Xianke Lin

Large displacement vertical translational actuator based on piezoelectric thin films.

A novel vertical translational microactuator based on thin-film piezoelectric actuation is presented, using a set of four compound bend-up/bend-down unimorphs to produce translational motion of a moving platform or stage. The actuation material is a chemical-solution deposited lead-zirconate-titanate (PZT) thin film. Prototype designs have shown as much as 120 μm of static displacement, with 80-90 μm displacements being typical, using four 920 μm long by 70 μm legs. Analytical models are presented that accurately describe nonlinear behavior in both static and dynamic operation of prototype stages when the dependence of piezoelectric coefficients on voltage is known. Resonance of the system is observed at a frequency of 200 Hz. The large displacement and high bandwidth of the actuators at low-voltage and low-power levels should make them useful to a variety of optical applications, including endoscopic microscopy.

Oxygen Vacancies Lead to Loss of Domain Order, Particle Fracture, and Rapid Capacity Fade in Lithium Manganospinel (LiMn2O4) Batteries

Spinel-structured lithium manganese oxide (LiMn2O4) has attracted much attention because of its high energy density, low cost, and environmental impact. In this article, structural analysis methods such as powder neutron diffraction (PND), X-ray diffraction (XRD), and high-resolution transmission and scanning electron microscopies (TEM & SEM) reveal the capacity fading mechanism of LiMn2O4 as it relates to the mechanical degradation of the material. Micro-fractures form after the first charge (to 4.45 V vs. Li(+/0)) of a commercial lithium manganese oxide phase, best represented by the formula LiMn2O3.88. Diffraction methods show that the grain size decreases and multiple phases form after 850 electrochemical cycles at 0.2 C current. The microfractures are directly observed through microscopy studies as particle cracks propagate along the (1 1 1) planes, with clear lattice twisting observed along this direction. Long-term galvanostatic cycling results in increased charge-transfer resistance and capacity loss. Upon preparing samples with controlled oxygen contents, LiMn2O4.03 and LiMn2O3.87, the mechanical failure of the lithium manganese oxide can be correlated to the oxygen vacancies in the materials, providing guidance for better synthesis methods.

Dynamics, sensing, and control of a thin-film piezoelectric vertical micro-stage

A novel thin-film piezoelectric vertical actuator with integrated strain gage position sensor is described, with sensor performance in simulated sliding mode control examined. The actuator utilizes four bending-beam thin-film lead-zirconate-titanate (PZT) legs to generate net translational out-of-plane motion of almost 100 μm, with higher speed and lower voltages than most MEMS vertical actuators. In addition, a portion of the top platinum electrode on the piezoelectric thin-film is used to perform position sensing, and shown to have good sensitivity during experimental operation of the actuator. A dynamic model of the stage based on a hysteresis model derived to fit experimental piezoelectric strain coefficient behavior is presented, and used to predict stage performance during sliding mode control using the integrated strain gage.Copyright