MODERN STRAIN MEASUREMENT USING POLYSILICON GAUGE
#1

MODERN STRAIN MEASUREMENT USING POLYSILICON GAUGE
VIKAS P
Roll no 69
S7 AEI,
College Of engineering, Trivandrum

Outline

General Overview of STRAIN GAUGE
Strain gauge, Classification ,Why Thin Polysilicon Strain Gauge?,
Miniaturation, Conventional strain gauge vs. polysilicon gauge

Fabrication Process of Thin Polysilicon Gauge
Fabrication steps,glass frit bonding,..

Experimental Analysis and Results
Performance evaluation…

Conclusion

Strain Gauge
Distribution of stress in structures are measured by strain measurement techniques(using strain gauge) since strain can be measured by Hooke’s law.
Basic principle-length change of a wire causes a resistance change, which is measured by a strain gauge.
To provide a means of comparing the performance of various gage materials, the gage factor, or strain sensitivity, of a gage is defined as



Classification

-Mechanical
-optical
-acoustic
-electrical
-semiconductor

Semiconductor Strain Gages

Strain-gage technology advanced in the 1960s with the introduction of the semiconductor strain-gage elements
Silicon gages are formed from single-crystal silicon whose orientation and doping are the most important design parameters.
Semiconductor gages are made by slicing sections from specially processed silicon crystals and are available in both n and p types. The high gage factor is accompanied by high-temperature sensitivity, nonlinearity, and mounting difficulties.
Polysilicon gages utilize the diffusion process employed in integrated-circuit manufacture. Lower manufacturing costs in some designs, since a large number of devices can be made on a single silicon wafer. The deviation from linearity is approximately 1%

Why SC strain gauge?
Improved performance
Batch fabrication-Reduced manufacturing cost and time
Miniaturization
Low power consumption
Higher speed & hence less delay
Higher resonant frequency
Reliability
Portability
Ruggedness
Nonlinearity 0.21%FS & hysteresis 0.17%FS
Improved Gauge factor (20-50)

Fabrication
Fabricated thin polysilicon gauge
Experimental Analysis & Results
Endpoint deflection of cantilever beam was measured by IR displacement sensor ,strain is given by

Length & thickness of cantilever beam is 200 & 3mm
Observe characteristics with changes in temperature, constant temperature chamber was installed around the polysilicon strain gauge.
GF, TCR, Nonlinearity, Hysteresis were measured


Conclusion
Proposed Thin Polysilicon Strain Gauge have all the desirable quality of good strain gauge.
Excellent linearity
Sensitivity is much higher than that of a conventional metal-foil strain gauge, and the TCR is significantly lower than that of monosilicon
strain gauges.
MEMS fabrication technology were used.
Use of glass frit bond improves mechanical properties of Hysteresis, Repeatability and Durability.
Minimum Nonlinearity

References
IEEE SENSORS JOURNAL, VOL. 10,NO. 8,AUGUST 2010 – THIN POLYSILICON GAUGE FOR STRAIN MEASUREMENT OF STRUCTURAL ELEMENTS BY YONGDAE KIM, YOUNGDEOK KIM, CUULSUB LEE, SEJIN KWON.
IEEE MICRO & NANO LETTERS,2010 ,VOL. 5, ISS. 3- RESISTIVITY DEPENDENCE OF GAUGE FACTOR OF POLYSILICON STRAIN GAUGE.
Wafer bonding A/P Francis Tay ,Dr. Ciprian Iliescu
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#2

Modern Strain Measurement using Thin Polysilicon Strain Gauge
SEMINAR REPORT
Submitted by
VIKAS P
DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING
COLLEGE OF ENGINEERING
TRIVANDRUM
2010

[attachment=7954]

ABSTRACT
The technology for measuring the strain is undergoing development at very high speed. The most commonly used strain gauge is metal foil/film strain gauges. Their large size and low sensitivity make accurate and precise strain measurement impossible. This paved the way for the development of Polysilicon Strain Gauge. The efficient performance of Polysilicon Strain Gauge is due to the glass frit bond backing. Unlike the other conventional strain gauges Thin Polysilicon Strain Gauges have improved Gauge Factor, Hysteresis, Nonlinearity and Temperature Coefficient of Resistance. The construction and principle of Thin Polysilicon Strain Gauge is also discussed.

Chapter 1
INTRODUCTION


Stress analysis is used to measure the distributions of stress in materials and structures that are subjected to static or dynamic loads. Such analyses commonly rely on strain techniques since stress can be calculated using Hooke’s Law. Hooke’s Law states that within the elastic limit, the stress is directly proportional to strain. The most widely used device to measure strain is a strain gauge. Invented by Edward E. Simmons and Arthur C. Ruge in 1938, the most common type of strain gauge consists of an insulating flexible backing which supports a metallic foil pattern. The gauge is attached to the object by a suitable adhesive, such as cyanoacrylate. This simple device has been used for many years
in all engineering fields and virtually all industries, including aerospace and
automobile industries. Even though wide variety of strain gauges are available, most commonly used strain gauge is electrical strain gauge, since they are characterized by relatively low cost, high level of accuracy, repeatability and reliability.

Chapter 2
STRAIN GAUGE

2.1 Overview
Strain Gauge is used to measure distributed strain in structures. The most widely used strain gauges are the electrical-resistance types, because they are characterised by a relatively low cost and a high level of accuracy, repeatability and reliability.

The operative principle of an electrical-resistance strain gauge has been known for more than a century. In general, a strain gauge is bonded onto the sensing element of the structure. The application of a load onto the sensing element causes a change in its shape, and a corresponding strain is applied to the strain gauge placed on the surface of the sensing element. The resistance of the strain gauge changes owing to the strain, and the degree of this change is used to calculate the magnitude of the load. The resistance variation is converted to voltage variation by Wheatstone bride configuration.

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