Improved composite piezoresistive strain sensors

Abstract

The relationship between strain and the fractional increase in electrical resistance ((Delta) R/R_o) of piezoresistive polyether-sulfone-matrix composite strain sensors was found to be much more linear and less noisy when the electrically conducting filler was 0.1 micrometer-diameter carbon filaments rather than the conventionally used 10 micrometer- diameter carbon fibers. For the fiber composite, the non-linearity manifested itself as (Delta) R/R_o increasing reversibly with increasing compressive strain -- an effect opposite to and occurring on top of piezoresistivity. This effect was absent in the filament composite. Furthermore, the percolation threshold was lower for the filament composite than the fiber composite. For both filament and fiber composites, (Delta) R/R_o became more negative as cycling progressed up to approximately 10 cycles and then stabilized, though the effect was more significant for the latter.