Capacitive Sensor Research Articles

Fabrication of fully bio-based malleable thermoset derived from cellulose, furfural and plant oil for advanced capacitive sensor

Fabrication of sustainable bio-based malleable thermosets (BMTs) with excellent mechanical properties and reprocessing ability for applications in electronic devices has attracted more and more attention but remains significant challenges. Herein, the BMTs with excellent mechanical robustness and reprocessing ability were fabricated via integrating with radical polymerization and Schiff-base chemistry, and employed as the flexible substrate to prepare the capacitive sensor. To prepare the BMTs, an elastic bio-copolymer derived from plant oil and 5-hydroxymethylfurfural was first synthesized, and then used to fabricate the dynamic crosslinked BMTs through Schiff-base chemistry with the amino-modified cellulose and polyether amine. The synergistic effect of rigid cellulose backbone and the construction of dynamic covalent crosslinking network not only achieved high tensile strength (8.61 MPa) and toughness (3.77 MJ/m3) but also endowed the BMTs with excellent reprocessing ability with high mechanical toughness recovery efficiency of 104.8 %. More importantly, the BMTs were used as substrates to fabricate the capacitive sensor through the CO2-laser irradiation technique. The resultant capacitive sensor displayed excellent and sensitive humidity sensing performance, which allowed it to be successfully applied in human health monitoring. This work paved a promising way for the preparation of mechanical robustness malleable bio-thermosets for electronic devices.

Integrated surface microstructure and enhanced dielectric constant for constructing simple, low-cost, and high-performance flexible capacitive pressure sensor

Designing microstructure surface or enhancing the dielectric constant of functional layer is a common useful strategy to improve the pressure sensing performances of flexible capacitive pressure sensors, but it usually involves complex preparation processes (such as artificial microstructure and preparation of composite materials). Considering the limitations of a single strategy in improving the pressure sensing performance of capacitive pressure sensor, herein, we propose a simple strategy that integrates surface microstructure and enhanced dielectric constant of functional layer for constructing a high-performance flexible capacitive pressure sensor. Specifically, the polyester fiber conductive tape and filter paper with intrinsic rough surfaces are selected as microstructure electrodes and dielectric layer, respectively. Meanwhile, by introducing the daily carbon ink into filter paper, the moderate conductivity of the carbon ink is utilized to enhance the dielectric constant of the filter paper dielectric layer. The results show that the proposed the pressure sensor has wide pressure detection range of 0.1−100 kPa, high sensitivity (1.47 kPa−1, 0.1−10 kPa) and good durability (4000 cycles at 20 kPa). Taking the pressure range of 10−100 kPa as an example, the sensitivity of carbon ink paper-based sensor is 60 times higher than that of sensor without carbon ink. The enhanced working mechanism of the sensor is clarified by combining testing and characterization. In addition, the proposed pressure sensor has potential applications in wrist pulse, respiratory rate, walking record, morse code transmission，and stoma bag detection. This work provides a useful reference for constructing simple, low-cost and high-performance flexible capacitive pressure sensor.

The Design and numerical simulation of a 3D-printed flexible capacitive pressure sensor with a composite structure

Abstract Flexible pressure sensors are crucial for many areas, such as electronic skins, human motion, robot monitoring, and medical treatment. However, conventional manufacturing methods limit the speed and accuracy of manufacturing sensor dielectric layers. In this paper, a unique capacitive pressure sensor with a composite structure is introduced that can be fabricated by 3D printing technology. The structure, which has 3D hierarchical pyramids microstructures and porous substrate, can be directly fabricated by a DLP 3D printer. This allows flexible dielectric layers to be fabricated quickly while maintaining their superior performance. The dimension of the produced sensor is 10×10×4.5 mm3. The sensor’s design process, numerical simulation, and performance are provided and elucidated. The performance of the sensor is measured between 0 and 1 MPa. It has low hysteresis and high sensitivity (6.83 MPa−1 within the scope of 0 to 0.5 MPa and 2.56 MPa−1 within the scope of 0.5 to 1 MPa).

96‐3: Invited Paper: Next‐Gen Interactions: Creative Sensing Solutions for Automotive Capacitive Knobs on Displays

Automakers are adding back mechanical knobs to modern car cabins to address concerns about the difficulty of adjusting vehicle setting controls through the touchscreen interface. Passive capacitive knobs attached to touchscreens are a great solution as they provide a seamless interface while using the same capacitive sensors that sense finger touches. Existing knobs rely on capacitive coupling to a user's hand, making it difficult to support gloved hands. The proposed knob resolves this by employing a unique sensing architecture while providing additional features such as initial state detection and fall‐off detection.

Study of Botanical Music Integration using the Touché method

This study explores the integration of Touché's Swept Frequency Capacitive sensing technique with plant biology to understand plant responses to touch and to generate music from these interactions. The research involves the collection of various indoor plants such as Money Plant, Bamboo Plant, Oyster Plant, and Philodendron Plant, each with unique properties and benefits. Capacitive sensors are integrated with the plants, and Arduino boards are utilized to measure changes in capacitance upon touch. The electrical signals from plants are converted into musical notes using Max8 software, providing a dynamic interface for plant interaction. Results indicate that plants with thicker stems, such as bamboo and oyster plants, exhibit heightened sensitivity, potentially due to their higher water content and conductivity. The study also suggests succulent plants show promise in this regard. Through this interdisciplinary approach, insights are gained into plant sensory mechanisms and adaptive responses, bridging the gap between technology, biology, and music. Further investigations could delve into the specific mechanisms underlying plant sensitivity and explore the impact of music on plant growth and behaviour, offering new perspectives on plant communication and environmental responsiveness. Ultimately, this integration of technology with nature aims to promote growth without negative environmental impact.

5‐2: Integrated Design of Capacitive Touch and Electromagnetic Sensor for Flexible OLED Display

This work presents a novel structure for integrating capacitive touch and electromagnetic resonance (EMR) sensors on thin film encapsulation (TFE) of OLED display. Through co‐layer design of touch bridge electrode and EMR coil, the number of mask can be reduced, and the module thickness can also be decreased. In addition, the Cs loading of touch and the resistance of EMR coils are both reduced by the unique pattern design. Finally, an 8‐inch prototype sample was developed, and the hybrid sensor achieved sensitive touch and EMR stylus scribing functions after debugging.

Beetle‐Inspired Gradient Slant Structures for Capacitive Pressure Sensor with a Broad Linear Response Range (Adv. Funct. Mater. 26/2024)

Beetle‐Inspired Gradient Slant Structures for Capacitive Pressure Sensor with a Broad Linear Response Range (Adv. Funct. Mater. 26/2024)

Flexible Capacitive Pressure Sensor Enhanced by Black Phosphorus-Au Nanocomposites/Ecoflex Sponge for Pressure and Proximity Detection

Flexible Capacitive Pressure Sensor Enhanced by Black Phosphorus-Au Nanocomposites/Ecoflex Sponge for Pressure and Proximity Detection

Sensitivity enhanced flexible capacitive pressure sensor microstructure optimization for biomedical applications

This paper explores the design and optimization of Flexible Capacitive Pressure Sensors (FCPS) using microfabrication technology for applications in the emerging field of flexible electronics, with a particular focus on measuring bio-signals characterized by lower pressure ranges. Sensitivity, a critical parameter for effective FCPS performance, is investigated through a comprehensive series of simulation analyses employing finite element modeling. The study involves varying geometrical and mechanical parameters that influence FCPS performance, individually adjusting each parameter while keeping others constant. Microstructures such as cuboids, truncated pyramids with an aspect ratio of 0.5, cylinders, pyramids, and cones are modeled on the dielectric material surface. The parameters considered include inter-space, base length, height, and elastic modulus, to enhance FCPS sensitivity and linearity. Among the different shapes modeled, the cone exhibits the highest sensitivity, followed by the pyramid structure. Comparative analysis indicates that the cone and pyramid shapes demonstrate 15- and 10-times higher sensitivity, respectively, compared to the cuboid structure under an applied pressure of 10 Pa. Simulation results suggest that sensitivity can be finely tuned, with higher inter-space and microstructure height, as well as lower base length and Young’s modulus of the dielectric material, contributing to increased sensitivity. However, it is noted that these conditions may lead to decreased capacitance in the absence of applied pressure due to air occupation relative to the dielectric material. The findings are further compared with existing literature, and the FCPS response analysis provides valuable insights for the future design of FCPS, particularly in the context of biomedical applications requiring precise low-pressure signal measurements. This research contributes to advancing the understanding of FCPS performance optimization and lays the groundwork for the development of sensors with enhanced sensitivity for bio-medical applications.

Structural Health Monitoring of Fiber Reinforced Composites Using Integrated a Linear Capacitance Based Sensor.

The demand for fiber-reinforced polymers (FRPs) has significantly increased in various industries due to their attributes, including low weight, high strength, corrosion resistance, and cost-efficiency. Nevertheless, FRPs, such as glass and Kevlar fiber composites, exhibit anisotropic properties and relatively low interlaminar strength, rendering them susceptible to undetected damage. The integration of real-time damage detection processes can effectively mitigate this issue. This paper introduces a novel method for fabricating embedded capacitive sensors within FRPs using a coating technique. The study encompasses two types of fibers, namely glass and Kevlar fiber/epoxy composites. The physical vapor deposition (PVD) technique is employed to coat bundle fibers with conductive material, thus creating embedded electrodes. The results demonstrate the uniform distribution of nanoparticles of gold (Au) along the fibers using PVD, resulting in a favorable resistance of approximately ≈100 Ω. Two sensor configurations are explored: axial and lateral embedding of the coated yarn (electrodes) to investigate the influence of load direction on the coating yarn. Axial-sensor configuration specimens undergo tensile testing, showcasing a linear response to axial loads with average sensitivities of 1 for glass and 1.5 for Kevlar fiber/epoxy composites. Additionally, onset damage is detected in both types of fiber composites, occurring before final fracture, with average stress at the turning point measuring 208 MPa for glass and 144 MPa for Kevlar. The lateral-sensor configuration for glass fiber-reinforced polymer (GFRP) exhibits good linearity towards strain until failure, with average gauge factors of 0.25 and -2.44 in the x and y axes, respectively.

Optimizing Capacitive Pressure Sensor Geometry: A Design of Experiments Approach with a Computer-Generated Model.

This study presents a comprehensive investigation into the design and optimization of capacitive pressure sensors (CPSs) for their integration into capacitive touch buttons in electronic applications. Using the Finite Element Method (FEM), various geometries of dielectric layers were meticulously modeled and analyzed for their capacitive and sensitivity parameters. The flexible elastomer polydimethylsiloxane (PDMS) is used as a diaphragm, and polyvinylidene fluoride (PVDF) is a flexible material that acts as a dielectric medium. The Design of Experiment (DoE) techniques, aided by statistical analysis, were employed to identify the optimal geometric shapes of the CPS model. From the prediction using the DoE approach, it is observed that the cylindrical-shaped dielectric medium has better sensitivity. Using this optimal configuration, the CPS was further examined across a range of dielectric layer thicknesses to determine the capacitance, stored electrical energy, displacement, and stress levels at uniform pressures ranging from 0 to 200 kPa. Employing a 0.1 mm dielectric layer thickness yields heightened sensitivity and capacitance values, which is consistent with theoretical efforts. At a pressure of 200 kPa, the sensor achieves a maximum capacitance of 33.3 pF, with a total stored electric energy of 15.9 × 10-12 J and 0.468 pF/Pa of sensitivity for 0.1 dielectric thickness. These findings underscore the efficacy of the proposed CPS model for integration into capacitive touch buttons in electronic devices and e-skin applications, thereby offering promising advancements in sensor technology.

Multimodal electrohydrodynamic jet printing-based microstructure-sensitized flexible pressure sensor

Surface modification with micro/nanostructures is a common approach for enhancing the performance of flexible pressure sensors. However, the current fabrication of the singular functionality of instruments and redundancy of processes increase the complexity of the sensor manufacturing process. In this study, we developed a multilayer microstructure-enhanced flexible capacitive pressure sensor based on the multimodal electrohydrodynamic jet (E-jet) printing technology. The experimental results demonstrate that the sensors incorporating the microstructure-sensitized electrode layer and the polyvinyl alcohol/graphene/polydimethylsiloxane dielectric layer exhibit the following characteristics: high sensitivity (0.3139 kPa−1/0–2 kPa), low limit of detection (∼100 mg), and stable performance even after 10,000 cycles. Moreover, microstructure-enhanced sensors have considerable potential for human behavior detection, such as detecting fluid flow, tracking muscle movements, and measuring pulse rates. Finally, microstructure-enhanced sensors fabricated using the E-jet printing method present a novel approach for designing sensitized structures in capacitive pressure sensors.

Development of a degradation method for evaluation of edible oils using a contactless quartz crystal complex capacitance sensor

AbstractA method for evaluating the degradation of edible oils using a contactless quartz‐based capacitive detector is reported herein. Oils easily oxidize, resulting in loss of flavor and nutritional value. Therefore, it is necessary to determine oil degradation. We attempted to evaluate the degradation of edible oils by heat and light using this sensor. The results showed the degradation of heated and irradiated oil could be detected. This is due to the compound was formed during heating and irradiation.

Programmed multimaterial assembly by synergized 3D printing and freeform laser induction

In nature, structural and functional materials often form programmed three-dimensional (3D) assembly to perform daily functions, inspiring researchers to engineer multifunctional 3D structures. Despite much progress, a general method to fabricate and assemble a broad range of materials into functional 3D objects remains limited. Herein, to bridge the gap, we demonstrate a freeform multimaterial assembly process (FMAP) by integrating 3D printing (fused filament fabrication (FFF), direct ink writing (DIW)) with freeform laser induction (FLI). 3D printing performs the 3D structural material assembly, while FLI fabricates the functional materials in predesigned 3D space by synergistic, programmed control. This paper showcases the versatility of FMAP in spatially fabricating various types of functional materials (metals, semiconductors) within 3D structures for applications in crossbar circuits for LED display, a strain sensor for multifunctional springs and haptic manipulators, a UV sensor, a 3D electromagnet as a magnetic encoder, capacitive sensors for human machine interface, and an integrated microfluidic reactor with a built-in Joule heater for nanomaterial synthesis. This success underscores the potential of FMAP to redefine 3D printing and FLI for programmed multimaterial assembly.

Microsphere-Structured Protein Hydrogel Dielectrics for Capacitive Wearable Sensors.

The desire for healthy living has created a crucial need for portable flexible health-monitoring devices based on biomaterials. Toward this end, we report a microsphere-structured hydrogel that uses bovine serum albumin (BSA) as a dielectric layer for capacitive pressure sensors. We developed a theoretical model that describes how stacking dielectric layers of spheres affects the performance of capacitive sensors. We also prepared a prototype sensor featuring the unique microsphere structure to create capacitive sensors with high sensitivity (360.91 strain sensitivity), excellent cyclical stability, and a long service life (over 5000 stretching-compression cycles). Furthermore, the design of the hydrogel sensor allows for easy integration into fabrics to create devices such as smart wristbands, which can collect a diverse range of health data. Thus, BSA-hydrogel-based sensors not only provide safe wearable devices but also advance the performance of high-sensitivity capacitive sensors.

Fabrication of a Capacitive 3D Spacer Fabric Pressure Sensor with a Dielectric Constant Change for High Sensitivity.

Smart wearable sensors are increasingly integrated into everyday life, interfacing with the human body to enable real-time monitoring of biological signals. This study focuses on creating high-sensitivity capacitive-type sensors by impregnating polyester-based 3D spacer fabric with a Carbon Nanotube (CNT) dispersion. The unique properties of conductive particles lead to nonlinear variations in the dielectric constant when pressure is applied, consequently affecting the gauge factor. The results reveal that while the fabric without CNT particles had a gauge factor of 1.967, the inclusion of 0.04 wt% CNT increased it significantly to 5.210. As sensor sensitivity requirements vary according to the application, identifying the necessary CNT wt% is crucial. Artificial intelligence, particularly the Multilayer Perception (MLP) model, enables nonlinear regression analysis for this purpose. The MLP model created and validated in this research showed a high correlation coefficient of 0.99564 between the model predictions and actual target values, indicating its effectiveness and reliability.

Shape Sensing and Kinematic Control of a Cable-Driven Continuum Robot Based on Stretchable Capacitive Sensors.

A Cable-Driven Continuum Robot (CDCR) that consists of a set of identical Cable-Driven Continuum Joint Modules (CDCJMs) is proposed in this paper. The CDCJMs merely produce 2-DOF bending motions by controlling driving cable lengths. In each CDCJM, a pattern-based flexible backbone is employed as a passive compliant joint to generate 2-DOF bending deflections, which can be characterized by two joint variables, i.e., the bending direction angle and the bending angle. However, as the bending deflection is determined by not only the lengths of the driving cables but also the gravity and payload, it will be inaccurate to compute the two joint variables with its kinematic model. In this work, two stretchable capacitive sensors are employed to measure the bending shape of the flexible backbone so as to accurately determine the two joint variables. Compared with FBG-based and vision-based shape-sensing methods, the proposed method with stretchable capacitive sensors has the advantages of high sensitivity to the bending deflection of the backbone, ease of implementation, and cost effectiveness. The initial location of a stretchable sensor is generally defined by its two endpoint positions on the surface of the backbone without bending. A generic shape-sensing model, i.e., the relationship between the sensor reading and the two joint variables, is formulated based on the 2-DOF bending deflection of the backbone. To further improve the accuracy of the shape-sensing model, a calibration method is proposed to compensate for the location errors of stretchable sensors. Based on the calibrated shape-sensing model, a sliding-mode-based closed-loop control method is implemented for the CDCR. In order to verify the effectiveness of the proposed closed-loop control method, the trajectory tracking accuracy experiments of the CDCR are conducted based on a circle trajectory, in which the radius of the circle is 55mm. The average tracking errors of the CDCR measured by the Qualisys motion capture system under the open-loop and the closed-loop control are 49.23 and 8.40mm, respectively, which is reduced by 82.94%.

Capacitive PVC gel pressure sensors with various interlinked microstructural dielectric middle layers

Our sharp tactile sense is largely attributable to an undulating layer of microstructures between the epidermis and dermis, amplifying tactile signals. Taking inspiration from the biological template, we propose a design of flexible capacitive pressure sensors with various microstructural dielectric middle layers, fabricated using a casting-based approach. This is the first confirmed use of microstructural polyvinyl chloride (PVC) gel in dielectric layers and the first example of casting in the fabrication of capacitive sensors. Notably, on account of its flexibility, the sensor also addresses the problem of microstructure fracture and misalignment during sensor bending. These sensors can achieve a maximum sensitivity of 1.34 kPa−1 (under 10 kPa) with a fast response time (50 ms), good cyclic stability (> 1000 cycles), and a wide pressure sensing range (0 ∼ 290 kPa). When attached to a cup or balloon, this study reveals that these sensors can detect the weight and rigidity of the objects, demonstrating their potential in human-machine interaction, as well as in wearable applications.

Fabrication of Flexible Capacitive Pressure Sensors by Adjusting the Height of the Interdigital Electrode

Fabrication of Flexible Capacitive Pressure Sensors by Adjusting the Height of the Interdigital Electrode

A Capacitive Transparent Liquid Concentration Detecting System Based on LabVIEW

The accurate detection of transparent liquid concentrations holds widespread applications in production and daily life, making the design and development of novel detection systems crucial. In this study, a capacitance-based detection system for measuring the concentration of transparent liquids was successfully designed and implemented. The system utilized a cylindrical capacitive sensor and FDC2214 module for capacitance measurement, with data acquisition, processing, and display accomplished through an Arduino microcontroller and a LabVIEW program. The results of practical detections demonstrate that the developed system exhibits advantages such as non-contact operation, low cost, high accuracy, minimal sample requirement, and rapid detection speed. This system effectively meets the demands for transparent liquid concentration detection.