Change In Electrical Capacitance Research Articles

Room temperature ammonia sensing with barium strontium titanate under humid air background

Within the field of chemical gas sensing, ammonia detection represents one of the nowadays challenges, due to its adverse effects for human health. Real operating investigations are imposed by the high solubility potential of NH3 at room temperature. Thick films of Ba0.75Sr0.25TiO3 material have been investigated by means of electrical resistance and capacitance changes and correlated with the photoacoustic outputs. The experimental findings have been discussed in terms of Grotthuss mechanism, with respect to the ionic/electronic conduction within BST, toward ammonia detection enhanced by the presence of water vapors when operated at room temperature. So an appropriate NH3 sensing mechanism was proposed.

To improve interfacial and mechanical properties of carbon fiber–modified nano-SiC–epoxy composites using dispersion and wetting control

Significant improvements in mechanical properties (particularly stiffness) result from the appropriate addition of micro-carbon fibers in the nano and heterostructures of modified nano-SiC-filled epoxy matrix composites. The optimum dispersion conditions were found to be significantly dependent upon both the amount of nano-SiC filler and the sonication time. To investigate these dispersion effects, composites were fabricated with five different nano-SiC filler concentrations and compared to the untreated composite. Changes in electrical capacitance were used as a measure of the comparative degree of dispersion in these nano-SiC–epoxy composites. FE-SEM was used to observe the interfacial changes for the different surface conditions, and the mechanical damage was evaluated by inspection of fractured surfaces. Optimal conditions of dispersion, interfacial adhesion, and aspect ratio of the modified nano-SiC fillers were found to improve the composites’ mechanical properties.

Restricted primitive model for electrolyte solutions in slit-like pores with grafted chains: Microscopic structure, thermodynamics of adsorption, and electric properties from a density functional approach

We apply a density functional theory to describe properties of a restricted primitive model of an ionic fluid in slit-like pores. The pore walls are modified by grafted chains. The chains are built of uncharged or charged segments. We study the influence of modification of the pore walls on the structure, adsorption, ion selectivity, and the electric double layer capacitance of ionic fluid under confinement. The brush built of uncharged segments acts as a collection of obstacles in the walls vicinity. Consequently, separation of charges requires higher voltages, in comparison to the models without brushes. At high grafting densities the formation of crowding-type structure is inhibited. The double layer structure becomes more complex in various aspects, if the brushes are built of charged segments. In particular, the evolution of the brush height with the bulk fluid density and with the charge on the walls depends on the length of the blocks of charged spheres as well as on the distribution of charged species along chains. We also investigated how the dependence of the double layer capacitance on the electrostatic potential (or on the charge on the walls) changes with grafting density, the chain length, distribution of charges along the chain, the bulk fluid density, and, finally, with the pore width. The shape of the electric double layer capacitance vs. voltage changes from a camel-like to bell-like shape, if the bulk fluid density changes from low to moderate and high. If the bulk density is appropriately chosen, it is possible to alter the shape of this curve from the double hump to single hump by changing the grafting density. Moreover, in narrow pores one can observe the capacitance curve with even three humps for a certain set of parameters describing brush. This behavior illustrates how strong the influence of brushes on the electric double layer properties can be, particularly for ionic fluids in narrow pores.

Label-Free Detection of Cardiac Troponin-I Using Carbon Nanofiber Based Nanoelectrode Arrays

A label-free biosensor is presented using carbon nanofiber (CNF) nanoelectrode arrays for the detection of cardiac troponin-I in the early diagnosis of myocardial infarction. Immobilization of anti-cTnI Ab on CNFs and the detection of human-cTnI were examined using electrochemical impedance spectroscopy and cyclic voltammetry techniques. Each step of the modification process was monitored, and the results show changes in electrical capacitance or resistance to charge transfer due to the specificity of corresponding adsorption of Ab-Ag interaction. The immunosensor demonstrates a good selectivity and high sensitivity against human-cTnI analytes and is capable of detecting cTnI at concentrations as low as ∼0.2 ng/mL, which is 25 times lower than that possible by conventional methods. Analysis of the electrode at various stages using atomic force microscopy and X-ray reflectivity provides information on the surface roughness and orientation of the antibody.

Response characteristics and tomographic monitoring of the electric capacitance after irrigation in the soil–plant (ginkgo tree) continuum in a laboratory

The temporal and spatial variations of electrical capacitance of the soil–plant continuum in a laboratory were investigated. Based on a potted ginkgo tree with six irrigations, the electrical capacitance of the soil, trunk, and soil–trunk electrode pairs was measured, corresponding soil water content was computed, and spatial imaging was conducted. The soil electrical capacitance increases to a local maximum value immediately after irrigation, and then decreases gradually with time. During the late period of each drying procedure, there is a decussation area of high water content at the middle part of the circular region in the spatial imaging, which indicates root distribution in soil to some degree. Upon irrigation under a dry soil condition, the trunk electrical capacitance gradually increases for a period, and then begins to fluctuate with time; whereas, under a wet soil condition, it always fluctuates with time. Under a stable condition of overall change, the trunk electrical capacitance changes saltatorially and daily periodically. The temporal variation of the soil–trunk electrical capacitance exhibits both the character of soil and trunk.

Gold nanoparticles mediated label-free capacitance detection of cardiac troponin I

It has been already proved that electrical capacitance increases at the electrode surface due to binding of highly charged antigens on the biointerface. In this paper, this capacitance change was used to demonstrate a novel detection for cardiac troponin I (cTnI). Citrate-capped gold nanoparticles (GNPs) were deposited on screen printed electrodes using an innovative one-step electrochemical technique. The gold (Au) nanostructuration onto the electrode surface was characterized by atomic force and field emission scanning electron microscopies. The highly specific anti-cTnI antibodies were immobilized onto the Au matrix, and characterized by confocal microscopy. The interaction of cTnI with its corresponding antibody was studied with respect to electrical capacitance changes as deduced by using the Randles model of the equivalent circuit of the electrochemical cell. The sensor-to-sensor measurements error was registered less than 2% on the average measured capacitance. cTnI was successfully detected in a label-free manner with a limit of detection equal to 0.2 ng mL −1. This obtained result was one order of magnitude better than that obtained with ELISA tests performed by using the same antibodies, with a detection limit of 4.3 ng mL −1.

A Highly Sensitive Capacitive Touch Sensor Integrated on a Thin-Film-Encapsulated Active-Matrix OLED for Ultrathin Displays

This paper presents ultrathin and highly sensitive input/output devices consisting of a capacitive touch sensor (Cap-TSP) integrated on thin-film-encapsulated active-matrix organic light-emitting diodes (OLEDs). The optimal structure of the electrically noise-free capacitive touch sensor, which is assembled on a thin-film-encapsulated active-matrix OLED (AMOLED) display, is obtained by investigating the internal electrical field distribution and capacitance change based on the Q3D Extractor model. Electrostatic simulations have verified malfunction-free electrical signals for 4-in diagonal-sized capacitive touch sensors on AMOLEDs possessing a 100-μm-thick optically clear adhesive (OCA, er = 1.4) layer. The prototype OLED platform using the capacitive touch sensors exhibits an overall thickness of 1.2 mm, which is the lowest thickness for commercially available OLED platforms.

43.2: Mutual Capacitance Touch Screen Integrated into Thin Film Encapsulated Active‐Matrix OLED

AbstractA thin and high performance input/output device consisting of capacitive touch sensors integrated on thin film encapsulated AMOLED is described. Internal electric field distribution and capacitance change trend was simulated to find and prove the optimal structure including touch input and display output units. To verify cross‐talk free operation of touch sensors on thin film encapsulated AMOLED, 4 inch diagonal size display‐TSP prototype was fabricated.

Surface-type humidity sensor based on cellulose-PEPC for telemetry systems

Au/cellulose-PEPC/Au surface-type humidity sensors were fabricated by drop-casting cellulose and poly-N-epoxypropylcarbazole (PEPC) blend thin films. A blend of 2wt% of each cellulose and PEPC in benzol was used for the deposition of humidity sensing films. Blend films were deposited on glass substrates with preliminary deposited surface-type gold electrodes. Films of different thicknesses of cellulose and PEPC composite were deposited by drop-casting technique. A change in electrical resistance and capacitance of the fabricated devices was observed by increasing the relative humidity in the range of 0–95% RH. It was observed that the capacitances of the sensors increase, while their resistances decrease with increasing the relative humidity. The sensors were connected to op-amp square wave oscillators. It was observed that with increasing the relative humidity, the oscillator's frequencies were also increased in the range of 4.2–12.0 kHz for 65 μm thick film sample, 4.1–9.0 kHz for 88 μm thick film sample, and 4.2–9.0 kHz for 210 μm sample. Effects of film thickness on the oscillator's frequency with respect to humidity were also investigated. This polymer humidity sensor controlled oscillator can be used for short-range and long-range remote systems at environmental monitoring and assessment of the humidity level.

A micromachined silicon capacitive temperature sensor for wide temperature range applications

A micromachined capacitive temperature sensor is designed and fabricated based on a multilayer cantilever. The top and bottom layers of the cantilever are Al and Si, respectively, which also serve as electrodes of the sensing capacitor. A composite Si3N4/SiO2 layer, a dielectric layer, is sandwiched between the top and bottom electrodes. The cantilever thermal response is due to differences in thermal expansion coefficients for the Al, Si3N4/SiO2 and silicon materials. With the effect of strain on the dielectric property as well as the geometry impact on the capacitance, the temperature variation is sensed and translated to an electrical capacitance change. The mechanical characteristics of the sensor are theoretically analyzed with the extension of Timoshenko's bilayer strip model. The sensor was fabricated with the silicon-on-insulator substrate. Experimental results show that the sensor provides a sensitivity of 7 fF °C−1 in the −70 to 100 °C range. This makes it suitable to serve as a temperature sensor for low power and wide temperature range applications.

Surface-type multifunctional sensor based on 5,10,15,20-tetrakis(4′-isopropylphenyl) porphyrin

In this study, an organic semiconductor 5,10,15,20-tetrakis(4′-isopropylphenyl) porphyrin (TIPP) was synthesized and investigated as an active material in surface-type multifunctional sensor. As electrodes, 100 nm thick Ag films were deposited on 25 mm × 25 mm glass substrate with 40 μm gap between them. Thin film of TIPP of area 15 mm × 15 mm was thermally sublimed to cover the gap between the silver electrodes. Thickness of TIPP film was 100 nm. A change in electrical resistance and capacitance of the fabricated device was observed with the increase in relative humidity (RH), temperature, and illumination. Hysteresis, response, and recovery times were investigated over a wide range of RH (0–94%). Activation energy of the TIPP was estimated. An equivalent circuit of the Ag/TIPP/Ag humidity, temperature, and illumination sensor was developed. Humidity, temperature, illumination dependent capacitive, and resistive properties of this sensor make it promising for use in a humidity, temperature, and lux multi-meters.

Cu(II) 5,10,15,20-tetrakis(4′-isopropylphenyl) porphyrin based surface-type resistive–capacitive multifunctional sensor

An organic semiconductor Cu(II) 5,10,15,20-tetrakis(4′-isopropylphenyl) porphyrin (CuTIPP) was synthesized and investigated as an active material in resistive–capacitive multifunctional sensor. A thin film of the CuTIPP was deposited by thermal evaporator on a glass substrate with preliminary deposited silver electrodes and Ag/CuTIPP/Ag surface-type multifunctional sensor was fabricated. Thickness of the CuTIPP film was 100 nm. Area of the semiconducting channel between metallic electrodes was 40 μm × 21 mm. A change in electrical resistance and capacitance was observed with the increase of temperature, relative humidity and illumination. An equivalent circuit of the Ag/CuTIPP/Ag capacitive–resistive humidity, temperature and illumination sensor was developed. Humidity, temperature and illumination dependent capacitance–resistance properties of this sensor make it beneficial for use in humidity, temperature and lux multimeters.

Glass transition andα-relaxation dynamics of thin films of labeled polystyrene

The glass transition temperature and relaxation dynamics of the segmental motions of thin films of polystyrene labeled with a dye, 4-[N-ethyl-N-(hydroxyethyl)]amino-4-nitroazobenzene (Disperse Red 1, DR1) are investigated using dielectric measurements. The dielectric relaxation strength of the DR1-labeled polystyrene is approximately 65 times larger than that of the unlabeled polystyrene above the glass transition, while there is almost no difference between them below the glass transition. The glass transition temperature of the DR1-labeled polystyrene can be determined as a crossover temperature at which the temperature coefficient of the electric capacitance changes from the value of the glassy state to that of the liquid state. The glass transition temperature of the DR1-labeled polystyrene decreases with decreasing film thickness in a reasonably similar manner to that of the unlabeled polystyrene thin films. The dielectric relaxation spectrum of the DR1-labeled polystyrene is also investigated. As the thickness decreases, the alpha -relaxation time becomes smaller, and the distribution of the alpha -relaxation times becomes broader. These results show that thin films of DR1-labeled polystyrene are a suitable system for investigating confinement effects of the glass transition dynamics using dielectric relaxation spectroscopy.

Wireless flexible capacitive sensor based on ultra-flexible epoxy resin for strain measurement of automobile tires

The measurement of strain of tires in-service is effective in improving the reliability of tires and ABS systems. Since conventional strain gages have high stiffness and require lead wires, conventional strain gages are cumbersome for the strain measurement of tires. The present study proposes a novel flexible patch-type strain sensor utilizing electric capacitance change. The sensor is made from flexible polyimide substrates and ultra-flexible epoxy resin, which makes the sensor low in stiffness and high in elongation as a whole structure. The sensor utilizes capacitance changes due to the applied strain, and wireless measurements are conducted using amplitude modulation. The sensor is applied to an automobile tire, and compression tests are performed. The effects of the temperature changes are also measured. The proposed sensor is found to successfully measure the applied strain of the tire wirelessly, and the effects of the temperature changes are minimized using a dummy sensor in a self-temperature compensation circuit.

Capacitive Detection in Ultrathin Chemosensors Prepared by Molecularly Imprinted Grafting Photopolymerization

The usual applications of capacitive detection in chemo- and biosensors are based on changes in effective thickness of insulating layers due to adsorption of analyte onto receptors. Ultrathin chemosensors based on molecularly imprinted polymerization enable a realization of another capacitive approach that exploits changes in electrical capacitance due to modification of the dielectric constant of the polymer. Such chemosensors were prepared by photografted molecularly imprinted polymerization on the surface of gold electrodes. An adsorbed layer of hydrophobic photoinitiator (benzophenone) provided grafted polymerization on the surface of the alkanethiol-modified gold electrode. The chemosensors were characterized by cyclic voltammetry, impedance spectroscopy, and scanning electron and atomic force microscopy. Binding of analyte was detected by measurements of electrical capacitance. The results indicate a decrease of the dielectric constant of the polymer layer due to analyte binding up to 20%.

2514 電気容量型柔軟センサを用いたタイヤの無線変形計測(J10-3 計測・モニタリング・解析(3),J10 知的材料・構造システム)

Measurement of strain of tires in-service is effective to improve reliability of tires and ABS system. Since conventional strain gages have high stiffness and require lead wires, the conventional strain gages are cumbersome for the strain measurement of the tires. The backgrounds require a new low cost wireless sensor for tires. In the present study, a new flexible patch-type strain sensor utilizing electric capacitance change is proposed and analytically investigated. The sensor is made from flexible polyimide substrates and ultra-flexible epoxy resin, which makes the sensor low in stiffness and high in elongation as a whole structure. The sensor utilizes capacitance changes due to the applied strain. The sensor is applied to an automobile tire, and compression tests are performed.

OS17-2-4 Wireless flexible capacitive sensor based on ultra-flexible epoxy resin for strain measurement of automobile tires

The measurement of strain of tires in-service is effective in improving the reliability of tires and ABS systems. Since conventional strain gages have high stiffness and require lead wires, conventional strain gages are cumbersome for the strain measurement of tires. The present study proposes a novel flexible patch-type strain sensor utilizing electric capacitance change. The sensor is made from flexible polyimide substrates and ultra-flexible epoxy resin, which makes the sensor low in stiffness and high in elongation as a whole structure. The sensor utilizes capacitance changes due to the applied strain, and wireless measurements are conducted using amplitude modulation. The sensor is applied to an automobile tire, and compression tests are performed. The effects of the temperature changes are also measured. The proposed sensor is found to successfully measure the applied strain of the tire wirelessly.

Smart Cure Monitoring Method of Carbon/Epoxy Laminates Using Electric Capacitance Change with Applied Alternating Current Frequency

Authors have developed an electric resistance change method for delamination monitoring of carbon/epoxy composite laminates. The method employs reinforcement fibers as sensors; electrodes are co-cured. Co-cured electrodes for delamination monitoring are adopted in the present study as sensors for monitoring the degree of cure. This study proposes a new method using electrical capacitance change for monitoring the degree of cure without using additional sensors. Applying alternating current between electrodes during the cure process provides dielectric properties of carbon/epoxy composites. As with the conventional cure monitoring method using extra dielectric sensors, the degree of cure of composites is monitored by measuring the dielectric constant of composites. The dielectric constant of epoxy resin changes concomitant with change of frequency of applied alternating current (AC). Using dependency of the applied AC frequency of the dielectric constant, the degree of cure is measured directly. The proposed method is applied to single and multi-ply carbon/epoxy composite laminates. The method demonstrates excellent estimations of the degree of cure without additional sensors.

Wireless strain monitoring of tires using electrical capacitance changes with an oscillating circuit

In-service strain monitoring of automobile tires is quite effective to improve reliability of tires and design tools. Conventional strain gages have high stiffness and require lead wires. For those reasons, they are cumbersome for strain measurement of tires. Therefore, a new low cost wireless sensor is required for tires. The present study proposes and experimentally investigates a new wireless strain measurement system using the electric capacitance change of steel-wire reinforced tires. A small CR oscillating circuit is embedded in the tire. Thereby, tire deformation engenders a capacitance change of the tire, which comprises steel wire and rubber. In turn, these changes in capacitance alter the oscillating frequency of the oscillating circuit. Measurement of the oscillating circuit frequency indicates the tire strain wirelessly. A rectangular specimen cut from a truck tire is adopted as a specimen for this study. Finally, feasibility of the proposed system is examined using a commercially available passenger car tire through performing static compression and a dynamic rotation test. Experimental results prove that the method is effective for wireless strain monitoring of tires.

タイヤの電気容量変化と発振回路を用いたひずみ無線モニタリング

The strain monitoring of automobile tires in-service is quite effective to improve reliability of tires and design tools. The conventional strain gages are cumbersome for the strain measurement of the tires because of their high stiffness and lead wire requirement. In the present study, a new strain measurement system utilize electric capacitance change of steel wire reinforced, low cost wireless sensor built-in tires is proposed and experimentally investigated. A small oscillating circuit in which the capacitor is composed with the rubber and the wire is embedded in the tire, then deformation of the tire causes change of the capacitance makes change of frequency. Measurement of the frequency enables us a remote measuring of the strain of the tire. A rectangular specimen cut from a truck tire is adopted as a specimen. Using the commercially available tire in which sensor embedded, dynamic test is performed and frequency change of the oscillating circuit is measured during the test. As a result, the method is experimentally proved to be effective for the wireless strain monitoring of tires.