In the literature, there are several examples where wires of magnetostrictive material are used for both sensing and
nondestructive inspection applications. However, the magnetostrictive material may not be suitable for certain
environments (such as corrosive environments). Therefore, designs where the magnetostrictive material is coupled to a
more robust waveguide material are of interest. The work presented in this paper examines a design based on a
cylindrical sleeve of magnetostrictive material. Experiments were conducted to compare the new sleeve design to the old
approach of using a brass coupling. In addition to simplifying the manufacturing process, the sleeve design was found to eliminate signal artifacts encountered in previous results.
In-situ measurements of specimens in research reactors and the health monitoring of commercial nuclear power plants
are difficult because of high operating temperatures and the presence of radiation. One possible solution is to transmit
ultrasonic guided waves into the harsh environment from a remote transducer. However, it is well known that large
changes in temperature can significantly alter guided-wave propagation. The work presented in this paper examines how
temperature, up to 700 K, influences guided-waves in a bar specimen of rectangular cross-section. The measurement
setup consists of a bar specimen connected to a magnetostrictive transducer via a long wire waveguide. This allows the
transducer to be located outside of the high temperature environment. Theoretical dispersion curve calculations as well
as time-domain finite element models have been used to predict the behavior of group velocity. Preliminary results
indicate that each wave mode has a unique response to temperature at a given frequency. Although higher order modes
are generally more sensitive to temperature, the results also suggest the possibility of selecting wave mode and
frequency to minimize the change in group velocity due to temperature.
Double wall structures are three-layered systems in which the second or intermediate layer is frequently a liquid. The
liquid aids in the cooling process when the interior is at high temperature. Examples are double wall steam pipes,
pressure vessels and heat exchanger plates. Structural health monitoring and nondestructive testing from the outside,
through three layers to the inside wall is difficult. This paper presents a viable solution by proposing the use of
ultrasonics to generate a slow guided wave in the structure enabling inspection of the inner wall for flaws. The results of
calculations, simulations and experiments are presented and compared. In particular, a two-dimensional model of the
setup is introduced and a procedure for obtaining group velocity dispersion diagrams. The model is validated using
theoretical and experimental results. Sample dispersion diagrams are presented and compared with those obtained with
matrix methods. Finally, the FEM simulation results depict the displacement profiles across the waveguide. The results
of both modeling techniques are in good agreement and they provide interesting insights into the wave mechanics of the
three-layered waveguide.
Sensor development and signal processing are two key issues in structural health monitoring (SHM). A process of PVDF annular array sensor design via guided ultrasonic wave propagation, excitation, and wave damage interaction modeling is presented in this paper. A sample problem to monitor the occurrence and progression of simulated corrosion damage in an aluminum plate is studied. An effective guided wave mode for easy corrosion depth assessment was selected based on guided wave propagation analysis. Three dimensional finite element method (FEM) analyses were performed to study the wave field excited from PVDF annular arrays and sectioned annular arrays in the aluminum plate. Annular arrays with enhanced mode selection capabilities were permanently bonded to a 1mm aluminum plate. Simulated corrosion damage with progressive corrosion depths was successfully detected in the structure using wave mode based signal analysis and feature extraction. The relation between the damage depth and the reflection wave amplitude from the signal were studied with both numerical simulation and experiments.
Current ultraviolet (UV) curable polymer techniques for MEMS fabrication pose certain challenges due to the electrical and mechanical properties of the polymer. A novel UV-curable polymer uniformly bonded with functionalized nanotubes was synthesized via a modified three-step in-situ polymerization. Purified multi-walled nanotubes, gained from the microwave chemical vapor deposition method, were functionalized by oxidation. X-ray photoelectron spectroscopy (XPS) was used to identify the -OH and -COOH groups attached to nanotube surface. The UV curable polymer was prepared from toluene diisocyanate (TDI), functionalized nanotubes, and 2-hydroxyethyl methacrylate (HEMA). The chemical bonds between -NCO groups of TDI and -OH, -COOH groups of functionalized nanotubes were confirmed by Fourier transform infrared (FTIR) spectra. This new UV-curable polymer is expected to be a cost-effective solution with a variety of applications in UV coating, phase shifters for telecommunications and global positioning systems, and polymer and BioMEMS devices.
Current ultraviolet (UV) curable polymer techniques for MEMS fabrication pose certain challenges due to the electrical and mechanical properties of the polymer. A novel UV-curable polymer uniformly bonded with functionalized nanotubes was synthesized via a modified threestep in-situ polymerization. Purified multi-walled nanotubes, gained from the microwave chemical vapor deposition method, were functionalized by oxidation. X-ray photoelectron spectroscopy (XPS) was used to identify the —OH and —COOH groups attached to nanotube surface. The UV curable polymer was prepared from toluene diisocyanate (TDI), functionalized nanotubes, and 2-hydroxyethyl methacrylate (HEMA). The chemical bonds between —NCO groups of TDI and —OH, -COOH groups of functionalized nanotubes were confirmed by Fourier transform infrared (FTIR) spectra. This new UV-curable polymer is expected to be a costeffective solution with a variety of applications in UV coating, phase shifters for telecommunications and global positioning systems, and polymer and BioMEMS devices.
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