Flexible Tactile Sensor Research Articles

A Flexible Tactile Sensor With Dual-Interlocked Structure for Broad Range Force Sensing and Gaming Applications

This article presents a novel flexible tactile sensor by using skin-like dual-interlocked structure to improve both the sensitivity and force detection range. The fully elastomeric graphene/carbon nanotube/silicon rubber nanocomposites are synthesized and used as a sensing material. The sandwich skin-like dual-interlocked structure enables the tactile sensor to easily transform external mechanical stimuli into tensile strain of the sensing material. A low-cost fabrication method and procedure is proposed to fabricate the flexible tactile sensor. The fabricated tactile sensor has <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3\times3$ </tex-math></inline-formula> (= 9) sensing units and features extremely high flexibility. Experimental tests showed that the developed tactile sensor has a linear and high sensitivity of 0.767 N <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> for a wide range of force (0–25 N) characterization. The tactile sensor is also tested with good dynamic response, good repeatability, and long serving life. Then, the flexible tactile sensor was worn on human foot to monitor body standing posture and large force sensing and further served as an extended interface for computer games’ application. The results indicated that our developed flexible tactile sensor would have a great potential in human–machine interface of wearable sensors for augmented reality, intelligent robotics, and prosthetics.

A brief review of miniature flexible and soft tactile sensors for interventional catheter applications

Interventional surgery has the advantages of small skin incisions, minimal blood loss, low postoperative infection and short recovery times, and thus has gradually become the preferred surgical approach over traditional open surgeries. Even though significant achievements have been made towards clinical applications, limitations still exist, among which the loss of the natural tactile perception of surgeons due to their indirect touch along the long catheter to the intervening human tissue is the crucial one. In recent years, researchers have dedicated great efforts to the development of advanced medical catheters with smart tactile perception ability, with considerable progress having been made. In this regard, we review the most recent developments of state-of-the-art miniature flexible and soft tactile sensors that are able to be integrated in the tip or on the side wall of medical catheters. We particularly focus on the sensing mechanisms, design requirements, device configuration and sensing performance of different types of sensors, as well as their application demonstration in synthetic anatomical models and in vivo animal experiments. After reviewing the representative research work, the challenges that still exist are summarized and the prospects toward future development are proposed.

Estimation of position of an object by contact motion using a flexible tactile sensor

Estimation of position of an object by contact motion using a flexible tactile sensor

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

High-Performance Flexible Self-Powered Triboelectric Tactile Sensor Based on Chemically Modified Micropatterned Pdms Film

High-Performance Flexible Self-Powered Triboelectric Tactile Sensor Based on Chemically Modified Micropatterned Pdms Film

Capacitive Flexible Three-Axis Force Tactile Sensor Based on Porous Composite Dielectric Layer for Dexterous Robotic Manipulation

Capacitive Flexible Three-Axis Force Tactile Sensor Based on Porous Composite Dielectric Layer for Dexterous Robotic Manipulation

Fabrication of Flexible Tactile Sensor with Changeable Sensitivity

Fabrication of Flexible Tactile Sensor with Changeable Sensitivity

Bioinspired design of highly sensitive flexible tactile sensors for wearable healthcare monitoring

The design of microscale architectures integrated with low-dimensional nanomaterials for tactile sensors has attracted considerable attention owing to their high performance for various potential applications, especially in the field of healthcare monitoring. However, there still remains a critical challenge to achieve high sensitivity in response to different magnitude external pressure. Herein, we introduce a high performance capacitive tactile sensor based on Silver nanowires coated biomimetic hierarchical array architecture, which consists of mini-domes by the way of vacuum adsorption from through-hole arrays and micro-cones by duplicating Calathea zebrina leaf, respectively. This hybrid graded microstructure as electrode exhibits remarkably improved sensitivity and stimulus responding range when compared with the other monotonous counterparts. Moreover, an optimized ionic gel film with remarkable interfacial capacitance is sandwiched by microstructured electrodes as the dielectric layer, further boosting the performance of the tactile sensor. As a result, the obtained sensor demonstrates a board detection range from 24 Pa to 90 kPa with a maximum sensitivity of 37.8 kPa−1, and a fast response time (<78 ms). These superior performances of our tactile sensor lay a foundation for various applications in healthcare monitoring. It can not only sense and distinguish subtle arterial pulse signals even under different ages, genders and states of motion but also monitor physiological activity with large pressure as well, such as breathing, plantar pressure, and so on. We envision this bionic tactile sensor holds great potential in wearable electronics.

Recent Development of Flexible Tactile Sensors and Their Applications.

With the rapid development of society in recent decades, the wearable sensor has attracted attention for motion-based health care and artificial applications. However, there are still many limitations to applying them in real life, particularly the inconvenience that comes from their large size and non-flexible systems. To solve these problems, flexible small-sized sensors that use body motion as a stimulus are studied to directly collect more accurate and diverse signals. In particular, tactile sensors are applied directly on the skin and provide input signals of motion change for the flexible reading device. This review provides information about different types of tactile sensors and their working mechanisms that are piezoresistive, piezocapacitive, piezoelectric, and triboelectric. Moreover, this review presents not only the applications of the tactile sensor in motion sensing and health care monitoring, but also their contributions in the field of artificial intelligence in recent years. Other applications, such as human behavior studies, are also suggested.

A flexible triboelectric tactile sensor for simultaneous material and texture recognition

Electronic skin with tactile perception enables intelligent robots and prostheses to perform dexterous manipulation and natural interaction with the human and surroundings. However, using single tactile sensing mechanism to simultaneously percept geometry features and materials properties remains a challenge due to the bottleneck of signal decoupling. Herein, we report the MTSensing system – a wireless and fully-integrated tactile sensing system that can simultaneously recognize materials and textures based on a single flexible triboelectric sensor. The proposed triboelectric sensor converts touch into electrical signals and meanwhile, the signal processing pipeline decouples the signals into macro/micro features and feeds them into the corresponding deep learning models, which simultaneously predict the materials and textures of the contacted objects with the accuracies of 99.07% and 99.32%, respectively. The systematic integration of MTSensing hopes to pave the way for deploying low-cost and scalable electronic skin with multi-functional perceptions.

A Biomimetic Drosera Capensis with Adaptive Decision‐Predation Behavior Based on Multifunctional Sensing and Fast Actuating Capability

AbstractThe sophistication, adaptability, and complexity of biological systems have provided enormous inspiration and have been a continuous source of numerous innovations. Soft living organisms like drosera capensis have amazing predatory behavior that can capture prey of ideal size, enabling them to interact with environmental stimuli efficiently. Mimicking such natural intelligence in artificial systems with systematical functions of multiple information perception, neuronal transmission, and adaptive motility remains a grand challenge. Here, a biomimetic drosera capensis is reported that is capable of multifunctional self‐sensing, automatic regulation, and adaptive actuation in response to diverse stimuli with intelligent predation capability in an entirely closed‐loop fashion. The functional system heterogeneously integrates the thermal‐responsive soft actuator as the muscle‐like motor and flexible tactile, strain, and piezoelectric multimodal sensors as somatosensory receptors. With the synergistic effect of multifunctional sensing and fast actuating schemes, the artificial drosera capensis deconvolutes multiple characteristics of the catching process (e.g., strain rate, magnitude, and direction) and thus holds impressive predatory behavior for ideal‐sized prey. This electronically innervated artificial drosera capensis with multimodal sensing and self‐regulated actuating capability through the closed‐loop control of sensing and actuating system paves the way for the development of adaptive soft robots.

Highly Sensitive Flexible Tactile Sensors in Wide Sensing Range Enabled by Hierarchical Topography of Biaxially Strained and Capillary‐Densified Carbon Nanotube Bundles (Small 50/2021)

Flexible Tactile Sensors In article number 2105334, Jongbaeg Kim and co-workers present a flexible tactile sensor based on the carbon nanotube-wrinkled structure. The strategies to improve the sensing performance are provided. In this cover image, the components of the tactile sensor, which is a hierarchical structure with aggregated carbon nanotube bundles, are expressed.

Wearable human-machine interaction device integrated by all-textile-based tactile sensors array via facile cross-stitch

Novel HMI devices have shown great potential application in somatosensory games, intelligent robot systems and artificial intelligence, attracting lots of researcher interests. However, the lack of suitable flexible sensors for signal input, reasonable signal processing and feedback schemes extremely restricts practical applications of the novel HMI devices. In this paper, a flexible wearable tactile sensors array based on textiles was prepared. A wearable HMI device was fabricated by setting finger tapings and sound as signal input as well as feedback. The textile based-sensor exhibits a high sensitivity of 0.84 kPa−1, fast response time less than 4 ms, outstanding cycle stability and washability after optimizing sensors configurations and woven structures. Collecting as well as processing of finger tapping data, and sound feedback were realized based on ESP32-DevKitC circuit, Bluetooth module and Android APP. A strategy of predicting signal trend before the maximum tapping value was proposed to reduce the response time of wearable HMI device. In addition, we also made a series of adjustments to the wearable HMI device feedback referring to the characteristics of electronic drums, which fully proved the huge application potential of this wearable HMI device.

Multifunctional Ternary Hybrid Hydrogel Sensor Prepared via the Synergistic Stabilization Effect.

Since highly stretchable hydrogels have demonstrated their promising applications in flexible tactile sensors and wearable devices, the current challenge has been imposed on stretchable and multifunctional electronics. Here, we report a multifunctional sensor composed of a liquid metal (LM) nanodroplet-adhered self-assembled polymeric network, anionic carboxymethylcellulose (CMC), and cationic polyacrylamide (PAAm). The synergistic effect, zeta potential reduction, by CMC and macromolecules enveloped by LM contributes to the stabilization of the ternary system during preparation and, thus, the homogenization of the products. By engineering and optimizing the ternary hybrid hydrogels, excellent extensibility (tensile strain near 300%), readily reversible hysteresis loops, and accessible deformability (low modulus of 104 Pa) are afforded. The fabricated sensor exhibits a high tensile strain gauge factor of around 0.7 and a high compressive stress sensitivity of up to 0.12 kPa-1, a fast response time below 125 ms, and a high stability and precision in usage. In a series of practical scenarios, the assembled sensor displays distinguished abilities to monitor bodily motions, record electrocardiograms, authenticate handwriting, discern temperature, and infer materials, making them highly promising for multifunctional intelligent soft sensing.

3D Printed, Solid-State Conductive Ionoelastomer as a Generic Building Block for Tactile Applications.

Shaping soft and conductive materials into preferential architectures via 3D printing is highly attractive for numerous applications ranging from tactile devices to bioelectronics. A landmark type of soft and conductive materials is hydrogels/ionogels. However, 3D-printed hydrogels/ionogels still suffer from a fundamental bottleneck: limited stability in their electrical-mechanical properties caused by the evaporation and leakage of liquid within hydrogels/ionogels. Although photocurable liquid-free ion-conducting elastomers can circumvent these limitations, the associated photocurable process is cumbersome and hence the printing quality is relatively poor. Herein, a fast photocurable, solid-state conductive ionoelastomer (SCIE) is developed that enables high-resolution 3D printing of arbitrary architectures. The printed building blocks possess many promising features over the conventional ion-conducting materials, including high resolution architectures (even ≈50µm overhanging lattices), good Young's modulus (up to ≈6.2MPa), and stretchability (fracture strain of ≈292%), excellent conductivity tolerance in a wide range of temperatures (from -30 to 80°C), as well as fine elasticity and antifatigue ability even after 10000 loading-unloading cycles. It is further demonstrated that the printed building blocks can be programmed into 3D flexible tactile sensors such as gyroid-based piezoresistive sensor and gap-based capacitive sensor, both of which exhibit several times higher in sensitivity than their bulky counterparts.

PVDF-bismuth titanate based self-powered flexible tactile sensor for biomechanical applications

Flexible piezoelectric tactile sensors have attracted tremendous attention towards bio-healthcare monitoring and wearable applications. For piezoelectric tactile sensors, a careful selection of materials is important to maximize the piezoelectric effect and improve the measurement sensitivity. In this work, we synthesized a bismuth titanate, Bi4Ti3O12 (BiTO), and polyvinylidene fluoride (PVDF) composite thin film-based self-powered tactile sensor. The electrical output was measured by alteration of the BiTO composition in the PVDF and the composite film thickness. The PENG device based on PVDF-10 wt% BiTO and 40 μm thickness deliver the highest voltage output of 41 V and maximum power density of 4.3 mW/m2. The sensor was further attached to the fingers or vocal cords demonstrating the detection of the different human motions without an external power source. These results pave the way towards the development of portable self-powered biomechanical sensors for rehabilitation, health care monitoring, and human–machine interface.

Highly Sensitive Flexible Tactile Sensors in Wide Sensing Range Enabled by Hierarchical Topography of Biaxially Strained and Capillary-Densified Carbon Nanotube Bundles.

Flexible tactile sensors with high sensitivity have received considerable attention for their use in wearable electronics, human-machine interfaces, and health-monitoring devices. Although various micro/nanostructured materials are introduced for high-performance tactile sensors, simultaneously obtaining high sensitivity and a wide sensing range remains challenging. Here, a resistive tactile sensor is presented based on the hierarchical topography of carbon nanotubes (CNTs) prepared by a low-cost and straightforward manufacturing process. The 3D hierarchical structure of the CNTs over large areas is formed by transferring vertically aligned CNT bundles to a prestrained elastomer substrate and subsequently densifying them through capillary forming, providing a monotonic increase in the contact area as applied pressure. The deformable and hierarchical structure of CNTs allows the sensor to exhibit a wide sensing range (0-100kPa), high sensitivity (141.72kPa-1 ), and low detection limit (10Pa). Additionally, the capillary-formed CNT structure results in increased durability of the sensor over repeated pressures. Based on these advantages, meaningful applications of tactile sensors, such as object recognition gloves and multidirectional force perceptions, are successfully realized. Given the scalable fabrication method, 3D hierarchically structured CNTs provide an essential step toward next-generation wearable devices.

Multifunctional Soft Robotic Finger Based on a Nanoscale Flexible Temperature-Pressure Tactile Sensor for Material Recognition.

Robotic hands with tactile perception can perform more advanced and safer operations, such as material recognition. Nanowires with high sensitivity, fast response, and low power consumption are suitable for multifunctional flexible tactile sensors to provide the tactile perception of robotic hands. In this work, we designed a multifunctional soft robotic finger with a built-in nanoscale temperature-pressure tactile sensor for material recognition. The flexible multifunctional tactile sensor integrates a nanowire-based temperature sensor and a conductive sponge pressure sensor to measure the temperature change rate and contact pressure simultaneously. The developed nanoscale temperature and conductive sponge pressure sensor can reach a high sensitivity of 1.196%/°C and 13.29%/kPa, respectively. With this multifunctional tactile sensor, the soft finger can quickly recognize four metals within three contact pressure ranges and 13 materials within a high contact pressure range. By combining tactile information and artificial neural networks, the soft finger can recognize the materials precisely with a high recognition accuracy of 92.7 and 95.9%, respectively. This work proves the application potential of the multifunctional soft robot finger in material recognition.

Ultrathin Superhydrophobic Flexible Tactile Sensors for Normal and Shear Force Discrimination.

Flexible tactile sensors, with the ability to sense and even discriminate between different mechanical stimuli, can enable real-time and precise monitoring of dexterous and complex robotic motions. However, making them ultrathin and superhydrophobic for practical applications is still a great challenge. Here, superhydrophobic flexible tactile sensors with hierarchical micro- and nanostructures, that is, warped graphene nanosheets adhered to micron-height wrinkled surfaces, were constructed using ultrathin medical tape (40 μm) and graphene. The tactile sensor enables the discrimination of normal and shear forces and senses sliding friction and airflow. Moreover, the tactile sensor exhibits high sensitivity to normal and shear forces, extremely low detection limits (15 Pa for normal forces and 6.4 mN for shear forces), and cyclic robustness. Based on the abovementioned characteristics, the tactile sensor enables real-time and accurate monitoring of the robotic arm's motions, such as moving, gripping, and lifting, during the process of picking up objects. The superhydrophobicity even allows the sensor to monitor the motions of the robotic arm underwater in real time. Our tactile sensors have potential applications in the fields of intelligent robotics and smart prosthetics.

MXene-enhanced β-phase crystallization in ferroelectric porous composites for highly-sensitive dynamic force sensors

Piezoelectric polyvinylidene fluoride (PVDF) has been widely utilized in flexible and self-powered tactile sensors, which require high ferroelectricity of polar phase PVDF. Herein, we demonstrate self-powered piezoelectric e-skins with high sensitivity and broad sensing range based on 3D porous structures of MXene (Ti 3 C 2 T x )/PVDF. MXene was used as a nucleation agent to increase the ferroelectric properties of PVDF. This was carried out considering its 2D geometry and abundant surface functional groups that facilitate intermolecular hydrogen bonding between the surface functional groups of MXene and the CH 2 group of PVDF. In addition, porous structures can increase the variation in contact area and localized stress concentration in response to applied pressure. This further enhances the piezoelectric sensitivity. Owing to structural deformation and localized stress concentration, the piezoelectric sensitivity of porous MXene/PVDF e-skin is 11.9 and 1.4 nA kPa −1 for low (< 2.5 kPa) and high (2.5–100 kPa) pressure ranges, respectively. These are 31 and 3.7 times higher, respectively, than that of planar MXene/PVDF e-skin (0.4 nA kPa −1 for <100 kPa). In addition, porous MXene/PVDF e-skin exhibits a broad sensing range of up to 100 kPa, and stable sensing performance (5000 repetitions). Our piezoelectric porous MXene/PVDF e-skins enable the monitoring of high-frequency dynamic signals such as acoustic sound waves as well as low-frequency radial artery pulses. In particular, the detection of high-frequency vibrations from sliding friction enables our sensor array to perceive various surface textures with different roughness and moduli, as well as the spatial distribution of words embossed on surfaces. This demonstrates its substantial potential for application in wearable devices, prosthetic limbs, robotics, and healthcare monitoring devices. MXene with a large specific surface area and abundant functional groups can be used as a heterogeneous nucleation agent to induce crystallization of the polar β-phase and enhance the ferroelectric properties of PVDF, which enables the monitoring of high-frequency dynamic signals such as acoustic sound waves as well as low-frequency radial artery pulses. In particular, the detection of high-frequency vibrations from sliding friction enables our sensor array to perceive various surface textures with different roughness and moduli, as well as the spatial distribution of words embossed on surfaces. • High-performance piezoelectric skin sensor is demonstrated using 3D porous structures of MXene (Ti 3 C 2 T x )/PVDF composites. • MXene is used as a nucleation agent to induce polar β-phase and enhance the ferroelectric properties of PVDF. • MXene/PVDF sensor perceives various surface textures as well as the spatial distribution of words embossed on surfaces.