Novel knitted fibre-meshed transducers

• Main Author: Wijesiriwardana, Ravindra
• Published: University of Manchester 2005
• Subjects: 681
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.556498

This thesis discusses the construction, analysis, performance and applications of "Novel Knitted Fibre Meshed Transducers" (KFMTs). Unobtrusive transducers play a major role in the wearable computing field. These transducers are being used in wearable personalized monitoring systems. Common practice is to embed sensors that are made separately into garments at a later stage, and therefore, these systems are not truly unobtrusive in nature. To overcome these disadvantages a new generation of more robust and unobtrusive sensors is required. One scenario is to make such sensors by using smart materials and integrating them into intelligent textile structures using mechanical methods of fibre assembling (weaving knitting and braiding). These are called fabric or textile sensors. Research has been carried out mostly into woven structures due to their structural stability. On the other hand, knitted structures are very attractive due to their superior adaptability. When a knitted fabric is subjected to biaxial stress in the fabric plane the geometry of the individual pattern elements is deformed and followed by the structure as a whole. The structures are knitted with yarns made out of smart materials that are capable of converting the deformations into variations of electrical parameters (resistance capacitance inductance). This new generation of transducers is named Fibre-Meshed Transducers (FMTs). These sensors can be used to measure proximity, touch, pressure, acceleration, force, displacement, vibration, sound, temperature, chemical & biological substances, light and radio frequencies and bio-potentials. Initially the feasibility of making resistive, capacitive and inductive knitted transducers has been explored by using conductive yarns and knitted structures. As a first attempt, a knitted resistive strain gauge and a knitted resistive displacement sensor were constructed. It was concluded that these types of KFMTs could be used to measure relative readings. A capacitive knitted transducer was made and used as a touch sensitive switch. A knitted solenoid was constructed by using conductive yarns and nonconductive elastomeric yarn in a tubular structure and was used as a strain and displacement measurement in wearable physiological information measuring systems. Knitted bio-potential electrodes were constructed by using stainless steel yarns, Ag coated polyester and Cu yarns and they were tested for their performance in ECG measurements. It was concluded that the performance of the wet electrodes were degraded over time.