Change In Electrical Capacitance Research Articles

Inkjet‐Printed Flexible Thin‐Film Thermal Sensors for Detecting Elevated Temperature Range

All inkjet‐printed thermal sensors are manufactured based on a metal–insulator–metal (MIM) interface or capacitor architecture, for the adapted device size ranging from 16 to 36 mm2 active area. Two different material inks, namely a nanoparticle conductive silver ink and an inorganic‐polymer‐based hybrid insulator ink, are applied layer by layer on a thin flexible polyimide substrate, for developing the printed MIM devices. To ensure the desired electronic conductivity and insulation from the layers, the manufacturing process steps and parameters are tuned, accordingly. The results show that the inkjet‐printed MIM devices could constitute up to 15 μm thickness and demonstrate average detection of a change in electrical capacitance ranging from 20 to 100 pF, when the temperature is varied between 100 and 300 °C. The investigations also summarize that the change in the electrical response is enough to detect an increment of 50 °C. The printed sensors also display high operational stability and repeatability, when subjected to thermal cycling.

Design of a novel aptamer/molecularly imprinted polymer hybrid modified Ag–Au@Insulin nanoclusters/Au-gate-based MoS2 nanosheet field-effect transistor for attomolar detection of BRCA1 gene

Early detection of breast cancer, the first main cause of death in women, with robust assay platforms using appropriate biomarkers is of great importance for diagnosis and follow-up of the disease progression. This paper introduces an extra selective and sensitive label-free aptasensor for the screening of BRCA1 gene biomarker by taking advantage of a gate modified with aptamer and molecularly imprinted polymer hybrid (MIP) as a new synthetic receptor film coupled with an electrolyte-gated molybdenum disulfide (MoS2) field-effect transistor (FET). The Au gate surface of FET was modified with insulin stabilized bimetallic Ag–Au@nanoclusters (Ag–Au@InsNCs), after which, the immobilization of the hybridized aptamer and o-phenylenediamine was electropolymerized to form an aptamer-MIP hybrid receptor. The output characteristics of Apta-MIP hybrid modified Au gate MoS2 FET device were followed as a result of change in electrical double layer capacitance of electrolye-gate interface. The magnitude of decrease in the drain current showed a linear response over a wide concentration range of 10 aM to 1 nM of BRCA1 ssDNA with a sensitivity as high as 0.4851 μA/decade of concentration and a limit of detection (LOD) of 3.0 aM while very low responses observed for non-imprinted polymer. The devised aptasensor not only was capable to the discrimination of the complementary versus one-base mismatch BRCA1 ssDNA sequence, but also it could detect the complementary BRCA1 ssDNA in spiked human serum samples over a wide concentration range of 10 aM to 1.0 nM with a low LOD of 6.4 aM and a high sensitivity 0.3718 μA/decade.

Changes in Electrical Capacitance of Cell Membrane Reflect Drug Partitioning-Induced Alterations in Lipid Bilayer

The plasma membrane is a lipid bilayer that establishes the outer boundary of a living cell. The composition of the lipid bilayer influences the membrane's biophysical properties, including fluidity, thickness, permeability, phase behavior, charge, elasticity, and formation of flat sheet or curved structures. Changes in the biophysical properties of the membrane can be occasioned when new entities, such as drug molecules, are partitioned in the bilayer. Therefore, assessing drugs for their effect on the biophysical properties of the lipid bilayer of a cell membrane is critical to understanding specific and non-specific drug action. Previously, we reported a non-invasive technique for real-time characterization of cellular dielectric properties, such as membrane capacitance and cytoplasmic conductivity. In this study, we discuss the potential application of the technique in assessing the biophysical properties of the cell membrane in response to interaction with amiodarone compared to aspirin/acetylsalicylic acid and glucose. Amiodarone is a potent drug used to treat cardiac arrhythmia, but it also exerts various non-specific effects. Compared to aspirin and glucose, we measured a rapid and higher magnitude increase in membrane capacitance on cells under amiodarone treatment. Increased membrane capacitance induced by aspirin and glucose quickly returned to baseline in 15 s, while amiodarone-induced increased capacitance sustained and decreased slowly, approaching baseline or another asymptotic limit in ~2.5 h. Because amiodarone has a strong lipid partitioning property, we reason that drug partitioning alters the lipid bilayer context and subsequently reduces bilayer thickness, leading to an increase in the electrical capacitance of the cell membrane. The presented microfluidic system promises a new approach to assess drug-membrane interactions and delineate specific and non-specific actions of the drug on cells.

Monitoring of Surgical Wounds with Purely Textile, Measuring Wound Pads—III: Detection of Bleeding or Seroma Discharge by the Measurement of Wound Weeping

To enable stating a final common sensor design of purely textile, measuring wound pads for the monitoring of surgically provided wounds with regard to tissue temperature, moisture release and stretching (as indicators for the most prominent wound healing disruptions bacterial inflammation, bleeding/seroma discharge, and haematoma/seroma formation), the aim of this investigation was to identify and quantify possible variables practically affecting the detection of water in a systematic study. The textile sensors comprise insulated electrical wires stitched onto a textile backing and parallel wires form a plane sensor structure whose electrical capacitance is increased by water (contained in blood or lymph) in the textiles. Only parallel sensor wires forming double meanders were examined because this structure enables all the parameters of interest to be measured. Surprisingly the results are complex, neither simple nor consistent. The change in electrical capacitance (measuring signal) upon the standardized addition of water was not additive, i.e., it was not found to be correlated to the moistened area of the sensor array, but inversely correlated to the diameter of the sensor wire, mildly pronounced in connection with smaller stitching spacing (stitching loops along the sensor wires). The measuring signal reached a maximum with medium sensor wire spacings and pronounced with a smaller stitching spacing. Without exception, the measuring signal was systematically higher in connection with smaller (compared with larger) stitching spacings. The results presented indicate that the optimization of the capacitive textile sensors cannot be calculated but must instead be carried out empirically.

Selective Recognition of Acetone in Air Against Hydrogen By Impedance Measurement of Two-Terminal Electrochemical Sensors Based on Ionic Liquids

Introduction Ionic Liquids (ILs) are molten salts at room temperature and have both solvent and electrolyte properties. ILs have been actively studied for use in electrochemical gas sensors, thanks to their gas absorption property, electrochemical stability, and low evaporation loss. For example, gas sensors based on the changes in electrical double layer capacitance or in bulk impedance induced by gas dissolution in ionic liquids have been reported [1, 2]. However, there are few reports on the selective recognition of volatile organic compounds such as metabolites in human exhaled air against interfering gases. In this study, we demonstrated selective recognitions of acetone, which is a typical low-molecular-weight metabolic gas in human exhaled air, against hydrogen, which is a metabolite of enterobacteria, by electrochemical impedance measurement using ionic liquids. Method The interdigitated electrodes made of Cr/Pt shown in Fig. 1 were fabricated on a glass substrate. The 3-nm-thick chromium film acting as the adhesion layer was deposited by electron beam evaporation technique, which was followed by the pattern definition and evaporation of 100-nm-thick platinum electrode acting as the main electrical conduction layer. The droplet of 3-μL 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, a kind of ionic liquids, was casted onto the electrodes, which completed the fabrication of a two-terminal electrochemical sensor. The impedance measurements were performed under various atmospheres. The following shows the sequence of atmospheres under which the impedance responses of the fabricated sensors were measured. ⅰ) Dry air (3 min) ⅱ) (case Ⅰ) 25-ppm H2 in dry air (3 min)ⅱ) (case Ⅱ) 25-ppm CH3COCH3 in dry air (3 min) ⅲ) dry air (3 min)In the second process ii), case I or case II was chosen from two target gases; hydrogen and acetone. The gas flow rate was kept constant at 200 sccm. Impedance measurements were performed using an LCR meter (Keysight E4980A) with DC bias of 0.0 V and AC amplitude of 10 mV. The measurement frequency was varied from 300 kHz to 20 Hz. Results Fig. 2 shows the measured sensor response at (a) 200 kHz, (b) 30 Hz, and (c) 350 Hz. The sensor response is defined as impedance change ΔZ re due to target molecules normalized by the impedance in dry air Z re(Air), where Z re represents the real part of the impedance. The equation used to extract the sensor response is shown in Fig. 2. We noticed that the sensor response was strongly dependent on the measured frequency. Z re decreases at 200 kHz in both the CH3COCH3 and H2 atmospheres (Fig. 2(a)), whereas it is increased by the target molecules at 30 Hz (Fig. 2(b)). The directions of the impedance changes were the same for both the target molecules. On the other hand, at 350 Hz (Fig. 2(c)), Z re decreases in the CH3COCH3 atmosphere, although it stays constant in the H2 atmosphere. This clearly demonstrates that CH3COCH3 can be selectively detected against H2 by impedance measurement with an appropriate measurement frequency. Discussion and Conclusion We consider that the equivalent circuit of the present system includes an element related with the bulk IL resistance and one related with the electrical double layer at the electrode/IL interfaces. The measurement of the impedance phase angle reveals that the phase angle is close to 0 degrees at 200 kHz and close to -90 degrees at 30 Hz. Therefore, we consider that high-frequency (200 kHz) Z re is affected by the bulk IL resistance change induced by dissolved gaseous molecules and that low-frequency (30 Hz) Z re is influenced by the change in electrical double layer characteristics. On the other hand, at medium frequencies; namely 350 Hz in this study, the gas-induced effects both on bulk IL resistance and on the electric double layer characteristics causing Z re modulation may be compensated with each other, and no sensor response was observed under the H2 atmosphere as shown in Fig. 2(c). We will extract the equivalent circuit model for the system used in this experiment and examine how the parameters of circuit elements change in the H2 and CH3COCH3 atmospheres in comparison with the standard dry air atmosphere. By investigating the frequency dependence of the impact of each parameter change on Z re, we will clarify the mechanism of Z re constancy in the H2 atmosphere at medium frequencies.

Outer diameter Curvature effects in Multi-Walled carbon nanotubes on the twistron energy harvester

We describe an experimental and computational study of increased electrical double layer capacitance (EDLC) changes and improved harvesting performances in multi-walled carbon nanotube (MWCNT) yarn-based energy harvesters using smaller-diameter MWCNTs. Twisted MWCNT yarn-based energy harvesters convert tensile mechanical energy into electrical energy by utilizing changes in the EDLC on the surface of MWCNTs. The correlation of the variance in EDLC and open circuit voltage (OCV) of the coiled MWCNT yarn was investigated under the mechanical stretch applied to the twistron energy harvester, and both OCV and capacitance increased as the MWCNT diameter decreased. We performed molecular dynamics (MD) simulations to elucidate the mechanisms of the increasing EDLC and OCV of twistron energy harvesters, which were verified by experiment. The computational results elucidate the relationship between the decrease in MWCNT diameters and the increasing number density of interstitial spaces between multi-walled MWCNTs. The decrease in the total surface area of the interstitial spaces is an important factor in the capacitance change of the twistron energy harvester under longitudinal stretching. Such novel findings are a foundation for the development of a twistron harvester with significantly improved energy harvesting performance.

Temperature-Controlled Assembly and Characterization of a Droplet Interface Bilayer.

The droplet interface bilayer (DIB) method for assembling lipid bilayers (i.e., DIBs) between lipid-coated aqueous droplets in oil offers key benefits versus other methods: DIBs are stable and often long-lasting, bilayer area can be reversibly tuned, leaflet asymmetry is readily controlled via droplet compositions, and tissue-like networks of bilayers can be obtained by adjoining many droplets. Forming DIBs requires spontaneous assembly of lipids into high density lipid monolayers at the surfaces of the droplets. While this occurs readily at room temperature for common synthetic lipids, a sufficient monolayer or stable bilayer fails to form at similar conditions for lipids with melting points above room temperature, including some cellular lipid extracts. This behavior has likely limited the compositions-and perhaps the biological relevance-of DIBs in model membrane studies. To address this problem, an experimental protocol is presented to carefully heat the oil reservoir hosting DIB droplets and characterize the effects of temperature on the lipid membrane. Specifically, this protocol shows how to use a thermally conductive aluminum fixture and resistive heating elements controlled by a feedback loop to prescribe elevated temperatures, which improves monolayer assembly and bilayer formation for a wider set of lipid types. Structural characteristics of the membrane, as well as the thermotropic phase transitions of the lipids comprising the bilayer, are quantified by measuring the changes in electrical capacitance of the DIB. Together, this procedure can aid in evaluating biophysical phenomena in model membranes over various temperatures, including determining an effective melting temperature (TM) for multi-component lipid mixtures. This capability will thus allow for closer replication of natural phase transitions in model membranes and encourage the formation and use of model membranes from a wider swath of membrane constituents, including those that better capture the heterogeneity of their cellular counterparts.

Измерение EGTA-опосредованного нарушения барьерной функции с помощью импедансной спектроскопии

For the widespread use of in vitro models of barrier tissues in practice, it is necessary to develop approaches to the automation of cultivation and monitoring of the state of cells. Impedance spectroscopy is a promising and informative method for assessing the state of cell barriers. In this work, the dynamics of electrical parameters in an in vitro model of the intestinal barrier with a high temporal resolution has been studied using impedance spectroscopy. For the first time, the detailed kinetics of changes in TEER, electrical capacitance and additional resistance of a monolayer of Caco-2 cells at various EGTA concentrations was recorded. It was demonstrated that spontaneous restoration of the integrity of the cell barrier is possible in the presence of 2 mM EGTA in the medium, which begins approximately 6 h after the compound addition. A strong increase in TEER was also found immediately after the addition of EGTA, which probably depended on the EGTA concentration and can be explained by a decrease in intracellular conductance due to the closure of transmembrane channels. impedance spectroscopy, intestine, TEER, electrical capacitance, EGTA The study was funded by the Russian Science Foundation (project 16-19-10597).

Theoretical Description for the Galvanostatic Electrode Pretreatment, Yielding Thiourea-Based Active Surface for Cathodic Conducting Polymer Deposition

The system with the electrode modification by thiourea basic derivatives for conducting polymer indirect cathodic deposition has been described from the theoretical point of view. The electrode pretreatment process has been analyzed using the linear stability theory and bifurcation analysis. It was shown that the steady-state is realized rapidly and provides efficient surface pretreatment. On the other hand, the oscillatory and monotonic behavior, in this case, is also possible due to the double electric layer capacitance changes during the doping stage and electrochemical reaction.

Frying Oil Evaluation by a Portable Sensor Based on Dielectric Constant Measurement.

A portable capacitive sensor was designed to assess frying oil degradation by measuring the changes in electrical capacitance. An interdigital electrode (IDE) was designed to be implemented as the testing probe (as IDEs are resistive to parasitic capacitance), together with an adjacent capacitive chip Pcap01 and a further microprocessor STM32, which were used as the data-processing elements. Experimental results demonstrated that viscosity could be a useful frying oil quality indicator, and also proved a preliminary correlation between IDE capacitance and oils’ total polar materials. This implies that IDE capacitance could be a suitable metric for conveniently assessing frying oil degradation. The designed capacitance sensor is light in weight, cost effective, and has excellent potential for simple, inexpensive, on-the-spot testing of the current quality of frying oil.

Piezoelectret-based and piezoresistivity-based stress self-sensing in steel beams under flexure

This work reports for the first time the structural self-sensing of stress in steel beams under flexure (elastic regime, ≤200 MPa) through measurement of the electric field (piezoelectret), capacitance (dielectricity) and resistance (piezoresistivity). Coplanar electrodes on the top or bottom surface are used. Under flexure, the electric field and resistance increase at the top surface, but decrease at the bottom surface, while the capacitance decreases at both surfaces. Under normal compression, the electric field, capacitance and resistance decrease at both surfaces. For flexure and normal compression, the resistance and capacitance changes are essentially completely reversible, whereas the electric field change is not. Longitudinal tension (whether in flexure or normal compression) causes the electric field to decrease, whereas longitudinal compression (in flexure) causes the electric field to increase. Longitudinal tension (whether in flexure or normal compression) causes the resistance to decrease, whereas longitudinal compression (in flexure) causes the resistance to increase (negative piezoresistivity). The capacitance (2 kHz) decreases due to the stress (whether flexure or normal compression and whether at the top or bottom surface) and is attributed to the permittivity decrease, except that the capacitance decrease under longitudinal compression (in flexure) is attributed to the AC voltage used to measure the capacitance penetrating the full thickness and the effect of longitudinal tension at the bottom surface dominating over that of longitudinal compression at the top surface. In contrast, the DC voltage used to measure the resistance is much smaller and does not penetrate the full thickness, so that the resistances at the top and bottom surfaces respond to flexure differently. The magnitude of the fractional change in electric field, capacitance or resistance increases with decreasing beam width.

Acoustic Length Sensor for Soft Extensible Pneumatic Actuators With a Frequency Characteristics Model

In this study, we present a length sensor that can be used for extensible soft pneumatic actuators. Conventional length sensors detect the changes in electrical resistance and capacitance owing to the deformation of the actuator; hence, deterioration and destruction occur when they are used with an actuator that has a large expansion ratio. In addition, their low resolution and linearity makes them unsuitable for use in actuator control. Our proposed sensor comprises only a speaker and a microphone installed at one end of the actuator. We propose a method to deterministically measure the length of a tube by generating a broadband acoustic signal in a tube and measuring the resonance characteristics determined by the shape of the tube. Our experimental results demonstrate that the error in the measurement with our sensor is not more than 4% with a strain up to 200%. Unlike conventional acoustic sensing methods that measure the time of flight by using ultrasound, our proposed method yields accurate results even when the tube is bent. Therefore, the proposed method can be applied to various types of pneumatic actuators.

Dependence of an electric capacitance on the constant voltage C\u2009=\u2009f(U) in pure bentonite, composites and semiconductors

The present paper is devoted to studying the effect of dc voltage on the amount of electrical capacitance in pure bentonite, composites and semiconductors with different conductivity, as well as the dependence of electrical conductivity on the external field. The reason for the dependence of the capacitance on the DC voltage may be the presence of potential barriers in them and the dependence of the electrical conductivity (σ) on the applied voltage. In those samples where there is a large range of variation of σ, there are also large changes in electrical capacitance. The principle of a change in electrical conductivity, a change in the electrical capacitance is observed, can be successfully used in microelectronics, electrical engineering, etc. Created capacities parameters can changed in a wide range of voltage and temperature.

Electrochemical Impedance Spectroscopy as a Practical Tool for Monitoring the Carbonation Process on Reinforced Concrete Structures

Carbonation results in a decrease in the pH of the cementation matrix when CO2(g) from the environment diffused into the concrete structure that can cause the loss of passivity condition on the reinforcing steel surface and leads to early failure of concrete by corrosion attack. There are several monitoring techniques to evaluate the process of lowering the pH in the concrete, named carbonation depth progress. In this research, an electrochemical AC impedance spectroscopy (EIS) technique has been used as an effective laboratory tool for monitoring the evolution of the carbonation progress. A comparison with the traditional phenolphthalein colorimetric technique was also discussed here. Particularly, monitoring is achieved by measuring the change in electrical resistance (Rpo) and capacitance (Cpo) of the concrete bulk, which is obtained from the semicircle at high-frequency region of a typical EIS diagram. According to the EIS results, carbonation progress was observed by a significant increase in the diameter of the semicircle, thus demonstrating the increase in resistivity of ions transmission due to blockade of pores by precipitation of CaCO3 compounds. Furthermore, it was possible to predict the specific time at which the carbonation front reaches the steel-rebar interface at low frequency region and possibly starting a considerable corrosion attack. Finally, the results suggested that EIS technique could be considered a practical tool for evaluating the carbonation progress of reinforced concrete structures without causing structural damage, in addition to the sensitivity of this technique with sufficient accuracy to predict the activation of the reinforcing steel.

Computational Modeling and Validation of Thermally Induced Electrical Capacitance Changes for Lipid Bilayer Membranes Irradiated by Pulsed Lasers.

Neural stimulation has widespread applications in investigating brain functions, restoring impaired neural functions, and treating numerous neurological/psychiatric diseases. Use of infrared pulses to stimulate neurons (infrared neural stimulation) offers a direct and non-invasive technique. Recent research has demonstrated that transient heating associated with the absorption of infrared light by the local aqueous medium around the cell membrane can stimulate nerves. One mechanism for this stimulation is due to a thermally induced increase in the membrane electrical capacitance, which causes cell depolarization as well as action potential production under certain physiological conditions. A theoretical and computational model helps better understand the mechanism of thermally induced electrical capacitance changes and optimize the stimulus parameters. In this article, we develop the existing theoretical models for membrane electrical capacitance and its thermally induced changes. We improve the formulation of Gouy-Chapman-Stern theory by Genet et al. and Shapiro et al. with the addition of a diffuse layer to the electrical double layer and by modifying the relation of Stern layer capacitance, to calculate the membrane capacitive charge and capacitive current. We also present a new method to calculate the membrane electrical capacitance and the rate of its thermally induced changes. In our calculations, two new factors are considered including the temperature dependence of the surface charge density and the hydrophobic core dielectric constant of the lipid bilayer. Our developed model predicts rates of 0.3 and 0.26%/°C for the thermally induced capacitance changes of the artificial lipid bilayer under two different sets of conditions previously reported by Shapiro et al. and Carvalho-de-Souza et al., respectively. Our model is in very good agreement with the corresponding experimental values given by these groups. The presented model is also able to calculate the membrane capacitive currents and investigate the voltage dependence of this current.

Mechanical and electrical behavior of carbon fiber structural capacitors: Effects of delamination and interlaminar damage

This paper studies the effects of delamination and interlaminar damage on the mechanical and electrical performance of carbon-fiber structural capacitor (CFSC) materials. An experimental program was carried out to characterize the mechanical behavior and electrical capacitance change of CFSCs, where unidirectional tension and double cantilever beam tests were performed on specimens having three dielectrics and four layup configurations. The degradation of electric capacitance was measured as a function of the applied mechanical load. Generally, the load-bearing capacities of CFSCs are lower than their carbon-fiber reinforced epoxy counterparts. Interlaminar damage initiates at the dielectric/carbon fiber interface during early stages of loading, causing capacitance decay and premature laminate failure. The dielectric material and layup configuration have impacts on both mechanical and electrical properties of the CFSC. In general, thinner dielectric separators lead to higher nominal strength and higher initial capacitance. Moreover, it was found that the load-induced capacitance deterioration is mainly attributed to interlaminar damage, and the electrical capacitance retention under loading depends largely on the interfacial fracture toughness between the separator and matrix polymer. Lastly, a capacitance deterioration model (CDM) was derived to calculate the capacitance decay taking account factors including the separator material type, fiber weave-pattern, and interfacial cracks propagation.

An In Vitro Model of the Blood-brain Barrier Using Impedance Spectroscopy: A Focus on T Cell-endothelial Cell Interaction.

Breakdown of the blood-brain barrier (BBB) is a critical step in the development of autoimmune diseases such as multiple sclerosis (MS) and its animal model experimental autoimmune encephalomyelitis (EAE). This process is characterized by the transmigration of activated T cells across brain endothelial cells (ECs), the main constituents of the BBB. However, the consequences on brain EC function upon interaction with such T cells are largely unknown. Here we describe an assay that allows for the evaluation of primary mouse brain microvascular EC (MBMEC) function and barrier integrity during the interaction with T cells over time. The assay makes use of impedance cell spectroscopy, a powerful tool for studying EC monolayer integrity and permeability, by measuring changes in transendothelial electrical resistance (TEER) and cell layer capacitance (Ccl). In direct contact with ECs, stimulated but not naïve T cells are capable of inducing EC monolayer dysfunction, as visualized by a decrease in TEER and an increase in Ccl. The assay records changes in EC monolayer integrity in a continuous and automated fashion. It is sensitive enough to distinguish between different strengths of stimuli and levels of T cell activation and it enables the investigation of the consequences of a targeted modulation of T cell-EC interaction using a wide range of substances such as antibodies, pharmacological reagents and cytokines. The technique can also be used as a quality control for EC integrity in in vitro T-cell transmigration assays. These applications make it a versatile tool for studying BBB properties under physiological and pathophysiological conditions.

Temperature compensation in a low cost frequency domain (capacitance based) soil moisture sensor

Frequency Domain Analysis is a well established technique in soil moisture determination, using the change in electrical capacitance of probes inserted into the soil caused by the presence of water. However it is known that temperature affects the determination of this capacitance. Here two different techniques are used, the first passing a fixed frequency through the soil via insulated probes, then measuring the amplitude of the resultant signal. The second uses the soil capacitance as the controlling component in a variable frequency oscillator, measuring the resultant times to charge and discharge. The measured capacitance is seen to be affected both by the temperature of the soil and, due to the sensitive nature of the monitoring electronics, also the temperature of critical components in the measurement circuits. Results from these experiments show that these two effects are complementary, soil temperature adding to the measured capacitance, whilst electronics temperature effectively decreases the measured capacitance. The daily profiles of the soil and electronics temperatures, whilst both rising during the day, and falling at night, show significant phase difference and therefore do not simply cancel out. Further, the strength of temperature compensation required is shown to vary with technique and moisture level. This paper explores these phenomena using results from a recently developed, four probe Frequency Domain capacitance based sensor costing around 12 Euros. These measurements are compared to those achieved by a commercial soil moisture system costing over 250 times this price. Preliminary results are presented from temperature compensation algorithms intended to minimize these effects.

Development of a Carbon Nanotube-Based Touchscreen Capable of Multi-Touch and Multi-Force Sensing.

A force sensing touchscreen, which detects touch point and touch force simultaneously by sensing a change in electric capacitance, was designed and fabricated. It was made with single-walled carbon nanotubes (SWCNTs) which have better mechanical and chemical characteristics than the indium-tin-oxide transparent electrodes used in most contemporary touchscreen devices. The SWCNTs, with a transmittance of about 85% and electric conductivity of 400 Ω per square; were coated and patterned on glass and polyethyleneterephthalate (PET) film substrates. The constructed force sensing touchscreen has a total size and thickness of 62 mm × 100 mm × 1.4 mm, and is composed of 11 driving line and 19 receiving line channels. The gap between the channels was designed to be 20 µm, taking visibility into consideration, and patterned by a photolithography and plasma etching processes. The mutual capacitance formed by the upper and lower transparent electrodes was initially about 2.8 pF and, on applying a 500 gf force with a 3 mm diameter tip, it showed a 25% capacitance variation. Furthermore, the touchscreen can detect multiple touches and forces simultaneously and is unaffected by touch material characteristics, such as conductance or non-conductance.

Evaluation of theophylline imprinted polypyrrole film

In this study some affinity and dielectric properties of molecularly imprinted (MIP) conducting polymer—polypyrrole (Ppy) based thin films were evaluated. Films of polypyrrole molecularly imprinted with theophylline (MIP–Ppy) and non-imprinted polypyrrole (NIP–Ppy) were formed on boron doped silicon (Si) substrates in order to evaluate the efficiency of Ppy to bind theophylline. The substrates were modified with boron-doped oxygen terminated nanocrystalline diamond (B:NCD:O) The dielectric properties of B:NCD:O/Ppy-based multi-layered structures were analyzed using spectroscopic ellipsometry and spectrophotometric techniques. Electrochemical impedance spectroscopy was applied for the investigation of kinetics of theophylline interaction with MIP–Ppy and NIP–Ppy. The sensitivity of molecularly imprinted and non-imprinted polymer films was analyzed by injection of different theophylline concentrations. Assuming that Ppy film electrical capacitance change is a result of Ppy dielectric constant change induced by absorbed theophylline molecules, the electrical capacitance change (ΔC) kinetics at different concentrations of theophylline was analyzed using first pseudo order kinetic equation. The dissociation equilibrium constant KD of MIP–Ppy/theophylline complex at room temperature was calculated as 1.7×10−8M, and Gibbs free energy change (ΔG) of MIP–Ppy/theophylline complex formation was calculated as −43.5kJ/mol. It was concluded that molecularly imprinted polypyrrole thin film could be used for the detection of theophylline.