The paper includes description of a novel approach for producing stretchable, conductive interconnects for wearable electronics. At first the current state-of-the-art and market solutions were reviewed, and then we described our optimization of the composition of conductive pastes used in the screen printing technology. Namely, the ratios of TPU (Thermoplastic Polyurethane) dissolved in DMF (Dimethylformamide) as a carrier were empirically optimized, followed by adding silver flakes as a filler. To test the quality of the final paste, a number of tracks were printed on 100% cotton fabric substrate. Changes in the electrical resistance were measured while the samples were stretched, twisted, soaked, and washed. Despite being pushed to the limits of the substrate physical capabilities, printed interconnects still retained their conductive properties, with electrical resistance increasing by no more than 10x relative to initial, very low resistances of a few ohms, and then decreasing over time. We have also discovered that ironing the samples did not destroy the tracks. Instead, the ironing process regenerated them, and their electrical resistances returned to initial values or even decreased. The method described in this paper is innovative because it enables printing directly onto textiles and the usage of a non-synthetic textile substrate while still retaining robustness in electrical conductivity.
In this work, new graphene-based screen-printed electrodes are proposed as a new, cheaper alternative to more common electrodes for determination of dopamine. Electrodes were designed, manufactured and tested to look for correlations between different graphene weight percentages used in electrodes and oxidation peaks and sensitivity in dopamine determination. All electrodes were tested using cyclic voltammetry. For a reference, graphite electrodes were tested. With sensitivity of 0.0161 μA/μM and detection limit of 5.549 μM those electrodes showed potential promise in use of graphene for electrode material. In electrodes manufacturing, Laroflex and PMMA based vehicles were mixed in with graphene platelets with diameters ranging over 2 μm and thickness between 8-15 nm. Initial tests with electrodes screen printed with graphene layers of 150 μM showed very low response. 0.0077 μA/μM sensitivity and 11.970 μM detection limit were achieved with Laroflex based electrodes. Further testing with thicker layers gave more impressive results with detection limit going as low as 1.349 μM and 0.1343 μA/μM sensitivity. Such results bring those electrodes to comparable level with other electrodes available.
Electrodes for measuring pH of the solution were fabricated by the means of screen-printing technology. Potentiometric sensors’ layers comprised of composite with polymer matrix and graphene nanoplatelets/ruthenium (IV) oxide nanopowder as functional phase. Transceivers were printed on the elastic PMMA foil. Regarding potential application of the sensors in the wearable devices, dynamic response of the electrodes to changing ultraviolet radiation levels was assessed, since RuO2 is reported to be UV-sensitive. Observed changes of the electrodes’ potential were of sub-millivolt magnitude, being comparable to simultaneously observed signal drift. Given this stability under varying UV conditions and previously verified good flexibility, fabricated sensors meet the requirements for wearable applications.
Modern methods of treatment of the surface layer allow improvement in mechanical properties of metals (an increase in the life and resistance to wear of mechanical elements as well as other properties, e.g., electrical ones). Owing to the very large temperature gradients (approximately 108 K/m) and great rates of crystallization obtained, the laser treatment method is the most efficient of them all. The range of changes in mechanical properties obtained through such treatment cannot be achieved by other methods. The method of laser doping of metal surface layers offers especially distinct advantages. This is related to obtaining various and atypical heterogeneous systems in these layers. In the paper the results have been discussed of the treatment of the surface layer using a Nd-YAG pulsed laser. Studies have been carried out for metals of significance in electrical engineering: Ag, W, Mo -- as base metals and Sn, Ni, Pd and Au -- as a doping material. Special attention has been paid to changes in the microhardness of the layers obtained compared with the properties of base metals and doping metals. The results point to strong possibilities of modification of microhardness through laser doping.
Laser radiation action on the surface of metals allows modification of material surface layer properties. One of the latest methods of such a treatment is the laser doping of the surface layer of metals with foreign atoms. Depending on the selection of the doping material as well as on the selection of the treatment parameters one can affect changes in certain properties of the surface layer of the material under treatment (micro hardness, resistance to abrasion and corrosion, electrical properties and others). In the article a study has been presented of changes in the laser doped surface layer of conducting materials used, among other things, for electric contacts. A comparative analysis of the resistivity of based materials (W, Ag, Ni) prior to treatment has been carried out. The optimization of doping conditions from the viewpoint of obtaining lasers of set parameters has been made.
Laser treatment of the surface of materials is of major importance for many fields technology. One of the latest and most significant methods of this treatment is laser alloying consisting of introducing foreign atoms into the metal surface layer during the reaction of laser radiation with the surface. This opens up vast possibilities for the modification of properties of such a layer (obtaining layers of increased microhardness, increased resistance to electroerosion in an electric arc, etc.). Conductivity of the material is a very important parameter in case of conductive materials used for electrical contacts. The paper presents the results of studies on change in electrical conductivity of the surface layer of metals alloyed with a laser. A comparative analysis of conductivity of base metal surface layers prior to and following laser treatment has been performed. Depending on the base metal and the alloying element, optical treatment parameters allowing a required change in the surface layer conductivity have been selected. A very important property of the contact material is its resistance to plastic strain. It affects the real value of contact surface coming into contact and, along with the material conductivity, determines contact resistance and the amount of heat generated in place of contact. These quantities are directly related to the initiation and the course of an arc discharge, hence they also affect resistance to electroerosion. The parameter that reflects plastic properties with loads concentrated on a small surface, as is the case with a reciprocal contact force of two real surfaces with their irregularities being in contact, is microhardness. In the paper, the results of investigations into microhardness of modified surface layers compared with base metal microhardness have been presented.
The use of laser radiation for alloying the surface layer ot metals is one of the latest and fst—t1evelopirj methods for the laser treatment of surfaces. Layers of a different area of concentration of the alloying flldterial Cdfl b? abtained in the alloying process with a pulod laser. The paper presents the results of the studies on the effect of some factors upon basic parameters of the illoyed layers in molybdenum, tungsten and nickel.
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