Interdigitated Research Articles

Development of conductive carbon-based interdigitated electrode array integrated with microfluidic channel for blood glucose sensing

PurposeThis study aims to provide a microfluidic blood glucose sensing platform based on integrated interdigitated electrode arrays (IDEAs) on a flexible quartz glass substrate, adhering closely to pertinent electrochemical characterizations.Design/methodology/approachSensors are the key elements of the modern electronics era through which all the possible physical quantities can be detected and converted into their equivalent electrical form and processed further. But to make the sensing environment better, various types of innovative architectures are being developed nowadays and among them interdigitated electrodes are quite remarkable in terms of their sensing capability. They are a well-qualified candidate in the field of gas sensing and biosensing, but even their sensitivities are getting saturated due to their physical dimensions. Most of the thin film IDEAs fabricated by conventional optical lithographic techniques do not possess a high surface-to-volume ratio to detect the target specified and that reduces their sensitivity factor. In this context, a classic conductive carbon-based highly sensitive three dimensional (3D) IDEA-enabled biosensing system has been conceived on a transparent and flexible substrate to measure the amount of glucose concentration present in human blood. 3D IDEA possesses a way better capacitive sensing behavior compared to conventional thin film microcapacitive electrodes. To transmit the target biological analyte sample property for the detection purpose to the interdigitated array-based sensing platform, the design of a microfluidic channel is initiated on the same substrate. The complex 3D Inter Digital array structure improves the overall capacitance of the entire sensing platform and the reactive surface area as well. The manufactured integrated device displays a decent value of sensitivity in the order of 5.6 µA mM−1 cm−2.FindingsDevelopment of a low-cost array-based integrated and highly flexible microfluidic biochip to extract the quantity of glucose present in human blood.Originality/valuePotential future research opportunities in the realm of integrated miniaturized, low-cost smart biosensing systems may arise from this study.

Study of the ZnO/MoS2 heterostructures-based gas sensor for humidity-independent response

In this study, several strategies including coating with a hydrophobic MoS2 layer, UV light illumination, raising temperature, alternating current (AC), and four-probe measurement have been systematically studied to overcome humidity dependence response behavior for the ZnO sensor. Catalyst-free CVD method was used to prepare pure ZnO nanorods and ZnO/MoS2 heterostructures, and the prototypes were then fabricated on the substrates with Pt interdigital (ID) electrodes, respectively. The gas sensing properties of two sensors were systematically investigated. The ZnO/MoS2 heterostructures-based sensor with four-probe measurement operating at 150 °C shows stable responses during a wide humidity variation range. Furthermore, the ZnO/MoS2 sensor obtains excellent sensing performance to NO2 with a high sensitivity of 12.6 %/ppm and high sensor responses at 150 °C and UV light illumination. Additionally, a low theoretical LoD of 6.5 ppb NO2 is achieved for ZnO/MoS2 heterostructures-based sensor.

Design of heterostructure one-port SAW resonator with improved bandwidth using Si and LiNbO3 layer

In this research work, we have designed a heterostructure one-port surface acoustic wave (SAW) resonator. The multi-layer one port SAW resonator is made of a silicon (Si) substrate as base material, 128 ͦ rotated Y-cut X- propagated lithium niobate (LiNbO3) as piezoelectric substrate, and Inter Digital Transducers (IDTs) made of aluminium. This model is designed to operate on a wide frequency of 4–5 GHz with a resonance frequency of 4.74 GHz. Various parameters are taken into consideration during the study and analysis such as high-quality factor, wider bandwidth, better electromechanical coupling coefficient, and a true Figure of merit (FoM). The obtained Quality factor and the electromechanical coupling coefficient (k2) of the designed model are 2700 and 0.18. By using the wide range of frequencies, the bandwidth for the designed model is 1.74 MHz. The obtained results show that the device’s performance of the one port multilayer SAW resonator using the Al/128°YXLiNbO3/Si multi-layered substrate exhibits a commercial application in the 5 G wireless communication system.

Demonstration of a roll-to-roll-configurable, all-solution-based progressive assembly of flexible transducer devices consisting of functional nanowires on micropatterned electrodes

We demonstrate continuous fabrication of flexible transducer devices consisting of interdigitated (IDT) Ag microelectrodes interconnected by ZnO nanowires (ZNWs), created via serially connected solution-processable micro- and nanofabrication processes. On an Ag layer obtainable from the mild thermal reduction of an ionic Ag ink coating, the roll-to-roll-driven photolithography process [termed photo roll lithography (PRL)] followed by wet-etching can be applied to continuously define the IDT microelectrode structure. Conformal ZNWs can then be grown selectively on the Ag electrodes to interconnect them via an Ag-mediated hydrothermal ZNW growth that does not require high-temperature seed sintering. Given that all of these constitutive processes are vacuum-free and solution-processable at a low temperature, and are compatible with continuous processing onto flexible substrates, they can be eventually configured into the roll-to-roll-processable progressive assembly. Through parametric optimizations of processes consisting of the roll-to-roll-configurable, solution-based progressive assembly of nanostructures (ROLSPAN), a flexible transducer consisting of ZNW-interconnected, PRL-ed IDT Ag electrodes can be developed. This flexible architecture faithfully performs UV sensing as well as optoelectronic transduction. The ROLSPAN concept along with its specific applicability to flexible devices may inspire many diverse functional systems requiring high-throughput low-temperature fabrication over large-area flexible substrates.

Low-Cost, High-Sensitivity Paper-Based Bacteria Impedance Sensor Based on Vertical Flow Assay

This study proposes a low-cost, portable paper-fluidic vertical flow assay bacterium counter with high accuracy. We designed sensors with low fabrication costs based on e-beam evaporation and three-dimensional printing based on the impedance measurement principle. Interdigitated (IDT) electrodes were coated on the filter membrane by e-beam evaporation with a shadow mask. We could print wafer-scale frames with low melting temperature three-dimensional-printing materials for confining liquid bacterial samples within the IDT sensing region. This novel fabrication technique significantly reduced the chip’s cost to less than 1% of that of silicon-based chips. Two equivalent circuit models were proposed for different concentration ranges to analyze the principle of paper-based impedance bacterial sensors. We proposed an improved model based on the Randles model for low concentrations by considering the leaky double-layer capacitor effect and spherical diffusion from the nano-structural electrodes of the gold-coated filter membrane. The phenomenon in which charge transfer resistance, Rct, declines at high concentration ranges was found and explained by the pearl chain effect. The pearl effect could cause a false-negative at high concentrations. We modeled the pearl chain effect as an R and C, connected parallel to the low-concentration model. When users properly applied both models for analyses, this sensor could quantitatively measure cell concentrations from 400 to 400 M per milliliter with superior linearity.

Analytical Evaluation of a Coplanar Interdigitated Sensor Capacitance for 1-N-1 Multilayered Structure

In this article, an analytical expression (model) for the capacitance of coplanar interdigitated (IDT) capacitive sensors of four 1- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$n$ </tex-math></inline-formula> -1 patterns (such as 1-1-1, 1-3-1, 1-5-1, and 1-11-1) based on conformal mapping (CM) techniques has been obtained. An important feature of the proposed model is that it is universal and independent of any specific application. The proposed model can be used for any number of layers (variable permittivity and thickness), finger width, and the gap between the fingers. In general, the capacitance of a particular IDT sensor depends on finger (electrode) length, the number of fingers, potential distribution of the fingers, dielectric permittivity (substrate and sensitive layers), and geometric parameters (nondimensional): 1) the ratio between the finger widths and gap and 2) the ratio between the top sensitive layer thickness and the sensor wavelength (spatial). Keeping these parameters in mind, comparisons with finite element analysis and experimental results have been made. Also, to confirm the effectiveness of the proposed model, different patterns of 1- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$n$ </tex-math></inline-formula> -1 structured IDT sensors have been developed to measure the water droplets on the leaf canopy by a noncontact method. The proposed sensor structure can be said to be a noncontact leaf wetness sensor (LWS), generally employed to quantify the leaf wetness duration (LWD).

Quantitative Analysis of H+ Transportation of Nafion film on Different Substrate using Planar Inter Digitated Electrodes

Introduction: Ionomer thin-film gained attraction because of their thickness- and morphology-dependent changes in ionic conductivity. In a fuel cell catalyst layer, ionomer thin films coating the carbon-supported Pt-based catalysts (Pt/C) is distributed in spatially heterogeneous manner with variation in thickness and connectivity. Thus, it is difficult to clarify the quantitative attribution of the true source of effective proton resistance among Pt and carbon-support. To evaluate the quantitative attribution of proton conductivity of a thin-film ionomer on relevant substrates (e.g., carbon), we have fabricated specially designed interdigitated electrodes (IDEs) to accommodate different substrates upon which ionomer film is coated. In this work, we present the Nafion (~55 nm) proton (H+) transportation over carbon and quartz substrate in N2 atmosphere. Also, we will discuss the true attribution of substrate-dependence to estimate the Nafion’s thin film conductivity. Experimental: Interdigitated electrodes (IDEs) with and without carbon pad were fabricated in clean room facilities. To prepare IDEs, the patterned carbon structure was developed and pyrolyzed at 1000 ºC in 2% H2/N2 gas before the Pt deposition. 1.2% Nafion dispersion was spin coated and dried at 40ºC under vacuum before electrochemical impedance spectroscopy (EIS) measurement in N2 atmosphere. Relative humidity (RH) dependence of in-plane H+ resistance was obtained and discussed through EIS measurements. Results and Discussion: Figure 1 (a) and (b) shows the side view of IDEs with (Pt_C_IDE) and without carbon pad (Pt_Q_IDE), and also Nafion’s (~55 nm) H+ resistance obtained from EIS measurement at various RH in N2 atmosphere. Nyquist plot (not shown) exhibited significant difference and ascribed film resistance (Mean value) for ionomer at carbon substrate was significantly lower (one order of magnitude) compared to that at the quartz substrate, as shown in Fig. 1 (c).In case of H+ resistance using Pt IDE with carbon (Pt_C_IDE), approximately 90% of the IDE area between the electrodes is carbon and the rest is quartz. Therefore, the method of estimation of Nafion’s thin film conductivity from impedance response must be reviewed carefully and will be discussed later in detail.

Fabrication of flexible carbon heaters and silver interdigitated electrodes using ink-jet printing technology for electro-chemical gas sensor applications

PurposeThe purpose of this paper is to deal with an identification of a novel ink-jet printing sensor fabrication technology for fabricating flexible carbon heaters of macro and micro sizes, carbon interdigitated (IDT) electrodes and silver IDT electrodes. The technology involved in the proposed ink-jet printing method and materials used for the formulation of homemade nano-conductive inks (digital inks) are discussed in detail. The ink-jet printed flexible carbon heaters of different sizes (macro and micro) and carbon IDT electrodes and flexible silver IDT electrodes can be used as the flexible sensing layers in electrochemical gas sensors for sensitive and selective gas sensing applications. The characterization of ink-jet printed carbon heaters on Kapton substrate and its results are discussed. Similarly, the results of formulation of silver nano-conductive ink and printing of silver IDT electrodes on Kapton and its characterization are reported here for the first time.Design/methodology/approachFlexible carbon heaters of different sizes (macro and micro), carbon micro-IDT electrodes and silver IDT electrodes patterns were developed using AutoCAD 2D and printed on the Kapton (polyimide sheet) flexible substrate using the home-made nano-conductive inks with the help of EpsonT60 commercial piezo-head-based drop-on demand technology printer with standard printing options.FindingsThe proposed novel method is able to print heater patterns and IDT electrode patterns of approximately 12 µm and approximately 1 µm thickness, respectively, on flexible substrate using the home-made nano-conductive inks of carbon and silver by using a commercial low-cost printer. The home-made nano-conductive inks can be re-used for multiple prints up to six months shelf life. The resistance of the carbon heater was measured as 88 O under normal atmospheric condition. The novel flexible carbon heater was tested for its functionality and found to be satisfactory. The resistance of the silver IDT flexible electrodes was measured as 9.5 O which is better than the earlier works carried out in this paper.Research limitations/implicationsThe main challenge is associated with cleaning of printing ink ejection system in the existing commercial printers. The customization of the existing printer in the near future can minimize the printing challenges.Practical implicationsThe novel ink-jet printing technology proposed in this work is cost-effective, capable of achieving bulk production of flexible sensor elements, and consumes the least device fabrication time and high material yielding. The printing can be done with commercial piezo-head-based ink-jet printers with custom-prepared nano-conductive inks. There is a huge market potential for this paper.Originality/valueBoth the carbon heaters and silver IDT electrodes were printed on Kapton flexible substrate by using the commercial printer for the first time. The paper is promising the revolution in flexible low-cost sensor fabrication for mass production, and it is an alternate for thin film and thick sensor fabrication methods. The future of sensor fabrication technology will be the ink-jet printing method. In this paper, the research developments of flexible carbon heaters and flexible silver IDT electrodes for the time are reported. The characterization of carbon heaters and silver IDT electrodes were carried out and confirmed that the results are favourable for gas sensor applications.

An A0 mode Lamb-wave AlN resonator on SOI substrate with vertically arranged double-electrodes

In this paper, a novel vertically arranged double-electrodes A0 mode Lamb-wave AlN resonator on SOI substrate with a high electromechanical coupling coefficient and high figure of merit (FOM) is reported. The AlN resonator has a sandwich structure with aluminum and N-type doped silicon as electrode layers and a 500 nm thick AlN film as piezoelectric layer. The resonator has only two electrodes vertically arranged rather than horizontal interdigitated (IDT) electrodes which is common in conventional Lamb-wave resonators. The electrode gaps for the vertically arranged double-electrodes resonators are defined by AlN layer thickness rather than by photolithography for lateral field excitation resonators, which results in higher electric field strength and higher electromechanical coupling efficient (). Compared with conventional thickness field excitation (TFE) resonators with floating bottom electrodes, the vertically arranged double-electrodes resonators have higher electric field strength as the potential difference is larger between the top electrode and bottom electrode than that between the IDT electrodes and floating electrode. As a result, a higher electromechanical coupling coefficient is achieved. Furthermore, the resonant frequency of the vertically arranged double-electrodes resonator presented in this work can be defined by photolithography by controlling the width of the silicon layer. The of the vertically arranged double-electrodes resonator calculated from the measurement results of admittance versus frequency by numerically fitting with the Butterworth Van Dyke model shows an increase by 3.85 times, from 0.073% to 0.281% compared with conventional TFE resonators, and the FOM also increases by three times, from 2.66 to 7.99. This work provides a new structure to design future AlN Lamb-wave resonators on SOI substrate.

Cobalt Iodate Microparticles for Highly Sensitive Acetone Gas Sensor Applications

Introduction Acetone is well known as a breath gas biomarker of diabetes patient, at concentration level greater than 1.8 ppm in exhaled breath gases1. Thus, the precise and selective detection of a low concentration (sub-ppm level) of acetone in breath gases containing over 1,000 kinds of gas species can characterize the diagnosis of diabetes. Therefore, reliable acetone gas sensors with highly sensitive and selective acetone response are essential for diagnosis of diabetes. Metal oxide semiconductor (MOS) is one of the most popular acetone gas sensing materials because of their high sensitivity, fast response, and low-cost fabrication2. In an effort to improve the selectivity and sensitivity, decoration of catalysts on MOS materials has been suggested. In this study, we used iodine as catalysts on cobalt oxide-based materials and fabricated gas sensors using sol-gel derived cobalt iodate [Co(IO3)2] which has a good sensitivity and selectivity toward a low concentration of acetone gas. We also thoroughly characterized the materials using scanning electron microscope (SEM), X-ray diffraction (XRD), electron probe micro-analyzer (EPMA), and polarization-electric field characteristics to figure out the gas sensing mechanism. Method Co(IO3)2 micro-particles were synthesized by precipitation method from aqueous solutions of Co(CH3COO)2·4H2O and HIO3 as precursors. For evaluation of effect of iodine doping on cobalt oxide-based materials on gas sensing performance, Co3O4 micro-particles were also synthesized by the same method using NH4OH precursor instead of HIO3. The obtained precipitates were washed with distilled water and ethanol, followed by drying step. We used the structure of interdigitated (IDT) electrodes for sensor fabrication, described in our previous work3. These powders were dispersed in DI water (1 wt%) and drop-casted on the IDT electrodes on a hot plate at 100 °C. After evaporation of the solvent, the devices were eventually calcined in air at various temperatures. Sensing measurements were done in a gas sensing system varying operating temperatures using a power supply. The gas concentrations were controlled diluting target gases with dry air. We tested gas responses by monitoring changes in resistances of Rg/Ra or Ra/Rg, where Rg is a resistance during exposure to the target gas, and Ra is a resistance in air, respectively. Results and Conclusions Figure 1(a) represents gas responses of samples based on Co(IO3)2 and Co3O4 toward 1.8 ppm of acetone at operating temperature of 250 °C. The gas responses of the Co3O4 sample are much smaller than that of Co(IO3)2 sample. Accordingly, iodine in a high concentration could play a beneficial role in acetone sensing processes for the sensors. Figure 1(b) shows gas responses for the Co(IO3)2 sample annealed at 300 °C toward various gases of 1.8 ppm such as acetone, toluene, NO2, NH3, H2, and H2S at 250 °C, representing a good selectivity. The optimum operating temperature is found to be 250 °C. Acknowledgments J.-S. Park was partially supported by the ATC program (Grant No. 10076984) from MOTIE of the Rep. of Korea. References C. Deng, J. Zhang, X. Yu, W. Zhang, and X. Zhang, J. Chromatogr. B, 810, 269–275 (2004).2. Y. Li, M. Zhang, and H. Zhang, Phys. B, 29, 90702 (2020) http://cpb.iphy.ac.cn.S. Nundy et al., Ceram. Int., 46 (2020). Figure 1

Recent Progress in the Topologies of the Surface Acoustic Wave Sensors and the Corresponding Electronic Processing Circuits.

In this paper, we present an overview of the latest achievements in surface acoustic wave (SAW) sensors for gas or liquid fluid, with a focus on the electrodes’ topology and signal processing, as related to the application of the sensing device. Although the progress in this field is mainly due to advances in the materials science and the sensing coatings, the interdigital (IDT) electrodes’ organization is also an important tool for setting the acoustic-wave-distribution mode, and, thus, for improvement of the SAW performance. The signal-conditioning system is of practical interest, as the implementation of the SAW, as a compact and mobile system is dependent on this electronic circuit. The precision of the detection of the SAW platform is related not only to the IDT electrodes’ geometry but also to their location around the sensing layer. The most commonly used architectures are shown in the present paper. Finally, we identify the needs for the future improvement of these prospective sensors.

Structural design and experimental analysis for AlN Lamb-wave resonators with different electrical boundary conditions

This paper presents an Aluminum Nitride (AlN) Lamb-wave resonator with high series-resonance quality factors (Qs) and good spectral purity. The influence of the interdigitated (IDT) electrode width and electrical boundary condition was theoretically analyzed to improve effective electro-mechanical coupling coefficient (k2eff) and spectral purity. According to the structural characteristic of the designed resonators, an advanced micro-manufacturing process was designed. A thermal oxide layer was employed to avoid the etching of inactive regions, which contributes to achieving the high Qs and high-yield fabrication. The measured results show the IDT-ground resonators with 12 μm and 6 μm electrode periods exhibit Qs values as high as 4457.1 and 2625.1, and k2eff of 0.61% and 0.33%, respectively. The IDT-IDT resonators have higher k2eff, but their Qs values are severely attenuated. Through observing their section morphologies, the measured shear angles of the bottom IDT electrodes with 12 μm and 6 μm periods are 54.95° and 65.7° respectively, and the surface AlN film has tiny cracks, which induces the performance deterioration of the IDT-IDT resonators. Moreover, the influence of the IDT material on the resonator’s performance was also analyzed.

High Quality-Factor and Spectrum-Clean AlN Lamb-Wave Resonators with Optimized Lateral Reflection Boundary Conditions and Transducer Design.

This paper presents a high quality-factor (Q) and spectrum-clean AlN Lamb-wave resonator (LWR). The width of its lateral reflection boundary was optimized to weaken the transverse modes’ coupling and wave guiding, and then to improve the LWR’s Q value and spectral purity, which was verified by finite element analysis and experimental characterization. In addition, the series resonance quality factor (Qs) value of the interdigitated (IDT)-Ground LWR is similar to that of the IDT-Floating LWR, but its parallel resonance quality factor (Qp) is nearly doubled, due to the reduction of the electrical loss induced by its static capacitance (C0). The measured results show that the designed LWR with optimized boundary reflection conditions and IDT-Ground structure exhibit Qs and Qp values as high as 4019.8 and 839.5 at 401.2 MHz and 402.9 MHz, respectively, meanwhile, it has good spectral purity. Moreover, the influence of the metal ratio and material of the LWR’s IDT electrodes on the device’s performance was also studied by theoretical analysis and experimental verification.

Characterization analysis of quality factor, electro-mechanical coupling and spurious modes for AlN Lamb-wave resonators with fs> 2 GHz

In this paper, a systematical study is performed to analyze the quality factor, electromechanical coupling (k2eff) and spurious modes of Lamb-wave resonators for the frequency above 2 GHz. The effect of the support tether width on the resonator's performance was studied through theoretical and experimental analysis. By extracting the equivalent electrical parameters of the interdigitated (IDT)-Ground and IDT-Floating resonators, the reasons for their differences in k2eff and parallel-resonance quality factor (Qp) values were clarified. Moreover, the spurious modes can be effectively suppressed by increasing the number of IDTs and reducing the length proportion of the bottom electrode to the effective electrode. The measurement results show that the optimized IDT-Floating resonator is free of spurious mode, meanwhile its series-resonance quality factor (Qs), and k2eff values can reach 1371.7, 448.8, and 0.82% at 2.092 GHz, respectively. Moreover, the influence of IDT materials on the resonators' performance was also analyzed.

Piezoelectric Vibration Energy Harvesters with Distinct Interdigital Electrodes Used for Toxic Gas Detection and in a Numerical Simulation for a Glucose Sensor Application

Introduction: In this paper, a surface acoustic wave sensor (SAW) for dangerous gas sensing applications has been designed and experimented. The Glucose Sensor applications has been simulated to show that the piezoelectric material has a high significance for use in detection. Background: Detection of gases is one of the major applications SAW gas sensor extend its services into the field of medical and even in power plants. A Surface Acoustic Wave (SAW) is an acoustic wave that propagates on the surface of an elastic material (usually a solid), with an amplitude that decreases with the depth of the substrate. Objectives: SAW devices typically use electrodes on a piezoelectric material to convert an electrical signal to a SAW. Methods: This paper reviews the significance of piezoelectric materials and focuses on MEMS based SAW, and we investigate the resonance frequencies of a SAW gas sensor, which consists of an Inter Digitated Transducer (IDT) etched onto a piezoelectric substrate and covered with a thin Poly Isobutylene (PIB) film. Results: The mass of the PIB film increases as PIB selectivity adsorbs CH2Cl2 (Dichloromethane, DCM) in the air. This causes a shift in resonance to a slightly lower frequency. Conclutions: Our characterization of the piezoelectric material have shown a high significance when a sensitive layer of gas is etch for detected the dangerous gases, we used it in another application Glucose Sensor to show the importance of our system. The sensor of the Glucose Gensor application has been designed and simulated by a finite element analysis which was conducted on LiNbO3 pellets. This model is applied to verify the sensing properties of DCM and the glucose. On the other hand, the Glucose Sensor and the toxic gas detection allow measurement of the concentration,whether it is for the dangerous gases or glucose. The concentration of external glucose and the current density versus glucose concentration were measured by a finite element.

MEASUREMENT OF THE DETERIORATION OF THE DIESEL ENGINE OIL USING THE IDT CAPACITOR SENSOR

A capacitor-type engine oil sensor is designed and fabricated to measure the property of the diesel engine oil depending on the vehicle mileage. This sensor has flat structure with the interdigitated (IDT) electrodes for the smooth oil flow and is constructed using printed circuit board (PCB) for the fabrication convenience. For the increased capacitance, the smaller spacing between the electrodes is preferred and determined with 0.5 mm based on the fabrication limit. The device is applied to actual trucks with diesel engine. From the experiment, the capacitance of vehicle A is initially constant and then increased upto approximately 6,000 km. And then, the output is dramatically decreased, which indicates that the engine oil has been degraded and should be replaced. The interval at which the reduction in capacitance occurs varies depending on each vehicle, which means the exchange interval of engine oil is different from each other. The degree of deterioration of the oil is also measured with the viscosity tests and total acid number (TAN) tests, and the results are compatible with the measurement of capacitance. From these results, it has been confirmed that the fabricated IDT capacitor sensor can measure the engine oil conditions depending on the mileage.

Flexible Temperature Sensor Utilizing MWCNT Doped PEG-PU Copolymer Nanocomposites.

In this study, polyethylene glycol (PEG) and polyurethane (PU)-based shape-stabilized copolymer nanocomposites were synthesized and utilized for developing low-cost and flexible temperature sensors. PU was utilized as a flexible structural material for loading a thermosensitive phase change PEG polymer by means of physical mixing and chemical crosslinking. Furthermore, the introduction of multi-walled carbon nanotubes (MWCNT) as a conductive filler in the PEG-PU copolymer resulted in a nanocomposite with thermoresistive properties. MWCNT loading concentrations from 2 wt.% to 10 wt.% were investigated, to attain the optimum conductivity of the nanocomposite. Additionally, the effect of MWCNT loading concentration on the thermosensitive behavior of the nanocomposite was analyzed in the temperature range 25 °C to 50 °C. The thermosensitive properties of the physically mixed and crosslinked polymeric nanocomposites were compared by spin coating the respective nanocomposites on screen printed interdigitated (IDT) electrodes, to fabricate the temperature sensor. The chemically crosslinked MWCNT-PEG-PU polymeric nanocomposite showed an improved thermosensitive behavior in the range 25 °C to 50 °C, compared to the physically mixed nanocomposite. The detailed structural, morphological, thermal, and phase transition properties of the nanocomposites were investigated using XRD, FTIR, and DSC analysis. XRD and FTIR were used to analyze the crystallinity and PEG-PU bonding of the copolymer nanocomposite, respectively; while the dual phase (solid–liquid) transition of PEG was analyzed using DSC. The proposed nanocomposite-based flexible temperature sensor demonstrated excellent sensitivity, reliability and shows promise for a wide range of bio-robotic and healthcare applications.

Modeling and Testing of Fringe-Field Capacitive Moisture Sensor Under Certain Electrode Area

Soil moisture is closely related to the occurrence frequency and the time of landslides disasters, precisely in-situ measurement for soil moisture becomes quite critical. The electrodes of conventional dielectric sensor for soil moisture are fragile, large and unsuitable for integrating. IDT(interdigital) fringing-field capacitive sensor based on PCB (printed circuit board) technology can be used for non-contact measurement and small-scale packaging. In this paper, to optimize the sensitivity and penetration depth of the IDT capacitive sensor with a fixed electrode contour area, the influences of IDT fingers shape and size on the sensitivity and penetration depth are discussed in a wide range by using equivalent capacitance theory. Then, the special working cases are intuitively and accurately analyzed by using the finite element analysis ( FEA ) method. The results show that the sensor with more electrode fingers and smaller finger-gap has high sensitivity, yet has thinner penetration depth, it requires a trade-off between sensitivity and penetration depth in practical applications. In addition, the performance of regular and circular IDT sensor with the same specifications are basically identical, the circular IDT sensor has a slightly better accuracy. Finally, the proposed IDT sensors with different electrode specifications as well the associated signal conditioning circuit are fabricated and calibrated to verify the theoretical and simulation results. The performance of the designed sensor was compared with other commercial sensors based on the thermogravimetric method. The experimental results meet the expected requirements well, with a repeatability correlation coefficient of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> =0.992 and a mean square error of 0.01089.

Tunable and facile fabrication of flexible interdigitated capacitors on Butter Paper using solvent-free method

Paper is one of the most ubiquitous materials. In the present work, it is employed as a flexible, inexpensive, degradable, lightweight and eco-friendly substrate for solvent-free fabrication of the Inter Digitated Capacitor (IDC). IDCs are employed in many sensing and energy harvesting applications recently, thus it was imperative to find a technique to fabricate IDCs using environment friendly and biodegradable processes. With fixed and controlled parameters, Butter paper exhibits the lowest resistance and maximum capacitance which were almost 1 kΩ and in the range of 20–30 pF respectively. Additionally, maximum capacitance per unit area was achieved through configuring the shape of graphite electrodes and it was observed that semi-circular geometry exhibits maximum capacitance, giving a value of almost 60 pF. Furthermore, the investigation has been made on green fabrication process to get the range of scalability and tune-ability of the capacitance of IDCs by impregnating Butter Papers in NaCl solution and also talking about the saturation point of these solutions, post which the IDCs start behaving erraticaly.The capacitance value in this case shows extrememly positive results and we managed to obtain a value of 18 nF which was a significant jump when compared to the untreated samples, which exhibted capacitance values in the range of pico-farads. Thus, it was discovered that Butter Paper(BP) could potentially function as a feasible and promising choice for flexible electronics.

Design and Fabrication of Fringing Field Capacitive Sensor for Non-Contact Liquid Level Measurement

The capacitive sensors are widely used for liquid level measurement in different applications, but the contact type capacitive sensors suffer from frequent maintenance and drift of the sensor output. The present paper proposes a simple noncontact interdigital (IDT) fringing field capacitance sensor for liquid level measurement. The sensor can be made using flexible /non-flexible substrate, and it can be used to measure the liquid level of the vessel for both planar and non-planar surfaces. Theory of level measurement using the sensor has been discussed. Four different IDT sensor (1-n-1) configurations such as 1-1-1, 1-3-1, 1-5-1 and 1-11-1 have been designed, analysed, simulated (finite element method), and fabricated to measure water and insulating transformer oil levels from 0 to 40 mm. The analytical expressions are derived for 1-n-1 configuration to estimate the value of capacitance and the maximum field penetration depth of the sensors. The capacitance value of all four sensors varies almost linearly with the variation of liquid level. Experimental results show that the sensitivity of the 1-5-1 IDT sensor is 40 fF/mm. Performances of the sensors were compared with other capacitive sensors reported in the literature. The sensor is capable to detect the water level with a resolution of 0.1 mm.