This study experimentally investigates the capabilities of iron-gallium nanowire arrays as artificial cilia transducers. The experiments are conducted with a custom manipulator device incorporated into the stage of a scanning electron microscope (SEM) for observation. Individual nanowires of varying size and composition are mechanically tested statically and dynamically to determine the elastic properties and failure modes. Entire arrays of close packed wires are mounted onto giant magnetoresistive (GMR) sensors to measure the coupled magnetic induction response resulting from bending the array. This data is compared with empirical and simulated results from previous macroscale research.
This project investigates the magnetic structure and mechanical properties of iron-gallium nanowires to facilitate the
modeling and design of sensor devices. Magnetic force microscopy (MFM) is employed to better understand the domain
orientation and size along the cross-section of a close packed wire array. Mechanical properties are identified by
conducting static tensile testing on individual nanowires using a manipulator stage designed for use within a scanning
electron microscope (SEM). The Young's modulus of the nanowires is found to agree well with the value for the bulk
material, but these structures do demonstrate a large increase in ultimate tensile strength. Other tests include resonance
identification of nanowire beam bending via dynamic excitation.
This paper presents a magneto-elastic model developed by coupling a finite element elastic and magnetic
formulations with an energy based probabilistic magnetostrictive model. Unidirectional coupled model is
presented first for both sensor and actuator applications and then a fully coupled bidirectional model is developed.
The unidirectional sensor model was validated against experimental results for a 1.58 mm diameter and 32.74 mm
long Galfenol cantilever beam. The model was further used to investigate the response of Galfenol nanowire array
that will be used in a nanowire acoustic sensor. Model predictions suggest that differences in the phase of bending
motion of nanowires in an array will not produce a significant effect on the magnetic response of the array. It also
predicts that the response of a single nanowire can be measured by a magnetic sensor with active measurement
area much larger than the nanowire dimensions.
This project investigates the magnetomechanical sensing behavior of iron-gallium alloys in response to applied bending loads in order to provide an experimental and analytic framework for implementing this material in novel sensor applications at the nanoscale. A series of experiments are conducted on millimeter sized cantilevered beams to verify that the material is mechanically sound as well as magnetically active in this loading configuration, with results showing a change in magnetic induction of as much as 0.3 T occurring at twice the frequency of beam vibration. These results agree well with an analytic system model based on nonlinear free energy terms. Initial work has begun on visualizing and characterizing arrays of iron-gallium nanowires, with an atomic force microscope providing preliminary images as well as force and deflection data.
Galfenol alloys (Fe100-x Gax) have been shown to combine significant magnetostriction (~400 ppm) with strong mechanical properties (tensile strengths ~500 MPa), making them well suited for use in robust actuators and sensors as an active structural material. This project investigates the magnetomechanical bending behavior of Galfenol to facilitate the design concepts for using Galfenol in a variety of novel sensor applications. To this end, a series of experiments are conducted on the magnetic response of cantilevered beams to dynamic bending loads. The samples studied include polycrystalline Fe81.6Ga18.4 and Fe80.5Ga19.5 (1/8” diameter x 2” long) and single crystal Fe84Ga16 and Fe79Ga21 (1/16” diameter x 1” long). Mechanical excitation was applied to the tip of each rod, with tests performed with sinusoidal and broadband random inputs. Measuring the magnetic response of the samples were a giant magnetoresistive (GMR) sensor located behind the beam and a pickup coil wound directly on each rod. A combination of permanent magnets and solenoid provided dc fields to magnetically bias the samples. Results of initial testing show that sinusoidal bending produces measurable output in which the GMR sensor agrees well with the pickup coil, and that the output increases when subjected to increased magnetic bias. Random input tests confirm that the various system resonances can be detected from the frequency spectra. Other results examine the effects of composition, crystal structure, and z-axis position of the GMR sensor. The system is modeled by incorporating classical continuum mechanics, the constitutive magnetostriction equations, and nonlinear magnetization terms, the results of which are compared with the experiments.
This paper presents recent advances in the design and characterization of hybrid transducers incorporating magnetostrictive and electrostrictive elements. In order to analyze and validate the properties inherent to hybrid concepts, a transducer was designed and constructed through a mechanical series arrangement of a PMN-PT stack and a Terfenol-D rod. This configuration provides a double resonant frequency response that can be tuned for a variety of applications. The primary objective of this study lies in the determination of the design criteria for achieving maximum transducer bandwidth on the 1 - 6 kHz range. To this end, a linear system model was developed utilizing concepts from vibrations, electroacoustic theory, and linearized constitutive relationships for each class of smart material for low to moderate drive levels. This model provides a means of completely describing the system response and the interactions between electrical and mechanical domains for this hybrid transducer. Experimental data collected from the test device indicate that the measured modes of vibration and resonance peaks agree with the theoretical results, and that the desired bandwidth has been achieved.