New concepts will be developed for sensing and control of noise and vibration in structures. Sensing of individual strain components in a plane requires three independent measurements, typically using a strain Rosette. The concept of the strain Rosette to piezoelectric materials that can be used for both directional sensing and directional actuation will be extended. This will be accomplished through designed anisotropy, an approach in which a combination of the physical structure, the crystallographic orientation, and the domain structure of the sensor/actuator element are concurrently designed to obtain desired couplings to the host structure. Research will involve feedback and control, optimal sensor/actuator location and spatial distribution, as well as exploration of feedback techniques based on negative capacitance amplifiers. New design and analysis tools will be developed for these sensor/actuator components. Student involvement will include undergraduate (UG) research helpers, MS students, and PhD students. An international component will bring in multicultural interactions and experience. Research results will be carried through to the classroom and UG instructional laboratories. Results will be broadly disseminated through journal publications, conference presentations, and collaborations with other research groups.
Piezoelectric sensor/actuator rosettes for noise, vibration, and smart structure shape control This project began with the concept of a new type of sensor that can not only sense strain, it can produce its own strain when a voltage is applied. The underlying phenomenon is called piezoelectricity and it is widely applied in systems such as sonar, medical devices, and automotive fuel injection. Strain is the stretching that occurs when force is applied to a solid object. This can be detected on the surface using strain gages. Piezoelectric strain gages are commercially available (Macro Fiber Composites) but lack the accuracy needed for high resolution strain measurements. They do, however, have the benefit of being able to produce a strain from an applied voltage. This enables vibration damping and was commercially used in a K2 ski a number of years ago. Strain is a directional quantity associated with the direction of bending. Rosettes have the ability to sense not only the magnitude of the strain, but also the direction. A three element rosette can be used to determine the principle strain directions associated with the bending. A piezoelectric rosette can also respond to this with a directional response to control this bending. This project focused on the development of design tools capable of designing these rosettes. Finite element codes are available, but they only model linear material properties. Designing the rosettes requires analysis of the polarization process and an assessment of the resulting non-linear material behavior. This accounts for most of the behavior of the rosettes when interdigitated electrodes are used. A finite element code was developed under this project and non-linear material models were developed and implemented in this code. The non-linear material models were based on micromechanics of ferroelectric materials and on phase field models of the material behavior. The micromechanical models are used to simulate the poling process at larger scales where the grains in the ceramic are smaller than other features. The phase field models were used to simulate details of the polarization process at the level of domains in single crystals. These codes were used to design in directional properties in the individual rosette elements. This is referred to as designed anisotropy. The resulting sensor/actuator package was then bonded to a large plate that was subjected to various bending modes and the results used to validate the computational models and the device design.. Intellectual impact: The intellectual impact of this proposed program resides in three areas: fundamental science, technology development, and human resource development. Fundamental Science: The contributions to fundamental science were the result of implementing a combination of multiscale modeling with experimental work. The multiscale physics based modeling contributed to our insight into the role of the polarization reorientation process on the resulting material behavior. The phase field modeling elucidated the contribution of domain wall motion and domain wall energy to the material behavior, and helped with the identification of parameters used to tune the micromechanical model. The micromechanical modeling captures material non-linearity associated with the crystal structure of the ceramic. A number of modeling efforts were begun during this project and have planted the seeds for ongoing efforts. New projects are underway where collaborations with the physics community is attempting to use atomic level modeling to predict the details of the material behavior. The atomic scale models can only simulate a few thousand atoms and thus cannot address the effects of defects in the crystal structure or other features such as domain walls and grains in a ceramic, but results of modeling at each length scale can be used to directly compute parameters needed by models at each higher length scale. As this type of modeling progresses, we should reach the stage of being able to design ferroelectric materials from the atomic scale up. Technology development: This program resulted in new technology being developed that has a broad range of applications. Applications to noise and vibration control were initially anticipated and were pursued. Additional applications were discovered in shape control. One of the undergraduate students supported on an REU supplement fabricated voltage controlled bending elements. These are sufficiently robust that they are under consideration for several solid state actuator applications. Human resource development: One PhD student was supported by this project. The work he performed laid the foundation for his doctoral work. In addition, this project supported 6 undergraduate researchers (one woman and two minority). Broader impacts: Students at all levels were involved in this research including undergraduate (UG) research helpers, MS students, and PhD students. Tools developed, such as custom finite element material models, have enhanced our educational infrastructure. Close interactions between this project and UCLA's Center for Excellence in Engineering and Diversity (CEED) have resulted in a number of talented undergraduates with diverse backgrounds working on projects associated with this NSF grant.
