Capacitive Sensor Research Articles

Controlling the fold: proprioceptive feedback in a soft origami robot.

We demonstrate proprioceptive feedback control of a one degree of freedom soft, pneumatically actuated origami robot and an assembly of two robots into a two degree of freedom system. The base unit of the robot is a 41 mm long, 3-D printed Kresling-inspired structure with six sets of sidewall folds and one degree of freedom. Pneumatic actuation, provided by negative fluidic pressure, causes the robot to contract. Capacitive sensors patterned onto the robot provide position estimation and serve as input to a feedback controller. Using a finite element approach, the electrode shapes are optimized for sensitivity at larger (more obtuse) fold angles to improve control across the actuation range. We demonstrate stable position control through discrete-time proportional-integral-derivative (PID) control on a single unit Kresling robot via a series of static set points to 17 mm, dynamic set point stepping, and sinusoidal signal following, with error under 3 mm up to 10 mm contraction. We also demonstrate a two-unit Kresling robot with two degree of freedom extension and rotation control, which has error of 1.7 mm and 6.1°. This work contributes optimized capacitive electrode design and the demonstration of closed-loop feedback position control without visual tracking as an input. This approach to capacitance sensing and modeling constitutes a major step towards proprioceptive state estimation and feedback control in soft origami robotics.

A Rational Design of Bio-Derived Disulfide CANs for Wearable Capacitive Pressure Sensor.

Classic approaches to integrate flexible capacitive sensor performance are to on-demand microstructuring dielectric layers and to adjust dielectric material compositions via the introduction of insoluble carbon additives (to increase sensitivity) or dynamic interactions (to achieve self-healing). However, the sensor's enhanced performances often come with increased material complexity, discouraging its circular economy. Herein, a new intrinsic self-healable, closed-loop recyclable dielectric layer material, a fully nature-derived dynamic covalent poly(disulfide) decorated with rich H bonding and metal-catechol complexations is introduced. The polymer network possesses a mechanically ductile character with an Arrhenius-type temperature-dependent viscoelasticity. The assembled capacitive pressure sensor is able to achieve a sensitivity of up to 9.26kPa-1, fast response/recovery time of 32/24ms, and can deliver consistent signals of continuous consecutive cycles even after being self-healed or closed-loop recycled for real-time detection of human motions. This is expected to be of high interest for current capacitive sensing research to move toward a life-like, high performance, and circular economy direction.

A highly sensitive, flexible capacitive pressure sensor based on strontium alginate with crater microstructure

Electronic skin plays an important role in the age of artificial intelligence. Capacitive pressure sensors, capable of sensing pressure changes through contact, still need to improve their basic performance and comfort of use. In this paper, a flexible strontium alginate film with finely folded crater microstructure prepared by spraying method is introduced as a dielectric layer, together with PDMS film and conductive cloth as a capacitive sensor. The internal and external displacement, potential, and elastic volume ratio of the sensor were simulated using finite element analysis. The sensor has good sensitivity (R2 up to 0.99), very low response and relaxation time (≤ 50 ms), and good cyclic stability. The sensor was also used for performing several simple applications tests.

Degradable, biocompatible, and flexible capacitive pressure sensor for intelligent gait recognition and rehabilitation training

Gait recognition and rehabilitation training based on pressure sensing technology have an important role in the field of rehabilitation medicine. However, existing pressure sensors that are used in this process are often fabricated from non-degradable or non-biocompatible source materials, which limits their application in long-term sustainable use. In this study, we propose a high-performance, degradable, biocompatible and flexible capacitive pressure sensor. Its dielectric layer is prepared using a polyvinyl alcohol/sodium alginate (PVA/SA) electrospun nanofiber membrane (ENM), while its upper and lower electrodes are fabricated from PVA@graphene screen-printed ENMs. Experimental results demonstrate the sensor's exceptional pressure sensing performance, characterized by its high sensitivity (0.54 kPa−1 at 0–10 kPa), low detection limit (∼2.2 Pa), rapid response time (26.6/29.9 ms), and excellent stability (5000 cycles). Furthermore, it exhibits outstanding biocompatibility, achieving a cell viability assay survival rate exceeding 97%, and remarkable degradability, completely degrading within one hour. A gait recognition and rehabilitation training system has been developed by integrating the sensors with a deep learning algorithm and wireless transmission technology. The system can effectively monitor and record dynamic parameters of lower limb swing during walking, exhibiting an impressive gait recognition accuracy of 98% over five normal and abnormal gaits. Moreover, it can guide patients in performing diverse rehabilitation actions as well as monitor their progress through action count recording. This innovative solution offers a sustainable approach to gait recognition and rehabilitation training within the field of rehabilitation medicine, thereby opening up new avenues for patient recovery.

A Passive Wireless Smart Washer for Locking Force Monitoring on the Orthopedic Pedicle Screw

A pedicle screw is a component for fixation in spine fusion surgery, often for patients with osteoporosis. Spine fusion condition highly depends on whether the pedicle screw is tightly fixed on spine, if not, spine fusion will not work properly. After the surgery, the first 3 months is the most crucial period, and bone healing situation cannot be shown through X-ray before the first radiologic images taken around the sixth week. Therefore, it is helpful to have a nonradiative method to monitor the locking force of the pedicle screw after surgery, especially during the early stage. Here a passive wireless force sensor is developed for monitoring the locking force of the pedicle screw, as we call it a smart washer. By integrating a capacitive ring-shape force sensor with an inductor, a passive LC sensor can be built by measuring the resonant frequency wirelessly. The smart washer is designed and calibrated to establish the relation between the locking force and resonant frequency, and then it is fixed with a screw in a porcine femur, with and without medium between the reader and inductor. When the locking force decreases from 8.3 to 0.9 N, the error is less than 0.5 N, and the maximum wireless sensing distance is 72 mm. However, the medium between the reader and the sensor inductor will affect the resonant frequency, but not the sensitivity. Therefore, the locking force variation can still be calculated by the resonant frequency shift accurately. Furthermore, by designing another five LC sensors with different operating resonant frequency ranges, it is possible to identify locking forces at different locations for more pedicle screws. To our knowledge, no LC force sensor was proposed to monitor the locking force of pedicle screws after surgery in the past.

Calibration and validation of a bleeding detector for beveled PMMA applicators in electron intraoperative radiotherapy

This study aimed to calibrate and validate a capacitive-sensor bleeding detector, originally designed for flat applicators, with beveled applicators (bPMMA), which are among the most commonly used applicators in intraoperative radiotherapy with electron mobile linacs. The detector will help prevent dose misadministration during irradiation in the event of fluid accumulation in the applicator, thus allowing for appropriate intervention. The handicap with employing this detector for bPMMA stems from the fact that the level of accumulated fluid depends on both the tilting angle and orientation of the applicator. Furthermore, the fluid remains accumulated at the bottom corner of the applicator, reducing the sensitivity of the sensor. A 5-strip capacitive sensor has been used, attached to a 4 cm diameter 30° beveled applicator with a tilting angle range from 0° to 30°. The sensor is read out using dedicated electronics, including a Wheatstone bridge circuit, amplifier, filter stages, and microcontroller. To calculate the sensitivity of the sensor, a prior calibration of the circuit has been carried out in order to obtain the relationship between the output voltage of the conditioning circuit and the height of the fluid present in the applicator for different inclinations. Using the average sensitivity over the inclination range of interest can provide accurate measurements of the estimated fluid height up to 12 mm, with a maximum deviation of approximately 2.0 mm and less than 1.0 mm for the 5 mm clinic threshold. The use of the mean sensitivity is a practical approach for detecting bleeding in beveled applicators because it simplifies the measurement process by avoiding the need to obtain detector sensitivity for each inclination and orientation of the applicator, which would be complex if not impractical in clinical use.

Measuring volume fractions of a three-phase flow without separation utilizing an approach based on artificial intelligence and capacitive sensors.

Many different kind of fluids in a wide variety of industries exist, such as two-phase and three-phase. Various combinations of them can be expected and gas-oil-water is one of the most common flows. Measuring the volume fraction of phases without separation is vital in many aspects, one of which is financial issues. Many methods are utilized to ascertain the volumetric proportion of each phase. Sensors based on measuring capacity are so popular because this kind of sensor operates seamlessly and autonomously without necessitating any form of segregation or disruption for measuring in the process. Besides, at the present moment, Artificial intelligence (AI) can be nominated as the most useful tool in several fields, and metering is no exception. Also, three main type of regimes can be found which are annular, stratified, and homogeneous. In this paper, volume fractions in a gas-oil-water three-phase homogeneous regime are measured. To accomplish this objective, an Artificial Neural Network (ANN) and a capacitance-based sensor are utilized. To train the presented network, an optimized sensor was implemented in the COMSOL Multiphysics software and after doing a lot of simulations, 231 different data are produced. Among all obtained results, 70 percent of them (161 data) are awarded to the train data, and the rest of them (70 data) are considered for the test data. This investigation proposes a new intelligent metering system based on the Multilayer Perceptron network (MLP) that can estimate a three-phase water-oil-gas fluid's water volume fraction precisely with a very low error. The obtained Mean Absolute Error (MAE) is equal to 1.66. This dedicates the presented predicting method's considerable accuracy. Moreover, this study was confined to homogeneous regime and cannot measure void fractions of other fluid types and this can be considered for future works. Besides, temperature and pressure changes which highly temper relative permittivity and density of the liquid inside the pipe can be considered for another future idea.

Piezoresistive and capacitive cement-based stress sensors designed by incorporating carbon nanotubes doped with graphene nanopowder for structural health monitoring

Piezoresistive and capacitive cement-based smart composites are promising candidates for stress monitoring applications in buildings. However, the drawbacks of designing cement-based smart composites with a piezoresistive mechanism sensitive to temperature variations or a capacitive mechanism sensitive to vibration can be solved with sensor designs based on two principles. To address this issue, cement-based smart composites with piezoresistive and capacitive stress sensitivity and significantly improved compressive strength were designed using carbon nanotubes (CNT) doped with graphene nanopowder. A maximum fractional change in electrical resistivity of 90.08% with a high linearity of 98% was obtained with a blend of 0.01 wt%, and the maximum fractional change in capacitance was 163.11% with a high linearity of 97% at 0.05 wt%. Cement-based smart composites have absolute piezoresistive stress sensitivities that vary from 1.38% MPa−1 to 4.16% MPa−1 and 2.54% MPa−1 to 2.57% MPa−1 for blended and impregnated low doses of 0.01 wt% to 0.05 wt% CNT doped with graphene. In addition, capacitive stress sensitivities of 22.74% MPa−1 and 5.1% MPa−1 were achieved by blending and impregnating 0.01 wt% CNT doped with graphene in cementitious composites. Furthermore, the conductive path, overlapping, and tunneling effect created by CNT doped with graphene in cementitious composites and the porous structure in the dielectric layer are responsible for the increased stress sensitivity.

An Integrated Capacitive Pressure Sensor Based on Gradient Charge Distribution with High Sensitivity and Fast Response

An Integrated Capacitive Pressure Sensor Based on Gradient Charge Distribution with High Sensitivity and Fast Response

Design of 12-Lead Electrocardiogram Smart Clothing Based on Capacitive Sensing Technique

Design of 12-Lead Electrocardiogram Smart Clothing Based on Capacitive Sensing Technique

Wide-range, durable, and adaptable miniature pressure sensor based on planar capacitance

Capacitive pressure sensor (CPS) is widely used in the field of industrial equipment, because of the merits of fast dynamic response and high resolution. However, the traditional laminated CPS makes it difficult to achieve a wide detection limit in a small size, and this structure is susceptible to electromagnetic interference. Here we developed a miniature planar capacitive pressure sensor (MPCPS) with high performance, which can realize the response to external touching stimuli through the deformation of the packaging material and the change of the equivalent resistance. A metal shielding layer was added under the insulating substrate to effectively isolate the external interference. The thickness of the sensor is about 200 μm, and the diameter of the core sensing area is less than 1 mm. Two types of electrodes with different shapes were designed, among which the spiral electrode MPCPS (S-MPCPS) has better performance than the linear electrode MPCPS. The S-MPCPS has a sensitivity of 99.2% MPa−1 in the low-pressure range (0–0.1 MPa), fast response (20 ms), wide detection limit (>1 MPa), and high durability (>2000 cycles). In addition, MPCPS is proven to have good resistance to high temperature and oil contamination. Finally, practical applications such as contact pressure measuring on the meshing surface of spur gears and mechanical gripper clamping force monitoring were successfully demonstrated. These results shed light on the potential application of the MPCPS in the pressure detection of industrial equipment.

Electrochemical Impedance Spectroscopy for Ion Sensors with Interdigitated Electrodes: Capacitance Calculations, Equivalent Circuit Models and Design Optimizations.

Electrochemical impedance spectroscopy (EIS) is becoming more and more relevant for the characterization of biosensors employing interdigitated electrodes. We compare four different sensor topologies for an exemplary use case of ion sensing to extract recommendations for the design optimizations of impedimetric biosensors. Therefore, we first extract how sensor design parameters affect the sensor capacitance using analytical calculations and finite element (FEM) simulations. Moreover, we develop equivalent circuit models for our sensor topologies and validate them using FEM simulations. As a result, the impedimetric sensor response is better understood, and sensitive and selective frequency ranges can be determined for a given sensor topology. From this, we extract design optimizations for different sensing principles.

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.

Nitrocellulose/acrylic resin coated screen-printed carbon electrode to construct a capacitive immunosensor for anti-BSA

The capacitive immunosensor, known for its label-free simplicity, has great potential for point-of-care diagnostics. However, the interaction between insulation and recognition layers on the sensing electrode greatly affects its performance. This study introduces a pioneering dual-layer strategy, implementing a novel combination of acrylic resin (AR) and nitrocellulose (NC) coatings on screen-printed carbon electrodes (SPCEs). This innovative approach not only enhances the dielectric properties of the capacitive sensor but also streamlines the immobilization of recognizing elements. Particularly noteworthy is the superior reliability and insulation offered by the AR coating, surpassing the limitations of traditional self-assembled monolayer (SAM) modifications. This dual-layer methodology establishes a robust foundation for constructing capacitive sensors optimized specifically for liquid medium-based biosensing applications. The NC coating in this study represents a breakthrough in effectively immobilizing BSA, unraveling the capacitive response intricately linked to the quantity of adsorbed recognizing elements. The results underscore the prowess of the proposed immunosensor, showcasing a meticulously defined linear calibration curve for anti-BSA (ranging from 0 to 25 μg/ml). Additionally, specific interactions with anti-HAS and anti-TNF-α further validate the versatility and efficacy of the developed immunosensor. This work presents a streamlined and highly efficient protocol for developing label-free immunosensors for antibody determination and introduces a paradigm shift by utilizing readily available electrodes and sensing systems. The findings are poised to catalyze a significant acceleration in the advancement of biosensor technology, opening new avenues for innovative applications in point-of-care diagnostics.

Synthesis of PDMS Chain Structure with Introduced Dynamic Covalent Bonding for High‐Performance Rehealable Tactile Sensor Application

AbstractIn addressing the increasing demand for wearable sensing systems, the performance and lifespan of such devices must be improved by enhancing their sensitivity and healing capabilities. The present work introduces an innovative method for synthesizing a healable disulfide bond contained in a polydimethylsiloxane network (PDMS−SS) that incorporates ionic salts, which is designed to serve as a highly effective dielectric layer for capacitive tactile sensors. Within the polymer network structure, the cross‐linking agent pentaerythritol tetrakis 3‐mercaptopropionate (PTKPM) forms reversible disulfide bonds while simultaneously increasing polymer softness and the dielectric constant. The incorporation of dioctyl sulfosuccinate sodium salt (DOSS) significantly improves the capacitance and sensing properties by forming an electrical double‐layer through interactions between the electrode charge and salt ions at the contact interface. The developed polymer material‐based tactile sensor shows a strong response signal at low pressure (0.1 kPa) and maintains high sensitivity (0.175 kPa−1) over a wide pressure range (0.1–10 kPa). It also maintains the same sensitivity over 10 000 repeated applications of external pressure and is easily self‐healed against mechanical deformation due to the dynamic disulfide covalent bonding, restoring ≈95% of its detection capacity.

A non-invasive capacitive sensor to investigate the Leidenfrost phenomenon: a proof of concept study

A volatile sessile liquid droplet or a sublimating solid manifests levitation on its own vapor when placed on a sufficiently heated surface, illustrating the Leidenfrost phenomenon. In this study, we introduce a non-invasive capacitance method for investigating this phenomenon, offering a potentially simpler alternative to existing optical techniques. The designed sensor features in-plane miniaturized electrodes forming a double-comb structure, also known as an interdigitated capacitor. Initially, the sensor’s capacitance is characterized for various distances between the sensor and a dielectric material. The influence of the sensor substrate material and the spacing between the electrodes on the sensor’s capacitance is also investigated. To demonstrate the feasibility of the method, a sublimating dry ice pellet is placed on the capacitive sensor, and its performance is evaluated. We present results for the dimensionless vapor layer thickness and the pellet’s lifetime at different substrate temperatures, derived from the capacitance output. The results are compared with Optical Coherence Tomography (OCT) data, serving as a benchmark. While the temporal evolution of the sensor’s output, variation in the dimensionless vapor layer thickness, and the lifetime of the dry ice pellet align with expected results from OCT, notable quantitative deviations are observed. These deviations are attributed to practical experimental limitations rather than shortcoming in the sensor’s working principle. Although this necessitates further investigation, the methodology presented in this paper can potentially serve as an alternative for the detection and measurement of Leidenfrost vapor layers.

Humidity Diode Sensors Based on 1D Nanosized Silicon Structures

Introduction. Humidity measurement is essential in microelectronics, aerospace, biomedical, and food industries, as well as in households for climate control. Currently, various types of devices have been used as humidity sensors: capacitive, resistive, diode, gravimetric, optical structures, field-effect transistors and devices based on surface acoustic waves.Problem Statement. Today, there is a need to develop IC-compatible humidity sensors that have high sensitivityand low cost. To this end, silicon nanowires have been successfully used in resistive and capacitive humidity sensors. However, there is a lack of research on the nanowire effect on device parameters of diode-type humidity sensors.Purpose. To develop diode sensors based on silicon nanowires and to determine the effect of process parameters of synthesis and structural features of nanowires on the performance of humidity sensors.Materials and Methods. The process of sensor fabrication includes several steps: chemical cleaning of silicon wafer, synthesis of silicon nanowires using standard or modified metal-assisted chemical etching, phosphorus diffusion to create a p-n junction, front and back metallization. The surface morphology of the nanostructures has been studied by scanning electron microscopy. The humidity-sensitive characteristics have been studied with theuse of salt hygrostats.Results. It has been shown that the addition of one-dimensional silicon nanostructures to the diode-type sensor signifi cantly improves its characteristics. The rectification ratio increases from 161 to 1807, the response ups from 4.5 to 25, the sensitivity grows from 1.6 to 4.02 (%RH)–1, while the response time and recovery time are reduced from 85/90 to 25/30 s, the hysteresis value goes down from 75 to 16%, the signal deviation after cycling drops from 15to 3%, and the signal fluctuation during continuous device operation decreases from 17 to 15%.Conclusions. The results have shown that the use of a simple and cheap nanowire synthesis technology is effective to produce humidity sensors.

Gait Pattern Analysis: Integration of a Highly Sensitive Flexible Pressure Sensor on a Wireless Instrumented Insole.

Gait phase monitoring wearable sensors play a crucial role in assessing both health and athletic performance, offering valuable insights into an individual's gait pattern. In this study, we introduced a simple and cost-effective capacitive gait sensor manufacturing approach, utilizing a micropatterned polydimethylsiloxane dielectric layer placed between screen-printed silver electrodes. The sensor demonstrated inherent stretchability and durability, even when the electrode was bent at a 45-degree angle, it maintained an electrode resistance of approximately 3 Ω. This feature is particularly advantageous for gait monitoring applications. Furthermore, the fabricated flexible capacitive pressure sensor exhibited higher sensitivity and linearity at both low and high pressure and displayed very good stability. Notably, the sensors demonstrated rapid response and recovery times for both under low and high pressure. To further explore the capabilities of these new sensors, they were successfully tested as insole-type pressure sensors for real-time gait signal monitoring. The sensors displayed a well-balanced combination of sensitivity and response time, making them well-suited for gait analysis. Beyond gait analysis, the proposed sensor holds the potential for a wide range of applications within biomedical, sports, and commercial systems where soft and conformable sensors are preferred.

Degradation of anti-rust oil film in a simulated coastal atmosphere: Inhibition mechanism and in-situ monitoring

Anti-rust oils (ARO) are widely used to inhibit atmospheric corrosion of metal structures, but their degradation mechanisms are unclear, particularly in coastal environments. In this work, we first prepared a kind of ARO made of sodium petroleum sulfonate (SPS) and white oil, then coated the ARO on a mild steel plate to investigate its deterioration process beneath saline water droplets by Quartz crystal microbalance (QCM) and electrochemical mapping techniques. It shows that the SPS concentration is crucial to the ARO inhibition property. When the SPS content is lower than its critical micelle concentration (CMC), saline droplets may intrude the barrier formed by the nonpolar paraffin groups of SPS and then adsorb on the steel surface, resulting in localised corrosion. However, once the SPS content exceeds its CMC, the saline droplets will be emulsified and captured in the oil phase by the reverse micelle effect, thus inhibiting the corrosion of steel substrates. Moreover, the atmospheric corrosion rate of mild steel obeys a power decaying under ARO film. Finally, a capacitive sensor was invented to evaluate the degree of degradation of ARO in situ by dielectric constant measurement.

Lantern-inspired capacitive pressure sensor with wide linear measuring range

In the field of pressure sensing, high sensitivity and linearity are two critical performance indicators, but striking a balance between them remains a prominent challenge for sensors. Existing solutions typically involve the structural design of electrodes or dielectric layers, often requiring complex and expensive techniques for designing microstructures. This study presents a novel flexible capacitive pressure sensor characterized by its low-cost nature, ease of manufacture, and scalability in design. The lantern accordion-like structure inspires the design of the dielectric layer and the porous structure is designed using thermally expandable microspheres (TEM). The synergy of surface microstructures and internal microstructures results in a high sensitivity of 3.07 × 10−3 kPa−1 within a wide linear response range of 0–100 kPa. The developed sensor is also evaluated for its weight detection capabilities, highlighting its promising weight and pressure data acquisition.