Design Of Capacitive Sensor Research Articles

Printed hybrid capacitive Kirigami sensor: enhancing flexibility and conformability for improved motion artifacts

Abstract Capacitive sensing of electrophysiological signals is a promising alternative to traditional contact-type sensing for long-term and ubiquitous health monitoring. Many researchers are focusing on developing flexible capacitive electrodes to improve the conformability and the quality of acquisition of this family of sensors. However, current flexible devices still present many limitations due to the negative Poisson’s ratio of the materials used, which affects the dimensions and characteristics of the materials when under stress, and their incompatibility with traditional manufacturing methods and solid-state devices. We present a novel, inkjet-printed, hybrid capacitive Kirigami sensor design. This novel structure comprises different layers with different functionalities, in order to allow improved flexibility and conformability of the flexible Kirigami printed electrode, while securing its inclusion on a traditional rigid printed circuit board for a quality signal acquisition. The novel sensor design has been tested on different shapes and dimensions of sensing target and with different weights applied. Capacitive and electrical measurements were performed to obtain the main basic sensor characteristics such as coupled capacitance, acquired signal amplitude and cutoff frequency. When compared to an analog but rigid sensor, the novel designed hybrid flexible sensor showed significant improvement and enhanced uniformity of measurements, with an increase in amplitude value up to + 82 % for the bigger curvatures, while maintaining good electrical contact and integrity of all the layers.

Moisture Distribution and Ice Front Identification in Freezing Soil Using an Optimized Circular Capacitance Sensor.

As the interface between frozen and unfrozen soil, the ice front is not only a spatial location concept, but also a potentially dangerous interface where the mechanical properties of soil could change abruptly. Accurately identifying its spatial position is essential for the safe and efficient execution of large-scale frozen soil engineering projects. Electrical capacitance tomography (ECT) is a promising method for the visualization of frozen soil due to its non-invasive nature, low cast, and rapid response. This paper presents the design and optimization of a mobile circular capacitance sensor (MCCS). The MCCS was used to measure frozen soil samples along the depth direction to obtain moisture distribution and three-dimensional images of the ice front. Finally, the experimental results were compared with the simulation results from COMSOL Multiphysics to analyze the deviations. It was found that the fuzzy optimization design based on multi-criteria orthogonal experiments makes the MCCS meet various performance requirements. The average permittivity distribution was proposed to reflect moisture distribution along the depth direction and showed good correlation. Three-dimensional reconstructed images could provide the precise position of the ice front. The simulation results indicate that the MCCS has a low deviation margin in identifying the position of the ice front.

Enhancing Sensing Performance of Capacitive Sensors Using Kirigami Structures.

Capacitive sensors have widespread applications in human-machine interaction, Internet of Things, and smart home systems due to their low cost, high sensitivity, and ease of integration. However, improving the sensitivity and sensing distance of capacitive sensors remains a challenging issue. This study proposes a novel capacitive sensor design method based on Kirigami structures, which enhances sensor performance by introducing specific cutting patterns into the conductive layer to leverage edge effects. Through experimental testing and statistical analysis, we systematically investigated the influence of Kirigami geometric parameters on sensor sensitivity and sensing distance. We designed and fabricated 12 different Kirigami structures, including circular flower patterns, array patterns, layered pointed flower patterns, and circular strip structures, and compared them with traditional non-cut structures. The results show that Kirigami structures significantly improved sensor performance. Compared to traditional sensors without Kirigami structures, optimally designed Kirigami capacitive sensors demonstrated approximately a 3-fold increase in sensitivity and up to 170 percent extension in sensing distance. Multivariate regression analysis and nonlinear models revealed complex relationships between Kirigami structural parameters and sensor performance. Notably, the circular strip (three-layer) structure exhibited the best performance, possibly due to its maximization of edge effects and optimization of electric field distribution. This study provides new design insights for developing high-performance capacitive sensors, with potential applications in improving smart home systems and indoor activity monitoring for solitary elderly individuals.

Design optimization of a phase-change capacitive sensor for irreversible temperature threshold monitoring and its eco-friendly and wireless implementation

Monitoring the temperature of perishable goods during transport and storage is essential to prevent waste and maintain product quality. Exploiting the unique property of phase-change materials (PCM), altering their physical state at specific temperatures, we optimize a capacitive sensor design based on a copper on polyimide interdigitated spiral (IDE) structure coated with a PCM to irreversibly detect temperature thresholds. The effect of the sensor dimensioning on its response is analyzed using a finite element model simulation. The model predicted up to 51% capacitance variation for optimal coverage of the PCM after spreading over the IDE, which was validated experimentally within a 5% error. Two melting concepts utilizing the spreading or the removal of the melted PCM over the IDE are investigated based on a capillary retention mechanism to maintain sensor sensitivity under inclination. Finally, an eco-friendly implementation of the capacitive structure and its wireless operation at 460 MHz is demonstrated on paper with a printed zinc transducer passivated with beeswax and covered with jojoba oil. Melting of the oil at a threshold temperature of 12.3 °C resulted in an irreversible shift in resonance frequency of 14 MHz. This study provides guidelines for the design and implementation of irreversible temperature monitoring capacitive sensors.

Electric Susceptibility at Partial Coverage of a Circular One-Side Access Capacitive Sensor with Rigid Polyurethane Foams.

The capability of dielectric measurements was significantly increased with the development of capacitive one-side access physical sensors. Complete samples give no opportunity to study electric susceptibility at a partial coverage of the one-side access sensor's active area; therefore, partial samples are proposed. The electric susceptibility at the partial coverage of a circular one-side access sensor with cylinders and shells is investigated for polyurethane materials. The implementation of the relative partial susceptibility permitted us to transform the calculated susceptibility data to a common scale of 0.0-1.0 and to outline the main trends for PU materials. The partial susceptibility, relative partial susceptibility, and change rate of relative partial susceptibility exhibited dependence on the coverage coefficient of the sensor's active area. The overall character of the curves for the change rate of the relative partial susceptibility, characterised by slopes of lines and the ratio of the change rate in the centre and near the gap, corresponds with the character of the surface charge density distribution curves, calculated from mathematical models. The elaborated methods may be useful in the design and optimization of capacitive OSA sensors of other configurations of electrodes, independent of the particular technical solution.

Determining the Quality of Measuring the Level of Lower Extremity Joint Movement in Inclusive Physical Education Using Electronic IT Resources

Objectives. The study aimed to investigate the quality characteristics of the tool developed based on electronic IT resources for measuring the level of movements in the joints of the lower limbs of students with disabilities caused by injuries. Material and methods. The experimental study involved 32 first-year students who had sustained lower limb injuries as a result of the war and were in remission. The methods used included analysis, synthesis, systematization, generalization, technical modeling, pedagogical experiments, and mathematical statistics. Results. A means of measuring movements in the joints of the lower limbs has been developed using electronic IT resources. The basis of the tool is a measuring line consisting of a printed circuit board on which is placed a design of capacitive sensors, a switching line, and a signal converter that measures the signal received by the sensors. The measurement results are transmitted to the controller and then to the PC via an interface implemented based on Bluetooth wireless technology. To implement the measuring tool, a controller is used, which has a board built on the synthesis of the Arduino electronic hardware platform and the Raspberry Pi minicomputer. The test results are displayed on the PC monitor screen. The determination of the qualitative characteristics of the test, in the case of recording the results of a tool developed on the basis of electronic IT resources for measuring the level of movements in the joints of the lower limbs of students with disabilities, established that the level of reliability of the test is above 0.90 (“excellent”) validity – from 0, 6 (“high”). Empirical data collected directly from the experiment have a low level of reliability: qualitative indicators of reliability in the range are below 0.70 (“may have limited applicability”), validity – < 0.3 (“low validity”). Conclusions. Developed based on electronic IT resources, the tool for measuring the level of movements in the joints of the lower limbs of students with disabilities due to limb injuries has significant advantages, such as the availability of functions, ease of use and efficiency. Ensuring high efficiency and objectivity of control contributes to performing control operations in real-time. By using assessment tools with a high level of reliability and validity, we ensure the detection of reliable changes in the state of the joints of the lower limbs of students with disabilities, thus eliminating the influence of errors in making managerial decisions in the planning process of their PE.

Design and simulation of capacitive sensor for grain moisture detection

The high moisture content of grain would result in quality deteriorations such as mold and mildew during storage and transportation. For effective detection of grain moisture, a forked-finger capacitive sensor in the form of triangular prism is proposed. The effect of the sensor structural parameters on its capacitance, electric field distribution, sensitivity and penetration depth are investigated using finite element simulations. The results show that an optimised effective penetration depth of 2.73 mm for grain moisture detection can be achieved when the finger width, number, length and spacing are 50 μm, 25.4 mm and 50 μm, respectively. This work may provide a new approach for the structural design of capacitive grain moisture sensors.

Design and Fabrication of Nondestructive Capacitive Sensors for the Moisture Measurement in Chickpeas and Mustard Seeds

Moisture in food grains, including chickpea and mustard seeds, plays a crucial role in their storage and processing, thus ensuring food quality. It helps in the improvement of preservation techniques. Moisture in these materials is an age-old problem; hence, it is important to monitor it in real time. The conventional gravimetric method is manual and time-consuming; some online electrical techniques are available in which grains are considered as a dielectric material, but they are relatively complex and costly. This present work describes a nondestructive concentric fringing field (CFF) capacitive sensor to detect moisture (4–33% by absolute weight) of chickpea grain and (12–30% by absolute weight) mustard seed. First, the proposed CFF sensor was modeled, and then three distinct concentric sensors were designed, simulated, fabricated, and experimentally validated to determine moisture in chickpea grains and mustard seeds. The capacitance values of all the sensors approximately linearly varied with the changes in the moisture of the grains. The average sensitivity of the most sensitive sensors was close to 20 fF/% wt for chickpeas and 31 fF/% wt for mustard seeds. The proposed sensor is sensitive, nondestructive, easy to use, inexpensive, and fast.

Non-Destructive Thin Film Thickness Measurement based on Coplanar Capacitive Sensor and Printed Circuit Board Platform

This paper presents a compact design of a coplanar capacitive sensor based on a printed circuit board (PCB) to apply in non-contact and non-destructive thin film thickness measurement. The capacitive sensor design is structured by two coplanar capacitors, including a reference coplanar capacitor and a sensing coplanar capacitor. Using this structure, the thin film thickness could be estimated through the imbalance voltage produced between the two signals from the reference capacitor and sensing capacitor. The size of the proposed sensor is 9.99 × 9.99 mm and the capacitor electrodes structured by shapes of spiral, interdigital, and round are studied and optimized. Those electrode structures have been modelled and simulated and the simulation results reveal that the spiral structure gives the best performance. The experiment was conducted using plastic thin films with thickness ranging from 10 to 230 µm and dielectric constants ranging from 1.375 to 3.19 to investigate the working principle of the sensor. Experiment results show the approximate linearity of the output voltage corresponding to the various thickness at measurement range from 0 to 90 µm. The sensitivity of the sensor is 13.5 and 29 mV/µm corresponding to the 1.375 and 3.19 dielectric constants of the thin films, respectively. The proposed coplanar capacitive sensor is fabricated based on the PCB platform and shows good performance with a minimum cost. The experiment results demonstrate that this sensor has a high potential to be applied in several biomedical and industrial thin film thickness measurement applications.

Design and fabrication of low-cost capacitive sensors for salinity level detection in water

Design and fabrication of low-cost capacitive sensors for salinity level detection in water

Performances evaluation and characterization of a novel design of capacitive sensors for in-flight oil-level monitoring aboard helicopters

Capacitive sensing is one of the most used sensing techniques for a large variety of applications. In particular, Capacitive Level Sensors (CLSs) are well suited for avionics, as they provide continuous measurements over the full range of the sensor, high reliability and low maintenance costs. However, industry standard CLSs used nowadays on helicopters show low sensitivity and poor dynamical characteristics. Hence, novel geometries were investigated and the simulation results (already presented in a previous manuscript) were encouraging. Therefore, three prototypes were built and tested. This manuscript is aimed at their experimental validation obtained using a mechatronic testbench with a high-precision positioning system purposely designed and built, able to move the probes in and out of an oil tank. The used oil had well-known electrical characteristics and many different tests were carried out. With the obtained data of capacity vs. oil level, an in-depth analysis of the probes' static (sensitivity, non-linearity, hysteresis) and dynamic (rise time, settling time, final error) behaviors were performed. From the analysis results it can be clearly seen that the novel design featuring a helicoidal slit along the external electrode of the cylindrical probe provides increased sensitivity, improved first-order response and negligible hysteresis phenomenon and non-linearity error.

Integrated Water-Level Sensor Using Thin-Film Transistor Technology.

A low-cost water-level sensor was developed utilizing a capacitive sensor design with only one thin-film transistor (TFT). The integration of the a-IGZO TFT process facilitated the complete integration of the water-level sensor on a substrate, including essential components, such as the transistor, capacitor, wires, and sensing electrode. This integration eliminates the need for a separate mounting process, resulting in a robust sensor assembly. To comprehensively assess the performance of the developed water-level sensor, rigorous evaluations were conducted using both MOSFET and TFT integration. In the case of the water-level sensor featuring a-IGZO TFT integration, a voltage output of 4.2 V was measured when the tank was empty, while a voltage output of 0.9 V was measured when the tank was full. Notably, the integrated sensor system demonstrated a higher output voltage compared with the MOSFET sensor, primarily due to the significantly reduced parasitic capacitance of the TFT. The use of a-IGZO TFT in the integrated sensor system contributes to enhanced sensitivity and accuracy. The lower parasitic capacitance inherent in TFT technology allows for improved voltage measurement precision, resulting in more reliable and precise water-level sensing capability. The development of this integrated water-level sensor holds immense potential for a wide range of applications that require a combination of cost-effectiveness, accurate monitoring, and flexibility in form factor. With its affordability, the sensor is accessible for various industries and applications.

Microstructure design and optimization of high-sensitivity interdigital capacitive humidity sensor based on uncertainty analysis

The microstructure of the interdigital capacitive humidity sensor plays a critical role in achieving high sensitivity in measurements. Performing a quantitative evaluation to assess the influence of structural parameters on sensor sensitivity is vital for improving the overall performance of the sensor. In this paper, a theoretical mathematical model and a structural uncertainty propagation model are developed for the interdigitated capacitive humidity sensor, considering the uncertain errors that occur during the processing and measurement processes. A quantitative analysis is conducted to investigate the impact of each structural component and its corresponding uncertainty on the output sensitivity. Moreover, by integrating the two constructed models, the paper formulates an optimal equation for sensor performance that mitigates the impact of structural errors on the system while improving sensor sensitivity. Researchers have the flexibility to adjust sensor material, environmental conditions, structural components, and other parameter variables within the model, according to specific application requirements, to achieve the optimal design scheme for a sensor with specific materials and structure. The proposed method and model presented in this article have undergone verification using finite element physical simulation. The sensitivity model achieves an accuracy rate of 94.45%, whereas the uncertainty model achieves an accuracy rate of 81.96%. Additionally, the model reduces the calculation time to 1/550th and the required computational resources to 1/5th of the simulation, thereby greatly improving the efficiency of sensor optimization design.

Effect of Voltage Boundary Conditions on the Sensitivity and Design of Coplanar Capacitive Sensors

Coplanar capacitive sensors are widely employed in various applications due to their advantages in noninvasive evaluation, fabrication simplicity, and versatility. While there have been several experimental demonstrations, optimization of the boundary conditions and geometry is lacking. In this letter, we investigate the effect of both the voltage boundary conditions and the electrode geometry on the sensitivity with respect to an overlaid insulating layered structure. We perform electrostatic analysis using finite element simulations to study the distribution of electric fields between two coplanar electrodes, with various combinations of applied voltages and shielding electrodes beneath the sensing electrodes. By combining this analysis with variations in electrode geometry and permittivity distribution of layers, we demonstrate how specific geometries and material properties can amplify the effect of voltage boundary conditions. Our results indicate that incorporating conductive shielding electrodes can enhance the total capacitance while enabling increased sensitivity within regions close to the electrodes. Furthermore, our study reveals that conductive shielding electrodes are more effective in achieving higher sensitivity when the gap is of similar size to the electrode width. The outcomes of this research can facilitate the more efficient design of coplanar capacitive sensors, particularly for pressure sensing and proximity sensing applications where the overlaid material under test may undergo deformation.

Design Optimization of a Capacitive Sensor for Mass Measurement of Nanometer-Sized Exhaust Carbon Particles

Nanometer-sized carbon particulates generated by incomplete combustion in heavy-duty vehicles are harmful to human health. A high-resolution technique is needed to detect and measure these pollutants. This study aims to optimize a capacitive sensor design for detecting and measuring particulates. Firstly, the effect of design parameters on particulate detection and sensor compliance sensitivity is investigated by using the finite element method. By comparing the simulation results with literature findings for performance validation, the sensor structure is optimized to detect lower particulate concentrations. The simulation result shows that particulate detection sensitivity has linear variations with changes in particulate mass. With optimum electrode spacing and top insulation layer thickness of 5 µm, the sensor can detect a particulate deposition of 0.033 mg/min and generate a maximum capacitance of 581 pF. Since the optimized design can measure particulate deposition at a lower range and with higher sensitivity, it is suitable to be applied to detect nanometer-sized carbon particulates.

A Calculation Method for the Optimal Initial Polar Distance of Capacitive Force Sensors

For capacitive sensors, the initial polar distance of capacitors has a vital influence on the performances of capacitive sensors; however, there are few current studies on the method of calculating the initial polar distance of capacitors, leading to a lack of corresponding theoretical basis for the design of capacitive sensors. In this article, a calculation method for the optimal initial polar distance based on minimum error is proposed. The total error expression is derived from error analysis, which clarifies the complex relationship between the total error and the initial polar distance, and the optimal initial polar distance is solved by Newton’s method. A capacitive torque sensor is used in the experiment to verify the calculation method for the optimal initial polar distance, the theoretical error and experimental error of the sensor are compared, and the results show that the experimental error is consistent with the theoretical error curve. The optimal initial polar distance obtained by the calculation method is 0.8479 mm, which is within the range of 0.8–0.9 mm determined by the experiment. The theoretical minimum total error is 0.211% and the experimental minimum total error is 0.208%. The total error expression proposed in this article is accurate, and the calculation method of the initial polar distance is effective. In addition, theoretical analysis reveals that the differential parallel plate capacitor has the characteristic that any small deformation of the moving plate can be equivalent to a translation whose magnitude is the mean value of the deformation.

Inkjet-printed plasma-functionalized polymer-based capacitive sensor for PAHs

The inkjet-printing technology is utilized to foster conducting layers, interconnections, and other features on different substrates of which its success greatly depends on the surface properties of the substrates. In the present work, we reported the use of low-temperature plasma (LTP) to assist in tailoring the surface properties of polyethylene terephthalate (PET). This facilitated the inkjet printing of a capacitive electrode sensor design using silver nano-ink (AgNI) for polycyclic aromatic hydrocarbons (PAHs). PAHs are ubiquitous environmental pollutants that are of great health concern. We have sifted methyl methacrylate (MMA), N-vinylpyrrolidone (VP), and oxygen (O2) as plasma fed-gases for improving the adhesion of printed AgNI on PET. We observed improved surface hydrophilicity of the plasma-treated PET (p-PET). This was evidenced by the decrease in water contact angle (WCA). The change in surface chemistry with plasma treatment was assessed using X-ray Photoelectron spectroscopy (XPS). Atomic Force Microscopy (AFM) was employed in determining the nanoscale surface roughness of PET. We then fabricated the capacitive sensor using AgNI to quantitatively sense the PAH from aqueous media. This sensor was subsequently characterized using Scanning Electron Microscopy (SEM) and Keyence 3D imaging. The capacitance values have shown a linear response with increased PAH concentration. The sensor design exhibits a high sensitivity for PAH concentrations up to 0.05 ng/mL. Ultimately, these results have demonstrated the potential of this polymer device for pollutant sensing applications.

Design and Optimization of Interdigital Capacitive Humidity Sensor with Highly Sensitive and Dynamic Response Time

Humidity sensors are widely used in various fields of life. In meteorological detection, the sensor must have high sensitivity and fast dynamic response time due to extreme environmental interference. However, the sensitive mechanism of the humidity sensor determines that the dynamic response time will inevitably be increased while improving the sensitivity, which undoubtedly creates difficulties for sensor design. This article takes the interdigitated capacitive humidity sensor as the research object and proposes an optimal design scheme for the sensor that considers high dynamic response time and sensitivity. By constructing the sensor’s theoretical mathematical model, the influence of each structure is analyzed. The theoretical model has been verified by finite element simulation to have an accuracy higher than 95%. The article constructs the sensor optimization objective equation based on this model. Through analysis, within the range of structural parameters set in the article, to improve the sensitivity and reduce the dynamic response time of the sensor, the width and spacing of the interdigital electrodes should have a minimum value of 3 μm and a maximum value of 14 μm, respectively. The thickness of the electrode layer and the moisture-sensitive layer should be flexibly adjusted according to the application to ensure the lowest value of the optimization objective function. To further improve the sensor’s performance, the article optimizes the electrode structure and heating strategy of the sensor heating layer, which not only enhances the uniformity of heat transfer but also increases the optimal heat transfer area by 6% compared with the traditional scheme.

Comparison study of high-sensitivity area-changed capacitive displacement transducers with low-impedance and high-impedance readout circuits.

Area-changed capacitive displacement transducers (CDTs) are widely used in the high-precision displacement measurement due to their high accuracy and large dynamic range. The preamplifier circuit is used to convert the capacitance variation signal into voltage, which requires low noise and is significant for the high-sensitivity area-changed CDTs. Current CDT preamplifiers are mainly categorized as the low-impedance preamplifier and the high-impedance preamplifier; however, their characteristics and application scopes have not been systematically compared. This paper builds comprehensive models of the low-impedance and the high-impedance preamplifiers. Then, three-electrode configurations with different electrode separations and gaps are designed to carry out displacement variation experiments with low-impedance and high-impedance readout circuits, respectively. The results show that the sensitivity decrease caused by the gap change with the high-impedance preamplifier is 70%, while the counterpart of the low-impedance preamplifier is 85%. When the gap is 0.1mm and the width-to-separation ratio varies from 1:1 to 5:1, the sensitivity of the CDT based on the low-impedance preamplifier is increased by 64%, while the counterpart with the high-impedance preamplifier is increased by 22%. Hence, this paper gives the universal guiding rules of preamplification circuit selections for different CDT electrode configurations and application requirements. For a capacitive sensor design with large and unavoidable parasitic capacitance, the low-impedance preamplifier and a CDT with a large electrode width-to-separation ratio match best. For a capacitive sensor design requiring both a large sensitivity and good robustness to out-of-plane interferences, the high-impedance preamplifier and a CDT with a small electrode width-to-separation ratio match best.

Tunable Proton Conductivity and Color in a Nonporous Coordination Polymer via Lattice Accommodation to Small Molecules.

Nonporous coordination polymers (npCPs) able to accommodate molecules through internal lattice reorganization are uncommon materials with applications in sensing and selective gas adsorption. Proton conduction, extensively studied in the analogue metal‐organic frameworks under high‐humidity conditions, is however largely unexplored in spite of the opportunities provided by the particular sensitivity of npCPs to lattice perturbations. Here, AC admittance spectroscopy is used to unveil the mechanism behind charge transport in the nonporous 1·2CH3CN. The conductance in the crystals is found to be of protonic origin. A vehicle mechanism is triggered by the dynamics of the weakly coupled acetonitrile molecules in the lattice that can be maintained by a combination of thermal cycles, even at low humidity levels. An analogue 1·pyrrole npCP is formed by in situ exchange of these weakly bound acetonitrile molecules by pyrrole. The color and conduction properties are determined by the molecules weakly bonded in the lattice. This is the first example of acetonitrile‐mediated proton transport in an npCP showing distinct optical response to different molecules. These findings open the door to the design of switchable protonic conductors and capacitive sensors working at low humidity levels and with selectivity to different molecules.