  We present a simple picture of the gauge factor (GF) enhancement in highly
heterogeneous materials such as thick-film resistors. We show that when the
conducting phase is stiffer than the insulating one, the local strains within
this latter are enhanced with respect to the averaged macroscopic strain.
Within a simple model of electron tunneling processes, we show that the
enhanced local strain leads to values of GF higher than those expected for a
homogeneous system. Moreover we provide formulas relating the enhancement of GF
to the elastic and microstructural characteristics of TFRs.
