Due to their simplicity and low-cost, resistive strain gauges are widely used for position control of piezoelectric actuators. Resistive strain gauges can be integrated into the actuator or bonded to the actuator surface. An example of a piezoelectric actuator and resistive strain gauge is pictured in Fig. 14(a). Other application examples can be found in references [28–31]. Resistive strain gauges are constructed from a thin layer of conducting foil laminated between two insulating layers. With a zig–zag conductor pattern, strain gauges can be designed for high sensitivity in only one direction, for example, elongation. When a strain gauge is elongated, the resistance increases proportionally.The change in resistance per unit strain is known as the gauge factor GF defined by