Wearable Flexible Strain Sensor Based on Three-Dimensional Wavy Laser-Induced Graphene and Silicone Rubber

Laser-induced graphene (LIG) has the advantages of one-step fabrication, prominent mechanical performance, as well as high conductivity; it acts as the ideal material to fabricate flexible strain sensors. In this study, a wearable flexible strain sensor consisting of three-dimensional (3D) wavy LIG and silicone rubber was reported. With a laser to scan on a polyimide film, 3D wavy LIG could be synthesized on the wavy surface of a mold. The wavy-LIG strain sensor was developed by transferring LIG to silicone rubber substrate and then packaging. For stress concentration, the ultimate strain primarily took place in the troughs of wavy LIG, resulting in higher sensitivity and less damage to LIG during stretching. As a result, the wavy-LIG strain sensor achieved high sensitivity (gauge factor was 37.8 in a range from 0% to 31.8%, better than the planar-LIG sensor), low hysteresis (1.39%) and wide working range (from 0% to 47.7%). The wavy-LIG strain sensor had a stable and rapid dynamic response; its reversibility and repeatability were demonstrated. After 5000 cycles, the signal peak varied by only 2.32%, demonstrating the long-term durability. Besides, its applications in detecting facial skin expansion, muscle movement, and joint movement, were discussed. It is considered a simple, efficient, and low-cost method to fabricate a flexible strain sensor with high sensitivity and structural robustness. Furthermore, the wavy-LIG strain senor can be developed into wearable sensing devices for virtual/augmented reality or electronic skin.

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Flexible strain sensor based on embedded three-dimensional annular cracks with high mechanical robustness and high sensitivity

Applied Materials Today ◽

10.1016/j.apmt.2021.101247 ◽

2021 ◽

Vol 25 ◽

pp. 101247

Author(s):

Duorui Wang ◽

Xiangming Li ◽

Hongmiao Tian ◽

Xiaoliang Chen ◽

Bangbang Nie ◽

...

Keyword(s):

Three Dimensional ◽

Strain Sensor ◽

High Sensitivity ◽

Flexible Strain Sensor ◽

Annular Cracks

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Highly sensitive and stretchable strain sensors based on chopped carbon fibers sandwiched between silicone rubber layers for human motion detections

Journal of Composite Materials ◽

10.1177/0021998319855758 ◽

2019 ◽

Vol 54 (3) ◽

pp. 423-434 ◽

Cited By ~ 4

Author(s):

MB Azizkhani ◽

Sh Rastgordani ◽

A. Pourkamali Anaraki ◽

J Kadkhodapour ◽

B Shirkavand Hadavand

Keyword(s):

Carbon Fibers ◽

Motion Detection ◽

Silicone Rubber ◽

Low Cost ◽

High Sensitivity ◽

Human Motion ◽

Strain Sensors ◽

Body Motion ◽

Gauge Factor ◽

Human Motion Detection

Tuning the electromechanical performance in piezoresistive composite strain sensors is primarily attained through appropriately employing the materials system and the fabrication process. High sensitivity along with flexibility in the strain sensing devices needs to be met according to the application (e.g. human motion detection, health and sports monitoring). In this paper, a highly stretchable and sensitive strain sensor with a low-cost fabrication is proposed which is acquired by embedding the chopped carbon fibers sandwiched in between silicone rubber layers. The electrical and mechanical features of the sensor were characterized through stretch/release loading tests where a considerably high sensitivity (the gauge factor about 100) was observed with very low hysteresis. This implies high strain reversibility (i.e. full recovery in each cycle) over 700 loading cycles. Moreover, the sensors exhibited ultra-high stretchability (up to ∼300% elongation) in addition to a low stiffness meaning minimal mechanical effects induced by the sensor for sensitive human motion monitoring applications including large and small deformations. The results suggest the promising capability of the present sensor in reflecting the human body motion detection.

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A Pressure-Insensitive Self-Attachable Flexible Strain Sensor with Bioinspired Adhesive and Active CNT Layers

Sensors ◽

10.3390/s20236965 ◽

2020 ◽

Vol 20 (23) ◽

pp. 6965

Author(s):

Minho Seong ◽

Insol Hwang ◽

Joosung Lee ◽

Hoon Eui Jeong

Keyword(s):

Tensile Strain ◽

High Strain ◽

Strain Sensor ◽

Adhesive Layer ◽

High Sensitivity ◽

Gauge Factor ◽

Tactile Sensors ◽

Surface Attachment ◽

Tactile Stimuli ◽

Flexible Strain Sensor

Flexible tactile sensors are required to maintain conformal contact with target objects and to differentiate different tactile stimuli such as strain and pressure to achieve high sensing performance. However, many existing tactile sensors do not have the ability to distinguish strain from pressure. Moreover, because they lack intrinsic adhesion capability, they require additional adhesive tapes for surface attachment. Herein, we present a self-attachable, pressure-insensitive strain sensor that can firmly adhere to target objects and selectively perceive tensile strain with high sensitivity. The proposed strain sensor is mainly composed of a bioinspired micropillar adhesive layer and a selectively coated active carbon nanotube (CNT) layer. We show that the bioinspired adhesive layer enables strong self-attachment of the sensor to diverse planar and nonplanar surfaces with a maximum adhesion strength of 257 kPa, while the thin film configuration of the patterned CNT layer enables high strain sensitivity (gauge factor (GF) of 2.26) and pressure insensitivity.

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Direct Patterning of Carbon Nanotube via Stamp Contact Printing Process for Stretchable and Sensitive Sensing Devices

Nano-Micro Letters ◽

10.1007/s40820-019-0323-8 ◽

2019 ◽

Vol 11 (1) ◽

Cited By ~ 9

Author(s):

Binghao Liang ◽

Zian Zhang ◽

Wenjun Chen ◽

Dongwei Lu ◽

Leilei Yang ◽

...

Keyword(s):

Carbon Nanotube ◽

Low Cost ◽

Flexible Substrate ◽

Strain Sensor ◽

High Sensitivity ◽

Gauge Factor ◽

Contact Printing ◽

Target Pattern ◽

Wearable Electronic Devices ◽

Application Prospects

Abstract Flexible and wearable sensing devices have broad application prospects in bio-monitoring such as pulse measurement, motion detection and voice recognition. In recent years, many significant improvements had been made to enhance the sensor’s performance including sensitivity, flexibility and repeatability. However, it is still extremely complicated and difficult to prepare a patterned sensor directly on a flexible substrate. Herein, inspired by typography, a low-cost, environmentally friendly stamping method for the mass production of transparent conductive carbon nanotube (CNT) film is proposed. In this dry transfer strategy, a porous CNT block was used as both the seal and the ink; and Ecoflex film was served as an object substrate. Well-designed CNT patterns can be easily fabricated on the polymer substrate by engraving the target pattern on the CNT seal before the stamping process. Moreover, the CNT film can be directly used to fabricate ultrathin (300 μm) strain sensor. This strain sensor possesses high sensitivity with a gauge factor (GF) up to 9960 at 85% strain, high stretchability (> 200%) and repeatability (> 5000 cycles). It has been used to measure pulse signals and detect joint motion, suggesting promising application prospects in flexible and wearable electronic devices.

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High-Performance Wearable Strain Sensor Based on MXene@Cotton Fabric with Network Structure

10.21203/rs.3.rs-184921/v1 ◽

2021 ◽

Author(s):

Lu Liu ◽

Libo Wang ◽

Xuqing Liu ◽

Wenfeng Yuan ◽

Mengmeng Yuan ◽

...

Keyword(s):

Cotton Fabric ◽

High Performance ◽

Mechanical Performance ◽

Active Material ◽

Large Body ◽

Strain Sensor ◽

Strain Range ◽

High Sensitivity ◽

Strain Sensors ◽

Gauge Factor

Abstract Although 2D nanomaterials such as MXene Ti3C2Tx have been used in flexible electronic devices for their unique properties such as high conductivity, excellent mechanical performance, flexibility, and good hydrophilicity, less research has focused on of MXene-based cotton fabric strain sensors. Moreover, fabrication of wearable strain sensors with a low cost, high sensitivity, good biocompatibility, and broad sensing range is still a challenge. In this work, a high-performance wearable strain sensor composed of 2D MXene d-Ti3C2Tx nanomaterials and cotton fabric is reported. As the active material in the sensor, MXene d-Ti3C2Tx exhibited an excellent conductivity and hydrophilicity and adhered well to the fabric fibers by electrostatic adsorption. Due to the unique structure of the fabric substrate and the properties of MXene sheets, the fabricated pressure sensor achieved a high sensitivity. The gauge factor of the MXene@cotton fabric strain sensor reached up to 4.11 within the strain range of 15 %. Meanwhile, the sensor possessed high durability (>500 cycles) and a low strain detection limit of 0.3%. Finally, the encapsulated strain sensor was used to detect subtle or large body movements and exhibited a rapid response. This study shows that the MXene@cotton fabric strain sensor reported here have great potential for use in flexible, comfortable, and wearable devices for health monitoring and motion detection.

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Piezotronic effect in AlGaN/AlN/GaN heterojunction nanowires used as a flexible strain sensor

Beilstein Journal of Nanotechnology ◽

10.3762/bjnano.11.166 ◽

2020 ◽

Vol 11 ◽

pp. 1847-1853

Author(s):

Jianqi Dong ◽

Liang Chen ◽

Yuqing Yang ◽

Xingfu Wang

Keyword(s):

Integrated Circuits ◽

Indium Tin Oxide ◽

Quantum Confinement Effect ◽

Strain Sensor ◽

Volume Ratio ◽

High Sensitivity ◽

Gauge Factor ◽

Oxide Electrodes ◽

Poly Ethylene ◽

Flexible Strain Sensor

1D semiconductor nanowires (NWs) have been extensively studied in recent years due to the predominant mechanical flexibility caused by a large surface-to-volume ratio and unique electrical and optical properties induced by the 1D quantum confinement effect. Herein, we use a top-down two-step preparation method to synthesize AlGaN/AlN/GaN heterojunction NWs with controllable size. A single NW is transferred to a flexible poly(ethylene terephthalate) substrate and fixed by indium tin oxide electrodes to form an ohmic contact for the strain sensor. An external mechanical stress is introduced to study the performance of the fabricated piezotronic strain sensor. The gauge factor is as high as 30 under compressive or tensile stress, which indicates a high sensitivity of the strain sensor. Periodic strain tests show the high stability and repeatability of the sensor. The working mechanism of the strain sensor is investigated and systematically analyzed under compressive and tensile strain. Here, we describe a strain sensor that shows a great application potential in wearable integrated circuits, in health-monitoring devices, and in artificial intelligence.

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A Sprayed Graphene Pattern-Based Flexible Strain Sensor with High Sensitivity and Fast Response

Sensors ◽

10.3390/s19051077 ◽

2019 ◽

Vol 19 (5) ◽

pp. 1077 ◽

Cited By ~ 5

Author(s):

Wei Xu ◽

Tingting Yang ◽

Feng Qin ◽

Dongdong Gong ◽

Yijia Du ◽

...

Keyword(s):

Strain Sensor ◽

High Sensitivity ◽

Fast Response ◽

Strain Sensors ◽

Biomedical Science ◽

Gauge Factor ◽

Experimental Conditions ◽

Simple Method ◽

Wide Range ◽

Flexible Strain Sensor

Flexible strain sensors have a wide range of applications in biomedical science, aerospace industry, portable devices, precise manufacturing, etc. However, the manufacturing processes of most flexible strain sensors previously reported have usually required high manufacturing costs and harsh experimental conditions. Besides, research interests are often focused on improving a single attribute parameter while ignoring others. This work aims to propose a simple method of manufacturing flexible graphene-based strain sensors with high sensitivity and fast response. Firstly, oxygen plasma treats the substrate to improve the interfacial interaction between graphene and the substrate, thereby improving device performance. The graphene solution is then sprayed using a soft PET mask to define a pattern for making the sensitive layer. This flexible strain sensor exhibits high sensitivity (gauge factor ~100 at 1% strain), fast response (response time: 400–700 μs), good stability (1000 cycles), and low overshoot (<5%) as well. Those processes used are compatible with a variety of complexly curved substrates and is expected to broaden the application of flexible strain sensors.

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Piezoresistive Multi-Walled Carbon Nanotube/Epoxy Strain Sensor with Pattern Design

Materials ◽

10.3390/ma12233962 ◽

2019 ◽

Vol 12 (23) ◽

pp. 3962 ◽

Cited By ~ 1

Author(s):

Mun-Young Hwang ◽

Dae-Hyun Han ◽

Lae-Hyong Kang

Keyword(s):

Carbon Nanotube ◽

Strain Gauge ◽

Low Cost ◽

Strain Sensor ◽

High Sensitivity ◽

Strain Sensors ◽

Gauge Factor ◽

Patch Type ◽

Multi Walled Carbon Nanotube ◽

Free Vibration Frequency

Carbon nanotube/polymer-based composites have led to studies that enable the realization of low-cost, high-sensitivity piezoresistive strain sensors. This study investigated the characteristics of piezoresistive multi-walled carbon nanotube (MWCNT)/epoxy composite strain sensors subjected to tensile and compressive loads in one direction at relatively small amounts of strain. A patterned sensor was designed to overcome the disadvantage of the load direction sensitivity differences in the existing sensors. The dispersion state of the MWCNTs in the epoxy polymer matrix with the proposed dispersion process was verified by scanning electron microscopy. An MWCNT/epoxy patterned strain sensor and a patch-type strain sensor were directly attached to an acrylic cantilever beam on the opposite side of a commercial metallic strain gauge. The proposed patterned sensor had gauge factors of 2.52 in the tension direction and 2.47 in the compression direction. The measured gauge factor difference for the patterned sensor was less than that for the conventional patch-type sensor. Moreover, the free-vibration frequency response characteristics were compared with those of metal strain gauges to verify the proposed patch-type sensor. The designed drive circuit compensated for the disadvantages due to the high drive voltage, and it was confirmed that the proposed sensor had higher sensitivity than the metallic strain gauge. In addition, the hysteresis of the temperature characteristics of the proposed sensor is presented to show its temperature range. It was verified that the patterned sensor developed through various studies could be applied as a strain sensor for structural health monitoring.

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A Flexible Strain Sensor Based on Embedded Ionic Liquid

Sensors ◽

10.3390/s21175760 ◽

2021 ◽

Vol 21 (17) ◽

pp. 5760

Author(s):

Huiyang Zhang ◽

Andrew Lowe ◽

Anubha Kalra ◽

Yang Yu

Keyword(s):

Ionic Liquid ◽

Low Cost ◽

Microfluidic Channel ◽

Strain Sensor ◽

Gauge Factor ◽

Peak Strain ◽

Healthcare Monitoring ◽

Flexible Strain Sensor ◽

A Minor ◽

Glycol Solution

We present a simple-structured strain sensor based on a low-cost ionic liquid. The ionic liquid was made of sodium chloride/propylene glycol solution and was embedded in a linear microfluidic channel fabricated using Ecoflex. The proposed sensor is capable of measuring strain up to 100% with excellent repeatability. The highest gauge factor is obtained as 6.19 under direct current excitation and 3.40 under alternating current excitation at 1 kHz. The sensor shows negligible hysteresis and overshoot, and survived 10,000 rapid stretch-release cycles of a 100% peak strain with a minor deviation in the response signal. The sensor can be mounted to different locations on the human body and suits a variety of applications in the field of motion detection, human–machine interface and healthcare monitoring.

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Design of a Sensitive Balloon Sensor for Safe Human–Robot Interaction

Sensors ◽

10.3390/s21062163 ◽

2021 ◽

Vol 21 (6) ◽

pp. 2163

Author(s):

Dongjin Kim ◽

Seungyong Han ◽

Taewi Kim ◽

Changhwan Kim ◽

Doohoe Lee ◽

...

Keyword(s):

High Performance ◽

Strain Sensor ◽

High Sensitivity ◽

Human Robot Interaction ◽

Large Area ◽

Tactile Sensors ◽

Robot Interaction ◽

Mechanical Crack ◽

Flexible Strain Sensor ◽

Contact Sensing

As the safety of a human body is the main priority while interacting with robots, the field of tactile sensors has expanded for acquiring tactile information and ensuring safe human–robot interaction (HRI). Existing lightweight and thin tactile sensors exhibit high performance in detecting their surroundings. However, unexpected collisions caused by malfunctions or sudden external collisions can still cause injuries to rigid robots with thin tactile sensors. In this study, we present a sensitive balloon sensor for contact sensing and alleviating physical collisions over a large area of rigid robots. The balloon sensor is a pressure sensor composed of an inflatable body of low-density polyethylene (LDPE), and a highly sensitive and flexible strain sensor laminated onto it. The mechanical crack-based strain sensor with high sensitivity enables the detection of extremely small changes in the strain of the balloon. Adjusting the geometric parameters of the balloon allows for a large and easily customizable sensing area. The weight of the balloon sensor was approximately 2 g. The sensor is employed with a servo motor and detects a finger or a sheet of rolled paper gently touching it, without being damaged.

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