This paper focuses on understanding and developing a new approach to dampen MEMS structures using both
experiments and analytical techniques. Thin film Nitinol and thin film Terfenol-D are evaluated as a damping solution
to the micro scale damping problem. Stress induced twin boundary motion in Nitinol is used to passively dampen
potentially damaging vibrations. Magnetic domain wall motion is used to passively dampen vibration in Terfenol-D.
The thin films of Nitinol, Nitinol/Silicon laminates and Nitinol/Terfenol-D/Nickel laminates have been produced using
a sputter deposition process and damping properties have been evaluated. Dynamic testing shows substantial damping
(tan &dgr;) measurable in each case. Nitinol film samples were tested in the Differential Scanning Calorimetry (DSC) to
determine phase transformation temperatures. The twin boundary mechanism by which energy absorption occurs is
present at all points below the Austenite start temperature (approximately 69°C in our film) and therefore allows
damping at cold temperatures where traditional materials fail. Thin film in the NiTi/Si laminate was found to produce
substantially higher damping (tan &dgr; = 0.28) due to the change in loading condition. The NiTi/Si laminate sample was
tested in bending allowing the twin boundaries to be reset by cyclic tensile and compressive loads. The thin film
Terfenol-D in the Nitinol/Terfenol-D/Nickel laminate was shown to produce large damping (tan &dgr; = 0.2). In addition to
fabricating and testing, an analytical model of a heterogeneous layered thin film damping material was developed and
compared to experimental work.
This paper describes evaluation of an autonomous-material system tailored for free-layer vibration damping of structural
elements. The magnetostrictive particulate composite (MPC) material described has moderate stiffness and minimal
temperature and frequency dependence. The composite is created by curing Terfenol particles {Tb(1-x)Dy(x)Fe(2),0.2
Thin film Nitinol is evaluated for a new damping solution to microscale damping. In this study, thin film Nitinol was mechanically tested under steady and cyclic tensile loads in a DMA Q800 load frame to determine stiffness and hysteric losses (tan δ = 0.17). A method of determining the damping properties of a multilayered laminate was derived and evaluated using measured and predicted values of Nitinol film damping. Hysteretic loss of tan δ = 0.76 was predicted for a tensile/compressive loading of a film indicative of loading in a MEMS structure. Damping in a silicon/Nitinol laminate using the tensile/compressive loading film damping prediction was calculated to be tan δ = 0.127.
Magnetostrictive particulate composites promises to be a revolutionary new damping solution with possible loss factors similar to current viscoelastic systems but coupled with a significantly higher modulus ~ 10GPa. Magnetostrictive particulate composites fabricated from Terfenol-D (TbxDy1-xFe1.92) particles and epoxy resin, were mechanically tested under cyclic compressive loads in an MTS load frame to determine hysteric losses, from which an approximate tanδ was derived to quantify damping performance. DMA results on the same composites corroborated the MTS results. Various off-stoichiometric compositions of Terfenol-D were studied with varying Tb composition of x = 0.35, 0.4, 0.45, 0.5, 0.75 and 1.0. Results indicated better damping with higher Tb compositions peaking at Tb=0.5.
Ti-Ni-Cu and Ti-Ni-Pd films are deposited on Si < 100 > substrate by d.c. magnetron sputtering technique. In this paper, the influence of target temperature on the properties of the film is discussed. The target temperature transitions from a low temperature value to a high temperature value during sputtering. As grown Ti-Ni-Cu films are amorphous and are crystallized by heating at 500 degreesC for 20 minutes in situ prior to removal from the sputtering system whereas, as grown Ti-Ni-Pd films are crystallized at 550 degrees C for one hour. DSC and electrical resistivity measurements are used to determine the transformation temperature whereas, TEM and XRD are used for structural characterization and composition of the film is determined by using EDAX. We find that the transformation temperatures and the shape memory characteristics are strongly influenced by target temperature. The films show more uniform stoichiometry if the target is hot during deposition.
A new process parameter viz.; target temperature, has been introduced to decrease the composition variables between the target and substrate. A DC magnetron sputtering system has been used for the deposition of NiTi film from equiatomic NiTi target on silicon substrate. The target transitions from a low temperature value to a high temperature value (>700 degree(s)C) during sputtering. The sputtered films were crystallized by heating to 500 degree(s)C for 10 minutes in situ prior to removal from the sputtering system. X-ray diffractogram shows that the film peaks correspond to martensite as well as austenite phases. The film developed under this process displays the two-way shape memory effect without post annealing. Electrical resistivity measurement reveals that there are three different phases present viz.; austenite, rhombohedral and martensite, which exists at different temperature ranges. The characteristic transformation temperatures determined by the electrical resistivity method are compared with those obtained with DSC thermograms.
In this paper we will present a novel method for depositing NiTi thin film by DC sputtering that produces films with transformation temperatures very close to that of the target. The new process involves heating the target to temperatures over 400 degrees C and does not require compositional modification of the 50/50atm percent NiTi target. Results from tensile testing, XRD, TEM, and DSC are presented. Conclusions are cold target produces films that were in the Austenite phase at rom temperature while hot target produces films that were Martensite at room temperatures, confirming that compositional modification can be produced by varying the target temperature. Films that were produced by gradual heating of the target, produced a gradation of composition through the film thickness. These gradation films exhibiting the two-way SME. The simplicity of this new process should increase the use of NiTi film sin microactuator devices.
The response time of TiNi has been the subject of several experimental and theoretical investigations over the past decade. One of the principal concerns with this material is the relatively low cycle speeds or operational bandwidth caused by the considerable length of time required to cool the material. In this paper a finite difference model of heat transfer including the latent heat dissipated during the phase transformation is used to predict the bandwidth of thin film TiNi. The film is modeled as a plate subjected to either forced or free convection along the exposed surfaces and clamped to a large thermal mass representative of silicon wafer at the ends of the specimens. Results indicate that both latent heat as well as the relative ratios of the transformation temperatures to ambient temperature strongly influence the bandwidth of the material. Good correlation between the analytical model and test data obtained on a 38 micron wire indicate the model contains the correct assumptions to predict bandwidths. The bandwidth of TiNi thin film are predicted to be on the order of 100 Hz necessary assuming that the transformation temperatures for the film are the same as the bulk material.
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