A piezoresistive carbon filament polymer-matrix composite strain sensor

The relationship between strain and the fractional increase in electrical resistance (ΔR/R₀) 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 μm diameter carbon filaments rather than the conventionally used 10 μm diameter carbon fibers. For the fiber composite, the non-linearity manifested itself as ΔR/R₀ increasing reversibly with increasing compressive strain - an effect opposite to and occurring on top of piezoresistivity. This effect was absent from the filament composite. Furthermore, the percolation threshold was lower for the filament composite than for the fiber composite. For both filament and fiber composites, ΔR/R₀ became more negative as cycling progressed up to ∼10 cycles and then stabilized though the effect was more significant for the latter.