An investigation of textile sensors and their application in wearable electronics
Abstract
Using a garment as a wearable sensing device has become a reality. New methods and
techniques in the field of wearable sensors are being developed and can now be
incorporated into the wearer’s everyday attire. This research focuses on two types of
textile based sensors – a wearable textile electrode used for ECG continuous monitoring,
and a stitch sensor for monitoring body movement. These sensors were designed into a
purposely engineered Smart Sports Bra (SSB) which can be regarded as a sensor itself.
After a thorough investigation, two optimum textile electrodes were created; a plain
electrode using cut and sew method (CSM) and a net type knitted electrode using knitting
method (KM). The CSM electrode was made with conductive fabric (MedTexTM P-130)
and the KM electrode was made with conductive thread (silver-plated nylon 234/34 four-ply), these materials having the lowest tested contact impedance; 450Ω and 500Ω,
respectively. Both electrodes demonstrated a level of noise and baseline drift comparable
with standard commercial wet-gel electrodes, which was corrected by optimising their
size to 20x40 mm, holding pressure of 4 kPa (30 mmHg) and the electrode position at the
6th intercostal space on the right and left mid-clavicular, with one placed at the scapular
line in the rear side (i.e. back horizontal formation) which gives clear and reliable ECG
signal. These optimum electrodes were integrated directly into SSBs, in which a novel
high shear, net structure, acting as a shock absorber to body movement that shows more
stable electrode to skin contact by reducing the body motion artefact.
During the investigation of the stitch stretch sensor the single jersey nylon fabric (4.44
tex two-ply) with 25% spandex (7.78 tex) had the highest elastic recovery (93%). Using
this fabric, the work went on to show that the stitch type 304 (Zig-zag lock stitch) using
the 117/17 two-ply thread demonstrated the best results i.e., maximum working range
50%, gauge factor 1.61, hysteresis 6.25% ΔR, linearity (R2
) is 0.98, and good
repeatability (drift in R2
is -0.00). The stitch stretch sensor was also incorporated into a
sports bra SSB and positioned across the chest for respiration monitoring.
This thesis contributes to a growing body of research in wearable E -textile solutions to
support health and well-being, with fully functional sensors and easy-to-use design, for
continues health monitoring.