Showing papers on "Capacitive sensing published in 2013"

Super-stretchable, Transparent Carbon Nanotube-Based Capacitive Strain Sensors for Human Motion Detection

Abstract: Realization of advanced bio-interactive electronic devices requires mechanically compliant sensors with the ability to detect extremely large strain. Here, we design a new multifunctional carbon nanotube (CNT) based capacitive strain sensors which can detect strains up to 300% with excellent durability even after thousands of cycles. The CNT-based strain gauge devices exhibit deterministic and linear capacitive response throughout the whole strain range with a gauge factor very close to the predicted value (strictly 1), representing the highest sensitivity value. The strain tests reveal the presented strain gauge with excellent dynamic sensing ability without overshoot or relaxation, and ultrafast response at sub-second scale. Coupling these superior sensing capabilities to the high transparency, physical robustness and flexibility, we believe the designed stretchable multifunctional CNT-based strain gauge may have various potential applications in human friendly and wearable smart electronics, subsequently demonstrated by our prototypical data glove and respiration monitor.

Ultrahigh humidity sensitivity of graphene oxide

Abstract: Humidity sensors have been extensively used in various fields, and numerous problems are encountered when using humidity sensors, including low sensitivity, long response and recovery times, and narrow humidity detection ranges. Using graphene oxide (G-O) films as humidity sensing materials, we fabricate here a microscale capacitive humidity sensor. Compared with conventional capacitive humidity sensors, the G-O based humidity sensor has a sensitivity of up to 37800% which is more than 10 times higher than that of the best one among conventional sensors at 15%–95% relative humidity. Moreover, our humidity sensor shows a fast response time (less than 1/4 of that of the conventional one) and recovery time (less than 1/2 of that of the conventional one). Therefore, G-O appears to be an ideal material for constructing humidity sensors with ultrahigh sensitivity for widespread applications.

Mesoporous materials as gas sensors

Abstract: Ordered mesoporous materials have great potential in the field of gas sensing. Today various template-assisted synthesis methods facilitate the preparation of silica (SiO2) as well as numerous metal oxides with well-defined, uniform and regular pore systems. The unique nanostructural properties of such materials are particularly useful for their application as active layers in gas sensors based on various operating principles, such as capacitive, resistive, or optical sensing. This review summarizes the basic aspects of materials synthesis, discusses some structural properties relevant in gas sensing, and gives an overview of the literature on ordered mesoporous gas sensors.

New generation "nanohybrid supercapacitor".

Abstract: To meet growing demands for electric automotive and regenerative energy storage applications, researchers all over the world have sought to increase the energy density of electrochemical capacitors. Hybridizing battery–capacitor electrodes can overcome the energy density limitation of the conventional electrochemical capacitors because they employ both the system of a battery-like (redox) and a capacitor-like (double-layer) electrode, producing a larger working voltage and capacitance. However, to balance such asymmetric systems, the rates for the redox portion must be substantially increased to the levels of double-layer process, which presents a significant challenge. An in situ material processing technology called “ultracentrifuging (UC) treatment” has been used to prepare a novel ultrafast Li4Ti5O12 (LTO) nanocrystal electrode for capacitive energy storage.This Account describes an extremely high-performance supercapacitor that utilizes highly optimized “nano-nano-LTO/carbon composites” prepared via ...

Flexible and stretchable electrodes for dielectric elastomer actuators

Abstract: Dielectric elastomer actuators (DEAs) are flexible lightweight actuators that can generate strains of over 100 %. They are used in applications ranging from haptic feedback (mm-sized devices), to cm-scale soft robots, to meter-long blimps. DEAs consist of an electrode-elastomer-electrode stack, placed on a frame. Applying a voltage between the electrodes electrostatically compresses the elastomer, which deforms in-plane or out-of plane depending on design. Since the electrodes are bonded to the elastomer, they must reliably sustain repeated very large deformations while remaining conductive, and without significantly adding to the stiffness of the soft elastomer. The electrodes are required for electrostatic actuation, but also enable resistive and capacitive sensing of the strain, leading to self-sensing actuators. This review compares the different technologies used to make compliant electrodes for DEAs in terms of: impact on DEA device performance (speed, efficiency, maximum strain), manufacturability, miniaturization, the integration of self-sensing and self-switching, and compatibility with low-voltage operation. While graphite and carbon black have been the most widely used technique in research environments, alternative methods are emerging which combine compliance, conduction at over 100 % strain with better conductivity and/or ease of patternability, including microfabrication-based approaches for compliant metal thin-films, metal-polymer nano-composites, nanoparticle implantation, and reel-to-reel production of μm-scale patterned thin films on elastomers. Such electrodes are key to miniaturization, low-voltage operation, and widespread commercialization of DEAs.

A review of nanometer resolution position sensors: Operation and performance

Abstract: Position sensors with nanometer resolution are a key component of many precision imaging and fabrication machines. Since the sensor characteristics can define the linearity, resolution and speed of the machine, the sensor performance is a foremost consideration. The first goal of this article is to define concise performance metrics and to provide exact and approximate expressions for error sources including non-linearity, drift and noise. The second goal is to review current position sensor technologies and to compare their performance. The sensors considered include: resistive, piezoelectric and piezoresistive strain sensors; capacitive sensors; electrothermal sensors; eddy current sensors; linear variable displacement transformers; interferometers; and linear encoders.

Elastomeric transparent capacitive sensors based on an interpenetrating composite of silver nanowires and polyurethane

Abstract: Highly flexible transparent capacitive sensors have been demonstrated for the detection of deformation and pressure. The elastomeric sensors employ a pair of compliant electrodes comprising silver nanowire networks embedded in the surface layer of polyurethane matrix, and a highly compliant dielectric spacer sandwiched between the electrodes. The capacitance of the sensor sheets increases linearly with strains up to 60% during uniaxial stretching, and linearly with externally applied transverse pressure from 1 MPa down to 1 kPa. Stretchable sensor arrays consisting of 10 × 10 pixels have also been fabricated by patterning the composite electrodes into X-Y addressable passive matrix.

A Circuit-Based Model for the Interpretation of Perfect Metamaterial Absorbers

Abstract: A popular absorbing structure, often referred to as Perfect Metamaterial Absorber, comprising metallic periodic pattern over a thin low-loss grounded substrate is studied by resorting to an efficient transmission line model. This approach allows the derivation of simple and reliable closed formulas describing the absorption mechanism of the subwavelength structure. The analytic form of the real part of the input impedance is explicitly derived in order to explain why moderate losses of the substrate is sufficient to achieve matching with free space, that is, perfect absorption. The effect of the constituent parameters for tuning the working frequency and tailoring the absorption bandwidth is addressed. It is also shown that the choice of highly capacitive coupled elements allows obtaining the largest possible bandwidth whereas a highly frequency selective design is achieved with low capacitive elements like a cross array. Finally, the angular stability of the absorbing structure is investigated.

A Flexible and Robust Large Scale Capacitive Tactile System for Robots

Abstract: Capacitive technology allows building sensors that are small, compact and have high sensitivity. For this reason it has been widely adopted in robotics. In a previous work we presented a compliant skin system based on capacitive technology consisting of triangular modules interconnected to form a system of sensors that can be deployed on non-flat surfaces. This solution has been successfully adopted to cover various humanoid robots. The main limitation of this and all the approaches based on capacitive technology is that they require to embed a deformable dielectric layer (usually made using an elastomer) covered by a conductive layer. This complicates the production process considerably, introduces hysteresis and limits the durability of the sensors due to ageing and mechanical stress. In this paper we describe a novel solution in which the dielectric is made using a thin layer of 3D fabric which is glued to conductive and protective layers using techniques adopted in the clothing industry. As such, the sensor is easier to produce and has better mechanical properties. Furthermore, the sensor proposed in this paper embeds transducers for thermal compensation of the pressure measurements. We report experimental analysis that demonstrates that the sensor has good properties in terms of sensitivity and resolution. Remarkably we show that the sensor has very low hysteresis and effectively allows compensating drifts due to temperature variations.

Single layer capacitive imaging sensors

Abstract: Embodiments of the invention generally provide an input device that includes a plurality of sensing elements that are interconnected in desired way to acquire positional information of an input object, so that the acquired positional information can be used by other system components to control a display or other useful system components. One or more of the embodiments described herein, utilizes one or more of the techniques and sensor electrode array configuration disclosed herein to reduce or minimize the number of traces and/or electrodes required to sense the position of an input object within a sensing region of the input device.

Polymer-based flexible capacitive sensor for three-axial force measurements

Abstract: We have developed a flexible-substrate-based three-axial force sensor, composed of finger-shaped electrode capacitors, whose operation is based on the measurement of a capacitance change induced upon applying a three-axial load. The electrode design supports high sensitivity to shear forces. An overall flexibility of the sensor and elasticity of the capacitor's dielectric is obtained by integrating three polymers in the sensor's technology process, namely polyimide, parylene-C, and polydimethylsiloxane, combined with standard metallization processes. We have theoretically modeled the sensor's capacitance and its three-axial force sensitivity. The unit capacitors have static capacitances in the range of 20 pF. The electro-mechanical characterization of the capacitors reveals in the normal direction a sensitivity Sz = 0.024 kPa−1 for pressures <10 kPa, whereas for higher pressures the measured sensitivity Sz = 6.6 × 10−4 kPa−1. Typical measured shear force sensitivity Sx = 2.8 × 10−4 kPa−1. These values give our transducer high potential for use in skin-like sensing applications.

Self-sensing dielectric elastomer actuators in closed-loop operation

Abstract: Because of their large output strain, dielectric elastomer actuators (DEAs) have been proposed for tunable optics applications such as tunable gratings. However, the inherent viscoelastic drift of these actuators is an important drawback and closed-loop operation of DEAs is a prerequisite for any accurate real-world application. In this paper, we show how capacitive self-sensing can be used to drive a DEA in closed-loop without the need for any external sensor. The method has been demonstrated on a DEA tunable grating based on a VHB acrylic and silicone membrane. The results show that the widely used VHB presents a time-dependent drift between the capacitance of the electrodes and their strain. The silicone-based grating does not exhibit such a drift, and its strain can be stabilized by regulating the capacitance of the device to a constant value. We also report on an new fabrication method for thin deformable gratings based on replication on a water-soluble master and a 27% change in the grating period has been obtained on a VHB-based device.

A 1.2-V 8.3-nJ CMOS Humidity Sensor for RFID Applications

Abstract: This paper presents a fully integrated CMOS humidity sensor for a smart RFID sensor platform. The sensing element is a CMOS-compatible capacitive humidity sensor, which consists of top-metal finger-structure electrodes covered by a humidity-sensitive polyimide layer. Its humidity-sensitive capacitance is digitized by an energy-efficient capacitance-to-digital converter (CDC) based on a third-order delta-sigma modulator. This CDC employs current-efficient operational transconductance amplifiers based on current-starved cascoded inverters, whose limited output swing is accommodated by employing a feedforward loop-filter topology. A programmable offset capacitor is included to remove the sensor's baseline capacitance and thus reduce the required dynamic range. To reduce offset errors due to charge injection of the switches, the entire system is auto-zeroed. The proposed humidity sensor has been realized in a 0.16- μm CMOS technology. Measurement results show that the CDC performs a 12.5-bit capacitance-to-digital conversion in a measurement time of 0.8 ms, while consuming only 8.6 μA from a 1.2-V supply. This corresponds to a state-of-the-art figure-of-merit of 1.4 pJ/conversion-step. Combined with the co-integrated humidity sensing element, it provides a resolution of 0.05% RH in the range from 30% RH to 100% RH while consuming only 8.3 nJ per measurement, which is an order-of-magnitude less energy than the state-of-the-art.

Extremely robust and conformable capacitive pressure sensors based on flexible polyurethane foams and stretchable metallization

Abstract: Microfabricated capacitive sensors prepared with elastomeric foam dielectric films and stretchable metallic electrodes display robustness to extreme conditions including stretching and tissue-like folding and autoclaving. The open cellular structure of the elastomeric foam leads to significant increase of the capacitance upon compression of the dielectric membrane. The sensor sensitivity can be adjusted locally with the foam density to detect normal pressure in the 1 kPa to 100 kPa range. Such pressure transducers will find applications in interfaces between the body and support surfaces such as mattresses, joysticks or prosthetic sockets, in artificial skins and wearable robotics.

Capacitive Mixing for Harvesting the Free Energy of Solutions at Different Concentrations

Abstract: An enormous dissipation of the order of 2 kJ/L takes place during the natural mixing process of fresh river water entering the salty sea. “Capacitive mixing” is a promising technique to efficiently harvest this energy in an environmentally clean and sustainable fashion. This method has its roots in the ability to store a very large amount of electric charge inside supercapacitor or battery electrodes dipped in a saline solution. Three different schemes have been studied so far, namely, Capacitive Double Layer Expansion (CDLE), Capacitive Donnan Potential (CDP) and Mixing Entropy Battery (MEB), respectively based on the variation upon salinity change of the electric double layer capacity, on the Donnan membrane potential, and on the electrochemical energy of intercalated ions.

Dual capacitive-inductive nature of periodic graphene patches: Transmission characteristics at low-terahertz frequencies

Abstract: We report on the dual nature (capacitive and inductive) of the surface impedance of periodic graphene patches at low-terahertz frequencies. The transmission spectra of a graphene-dielectric stack shows that patterned graphene exhibits both the low-frequency (capacitive) passband of metal patch arrays and the higher-frequency (inductive) passband of metal aperture arrays in a single tunable configuration. The analysis is carried out using a transfer-matrix approach with two-sided impedance boundary conditions, and the results are verified using full-wave numerical simulations. In addition, the Bloch-wave analysis of the corresponding infinite periodic structure is presented in order to explain the passband and stopband characteristics of the finite graphene-dielectric stack.

Clean energy generation using capacitive electrodes in reverse electrodialysis

Abstract: Capacitive reverse electrodialysis (CRED) is a newly proposed technology to generate electricity from mixing of salt water and fresh water (salinity gradient energy) by using a membrane pile as in reverse electrodialysis (RED) and capacitive electrodes. The salinity difference between salt water and fresh water generates a potential difference over ion selective membranes, which can be used as a renewable power source. The strength and unique characteristic of CRED in comparison to the other technologies is that it allows multiple membrane cells between a single set of electrodes and at the same time avoids redox reactions using capacitive electrodes. The capacitive electrodes use activated carbon on a support of Ti/Pt mesh to store ions and their charge. A periodic switching of the feed waters, combined with a switching of the direction of the electric current, ensures that the capacitive electrodes do not get saturated. The large membrane pile enables the electrodes to be charged more than in previous approaches for capacitive mixing. As a consequence, the energy cycle of CRED has a larger range in both voltage and accumulated charge compared to previous capacitive mixing technologies. The power density obtainable with CRED stacks with capacitive electrodes is an order of magnitude higher than in previous attempts for capacitive energy extraction and close to or even better than similar RED stacks with conventional redox based electrode systems. CRED is considered to be a stable, safe, clean and high performing technology to obtain energy from mixing of salt water and fresh water.

Robust Flexible Capacitive Surface Sensor for Structural Health Monitoring Applications

Abstract: Early detection of possible defects in civil infrastructure is vital to ensuring timely maintenance and extending structure life expectancy. The authors recently proposed a novel method for structural health monitoring based on soft capacitors. The sensor consisted of an off-the-shelf flexible capacitor that could be easily deployed over large surfaces, the main advantages being cost-effectiveness, easy installation, and allowing simple signal processing. In this paper, a capacitive sensor with tailored mechanical and electrical properties is presented, resulting in greatly improved robustness while retaining measurement sensitivity. The sensor is fabricated from a thermoplastic elastomer mixed with titanium dioxide and sandwiched between conductive composite electrodes. Experimental verifications conducted on wood and concrete specimens demonstrate the improved robustness, as well as the ability of the sensing method to diagnose and locate strain.

Physical force capacitive touch sensors

Abstract: A physical force capacitive touch sensor comprises a capacitive sensor element on a substrate, a physically deformable electrically insulating spacer over the capacitive sensor element and a conductive deformable plane over the physically deformable electrically insulating spacer. A protective deformable fascia may be placed over the conductive deformable plane to provide an environmental seal for physical and weather protection, but is not essential to operation of the capacitive touch sensor. Back lighting is accomplished through a light transmissive layer(s) in the capacitive touch sensor. When the conductive deformable plane is displaced toward the capacitive touch sensor element, the capacitance value of the capacitive touch sensor element changes and that change may be detected and used as an actuation signal.

Capacitive Touch Sensor for Identifying a Fingerprint

Abstract: A capacitive sensor includes at least one substrate, a capacitive touch position sensor, and a capactive fingerprint sensor. The capacitive touch position sensor is included on the at least one substrate and in a touch sensing area. The capactive touch position sensor includes electrodes configured to enable detection of the presence and position of a touch in the touch sensing area. The capactive fingerprint sensor is included on the at least one substrate and in a fingerprint sensing area. The capacitive fingerprint sensor includes electrodes configured to enable identification of the fingerprint of a finger placed in the fingerprint sensing area.

A Novel Piezoelectric Strain Sensor for Simultaneous Damping and Tracking Control of a High-Speed Nanopositioner

Abstract: This paper presents a novel piezoelectric strain sensor for damping and accurate tracking control of a high-speed nanopositioning stage. Piezoelectric sensors have the benefit of simple interface circuitry, low cost, high sensitivity, and high bandwidth. Although piezoelectric sensors have been successfully used as vibration sensors in smart structures, complications arise when they are used in a feedback loop for tracking. As piezoelectric strain sensors exhibit a capacitive source impedance, a high-pass filter is created, typically with a cut-off frequency of 1 to 10 Hz. This filter can cause significant errors and destabilize a tracking control system. Here, we overcome this problem by using a low-frequency bypass technique to replace the low-frequency component of the strain measurement with an estimate based on the open-loop system. Once the low-frequency filter is accounted for, any standard control system can be applied. In this paper, an analog integral resonant controller together with an integral tracking controller are implemented on a flexure-guided nanopositioner. The resulting closed-loop bandwidth is experimentally demonstrated to be 1.86 kHz. The nanopositioner is installed in an Atomic Force Microscope to obtain open- and closed-loop images at line rates of 40 and 78 Hz. Images recorded in closed loop show a significant improvement due to the elimination of nonlinearity.

Mems capacitive pressure sensor

Abstract: A pressure sensor measures pressure by measuring the deflection of a MEMS membrane using a capacitive read-out method. There are two ways to implement the invention. One involves the use of an integrated Pirani sensor and the other involves the use of an integrated resonator, to function as a reference pressure sensor, for measuring an internal cavity pressure.

A cuttable multi-touch sensor

Abstract: We propose cutting as a novel paradigm for ad-hoc customization of printed electronic components. As a first instantiation, we contribute a printed capacitive multi-touch sensor, which can be cut by the end-user to modify its size and shape. This very direct manipulation allows the end-user to easily make real-world objects and surfaces touch-interactive, to augment physical prototypes and to enhance paper craft. We contribute a set of technical principles for the design of printable circuitry that makes the sensor more robust against cuts, damages and removed areas. This includes novel physical topologies and printed forward error correction. A technical evaluation compares different topologies and shows that the sensor remains functional when cut to a different shape.

CORRIGENDUM: Super-stretchable, Transparent Carbon Nanotube-Based Capacitive Strain Sensors for Human Motion Detection

Abstract: CORRIGENDUM: Super-stretchable, Transparent Carbon Nanotube-Based Capacitive Strain Sensors for Human Motion Detection

OpenCapSense: A rapid prototyping toolkit for pervasive interaction using capacitive sensing

Abstract: Capacitive sensing allows the creation of unobtrusive user interfaces that are based on measuring the proximity to objects or recognizing their dielectric properties. Combining the data of many sensors, applications such as in-the-air gesture recognition, location tracking or fluid-level sensing can be realized. We present OpenCapSense, a highly flexible open-source toolkit that enables researchers to implement new types of pervasive user interfaces with low effort. The toolkit offers a high temporal resolution with sensor update rates up to 1 kHz. The typical spatial resolution varies between one millimeter at close object proximity and around one centimeter at distances of 35cm or above.

Ultrafast nonlinear control of progressively loaded, single plasmonic nanoantennas fabricated using helium ion milling.

Abstract: We demonstrate milling of partial antenna gaps and narrow conducting bridges with nanometer precision using a helium ion beam microscope. Single particle spectroscopy shows large shifts in the plasmonic mode spectrum of the milled antennas, associated with the transition from capacitive to conductive gap loading. A conducting bridge of nanometer height is found sufficient to shift the antenna from the capacitive to the conductive coupling regime, in agreement with circuit theory. Picosecond pump–probe spectroscopy reveals an enhanced nonlinear response for partially milled antennas, reaching an optimum value for an intermediate bridge height. Our results show that manipulation of the antenna load can be used to increase the nonlinear response of plasmonic antennas.

Pressure-sensing touch system utilizing optical and capacitive systems

Abstract: A hybrid touch system that utilizes a combination of a capacitive touch system for position sensing and an optical touch system for pressure sensing is disclosed. The optical touch system includes a transparent sheet having a surface, at least one light source and at least one detector which are operably arranged relative to the transparent sheet to transmit light through the sheet and to detect the transmitted light. Performing position sensing using the capacitive touch system simplifies the pressure-sensing optical touch system.