| Abstract Scope |
Piezopermittivity (the effect of stress/strain on the permittivity) enables capacitance-based stress/strain sensing. It differs from piezoelectricity, which may not involve a permittivity change. The permittivity of conductors stems from carrier-atom interaction, whereas that of nonconductors stems from structural asymmetry. Piezopermittivity stems from the effect of stress/strain on these mechanisms. It is exhibited by a large variety of materials, including nonconductors (polymers and ceramics) and conductors (carbons and metals), which, in the unpoled state, are comparably effective for capacitance-based sensing. Poling of the perovskite ceramic does not alter the piezopermittivity behavior. The piezopermittivity coefficient (defined as the fractional change in permittivity per unit strain) can be positive or negative, with positive values being more common. The value is +1.99×103 and -4.81×102 for uncoated and nickel-coated carbon fibers, respectively. The value for the uncoated carbon fiber is close to the value of +1.21×103 for a perovskite ceramic. |