Characterisation and biomedical application of fabric sensors

The sensors commonly used today to measure human physiological parameters are hard and discrete and not suitable for long term monitoring. A wearable garment with integrated fabric sensors incorporated in an unobtrusive way is highly desirable for long term physiological monitoring, particularly in a non-clinical environment.<br><br>The aim of this work is to investigate fabric sensors which can be integrated into a garment to allow the unobtrusive monitoring of physiological parameters, primarily for measuring the electrocardiograph (ECG) and respiration.<br><br>The work focuses on using only dry fabric electrodes where skin preparation and the use of chemical gels or adhesives are not employed. The textile structure used in this study was designed to provide controlled contact pressure, enable construction using common textile processing methods, allow accurate placement of electrodes on the body, allow comfortable fit and be unobtrusive to wear. It was decided to use the knitting method to make bands which incorporated conductive electrodes in order to evaluate different fabric electrodes materials. The detection of respiration using fabric strain sensors did not require electrical contact with the skin.<br><br>Preliminary experiments were conducted on a single subject to develop a device and methodology. Galvanic skin response and ECG was initially investigated to determine the effectiveness of electrode materials. ECG was established as a more reliable measure and was subsequently used to evaluate the initial performance of the fabric electrodes, and further refine the test methodology on a single subject. Experiments were then conducted on 10 male volunteer participants of reasonable general health having no known heart conditions, with ages 30-55 and BMI 20-30. <br><br>It was found that fabric sensors which were soft, pliable and flexible have advantages in terms of ability to provide better quality ECG signals and a comfortable bio-interface. Variation in the pressure applied to the electrode directly affects the acquired signal level and a pressure of 2.5KPa is preferred. Multifilament conductive yarns are more easily processed into fabric than monofilament yarns and are generally preferred. Electrodes comprising a conductive polymer treated fabric gave better performance than metal or metal coated yarns. <br><br>Fabric strain sensors were tested and used to detect respiration on a single subject. It was found that human respiration can be measured using strain sensors such as those comprised of a conductive polymer treated fabric or a fabric incorporating a rigid conductive monofilament fibre.