ECE_432_Fall_2007_Final_modified

# ECE_432_Fall_2007_Final_modified - Cornell University...

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Cornell University School of Electrical and Computer Engineering ECE 432 Take-Home Final Exam Fall 2007 Prof. Sunil A. Bhave December 2007 Your name: ______________________________ Your Cornell login: ______________________________ Guidelines There is no collaboration allowed on this exam. Please work independently. The exam is due at noon on Wednesday December 5th, in the HW Drop Box. Please label all your work sheets with your name and CUID on them. Partial credit will be given if a reasonable argument for the correct answer is made. Score Problem Points Possible Score 1 18 2 27 3 15 4 15 5 20 Total 95 1

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1. Short Questions a. Folded beams are often used to build MEMS sensors and actuators. Name two reasons why? b. In piezoresistive pressure sensors with a square diaphragm, four piezoresistors are usually used along the four sides of the square. Briefly explain why this is done instead of using two resistors along only two sides. c. The ratio of stress to strain in a microstructure is given by (circle all that apply): a) shear modulus b) potential energy c) momentum d) Poisson's ratio e) Elastic modulus f) Bulk modulus d. What is the Poisson's ratio, briefly explain? e. Varying gap parallel-plate capacitors are often used for sensing applications. Name three shortcomings of this sensing mechanism? f. As discussed in class, in order to support mechanical structures we use several different beam designs, including a cantilever beam, a bridge structure, folded beams, and crab leg beams. The crab leg support is sometimes used because (for the following assume the same beam length, width, and thickness for all designs): a) It is more flexible than a bridge structure b) It occupies less area than a bridge structure c) It can accommodate a larger intrinsic stress than a bridge structure

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ECE_432_Fall_2007_Final_modified - Cornell University...

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