Showing papers on "Capacitive sensing published in 2019"

Microstructured Porous Pyramid-Based Ultrahigh Sensitive Pressure Sensor Insensitive to Strain and Temperature

Abstract: An ultrahigh sensitive capacitive pressure sensor based on a porous pyramid dielectric layer (PPDL) is reported. Compared to that of the conventional pyramid dielectric layer, the sensitivity was drastically increased to 44.5 kPa-1 in the pressure range <100 Pa, an unprecedented sensitivity for capacitive pressure sensors. The enhanced sensitivity is attributed to a lower compressive modulus and larger change in an effective dielectric constant under pressure. By placing the pressure sensors on islands of hard elastomer embedded in a soft elastomer substrate, the sensors exhibited insensitivity to strain. The pressure sensors were also nonresponsive to temperature. Finally, a contact resistance-based pressure sensor is also demonstrated by chemically grafting PPDL with a conductive polymer, which also showed drastically enhanced sensitivity.

Flexible Capacitive Pressure Sensor Enhanced by Tilted Micropillar Arrays

Abstract: Sensitivity of the sensor is of great importance in practical applications of wearable electronics or smart robotics. In the present study, a capacitive sensor enhanced by a tilted micropillar array-structured dielectric layer is developed. Because the tilted micropillars undergo bending deformation rather than compression deformation, the distance between the electrodes is easier to change, even discarding the contribution of the air gap at the interface of the structured dielectric layer and the electrode, thus resulting in high pressure sensitivity (0.42 kPa-1) and very small detection limit (1 Pa). In addition, eliminating the presence of uncertain air gap, the dielectric layer is strongly bonded with the electrode, which makes the structure robust and endows the sensor with high stability and reliable capacitance response. These characteristics allow the device to remain in normal use without the need for repair or replacement despite mechanical damage. Moreover, the proposed sensor can be tailored to any size and shape, which is further demonstrated in wearable application. This work provides a new strategy for sensors that are required to be sensitive and reliable in actual applications.

Flexible, Tunable, and Ultrasensitive Capacitive Pressure Sensor with Microconformal Graphene Electrodes

Abstract: High-performance flexible pressure sensors are highly desirable in health monitoring, robotic tactile, and artificial intelligence. Construction of microstructures in dielectrics and electrodes is the dominating approach to improving the performance of capacitive pressure sensors. Herein, we have demonstrated a novel three-dimensional microconformal graphene electrode for ultrasensitive and tunable flexible capacitive pressure sensors. Because the fabrication process is controllable, the morphologies of the graphene that is perfectly conformal with the electrode are controllable consequently. Multiscale morphologies ranging from a few nanometers to hundreds of nanometers, even to tens of micrometers, have been systematically investigated, and the high-performance capacitive pressure sensor with high sensitivity (3.19 kPa–1), fast response (30 ms), ultralow detection limit (1 mg), tunable-sensitivity, high flexibility, and high stability was obtained. Furthermore, an ultrasensitivity of 7.68 kPa–1 was succ...

Ultrahigh-Sensitivity Microwave Sensor for Microfluidic Complex Permittivity Measurement

Abstract: The conventional resonant-type microwave microfluidic sensors made of planar resonators suffer from limited sensitivities. This is due to the existence of several distributed capacitors in their structure, where just one of them acts as a sensing element. This article proposes a very high-sensitivity microwave sensor made of a microstrip transmission line loaded with a shunt-connected series LC resonator. A large sensitivity for dielectric loadings is achieved by incorporating just one capacitor in the resonator structure. Applying sample liquids to the microfluidic channel implemented in the capacitive gap area of the sensor modifies the capacitor value. This is translated to a resonance frequency shift from which the liquid sample is characterized. The sensor performance and working principle are described through a circuit model analysis. Finally, a device prototype is fabricated, and experimental measurements using water/ethanol solutions are presented for verification of the sensing principle.

Rapid-Response, Low Detection Limit, and High-Sensitivity Capacitive Flexible Tactile Sensor Based on Three-Dimensional Porous Dielectric Layer for Wearable Electronic Skin

Abstract: Three-dimensional (3D) porous conductive composites explored in highly sensitive tactile sensors have attracted extensive close attention in recent years owing to their peculiar porous structure and unique physical properties in terms of excellent mechanical flexibility, high relative dielectric permittivity, and good elastic property. Herein, we report an practical, efficient, and macroscopic dip-coating process to manufacture rapid-response, low detection limit, high-sensitivity, and highly sensitive capacitive flexible tactile sensors. The fabrication process, tactile perception mechanism, and sensing performance of the developed devices are comparatively investigated. The homogeneous 3D hybrid network constructed by graphene nanoplatelets/carboxyl-functionalized multiwalled carbon nanotubes/silicone rubber composites anchored on polyurethane sponge skeletons exhibits a significantly improved dielectric property, resulting in a high-performance capacitive flexible tactile sensor with a fast response time (∼45 ms), an extremely low-pressure detection limit of ∼3 Pa, excellent sensitivity (∼0.062 kPa-1), and excellent durability and stability over 2000 cycles. Importantly, the flexible devices can be used as the wearable electronic skin and successfully mounted on human skin or a soft-bodied robot to achieve the capability of physiological stimuli monitoring, micropressure monitoring, soft grabbing, etc. Our rapid-response, low detection limit, and high-sensitivity capacitive flexible tactile sensor with a novel 3D porous dielectric layer could be a prospective candidate for the wearable applications in real-time and high-accuracy portable healthcare monitoring devices, advanced human-machine interfaces, and intelligent robot perception systems.

Ultrasensitive Interfacial Capacitive Pressure Sensor Based on a Randomly Distributed Microstructured Iontronic Film for Wearable Applications

Abstract: The rapid development of pressure sensors with distinct functionalities, notably, with increased sensitivity, fast response time, conformability, and a high degree of deformability, has increased the demand for wearable electronics. In particular, pressure sensors with an excellent sensitivity in the low-pressure range (<2 kPa) and a large working range simultaneously are strongly demanded for practical applications in wearable electronics. Here, we demonstrate an emerging class of solid polymer electrolyte obtained by incorporating a room-temperature ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide with poly(vinylidene fluoride-co-hexafluoropropylene) as a high-capacitance dielectric layer for interfacial capacitive pressure sensing applications. The solid polymer electrolyte exhibits a very high interfacial capacitance by virtue of mobile ions that serve as an electrical double layer in response to an electric field. The randomly distributed microstructures created on the soli...

Soft Wearable Pressure Sensors for Beat-to-Beat Blood Pressure Monitoring

Abstract: Wrinkled gold thin films on elastomeric substrates are used as robust parallel plate electrodes for soft capacitive pressure sensors. The wrinkled structures create a robust integration with the polymer, allowing repeated normal force to deform the thin film without failure. By incorporating microridged structures that support the counter electrodes to create air cavities within the elastomeric dielectric layer, pressure sensitivity is further increased to 0.148 kPa-1 over a wide dynamic range of up to 10 kPa. The wide dynamic range and pressure sensitivity of the pressure sensor allow for consistent measurements of the pressure exerted by the radial artery located on the wrist. The soft capacitive pressure sensor displays comparable results when tested against an FDA approved device (Clearsight, Edwards Lifesciences, Irvine, CA) measuring beat-to-beat blood pressure. These soft pressure sensors using wrinkled thin films, therefore, illustrate considerable potential to continuously monitor beat-to-beat blood pressure.

Anodized Aluminum Oxide-Assisted Low-Cost Flexible Capacitive Pressure Sensors Based on Double-Sided Nanopillars by a Facile Fabrication Method

Abstract: Flexible pressure sensors have garnered enormous attention in recent years as they hold great promise in wearable electronic devices. However, the realization of a high-performance flexible pressure sensor via a facile and cost-effective approach still remains a challenge. In this work, a capacitive pressure sensor based on a poly(vinylidenefluoride-co-trifluoroethylene) [P(VDF-TrFE)] dielectric film that incorporates nanopillars into both sides is demonstrated. Unlike the previous complicated and expensive methods, large-scale regular and uniform nanopillars are easily and economically achieved by the pattern transfer of anodized aluminum oxide templates. The double-sided nanopillars constituting the P(VDF-TrFE) dielectric layer enable the pressure sensor with high sensitivity (∼0.35 kPa-1), wide working range (4 Pa to 25 kPa), short response time (∼48 ms), and excellent durability. In addition to these salient features, our sensor also exhibits superior performances under bending states, ensuring that it can be used for detecting diverse practical stimuli as experimentally validated by perceiving real-time and in-site human physiological signals and body motions that, respectively, correspond to the low- and high-pressure range. A sensor array is finally constructed and is shown to be capable of perceiving the spatial pressure distribution of either a contact or noncontact object. These demonstrations show a promising future of our sensor in healthcare monitoring, smart robot skin, and human-machine interfaces.

Fingerprint-Enhanced Capacitive-Piezoelectric Flexible Sensing Skin to Discriminate Static and Dynamic Tactile Stimuli

Abstract: Inspired by the structure and functions of the human skin, a highly sensitive capacitive‐piezoelectric flexible sensing skin with fingerprint‐like patterns to detect and discriminate between spatiotemporal tactile stimuli including static and dynamic pressures and textures is presented. The capacitive‐piezoelectric tandem sensing structure is embedded in the phalange of a 3D‐printed robotic hand, and a tempotron classifier system is used for tactile exploration. The dynamic tactile sensor, interfaced with an extended gate configuration to a common source metal oxide semiconductor field effect transistor (MOSFET), exhibits a sensitivity of 2.28 kPa−1. The capacitive sensing structure has nonlinear characteristics with sensitivity varying from 0.25 kPa−1 in the low‐pressure range (<100 Pa) to 0.002 kPa−1 in high pressure (≈2.5 kPa). The output from the presented sensor under a closed‐loop tactile scan, carried out with an industrial robotic arm, is used as latency‐coded spike trains in a spiking neural network (SNN) tempotron classifier system. With the capability of performing a real‐time binary naturalistic texture classification with a maximum accuracy of 99.45%, the presented bioinspired skin finds applications in robotics, prosthesis, wearable sensors, and medical devices.

A bio-inspired cilia array as the dielectric layer for flexible capacitive pressure sensors with high sensitivity and a broad detection range

Abstract: Recently, electronic skins that simulate the human sophisticated somatosensory system by transforming physiological signals into electrical signals have attracted considerable interest in various fields such as intelligence robots, human–machine interfaces, various wearable devices, etc. Herein, inspired by the human hairy skin, we reported a flexible capacitive pressure sensor with high sensitivity and a broad detection range using a hair-like micro cilia array (MCA) as the dielectric layer through a facile and cost-effective methodology. For the first time, we demonstrated that the MCA can be conveniently obtained with tunable morphologies taking advantage of the magnetic field simply from a portable magnet to serve as the dielectric layer for flexible capacitive pressure sensors. The shape controllability of the MCA structure was systematically investigated using various preparation parameters, e.g. the magnetic field, mass ratio of the composite, etc. With the optimized structure, the proposed sensor exhibits a high sensitivity of 0.28 kPa−1 (0–10 kPa), a broad detection range of up to 200 kPa (sensitivity of 0.02 kPa−1 within 50–200 kPa), a detection limit of 2 Pa and excellent structural robustness and stabilities. Practical applications such as pulse-sensing, voice recognition, gas-flow monitoring, high pressure monitoring (bending, walking, jumping, etc.), spatial distributions, etc. were successfully demonstrated. Thanks to the facile and cost-effective fabrication approach as well as the outstanding sensing capability, the proposed pressure sensor can be of profound significance for future applications including wearable electronic devices, artificial intelligence, interactive robotics, and other actual fields.

Polymeric foams for flexible and highly sensitive low-pressure capacitive sensors

Abstract: Flexible low-pressure sensors (<10 kPa) are required in areas as diverse as blood-pressure monitoring, human-computer interactions, robotics, and object detection. For applications, it is essential that these sensors combine flexibility, high sensitivity, robustness, and low production costs. Previous works involve surface micro-patterning, electronic amplification (OFET), and hydrogels. However, these solutions are limited as they involve complex processes, large bias voltages, large energy consumption, or are sensitive to evaporation. Here, we report a major advance to solve the challenge of scalable, efficient and robust e-skin. We present an unconventional capacitive sensor based on composite foam materials filled with conductive carbon black particles. Owing to the elastic buckling of the foam pores, the sensitivity exceeds 35 kPa −1 for pressure <0.2 kPa. These performances are one order of magnitude higher than the ones previously reported. These materials are low-cost, easy to prepare, and display high capacitance values, which are easy to measure using low-cost electronics. These materials pave the road for the implementation of e-skin in commercialized applications. npj Flexible Electronics (2019) 3:7 ; https://doi.

Insights into the influence of the pore size and surface area of activated carbons on the energy storage of electric double layer capacitors with a new potentially universally applicable capacitor model

Abstract: The electric double layer formation of supercapacitors is governed by ion electrosorption at the electrode surface. Large surface areas are beneficial for the energy storage process, typically achieved by carbon electrode materials. It is a matter of debate whether pores provide the same contribution to the capacitance regardless of the size, or if subnanometer pores lead to an anomalous increase of capacitance. In our work, we developed a new model for normalized capacitance depending on pore sizes, using a combination of a sandwich type capacitor for micropores and double-cylinder capacitor model for larger pores. Modification factors for each capacitance value were calculated using the nonlinear generalized reduced gradient method to obtain a modified electric sandwich double-cylinder capacitor (ESDCC) model. The model was validated by comparing the measured capacitance values of a set of prepared activated carbons in organic electrolytes with simulated values according to the modified ESDCC model, using combined physisorption data of carbon dioxide and nitrogen. We concluded a non-constant capacitive contribution, with pores having the size of bare cations contributing to the capacitance to a larger extent and mesopores with the size of three solvated ions providing an unusual low contribution to the overall capacitance.

Flexible and Washable Poly(Ionic Liquid) Nanofibrous Membrane with Moisture Proof Pressure Sensing for Real-Life Wearable Electronics.

Abstract: Real-life wearable electronics with long-term stable sensing performance are of significant practical interest to public. Wearable pressure sensors with washable, comfortable, breathable, and stable sensing ability are a key requirement to meet the desire. However, effects of ubiquitous ambient moisture and intrinsic defects of current capacitive sensing materials are two factors leading to unstable sensing performance of current pressure sensors. Existing ionic liquid-based materials (i.e., ionic hydrogel, ionic film, or ionic/elastomers composite) have been used for efficient capacitive pressure sensing but are highly sensitive and especially affected by moisture. In this work, we introduce a washable capacitive pressure-sensing textile based on the use of a hydrophobic poly(ionic liquid) nanofibrous membrane (PILNM) with good mechanical properties and satisfactory moisture proof sensing performance. The PILNM membranes possessing rich ions and microporous structures are novel ideal polymeric dielectric materials for amplification of signals with negligible stimulations. Moreover, the PILNMs exhibit very high stable sensing signals under moisture interference (up to 70% relative humidity) and repeated washings (more than 10 washings), especially suitable for wearable electronics. Notably, the PILNM-based wearable pressure-sensing textiles offer high sensitivity for low pressure and bent chord length changes with a low-pressure detection limit even under harsh deformations. Owing to the superior performance, the PILNM-based wearable pressure-sensing textiles are comfortable to wear and suitable for monitoring different human motions and pulse vibrations at various body positions. Meanwhile, the assembled multiple wearable pressure-sensing array can spatially map the contact area of the pressure stimuli and synchronously reflect finger movements.

Flexible capacitive pressure sensor with sensitivity and linear measuring range enhanced based on porous composite of carbon conductive paste and polydimethylsiloxane

Abstract: In recent years, the development of electronic skin and smart wearable body sensors has put forward high requirements for flexible pressure sensors with high sensitivity and large linear measuring range. However, it turns out to be difficult to increase both of them simultaneously. In this paper, a flexible capacitive pressure sensor based on a porous carbon conductive paste-polydimethylsiloxane composite is reported, the sensitivity and the linear measuring range of which were developed using multiple methods including adjusting the stiffness of the dielectric layer material, fabricating a microstructure and increasing the dielectric permittivity of the dielectric layer. The capacitive pressure sensor reported here has a relatively high sensitivity of 1.1 kPa-1 and a large linear measuring range of 10 kPa, making the product of the sensitivity and linear measuring range 11, which is higher than that of the most reported capacitive pressure sensors to our best knowledge. The sensor has a detection of limit of 4 Pa, response time of 60 ms and great stability. Some potential applications of the sensor were demonstrated, such as arterial pulse wave measuring and breath measuring, which shows it as a promising candidate for wearable biomedical devices. In addition, a pressure sensor array based on the material was also fabricated and it could identify objects in the shape of different letters clearly, which shows promising application in future electronic skins.

A flexible capacitive sensor based on the electrospun PVDF nanofiber membrane with carbon nanotubes

Abstract: Flexible pressure sensors have been increasingly recognized over the past several decades, but there is still a challenge to fabricate them with a superb sensitivity and large sensing range. In this paper, a flexible capacitive pressure sensor based on the electrospun polyvinylidene fluoride (PVDF) nanofiber membrane with carbon nanotubes (CNTs) was developed to measure the pressure. The electrospinning CNT-PVDF nanofiber membrane can overcomes the limitations of the traditional solution-dip-coating for adhering conductive materials to the porous surface. The microstructure and characterization of the CNT-PVDF nanofiber membrane were analyzed by SEM, AFM and FTIR. By increasing the permittivity and decreasing the Young's modulus of the CNT-PVDF dielectric layer, the capacitive sensor exhibits high sensitivity (∼0.99/kPa), fast response (∼29 ms) and excellent cyclic loading/unloading stability (＞1000 cycles). Moreover, experiments were also conducted to investigate influence of the thickness and bending radius of the sensor as well as temperature and humidity of the environment. In addition, a 3 × 3 sensor network attached on the hand was used to measure the spatial distribution and magnitude of tactile pressure. The proposed sensor has great potential for application in soft robotics and electronic skin.

Highly Ordered 3D Microstructure-Based Electronic Skin Capable of Differentiating Pressure, Temperature, and Proximity.

Abstract: Electronic skin are devices that mimic the functionalities of human skin, which require high sensitivity, large dynamic range, high spatial uniformity, low-cost and large-area processability, and the capacity to differentiate various external inputs. We herein introduce a versatile droplet-based microfluidic-assisted emulsion self-assembly process to generate three-dimensional microstructure-based high-performance capacitive and piezoresistive pressure sensors for electronic skin applications. Our technique can generate uniformly sized micropores that are self-assembled in an orderly close-packed manner over a large area, which results in high spatial uniformity. The size of the micropores can easily be tuned from 100 to 500 μm, through which sensitivity and dynamic range were controlled as high as 0.86 kPa-1 and up to 100 kPa. Our device can be printed on curvilinear surfaces and be molded into various shapes. We furthermore demonstrate that by simultaneously utilizing capacitive and piezoresistive pressure sensors, we can distinguish between pressure and temperature, or between pressure and proximity. These demonstrations make our process and sensors highly useful for a wide variety of electronic skin applications.

Highly porous and flexible capacitive humidity sensor based on self-assembled graphene oxide sheets on a paper substrate

Abstract: This paper reports the fabrication of capacitive humidity sensors by integrating a graphene oxide sensing layer inside paper substrates. Graphene oxide sheets were self-assembled on the papers’ fibers. A comparative study between several sensors with different concentrations of graphene oxide and different processing times in the graphene oxide suspension is reported. Its aim is to optimize the sensing layer in terms of concentration and thickness towards the fabrication of highly sensitive and porous sensors. The morphology of the fabricated sensors was characterized using scanning electron microscopy, their structure and chemical composition using Raman and infrared spectroscopies. The washability and mechanical strength of the graphene oxide coated paper were tested in water and in an ultrasonic bath. Last, the sensing capabilities of the fabricated devices were tested for a relative humidity ranging from 30% to 90% RH. The optimal sensor is highly porous, hydrophobic and exhibits a good response towards humidity with a low hysteresis. This work presents a low cost alternative for the use of polymers and coated-papers as substrates for flexible electronics. It is also a first step towards the integration of flexible electronics into substrates, which enables the fabrication of highly porous, economical and flexible devices ideal for air flow monitoring, e-dressings and e-textiles.

Miniaturized Low-Profile Circularly Polarized Metasurface Antenna Using Capacitive Loading

Abstract: A miniaturized circularly polarized (CP) metasurface (MS) antenna using capacitive loading is investigated. First, one novel miniaturized MS unit cell is proposed. By introducing a pair of capacitive-loading strips inserted along the diagonal of a corner-truncated patch, 56% size reduction is achieved for this miniaturized unit cell. Accordingly, a compact CP MS antenna of a $4\,\,\times \,\,4$ array composed by the miniaturized unit cells is designed and fed by a slot structure. Compared with the conventional CP MS antenna without capacitive-loading strips, 63% overall size reduction can be achieved. Furthermore, the CP radiation mechanism of the CP MS antenna is revealed and explained clearly using the characteristic mode analysis (CMA). For demonstration, a prototype of the proposed CP antenna was fabricated and measured. The measured 3 dB axial ratio (AR) band is from 3.33 to 3.63 GHz, and the 10 dB impedance band is from 3.02 to 3.82 GHz, while 6.5 dBi gain is realized within the CP operating band.

A New Design Approach to Mitigating the Effect of Parasitics in Capacitive Wireless Power Transfer Systems for Electric Vehicle Charging

Abstract: This paper introduces a new design approach to mitigate the effect of parasitic capacitances and achieve high performance in large air-gap capacitive wireless power transfer (WPT) systems for electric vehicle (EV) charging. In a capacitive WPT system for EVs, the vehicle chassis and roadway introduce multiple parasitic capacitances that can overwhelm the coupling capacitance and severely degrade power transfer and efficiency. The proposed approach addresses this challenge by employing split-inductor matching networks, which allow the complex network of parasitic capacitances to be simplified into an equivalent four-capacitance model. The shunt capacitances of this model are directly utilized as the matching network capacitors, hence, absorbing the parasitic capacitances and eliminating the need for discrete high-voltage capacitors. A systematic procedure is developed to accurately measure the equivalent capacitances of the model, enabling the system’s performance to be reliably predicted. The proposed approach is used to design two 6.78–MHz 12-cm air-gap prototype capacitive WPT systems with capacitor-free matching networks. The first system transfers up to 590 W using 150-cm2 square coupling plates and achieves an efficiency of 88.4%. The second prototype system transfers up to 1217 W using 118-cm2 circular coupling plates, achieving a power transfer density of 51.6 kW/m2. The measured output power profiles of the two systems match well with their predicted counterparts, validating the proposed design approach.

High sensitivity portable capacitive humidity sensor based on In2O3 nanocubes-decorated GO nanosheets and its wearable application in respiration detection

Abstract: Portable humidity sensors fabricated in wearable devices have promising application in disease diagnostics and personal health monitoring. In this work, a capacitive humidity sensor based on indium oxide (In2O3) nanocubes/graphene oxide (GO) nanosheets hybrid film was developed with Cu/Ni electrodes on an epoxy substrate. The In2O3/GO composite was analyzed through XRD, SEM, TEM and XPS for its composition, morphology and structure. The In2O3/GO film sensor was exposed to a wide range of relative humidity and its characteristics of capacitance performance with humidity were found to be better than humidity sensors based on pristine In2O3 or GO in terms of sensitivity, stability, response and recovery times. Meanwhile, a low-cost humidity and respiration monitoring system was developed on a print circuit board (PCB) based on STM32F405RGT6 microcontroller and Android Mobile APP. The curve of humidity and capacitance value can be shown on the smartphone, which can distinguish whether a person is breathing normally. The respiration detector designed holds great potential in the monitoring of asthma and irregular respiratory diseases due to its portability, instantaneity, accuracy and low power consumption.

Bio-Physical Modeling, Characterization, and Optimization of Electro-Quasistatic Human Body Communication

Abstract: Human body communication (HBC) has emerged as an alternative to radio wave communication for connecting low power, miniaturized wearable, and implantable devices in, on, and around the human body. HBC uses the human body as the communication channel between on-body devices. Previous studies characterizing the human body channel has reported widely varying channel response much of which has been attributed to the variation in measurement setup. This calls for the development of a unifying bio-physical model of HBC, supported by in-depth analysis and an understanding of the effect of excitation, termination modality on HBC measurements. This paper characterizes the human body channel up to 1 MHz frequency to evaluate it as a medium for the broadband communication. The communication occurs primarily in the electro-quasistatic (EQS) regime at these frequencies through the subcutaneous tissues. A lumped bio-physical model of HBC is developed, supported by experimental validations that provide insight into some of the key discrepancies found in previous studies. Voltage loss measurements are carried out both with an oscilloscope and a miniaturized wearable prototype to capture the effects of non-common ground. Results show that the channel loss is strongly dependent on the termination impedance at the receiver end, with up to 4 dB variation in average loss for different termination in an oscilloscope and an additional 9 dB channel loss with wearable prototype compared to an oscilloscope measurement. The measured channel response with capacitive termination reduces low-frequency loss and allows flat-band transfer function down to 13 KHz, establishing the human body as a broadband communication channel. Analysis of the measured results and the simulation model shows that instruments with 50 Ω input impedance (Vector Network Analyzer, Spectrum Analyzer) provides pessimistic estimation of channel loss at low frequencies. Instead, high impedance and capacitive termination should be used at the receiver end for accurate voltage mode loss measurements of the HBC channel at low frequencies. The experimentally validated bio-physical model shows that capacitive voltage mode termination can improve the low frequency loss by up to 50 dB, which helps broadband communication significantly.

Hierarchical Porous Carbon Materials Derived from Kelp for Superior Capacitive Applications

Abstract: The lack of high-performance electrode materials is the main factor restricting the breakthrough of capacitive applications. Recently, integrating the advantages of different pore structures to opt...

A transparent stretchable sensor for distinguishable detection of touch and pressure by capacitive and piezoresistive signal transduction

Abstract: Transparent stretchable (TS) sensors capable of detecting and distinguishing touch and pressure inputs are a promising development in wearable electronics. However, realization of such a device has been limited by difficulties in achieving optical transparency, stretchability, high sensitivity, stability, and distinguishable responsivity to two stimuli simultaneously. Herein, we report a TS sensor in which touch and pressure stimuli can be detected and distinguished on a substrate with a stress-relieving three-dimensional (3D) microstructured pattern providing multidirectional stretchability and increased pressure sensitivity. The TS capacitive device structure is a dielectric layer sandwiched between an upper piezoresistive electrode of a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)/ionic liquid composite, which enables touch and pressure stimuli to be distinguished, and a lower electrode of metal/indium tin oxide/metal multilayer. The TS sensor array was demonstrated as a wearable input device for controlling a small vehicle. The TS touch-pressure sensor has great potential to be used as a multimodal input device for future wearable electronics. A 3D-textured material has helped researchers develop a transparent patch that can act as an ergonomic electronic controller. Nae-Eung Lee from Sungkyunkwan University in Suwon, South Korea, and colleagues created a body-attachable touchscreen using an organic polymer that conducts different amounts of electricity depending on how hard it is pressed. After assembling this polymer into a transparent thin-film capacitor, the team encased it in a silicone material with thousands of microscale dimples. Experiments showed that the bumpy coating randomized the effects of mechanical stress effects occurring when the patch was attached to the wrist of human volunteers, extending device lifetime to over 10,000 cycles. The polymer device could electronically distinguish between a light touch and sustained pressure, enabling subjects to steer or accelerate a toy car with just one finger. A transparent stretchable (TS) capacitive sensor, which can detect pressure (force) and touch inputs distinguishably was fabricated by forming with a TS dielectric layer sandwiched between the upper piezoresistive electrode of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)–ionic liquid composite enabling to distinguish touch and pressure stimuli and the lower TS electrode of metal/indium tin oxide/metal multilayer on a transparent elastomeric substrate with stress-relieving three-dimensional microstructured pattern providing multi-directional stretchability and high pressure sensitivity. The TS sensor array demonstrated a good control of the interaction with a small vehicle as a multi-functional input device for future wearable electronics.