Conductive yams resistance measurement

The electrical resistance of a material is determined by the material itself and the geometric shape of the conductor. In general. Ohm s law is applied to calculate the electrical resistance. This principle can be applied to measure pressure by applying conductive yams in textiles that are bent and deformed when a mechanical load is applied on them. Measuring elongation using electrical resistance is a well-known concept in the world of smart textiles. 

Copper-coated PBO yams were obtained from the AmberStrand company [24]. They are made from a number of very thin copper-coated PBO filaments, bunched together to form a filament yam (about 10 pm diameter). Silver-coated PBO yams were also obtained from AmberStrand company [24]. They are similar to the copper-coated PBO filaments except that they use silver metal to clad the PBO filaments. Stainless steel filament yam electrodes were obtained from the Bekintex company [25]. The conductive yams were of different sized constmction and diameters, and a standard measurement was performed to determine the resistance per meter of each conductive yam. The material specifications of these conductive yams are presented in Table 20.1. 

At each heartbeat, tiny impulsions are emitted through the skin, which can be detected and converted by conductive electrodes (Pola and Vanhala, 2007), from ionic flow to electrical current (ECG), and more easily measured. The electrodes are made from conductive yams that are often in silver due to its antibacterial properties (Kim et al., 2007) and its biocompatibility or in stainless steel for its resistance to humidity (Schwarz et al., 2011). Manufacturing modes can differ from knitted textiles to embroidered yams. However, CTT Group has favoured the knitted stmcture in order to allow better stretchability and, therefore, better contact with the skin. 

Characterization of textiles that have both a classical textile dimension and an extra electrical one needs consideration. Compared to classical electrical devices, textiles are soft, flexible, and of poor dimension stability. Using conventional electrical measurement methods and devices may result in imprecise or even wrong measurement results. In this chapter, the suitable resistance measurement methods for both conductive fibers and yams and textiles are introduced. Special measurement devices are demonstrated. In addition, the measurement dynamic electrical properties, ie, the electromechanical properties, are also presented. 

Linear resistance can be simply measured by an ohmmeter (Fig. 28.11, top), a so-called two-points measurement method. The equivalent circuit of this measurement setup is shown in Fig. 28.12. The ohmmeter is actually giving the total resistance of the subject and the measurement wires. This method is applicable when the resistance of the measured subject is much greater than the wires. However, conductive yams are usually expected to be highly conductive, and the measurement error introduced by the wire resistance will then be substantial. 

The current is the same at all points in the circuit. In this method, voltage drop across the subject resistance is measured together with the current, therefore, the calculated resistance is closer to the real value of the subject component (the conductive yam). Four-point measurement is preferable when resistance of the conductive yams is low. 

In practical terms, the electrical resistance measurements on conductive fibers/yams is always problematic due to their soft, flexible, and poor dimensional stabilities. Very few publications have reported research regarding electrical measurements on fibrous stmctures. Usually, the conventional method, in which crocodile clips are attached with a voltmeter, is used for this purpose. Crocodile clips hold the conductive fibers/yarns of specific length and then electrical resistance is measured on particular voltage values. However, the hard grip of crocodile clips damages any conductive coatings or creates internal cracks in the fibrous stmctures, which cause the permanent loss in electrical properties of conductive threads. Consequently, consistent results with crocodile clips cannot be obtained. 

The measurement of static charge on textile fibers, fabrics, and yams has also received a considerable amount of scientific attention and is relevant to this same subject on human hair. The books by Meredith and Hearle [141] and Morton and Hearle [136] provide a good introduction into this subject. The measurement of electrical resistance (reciprocal of conductance) of fibers is also fundamental to their static electrification and is described by Hersh [142] for human hair and other fibers and by Meredith and Hearle [141] for textile fibers. 

The plausible explanation for the relatively high resistance can be found in die structure of jersey. There is not a natural padi for the current to flow as it hiqipetis udien the resistance is measured in the course direction. The current flows throughout each contact between a loop located of die previous course and a loop of the course immediately located above (or below). This results in a small metallic contact surface, thus resulting in a higher resistance. On the contrary, the electrical conductivity of jersey fabric when measured in a course direction is quite inoeased since the yam is part of each loop of that course. As a consequence, the renstance dramatically decreases. 

Thus, the research work of Trifigny (2013) has consisted of observing the kinematics of the weaving process by checking aU the contacts and dynamic loads applied on yams. Based on these observations, the design of electrically sensitive and mechanically resistant sensor yams has been achieved, tested and calibrated. Then, dynamic measurements on the different loom locations have been conducted to detect the local distribution of elongation on different warp yams, especially applied on two different tow counts of continuous E-glass yams inserted into 3D warp interlock fabrics. 

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