Showing papers on "Capacitive sensing published in 2018"

Transparent and flexible fingerprint sensor array with multiplexed detection of tactile pressure and skin temperature.

Abstract: We developed a transparent and flexible, capacitive fingerprint sensor array with multiplexed, simultaneous detection of tactile pressure and finger skin temperature for mobile smart devices. In our approach, networks of hybrid nanostructures using ultra-long metal nanofibers and finer nanowires were formed as transparent, flexible electrodes of a multifunctional sensor array. These sensors exhibited excellent optoelectronic properties and outstanding reliability against mechanical bending. This fingerprint sensor array has a high resolution with good transparency. This sensor offers a capacitance variation ~17 times better than the variation for the same sensor pattern using conventional ITO electrodes. This sensor with the hybrid electrode also operates at high frequencies with negligible degradation in its performance against various noise signals from mobile devices. Furthermore, this fingerprint sensor array can be integrated with all transparent forms of tactile pressure sensors and skin temperature sensors, to enable the detection of a finger pressing on the display. Next-generation mobile security devices require fingerprint sensors that can be incorporated directly into the display. Here, Park et al. demonstrate a highly transparent, multifunctional capacitive fingerprint sensor array that simultaneously detects tactile pressure and finger skin temperature.

An Elastic Autonomous Self-Healing Capacitive Sensor Based on a Dynamic Dual Crosslinked Chemical System

Abstract: Adopting self-healing, robust, and stretchable materials is a promising method to enable next-generation wearable electronic devices, touch screens, and soft robotics. Both elasticity and self-healing are important qualities for substrate materials as they comprise the majority of device components. However, most autonomous self-healing materials reported to date have poor elastic properties, i.e., they possess only modest mechanical strength and recoverability. Here, a substrate material designed is reported based on a combination of dynamic metal-coordinated bonds (β-diketone-europium interaction) and hydrogen bonds together in a multiphase separated network. Importantly, this material is able to undergo self-healing and exhibits excellent elasticity. The polymer network forms a microphase-separated structure and exhibits a high stress at break (≈1.8 MPa) and high fracture strain (≈900%). Additionally, it is observed that the substrate can achieve up to 98% self-healing efficiency after 48 h at 25 °C, without the need of any external stimuli. A stretchable and self-healable dielectric layer is fabricated with a dual-dynamic bonding polymer system and self-healable conductive layers are created using polymer as a matrix for a silver composite. These materials are employed to prepare capacitive sensors to demonstrate a stretchable and self-healable touch pad.

A Highly Sensitive Flexible Capacitive Tactile Sensor with Sparse and High-Aspect-Ratio Microstructures

Abstract: DOI: 10.1002/aelm.201700586 electrical signals.[5] The key parameters that evaluate flexible tactile sensors include sensitivity, response speed, limit of detection (LOD), and reliability. In recent years, various approaches have been investigated to fabricate tactile sensors and improve their performance. There are typically four types of sensing mechanisms for realizing tactile sensors, including piezoresistive,[7–9] capacitive,[10–13] piezoelectric,[14,15] and triboelectric types.[16,17] Capacitive tactile sensors utilize capacitance changes upon external pressure, presenting advantages of simple device construction, fast responding speed, low power consumption, and compact circuit layout, and are thereby widely investigated.[2,18–20] A capacitive tactile sensor typically consists of two parallel plates that sandwich a dielectric layer. The capacitance (C) of a capacitor is determined by the effective area of two electrodes (A), the distance between plate electrodes (d), and the permittivity of dielectric layer (ε),[5] expressed as

A Highly Sensitive Capacitive-Based Soft Pressure Sensor Based on a Conductive Fabric and a Microporous Dielectric Layer

Abstract: DOI: 10.1002/admt.201700237 parallel plate capacitive sensing technology is popular due to signal repeatability, temperature insensitivity, and relative simplicity of design and construction.[34,35] In this approach, when an external force is applied to the soft pressure sensor, the dielectric layer thickness of the sensor varies, which leads to a change in the capacitance of the sensor. However, due to relatively small changes in the capacitance of parallel plate sensors under loading, achievable sensitivities are typically very low.[21] Therefore, most studies focus on the modification of the dielectric layer to increase sensitivity. In this context, efforts toward increased sensitivity can be grouped into two main categories: surface modification of the elastomer layers and the creation of micropores within the dielectric layer. In the first approach, topographical features[36–40] (such as nanoscale pyramids, microstructured line patterns, or micrometer-scale circular pillars) are created on the elastomer surface via surface micromachining methods (such as photolithography and molding). However, It should be noted here that, even though high sensitivity can be achieved using surface micromachining, the working range is typically limited to <10 kPa that is undesirable for most wearable applications. The latter approach focuses on the creation of a porous dielectric layer[41–44] and a recent trend is to use solid particle leaching[44–48] to create micropores within the silicone elastomer. As commercially available sugar cubes and silicone elastomers can be used, manufacturing is quick, simple, and low cost. It has been shown that increased sensitivity over the tactile pressure range was achieved using this method due to the reduced stiffness of the dielectric material as well as increased effective dielectric constant due to the presence of air gaps within the microporous structure. Capacitance values are typically on the order of several femtofarads due to the dielectric layer thickness (height of the sugar cube templates is around 10 mm), but a higher baseline capacitance is needed for sufficient signal-to-noise in the presence of parasitic capacitances within the readout circuitry in these systems. Beside, carbon-based materials,[46] conductive thin films[48] are generally employed to construct electrode layers and are used in combination with the modified dielectric layer for the formation of the soft sensor. However, to integrate these sensors into the system for the creation of wearable electronic devices, the sensors themselves must be flexible, robust, and have mechanically In this paper, the design and manufacturing of a highly sensitive capacitivebased soft pressure sensor for wearable electronics applications are presented. Toward this aim, two types of soft conductive fabrics (knitted and woven), as well as two types of sacrificial particles (sugar granules and salt crystals) to create micropores within the dielectric layer of the capacitive sensor are evaluated, and the combined effects on the sensor’s overall performance are assessed. It is found that a combination of the conductive knit electrode and higher dielectric porosity (generated using the larger sugar granules) yields higher sensitivity (121 × 10−4 kPa−1) due to greater compressibility and the formation of air gaps between silicone elastomer and conductive knit electrode among the other design considerations in this study. As a practical demonstration, the capacitive sensor is embedded into a textile glove for grasp motion monitoring during activities of daily living.

Ultrastretchable Strain Sensors Using Carbon Black-Filled Elastomer Composites and Comparison of Capacitive Versus Resistive Sensors

Abstract: Keywords: strain sensors ; soft robotics ; wearable devices ; carbon black ; silicone elastomers Reference EPFL-ARTICLE-232604 Record created on 2017-11-30, modified on 2017-11-30

Toward Superior Capacitive Energy Storage: Recent Advances in Pore Engineering for Dense Electrodes

Abstract: With the rapid development of mobile electronics and electric vehicles, future electrochemical capacitors (ECs) need to store as much energy as possible in a rather limited space. As the core component of ECs, dense electrodes that have a high volumetric energy density and superior rate capability are the key to achieving improved energy storage. Here, the significance of and recent progress in the high volumetric performance of dense electrodes are presented. Furthermore, dense yet porous electrodes, as the critical precondition for realizing superior electrochemical capacitive energy, have become a scientific challenge and an attractive research focus. From a pore-engineering perspective, insight into the guidelines of engineering the pore size, connectivity, and wettability is provided to design dense electrodes with different porous architectures toward high-performance capacitive energy storage. The current challenges and future opportunities toward dense electrodes are discussed and include the construction of an orderly porous structure with an appropriate gradient, the coupling of pore sizes with the solvated cations and anions, and the design of coupled pores with diverse electrolyte ions.

Capacitive neural network with neuro-transistors.

Abstract: Experimental demonstration of resistive neural networks has been the recent focus of hardware implementation of neuromorphic computing. Capacitive neural networks, which call for novel building blocks, provide an alternative physical embodiment of neural networks featuring a lower static power and a better emulation of neural functionalities. Here, we develop neuro-transistors by integrating dynamic pseudo-memcapacitors as the gates of transistors to produce electronic analogs of the soma and axon of a neuron, with “leaky integrate-and-fire” dynamics augmented by a signal gain on the output. Paired with non-volatile pseudo-memcapacitive synapses, a Hebbian-like learning mechanism is implemented in a capacitive switching network, leading to the observed associative learning. A prototypical fully integrated capacitive neural network is built and used to classify inputs of signals.

A Double-Sided LC-Compensation Circuit for Loosely Coupled Capacitive Power Transfer

Abstract: This paper proposes a double-sided LC -compensation circuit for a loosely coupled, long-distance capacitive power transfer (CPT) system. A CPT system usually contains two pairs of metal plates as the capacitive coupler. An LC -compensation circuit resonates with the coupler to generate high voltages, and corresponding electric fields, to transfer power. When the compensation circuit is used on both the primary and secondary sides, it results in a double-sided LC -compensated CPT system. The working principle and frequency properties of the CPT system are analyzed. The results show a similarity with the series–series-compensated inductive power transfer system, which has both constant-voltage (CV) and constant-current (CC) working modes. LC -compensation is also compared with LCLC -compensation in terms of power, frequency properties, and output efficiency. A 150-W double-sided LC -compensated CPT prototype is designed and implemented to demonstrate a loosely coupled CPT system with 2.16% coupling coefficient. For both CC and CV working modes, the experimental results achieve dc–dc efficiencies higher than 70% across an air-gap distance of 180 mm with a switching frequency of 1.5 MHz.

In Situ High-Level Nitrogen Doping into Carbon Nanospheres and Boosting of Capacitive Charge Storage in Both Anode and Cathode for a High-Energy 4.5 V Full-Carbon Lithium-Ion Capacitor

Abstract: To circumvent the imbalances of electrochemical kinetics and capacity between Li+ storage anodes and capacitive cathodes for lithium-ion capacitors (LICs), we herein demonstrate an efficient solution by boosting the capacitive charge-storage contributions of carbon electrodes to construct a high-performance LIC. Such a strategy is achieved by the in situ and high-level doping of nitrogen atoms into carbon nanospheres (ANCS), which increases the carbon defects and active sites, inducing more rapidly capacitive charge-storage contributions for both Li+ storage anodes and PF6– storage cathodes. High-level nitrogen-doping-induced capacitive enhancement is successfully evidenced by the construction of a symmetric supercapacitor using commercial organic electrolytes. Coupling a pre-lithiated ANCS anode with a fresh ANCS cathode enables a full-carbon LIC with a high operating voltage of 4.5 V and high energy and power densities thereof. The assembled LIC device delivers high energy densities of 206.7 and 115.4 W...

A highly sensitive and flexible capacitive pressure sensor based on a micro-arrayed polydimethylsiloxane dielectric layer

Abstract: A flexible pressure sensor with high sensitivity has been proposed which consists of a typical sandwich structure by integrating a polydimethylsiloxane (PDMS) substrate with a micro-arrayed PDMS dielectric layer. A PDMS flexible substrate coated with silver nanowires (AgNWs) is used as a top/bottom electrode material, and a PDMS dielectric layer with micro-array structure is used to ensure high sensitivity of the pressure sensor. As a result, compared with conventional parallel board capacitive sensors, such sensors exhibit good performance, high sensitivity (2.04 kPa−1) in low pressure ranges (0–2000 Pa), low detection limits (<7 Pa) and fast response times (<100 ms). Furthermore, the integration of the sensor electrode and the dielectric layer ensures good bending stability and cycling stability of the sensor. Flexible capacitive pressure sensors can be used to measure the pressure distribution of finger tips when holding an object and grabbed with fingers. The spatial distribution of the applied pressure can also be clearly identified by fabricating a pressure sensor array. Due to its outstanding performance, the flexible pressure sensor shows bright application prospects in wearable sensing devices, electronic skins and humanoid robotics.

A Two-Plate Capacitive Wireless Power Transfer System for Electric Vehicle Charging Applications

Abstract: This letter proposes a two-plate capacitive wireless power transfer (CPT) system for electric vehicle charging applications. The vehicle chassis and the earth ground are used to transfer power, which can replace two plates in a conventional four-plate CPT system. Therefore, only two external plates are required in the proposed CPT system. The coupling capacitance between the plates allows the current to flow forward to the vehicle side, and the stray capacitance between the chassis and the earth ground provides the current-returning path. After analyzing the working principle of a CPT system, it shows that the voltage on the vehicle chassis can be reduced through switching frequency, the coupler structure design, and the compensation circuit design. Then, a downsized prototype is implemented to validate the proposed system, in which two inductors are used to compensate the capacitive coupler. Experimental results show that the prototype achieves 350-W power transfer with 74.1% dc–dc efficiency over an air-gap distance of 110 mm, and the RMS voltage on vehicle chassis is limited to 132 V.

Six-Plate Capacitive Coupler to Reduce Electric Field Emission in Large Air-Gap Capacitive Power Transfer

Abstract: This paper proposes a six-plate capacitive coupler for large air-gap capacitive power transfer to reduce electric field emissions to the surrounding environment. Compared to the conventional four-plate horizontal structure, the six-plate coupler contains two additional plates above and below the inner four-plate coupler to provide a shielding effect. Since there is a capacitive coupling between every two plates, the six-plate coupler results in a circuit model consisting of 15 coupling capacitors. This complex model is first simplified to an equivalent three-port circuit model, and then to a two-port circuit model which is used in circuit analysis and parameter design. This six-plate coupler can eliminate the external parallel capacitor in the previous LCLC topology, which results in the LCL compensation and reduces the system cost. Due to the symmetry of the coupler structure, the voltage between shielding plates is limited, which reduces electric field emissions. Finite element analysis by Maxwell is used to simulate the coupling capacitors and electric field distribution. Compared to the four-plate horizontal and vertical structures, the six-plate coupler can significantly reduce electric field emissions and expand the safety area from 0.9 to 0.1 m away from the coupler in the well-aligned case. A 1.97 kW prototype is implemented to validate the six-plate coupler, which achieves a power density of 1.95 kW/m2 and a dc–dc efficiency of 91.6% at an air-gap of 150 mm. Experiments also show that the output power maintains 65% of the well-aligned value at 300 mm X misalignment, and 49% at 300 mm Y misalignment.

Highly sensitive and selective SO2 MOF sensor: the integration of MFM-300 MOF as a sensitive layer on a capacitive interdigitated electrode

Abstract: We report on the fabrication of an advanced chemical capacitive sensor for the detection of sulfur dioxide (SO2) at room temperature. The sensing layer based on an indium metal–organic framework (MOF), namely MFM-300, is coated solvothermally on a functionalized capacitive interdigitated electrode. The fabricated sensor exhibits significant detection sensitivity to SO2 at concentrations down to 75 ppb, with the lower detection limit estimated to be around 5 ppb. The MFM-300 MOF sensor demonstrates highly desirable detection selectivity towards SO2vs. CH4, CO2, NO2 and H2, as well as an outstanding SO2 sensing stability.

Transparent, Flexible, Conformal Capacitive Pressure Sensors with Nanoparticles

Abstract: The fundamental challenge in designing transparent pressure sensors is the ideal combination of high optical transparency and high pressure sensitivity. Satisfying these competing demands is commonly achieved by a compromise between the transparency and usage of a patterned dielectric surface, which increases pressure sensitivity, but decreases transparency. Herein, a design strategy for fabricating high-transparency and high-sensitivity capacitive pressure sensors is proposed, which relies on the multiple states of nanoparticle dispersity resulting in enhanced surface roughness and light transmittance. We utilize two nanoparticle dispersion states on a surface: (i) homogeneous dispersion, where each nanoparticle (≈500 nm) with a size comparable to the visible light wavelength has low light scattering; and (ii) heterogeneous dispersion, where aggregated nanoparticles form a micrometer-sized feature, increasing pressure sensitivity. This approach is experimentally verified using a nanoparticle-dispersed polymer composite, which has high pressure sensitivity (1.0 kPa-1 ), and demonstrates excellent transparency (>95%). We demonstrate that the integration of nanoparticle-dispersed capacitor elements into an array readily yields a real-time pressure monitoring application and a fully functional touch device capable of acting as a pressure sensor-based input device, thereby opening up new avenues to establish processing techniques that are effective on the nanoscale yet applicable to macroscopic processing.

Carbon Nanofiber versus Graphene-Based Stretchable Capacitive Touch Sensors for Artificial Electronic Skin.

Abstract: Stretchable capacitive devices are instrumental for new-generation multifunctional haptic technologies particularly suited for soft robotics and electronic skin applications. A majority of elongating soft electronics still rely on silicone for building devices or sensors by multiple-step replication. In this study, fabrication of a reliable elongating parallel-plate capacitive touch sensor, using nitrile rubber gloves as templates, is demonstrated. Spray coating both sides of a rubber piece cut out of a glove with a conductive polymer suspension carrying dispersed carbon nanofibers (CnFs) or graphene nanoplatelets (GnPs) is sufficient for making electrodes with low sheet resistance values (≈10 Ω sq-1). The electrodes based on CnFs maintain their conductivity up to 100% elongation whereas the GnPs-based ones form cracks before 60% elongation. However, both electrodes are reliable under elongation levels associated with human joints motility (≈20%). Strikingly, structural damages due to repeated elongation/recovery cycles could be healed through annealing. Haptic sensing characteristics of a stretchable capacitive device by wrapping it around the fingertip of a robotic hand (ICub) are demonstrated. Tactile forces as low as 0.03 N and as high as 5 N can be easily sensed by the device under elongation or over curvilinear surfaces.

Polyimide-Based Capacitive Humidity Sensor.

Abstract: The development of humidity sensors with simple transduction principles attracts considerable interest by both scientific researchers and industrial companies. Capacitive humidity sensors, based on polyimide sensing material with different thickness and surface morphologies, are prepared. The surface morphology of the sensing layer is varied from flat to rough and then to nanostructure called nanograss by using an oxygen plasma etch process. The relative humidity (RH) sensor selectively responds to the presence of water vapor by a capacitance change. The interaction between polyimide and water molecules is studied by FTIR spectroscopy. The complete characterization of the prepared capacitive humidity sensor performance is realized using a gas mixing setup and an evaluation kit. A linear correlation is found between the measured capacitance and the RH level in the range of 5 to 85%. The morphology of the humidity sensing layer is revealed as an important parameter influencing the sensor performance. It is proved that a nanograss-like structure is the most effective for detecting RH, due to its rapid response and recovery times, which are comparable to or even better than the ones of commercial polymer-based sensors. This work demonstrates the readiness of the developed RH sensor technology for industrialization.

Flexible, Transparent, Sensitive, and Crosstalk-Free Capacitive Tactile Sensor Array Based on Graphene Electrodes and Air Dielectric

Abstract: The development of sensitive, flexible, and transparent tactile sensors is of great interest for next-generation flexible displays and human–machine interfaces. Although a few materials and structural designs have been previously developed for high-performance tactile sensors, achieving flexibility, full transparency, and highly sensitive multipoint recognition without crosstalk remains a significant challenge for such systems. This work demonstrates a capacitive tactile sensor composed of two sets of facing graphene electrodes separated by spacers, which forms an air dielectric between them. The air gap facilitates more effective deformation of the top graphene electrode under pressure compared to typical elastomer dielectrics, resulting in a high sensitivity of 6.55% kPa−1 and a fast response time of ≈70 ms. Taking advantage of the remarkable properties of graphene for electrode usage, the tactile sensor presents sufficient transparency (over 70% at 550 nm) as well as excellent electrical and mechanical flexibility for 500 cycles at a bending radius of 8 mm. Simulated and experimental results validate that the isolation of each tactile cell by the spacers allows the pixelated sensor array to recognize the spatial distribution of applied pressure without crosstalk. The proposed sensor would be a promising candidate for tactile sensing components that require both flexibility and transparency.

Enhanced-Selectivity High-Linearity Low-Noise Mixer-First Receiver With Complex Pole Pair Due to Capacitive Positive Feedback

Abstract: A mixer-first receiver (RX) with enhanced selectivity and high dynamic range is proposed, targeting to remove surface acoustic-wave-filters in mobile phones and cover all frequency bands up to 6 GHz. Capacitive negative feedback across the baseband (BB) amplifier serves as a blocker bypassing path, while an extra capacitive positive feedback path offers further blocker rejection. This combination of feedback paths synthesizes a complex pole pair at the input of the BB amplifier, which is upconverted to the RF port to obtain steeper RF bandpass filter roll-off and reduced distortion. This paper explains the circuit principle and analyzes RX performance. A prototype chip fabricated in 45-nm partially depleted silicon on insulator (SOI) technology achieves high out-of-band linearity (input-referred third-order intercept point (IIP3) = 39 dBm and input-referred second-order intercept point (IIP2) = 88 dB) combined with sub-3-dB noise figure. Desensitization due to a 0-dBm blocker is only 2.2 dB at 1.4 GHz.

An Inductive and Capacitive Combined Parallel Transmission of Power and Data for Wireless Power Transfer Systems

Abstract: A new parallel transmission method of power and data is proposed for peer-to-peer wireless power transfer (WPT) systems. Essentially, data are modulated and transferred via high-frequency electric field generated by the parasitic capacitances of the coupling coils and the metal shield plates, while power is transferred through relatively low-frequency magnetic field generated by the coupling coils. Coupling structure and operation principle are illustrated and analyzed. Besides, the signal to noisy ratio performance is studied and optimized. With the proposed method, a 40 W prototype is built and the data transmission rate reaches 230 kbps. Experimental results have verified that the proposed method is valid and has the advantages of good flexibility and large spatial position offset redundancy. Because the method does not do any modification on the main circuit of the WPT system, it also has advantages of low cost and easy to implement.

Resonant wave energy harvester based on dielectric elastomer generator

Abstract: Dielectric elastomer generators (DEGs) are a class of capacitive solid-state devices that employ highly stretchable dielectrics and conductors to convert mechanical energy into high-voltage direct-current electricity Their promising performance in terms of convertible energy and power density has been mostly proven in quasi-static experimental tests with prescribed deformation However, the assessment of their ability in harvesting energy from a dynamic oscillating source of mechanical energy is crucial to demonstrate their effectiveness in practical applications This paper reports a first demonstration of a DEG system that is able to convert the oscillating energy carried by water waves into electricity A DEG prototype is built using a commercial polyacrylate film (VHB 4905 by 3M) and an experimental campaign is conducted in a wave-flume facility, ie an artificial basin that makes it possible to generate programmed small-scale waves at different frequencies and amplitudes In resonant conditions, the designed system demonstrates the delivery of a maximum of 087 W of electrical power output and 064 J energy generated per cycle, with corresponding densities per unit mass of dielectric elastomer of 197 W kg−1 and 145 J kg−1 Additionally, a notable maximum fraction of 18% of the input wave energy is converted into electricity The presented results provide a promising demonstration of the operation and effectiveness of ocean wave energy converters based on elastic capacitive generators

3D printed mould-based graphite/PDMS sensor for low-force applications

Abstract: This paper concerns the design, fabrication and characterization of graphite/PDMS sensors for low-force sensing applications. Exploiting the design flexibility of 3D printing, moulds of specific dimensions were prepared onto which graphite powder and PDMS were cast, to develop sensor patches. The sensor patches were highly flexible with repeatable responses to iterative bending cycles. The patches were tested in terms of stretchability, strain and bending-cycle responses. The sensor patches had interdigitated electrodes operating on capacitive sensing, where the effective capacitance changes with an applied force because of changes in their dimensions. Forces ranging from 3.5 mN to 17.5 mN were applied to determine the capability of these sensor patches for low-force sensing applications. The sensor patches had a quick recovery having a sensitivity and SNR per unit force of 0.2542 pF mN−1 and 10.86 respectively. The patches were capable of differentiating the forces applied on them, when they were attached to different objects in daily use.

Effect of interdigital electrode gap on the performance of SnO2-modified MoS2 capacitive humidity sensor

Abstract: To improve the sensitivity of humidity sensors, the interdigital electrode size should be paid more attention, apart from the development of high performance sensing materials. This paper investigated the interaction between testing electrode and the performance of capacitive humidity sensor. To our best knowledge, no other reported papers have investigated it before. We found that the gap size of interdigital electrode had crucial influence on the response of SnO2/MoS2 based capacitive humidity sensors due to the different surface electrical conduction mechanisms. For the sensor with small gap interdigital electrode structure, the capacitance decreases exponentially as relative humidity (RH) rises so that high sensitivity is obtained at low humidity range (0%–45% RH). While the gap is wide enough, the capacitance increases exponentially as RH grows to get ultrahigh sensitivity at high humidity range (45%–90% RH). The experimental results show that the sensor with 5 μm gap have the largest sensitivity (161 μF/% RH) at low humidity range while the best sensitivity of 3170 pF/% RH is obtained at high humidity range for the sensor with gap of 100 μm. The as-prepared SnO2/MoS2 hybrid sensing nanocomposite was synthesized through a two-step hydrothermal route and its morphology and structure were further characterized using field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD). Moreover, the SnO2/MoS2 based capacitive humidity sensors have fast response, short recovery time, little hysteresis and good repeatability.

Textile-Based, Interdigital, Capacitive, Soft-Strain Sensor for Wearable Applications.

Abstract: The electronic textile area has gained considerable attention due to its implementation of wearable devices, and soft sensors are the main components of these systems. In this paper, a new sensor design is presented to create stretchable, capacitance-based strain sensors for human motion tracking. This involves the use of stretchable, conductive-knit fabric within the silicone elastomer matrix, as interdigitated electrodes. While conductive fabric creates a secure conductive network for electrodes, a silicone-based matrix provides encapsulation and dimensional-stability to the structure. During the benchtop characterization, sensors show linear output, i.e., R² = 0.997, with high response time, i.e., 50 ms, and high resolution, i.e., 1.36%. Finally, movement of the knee joint during the different scenarios was successfully recorded.

Spatio-temporal analysis of the electron power absorption in electropositive capacitive RF plasmas based on moments of the Boltzmann equation

Abstract: Power absorption by electrons from the spaceand time-dependent electric field represents the basic sustaining mechanism of all radio-frequency driven plasmas. This complex phenomenon has attracted significant attention. However, most theories and models are, so far, only able to account for part of the relevant mechanisms. The aim of this work is to present an in-depth analysis of the power absorption by electrons, via the use of a moment analysis of the Boltzmann equation without any ad-hoc assumptions. This analysis, for which the input quantities are taken from kinetic, particle based simulations, allows the identification of all physical mechanisms involved and an accurate quantification of their contributions. The perfect agreement between the sum of these contributions and the simulation results verifies the completeness of the model. We study the relative importance of these mechanisms as a function of pressure, with high spatial and temporal resolution, in an electropositive argon discharge. In contrast to some widely accepted previous models we find that high spaceand time-dependent ambipolar electric fields outside the sheaths play a key role for electron power absorption. This ambipolar field is timedependent within the RF period and temporally asymmetric, i.e., the sheath expansion is not a ‘mirror image’ of the sheath collapse. We demonstrate that this time-dependence is mainly caused by a time modulation of the electron temperature resulting from the energy transfer to electrons by the ambipolar field itself during sheath expansion. We provide a theoretical proof that this ambipolar electron power absorption would vanish completely, if the electron temperature was constant in time. This mechanism of electron power absorption is based on a time modulated electron temperature, markedly different from the Hard Wall Model, of key importance for energy transfer to electrons on time average and, thus, essential for the generation of capacitively coupled plasmas. Supplementary material for this article is available online

Fabrication and characterization of bending and pressure sensors for a soft prosthetic hand

Abstract: We demonstrate fabrication, characterization, and implementation of 'soft-matter' pressure and bending sensors for a soft robotic hand. The elastomer-based sensors are embedded in a robot finger composed of a 3D printed endoskeleton and covered by an elastomeric skin. Two types of sensors are evaluated, resistive pressure sensors and capacitive pressure sensors. The sensor is fabricated entirely out of insulating and conductive rubber, the latter composed of polydimethylsiloxane (PDMS) elastomer embedded with a percolating network of structured carbon black (CB). The sensor-integrated fingers have a simple materials architecture, can be fabricated with standard rapid prototyping methods, and are inexpensive to produce. When incorporated into a robotic hand, the CB–PDMS sensors and PDMS carrier medium function as an 'artificial skin' for touch and bend detection. Results show improved response with a capacitive sensor architecture, which, unlike a resistive sensor, is robust to electromechanical hysteresis, creep, and drift in the CB–PDMS composite. The sensorized fingers are integrated in an anthropomorphic hand and results for a variety of grasping tasks are presented.

Modeling and Experimental Validation of a Capacitive Link for Wireless Power Transfer to Biomedical Implants

Abstract: This brief reports on the modeling and experimental validation of a capacitive link as an emerging strategy for wireless power transfer to biomedical implants. The capacitive link comprises two pairs of coated parallel plates that are placed at a distance of ${L}$ apart, with a tissue layer acting as the dielectric material. A series-resonant structure is then formed by placing two inductors in series with the capacitive link. A comprehensive circuit model is proposed that accounts for the ${L}$ -dependent, parasitic, cross-coupled, and longitudinal resistive elements contributed by the tissue between the two pairs. The series-resonant capacitive link is also realized with 400-mm $^{2}$ capacitive pads on printed-circuit boards that are coated with a 1- $\mu \text{m}$ -thick layer of Parylene- ${N}$ , aligned around a 5-mm-thick tissue layer, and placed in series with two 100- $\mu \text{H}$ inductors, resulting in resonance frequencies of ~115 and 127 kHz. At an operation frequency of 120 kHz and over a wide range of load resistance from $10~\Omega $ to 100 $\text{k}\Omega $ , the effect of ${L}$ on the power delivered to the load and power transfer efficiency parameters of the link is measured from 2 cm to $\infty $ and shown to be in very good agreement with simulation results from the related circuit model.