Hybrid Structure of Stretchable Interconnect for Reliable E-skin Application

This paper presents the methodology for realisation of stretchable interconnects based on hybrid thin film stack of spray-coated conductive polymer PEDOT: PSS and evaporated gold (Au) film. The PEDOT: PSS film, with its properties in electrical conductivity and mechanical softness, serves as a stress release buffer in the layered hybrid structure. With the serpentine-shape design, the stretchable interconnects can accommodate larger deformation in comparison with a straight line. The correlation between interconnects' morphology (i.e. cracks propagation) with their electrical behaviour has been studied through microscope in along with electrical characterisation under external strain. Furthermore, a comparison in failure strain among different serpentine-shaped designs has been studied. Higher level in stretchability of interconnects can be achieved with a larger arc degree in design. The fabricated stretchable interconnects can accommodate significant deformations up to 72% external strain while maintaining electrically conductive

Printable stretchable interconnects

This article presents recent progress and a comprehensive overview of stretchable interconnects based on printable nanocomposites. Nanocomposite-based inks for printed stretchable interconnects have been categorized according to dispersed filler materials. They comprise of carbon-based fillers and metal-based fillers. Benefits in terms of excellent electrical performance and elastic properties make nanocomposites the ideal candidates for stretchable interconnect applications. Deeper analysis of nanocomposites-based stretchable interconnects includes the correlation between the size of fillers, percolation ratio, maximum electrical conductivity and mechanical elasticity. The key trends in the field have been highlighted using curve fitting methods on large data collected from the literature. Furthermore, a wide variety of applications for stretchable interconnects are presented

Metal-organic dual layer structure for stretchable interconnects

This paper reports a novel method for obtaining stretchable interconnects using gold and organic material (PEDOT:PSS) in a dual-layer structure on PDMS substrate. With an appropriate design and carefully carried out microfabrication steps, the structure was successfully patterned into serpentine shape and highly stretchable interconnects were obtained. The fabricated interconnects can be stretched up to 170% of their original length while retaining an adequate level of conductivity

Stretchable pH Sensing Patch in a Hybrid Package

This work presents a novel stretchable pH sensing patch to detect the pH in body fluid which is one of the most important parameters in human health monitoring. The sensing patch is a hybrid package comprising of polyimide/gold-based stretchable interconnects and graphite composite-based flexible pH sensor. With the integration of stretchable interconnects, the patch is able to withstand external stretching up to 50% longer than its original length. Moreover, the electrical behavior of the patch does not degrade as studied by the real-time resistance investigation. In order to protect the connecting electrodes and wirings from direct contacting with solution under analysis, the sensing patch is encapsulated with elastic polymer with the active sensing area exposed. The fabricated patch reveals a high pH sensitivity of 36.2 μA/pH in the pH range between 5 and 9 which is validated through electrochemical and electroanalytical studies

Stretchable interconnects for smart integration of sensors in wearable and robotic applications

Stretchable electronic systems are needed in realising a wide range of applications, such as wearable healthcare monitoring where stretching movements are present. Current electronics and sensors are rigid and non-stretchable. However, after integrating with stretchable interconnects, the overall system is able to withstand a certain degree of bending, stretching and twisting. The presence of stretchable interconnects bridges rigid sensors to stretchable sensing networks. In this thesis, stretchable interconnects focusing on the conductive polymer Poly (3,4-ethylenedioxythiophene): poly (4-styrenesulfonate) (PEDOT:PSS) , the composite and the metallic-polyimide (PI) are presented. Three type of stretchable interconnects were developed including gold (Au) -PEDOT:PSS hybrid film interconnects, Graphite-PEDOT:PSS composite interconnects and Au-PI dual-layered interconnects. The Au-PEDOT:PSS hybrid interconnects’ stretchability can reach 72%. The composite exhibits a stretchability of 80% but with an extremely high variation in resistance (100000%). The Au-PI interconnects that have a serpentine shape with the arc degree of 260° reveal the highest stretchability, up to 101%, and its resistance variation remains within 0.2%. Further, the encapsulation effect, cyclic stretching, and contact pad’s influence, are also investigated. To demonstrate the application of developed stretchable interconnects, this thesis also presents the optimised interconnects integrated with the electrochemical pH sensor and CNT-based strain sensor. The integrated stretchable system with electrochemical pH sensor is able to wirelessly monitor the sweat pH. The whole system can withstand up to 53% strain and more than 500 cycles at 30% strain. For the CNT-based strain sensor, the sensor is integrated on the pneumatically actuated soft robotic finger to monitor the bending radius (23 mm) of the finger. In this way, the movement of the soft robotic finger can be controlled. These two examples of sensor’s integration with stretchable interconnects successfully demonstrate the concept of stretchable sensing network. Further work will focus on realising a higher density sensing and higher multifunctional sensing stretchable system seamlessly integrated with cloth fibres

Textile-Based Potentiometric Electrochemical pH Sensor for Wearable Applications

In this work, we present a potentiometric pH sensor on textile substrate for wearable applications. The sensitive (thick film graphite composite) and reference electrodes (Ag/AgCl) are printed on cellulose-polyester blend cloth. An excellent adhesion between printed electrodes allow the textile-based sensor to be washed with a reliable pH response. The developed textile-based pH sensor works on the basis of electrochemical reaction, as observed through the potentiometric, cyclic voltammetry (100 mV/s) and electrochemical impedance spectroscopic (10 mHz to 1 MHz) analysis. The electrochemical double layer formation and the ionic exchanges of the sensitive electrode-pH solution interaction are observed through the electrochemical impedance spectroscopic analysis. Potentiometric analysis reveals that the fabricated textile-based sensor exhibits a sensitivity (slope factor) of 4 mV/pH with a response time of 5 s in the pH range 6–9. The presented sensor shows stable response with a potential of 47 ± 2 mV for long time (2000 s) even after it was washed in tap water. These results indicate that the sensor can be used for wearable applications

An Experimental Investigation on the Effects of Limestone Fines in Manufactured Sands on the Performance of Magnesia Ammonium Phosphate Mortar

Magnesium ammonium phosphate cement (MAPC) prepared with ammonium dihydrogen phosphate (NH4H2PO4, ADP) and dead-burned Magnesium oxide (MgO) is a new type of rapid patch repair material for concrete structures. In order to reduce the material costs of MAPC mortar, manufactured limestone sands, being a more widely-available resource with lower cost, was investigated in this study as an alternative to quartz sands for the preparation of MAPC mortar. The limestone fines in manufactured sands were found to be the key factor that influences properties of MAPC mortar by causing bubbling and volume expansion before hardening. As a result, the mechanical strength of MAPC mortar decreased with the increasing content of limestone fines due to increased porosity. According to microstructure analysis, the mechanism of these negative effects can be inferred as the reaction between limestone fines and ADP with the gas generation of CO2 and NH3. This reaction mainly occurred during a short period before setting while most limestone fines remained unreactive in the hardened MAPC mortar. Based on the above detailed experimental findings on the effects of limestone fines in manufactured sand on the properties of MAPC mortar, this paper pointed out that effective defoaming methods for inhibiting bubbling was the key to the utilization of manufactured sands in preparation of high performance MAPC mortar.</jats:p

Flexible self-charging supercapacitor based on graphene-Ag-3D graphene foam electrodes

A flexible three-dimensional porous graphene foam-based supercapacitor (GFSC) is presented here for energy storage applications. With a novel layered structure of highly conductive electrodes (graphene-Ag conductive epoxy–graphene foam), forming an electrochemical double layer, the GFSC exhibits excellent electrochemical and supercapacitive performance. At a current density of 0.67 mA cm−2, the GFSCs show excellent performance with areal capacitance (38 mF cm−2) about three times higher than the values reported for flexible carbon-based SCs. The observed energy and power densities (3.4 µW h cm−2 and 0.27 mW cm−2 respectively) are better than the values reported for carbon-based SCs. Analyzed under static and dynamic bending conditions, the GFSCs are stable with up to 68% capacitance retention after 25000 charge–discharge cycles. The light-weight, cost-effective fabrication and no self-heating make the GFSCs a promising alternative to conventional source of energy in the broad power density ranging from few nW cm−2 to mW cm−2. In this regard, GFSC was integrated with a flexible photovoltaic cell resulting in a flexible self-charging power pack. This pack was successfully utilized to power continuously a wearable CuO nanorod based chemi-resistive pH sensor

Soft Robotic Finger with Integrated Stretchable Strain Sensor

This work presents an advanced soft robotic finger with integrated strain sensor based on carbon nanotubes (CNTs). The interdigitated strain sensor is obtained by dielectrophoretic assembled CNT network. The sensor is connected to stretchable interconnects to ensure robust electrical connection during movements of the soft finger. The sensor is highly sensitive with up to 1300% change in the resistance for 11% strain. Finally, the CNT strain sensor is integrated with a soft robotic finger to monitor the bending for real time kinesthetic tactile feedback

Mehrgitterverfahren fuer die Loesung der Reynolds-gemittelten Navier-Stokes-Gleichung

The present paper presents a numerical method for calculating the flow around ships and small boats. It restricts itself to acquiring viscous turbulent phenomena while neglecting ship movements and the free water surface. The method is based on the numerical solution of the discrete time-averaged Navier-Stokes equation. Turbulent effects were taken into account by means of the vortex viscosity hypothesis, while using the #kappa#-#epsilon# turbulence model for calculating the turbulent viscosity. The method uses a cell-centered discretization of the velocity components, pressure and the turbulence parameters in a three-dimensional curvilinear non-orthogonal grid. Partial derivations in the dominating equations are discretized with first order to second order finite differences. The numerical method of solution is based on the known SIMPLE scheme. Such methods require a very high computational effort for numerically solving the algebraic systems of equations. One focus in the development was therefore to implement from the start an efficient multigrid based method of solution. The multigrid scheme used here accelerates both the internal iteration by means of a linear correction scheme and the external iteration with a ''Full Approximation Scheme''. An incomplete LU decomposition method in the internal iteration and the SIMPLE algorithm in the global iteration were used as smoothers. A key role is assumed by the determination of optimum initial values of the iterative calculation. This method of solution exhibited an almost optimal behavior in the test calculations performed here, i.e. an almost linear increase in computing time with increasing number of discretization cells. The runtime behavior improved as the Reynolds number increased. (orig./AKF)Available from TIB Hannover: RA 489(543) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman