Knitted electrodes

For the knitted structure, the opposite effect is observed. Because of its elastic structure, the knitted electrode will adapt to the shape of the holders and fittings used in the electrochemical cell. At the surface of the knitted... 

Knitted and embroidered electrodes were also investigated to stimulate the blood flow and, hence, to reduce the risk of patients developing pressure ulcers if they have to rest in bed for a long period (Schwarz, 2011). A typical knitted electrode is shown in Fig. 2.11. 

Hertleer et al. (2004) describe a smart suit where stainless steel yams are used to produce knitted electrodes (textrodes), abelt to detect respiration rates and an embroidered coil for a wireless link. 

In the last few decades, many attempts have been made to integrate electronic functionality with textiles. Early medical sensing vests, for example, incorporated knitted electrodes for ECG monitoring, knitted stretch sensors for respiratory monitoring and... 

Similar to the experiments carried out at palladium electrodes and described in Chapter3, the concentration of electrolyte (c), the electrode surface area (A) and the distance between the electrodes (d) will be studied as a function of type of textile structure. In this work, three structures will be studied knitted, woven and non-woven textile structures, all obtained from stainless-steel fibres. To complete the data of this work, palladium sheets will also be inserted in the study as a fourth set of electrodes. Therefore, for palladium electrodes, the work described in section 9.2 will actually be repeated here in order to have a direct comparison between results obtained with palladium electrodes and textile electrodes. Of course, correlation with the data obtained in section 9.2 will be verified. 

Nyquist plots recorded at an electrochemical cell with palladium electrodes or woven, non-woven or knitted textile electrodes with /4=180mm2 and d=103mm for a NaCI concentration of (1) 1x10 2, (2) 1 x10 3 and (3) 1 x10 4mol I- at T=298.0K. Part b is an enlargement of part a. 

Logarithmic plot of the impedance at zero phase-angle shift as a function of electrolyte concentration obtained from the electrochemical cell with palladium electrodes, woven, knitted and non-woven electrodes for > =180mm2, d=103mm and 7=298.0 K. 

Scheme showing the positioning of a palladium electrode (a) and a woven (b) and knitted (c) textile electrode in the cell, and the influence on the configuration of the electrodes due to positioning. (1) Rubber fittings, (2) part of the PVC tubing filled with electrolyte and (3) electrolyte solution. 

Table 9.5 Data for factors k, k2 and k3 for knitted textile-structure electrodes according to Equations 9.2-9.7...

Long-term stability tests of (1) palladium sheet electrodes and (2) woven, (3) knitted and (4) non-woven textile electrodes, obtained by measurement of R as a function of time in the electrochemical cell for NaCI electrolyte concentrations of (a) 1x10 4, (b) 1x10 3, (c) 1 x10 2 and (d) 1 x10 1 mol I-1. 

Experimental proof for the above-described hypothesis was found by taking microscopic photographs of the textile structures in dry and wet conditions using a fluorescent solution. From these images, it could be seen that air bubbles were indeed trapped in the wet structures, but due to the more regular structure of the non-woven fabrics compared with woven and knitted fabrics, much less air was trapped. Confirmation for the dissolution of these bubbles is found by the absence of air when the textile electrodes were immersed for about 3 days in the fluorescent solution. 

Table 9.14 Resistance, Ft (Q) measured in the electrochemical cell at certain time, t (h). Between the short R measurements, the textile electrodes were immersed in NaCI, artificial sweat, waste-water solutions or water. (Knit knitted wov woven nonw non-woven.)...

Nickel-hydrogen batteries (Ni/T ) were developed in 1970 for aerospace applications. These batteries are a combination of the Ni-Cd technology (Ni electrode) and the fuel-cell technology (H2 electrode). They use nickel hydroxide as cathode active material, a hydrogen electrode as anode, and an aqueous solution of potassium hydroxide as electrolyte. Asbestos (fuel-cell grade asbestos paper) and Zircar (untreated knit ZYK-15 Zircar cloth) are used... 

Detector E, Bioanalytical systems Model LC-4B, dual glassy-carbon working electrode used in parallel mode, +0.65 V and +0.80 V (monitored), stainless steel auxiliary electrode, Ag/AgCl reference electrode following post-column reaction. The column effluent flowed at 0-5° through a 2 mL knitted coil of 0.5 mm i.d. PTFE tubing irradiated with a low pressure mercury lamp (Photronix Model 816) to the detector. 

Figure 10.5 SmartLife has developed softsensor systems aimed for the improvement of lifestyle. The HealthVest is created with integrally knitted ECG electrodes, respiratory sensors, and conductive pathways.

Research in textile electrodes has led to encouraging findings globally and to some product launches. Investigating textile electrodes for medical purposes, Hertleer et al. (2004) demonstrated that heart beat signals obtained from conventional electrodes with electrogel are comparable with knitted textile electrodes made with yams of metallic fibres. No gel was needed for the textile electrode, which can be a benefit in terms of convenience and user comfort. De Rossi et al. (2003) also found that their... 

From a manufacturing perspective, it has been demonstrated that it is possible to seamlessly fully integrate conductive yam electrodes into mass produced knitted garments (NuMetrex, 2014 SmartLife, 2014). In the case of the NuMetrex garments, the data from the electrodes are collected and transmitted to an external device by a small electronic device to be inserted manually in a pocket on the garment prior to use. 

Several efforts to create prototypes of wearable functional devices have been made in the last years. Most of them consider the approach of joining conventional off-the-shelf electronic devices to fabrics, such as microcontrollers, LED s, optical fibres and all kinds of sensors, especially electrodes for ECG measurement. The consolidated textile technology for integrating conductive yams into knitted or woven fabrics and the implementation of sensors through embroidery has encouraged their use as suitable means for connection, data communication and power transfer. 

Over the past years different textile technologies were explored to design and develop textile electrodes, which were integrated in garments and provide an ECG. Knitting is by far the most applied technology. It was for instance used to produce electrodes integrated into a belt for children to be worn in a hospital (Catrysse et al., 2004) to prevent sudden infant death (Fig. 2.1). 

Figure 2.1 Knitted belt with integrated stainless steel electrodes (Courtesy of UGent).

A Swedish research team investigated commercially available silver-coated knitted fabrics for their applicability as EEG electrodes. They stated that it is possible to record EEGs with the knitted fabrics when applying a contact gel. However, the long-term properties have to be assessed (Lofhede et al., 2012). 

Respiratory rate is measured by techniques based on either measuring thoracic expansion or based on measuring changes in skin impedance. For the former technique, most systems use strain gauges made from piezoresistive material combined with textile structures. Hertleer et al. reported a fabric sensor made of SS yam knitted in spandex belt [18]. For the latter technique, noninvasive skin electrodes are placed on the thorax, and the variation of the electrical impedance can be detected during respiration cycles. 

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