectric crystals under temperature-stress-field conditions relevant to naval SONAR systems. The domain of phase stability and property linearity for first generation binary, second generation ternary, and third generation doped materials should be assessed to optimize naval SONAR transducer designs.

DESCRIPTION: More than a decade ago a class of materials (relaxor piezoelectric single crystals) came to the fore whose electromechanical transduction properties greatly exceeded those of legacy materials (primarily, piezoelectric ceramics): electromechanical coupling greater than 90% (versus 70-75%) and strain levels greater than 1% (versus, less than 0.1%) [References 1 and 2]. Based on these materials acoustic transducers have been demonstrated with dramatically enhanced performance over what is achievable with the legacy technology --- for example, increased bandwidth (>x2), source level (+12 dB), sensitivity (+12 dB), compactness (>x3) and lightness (>x2) [Reference 3]. These device performance gains (totaling one to two orders of magnitude) have yielded gains, at the system level, of factors of two to six [Reference 4]. Indeed, the PiezoCrystal transducer technology makes possible some systems that simply would not be practical with the legacy technology. Navy SONAR systems have already completed the technology development and demonstration phase and are entering the system development and demonstration phase of the acquisition process. The materials technology has undergone similar evolution. The initial binary compositions (for example, Lead Magnesium Niobate - Lead Titanate) have been supplemented with ternary compositions (for example, Lead Magnesium Niobate - Lead Indium Niobate - Lead Titanate) with expanded temperature-field-stress operating domain and with doped compositions with specific properties enhanced (for example, Manganese doping yielding reduced mechanical losses under high drive). A PiezoCrystals Standards Committee is actively drafting a set of material specifications for ratification through the IEEE as international standards for composition/properties; materials with the delineated compositions/properties will ultimately dominate the market. Work under this topic will characterize the linear and non-linear electromechanical properties of a broad range of materials compositions under a broad range of temperature-field-stress conditions to delineate the composition/properties that optimize a variety of naval SONAR transducers.

PHASE I: Identify a targeted naval SONAR transducer application and select one material composition for assessment. Devise an experimental procedure and evaluate that compositions' linear and non-linear electromechanical properties under a reasonable spectrum of thermal-electrical-mechanical boundary conditions. Assess the suitability of the selected composition for the targeted application. Only materials characterization is to be performed in this phase -- no transducer fabrication and testing.

PHASE II: Two thrusts are to be developed in parallel. In the first the Phase I activities will be expanded: additional experimental measurement techniques will be developed; additional materials compositions will be evaluated and additional SONAR applications will be targeted; the materials properties emerging from these measurements will be contributed to the PiezoCrystals Standards Committee to ensure that the materials compositions/properties delineated by those standards are serviceable for naval SONAR transducer applications. In the second thrust a linkage will be established with a single specific naval SONAR transducer development effort and materials assessments performed in support of those development efforts (a limited amount of transducer fabrication and evaluation may be performed under this topic in this phase to validate the utility of the materials characterization work).

PHASE III: The characterization methods developed by this research will be applied to new PiezoCrystal compositions as they emerge and applied in development and production of PiezoCrystal transducers for a broad spectrum of Navy SONAR systems: countermeasures, mine hunting, torpedoes, acoustic modems, towed arrays, moored arrays, sonobuoys, and the like.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: The technology developed for defense transducers will be immediately applicable to transducers in civilian SONAR systems. These property assessments will be readily transferred to making electromechanical sensors and actuators for a broad spectrum of civilian applications ranging from hydraulic servo valves, through vibration energy harvesters, to robotic manipulators.

REFERENCES:
1. S.E. Park and T.R. Shrout, "Ultrahigh Strain and Piezoelectric Behavior in Relaxor based Ferroelectric Single Crystals," J. Appl. Phys., 82[4], 1804-1881 (1997).

2. S.-E Park and T.R. Shrout, "Characteristics of Relaxor-Based Piezoelectric Single Crystals for Ultrasonic Transducers," IEEE Trans. On Ultrasonic Ferroelectrics and Frequency Control, Vol. 44, No. 5, 1140-1147 (1997).

3. J. M. Powers, M. B. Moffett, and F. Nussbaum, "Single Crystal Naval Transducer Development," Proceedings of the IEEE International Symposium on the Applications of Ferroelectrics, 351-354 (2000).

4. T. C. Montgomery, R. J. Meyer, and E. M. Bienert, "Broadband Transduction Implementation and System Impact," Oceans 2007, 1-5 (2007).

KEYWORDS: piezoelectric single crystals; optimized SONAR transducers; linear materials properties; non-linear materials properties; materials phase stability; temperature-field-stress dependence of materials properties

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