This study aims to expand the body of knowledge about the optical properties of battery cathode materials. Although
some studies have been conducted on the optical properties of Lithium Iron Phosphate (LiFePO<sub>4</sub>), to the authors’
knowledge, this is the first study of its kind on electrodes extracted from commercially available LiFePO<sub>4</sub> batteries. The use of Vis/NIR and FTIR spectroscopy provides for a methodology to study the optical properties of LiFePO<sub>4</sub> and may allow for the characterization of other properties such as particle size and the proportions of <sub>LiFePO4 </sub>versus FePO<sub>4</sub> material. Knowledge of these properties is important for the development of a mechanism to measure the state-of charge (SOC) in lithium ion batteries. These properties are also important in a host of other applications including battery modeling and materials characterization.
Cylindrical LiFePO<sub>4</sub> batteries (from A123 Systems Inc.) were acquired from the commercial market and charged to 10 different states between 30% and 80% of their nominal capacity using a constant-current, constant-voltage (CCCV)
cycling method. Visual inspection of the extracted electrodes shows that the LiFePO<sub>4/</sub>C-cathodes display subtle changes in color (shades of grey) with respect to SOC. Vis/NIR measurements support the visual observation of uniform intensity variations versus SOC. FTIR measurements show an absorbance signature that varies with SOC and is distinct from
results found in the literature for similar LiFePO<sub>4</sub>-based material systems, supporting the uniqueness of the absorbance fingerprint.
In this paper, a new MEMS capacitive temperature sensor is presented which is based on a circular silicon plate with a gold annulus deposited on top forming a novel bimaterial structure. The bimaterial structure is anchored to a substrate on its edge and forms the top electrode of a capacitor. A stationary silicon electrode beneath the bimaterial structure forms the second electrode. The PolyMUMPs® foundry process has been used to fabricate the device. Experiments show that for an effective area of about 0.1 mm<sup>2</sup> this MEMS capacitive temperature sensor achieves a sensitivity of 0.75±0.25 fF/°C over the temperature range of 25 to 225 °C, which shows an improvement of more than 25% over equivalent microcantilever devices with the same effective area. Numerical modeling is used to show that the new design exhibits high flexibility in tailoring its thermomechanical response over the desired temperature range. The simplicity of its design and flexibility of the materials from which it can be constructed also makes this new MEMS sensor a good onchip temperature measurement device for MEMS characterization.
In this article, velocity and position controllers for magnetostrictive materials are designed and discussed.
Magnetostrictive materials are a competitive choice for micro-positioning actuation tasks because of the large force and
strain they provide. Unfortunately, they are highly nonlinear and hysteretic, which makes them difficult to control. In
this article, the passivity approach is used to establish stability for velocity control. Using a physical argument, passivity
of the system under discussion is proved. No model for magnetostrictive material is used in this proof and the result can
be used in any hysteresis model for the material. This result is used to develop a stabilizing velocity controller. For
position control, it is shown that a PI controller can provide stability and tracking if the hysteretic plant satisfies certain
conditions. It is shown that these conditions are satisfied for the Preisach model under mild assumptions. Using this
result, a class of stabilizing position controllers is identified. The velocity and position controllers are evaluated
experimentally and their performances discussed.
In many applications, it is desired to amplify the motion provided by micropositioning actuators. It is shown that
mechanical amplification by lever mechanisms reduces the overall system stiffness, which limits the ability of high
frequency operations. In this paper, a hydraulic booster is proposed. If the hydraulic fluid used is not compressible, the
system stiffness is not affected. Different designs of the booster are examined experimentally to find a booster without
hysteresis. Several experiments are performed to characterize the booster. A model for the booster is proposed and
evaluated using experimental data.
In the analysis and modeling of MEMS devices, a general finite element formulation is necessary to solve a multidisciplinary
domain of the device with large number of nodes and elements.
In this paper, we present a step by step finite element formulation for automated modeling of multi-disciplinary domains.
The electro-thermo-mechanical domain is explained and an algorithmic approach for sequential analysis of an arbitrary
ground structure with multi-disciplinary boundaries is developed and implemented in Matlab with a graphical user
interface. The results of the finite element approach is compared and verified with exact solutions and test results from
literature. The agreement of results verifies the application of proposed finite element formulation to the analysis of
This formulation provides a fast and reliable tool to analyze electro-thermo-elastic devices which allows large flexibility
in the selection of mechanical and electrical boundary conditions.
In this paper, based on a general formulation for linear complex systems, an in situ frequency-domain model identification method is introduced. In this technique, frequency response function (FRF) models of the subsystems are extracted without the need for disassembling the system. The FRF-based substructuring (FBS) synthesis and standard NVH testing are used to obtain FRF models of the overall system model. The model is linked to an optimization routine to predict the optimum set of vibration isolation devices for a desired objective function. Three automotive applications of this method are presented: engine mount optimization, body mount optimization, and engine rigid body inertia identification.