Capacitive Tactile Sensor Research Articles

Design of a Capacitive Tactile Sensor Array System for Human-Computer Interaction.

This paper introduces a novel capacitive sensor array designed for tactile perception applications. Utilizing an all-in-one inkjet deposition printing process, the sensor array exhibited exceptional flexibility and accuracy. With a resolution of up to 32.7 dpi, the sensor array was capable of capturing the fine details of touch inputs, making it suitable for applications requiring high spatial resolution. The design incorporates two multiplexers to achieve a scanning rate of 100 Hz, ensuring the rapid and responsive data acquisition that is essential for real-time feedback in interactive applications, such as gesture recognition and haptic interfaces. To evaluate the performance of the capacitive sensor array, an experiment that involved handwritten number recognition was conducted. The results demonstrated that the sensor accurately captured fingertip inputs with a high precision. When combined with an Auxiliary Classifier Generative Adversarial Network (ACGAN) algorithm, the sensor system achieved a recognition accuracy of 98% for various handwritten numbers from "0" to "9". These results show the potential of the capacitive sensor array for advanced human-computer interaction applications.

Screen-Printed Capacitive Tactile Sensor for Monitoring Tool–Tissue Interactions and Grasping Performances of a Surgical Magnetic Microgripper

Screen-Printed Capacitive Tactile Sensor for Monitoring Tool–Tissue Interactions and Grasping Performances of a Surgical Magnetic Microgripper

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.

Recent Advances in Tactile Sensory Systems: Mechanisms, Fabrication, and Applications.

Flexible electronics is a cutting-edge field that has paved the way for artificial tactile systems that mimic biological functions of sensing mechanical stimuli. These systems have an immense potential to enhance human-machine interactions (HMIs). However, tactile sensing still faces formidable challenges in delivering precise and nuanced feedback, such as achieving a high sensitivity to emulate human touch, coping with environmental variability, and devising algorithms that can effectively interpret tactile data for meaningful interactions in diverse contexts. In this review, we summarize the recent advances of tactile sensory systems, such as piezoresistive, capacitive, piezoelectric, and triboelectric tactile sensors. We also review the state-of-the-art fabrication techniques for artificial tactile sensors. Next, we focus on the potential applications of HMIs, such as intelligent robotics, wearable devices, prosthetics, and medical healthcare. Finally, we conclude with the challenges and future development trends of tactile sensors.

Simple fabrication of high-sensitivity capacitive tactile sensor based on a polydimethylsiloxane dielectric layer using a biomimetic gray kangaroo leg structure

Design of the capacitive tactile sensor with ultra-high sensitivity and fast response/recovery times is critical to the advancement of wearable devices. However, achieving both fast response/recovery time and ultra-high sensitivity simultaneously is a huge challenge. In this work a simple and easy-to-prepare flexible capacitive tactile sensor is presented, using a biomimetic gray kangaroo structured dielectric layer of polydimethylsiloxane. By using finite element analysis to study the influences of various structures, the test result of the experimentally optimized tactile sensor showed ultra-high sensitivity (1.202 kPa−1), outstanding response and recovery time (60/85 ms), wide pressure range (0–220 kPa), and excellent stability. Finally, the tactile sensors are tested for practical applications, including robot tactile, human motion monitoring, and Morse code detection.

Sensitive, Robust, Wide-Range, and High-Consistency Capacitive Tactile Sensors with Ordered Porous Dielectric Microstructures.

Flexible capacitive tactile sensors show great promise in personalized healthcare monitoring and human-machine interfaces, but their practical application is normally hindered because they rarely possess the required comprehensive performance, that is, high pressure sensitivity and fast response within a broad pressure range, high structure robustness, performance consistency, etc. This paper aims to engineer flexible capacitive pressure sensors with highly ordered porous dielectric microstructures and a 3D-printing-based fully solution-processable fabrication process. The proposed dielectric layer with uniformly distributed interior microporous can not only increase its compressibility and dynamic response within an extended pressure range but also enlarge its contact area with electrodes, contributing to a simultaneous improvement in the sensitivity, response speed, detection range, and structure robustness. Meanwhile, owing to its superior abilities in complex structure manufacturing and dimension controlling, the proposed 3D-printing-based fabrication process enables the consistent fabrication of the porous microstructure and thus guarantees device consistency. As a result, the prepared pressure sensors exhibit a high sensitivity of 0.21 kPa-1, fast response and relaxation times of 112 and 152 ms, an interface bonding strength of more than 455.2 kPa, and excellent performance consistency (≤5.47% deviation among different batches of sensors) and tunability. Encouraged by this, the pressure sensor is further integrated with a wireless readout circuit and realizes wireless wearable monitoring of various biosignals (pulse waves and heart rate) and body movements (from slight finger touch to large knee bending). Finally, the influence law of the feature parameters of the porous microstructure on device performance is established by the finite element method, paving the way for sensor optimization. This study motivates the development of flexible capacitive pressure sensors toward practical application.

River valley-inspired, high-sensitivity, and rapid-response capacitive three-dimensional force tactile sensor based on U-shaped groove structure

High-performance three-dimensional force (3D-force) tactile sensors with the capability of distinguishing normal and tangential forces in sync play a vital role in emerging wearable devices and smart electronics. And there is an urgent need for 3D-force tactile sensors with fast response and high flexibility. Herein, we design a capacitive 3D-force tactile sensors inspired by the U-shaped river valley surface morphology, which has satisfactory performance in terms of rapid response/recovery time (∼36 ms/∼ 36 ms), low hysteresis (4.2%), and high sensitivity (0.487 N−1). A theoretical model of general value for congener sensors is also proposed, obtaining a higher sensitivity through optimizing parameters. To verify the application potential of our device in actual scenarios, the robustness testing and gripping gamepad application were carried out. And it can recognize different motions in humans. Furthermore, principal component analysis is also conducted to demonstrate the distinct classification of different motions. Therefore, our work is eligible for the applications in wearable electronics, human–machine interaction, and soft intelligent robots.

Fabrication and Investigation of Deformable Rubber-Carbon Nanotube-Glue Gel-Based Impedimetric and Capacitive Tactile Sensors for Pressure and Displacement Measurements.

Carbon nanotube-glue composite gel-based surface-type elastic sensors with a cylindrical shape deformable (flexible) metallic body were fabricated for tactile pressure and compressive displacement sensing. The fabrication of the sensors was performed using the rubbing-in technique. The effect of the pressure and the compressive displacement on the capacitance and the impedance of the sensors were investigated at various frequencies (in the range of 1 kHz to 200 kHz). It was found that under the effect of pressure from 0 to 9 g/cm2, the capacitance increased by 1.86 and 1.78 times, while the impedance decreased by 1.84 and 1.71 times at the frequencies of 1 kHz to 200 kHz, respectively. The effect of displacement on the impedance and the capacitance of the device was also investigated at various frequencies from 1 kHz to 200 kHz. The results showed that under the effect of compressive displacement up to 25 µm, the impedance of the sensors decreased on average by 1.19 times, while the capacitance increased by 1.09 times, accordingly. The frequency response of the displacement sensor showed that it matched with the low-pass filter. The obtained results are explained based on changes in the shape and geometrical parameters of the cylindrical-shaped conductive body. These results have also been explained on the basis of the distance between the conductive plates of the capacitive sensors during compression, which takes place under the effect of applied pressure or displacement. Moreover, the design of the sensors is simple and easy to fabricate, and their use is also earthy. The fabricated sensors have great potential for commercialization.

A Nonarray Soft Capacitive Tactile Sensor With Simultaneous Contact Force and Location Measurement for Intelligent Robotic Grippers

A Nonarray Soft Capacitive Tactile Sensor With Simultaneous Contact Force and Location Measurement for Intelligent Robotic Grippers

Stretchable Capacitive Tactile Sensor Array for Accurate Distributed Pressure Recognition

Stretchable Capacitive Tactile Sensor Array for Accurate Distributed Pressure Recognition

An ultra-soft conductive elastomer for multifunctional tactile sensors with high range and sensitivity.

Flexible tactile sensors have become important as essential tools for facilitating human and object interactions. However, the materials utilized for the electrodes of capacitive tactile sensors often cannot simultaneously exhibit high conductivity, low modulus, and strong adhesiveness. This limitation restricts their application on flexible interfaces and results in device failure due to mechanical mismatch. Herein, we report an ultra-low modulus, highly conductive, and adhesive elastomer and utilize it to fabricate a microstructure-coupled multifunctional flexible tactile sensor. We prepare a supramolecular conductive composite film (SCCF) as the electrode of the tactile sensor using a supramolecular deep eutectic solvent, polyvinyl alcohol (PVA) solution, poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), and MXene suspension. We employ a polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) film containing 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM:TFSI) as the dielectric layer to fabricate capacitive sensors with an electrical double layer structure. Furthermore, we enhance the performance of the device by incorporating coupled pyramid and dome microstructures, which endow the sensor with multi-directional force detection. Our SCCF exhibits extremely high conductivity (reaching 710 S cm-1), ultra-low modulus (0.8 MPa), and excellent interface adhesion strength (>120 J m-2). Additionally, due to the outstanding conductivity and unique structure of the SCCF, it possesses remarkable electromagnetic shielding ability (>50 dB). Moreover, our device demonstrates a high sensitivity of up to 1756 kPa-1 and a wide working range reaching 400 kPa, combining these attributes with the requirements of an ultra-soft human-machine interface to ensure optimal contact between the sensor and interface materials. This innovative and flexible tactile sensor holds great promise and potential for addressing various and complex demands of human-machine interaction.

Skin‐Inspired Capacitive Flexible Tactile Sensor with an Asymmetric Structure for Detecting Directional Shear Forces

AbstractFlexible pressure sensors based on micro‐/nanostructures can be integrated into robots to achieve sensitive tactile perception. However, conventional symmetric structures, such as pyramids or hemispheres, can sense only the magnitude of a force and not its direction. In this study, a capacitive flexible tactile sensor inspired by skin structures and based on an asymmetric microhair structure array to perceive directional shear force is designed. Asymmetric microhair structures are obtained by two‐photon polymerization (TPP) and replication. Owing to the features of asymmetric microhair structures, different shear force directions result in different deformations. The designed device can determine the directions of both static and dynamic shear forces. Additionally, it exhibits large response scales ranging from 30 Pa to 300 kPa and maintains high stability even after 5000 cycles; the final relative capacitive change (ΔC/C0) is <2.5%. This flexible tactile sensor has the potential to improve the perception and manipulation ability of dexterous hands and enhance the intelligence of robots.

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.

Bimodal capacitive tactile sensor assisted by shield effect of triboelectric nanogenerator

Tactile sensors are increasingly important in advancing future robotic technologies, human-machine interfaces, health monitoring devices, and artificial receptors. However, the output signals of layered capacitive tactile sensors are often susceptible to interference from adjacent touch-induced movements caused by electrostatic effects. In contrast, tactile sensors based on triboelectric nanogenerators (TENG) offer enhanced sensitivity to pressure stimuli and object recognition capabilities. Here, we developed a bimodal capacitive tactile sensor that incorporates TENG layers, resulting in a sensor design that closely mimics the mechanical receptors found in humans. The bimodal tactile sensors consist of seven stacked layers, exhibiting reliable tactile sensing abilities while being shielded by the top TENG layers. Nevertheless, The TENG layers acts as a pioneer during the touching to recognize the adjacent objects. Furthermore, we illustrate the capabilities of such sensors by utilizing them in a self-developed two-tier authentication system accepting designative pressure pattern and prescriptive individual as passwords. Such form of application no only suggests immense potential of this sensor but also proves the huge function of bimodal sensor for internet of things (IoT) interaction with human.

Highly stable capacitive tactile sensors with tunable sensitivity facilitated by electrostatic interaction of layered double hydroxide, MXene, and Ag NWs

Highly stable capacitive tactile sensors with tunable sensitivity facilitated by electrostatic interaction of layered double hydroxide, MXene, and Ag NWs

Wearable Capacitive Tactile Sensor Based on Porous Dielectric Composite of Polyurethane and Silver Nanowire.

In recent years, the implementation of wearable and biocompatible tactile sensing elements with sufficient response into healthcare, medical detection, and electronic skin/amputee prosthetics has been an intriguing but challenging quest. Here, we propose a flexible all-polyurethane capacitive tactile sensor that utilizes a salt crystal-templated porous elastomeric framework filling with silver nanowire as the composite dielectric material, sandwiched by a set of polyurethane films covering silver nanowire networks as electrodes. With the aids of these cubic air pores and conducting nanowires, the fabricated capacitive tactile sensor provides pronounced enhancement of both sensor compressibility and effective relative dielectric permittivity across a broad pressure regime (from a few Pa to tens of thousands of Pa). The fabricated silver nanowire-porous polyurethane sensor presents a sensitivity improvement of up to 4-60 times as compared to a flat polyurethane device. An ultrasmall external stimulus as light as 3 mg, equivalent to an applied pressure of ∼0.3 Pa, can also be clearly recognized. Our all-polyurethane capacitive tactile sensor based on a porous dielectric framework hybrid with conducting nanowire reveals versatile potential applications in physiological activity detection, arterial pulse monitoring, and spatial pressure distribution, paving the way for wearable electronics and artificial skin.

Mathematical Model and Experimental Characterization of Vertically Stacked Capacitive Tactile Sensors

Mathematical Model and Experimental Characterization of Vertically Stacked Capacitive Tactile Sensors

Cone‐Shaped Electrodes for Capacitive Tactile Sensors with High Sensitivity and Broad Linearity Range

Flexible tactile sensors with high sensitivity typically suffer from a dramatically reduces pressure resolution with increasing pressure, resulting in narrow linear ranges and limited application scenarios. Herein, a capacitive tactile sensor based on cone‐shaped electrodes (CSE) that can maintain high sensitivity over a broad linearity range is proposed. The linear response comes from the novel sensing mechanism based on the change in the facing electrode area and the rational design of the conical architecture. Finite element analysis (FEA) confirms that the interfacial contact area between the elastic electrodes and the dielectric layer can respond linearly to pressure over a broad spectrum. Based on this strategy, the fabricated sensors perform a high sensitivity (0.23 kPa−1) and superior linearity (R2 = 0.999) across a wide pressure range of up to 130 kPa. The sensors demonstrate several key features, such as good repeatability, fast response speed, low detection limit, and high durability. These attributes enable the successful use of the sensors for monitoring artery pulses and providing weighting capabilities to robots, showing promising potential for applications in daily health monitoring and human‐machine interaction.

Elderly Fall Detection Based on GCN-LSTM Multi-Task Learning Using Nursing Aids Integrated with Multi-Array Flexible Tactile Sensors.

Due to the frailty of elderly individuals' physical condition, falling can lead to severe bodily injuries. Effective fall detection can significantly reduce the occurrence of such incidents. However, current fall detection methods heavily rely on visual and multi-sensor devices, which incur higher costs and complex wearable designs, limiting their wide-ranging applicability. In this paper, we propose a fall detection method based on nursing aids integrated with multi-array flexible tactile sensors. We design a kind of multi-array capacitive tactile sensor and arrange the distribution of tactile sensors on the foot based on plantar force analysis and measure tactile sequences from the sole of the foot to develop a dataset. Then we construct a fall detection model based on a graph convolution neural network and long-short term memory network (GCN-LSTM), where the GCN module and LSTM module separately extract spatial and temporal features from the tactile sequences, achieving detection on tactile data of foot and walking states for specific time series in the future. Experiments are carried out with the fall detection model, the Mean Squared Error (MSE) of the predicted tactile data of the foot at the next time step is 0.0716, with the fall detection accuracy of 96.36%. What is more, the model can achieve fall detection on 5-time steps with 0.2-s intervals in the future with high confidence results. It exhibits outstanding performance, surpassing other baseline algorithms. Besides, we conduct experiments on different ground types and ground morphologies for fall detection, and the model showcases robust generalization capabilities.

Laser‐Induced Hierarchical Microcone Arrays for Flexible Tactile Sensors with High Sensitivity and Ultrabroad Detection Range

Flexible tactile sensors have received widespread attention in many potential applications such as intelligence robots, the Internet of Things, and various wearable devices. However, most structure‐enhanced devices are in single‐patterns with limited improvement of sensitivity and working range. Herein, a double‐layered capacitive tactile sensor (DLCTS) with hierarchical microcone arrays, which consists of carbon nanotubes (CNTs) and polydimethylsiloxane (PDMS) is reported. Relying on its intrinsic hierarchical framework and optimized CNTs/PDMS ratios, the DLCTS exhibits an ultrabroad working range of 0–1400 kPa and a high sensitivity of 0.082 kPa−1. Moreover, this sensor shows favorable sensing performance with excellent durability (over 5500 cycles) and a fast response time (≈40 ms). Diverse powerful applications are demonstrated, including active monitoring of human elbow/knee flexion, respiratory state, walking mode, and convenient Morse code communication. It is envisioned that this sensor should be widely used in potential scenarios such as intelligent wearable devices and medical monitoring.