A design approach for a configurable high-power magnetostrictive drive made from iron-gallium alloy (Galfenol)
Magnetostrictive gallium-iron alloys (collectively known as Galfenol) have been identified as a candidate active materials for use in sonar transducers. Among the interesting characteristics of Galfenol are its competitive strain capability, attractive magnetic permeability, and mechanical robustness. The latter property is especially noteworthy as it allows access to a design space inaccessible to other high-strain active materials, both magnetostrictive and piezoelectric.
This dissertation develops a design approach for leveraging Galfenol's unique properties to create a self-contained magnetostrictive drive constructed from finely laminated structures. The approach relies on using a generalized design framework that is flexible enough to be configured for different applications. Flexibility is achieved through the adjustment of the laminated structure dimensions, the modular assembly of these structures, and the ability to bias the system with either permanent magnets or direct current. A key outcome of this study is a one-dimensional design model that simplifies the process of tailoring the drive to potential applications.
Validation of this configurable drive concept is accomplished through designing, fabricating, and modeling a prototype drive that seeks to optimize the material's use. The one-dimensional design model is used to produce the prototype design and the results are corroborated with three-dimensional, nonlinear finite element analysis. Fabrication of the device is accomplished by assembling thin layers of Galfenol steel into two laminated structures, winding drive coils on these structures, and placing permanent magnets in between. Finally, a full one-dimensional, multi-domain model is created to simulate the behavior of the device.
To investigate the performance of Galfenol in sonar applications, the drive is assembled into a tonpilz-style transducer and tested in a water-filled anechoic tank. Simulation is accomplished by updating the one-dimensional model of the drive to represent the testing scenario and by employing finite element modeling. The model results are then compared to measurement with good agreement.
Finally, measured values for the quality factor, electromechanical coupling coefficient, and efficiency of the Galfenol tonpilz are compared to published data for various nickel and Terfenol-D designs. The result is that the Galfenol transducer achieves comparable results in all three areas. It is concluded that Galfenol is competitive with other magnetostrictive materials and merits consideration for future magnetostrictive designs.