Flexible Capacitive Tactile Sensor Research Articles

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.

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.

Investigating capacitive flexible tactile sensor with a wide measuring range using PVDF and conductive sponge

Flexible tactile sensors have important application value in the field of artificial intelligence and internet of things. At present, it is a great challenge for tactile sensors to maintain high sensitivity and stability in a large pressure range. This article proposes a flexible capacitive tactile sensor with high sensitivity and large measuring range, which has a sandwich structure. The purpose of this paper is to determine the relationship between the thickness, surface microstructure, sensitivity, and sensing range of poly(vinylidene fluoride) (PVDF) films. The sensor uses conductive sponge with a microstructure surface and an ultra-thin PVDF film as the electrode and dielectric layer, respectively, and provides a comprehensive study in terms of sensor design, theoretical calculation, computer simulation and applications. The minimum detection limit of the sensor are tested by sound vibration, needle blowing, and human physiological signals. It has been shown that the thicker the PVDF film, the lower the sensitivity and the wider the sensing range. The proposed sensor can accurately identify physiological signals such as respiration, pulse and swallowing, and can perceive the softness, hardness and weight of the object as well as identifying the grasping posture. Moreover, the sensor has the characteristics of short response time, good recoverability and stability.

All-printed flexible capacitive array tactile force sensors with tunable sensitivity and low crosstalk for micro motion detection

All-printed flexible capacitive array tactile force sensors with tunable sensitivity and low crosstalk for micro motion detection

A Novel Sensor for Fruit Ripeness Estimation Using Lithography Free Approach

A flexible tactile sensor has the ability to sense and characterize the firmness and mechanical stiffness of the object. In this work, we demonstrate a low-cost, highly sensitive, flexible capacitive tactile sensor using a nanoneedle-patterned polydimethylsiloxane (PDMS) as a dielectric layer to detect the ripeness of the fruits. The nanoneedle-patterned PDMS was formed using an anodic oxidized porous alumina film as a mold. The developed tactile sensor exhibited high sensitivity due to the high deformity and elasticity of the nanoneedles on the PDMS layer. The higher sensitivity of 1.042–0.67 kPa−1 for a low-pressure regime below 0.2 kPa and the lower sensitivity of 0.35 kPa−1 for a pressure range above 0.6 kPa were demonstrated. This corresponds to a ~12% change in capacitance at 0.1-kPa pressure. Loading unloading tests for over 500 cycles were performed to confirm the absence of hysteresis. The mechanical elastic modulus of different tomato samples was tested using the tactile sensor and a universal test machine. The device could easily discriminate tomatoes of different stiffness. The tomato ripeness detection experiments demonstrate that the sensor can be used in robotic sensors, to estimate the qualitative ripeness of the fruits, during harvesting and transportation. This concept can be utilized in assessing ripeness levels of fruits like mangoes, kiwis, pears, avocados, sapodilla, and so on, after adequate recalibration of the sensor, leading to different sensing ranges.

High-sensitivity flexible tri-axial capacitive tactile sensor for object grab sensing

In this paper, a high sensitivity, flexible capacitive tri-axial tactile sensor is constructed by pyramid-shaped microarray dielectric layer. The tactile sensor consists of a staggered 2 × 2 capacitive sensor array. Through the measure and analysis of the three-dimensional force, which was applied on the sensor, it could decompose into normal and shear force components. The sensor exhibits high sensitivity due to the pyramidal-shaped microarray and low modulus of the dielectric layer. The sensitivity of the sensor in the x,y and z-axis are 56.47, 53.45 and 90.39 %/N in the ranges of 0 ∼ 0.8, 0 ∼ 0.8 and 0 ∼ 0.6 N, respectively. In addition, the sensor also exhibits fast response and recovery times (60 ms), and longtime cycling stability. The low average test error (about 10.4 %) of the tri-axial tactile sensor provides the technical basis for the application of robotics and wearable devices.

Carbon Black/PDMS Based Flexible Capacitive Tactile Sensor for Multi-Directional Force Sensing.

Flexible sensing tends to be widely exploited in the process of human–computer interactions of intelligent robots for its contact compliance and environmental adaptability. A novel flexible capacitive tactile sensor was proposed for multi-directional force sensing, which is based on carbon black/polydimethylsiloxane (PDMS) composite dielectric layer and upper and lower electrodes of carbon nanotubes/polydimethylsiloxane (CNTs/PDMS) composite layer. By changing the ratio of carbon black, the resolution of carbon black/PDMS composite layer increases at 4 wt%, and then decreases, which was explained according to the percolation theory of the conductive particles in the polymer matrix. Mathematical model of force and capacitance variance was established, which can be used to predict the value of the applied force. Then, the prototype with carbon black/PDMS composite dielectric layer was fabricated and characterized. SEM observation was conducted and a ratio was introduced in the composites material design. It was concluded that the resolution of carbon sensor can reach 0.1 N within 50 N in normal direction and 0.2 N in 0–10 N in tangential direction with good stability. Finally, the multi-directional force results were obtained. Compared with the individual directional force results, the output capacitance value of multi-directional force was lower, which indicated the amplitude decrease in capacity change in the normal and tangential direction. This might be caused by the deformation distribution in the normal and tangential direction under multi-directional force.

Recognition of Contact Force and Position of a Flexible Array-Less Capacitive Tactile Sensor

As an important medium of human-computer interaction, flexible tactile sensors have a vital influence on the intelligence and safety of a system by accurately identifying the contact position and force. For now, most of the existing flexible capacitive pressure sensors adopt an array structure, which still cannot meet the requirements including simple manufacturing, simple wiring, and low cost. This paper innovatively proposes a flexible array-less capacitive tactile sensor, a 30 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times30$ </tex-math></inline-formula> mm sensor prototype, consisting of flexible electrodes and a dielectric layer of a polydimethylsiloxane (PDMS) and multiwalled carbon nanotube (MWCNT) composite. Under the action of a contact force, the contact area is deformed, resulting in a capacitance change in the flexible sensor. First, Poisson’s equation is used to determine the relationship between the electric potential and position. Then, elastic contact mechanics is adopted to describe the relationship between the electric charges and force. Finally, the contact position and force are recognized by measuring the change in capacitance in real time, based on the classical principle of capacitance. Simulation and experimental results verified the effectiveness of the proposed recognition method, showing that the recognition resolution of contact position can reach <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$500\,\,\mu \text{m}\,\,\times 100\,\,\mu \text{m}$ </tex-math></inline-formula> , and the accuracy of contact force is 95.85%. Theoretically, the proposed flexible array-less sensor in this paper has infinite spatial resolution, and most importantly, it does not rely on complex manufacturing, redundant circuits, or sensor cell arrays. Therefore, it has broad application prospects in related fields such as electronic skin and wearable electronic devices.

Fully Printed Flexible Capacitive Array Tactile Force Sensors with Tunable Sensitivity and Low Crosstalk for Monitoring Human Motion and Sound Signals

Fully Printed Flexible Capacitive Array Tactile Force Sensors with Tunable Sensitivity and Low Crosstalk for Monitoring Human Motion and Sound Signals

Tailorable Capacitive Tactile Sensor Based on Stretchable and Dissolvable Porous Silver Nanowire/Polyvinyl Alcohol Nanocomposite Hydrogel for Wearable Human Motion Detection (Adv. Mater. Interfaces 20/2021)

Nanocomposite Hydrogel for Flexible Tactile Sensors In article number 2100998, Peng Wang, Chuizhou Meng, Changhong Liu, and co-workers develop a stretchable porous silver nanowire/polyvinyl alcohol nanocomposite hydrogel for flexible capacitive tactile sensors with enhanced sensing performance towards wearable human motion detection. It has the unique tailorable property that small sensors with desired shapes can be made by directly cutting from a large-area integrated sensor sheet.

A Review on 3D printed force sensors

A force sensor plays major role in robotics, wearable electronics and meteorological applications. Three dimensional (3D) printing is an exceptional technology and provides easy and economical fabrication process for the force sensors. Some salient features of 3D printing and development of force sensors in recent times have been represented in this paper. All possible forms of force sensors, for instance flexible, transparent, stretchable and highly sensitive can be developed using 3D printing technologies in an economical, quick and environmental-friendly approach. Over the years, fused deposition modeling (FDM) is gaining attention for the fabrication of force sensors. Also, due to advancements in materials and fabrication process, these sensors are being developed with enormous benefits. Some recent developments include flexible capacitive force sensor, wearable sensor and tactile sensor that are popular with 3D printing.

All-Solution-Processed, Oxidation-Resistant Copper Nanowire Networks for Optoelectronic Applications with Year-Long Stability.

Copper nanowires (Cu NWs) hold promise as they possess equivalent intrinsic electrical conductivity and optical transparency to silver nanowires (Ag NWs) and cost substantially less. However, poor resistance to oxidation is the historical challenge that has prevented the large-scale industrial utilization of Cu NWs. Here, we use benzotriazole (BTA), an organic corrosion inhibitor, to passivate Cu NW networks. The stability of BTA-passivated networks under various environmental conditions was monitored and compared to that of bare Cu NW control samples. BTA passivation greatly enhanced the stability of networks without deteriorating their optoelectronic performance. Moreover, to demonstrate their potential, BTA-passivated networks were successfully utilized in the fabrication of a flexible capacitive tactile sensor. This passivation strategy has a strong potential to pave the way for large-scale utilization of Cu NW networks in optoelectronic devices.

A Flexible Capacitive 3D Tactile Sensor With Cross-Shaped Capacitor Plate Pair and Composite Structure Dielectric

This paper presents a novel flexible capacitive 3D tactile sensor using cross-bar polydimethylsiloxane (PDMS) walls and micropillar arrays as the composite structure dielectric layer. The tactile sensor unit consists of a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\times 2$ </tex-math></inline-formula> capacitor array where electrode pairs are arranged in a cross-bar pattern to ensure a fixed overlap area for these capacitors. A top bump is introduced for the sensor to ensure the force is applied uniformly on the sensor. When a force is applied on the sensor, it changes the capacitances of the four capacitors, distinguishing the forces from different directions. The sensitivities of the sensor in the x-, y- and z- directions are 95.08%/N, 98.30%/N and 237.48%/N, in the ranges of 0-0.15 N, 0-0.15 N and 0-0.1 N respectively, much better than most of reported ones. The high sensitivities of the proposed sensor unit are attributed to the composite structure dielectric layer and the optimized Young’s modulus of PDMS. The flexible capacitive tactile sensor shows great potential for applications in robot technology.

A Highly Sensitive Flexible Capacitive Tactile Sensor with Sparse and High‐Aspect‐Ratio Microstructures

AbstractHighly sensitive flexible tactile sensors that can be fabricated in a low cost and efficient way are in great demand for intelligent soft robotics and friendly human–machine interaction. Herein, a highly sensitive flexible tactile sensor is developed by using bionic micropatterned polydimethylsiloxane (m‐PDMS) replicated from lotus leaf. The m‐PDMS substrate consists of high‐aspect‐ratio and low‐density microtowers, and is covered by ultrathin silver nanowires as a bottom electrode. The capacitive sensing device is constructed by sandwiching the bottom electrode, a colorless polyimides dielectric layer, and a top electrode, and exhibits a high sensitivity of ≈1.2 k Pa−1, a ultralow limit of detection &lt;0.8 Pa, and a fast response time of 36 ms. The finite‐elemental analysis indicates that the sparse and high‐aspect‐ratio microtowers are critical to achieve high sensitivity, low limit of detection, and fast response to external stimulus. The flexible tactile sensor also exhibits high robustness: it can be tested for at least 100 000 cycles without showing fatigue. More importantly, the flexible tactile sensors are potentially useful in intelligent soft robots, health monitoring, and motion detection. Besides, the fabrication strategy may offer a guideline to design other microstructures for improving the performance of flexible tactile sensors.

Flexible Tactile Sensor Array Mounted on the Curved Surface: Analytical Modeling and Experimental Validation

This paper presents an analytical model to study the sensing performance of the flexible capacitive tactile sensor array when mounted on a curved surface. To predict the deformation of the sensor unit, a cylindrical coordinate is constructed for the upper Polyethylene Terephthalate (PET) and truncated pyramids dielectric layer. The displacement functions model is developed and solved by using the Ritz method. Then, this model is utilized to investigate the capacitance change of the sensor unit and the model-calculated results are compared with the experiment data. Both model calculated and experiment measured results indicate that the capacitances of the sensor array are increased by about 30% when the sensor is mounted on the curved surface with a radius of curvature of 10 mm. Due to the bending effects of the curved surface, the sensitivities of the sensor array are decreased based on the model calculation and are confirmed by experimental validation. Thus, results demonstrate that the developed analytical model can accurately predict the sensing performance of the tactile sensor array on the curved surface and could be utilized for the real applications. [2016-0235]

All-transparent graphene-based flexible pressure sensor array

In this work, we propose and demonstrate a flexible capacitive tactile sensor array based on graphene served as electrodes. The sensor array consists of 3 × 3 units with 3 mm spatial resolution, similar to that of human skin. Each unit has three layers. The middle layer with microstructured PDMS served as an insulator is sandwiched by two perpendicular graphene-based electrodes. The size of each unit is 3 mm × 3 mm and the initial capacitance is about 0.2 pF. High sensitivities of 0.73 kPa[Formula: see text] between 0 and 1.2 kPa and 0.26 kPa[Formula: see text] between 1.2 and 2.5 kPa were achieved on the fabricated graphene pressure sensors. The proposed flexible pressure sensor array shows a great potential on the application of electric skin or 3D touch control.

Pressure Sensors: (Small 36/2016)

SmallVolume 12, Issue 36 p. 4912-4912 Inside Front CoverFree Access Pressure Sensors: (Small 36/2016) First published: 22 September 2016 https://doi.org/10.1002/smll.201670181AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Graphical Abstract On page 5042, T. Zhang and co-workers demonstrate a feasible bionic strategy to fabricate the flexible micro-patterned electrodes by using the microstructures of the lotus leaf as an effective soft mold. The novel flexible capacitive tactile sensor based on the micropatterned flexible polydimethylsiloxane (PDMS)/Au electrodes and polystyrene (PS) microspheres was developed with high sensitivity (0.815 kPa−1), fast response time (38 ms) and low detection limit (17.5 Pa), which presents the ability to “feel” not only the pressure caused by an ultra-light object, but also the bending and stretching force. Volume12, Issue36Special Issue: SINANO 10th AnniversarySeptember 28, 2016Pages 4912-4912 RelatedInformation

Flexible Capacitive Tactile Sensor Based on Micropatterned Dielectric Layer

Flexible tactile sensors are considered as an effective way to realize the sense of touch, which can perform the synchronized interactions with surrounding environment. Here, the utilization of bionic microstructures on natural lotus leaves is demonstrated to design and fabricate new-type of high-performance flexible capacitive tactile sensors. Taking advantage of unique surface micropattern of lotus leave as the template for electrodes and using polystyrene microspheres as the dielectric layer, the proposed devices present stable and high sensing performance, such as high sensitivity (0.815 kPa-1 ), wide dynamic response range (from 0 to 50 N), and fast response time (≈38 ms). In addition, the flexible capacitive sensor is not only applicable to pressure (touch of a single hair), but also to bending and stretching forces. The results indicate that the proposed capacitive tactile sensor is a promising candidate for the future applications in electronic skins, wearable robotics, and biomedical devices.

A flexible three-axial capacitive tactile sensor with multilayered dielectric for artificial skin applications

In this paper, a new flexible three-axial force sensor was designed and investigated, which was composed of four capacitors, and the mechanism was based on the capacitance change induced by an applying three-axial force. For the configuration of the electrodes, four sensing electrodes and a public electrode were in the same plane, which was based on fringe effect theory. Different from the traditional dielectric layer with single material, this multilayered dielectric consisted of both the air gap and polydimethylsiloxane. The structure of the multilayered dielectric changed under the external/applied force, leading to variation of dielectric constant ź, which caused the capacitance change. Measurement results showed that the full-scale range of detectable force was around 0---10 N for all three axes. The average sensitivities of the force sensor units were 0.0095, 0.0053, and 0.0060 Nź1 for the normal, X-axis, and Y-axis shear forces, and more test proved its high potential for application in skin-like sensing field.