Semiconductor or Piezoresistance-Type
The major advantage of using a semiconductor or piezoresistive strain gauge is its greater sensitivity when compared to a metallic strain gauge. Gauge factors for a silicon semiconductor gauge is approximately 130, whereas the typical gauge factor for a metallic equivalent is 2-3.5. Some of the disadvantages of semiconductor gauges are: the nonlinear output versus strain, the temperature dependence of the gauge sensitivity, its relative fragility, the relatively limited strain range (typically 3000 to 10,000 microstrain units compared to the 100,000 microstrain units for a metallic resistance gauge), it is generally more expensive than metal gauges and the non-linear feature of the strain gauge bridge circuit must be considered due to the higher output of the semiconductor gauge.
The behaviour of a semiconductor gauge can be described by the following relationships:
DR/R0 = (T0/T) (F0) e + (T0/T)2 (C0) e2
where e is the strain, T0 is the reference temperature (generally 298 Kelvin), T is the temperature, R0 is the resistance at the reference temperature, DR is the change in gage resistance, F0 is the gage factor ((DR/R0)/e) and C0 is a constant for a particular gauge which describes the nonlinearity of the gauge. A representative graph of the change in resistance versus strain for P (positive slope) and N (negative slope) semiconductor strain gauge is shown in Figure 19.
Figure 19 Characteristic Graph for a N-type and P-type Semiconductor Strain Gauges 
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Support for the development of this module was provided by the National Science Foundation and The Cooper Union for the Advancement of Science and Art.
Please send questions or comments to Professor Ron Adrezin or Professor Daniel Raichel.