Michael C. Emmons

Influence of mechanical load bias on converse magnetoelectric laminate composites

A piezofiber/Metglas (PFM) magnetoelectric (ME) laminate has been integrated into a graphite epoxy composite (GEC) to study the converse ME effect (CME). Experimental data on a PFM/GEC subjected to both a dc magnetic field bias and a dc mechanical load bias while exciting it with an ac electric driving voltage are presented. Results of these tests indicate that both the mechanical load and the dc magnetic field strongly influence the CME response. Furthermore, an optimum mechanical load exists to maximize the CME coefficient, which should also be present in standalone ME laminates. These results reveal that the CME coefficient can be further increased with a proper mechanical load bias. Therefore, the selection of an appropriate mechanical preload as well as dc magnetic bias will maximize the CME response and sensitivity in ME laminates as well as integrated structural systems.

Alternate evaluation criteria of piezoelectric motors

In this article, four types of piezoelectrically driven motors are evaluated: linear, horn-type, unidirectional rotary, and bidirectional traveling wave. Experimental results for velocity, power, and specific power are presented as a function of mechanical load. Analytical and experimental energy densities are compared based upon applied electrical potential. The bidirectional ultrasonic motor exhibited 34% of its available energy density, while the other motors produced values ranging from 0.63 to 9.5% of their respective available energies. The piezoelectric material specific power values ranged from 4500 W/kg for the bidirectional motor to 6.53 W/kg for the linear piezo motor. Results suggest that comparing piezoelectric motors based on individual mechanical parameters does not accurately describe motor design and drive train energy transmission.

Thin film NiTi coatings on optical fiber Bragg sensors

This paper describes the sputter deposition and characterization of nickel titanium (NiTi) thin film shape memory alloy onto the surface of an optical fiber Bragg grating. The NiTi coating uniformity, crystallinity, and transformation temperatures are measured using scanning electron microscope, x-ray diffraction, and differential scanning calorimeter, respectively. The strain in the optical fiber is measured using centroid calculation of wavelength shifts. Results show distinct and abrupt changes in the optical fiber signal with the four related transformation temperatures represented by the austenite-martensite forward and reverse phase transformations. These tests demonstrate a coupling present between optical energy and thermal energy, i.e., a modified multiferroic material.

Modeling and experimental analysis of the hyperelastic thin film nitinol

Many flexible electronic devices or endovascular biomedical devices require large deformation; however, potential materials produce limited elastic response, that is, 10% when 400% is required. In this article, a finite element model is used to design a hyperelastic thin film nitinol structure containing geometric fenestrations. The hyperelastic response is dependent upon geometric factors that produce buckling. Parametric studies provide the influence-specific parameters have on buckling load. These results are used to select three designs to manufacture and test. Experimental results indicate that elongations greater than 700% are possible.

Computational Modeling and Experimental Characterization of Hyperelastic Thin Film NiTi for Neurovascular Microstent Applications

A novel hyperelastic thin film NiTi covered neurovascular microstent was developed for treating wide-neck and fusiform neurovascular aneurysms. This device requires 300–500% recoverable elongation for both collapsing and deployment. Nonlinear buckling and static analysis of Finite Element Modeling (FEM: ANSYS software used) was applied for obtaining critical buckling stress and critical strain values depending on thickness, strut width and pore height. A maximum theoretical critical strain for one geometry as high as 316% while a different experimentally tested film was found to strain 600% elastically without any signs of permanent deformation.Copyright

Characterization and birefringence effect on embedded optical fiber Bragg gratings

This study characterizes the performance of embedded optical fiber Bragg gratings (FBGs) used as strain sensors. Focus is provided to FBGs embedded in a quasi-isotropic lay-up of carbon fiber epoxy lamina both parallel and perpendicular to adjacent structural fibers. It studies the birefringence induced during curing and quantifies the residual transverse strain differences on the fibers by measuring the split from a single reflected Bragg wavelength into two. The association between light polarization and loading directions relative to the optical fiber (in-plane parallel, in-plane transverse, and out-of-plane transverse) are analyzed. Birefringence was seen to increase when a compressive out-of-plane load was applied to the embedded optical fiber. In contrast, in-plane loads did not lead to an increase in birefringence as indicated by reflected wavelengths that split during curing shifting equally and linearly during tensile load tests. An effective strain-optic coefficient was determined that resulted in strong correlations between FBG and surface mounted electrical strain gauge measurements.

Magnetoelectric laminate composites with prestress consideration

The converse magnetoelectric effect of an asymmetric Piezo-fiber/Metglas bilayer laminate composite subjected to mechanical prestress is presented. The mechanical prestress is applied by either dc electric voltage bias or direct mechanical load bias. It is found that a mechanical prestress strongly influences the converse magnetoelectric coupling response. The optimum dc magnetic field bias shifts with different prestress and compressive stress requires higher dc magnetic field bias. Additionally, an optimum prestress exists to maximize the converse magnetoelectric response under certain dc magnetic field bias ranges. Therefore, in order to integrate magnetoelectric composite into actual structures, a proper prestress needs to be employed to maximize the CME coefficient.

Characterization of Optical Fiber Bragg Gratings as Strain Sensors Considering Load Direction

This study investigates the influence of lay-up and load direction on embedded optical fiber Bragg gratings (FBGs) used as strain sensors. FBGs have shown great promise for application to structural health monitoring with advantages of small size and cylindrical geometry readily allowing for embedment within fiber reinforced composites. Characterization of the embedded FBGs is necessary to develop a rugged and reliable strain sensor. This paper specifically explores the effects of loading direction on the FBG strain outputs. A well behaved baseline case is established with results for gratings loaded parallel to the optical fiber direction while embedded parallel to the adjacent structural fibers in a quasi-isotropic composite. Results and analysis are also presented for a case involving a composite fabricated with the optical and structural fibers parallel to each other but perpendicular to the loading direction. Extremely good results are obtained relating FBG strain measurements with that of surface mounted resistance strain gauges.Copyright

Response of Optical Fiber Bragg Sensors With a Thin Film Shape Memory Alloy Coating

This paper describes the sputter deposition and characterization of nickel titanium (NiTi) shape memory alloy thin film onto the surface of an optical fiber Bragg sensor. The NiTi coating uniformity, crystallinity and transformation temperatures are measured using scanning electron microsocopy, x-ray diffraction and differential scanning calorimetry respectively. The strain in the optical fiber is measured using centroid calculation of wavelength shifts. Results show distinct and abrupt changes in the optical fiber signal with the four related transformation temperatures represented by the austenite-martensite forward and reverse phase transformations. These tests demonstrate a coupling present between optical energy and thermal energy, i.e. a modified multiferroic material.© 2008 ASME