Capacitive Sensor Research Articles

Application of cosmic‐ray neutron probes for measuring soil moisture in rocky areas of the Taihang Mountains, North China

AbstractThe cosmic‐ray neutron probe (CRNP) is a mesoscale and noninvasive method for measuring soil moisture and has been widely studied and applied. However, studies of its applicability in rocky mountainous areas are still challenging in complex topography and high gravel content. In this study, a field experiment was carried out to assess the applicability of the CRNP for measuring soil moisture in rocky areas of Taihang Mountains of North China. The results showed that the Pearson correlation coefficient and the root mean square error between the soil moisture from CRNP and the drying method are 0.911 and 0.025 m3 m−3, respectively, indicating that the CRNP can estimate the average soil moisture well in the study area. Compared with the capacitive sensor, the CRNP overestimated soil moisture when small rainfall events occurred, which was caused by the interception of canopy and litter. The nonlinear weighting method performed better than the linear weighting method in representing average soil moisture within the CRNP footprint. The high gravel content that contained high lattice water content reduced the penetration depth of CRNP. Biomass reduces the accuracy of the CRNP by affecting the neutron intensity. In summary, CRNP can measure soil moisture accurately in rocky areas of the Taihang Mountains, especially in dry environments with low biomass.

Research on Online Gas Volume Monitoring Technology of Intelligent Gas Relay

The gas relay is the main non-electrical protection device of the transformer, which plays an important role. Traditional detection methods can not reflect the gas relay level, and there will be gas relay false alarms in operation and maintenance. Firstly, the working principle of the gas relay was analyzed, and a non-conductive capacitance sensor was proposed to realize the real-time monitoring of gas volume in the gas relay. Then, a new online monitoring scheme for intelligent gas relays was constructed through the selection analysis and optimization design of the gas protection module and liquid-level measurement module. Based on the changing state of gas volume in the gas relay, a more accurate and timely fault diagnosis of the power transformer was realized, and the prototype processing was completed. Finally, the feasibility of the volumetric testing method was verified by comparing the two conditions of different liquid-level heights and different ambient temperatures. The proposed method is of great significance for discovering the latent faults of transformers and realizing the condition monitoring of oil-immersed power transformers, which ensures the safety of power grid equipment and personnel.

Capacitive flexible haptic sensor based on micro-cylindrical structure dielectric layer and its decoupling study

With the advancement of robotics, flexible sensors have undergone significant development. Extensive research has been conducted on the sensor structure to enhance its sensing capabilities. However, due to the absence of a definitive theory on the relationship between input force and output signal, and the unclear mechanism of force and deformation, decoupling the force remains challenging. To address this, we propose a capacitive flexible tactile sensor that utilizes a dielectric layer with a microcylindrical structure for detecting external loads. The micro-cylindrical structure of the dielectric layer enhances the strain capacity, thereby improving the sensor's performance. We also present a decoupling model based on the deformation mechanism by analyzing the sensor coupling. Furthermore, we validate the sensor's application in tangential detection and object grasping by integrating it into a soft rehabilitation glove and a soft gripper. This research lays the foundation for future self-aware operations.

Patterning Techniques in Coplanar Micro/Nano Capacitive Sensors.

Rapid technological advancements have led to increased demands for sensors. Hence, high performance suitable for next-generation technology is required. As sensing technology has numerous applications, various materials and patterning methods are used for sensor fabrication. This affects the characteristics and performance of sensors, and research centered specifically on these patterns is necessary for high integration and high performance of these devices. In this paper, we review the patterning techniques used in recently reported sensors, specifically the most widely used capacitive sensors, and their impact on sensor performance. Moreover, we introduce a method for increasing sensor performance through three-dimensional (3D) structures.

Smart-Data-Glove-Based Gesture Recognition for Amphibious Communication.

This study has designed and developed a smart data glove based on five-channel flexible capacitive stretch sensors and a six-axis inertial measurement unit (IMU) to recognize 25 static hand gestures and ten dynamic hand gestures for amphibious communication. The five-channel flexible capacitive sensors are fabricated on a glove to capture finger motion data in order to recognize static hand gestures and integrated with six-axis IMU data to recognize dynamic gestures. This study also proposes a novel amphibious hierarchical gesture recognition (AHGR) model. This model can adaptively switch between large complex and lightweight gesture recognition models based on environmental changes to ensure gesture recognition accuracy and effectiveness. The large complex model is based on the proposed SqueezeNet-BiLSTM algorithm, specially designed for the land environment, which will use all the sensory data captured from the smart data glove to recognize dynamic gestures, achieving a recognition accuracy of 98.21%. The lightweight stochastic singular value decomposition (SVD)-optimized spectral clustering gesture recognition algorithm for underwater environments that will perform direct inference on the glove-end side can reach an accuracy of 98.35%. This study also proposes a domain separation network (DSN)-based gesture recognition transfer model that ensures a 94% recognition accuracy for new users and new glove devices.

Mapping spatiotemporal soil moisture in highly heterogeneous agricultural landscapes using mobile dual‐spectra cosmic‐ray neutron sensing

AbstractAccurate large‐scale soil moisture (SM) maps are crucial for catchment‐scale hydrological models used for water resource management and warning systems for droughts, floods, and wildfires. SM can be mapped by mobile cosmic‐ray neutron (CRN) systems of moderated detectors at homogeneous landscapes of similar soil and vegetation. In this study, we present a new approach for mobile CRN detection to perform to its full potential, where CRN measurements can also be converted to SM at heterogeneous landscapes. The approach is based solely on thermal and epithermal neutron datasets obtained from mobile dual‐spectra CRN detection, combined with theoretical developments using a particle transport model. For each measurement point, the land cover type is identified using the thermal‐to‐epithermal (T/E) ratio, and the relevant neutron‐count‐to‐soil‐moisture conversion function is estimated from CRN stations located at the main land cover types in the catchment. With this approach, the requirement of collecting 100+ soil samples for each point along the survey route is omitted. We use this T/E‐dependent approach to obtain SM maps from 12 CRN surveys and compare it with a simple approach where only the conversion function from the agricultural site is used. SM by the simple approach is comparable to the estimates of the agricultural stations of a capacitance sensor network, while the estimates of the T/E‐dependent approach also compare well with the heathland and forest stations. With accurate SM estimates for all landcover types, the average error is reduced from 0.089 to 0.038 when comparing CRN SM with space‐borne Soil Moisture Active Passive Mission estimates.

The Efficiency of the Application of Electronic Techniques in the Control of Dynamic Balance in the Process of Inclusive Physical Education

The purpose of the study was to determine the authenticity of the dynamic balance control device developed on the basis of modern trends in the field of electronic equipment for students with disabilities. Materials and methods. 32 students with disabilities, aged 18–24 years, I–III years of study, who received a doctor’s permission to participate in testing and had vestibular disorders, were selected for the studied sample, in accordance with the provisions of voluntariness and anonymity. General scientific methods of gathering theoretical information, the method of technical modeling, pedagogical testing and methods of mathematical statistics were used. Results. A dynamic balance control device was developed on the basis of the most up-to-date electronic equipment and programming. The device consists of an integrated electronic unit, a programmable microcontroller system unit, and a PC. The information received by the capacitive sensors placed in the unit of the integrated electronic unit during the student’s performance of the test task is processed in the unit of the programmable microcontroller system and transmitted via non-contact infrared communication lines to the PC where it is graphically presented. To establish the authenticity of testing using the developed device, reliability and validity coefficients were determined, which in numerical values reached a “high” level, in contrast to the test the results of which were recorded directly by the teacher and numerically corresponded to the limits of “low” and “medium”. Conclusions. The dynamic balance control device presented in the work is designed using the most up-to-date electronic equipment and programming. Considering the importance of eliminating vestibular disorders and related dynamic balance disorders in students with disabilities, the use of the presented development of the control device in the practice of inclusive PE is aimed at ensuring the effectiveness of this process. The integration of a control device developed based on current trends in the field of electronic equipment into the inclusive physical education of students with disabilities is the basis for the development of new approaches in the process of dynamic balance testing based on objective assessment.

High-precision phase-shift method for heavy-load reference mirror based on capacitance sensor monitoring

To address the problems associated with the high-precision phase shift of heavily loaded reference mirrors in large-aperture interferometry, this study proposes a high-precision phase-shifting method based on capacitance sensor monitoring. This method achieves spatial nanoscale phase shifting for a heavy-load reference mirror via spatial three-point synchronous driving of piezoelectric ceramics combined with flexible hinges. The highly sensitive spatial translation of a heavy-load reference mirror is achieved through the gravitational loading of air-floating support and the spatial translation motion modeling of the reference mirror. Nano precision phase-shifting feeds are achieved through spatial in-situ monitoring by combining capacitive sensors and piezoelectric ceramics with a proportion integration differentiation closed-loop drive. Finally, high-precision and high-stability mechanical phase shifting in large-aperture interferometry circumvent the principal shortcomings of existing large-aperture wavelength-tuned phase shifting. The experimental results reveal that the established heavy-load reference mirror mechanical phase shift system has a resolving power of 1.1 nm, frequency response of 120 Hz, and synchronization accuracy of 2° for three-phase shift quantities. This method provides a novel phase-shifting technique for constructing large-aperture phase-shifting interferometers.

Data-driven Shape Sensing of Continuum Dexterous Manipulators Using Embedded Capacitive Sensor.

We propose a novel inexpensive embedded capacitive sensor (ECS) for sensing the shape of Continuum Dexterous Manipulators (CDMs). Our approach addresses some limitations associated with the prevalent Fiber Bragg Grating (FBG) sensors, such as temperature sensitivity and high production costs. ECSs are calibrated using a vision-based system. The calibration of the ECS is performed by a recurrent neural network that uses the kinematic data collected from the vision-based system along with the uncalibrated data from ECSs. We evaluated the performance on a 3D printed prototype of a cable-driven CDM with multiple markers along its length. Using data from three ECSs along the length of the CDM, we computed the angle and position of its tip with respect to its base and compared the results to the measurements of the visual-based system. We found a 6.6% tip position error normalized to the length of the CDM. The work shows the early feasibility of using ECSs for shape sensing and feedback control of CDMs and discusses potential future improvements.

Highly Stretchable Textile Knitted Interdigital Sensor for Wearable Technology Applications

AbstractWearable technology applications have experienced remarkable development and advancements, with soft and stretchable strain sensors playing a significant role in this progress. Despite the promising potential of combed‐shaped interdigital capacitive strain sensors in wearable electronics, several challenges exist, including limited stretchability, universal mass fabrication, and seamless integration into diverse clothing parts. This study presents a textile knitted interdigital capacitive sensor that incorporates stretchable conductive yarn, produced using textile twisting technology, to achieve stretchability and adaptability, allowing seamless conformation to human body movements and textile materials. The fabrication process involves embedding the interdigital electrodes and interconnections directly into the fabric through textile knitting technology, ensuring robust integration. Furthermore, this work presents opportunities for commercializing the stretchable interdigital strain sensor through a low‐cost and mass production strategy. Electromechanical characterization demonstrates exceptional performance with high stretchability (≈230%), excellent linearity (R2 = 0.997), a gauge factor (GF) of −0.68 representing relative capacitance change, and a rapid response time of 66 ms. To validate the usability of sensors in wearable technology, a knee brace application is employed to investigate capacitance changes during walking and cycling exercises. This approach will accelerate the accessibility of wearable stretchable interdigital sensors for all.

Spatial distribution of void fraction in the liquid slug in vertical Gas-Liquid slug flow

Vertical slug flow is characterized by the intermittent passage of two structures, the Taylor bubble and the liquid slug. The Taylor bubble is an elongated gas bubble with a bullet shape that flows upward and fills most of the radial cross-section, leaving room for an annular downward flow of a liquid film. The liquid slug is composed of the liquid phase carrying small, scattered bubbles and flowing upwards. The liquid slug presents three main regions: the wake, the development and the fully developed one. The liquid slug has a high concentration of dispersed bubbles in the wake region because of the entrainment mechanism. The detachment point (Dt) is a stagnation point with almost no dispersed bubbles around it, occurring close to the wall in the wake region end. Experimental data for the gas fraction in three different pipe diameters (26, 40.8 and 50 mm) were gathered in the 14-meter-high vertical flow experimental facility of the NUEM/UTFPR MULTILAB. The gas fraction along the liquid slug was evaluated by using a capacitive wire-mesh sensor (WMS) for quantitative results and a high-speed camera was used to analyze qualitative results. A new correlation to predict the average volumetric gas fraction along the unit cell is proposed. Radial and axial gas fraction distribution were analyzed and the detachment point was identified. The Reynolds and Froude number influence on the Dt point was evaluated and a new correlation to predict the Dt location (LDt) is proposed.

Touch, press and stroke: a soft capacitive sensor skin

Soft sensors that can discriminate shear and normal force could help provide machines the fine control desirable for safe and effective physical interactions with people. A capacitive sensor is made for this purpose, composed of patterned elastomer and containing both fixed and sliding pillars that allow the sensor to deform and buckle, much like skin itself. The sensor differentiates between simultaneously applied normal force and shear using summation and differences of signals from four deformable capacitors. Cross talk from shear to normal force is less than 2.5%, and between shear axes is less than 10%. Normal and shear stress sensitivity is 0.49 kPa and 0.31 kPa respectively, with a minimum displacement resolution of 40 μm. In addition, finger proximity is detectable at a range of up to 15 mm. The operation is demonstrated on a simple gripper holding a cup. The combination of features and the straightforward fabrication method make this sensor a candidate for implementation as a sensing skin for humanoid robotics applications.

Failure identification and location in asphalt materials using coplanar capacitance technology

Compared to traditional non-destructive testing (NDT) methods, coplanar capacitance technology has advantages in intuitive identification and accurate location for identifying and locating the various failures in asphalt materials. At present, research on coplanar capacitance technology for various failure detection and location in asphalt materials is missing. Therefore, this paper aims to develop a various failure detection and location method in asphalt materials using coplanar capacitance technology. Firstly, the capacitance distribution measurement on the single-pair electrode capacitance sensor with constant area (CSCS) is utilized to locate the various failures of asphalt materials. Then, the various failure depth inside asphalt materials can be predicted using a standard curve of the various failure depth-maximum change capacitance. Finally, based on the single-pair electrode capacitance sensor with variable area (VSCS), the spatially resolved capacitance measurement determines the various failure shape details of asphalt materials. It is found that the Ultrasonic Tomography Technology (UTT) method can only identify internal various failures in asphalt materials and is unable to determine the location of various failures. Nevertheless, the capacitance distribution measurement can identify air void and water intrusion various failures in asphalt materials. And the relative error of the measured location results inside asphalt materials is within 7. The predicted curves of various failure depths in asphalt materials have a coefficient of determination (R2) of greater than 0.984. The maximum change capacitance can be utilized to estimate the various failure depth in asphalt materials. The UTT method makes it difficult to determine the shapes and sizes of various failures in asphalt materials. But the spatially resolved capacitance measurement can determine the various failure shape details of asphalt materials. And the errors in the reconstructed results with failure shape details inside asphalt materials are less than 11%. The findings of this investigation can help engineers realize intuitive identification and precise location of invisible failures in shallow asphalt layers in bridge deck asphalt pavement using coplanar capacitance technology.

Dual-mode sensor for intelligent solution monitoring: Enhancing sensitivity and recognition accuracy through capacitive and triboelectric sensing

Monitoring solution parameters is of utmost importance in various industries and daily applications. However, the challenge lies in using a single sensor to effectively monitor different parameters in the solution. In this study, a dual-mode sensor is proposed, capable of monitoring multiple solution parameters combined with deep learning method. The fabrication process of the dual-mode sensor is simple, involving a substrate, interdigital electrodes, and a dielectric layer. The sensitivity of the dual-mode sensor is improved by increasing the dielectric constant of the dielectric layer and optimizing the design of the interdigital electrodes. Under the capacitive sensing mode, the sensor effectively identifies solution type by detecting capacitance changes due to the conductivity of the mixed solution. Under the triboelectric sensing mode, the sensor exhibits high sensitivity to solution concentration through the coupling of the capacitive enhancement effect and the triboelectric effect. An electric switch is incorporated into the design to control the signal acquisition of the dual-mode sensor. By combining the deep learning method with the dual-mode sensor, high recognition accuracies have been achieved for both solution type and concentration, with average accuracies exceeding 95%. Furthermore, the dual-mode sensor is not limited to monitoring liquid droplets; it can also be used for monitoring the types of liquids in bottles. In addition, an intelligent system is developed to visualize the intelligent monitoring process. This work not only contributes to a better understanding of the underlying mechanisms of planar capacitive sensors (PCS) and free-standing triboelectric nanogenerators (FS-TENG), but also presents a promising method for intelligent solution monitoring.

Advancements of Upper Limb Prostheses can Improve Patient Quality of Life: A Technology Review

Introduction: Based on the evolution of hand prosthetics, many original shortcomings have been addressed and further rectified. Some common past limitations include limited degrees of freedom, strained motion control/fine movements, the weight of the design, and lack of ability to do thumb-index pinch. Henceforth, this review highlights and assesses the effects of hand- prosthetics advancements on the quality of life of patients with/requiring joint replacements. Methods: Relevant literature between 2013 to 2023 was obtained using Web of Science and PubMed. Search terms were “Upper limb prostheses” OR “Body replacement technologies” AND “technology” as well as “Upper limb prostheses” AND “technology” AND “Quality of life” OR “Improvement”. Literature was selected based on applicability to key aspects of the research topic after assessing the results and abstracts. Results: Studies support the theory that over the decade, the ability to accomplish fine motion control with hand-prosthetics has aided in improving patients' quality of life. Overall, advancements to prosthetic design, prosthetic sensors, and waterproofing designs via myoelectricity, insulated and biopotential sensors, as well as waterproofing technologies, were reported to contribute greatly to patients’ quality of life. Discussion: As technological advances aid in improved dexterity and motility, recently advanced prosthetics help promote independence and confidence, and in some cases, decrease the cost of living for some patients. Myoelectric prostheses, flexible insulated sensors, capacitive biopotential sensors, and waterproofing technologies, have shown trends in increased dexterity, patient comfort and flexibility, as well as increased degrees of freedom of movement. The most notable limitations to these advancements were limited accessibility, comfort challenges, and lack of large-scale patient assessment. Hence, future advancements in further research and patient testing of these technologies were suggested. Conclusion: This review will be deemed as supporting material for healthcare providers and policy makers while making decisions on the allocation of resources to ensure that patients from all demographics can acquire accessible technologies, improving their qualities of life. In addition, the advancements of hand prosthetic technologies from mechanics and robotics research can provide implications for the next-generation technologies with the determination to improve patients’ life.

Gelatin Biogel–Liquid Metal Composite Transient Circuits for Recyclable Flexible Electronics

AbstractTransient electronics with degradability or dissolvability on demand possess remarkable characteristics for wearable, bioelectronic, and implanted electronic devices. While synthetic materials have made significant progress in degradability and stretchability, they suffer from intrinsic limitations, including low degradation rates, poor mechanical compliance, and high production cost, which restrict the growth of transient electronic devices. Herein, a versatile fabrication strategy is presented for transient electronics that combine a resilient biopolymer substrate (gelatin biogels) with liquid metal (Galinstan). The circuits made from gelatin biogel‐based and liquid metal are mechanically resilient and durable, exhibiting good compliance with irregular and deformable surfaces, and thus can withstand long‐term exposure to dynamic deformation (about 60 000 cycles at a strain of 50%). More importantly, gelatin biogels are naturally derived and endowed with thermally reversible gelling, which enables on‐demand rapid dissolution and recycling of the materials. As a proof‐of‐concept, transient circuit‐based capacitive sensors, which can be degraded within 20 s, are fabricated for monitoring finger touching, morse code generation, and electrical touchpad. Such a strategy provides a guideline for designing transient electronics with a combination of biopolymer gels and liquid metal, and this approach is anticipated to find applications in human–machine interfaces and wearable devices.

Template‐free Formation of Hybrid Dielectric for Flexible Capacitive Sensors with Wide‐Pressure‐Range Linear Detection

AbstractWearable and flexible capacitive pressure sensors have recently attracted significant attention in the fields of healthcare monitoring and intelligent human‐machine interaction. While considerable progress is made in achieving high‐pressure resolution over a wide linearity range, practical implementation still faces significant challenges due to complex manufacturing processes, as well as limited accuracy and stability for information transmission. To address these issues, inspiration is drawn from human skin and develop a new hybrid dielectric comprising a low‐permittivity (low‐k) micro‐cilia array and a high‐permittivity (high‐k) foam. Without assistance from an elaborate fabrication methodology, the template‐free method provides a cost‐effective and convenient way to realize the functional dielectric for flexible capacitive sensors. The hybrid dielectric exhibits a pressure‐induced series‐parallel conversion mechanism, enabling effective manipulation of the linear effective dielectric constant and controlled initial/resultant capacitance. Through systematic optimization, the sensor demonstrates a high sensitivity of 0.236 kPa−1 within an ultrabroad linearity range of up to 1100 kPa. Thanks to the unique characteristics of the hybrid dielectric, this device showcases potential applications in various domains including human joint motion analysis, healthcare monitoring, accurate message transmission, and convenient Morse code communication utilizing non‐overlapping capacitance signals.

Propellant Mass Gauging in a Spherical Tank under Micro-Gravity Conditions Using Capacitance Plate Arrays and Machine Learning.

Propellant mass gauging under micro-gravity conditions is a challenging task due to the unpredictable position and shape of the fuel body inside the tank. Micro-gravity conditions are common for orbiting satellites and rockets that operate on limited fuel supplies. Capacitance sensors have been investigated for this task in recent years; however, the effect of various positions and shapes of the fuel body is not analyzed in detail. In this paper, we investigate this with various fill types, such as annular, core-annular, and stratified fills at different positions. We compare the performance among several curve-fitting-based approaches and a machine-learning-based approach, the latter of which offers superior performance in estimating the fuel content.

Soil total suction sensing using fiber-optic technology

Measurement of the soil water suction is important for investigating geotechnical problems and mitigating associated risks; however, conventional high-range suction measurement techniques have some limitations for accurate, long-term, and quasi-distributed suction measurement in the field. Fiber-optic humidity sensors provide a viable solution due to their unique properties. Here, we present a novel microfabricated fiber-optic suction sensor for measuring the suction of water in unsaturated soils. We evaluated the performance of the sensor on four bentonite–sand mixtures by comparing it with two laboratory suction measurement methods (chill-mirror hygrometer, salt solution vapor equilibrium) and a capacitive relative humidity sensor. We determined that this sensor has a measurement range of 5–300 MPa with a root mean square error of less than 3.5 MPa, and a response time of 2–9 min over the tested suction variation range (6.5–80.5 MPa). The results of the evaporation model test showed that three fiber-optic sensors installed at different depths of bentonite could effectively capture changes in temperature, relative humidity in soil pores, and total suction during evaporation. Together, these results demonstrate the great potential of the fiber-optic suction sensor for in-situ, long-term, and quasi-distributed suction monitoring.

Low-cost, interdigitated capacitive sensor using laser-written graphene foam for touch, proximity, and liquid level detection

Flexible capacitive sensors are gaining popularity in place of sophisticated optical sensing or bulky mechanical designs for specific applications such as proximity/gesture detection and liquid level sensing. So, here, we propose Laser Induced Graphene Foam (LIGF) based planar capacitive sensors, which are flexible, highly sensitive, energy-efficient, and cost-effective, making them accessible for various applications. The working of these sensors involves the interdigitated planar electrode configuration and the fringing effect, influencing capacitance when the permittivity or the electric charge of the surrounding medium changes. LIGF planar capacitive elements were produced on a commercially availed polymer polyimide by using direct laser writing technique employing a low-cost diode laser. The developed LIGF-based planar capacitive touch sensor showed an average touch response (|ΔC/Co|) of more than 49%; moreover, when used for proximity sensing, this sensor could detect the presence of human hand up to a maximum distance of 170 mm from the sensor surface. An extended design of the sensor has demonstrated liquid level sensing with an accuracy of 0.97 mm. As a result of its ability to sense dielectric materials, contactless operation, long-range sensing, cost-effectiveness, low-power consumption, and environmental friendliness, the LIGF electrode-based capacitive sensor can be incorporated into a variety of modern technology and devices.