Showing papers on "Capacitive sensing published in 2014"

Solid‐State Supercapacitor Based on Activated Carbon Cloths Exhibits Excellent Rate Capability

Abstract: Activated carbon cloth is used as an electrode, achieving an excellent areal capacitance of 88 mF/cm(2) (8.8 mF/g) without the use of any other capacitive materials. Significantly, when it is incorporated as part of a symmetric solid-state supercapacitor device, a remarkable charge/discharge rate capability is observed; 50% of the capacitance is retained when the charging rate increases from 10 to 10,000 mV/s.

Tunable Flexible Pressure Sensors using Microstructured Elastomer Geometries for Intuitive Electronics

Abstract: Pressure and touch sensitivity is crucial for intuitive human-machine interfaces Here, we investigate the use of different microstructured elastomers for use as dielectric material in capacitive pressure sensors We use finite element modeling to simulate how different microstructures can reduce the effective mechanical modulus We found that pyramidal structures are optimal shapes that reduce the effective mechanical modulus of the elastomer by an order of magnitude We also investigate the dependence of spacing of the pyramidal microstructures and how it impacts mechanical sensitivity We further demonstrate the use of these elastomeric microstructures as the dielectric material on a variety of flexible and stretchable substrates to capture touch information in order to enable large area human-computer interfaces for next generation input devices, as well as continuous health-monitoring sensors

Flexible Three‐Axial Force Sensor for Soft and Highly Sensitive Artificial Touch

Abstract: using liquid capacitors to address deformability. Here we show the fast and easy fabrication of a fully fl exible capacitive three-axial force sensor made with conductive fabric electrodes and an elastomeric material. This unique sensor presented a high com-pliance, robustness and stability under manipulation and very appealing performances in terms of sensitivity (less than 10 mg and 8 µm, minimal detectable weight and displacement, respec-tively) and detection range (measured up to 190 kPa, and esti-mated up to 400 kPa) against the existing state-of-the-art sensors. This work intersects with the recent and exciting direction taken by the research fi eld towards smart, integrated, and fl exible elec-tronic devices using an ancestral composite material: textile.

Capacitive Epidermal Electronics for Electrically Safe, Long-Term Electrophysiological Measurements

Abstract: Integration of capacitive sensing capabilities to epidermal electronic systems (EES) can enhance the robustness in operation for electrophysiological signal measurement. Capacitive EES designs are reusable, electrically safe, and minimally sensitive to motion artifacts. Experiments on human subjects illustrate levels of fidelity in ECG, EMG, and EOG recordings comparable to those of standard gel electrodes and of direct contact EES electrodes.

Carbon flow electrodes for continuous operation of capacitive deionization and capacitive mixing energy generation

Abstract: Capacitive technologies, such as capacitive deionization and energy harvesting based on mixing energy (“capmix” and “CO2 energy”), are characterized by intermittent operation: phases of ion electrosorption from the water are followed by system regeneration. From a system application point of view, continuous operation has many advantages, to optimize performance, to simplify system operation, and ultimately to lower costs. In our study, we investigate as a step towards second generation capacitive technologies the potential of continuous operation of capacitive deionization and energy harvesting devices, enabled by carbon flow electrodes using a suspension based on conventional activated carbon powders. We show how the water residence time and mass loading of carbon in the suspension influence system performance. The efficiency and kinetics of the continuous salt removal process can be improved by optimizing device operation, without using less common or highly elaborate novel materials. We demonstrate, for the first time, continuous energy generation via capacitive mixing technology using differences in water salinity, and differences in gas phase CO2 concentration. Using a novel design of cylindrical ion exchange membranes serving as flow channels, we continuously extract energy from available concentration differences that otherwise would remain unused. These results may contribute to establishing a sustainable energy strategy when implementing energy extraction for sources such as CO2-emissions from power plants based on fossil fuels.

Electrostatic vibration energy harvester with combined effect of electrical nonlinearities and mechanical impact

Abstract: This paper presents an advanced study including the design, characterization and theoretical analysis of a capacitive vibration energy harvester. Although based on a resonant electromechanical device, it is intended for operation in a wide frequency band due to the combination of stop-end effects and a strong biasing electrical field. The electrostatic transducer has an interdigited comb geometry with in-plane motion, and is obtained through a simple batch process using two masks. A continuous conditioning circuit is used for the characterization of the transducer. A nonlinear model of the coupled system ‘transduce-conditioning circuit’ is presented and analyzed employing two different semi-analytical techniques together with precise numerical modelling. Experimental results are in good agreement with results obtained from numerical modelling. With the 1 g amplitude of harmonic external acceleration at atmospheric pressure, the system transducer-conditioning circuit has a half-power bandwidth of more than 30% and converts more than 2 μ Wo f the power of input mechanical vibrations over the range of 140 and 160 Hz. The harvester has also been characterized under stochastic noise-like input vibrations.

A self-calibration water level measurement using an interdigital capacitive sensor

Abstract: A water level measurement using an interdigital capacitive sensor with low-cost, low-energy, good repeatability, high linearity, and ease of installation is proposed with a support of experimental results. This sensor comprises a printed circuit board (PCB) with configuration of two interpenetrating comb electrodes. The comb electrode is 70–80 mm width, 300 mm height with 1–2 mm spacing between each comb. This configuration of electrode causes the capacitance between comb electrodes to vary by the water level. Microcontroller is used to calculate the capacitance between comb electrodes in terms of a discharge time correlated to the water level. A practical water level measurement technique using two comb electrodes designated as level and reference sensors is presented. This technique can directly be applied to water with different conditions without recalibration. This sensor is able to measure absolute levels of water with 0.2 cm resolution over 30 cm range. In addition, it is also sensitive enough to trace the variability of water level. A flood monitoring simulation is carried out in wave flume where this sensor is used to detect the rising wave.

Calibrated complex impedance and permittivity measurements with scanning microwave microscopy.

Abstract: We present a procedure for calibrated complex impedance measurements and dielectric quantification with scanning microwave microscopy. The calibration procedure works in situ directly on the substrate with the specimen of interest and does not require any specific calibration sample. In the workflow tip‐sample approach curves are used to extract calibrated complex impedance values and to convert measured S11 reflection signals into sample capacitance and resistance images. The dielectric constant of thin dielectric SiO2 films were determined from the capacitance images and approach curves using appropriate electrical tip‐sample models and the"r value extracted at fD 19:81 GHz is in good agreement with the nominal value of"r 4. The capacitive and resistive material properties of a doped Si semiconductor sample were studied at different doping densities and tip‐sample bias voltages. Following a simple serial model the capacitance‐voltage spectroscopy curves are clearly related to the semiconductor depletion zone while the resistivity is rising with falling dopant density from 20 to 20 k. The proposed procedure of calibrated complex impedance measurements is simple and fast and the accuracy of the results is not affected by varying stray capacitances. It works for nanoscale samples on either fully dielectric or highly conductive substrates at frequencies between 1 and 20 GHz.

Aerodynamic Fluid Bearings for Translational and Rotating Capacitors in Noncontact Capacitive Power Transfer Systems

Abstract: Wireless power transfer (WPT) is commonly accomplished with magnetic (inductive) techniques for a wide range of applications. Electrostatic or capacitive power transfer (CPT) approaches to WPT have had limited exposure primarily due to lower achievable power density when compared to inductive WPT techniques. Recently, high-frequency (in kilohertz to megahertz) power electronics have reintroduced capacitive techniques as an option for WPT over short distances ( <; 2 mm) for applications such as slip ring replacement. To further the practicality of CPT, capacitive coupling must be maximized in an effective manner, i.e., the volumetric capacitance density of rotating/translational capacitors must be significantly increased. This paper proposes the use of aerodynamic fluid bearings to maximize capacitive coupling between stationary and moving surfaces, by minimizing their separation distance, allowing for greater surface area per unit volume. The technique allows micrometers of separation distance between moving surfaces while maintaining manufacturability and mechanical robustness. Coupling capacitance is increased up to 100 times greater than rigid plate rotating and translational CPT systems. Additional benefits include the estimation of mechanical system parameters such as speed. Operational characteristics and design highlights are presented and corroborated with experimental results for general slip ring replacement applications.

Design and characterization of a low thermal drift capacitive humidity sensor by inkjet-printing

Abstract: Small, low-cost and flexible humidity sensors were designed, fabricated by using an inkjet-printing process, and fully characterized. Based on the principles of the capacitor and the ability of a polyimide to absorb humidity, the sensor was fabricated by printing silver interdigitated electrodes on a thin polyimide film of 75 μm thickness. After modeling, the total area of the printed sensor was optimized to be 11.65 mm 2 . A relative humidity sensitivity of 4.5 fF/%RH and a thermal coefficient of −0.4 fF/°C were measured at 100 kHz, whereas the sensitivity and the thermal coefficient were 4.2 fF/%RH and −0.21 fF/°C, respectively, at 1 MHz. This latter result implies that it could not be necessary to include thermal compensation to use this sensor depending on the required accuracy and the chosen frequency. This work shows a reliable, fast, simple and low-cost manufacturing process to make small humidity sensors with low thermal drift and high temporal stability. These sensors could be easily integrated into inkjet-printed RFID tags for monitoring of environmental humidity in diverse applications.

Iontronic microdroplet array for flexible ultrasensitive tactile sensing

Abstract: An iontronic microdroplet array (IMA) device, using an ultra-large interfacial capacitance at the highly elastic droplet–electrode contact, has been proposed for flexible tactile sensing applications. The transparent IMA sensors consist of an array of nanoliter droplets sandwiched between two polymeric membranes with patterned transparent electrodes, forming the electrical double layers with remarkable unit-area capacitance. Under external loading, the membrane deformation results in the circumferential expansion at the highly elastic droplet–electrode contact, which offers a completely new capacitive sensing scheme with a dramatic increase in sensitivity. Under the simple device architecture, the IMA has achieved device sensitivity of 0.43 nF kPa−1 and a minimal detectable pressure of 33 Pa, the highest reported values for its dimension. In addition, the hysteresis of the droplet deformation has been reduced by introducing a layer of hydrophobic coating to the conductive electrode surface, ensuring a fast mechanical response (on the order of several milliseconds). To demonstrate the utility of the transparent flexible IMA sensor, it has been successfully mounted onto a fingertip setting to map different surface topologies and embedded into a wristband to resolve dynamic pressure waves throughout cardiovascular cycles.

Polarity control for remote plasma

Abstract: Methods of controlling the polarity of capacitive plasma power applied to a remote plasma are described. Rather than applying a plasma power which involves both a positive and negative voltage swings equally, a capacitive plasma power is applied which favors either positive or negative voltage swings in order to select desirable process attributes. For example, the plasma power may be formed by applying a unipolar oscillating voltage between an electrode and a perforated plate. The unipolar oscillating voltage may have only positive or only negative voltages between the electrode and the perforated plate. The unipolar oscillating voltage may cross electrical ground in some portion of its oscillating voltage.

Dual functional transparent film for proximity and pressure sensing

Abstract: Over the past few years, the rapid development of tactile sensing technology has contributed significantly to the realization of intuitional touch control and intelligent human-machine interaction. Apart from physical touch or pressure sensing, proximity sensing as a complementary function can extend the detection mode of common single functional tactile sensors. In this work, we present a transparent, matrix-structure dual functional capacitive sensor which integrates the capability of proximity and pressure sensing in one device, and the excellent spatial resolution offered by the isolated response of capacitive pixels enables us to realize precise location identification of approaching objects and loaded pressure with fast response, high stability and high reversibility.

Analytical Modeling of Graphene Ribbons as Optical Circuit Elements

Abstract: We demonstrate that graphene ribbons can be modeled as circuit elements, which have dual capacitive-inductive nature. In the subwavelength regime, the surface current density on a single graphene ribbon subject to an incident p-polarized plane wave is derived analytically and then it is extended to coplanar arrays of graphene ribbons by applying perturbation theory. It is demonstrated that even isolated graphene ribbons have capacitive properties and the interaction between them in an array only changes the capacitance. Finally, we propose an accurate circuit model for the ribbon array by applying appropriate boundary conditions.

Improved Split-Ring Resonator for Microfluidic Sensing

Abstract: We present a method of making low-loss split-ring resonators (SRRs) for microfluidic sensing at microwave frequencies using silver-coated copper wire We show that a simple geometric modification and the use of square cross-section wire give greater electric field confinement in the capacitive region of the resonant sensor We use a combination of theoretical analysis, finite-element simulations, and empirical measurements to demonstrate the subsequent increases in the sensitivity of these SRRs for complex permittivity measurements of some common solvents

Using Thick Substrates and Capacitive Probe Compensation to Enhance the Bandwidth of Traditional CP Patch Antennas

Abstract: The simplicity and intuitive design of traditional circularly polarized (CP) patch antennas, such as the truncated corner patch antenna, has led to their widespread popularity. However, they are limited to a narrowband performance on the order of 0.1%-2% for simultaneously good S11 and axial ratio (AR). We will prove theoretically that this is a direct result of the probe reactance hindering the use of thicker substrates to increase the bandwidth. Furthermore, we propose a novel compensation technique to enhance the bandwidth capabilities of these CP patch antennas. Our method inserts a capacitive element, such as an annular gap or parallel plate, in series with the probe inductance to remove its effect. We demonstrate this technique with simulations and measurements to obtain AR- S11 bandwidth capabilities as high as 12.6%. To the authors' best knowledge, this is the first time that capacitive compensation and thick substrates have been jointly employed to enable broadband CP patch antennas.

Signal strength enhancement in a biometric sensor array

Abstract: A biometric imager may comprise a plurality of sensor element traces formed in or on a sensor substrate which may comprise at least a portion of a display screen defining a biometric sensing area and forming in-active pixel locations; an auxiliary active circuit formed in or on the sensor substrate on the periphery of the biometric sensing area and in direct or indirect electrical contact with the sensor element traces; and providing a signal processing interface to a remotely located controller integrated circuit. The sensor element traces may form a portion of one dimensional linear sensor array or pixel locations in a two dimensional grid array capacitive gap biometric imaging sensor. The auxiliary circuit may provide pixel location selection or pixel signal amplification. The auxiliary circuit may be mounted on a surface of the display screen. The auxiliary circuit further comprising a separate pixel location selection controller circuit.

A Robust ISFET pH-Measuring Front-End for Chemical Reaction Monitoring

Abstract: This paper presents a robust, low-power and compact ion-sensitive field-effect transistor (ISFET) sensing front-end for pH reaction monitoring using unmodified CMOS. Robustness is achieved by overcoming problems of DC offset due to trapped charge and transcoductance reduction due to capacitive division, which commonly exist with implementation of ISFETs in CMOS. Through direct feedback to the floating gate and a low-leakage switching scheme, all the unwanted factors are eliminated while the output is capable of tracking a pH reaction which occurs at the sensing surface. This is confirmed through measured results of multiple devices of different sensing areas, achieving a mean amplification of 1.28 over all fabricated devices and pH sensitivity of 42.1 mV/pH. The front-end is also capable of compensating for accumulated drift using the designed switching scheme by resetting the floating gate voltage. The circuit has been implemented in a commercially-available 0.35 $\mu$ m CMOS technology achieving a combined chemical and electrical output RMS noise of 3.1 mV at a power consumption of 848.1 nW which is capable of detecting pH changes as small as 0.06 pH.

Modulated power supply for reduced parasitic capacitance

Abstract: An input device comprising a display device having an integrated capacitive sensing device. The input device includes a plurality of sensor electrodes a plurality of display electrodes, a modulated power supply configured to provide a modulated reference signal, and a processing system. The processing system includes a sensor module configured to drive a plurality of sensor electrodes with a modulated capacitive sensing signal that is based on the modulated reference signal for capacitive sensing during a first time period. The processing system also includes a display driver module configured to drive a plurality of display electrodes of a display device with modulated signals based on the modulated reference signal during the first time period. The modulated signals cause voltage between the plurality of display electrodes and the plurality of sensor electrodes to remain substantially constant.

A Review on Capacitive-Type Sensor for Measurement of Height of Liquid Level

Abstract: The capacitive sensors are used in a variety of industrial and automotive application. A capacitive sensor converts a change in position, or properties of dielectric material into an electrical sig...

12.6 A 160nW 63.9fJ/conversion-step capacitance-to-digital converter for ultra-low-power wireless sensor nodes

Abstract: Recent advances in nW-level wireless sensor nodes have created opportunities in emerging applications such as bio-implantable telemetry, smart healthcare, and environmental monitoring [1]. At the same time, there are many circuit and system design challenges to achieving high functionality in such ultra-low-power microsystems. One of the key sensing modalities in these systems is capacitive sensing. With zero static current during signal readout, capacitive sensing is well suited to ultra-low-power microsystems and has been widely adopted in the sensing of pressure [2,3], displacement [4], and humidity [5].

Control of Inverters Via a Virtual Capacitor to Achieve Capacitive Output Impedance

Abstract: Mainstream inverters have inductive output impedance at low frequencies (such inverters are called L-inverters). In this paper, a control strategy is proposed to make the output impedance of an inverter capacitive at low frequencies (such inverters are called C-inverters). The proposed control strategy involves the feedback of the inductor current through an integrator, which is actually the impedance of a virtual capacitor. The gain of the integrator or the virtual capacitance is first selected to guarantee the stability of the current feedback loop and then optimized to minimize the total harmonic distortion (THD) of the output voltage. Moreover, some guidelines are developed to facilitate the selection of the filter components for C-inverters. Simulation and experimental results are provided to demonstrate the feasibility and excellent performance of C-inverters, with the filter parameters of the test rig selected according to the guidelines developed. It is shown that, with the same hardware, the lowest voltage THD is obtained when the inverter is designed to be a C-inverter. A by product of this study is that, as long as the current ripples are kept within the desired range, the filter inductor should be chosen as small as possible in order to reduce voltage harmonics. This helps reduce the size, weight, and volume of the inductor and improve the power density of the inverter.

A novel electrode structure compared with interdigitated electrodes as capacitive sensor

Abstract: Serpentine structure is a novel electrode structure presented in this work. It consists of a combination of meandering and interdigitated electrodes in a single structure with the aim of improving the transduction sensitivity. Capacitors based on this structure, known as serpentine, have been numerically simulated, comparing their capacitance with the interdigitated electrode structure. Simulation results show a bigger capacitance in the serpentine structures than in the interdigitated ones, enhanced for increasing number of fingers. Theoretical calculations agree with results obtained from the experimental characterization of inkjet-printed serpentine and interdigitated structures used as humidity capacitive sensors. We have measured an increase of 28% in humidity sensitivity with capacitors of the same area. Other sensor characteristics such as dynamic response, hysteresis and time drift remained unchanged for both capacitive structures. As this novel serpentine electrode structure presents a bigger geometrical capacitance factor compared to the interdigitated capacitor, in our opinion, it will be a promising base structure for multiple applications in the field of signal transduction.

A High Resolution Capacitive Sensing System for the Measurement of Water Content in Crude Oil

Abstract: This paper presents the design of a non-intrusive system to measure ultra-low water content in crude oil. The system is based on a capacitance to phase angle conversion method. Water content is measured with a capacitance sensor comprising two semi-cylindrical electrodes mounted on the outer side of a glass tube. The presence of water induces a capacitance change that in turn converts into a phase angle, with respect to a main oscillator. A differential sensing technique is adopted not only to ensure high immunity against temperature variation and background noise, but also to eliminate phase jitter and amplitude variation of the main oscillator that could destabilize the output. The complete capacitive sensing system was implemented in hardware and experiment results using crude oil samples demonstrated that a resolution of ±50 ppm of water content in crude oil was achieved by the proposed design.

Water rejection and wet finger tracking algorithms for truetouch panels and self capacitance touch sensors

Abstract: A method, apparatus, and system to detect a self-capacitance activation in view of a self-capacitance measurement of a first electrode The method, apparatus, and system further to detect a mutual capacitance activation in view of a mutual capacitance measurement of a pair of electrodes, and to determine the presence of water proximate to the capacitive button when the self-capacitance activation is false and the mutual capacitance activation is true The capacitive button is disposed on a substrate

Systems, articles and methods for wearable electronic devices employing contact sensors

Abstract: Wearable electronic devices that employ one or more contact sensors (e.g., capacitive sensors and/or biometric sensors) are described. Contact sensors include electromyography sensors and/or capacitive touch sensors. Capacitive touch sensors include single-frequency capacitive touch sensors, recently-proposed swept frequency capacitive touch sensors, and a generalized version of swept frequency capacitive touch sensors referred to as multi-frequency capacitive touch sensors. The contact sensors are integrated into various devices, including generic watchstraps that may be substituted for the existing watchstrap in any wristwatch design, generic watch back-plates that may be substituted for the existing back-plate in any wristwatch design, and wearable electromyography devices that provide gesture-based control in a human-electronics interface.

Multi-sensor touch integrated display driver configuration for capacitive sensing devices

Abstract: Embodiments of the disclosure generally provide an integrated control system having an integrated controller that is configured to provide both display updating signals to a display device and a capacitive sensing signal to a sensor electrode that is disposed within the integrated input device. The internal and/or external signal routing configurations described herein can be adapted to reduce signal routing complexity typically found in conventional devices and reduce the effect of electrical interference created by the capacitive coupling formed between the display routing, capacitive sensing routing and/or other components within the integrated control system. Embodiments can also be used to reduce electromagnetic interference (EMI) on the display and touch sensing signals received, transmitted and processed within the integrated control system.