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Helen Lai Wah Chan

Publications and source records attributed to Helen Lai Wah Chan.

2 recordsLinked to original sources
PubMed2005

Analyzing core-shell structured zinc doped MgO Wrapped Ba(1-x)Sr(x)TiO3 nanoparticles.

BST nanoparticles were directly synthesized from solution at 70 degrees C and then wrapped with zinc doped MgO in solution. This core-shell structure was analyzed by a conjunction of XRD, HRTEM, and FE-SEM. The lattice cell parameter of BST core was found to have shrinkage. The lattice cell mismatch between core and shell creates a variation of lattice cell parameter of BST core and we proposed a new method to estimate it by the XRD peak broadening effect. Two possible modes of matching the BST core and MZO shell were suggested and mode II was assigned to our core-shell structure by the observation of HRTEM and analysis of XRD data. Un-grown BST nanoparticles can also be observed by FE-SEM in fracture grains of the ceramics, which was sintered at 1350 degrees C.

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PubMed2004

Finite element analysis on piezoelectric ring transformer.

The use of a piezoelectric ring as transformer is reported and studied in this paper. By using a concentric electrode pattern, a ring-shaped transformer can be designed to operate at its high order extensional modes. Lead zirconate titanate (PZT) ceramic rings with 12.7-mm outer diameter, 5.1-mm inner diameter and 1.2-mm thickness were used to fabricate the prototypes. Three-dimensional (3-D) finite element models are built to study and analyze the vibration characteristics of the piezoelectric transformers (PTs) using higher order modes (>3). The resonant frequencies, mean coupling effect, mode shapes, and other open-circuit characteristics are simulated and compared with experimental measurements. Prototypes of PTs using mode order three and four were fabricated and characterized. Good agreement can be obtained between experimental results and finite element model (FEM) simulations. The dimensions for the PTs using higher order symmetric extensional modes are optimized by FEM. To avoid mode coupling with the thickness mode, the ideal ring thickness has to be less than or equal to 0.6 mm. The ring PT offers advantages of simple structure and small size. It has a good potential in making low cost PT for low-voltage applications.

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