Semiconductor strain gauge

Table of Contents

Introduction

Semiconductor strain gauge uses the property of piezoresistive effect in few semiconductor materials such as silicon and germanium to achieve greater sensitivity and higher levels of output. Semiconductor gauges can be produced to change positively or negatively when tensioned. They can be made physically smaller while maintaining a high nominal resistance. Semiconductor strain gauge bridges can have up to thirty times the sensitivity of bridges employing metal films, but are sensitive to temperature and difficult to compensate. Their change in resistance with tension is also nonlinear. They are not in widespread use as more stable metal-film devices for precision work; however, where sensitivity is important and temperature variations are small, they may have some advantage. A comparison chart of metal strain gauge vs. semiconductor strain gauges is showing as follows-

Metal gauge vs semiconductor strain gauge

Construction-

Semiconductor strain gauges are commonly fabricated as foil type arrangement. It consists of a semiconductor material usually of P type or N- type Silicon or germanium diffused in a substrate or wafer and enclosed in a protective casing.

These gauges can be fabricated in a single unit with one gauge element or complex rosette pattern. Single unit can have different formats in the form of bars (straight or U shaped thin strips). The diffused regions of the included units may have the variable patterns, such as complex rosettes or simple squares. A diagram for semiconductor strain gauge is shown as follows-

Semiconductor Strain Gauge

Semiconductor Strain Gauge rosette

Different semiconductor materials sensitivity to strain (i.e. Gauge factor) is shown in table-

Semiconductor material gauge factor

Working

A strain gauge can be used to measure force, as shown in Figure, where a cantilever beam is slightly deflected by an applied force. Four strain gauges are used to measure the flex of a beam, two at the top and two at the bottom. The gauges are connected in a four-element bridge configuration. This gauge configuration provides maximum sensitivity and is inherently linear. This configuration also provides first-order correction for the temperature drift in the individual strain gauges.

full bridge using 4 gauges

To read more about other strain gauge types click on individual links here-

 

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