SBIR-STTR Award

This proposed project is for the new application of PMN-PT based piezoelectric crystals. Shear modes of PMN-PT crystals show the supreme properties: k15 poled PMN-PT crystal has a coupling coefficient greater than 0.95 and k36 poled PMN-PT crystal gives a coupling coefficient greater than 0.90. The k36 has a unique re-pole-ability and larger coercive field over 5 kV/cm (2 times higher than poled k33 mode) that more promising for high power projectors. The proposed device is designed to replace the transducer which is being used in a mine counter measure (MCM) application on an autonomous underwater vehicle (AUV). The proposed shear mode transducer will give the following advantages over the existing transducer: insensitive to the hydrostatic pressure (under water depth), compact volume, less reactive load to the system power amplifier and broaden sandwich. The proposed work will investigate these material properties to produce a compact low frequency SONAR projector capable of very high bandwidth. Anticipated work in Phase II would enable the fabrication of the shear mode transducers for military and commercial applications.

Benefit:
(1) Identification and Significance of the Problem or Opportunity The properties of single crystal piezoelectric materials promise excellent performance when used in SONAR transducers. This proposal outlines a novel shear mode projector utilizing PMN-PT single crystal. Robert Manning of the Office of Naval Research (ONR) has been identified as a potential champion for the technology described herein. The proposed device is designed to replace the transducer described in [4], which is being used in a mine counter measure (MCM) application on an autonomous underwater vehicle (AUV). The existing transducer has a very low coupling coefficient and presents a highly reactive load to the system power amplifier. That reactive load requires the power amplifier to be much larger and draw more power than desired. Since the application is on an AUV, volume and power are at a premium. The existing transducer is also sensitive to hydrostatic pressure. These issues can be eliminated with the proposed transducer design. The shear mode properties of two cuts of PMN-PT show great promise for use in a SONAR transducer. poled PMN-PT has a coupling coefficient greater than 0.95 [1, 2 and 5], which has the potential excellent useable bandwidth in a device. The shear modulus of this material is also much lower than traditional piezoelectric materials, allowing a compact acoustic source design. A second crystal orientation of interest is poled PMN-PT. This mode may be even more promising for high power projectors based on preliminary material property values because the domain structure of the k36 mode of poling [5] is more stable and a bias field can be applied, like 33-mode of poling. The proposed work will investigate these material properties to produce a compact low frequency SONAR projector capable of very high bandwidth. The high coupling coefficient and high compliance of a piezoelectric single crystal in shear allows us to design a very broad bandwidth, compact transducer. Using the k36 mode may allow higher power applications of this transducer. Either of the two cases presented represents a dramatic improvement in bandwidth compared to existing transducers of this frequency. A classic flextensional transducer may have comparable volume (mm3) for the same frequency, but its bandwidth will be far less. A classic tonpilz transducer using piezoelectric ceramic will have less bandwidth and will be far larger. This transducer design has several potential advantages over the low frequency projector currently used in the application of interest. The current projector is described in [4]. A list of the improvements follows. 1. The coupling coefficient and bandwidth of the shear mode single crystal transducer are far better than the existing projector. 2. The effective bandwidth of the shear mode single crystal transducer will be far higher than the existing projector, reducing the volume and power required by the transmitter. 3. The size and weight of the shear mode single crystal transducer is expected to be about the same as the existing projector and its accompanying baffle. The baffle, while not described in [4], is required to allow acoustic radiation in one direction only. Single sided radiation is built into the proposed shear mode single crystal transducer, so a separate baffle will not be required. 4. The application of interest, while spanning the range from 1-30 kHz, is primarily interested in the lowest octaves of that spectrum. The shear mode single crystal transducer should be capable of producing much more acoustic power at those frequencies if the transmitter capacity remains the same. Conversely, the shear mode single crystal transducer should be capable of producing the same acoustic power output with a reduced transmitter capacity. These options can be traded off in the system design. 5. The shear mode single crystal transducer can be housed in such a way that hydrostatic pressure does not affect its performance.

Keywords:
Shear mode transducer, Shear mode transducer, k36 shear mode., Acoustic Transducer, k15 shear mode, PMN-PT Piezoelectric Crystals

This program is intended to advance the state-of-the-art d36 shear mode projector. Phase I of this effort produced a projector which demonstrates promising bandwidth and source level, especially considering its compact size. It is also the first known d36 underwater projector in the history of piezoelectrics. To develop a robust, high power, and broad bandwidth d36 shear mode projector array and bring it to a usable stage, we propose the following tasks for the phase II project: 1) Measure and establish full set material properties for selected crystals. Accurate material properties are critical to transducer design and optimization because inaccuracy in material property directly affect the outcomes of transducer modeling; 2) Refine the d36 transducer design and optimize transducer performance characteristics based on the measured property values; 3) Validate transducer design with in situ transducer tests. By the end of the Phase II project, we will develop and build a robust, high power, and broad bandwidth shear mode projector array. We propose a budget of $749,763 to carry out the proposed works in a period of 24 months. A subcontract to the Applied Research Laboratory at Penn State is for the design, optimization and validation of the prototype d36 shear mode crystal transducers. By the end of the contract period, we will evaluate the design and techniques developed and prepare for the commercialization of the shear mode crystal transducer.

Benefit:
The proposed tasks in the Phase II will establish full set material properties with great accuracy for the poled PMN-PT and/or PIN-PMN-PT crystals. Such a property dataset is vital not only for the d36 shear mode application which is the focus of the proposed project, but also for the d31 transverse mode such as torpedo countermeasure design. The d36 property is unique to the piezoelectric crystals whereas piezoelectric ceramics do not have. The new ternary PIN-PMN-PT crystals with significantly increased coercive field and depoling temperature will improve the transducer robustness by allowing higher driving fields and higher operating temperatures. The full set material property enables the design refinement and performance optimization for the d36 shear mode transducer. At the end of the Phase II project, the performance characteristics of the designed transducers will be validated through in air and in water transducer tests. The d36 shear mode crystal transducers offer broad bandwidth, high power and low frequency with compact size. The accomplishment of the proposed work (see section 4 Technical Objectives) will prepare the d36 crystal transducer technology for naval applications.

Keywords:
high drive, Reliability, PIN-PMN-PT, transducer design, Optimization, PMN-PT, Piezoelectric crystals, property matrix