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MNE / EAS Ph.D. Dissertation Defense: Ms. Jinya Liu

When: Friday, August 25, 2017
2:00 PM - 4:00 PM
Where: Textiles Building 101E
Description: Mechanical Engineering (MNE) / Engineering Applied Science (EAS) Ph.D. Dissertation Defense by Ms. Jinya Liu


DATE: August 25, 2017

TIME: 2:00 p.m. - 4:00 p.m.

LOCATION: Textile Building, Room 101E

TOPIC: Statistical Regular-Fractal Topography Modeling and Contact Analysis of RF MEMS Surface

ABSTRACT:

Surface contact quality of electrodes has been recognized as a key factor in RF MEMS switch performance and reliability design. Topography of the surfaces and contact mechanics determine the quality of the contact. Surface topography contains complex and random features, which make measurement, surface characterization/modeling and contact simulation a big challenge in predicting the contact quality. The objective of our research is to develop a methodology to measure, characterize, and model topography for contact modeling and correlating contact properties to the surface characterization.
An interdisciplinary approach, which integrates metrology, statistics, fractal mathematics, and contact mechanics, is proposed to achieve the research goal.

Specifically it includes:
· Multi-scale sampling plan design: A sampling plan is proposed for surface measurement using atomic force microscopy (AFM). Topography on RF MEMS switch contacting surfaces are scanned by AFM at different length scales (e.g. 1x1, 10x10 and 60x60 mm2). A sample allocation plan is designed to maximize the spatial representative of the AFM scanning patches with different resolutions and uniformly distributed sample patches. The scanning data are used for characterizing, model estimation and contact analysis.
· Topography characterization and statistical modeling: A flexible framework is created to accommodate various pattern structures. Regular patterns are found at coarser scales (e.g. 10x10 and 60x60 mm2). Random irregularity and the fractal structure are observed at finer scales (e.g. 1x1 mm2). A regular-fractal model is proposed to decompose and characterize the regular and fractal structures with two model components: one for the regular geometric pattern and the other for fractal irregularity. The model validation is made through the comparisons of topography and conventional roughness parameters between the results of simulation from the proposed model and that derived from AFM scanned data.
· Elasto-plastic contact analysis: A non-adhesive, frictionless contact analysis is carried out to investigate the contact aspects of RF MEMS capacitive switches by finite element software COMSOL. Elastic-plastic contact model is employed based on the AFM data of different scales (e.g. 1x1, 10x10 and 60x60 mm2) to represent the regular pattern dominate surface, and regular-fractal and fractal structure dominate surfaces. Loading/ unloading cycles are applied to simulate the working status of RF MEMS switch. Dimensionless contact area vs dimensionless load curve were determined and compared for different cycles. Dominant micro-scale regular patterns were found to significantly change the contact behavior. Contact areas mainly clusters around the regular pattern. The contribution from fractal structure is not significant. Under cyclic loading conditions, plastic deformation in 1st loading/unloading cycle smoothen the surface. The subsequent repetitive loading-unloading cycles undergo elastic contact without changing the morphology of the contacting surfaces.

The work is expected to shed light on the quality of switch surface contact as well as optimum design of RF MEM switch surfaces.

ADVISORS:
Dr. Wenzhen Huang (whuang@umassd.edu, 508-910-6568)
Dr. Vijaya B. Chalivendra (vchalivendra@umassd.edu, 508-910-6572)


COMMITTEE MEMBERS:
Dr. Wenzhen Huang, Department Mechanical Engineering, UMD
Dr. Vijaya B. Chalivendra, Department of Mechanical Engineering, UMD
Dr. Sherif D. El Wakil, Department of Mechanical Engineering, UMD
Dr. Jianyi Jay Wang, Department of Physics, UMD
Dr. Charles L. Goldsmith, President, MEMtronics Corporation

Open to the public and all are welcome! Mechanical Engineering and Engineering Applied Science students are encouraged to attend.

For more information, please contact Dr. Wenzhen Huang (whuang@umassd.edu) or Dr. Vijaya Chalivendra (vchalivendra@umassd.edu).
Topical Areas: Faculty, General Public, Staff and Administrators, Students, Graduate, University Community, Bioengineering, College of Engineering, Mechanical Engineering, Physics