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

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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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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High-sensitivity crack-based flexible strain sensor with dual hydrogen bond-assisted structure for monitoring tiny human motions and writing behavior

Organic Electronics ◽

10.1016/j.orgel.2020.105977 ◽

2021 ◽

Vol 88 ◽

pp. 105977

Author(s):

Caixia Liu ◽

Mengdi Li ◽

Baisheng Lu ◽

Ying Huang ◽

Yangyang Zhang ◽

...

Keyword(s):

Hydrogen Bond ◽

Strain Sensor ◽

High Sensitivity ◽

Flexible Strain Sensor ◽

Human Motions

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Retracted Article: 3D printed highly flexible strain sensor based on TPU–graphene composite for feedback from high speed robotic applications

Journal of Materials Chemistry C ◽

10.1039/c8tc03423k ◽

2019 ◽

Vol 7 (16) ◽

pp. 4692-4701 ◽

Cited By ~ 13

Author(s):

Jahan Zeb Gul ◽

Memoon Sajid ◽

Kyung Hyun Choi

Keyword(s):

High Speed ◽

Thermoplastic Polyurethane ◽

Three Dimensional ◽

Strain Sensor ◽

Graphene Composite ◽

Retracted Article ◽

3D Printed ◽

Resistive Type ◽

Flexible Strain Sensor ◽

Robotic Applications

A novel, highly flexible and electrically resistive-type strain sensor with a special three-dimensional conductive network was 3D printed using a composite of conductive graphene pellets and flexible thermoplastic polyurethane (TPU) pellets.

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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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Cost-Effective Fabrication of Transparent Strain Sensors via Micro-Scale 3D Printing and Imprinting

Nanomaterials ◽

10.3390/nano12010120 ◽

2021 ◽

Vol 12 (1) ◽

pp. 120

Author(s):

Rui Wang ◽

Xiaoyang Zhu ◽

Luanfa Sun ◽

Shuai Shang ◽

Hongke Li ◽

...

Keyword(s):

3D Printing ◽

Health Monitoring ◽

Strain Sensor ◽

High Sensitivity ◽

Wearable Devices ◽

Strain Sensors ◽

Expression Recognition ◽

Wrist Flexion ◽

Multiwalled Carbon ◽

Flexible Strain Sensor

The development of strain sensors with high sensitivity and stretchability is essential for health monitoring, electronic skin, wearable devices, and human-computer interactions. However, sensors that combine high sensitivity and ultra-wide detection generally require complex preparation processes. Here, a novel flexible strain sensor with high sensitivity and transparency was proposed by filling a multiwalled carbon nanotube (MWCNT) solution into polydimethylsiloxane (PDMS) channel films fabricated via an electric field-driven (EFD) 3D printing and molding hybrid process. The fabricated flexible strain sensor with embedded MWCNT networks had superior gauge factors of 90, 285, and 1500 at strains of 6.6%, 14%, and 20%, respectively. In addition, the flexible strain sensors with an optical transparency of 84% offered good stability and durability with no significant change in resistance after 8000 stretch-release cycles. Finally, the fabricated flexible strain sensors with embedded MWCNT networks showed good practical performance and could be attached to the skin to monitor various human movements such as wrist flexion, finger flexion, neck flexion, blinking activity, food swallowing, and facial expression recognition. These are good application strategies for wearable devices and health monitoring.

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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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