Influence of Rib Structure and Elastic Yarn Type Variations on Textile Piezoresistive Strain Sensor Characteristics

Abstract

Production parameters have been established to play a fundamental role in dictating the physical characteristics and sensing properties of knitted sensors. This research studied the influence of yarn type and rib fabric structure variation on the physical, tensile and conductive properties and sensitivity performance of knitted underwear strain sensors to be used for breathing mensuration. Four different structures in 1×1, 1×2, 1×3 and 2×2 mock ribs were knitted using covered elastic (CY) and bare strand elastic yarn (BS) combinations. These two parameters proffered unique physical, conductive and tensile characteristics to the samples. Wear and machine tests were conducted to ascertain the sensor’s piezoresistive responses. The machine test showed a higher piezoresistive response, with an average peak value (APV) from 1.70Ω to 0.24Ω, while those for the wear test recorded were around 0.0110Ω to 1.867Ω for all sample categories. However, sensors knitted with covered elastic yarns produced the best breathing test results (APV of 1.089Ω – 1.86Ω) compared to bare strand elastic yarns (APV 0.0027Ω - 0.0790Ω) when used in a wearable environment. Fabric structure variation had influences on both conductive and tensile characteristics; however, the effects on the piezoresistive response were negligible. The influences of the unique characteristics provided by these core parameters on sensor resistance values, piezoresistance, aging, ease of deformation and dimensional stability have also been discussed.