Showing papers on "Capacitive sensing published in 2020"

Highly Morphology-Controllable and Highly Sensitive Capacitive Tactile Sensor Based on Epidermis-Dermis-Inspired Interlocked Asymmetric-Nanocone Arrays for Detection of Tiny Pressure

Abstract: The tactile sensor lies at the heart of electronic skin and is of great importance in the development of flexible electronic devices. To date, it still remains a critical challenge to develop a large-scale capacitive tactile sensor with high sensitivity and controllable morphology in an economical way. Inspired by the interlocked microridges between the epidermis and dermis, herein, a highly sensitive capacitive tactile sensor by creating interlocked asymmetric-nanocones in poly(vinylidenefluoride-co-trifluoroethylene) film is proposed. Particularly, a facile method based on cone-shaped nanoporous anodized aluminum oxide templates is proposed to cost-effectively fabricate the highly ordered nanocones in a controllable manner and on a large scale. Finite-element analysis reveals that under vertical forces, the strain/stress can be highly strengthened and localized at the contact apexes, resulting in an amplified variation of film permittivity and thickness. Benefiting from this, the developed tactile sensor presents several conspicuous features, including the maximum sensitivity (6.583 kPa-1 ) in the low pressure region (0-100 Pa), ultralow detection limit (≈3 Pa), rapid response/recovery time (48/36 ms), excellent stability and reproducibility (10 000 cycles). These salient merits enable the sensor to be successfully applied in a variety of applications including sign language gesture detection, spatial pressure mapping, Braille recognition, and physiological signal monitoring.

Sensitive pressure sensors based on conductive microstructured air-gap gates and two-dimensional semiconductor transistors

Abstract: Microscopic pressure sensors that can rapidly detect small pressure variations are of value in robotic technologies, human–machine interfaces, artificial intelligence and health monitoring devices. However, both capacitive and transistor-based pressure sensors have limitations in terms of sensitivity, response speed, stability and power consumption. Here we show that highly sensitive pressure sensors can be created by integrating a conductive microstructured air-gap gate with two-dimensional semiconductor transistors. The air-gap gate can be used to create capacitor-based sensors that have tunable sensitivity and pressure-sensing range, exhibiting an average sensitivity of 44 kPa−1 in the 0–5 kPa regime and a peak sensitivity up to 770 kPa−1. Furthermore, by employing the air-gap gate as a pressure-sensitive gate for two-dimensional semiconductor transistors, the pressure sensitivity of the device can be amplified to ~103–107 kPa−1 at an optimized pressure regime of ~1.5 kPa. Our sensors also offer fast response speeds, low power consumption, low minimum pressure detection limits and excellent stability. We illustrate their capabilities by using them to perform static pressure mapping, real-time human pulse wave measurements, sound wave detection and remote pressure monitoring. Pressure sensors with a sensitivity of ~103−107 kPa−1, as well as rapid response speeds, low power consumption and excellent stability, can be created by integrating a conductive microstructured air-gap gate with two-dimensional semiconductor transistors.

Boosting supercapacitor and capacitive deionization performance of hierarchically porous carbon by polar surface and structural engineering

Abstract: Heteroatom doped hierarchically porous carbon materials are considered as promising candidates for high performance capacitive deionization and supercapacitor applications. However, the development of carbons simultaneously having both a reasonable polar surface and a hierarchically porous structure via a flexible synthetic strategy is critical but still a great challenge. Herein, a facile and effective strategy is presented for the preparation of N and P dual-doped hierarchically porous carbon networks by one-pot carbonization of a rationally designed precursor that was built using a metal–organic gel with a zinc ion metallic cluster and nitrogen/phosphorus chelate ligands. Due to the abundant exposed polar surface groups and the highly developed interconnected macro-/meso-/microporous structure, the optimal sample delivers a high specific capacitance of 373 F g−1 at a current density of 1 A g−1 and retains 270 F g−1 at 100 A g−1 with a capacitive retention of 72.3%. Furthermore, the symmetric supercapacitors assembled in aqueous and PVA/KOH solid electrolytes exhibit excellent energy outputs of 38.5 and 7.5 W h kg−1, respectively. For capacitive deionization, the sample displays a superior salt adsorption capacity of 7.7, 10.3 and 18.1 mg g−1 in NaCl solution with an initial concentration of 250 mg L−1 at applied voltages of 1, 1.2 and 1.4 V, respectively. Additionally, kinetics studies and density functional theory simulations reveal that N/P dual-doping not only reliably introduces pseudocapacitance, but also greatly enhances the chemisorption of Na and Cl, resulting in a remarkable electrochemical performance. This work provides a new insight into the relationship between polar surface/structural engineering and the capacitive performance of the designed materials.

Insights into Enhanced Capacitive Behavior of Carbon Cathode for Lithium Ion Capacitors: The Coupling of Pore Size and Graphitization Engineering.

Abstract: The lack of methods to modulate intrinsic textures of carbon cathode has seriously hindered the revelation of in-depth relationship between inherent natures and capacitive behaviors, limiting the advancement of lithium ion capacitors (LICs). Here, an orientated-designed pore size distribution (range from 0.5 to 200 nm) and graphitization engineering strategy of carbon materials through regulating molar ratios of Zn/Co ions has been proposed, which provides an effective platform to deeply evaluate the capacitive behaviors of carbon cathode. Significantly, after the systematical analysis cooperating with experimental result and density functional theory calculation, it is uncovered that the size of solvated PF6− ion is about 1.5 nm. Moreover, the capacitive behaviors of carbon cathode could be enhanced attributed to the controlled pore size of 1.5–3 nm. Triggered with synergistic effect of graphitization and appropriate pore size distribution, optimized carbon cathode (Zn90Co10-APC) displays excellent capacitive performances with a reversible specific capacity of ~ 50 mAh g−1 at a current density of 5 A g−1. Furthermore, the assembly pre-lithiated graphite (PLG)//Zn90Co10-APC LIC could deliver a large energy density of 108 Wh kg−1 and a high power density of 150,000 W kg−1 as well as excellent long-term ability with 10,000 cycles. This elaborate work might shed light on the intensive understanding of the improved capacitive behavior in LiPF6 electrolyte and provide a feasible principle for elaborate fabrication of carbon cathodes for LIC systems.

A Review on Applications of Capacitive Displacement Sensing for Capacitive Proximity Sensor

Abstract: Capacitive proximity sensors (CPSs) are ubiquitous because of their simple design, low cost and low consumption. Capacitive displacement sensing, as one of the three sensing modalities, works for long distance and can be unitized to measure more physical quantities compared with capacitive volume and deformation sensing. In this paper, we firstly introduce the concept of capacitive displacement sensing. After that, we present applications of capacitive displacement sensing under three broad categories: distance measurements, indirect measurements, and the applications applied in smart environments. Finally, we discuss the challenges and possible solutions for CPSs development. We show that both the detection range and accuracy of CPS can be improved by multi-sensor fusion, and the application scenarios can be extensive through machine/deep learning approaches. We aim to provide a comprehensive, and state-of-the-art review of the capacitive displacement sensing, and inspire more researchers and developers to find wide application perspectives.

Maximization of Spatial Charge Density: An Approach to Ultrahigh Energy Density of Capacitive Charge Storage

Abstract: Capacitive energy storage has advantages of high power density, long lifespan, and good safety, but is restricted by low energy density. Inspired by the charge storage mechanism of batteries, a spatial charge density (SCD) maximization strategy is developed to compensate this shortage by densely and neatly packing ionic charges in capacitive materials. A record high SCD (ca. 550 C cm-3 ) was achieved by balancing the valance and size of charge-carrier ions and matching the ion sizes with the pore structure of electrode materials, nearly five times higher than those of conventional ones (ca. 120 C cm-3 ). The maximization of SCD was confirmed by Monte Carlo calculations, molecular dynamics simulations, and in situ electrochemical Raman spectroscopy. A full-cell supercapacitor was further constructed; it delivers an ultrahigh energy density of 165 Wh L-1 at a power density of 150 WL-1 and retains 120 Wh L-1 even at 36 kW L-1 , opening a pathway towards high-energy-density capacitive energy storage.

Textile-Based Capacitive Sensor for Physical Rehabilitation via Surface Topological Modification.

Abstract: Wearable sensor technologies, especially continuous monitoring of various human health conditions, are attracting increased attention. However, current rigid sensors present obvious drawbacks, like lower durability and poor comfort. Here, a strategy is proposed to efficiently yield wearable sensors using cotton fabric as an essential component, and conductive materials conformally coat onto the cotton fibers, leading to a highly electrically conductive interconnecting network. To improve the conductivity and durability of conductive coatings, a topographical modification approach is developed with genus-3 and genus-5 structures, and topological genus structures enable cage metallic seeds on the surface of substrates. A textile-based capacitive sensor with flexible, comfortable, and durable properties has been demonstrated. High sensitivity and convenience of signal collection have been achieved by the excellent electrical conductivity of this sensor. Based on results of deep investigation on capacitance, effects of distance and angles between two conductive fabrics contribute to the capacitive sensitivity. In addition, the textile-based capacitive sensor has successfully been used for real-time monitoring human breathing, speaking, blinking, and joint motions during physical rehabilitation exercises.

An Overview of Capacitive DC-Links-Topology Derivation and Scalability Analysis

Abstract: Capacitive dc-links are widely used in voltage source converters for power balance, voltage ripple limitation, and short-term energy storage. A typical solution, which uses aluminum electrolytic capacitors for such applications, is assumed to be one of the weakest links in power electronic systems, therefore, also becoming one of the lifetime bottlenecks of power electronic systems. Various passive and active capacitive dc-link solutions have been proposed intending to improve the reliability of the dc-links qualitatively, making great effort to diverting the instantaneous pulsating power into extra reliable storage components. In this paper, a generic topology derivation method for single-phase power converters with active capacitive dc-link integrated has been proposed, which can derive all existing topologies, and identify a few new topologies. According to the synthesis results, the main achievements in research on capacitive dc-link solutions are reviewed and presented chronologically as well as thematically ordered. Furthermore, the reliability-oriented design procedure is applied to size the chip area of active switching devices and the passive components to fulfill a specific lifetime target and system specification, as well as compare the overall capacitive energy storage, energy buffer ratio, and the cost of different solutions. The cost comparisons are performed with a scalable lifetime target and power rating. It reveals that different conclusions can be drawn with different lifetime targets in terms of cost-effectiveness.

A Review of MEMS Capacitive Microphones

Abstract: This review collates around 100 papers that developed micro-electro-mechanical system (MEMS) capacitive microphones. As far as we know, this is the first comprehensive archive from academia on this versatile device from 1989 to 2019. These works are tabulated in term of intended application, fabrication method, material, dimension, and performances. This is followed by discussions on diaphragm, backplate and chamber, and performance parameters. This review is beneficial for those who are interested with the evolutions of this acoustic sensor.

Analysis and Design of Inductive and Capacitive Hybrid Wireless Power Transfer System for Railway Application

Abstract: Inductive power transfer (IPT) and capacitive power transfer (CPT) are mainly two effective ways to achieve wireless power transfer (WPT). IPT system needs capacitor to compensate the system, while the CPT system requires inductor to tune the system. Therefore, IPT coupler can be used to compensate the CPT coupler and vice versa. In this article, an inductive and capacitive hybrid wireless power transfer (HWPT) system is proposed to improve the system coupler antimisalignment ability. The couplers of IPT and CPT are employed together to compensate each other and transfer power together. Superposition theory is used to analyze the system working principle in detail. With the analysis results, a scaled-down system is built to validate the performance of the proposed approach. Experimental results show that the proposed HWPT system can achieve 653 W output power with 87.7% dc–dc efficiency at the well-aligned condition, and the maximum variation of the output power is 8.3% with the coupler misalignment from 0 to 270 mm (halfwidth of the coupler), which agree well with the analysis results.

3D Dielectric Layer Enabled Highly Sensitive Capacitive Pressure Sensors for Wearable Electronics.

Abstract: Flexible capacitance sensors play a key role in wearable devices, soft robots, and the Internet of things (IoT). To realize these feasible applications, subtle pressure detection under various conditions is required, and it is often limited by low sensitivity. Herein, we demonstrate a capacitive touch sensor with excellent sensing capabilities enabled by a three-dimensional (3D) network dielectric layer, combining a natural viscoelastic property material of thermoplastic polyurethane (TPU) nanofibers wrapped with electrically conductive materials of Ag nanowires (AgNWs). Taking advantage of the large deformation and the increase of effective permittivity under the action of compression force, the device has the characteristics of high sensitivity, fast response time, and low detection limit. The enhanced sensing mechanism of the 3D structures and the conductive filler have been discussed in detail. These superior functions enable us to monitor a variety of subtle pressure changes (pulse, airflow, and Morse code). By detecting the pressure of fingers, a smart piano glove integrated with 10 circuits of finger joints is made, which realizes the real-time performance of the piano and provides the possibility for the application of intelligent wearable electronic products such as virtual reality and human-machine interface in the future.

3D printed conductive thermoplastic polyurethane/carbon nanotube composites for capacitive and piezoresistive sensing in soft pneumatic actuators

Abstract: With applications in flexible electronics and soft robotics, the ability to fabricate elastic functional materials with complex geometries has become highly desirable. In this work, flexible thermoplastic polyurethane/multiwalled carbon nanotube (TPU-MWCNT) composites were printed using multi-material fused filament fabrication (FFF) to study their feasibility towards built-in sensing capabilities in soft robotics. The microstructure, electrical conductivity, capacitive sensing, and piezoresistive sensing of the printed samples were investigated. MWCNT content, print orientation, and layer height was found to be the most influential parameters on the electrical properties while the nozzle and bed temperatures showed insignificant impacts. Overall, the in-line and through-line conductivities were one order of magnitude higher than the through-layer conductivity. Once the printing process was optimized, nanocomposites with 3 and 4 wt.%MWCNT showed repeatable and frequency independent conductivity behavior, reaching to a maximum value of 0.10 and 0.32 S/cm, respectively. A soft pneumatic actuator was then designed and printed out of TPU-MWCNT using the optimized process conditions. The built-in capacitive and piezoresistive sensing capabilities of the printed actuators were successfully demonstrated upon gripping contact and actuation at three different pressure levels. This work unveils the potential of integrating a variety of feedback sensors in robotic actuators through FFF process.

Capacitive and diffusion-controlled mechanism of strontium oxide based symmetric and asymmetric devices

Abstract: A systematic approach has been employed to statistically analyze the Faradaic and non-Faradaic mechanism on electrodes. Two strategies have been adopted for device design, i.e. symmetric and asymmetric, by using the metal oxide synthesized via sonochemical method and activated carbon electrode. Structural and electrochemical characterization have been performed to investigate the morphological and electrochemical properties of electrode material. Both devices are electrochemically examined by using cyclic voltammetry (CV) and Galvanostatic charge discharge (GCD) measurements to evaluate the electrochemical performance. CV curves are further explored to study the capacitive and diffusive contribution in both devices. The diffusive-controlled contribution at low scan rate in asymmetric device is about 65% which is suitable for supercapattery applications while the symmetric device shows 91% diffusive contribution presenting better performance for battery applications. The strategy unveils the high capacitive and diffusive contribution in asymmetric and symmetric devices, respectively. Results reveal that same material can be exploited for supercapattery and battery applications by implementing different device architectures.

A porous and air gap elastomeric dielectric layer for wearable capacitive pressure sensor with high sensitivity and a wide detection range

Abstract: A flexible and highly sensitive capacitive sensor capable of detecting pressure over a wide range was prepared using an elastomeric dielectric layer with high porosity and air gaps sandwiched between conducting polymer/filter paper electrodes Porous polydimethylsiloxane (PDMS) with air gaps (ie through holes) was prepared by using NaCl powders and an array of metal pins as a template during the curing process An as-fabricated capacitive sensor based on the PDMS layer with ∼60% porosity and an array of 6 × 6 air gaps with diameters of ∼850 μm showed high sensitivity for the pressure range from ∼5 Pa to 1 MPa, a quick response time and good durability Potential applications of the capacitive pressure sensor in human motion monitoring and spatial pressure mapping were demonstrated

Multimodal Capacitive and Piezoresistive Sensor for Simultaneous Measurement of Multiple Forces.

Abstract: Quantitative information on the magnitudes and directions of multiple contacting forces is crucial for a wide range of applications including human-robot interaction, prosthetics, and bionic hands. Herein we report a highly stretchable sensor integrating capacitive and piezoresistive mechanisms that can simultaneously determine multiple forces. The sensor consists of three layers in a sandwich design. The two facesheets serve as both piezoresistive sensors and electrodes for the capacitive sensor, with the core being a porous structure made by using a simple sugar particle template technique to give them high stretchability. The two facesheets contain segregated conductive networks of silver nanowires (AgNWs) and carbon nanofibers (CNFs). By measuring the changes in the electrical resistance of the facesheets and the capacitance between the facesheets, three separate mechanical stimuli can be determined, including normal pressure, in-plane stretch, and transverse shear force. The newly developed multidirectional sensor offers a significant opportunity for the next generation of wearable sensors for human health monitoring and bionic skin for robots.

Super-soft solvent-free bottlebrush elastomers for touch sensing

Abstract: The sensitivity of capacitive pressure sensors is primarily determined by the modulus of a soft dielectric layer that reversibly deforms to produce an electrical signal. Unfortunately, the mechanical properties of conventional linear networks are constrained such that a lower limit on softness translates to poor capacitive pressure sensor performance. Here, we overcome this paradigm by leveraging the intrinsic “super-soft” characteristic of bottlebrush polymers. A simple light-induced crosslinking strategy is introduced to facilitate device fabrication and parallel plate capacitive pressure sensors constructed with these bottlebrush polymer networks exhibit up to a 53× increase in sensitivity compared to traditional material formulations, e.g., Sylgard 184. This combination of contemporary synthetic chemistry and application-driven materials design accentuates the opportunities available at the intersection of science and engineering.

Characterization of Low-Cost Capacitive Soil Moisture Sensors for IoT Networks.

Abstract: The rapid development and wide application of the IoT (Internet of Things) has pushed toward the improvement of current practices in greenhouse technology and agriculture in general, through automation and informatization. The experimental and accurate determination of soil moisture is a matter of great importance in different scientific fields, such as agronomy, soil physics, geology, hydraulics, and soil mechanics. This paper focuses on the experimental characterization of a commercial low-cost “capacitive” coplanar soil moisture sensor that can be housed in distributed nodes for IoT applications. It is shown that at least for a well-defined type of soil with a constant solid matter to volume ratio, this type of capacitive sensor yields a reliable relationship between output voltage and gravimetric water content.

Ultra-Sensitive Flexible Pressure Sensor Based on Microstructured Electrode.

Abstract: Flexible pressure sensors with a high sensitivity in the lower zone of a subtle-pressure regime has shown great potential in the fields of electronic skin, human–computer interaction, wearable devices, intelligent prosthesis, and medical health. Adding microstructures on the dielectric layer on a capacitive pressure sensor has become a common and effective approach to enhance the performance of flexible pressure sensors. Here, we propose a method to further dramatically increase the sensitivity by adding elastic pyramidal microstructures on one side of the electrode and using a thin layer of a dielectric in a capacitive sensor. The sensitivity of the proposed device has been improved from 3.1 to 70.6 kPa−1 compared to capacitive sensors having pyramidal microstructures in the same dimension on the dielectric layer. Moreover, a detection limit of 1 Pa was achieved. The finite element analysis performed based on electromechanical sequential coupling simulation for hyperelastic materials indicates that the microstructures on electrode are critical to achieve high sensitivity. The influence of the duty ratio of the micro-pyramids on the sensitivity of the sensor is analyzed by both simulation and experiment. The durability and robustness of the device was also demonstrated by pressure testing for 2000 cycles.

Cobalt-doping in hierarchical Ni3S2 nanorod arrays enables high areal capacitance

Abstract: Areal capacitance is an important metrics for miniaturized capacitive energy storage devices due to the constraint of device area In the present work, we proposed a free-standing hierarchical cobalt-doped Ni3S2 (Co-Ni3S2) nanorod arrays as a novel pseudocapacitive electrode to realize impressively high areal capacitance With enhanced surface area donated by the introduction of cobalt, the Co-Ni3S2 nanorods exhibit an ultrahigh areal capacitance of 346 F cm−2 at 8 mA cm−2, which is more than three-fold over that of pristine Ni3S2 When coupled with an FeOOH anode, the fabricated Co-Ni3S2//FeOOH hybrid supercapacitor can deliver a large areal capacitance of 161 F cm−2, a peak energy density of 073 mW h cm−2, and a peak power density of 3600 mW cm−2 Besides, the as-fabricated hybrid supercapacitor also exhibits stable capacitive performance (835% capacity retention after 5000 cycles) The advanced and stable Co-Ni3S2 electrode developed in this work is highly desirable for micro supercapacitor devices

Laser-Induced Flexible Electronics (LIFE) for Resistive, Capacitive and Electrochemical Sensing Applications

Abstract: Engineering a cost-effective, flexible electronic device in a one-step fabrication process is quite challenging to perform. Herein, we have introduced a simple, low-cost, solid-state process for producing and printing of complex circuits using Laser-Induced Graphene (LIG). In the present work, LIG has been effectively and selectively formed from direct CO2 laser ablation on a polyimide sheet. Varying CO2 laser power and speed, the electrical conductivity of the LIG has shown a linear increment in the conductivity measurement. The laser-induced samples were structurally characterized using Scanning Electron Microscopy (SEM), EDX, X-ray Photoelectron Spectroscopy (XPS), Raman spectroscopy. The results show a one-step method to create Graphene-derived structures on the polyimide sheet surface. This method of generating LIG on a flexible substrate (polyimide sheet) offers an easy way to fabricate Laser-Induced Flexible electronics (LIFE) circuits. Using this, the feasibility and the realization of a capacitive touch sensor and liquid level sensor has been successfully demonstrated. Further, as a prototype system, the LIG was examined for the H2O2 electrochemical sensing application. It gives an appreciable response for the detection of H2O2 in comparison to other carbon-based electrodes with limit-of-detection (LOD) as $0.3~\mu \text{M}$ in a linear range from $1~\mu \text{M}$ to 10 $\mu \text{M}$ .

Insight into the significant contribution of intrinsic carbon defects for the high-performance capacitive desalination of brackish water

Abstract: Carbon-based electrodes have experienced great progress for capacitive desalination owning to their high conductivity and low cost. However, the fundamental issue of the origin of their capacitive activity is far from clarified. In particular, a systematic exploration of the influences of intrinsic defects ubiquitous in carbon on capacitive desalination is still a great challenge. Herein, porous carbons with different degrees of intrinsic defects were first designed via an effective dual-templating approach. The optimized carbon framework showed a high specific capacitance of 181 F g−1 at 2 mV s−1 in 1.0 M NaCl electrolyte. Moreover, it displayed a superb salt-adsorption capacity of 47.2 mg g−1 in 1000 mg L−1 NaCl solution at 1.2 V. The experimental results demonstrated that the abundant intrinsic carbon defects play crucial roles in the salt-adsorption capacity and rate capability, and can enable an exceptional electrical double-layer capacitance and facilitate the adsorption behavior of ions. Additionally, from density functional theory simulation results, we observed that abundant intrinsic defects in carbon can greatly promote the charge density redistribution, thereby enhancing the ion-adsorption ability. This work presents deep insights into defective carbon-based materials for further understanding the effects of intrinsic defects on the capacitive desalination performance.