Interdigitated Pattern Research Articles

A millimetre-scale capacitive biosensing and biophysical stimulation system for emerging bioelectronic bone implants.

Bioelectronic bone implants are being widely recognized as a promising technology for highly personalized bone/implant interface sensing and biophysical therapeutic stimulation. Such bioelectronic devices are based on an innovative concept with the ability to be applied to a wide range of implants, including in fixation and prosthetic systems. Recently, biointerface sensing using capacitive patterns was proposed to overcome the limitations of standard imaging technologies and other non-imaging technologies; moreover, electric stimulation using capacitive patterns was proposed to overcome the limitations of non-instrumented implants. We here provide an innovative low-power miniaturized electronic system with ability to provide both therapeutic stimulation and bone/implant interface monitoring using network-architectured capacitive interdigitated patterns. It comprises five modules: sensing, electric stimulation, processing, communication and power management. This technology was validated using in vitro tests: concerning the sensing system, its ability to detect biointerface changes ranging from tiny to severe bone-implant interface changes in target regions was validated; concerning the stimulation system, its ability to significantly enhance bone cells' full differentiation, including matrix maturation and mineralization, was also confirmed. This work provides an impactful contribution and paves the way for the development of the new generation of orthopaedic biodevices.

Design and Characterization of Printed Flexible Humidity Sensor

The development of humidity sensors is essential for applications in the environmental, agriculture, medical and semiconductor industries [1-2]. The basic mechanism of humidity sensors is explained by a Grotthuss chain reaction, which is usually simplified as a proton-hopping process [3]. This refers to a dynamic charge transfer process at a certain relative humidity (RH). The humidity sensors can be of different types such as capacitive type, resistive, colorimetric and surface acoustic wave [4-7]. Capacitive type sensors are linear, require less complex circuitry and can operate for a wide range of humidity [8]. A typical capacitive type humidity sensor uses hydrophilic films as sensing layers which are stable at higher humidity levels [9]. Polymers that are being used for the fabrication of capacitive type humidity sensors include poly (2-hydroxyethyl methacrylate) (pHEMA) [9], cellulose acetate butyrate (CAB) [10], polyimide [11] and polymethyl methacrylate (PMMA) [12]. In this work, a humidity sensor has been fabricated on glass and flexible substrates.The design of humidity sensor consists of printed pattern of a conductor such as silver and a spin coated dielectric such as polymer poly (2-hydroxyethyl methacrylate) (p-HEMA) and polyimide. The printing of conductor was done in an interdigitated pattern as shown in figure 1. The thickness of sensitive materials was controlled by varying the spin time from 10 to 30 seconds. A thick solution of sensitive materials was prepared by adding a 3 gm of polymer in 50 mL ethanol in the case of p-HEMA. Currently we are preparing one more set of samples using polyimide and we will present a comparison of two humidity sensors- one with p-HEMA and another with polyimide. A humidity sensor that employs interdigitated capacitors (IDC) printed with silver on a glass and flexible substrate was successfully fabricated using p-HEMA and polyimide at spin speed of 2000 rpm for 20 seconds. Our goal is to integrate the humidity sensor into a robotic arm to perform real-time object characterization in agricultural applications via comprehensive understanding of the operations of harvesting robots in various crop types and environmental conditions.

Broadband optically transparent microwave absorber made of interdigital metasurfaces in rotational symmetry with a single air spacer

A broadband optically transparent metasurface microwave absorber (MMA) is designed and experimentally studied. The MMA is made of two indium tin oxide (ITO) resistive films deposited on two transparent polyethylene terephthalate substrates respectively, between which is sandwiched a single air spacer. The top ITO resistive film is etched with periodic interdigital metasurface patterns in rotational symmetry, while the bottom ITO resistive film is an integrated sheet with a low resistance working as the backplane. By carefully optimizing the functional interdigital metasurface structures in a numerical solver, a desirable 4-octave broadband MMA is achieved. The absorbing bandwidth is 4.53–18.71 GHz (122.03%) in the numerical predictions for the perpendicular incidence, in which the absorptivity is greater than 90%. Its total thickness is only 5.8 mm or 0.088λ L, where λ L is the wavelength (66.23 mm) at the lowest 4.53 GHz. The absorber is validated in experiments. Results are observed in good agreement with the simulated ones. The interdigital MMA is polarization-insensitive and able to operate for wide-angle incidences up to 45°. These properties are demonstrated in both simulations and experiments.

Graphene Quantum Dots Based Ultrahigh Rate On-Chip Planar Micro-Supercapacitors with Winding Interdigitated Electrode Pattern

With the rapid development of intelligent electronic devices, and the demand for the shape of the electronic devices with different patterns, people have put forward higher requirements for the design and preparation of the corresponding energy storage devices. Graphene quantum dots are widely used due to their good properties. In this paper, graphene quantum dots were used as electrode materials for patterned planar micro-supercapacitors, and electrode film was prepared by a modified liquid-air interface self-assembly method with an electrode width/interdigital gap of 300 µm/100 µm. Then pattern design is conducted on this basis, and the patterned planar micro-energy storage device was prepared. The electrochemical properties of the devices were investigated at scan rates of 0.01–10000 Vs−1. At a scan rate of 0.01 Vs−1, the area capacitance and energy density were 12.52 µFcm−2 and 1.74 nWhcm−2, density was 44.36 µWcm−2.

Hierarchical global and local auxin signals coordinate cellular interdigitation in Arabidopsis.

The development of multicellular tissues requires both local and global coordination of cell polarization, however, the mechanisms underlying their interplay are poorly understood. In Arabidopsis, leaf epidermal pavement cells (PC) develop a puzzle-piece shape locally coordinated through apoplastic auxin signaling. Here we show auxin also globally coordinates interdigitation by activating the TIR1/AFB-dependent nuclear signaling pathway. This pathway promotes a transient maximum of auxin at the cotyledon tip, which then moves across the leaf activating local PC polarization, as demonstrated by locally uncaged auxin globally rescuing defects in tir1;afb1;afb2;afb4;afb5 mutant but not in tmk1;tmk2;tmk3;tmk4 mutants. Our findings show that hierarchically integrated global and local auxin signaling systems, which respectively depend on TIR1/AFB-dependent gene transcription in the nucleus and TMK-mediated rapid activation of ROP GTPases at the cell surface, control PC interdigitation patterns in Arabidopsis cotyledons, revealing a mechanism for coordinating a local cellular process with the development of whole tissues.

Centrifugal-Gravity-Enforced Deposition of MXene Electrodes for High-Performance and Ultrastable Microsupercapacitors.

Two-dimensional (2D) transition metal carbides, known as MXenes, have captured much attention for their excellent electrical conductivity and electrochemical capability. However, the susceptibility of MXenes to oxidation, particularly Ti3C2Tx transforming into titanium dioxide upon exposure to ambient air, hinders their utilization for extended operational life cycles. This work introduces a simple and straightforward method for producing ultrathin MXene electrode films tailored for energy storage applications, employing centrifugal-gravity force. Our approach significantly suppresses the oxidation phenomenon that arises in MXene materials and also effectively prevents the recrystallization of potentially residual LiF during the film formation. Additionally, the utilization of this MXene electrode in an all-solid-state microsupercapacitor (MSC) with an interdigitated pattern demonstrates an exceptionally improved and stable electrochemical performance. This includes a high volumetric capacitance of approximately 467 F cm-3, an energy density of around 65 mWh cm-3, and impressive long-term cycle stability, retaining about 94% capacity after 10 000 cycles. Moreover, a downsized MSC device exhibits remarkable mechanical durability, retaining over 98% capacity even when folded and sustaining stability over extended periods. Therefore, we believe that this study provides valuable insights for advancing highly integrated energy storage devices, ensuring exceptional electrochemical efficiency and prolonged functionality in diverse environments, whether ambient or humid.

Fully Printed Cellulose Nanofiber-Ag Nanoparticle Composite for High-Performance Humidity Sensor.

This paper reports a high-performance humidity sensor made using a novel cellulose nanofiber (CNF)-silver nanoparticle (AgNP) sensing material. The interdigital electrode pattern was printed via reverse-offset printing using Ag nano-ink, and the sensing layer on the printed interdigitated electrode (IDE) was formed by depositing the CNF-AgNP composite via inkjet printing. The structure and morphology of the CNF-AgNP layer are characterized using ultraviolet-visible spectroscopy, an X-ray diffractometer, field emission scanning electron microscopy, energy-dispersive X-ray analysis, and transmission electron microscopy. The humidity-sensing performance of the prepared sensors is evaluated by measuring the impedance changes under the relative humidity variation between 10 and 90% relative humidity. The CNF-AgNP sensor exhibited very sensitive and fast humidity-sensing responses compared to the CNF sensor. The electrode distance effect and the response and recovery times are investigated. The enhanced humidity-sensing performance is reflected in the increased conductivity of the Ag nanoparticles and the adsorption of free water molecules associated with the porous characteristics of the CNF layer. The CNF-AgNP composite enables the development of highly sensitive, fast-responding, reproducible, flexible, and inexpensive humidity sensors.

Study on liquid dielectrophoresis based on double flexible electrodes simulating interdigitated pattern electrodes

Dielectrophoresis affects the surface wettability by applying a non-uniform electric field to dipoles inside dielectric liquid, achieving adjustable droplet contact angle and overcoming the saturation limitation of contact angle caused by the electrowettability effect. However, it is difficult to realize useful three-dimensional tunable optical devices because most of the driving electrodes need to be patterned. In this work, a model of double flexible electrodes simulating planar interdigitated pattern electrodes is proposed based on the dielectrophoresis. Double flexible electrodes, which are wrapped with an insulating dielectric layer and are not conductive to each other are arranged at close intervals and wound along the plane substrate to form a two-dimensional planar line wall. A hydrophobic layer is used to fill the gap and increase the initial contact angle. Ultimately, the “droplet-interdigitated planar line wall” dielectrophoresis driven-droplet model is formed after the dielectric droplets have been deposited on the line wall surface. Firstly, considering the influence of penetration depth and electrode gap area, Young’s equation is theoretically modified to adapt to this model. Then, the finite element algorithm simulation is used to used to comparatively analyze the potential distribution of this model and the planar interdigitated pattern electrode model. The field strength distributions of the electrodes with different wire diameters and insulating layer thickness values are analyzed. It can be found that with the increase of the diameter of the electrode wire and the thickness of the insulating layer, the morphology of the model changes from the tip electrode into the planar electrode, the surface field strength attenuates exponentially and the peak value decreases. This shows that the structure of this electrode in this model is superior to that of the planar electrode. After that, the contact angle of the model is measured experimentally in a range of 58°－90° under 0–250 <i>V</i><sub>rms</sub> voltage, which is in line with the theoretical expectation. At the same time, neither obvious contact angle lag nor saturation is observed in the experiment. Finally, the new electrophoretic driving droplet model constructed in this paper transforms the dielectric electrophoretic driving mode from a two-dimensional planar electrode to a one-dimensional flexible linear electrode. Because of its flexibility and plasticity, it is convenient to form a three-dimensional cavity and can be applied to more complex device structures.

Preparation of graphene oxide composited zinc oxide films by electrostatic spray deposition for humidity sensors

This work aimed to study the preparation of graphene oxide (GO) and zinc oxide (ZnO) composited films by electrostatic spray deposition for use in fabricated humidity sensors. The physical properties of prepared films were examined with X-ray diffraction, Raman spectroscopy, and scanning electron microscope. Subsequently, a humidity sensor was fabricated using a low-cost interdigitated electrode pattern with the print circuit board. The humidity sensing behaviors were assessed with fixed humidity levels in a saturated aqueous salt solution in the humidity range of 11 – 93%RH. The impedance value of the device was obtained with a precision LCR meter. It was found that the composited film of 0.50 %wt. GO demonstrated the highest humidity response with optimized humidity sensitivity, hysteresis error, and response/recovery times of 2.68 ´ 103, 4.89%, and 228/19 s, respectively. Moreover, the equivalent circuits for the prepared device at various humidity levels were acquired with impedance spectroscopy to propose the mechanism for the humidity sensing of the device.

(Invited) 2D Mxenes for Energy Storage Applications

MXenes are a family of two-dimensional (2D) transition metal carbides and nitrides, with a general structure of Mn+1XnT x , where M is the transition metal, X is carbon and/or nitrogen, and T represents the surface terminations (F, O, OH). MXenes have attracted attention in a multitude of energy storage applications due to their high electronic conductivity, tunable interlayer spacing, redox-active transition metals, and hydrophilic surface groups. In this talk, we discuss the use of MXene electrodes in supercapacitor applications, including aqueous, non-aqueous, and water-in-salt electrolytes. The variability of MXenes is demonstrated with each electrolyte system showing unique electrochemical responses, not limited to redox and/or intercalation pseudocapacitance, and hydrated cation intercalation. Furthermore, the versatility of the hydrophilic, 2D morphology of MXenes is demonstrated through its use in multiple form factors, not limited to flexible free-standing films, multilayer powder electrodes, interdigitated microsupercapacitors, knitted textiles, and more. New directions and perspectives for MXenes in energy storage are discussed, including MXenes’ use as passive components (separators, current collectors, binders, scaffolds, conductive additives) in energy storage systems. Figure 1 (A) Schematic illustration showing MXenes’ electrochemical properties for ion storage applications. (B) Cyclic voltammetry (CV) data collected at scan rates from 10 to 100,000 mV·s−1 for a 90-nm-thick Ti3C2T x film. (C) Influence of an electrolyte’s solvent on the lithium-ion storage capacity of Ti3C2T x ; CV curves of microporous Ti3C2T x electrode in 1 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in DMSO, acetonitrile (ACN), or propylene carbonate (PC) electrolytes. (D) A digital photograph showing the wafer scale fabrication of an array of 143 MXene microsupercapacitors. (E) Photograph of a knitted textile with an interdigitated pattern made using Ti3C2T x MXene-coated cotton yarn to produce electrodes for wearable textile supercapacitor.Reference[1] A. VahidMohammadi, J. Rosen, Y. Gogotsi, Science, 2021, 372, eabf1581. Figure 1

Carbon Nanotube-Polyaniline Reinforced Flexible and Stretchable Strain Sensor with Enhanced Sensitivity for Smart Wearable and Skin-Mounted Applications

Flexible and stretchable strain sensors have emerged as promising components for integration into smart wearable devices and skin-mounted applications. These sensors enable accurate detection of physiological signals, thereby finding unique applications in diverse fields such as human health monitoring, soft robotics, human-machine interface, prosthetics, virtual reality, and professional sports. Two commonly utilized types of strain sensors are capacitive and resistive strain gauges, owing to their low production cost, simplified circuitry, and ease of construction. While resistive strain gauges exhibit high sensitivity, they are prone to nonlinearity and hysteresis. On the other hand, capacitive strain gauges demonstrate linear behavior with minimal hysteresis but offer lower sensitivity. In this study, we capitalize on the exceptional properties of carbon nanotubes, including high mechanical strength, electrical conductivity, and thermal stability, along with using polyaniline as an exemplary conductive polymer. These materials are employed as a reinforcing phase within the polymer matrix, while the dielectric layer is comprised of Ecoflex® 00-30. An interdigitated pattern is specifically designed for this strain gauge to enhance sensitivity. Through this research, we aim to develop a flexible and stretchable strain sensor with enhanced sensitivity and improved performance characteristics.

Finite element analysis of the influence of interdigitation pattern and collagen fibers on the mechanical behavior of the midpalatal suture.

The midpalatal suture (MPS) corresponds to the tissue that joins the two maxillary bones. Understanding the mechanical behavior of this tissue is of particular interest to those patients who require orthodontic treatments such as Rapid Maxillary Expansion (RME). The objective of this research was to observe the influence of interdigitation and collagen fibers on the mechanical response of MPS. To this end, a finite element analysis in two-dimensional models of the bone-suture-bone interface was performed considering the characteristics of the MPS. The geometry of the suture was modeled with 4 different levels of interdigitation: null, moderate, scalloped and fractal. The influence of collagen fibers, aligned transversely along the suture, was considered by incorporating linked structures of the bone fronts. According to the results, the factor that has the greatest impact on the magnitude and distribution of stresses is the interdigitation degree. A higher level of interdigitation produces an increase in tissue stiffness and a lower influence of collagen fibers on the mechanical response of the tissue. Therefore, this research contributes to the understanding of the MPS biomechanics by providing information that may be useful to health staff when evaluating the feasibility of procedures such as RME.

Direct ink writing of PEDOT:PSS inks for flexible micro-supercapacitors

Here, we fabricate poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)(PEDOT:PSS)-based flexible micro-supercapacitors (MCSs) using direct ink writing (DIW) printing. To produce inks suitable for DIW printing, inks with various PEDOT:PSS concentrations are prepared, and their rheological properties and printability are systematically investigated. The optimized PEDOT:PSS ink allows stable printing without spreading and nozzle clogging issues, leading to the successful fabrication of well-defined interdigitated electrode patterns. The resulting PEDOT:PSS-based MSC exhibits high energy storage performance (2005 μF/cm2 at 10 μA/cm2) and outstanding cycle stability (capacitance retention of 87% after 10,000 cycles). Taking advantage of the flexibility of the PEDOT:PSS electrode, the MSC maintains its performance even under bending stress. Moreover, the practicality of the system is demonstrated by tailoring the overall operating voltage and output capacitance through printing MSCs connected in series and parallel.

In Situ Synthesis of ZIF-67 Thin Films Using Low Temperature Chemical Vapor Deposition to Fabricate All-Solid-State Flexible Interdigital in-Planar Microsupercapacitors

This work describes the fabrication of a flexible all-solid-state interdigital in-planar microsupercapacitor (μSC) using the in situ synthesized ZIF-67 thin films as the interdigital finger-electrode materials, platinum (Pt) thin film as the interdigital finger-electrode current collector, laser print technology for the fabrication of interdigital patterns, and low-cost commercial polyethylene terephthalate (PET) sheet as the flexible substrates, assembled with the NaOH/PVA gel electrolyte. ZIF-67 thin films are in situ synthesized onto PET substrate by ultralow temperature (ULT) chemical vapor deposition (CVD) technology at a low temperature of 140°C. We herein report the ULT CVD approach for gas phase synthesizing ZIF-67 thin films, the exactly heating temperature can produce vaporized water steam, sublimated 2-methylimidazole (2-MIM) and cobalt(II) acetylacetonate (Co(acac)2) vapors at the same time. The vaporized and sublimated gaseous precursors demonstrated molecular-level reactions, including the deprotonation of 2-MIM via water steam, and the following coordinated reactions with cobalt ions decomposed from Co(acac)2, for the efficiently straightforward deposition to form the uniform ZIF-67 thin films onto the substrate surface. Herein, the integration of pattern printing, CVD depositing ZIF-67 thin films, and lift-off patterning processes demonstrated a comprehensive achievement and good compatibility to integrate MOFs into miniaturized energy-storage devices.

SkinCell: A Modular Tactile Sensor Patch for Physical Human–Robot Interaction

In this article, we present the design, fabrication, integration, and performance evaluation of SkinCell sensors, a novel tactile array targeting human–robot interaction applications. A polyimide sheet is selected as the substrate of the sensor, and gold electrodes with circular interdigitated finger patterns are deposited through dc sputtering, creating a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4\times $ </tex-math></inline-formula> 4 sensor array with 16 tactile elements. Sensing elements are completed with a thin layer of spin-coated poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT: PSS) organic polymer solution. Two individual sensor sheets are being laminated in a back-to-back fashion to create a half-Wheatstone-bridge configuration to reduce temperature coupling while improving sensitivity. The sensor array is then sandwiched between two layers of silicone elastomer with internal dimples and cavities to improve sensitivity, repeatability, and center of force detection resolution. A COMSOL simulation was performed to study the influence of adding the silicone encapsulation as well as design parameters to the sensor substrate. Our simulation results indicate an effective improvement of touch, i.e., voltage sensitivity by employing the featured encapsulation. Characterization experiments have been conducted to identify the sensitivity profile of each sensor on the array, which indicates an average sensitivity of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$26.5~\mu $ </tex-math></inline-formula> V/N. In subsequent experiments, the calibration profiles are used to identify the resultant force during pressing, as well as the location of the center of pressure (COP) on the SkinCell sensor. Finally, SkinCell sensors have been integrated into the OctoCan, a structural electronic device that can acquire squeezing pressure data during physical human–robot interaction (pHRI).

A 640 × 640 ISFET array for detecting cell metabolism

Ion sensitive field effect transistor (ISFET) devices are highly accurate, convenient, fast and low-cost in the detection of ions and biological macromolecules, such as DNA molecules, antibodies, enzymatic substrates and cellular metabolites. For high-throughput cell metabolism detection, we successfully designed a very large-scale biomedical sensing application specific integrated circuit (ASIC) with a 640 × 640 ISFET array. The circuit design is highly integrated by compressing the size of a pixel to 7.4 × 7.4 μm2 and arranging the layout of even and odd columns in an interdigital pattern to maximize the utilization of space. The chip can operate at a speed of 2.083M pixels/s and the dynamic process of the fluid flow on the surface of the array was monitored through ion imaging. The pH sensitivity is 33 ± 4 mV/pH and the drift rate is 0.06 mV/min after 5 h, indicating the stability and robustness of the chip. Moreover, the chip was applied to monitor pH changes in CaSki cells metabolism, with pH shifting from 8.04 to 7.40 on average. This platform has the potential for continuous and parallel monitoring of cell metabolism in single-cell culture arrays.

3D Heterogenous Integrated Wideband Switchable Bandpass Filter Bank for Millimeter Wave Applications

This article proposes a three-dimensional heterogenous-integrated (3DHI) switchable bandpass filter bank with two independent wideband filter channels that cover 26–40 GHz and 32.5–40 GHz, respectively. An accurate wafer-level process with a high hollowed ratio of the applied 8-inch high-resistivity-silicon (HR-Si) interposer wafers is presented to form both compact filter channels. Above the interdigital filter patterns fabricated on the bottom interposer wafer, deep cavities are etched in the cap interposer wafer to improve the quality factor of the filter bank. Besides the cavities, the cap interposer wafer is 35% hollow inside, which two bare dies of GaAs single-pole double-throw (SPDT) switches and two thin film resistors are attached to the bottom interposer after the wafer-to-wafer (W2W) bonding. To ensure good out-of-band performance, a 3D EM co-simulation of the switch layout at the chip level and filter patterns at the package level is applied. Measurement results show that the switchable filter bank achieves a high isolation of 50 dB and a competitive shape factor (BW30dB/BW3dB) of about 1.3. In addition, the size of the switchable filter bank is only 7.0 mm × 3.5 mm × 0.6 mm, and the weight is only 0.1 g.

Effect of Humidity on the Electrical Response of Interdigitated Circuit Patterns

Environmental factors can play a significant role on the performance of electronic devices. This can be controlled for by designing electronic components with materials that operate suitably under the working conditions of a device. Humidity is a highly variable factor that is unavoidable in ambient conditions, capable of affecting the electrical performance of components especially when they are hydrophilic in nature. Components with such properties can allow water molecules to either permeate through or reside on the circuit surfaces over time. Due to this, it is expected that the relative humidity in the environment of hydrophilic components will vary the circuit’s performance. Previous work [1] was conducted at a single humidity of 50%RH to assess the repeatability of the measured properties. In this study, interdigitated circuits were characterized using impedance spectroscopy at multiple relative humidity levels under a fixed temperature over a frequency range of 100 mHz to 10 MHz. Five interdigitated identical circuits were fabricated on a single solder coated circuit board, followed by no additional surface treatments. The circuits on these uncoated solder boards exhibit capacitive behavior at low humidity levels as expected. With increasing relative humidity, the circuit response transitions towards resistive behavior while exhibiting a reduction in real and imaginary impedance due to increased water molecule concentration at the interfaces of the circuit. Nyquist plots exhibit this transformation as the forming of a semicircle that decreases in size with increased humidity. When the impedance data is converted to the electrical modulus formalism [2], humidity increases result in the formation of peaks in the imaginary electric modulus function as shown in Figure 1. The surface topology of the different circuits, consisting of 50 electrodes each, was examined to better understand the significant effect of relative humidity on the impedance response of the circuit. Using optical and laser microscopy, it was found that the solder coat and interdigitated combs on the uncoated boards are porous in nature and have repeated units of inhomogeneous topologies, leaving many opportunities for water to gather or permeate at surfaces between the interdigitated combs. Five distinctive regions were found to repeat across the width of the circuits. Due to this, surface roughness parameters were also examined to investigate the possible link between topology and impedance response found. Figure 1

Transparent, elastomer-free capacitive pressure sensors using CuNWs and ultrathin UV-cured polymer

• Transparent, elastomer-free capacitive sensors are obtained based on CuNWs. • The sensor can resist 1000 bending cycles at a curvature radius of 0.5 mm. • The senor possesses a high optical transmittance of 81.1%. • A suggested mechanism of capacitance change for the sensor is proposed. • The senor possesses a high sensitivity. Highly flexible transparent piezo-capacitive sensors have been prepared via using a combination of Cu nanowire (NW) conductive network and UV-curable resin. The CuNWs are interconnected and randomly distributed on the substrate. The percolating network structure of CuNW electrode and the ultrathin thickness (4 μm) of polymer film, make the senor possess a high optical transmittance of 81.1 %. The strong affinity of resin to the CuNW networks stabilizes the sensor mechanically that it can resist 1000 bending cycles at a curvature radius of 0.5 mm. The capacitance is generated via the CuNW interdigital electrode pattern by the fringing effect, and increased with increasing the pressure acted on the surface of the sensor. The sensitivity is seven times larger than that of an elastomeric piezo-capacitive sensor with the same sensor design.

Polypyrrole and cotton fabric‐based flexible micro‐supercapacitors

AbstractWith the development of wearable electronic devices, there has been extensive research interest in portable energy supply systems. In this study, traditional cotton fabrics are finished with a water repellent coating and a single‐sided polyurethane (PU) coating to impart hydrophobicity. The hydrophobic lightweight cotton fabric can float on the surface of the pyrrole polymerization system solution. With increasing polymerization time, the pyrrole continues to polymerize and deposit on the side in contact with the fabric, resulting in a one‐sided conductive fabric. The highest doping level was obtained for the polypyrrole (PPy) coating for polymerization time of 12 h. For PPy coating thickness of 18 μm, the square resistance was as low as 220 Ω/sq. The PPy‐12 fabric electrode showed excellent electrochemical performance and cycling stability. An interdigitated pattern was etched on the surface of the one‐sided conductive fabric (PPy‐12) using a N, N‐dimethylformamide solution. Fabric micro‐supercapacitors were obtained by assembling with a H2SO4/PVA gel electrolyte. The fabric micro‐supercapacitor exhibited good flexibility and electrochemical energy storage properties. For current density of 0.08 mA/cm2 and power density of 19.1 μW/cm2, the energy density of the device was 0.09 μWh/cm2. After 3000 cycles, the micro‐supercapacitor retained approximately 85% of the capacitance. Thus, fabric‐based flexible micro‐supercapacitors have excellent application potential in the field of energy storage.