Rapid Microwave Polymerization of Porous Nanocomposites with Piezoresistive Sensing Function

In this paper, polydimethylsiloxane (PDMS) and multi-walled carbon nanotube (MWCNT) nanocomposites with piezoresistive sensing function were fabricated using microwave irradiation. The effects of precuring time on the mechanical and electrical properties of nanocomposites were investigated. The increased viscosity and possible nanofiller re-agglomeration during the precuring process caused decreased microwave absorption, resulting in extended curing times, and decreased porosity and electrical conductivity in the cured nanocomposites. The porosity generated during the microwave-curing process was investigated with a scanning electron microscope (SEM) and density measurements. Increased loadings of MWCNTs resulted in shortened curing times and an increased number of small well-dispersed closed-cell pores. The mechanical properties of the synthesized nanocomposites including stress–strain behaviors and Young’s Modulus were examined. Experimental results demonstrated that the synthesized nanocomposites with 2.5 wt. % MWCNTs achieved the highest piezoresistive sensitivity with an average gauge factor of 7.9 at 10% applied strain. The piezoresistive responses of these nanocomposites were characterized under compressive loads at various maximum strains, loading rates, and under viscoelastic stress relaxation conditions. The 2.5 wt. % nanocomposite was successfully used in an application as a skin-attachable compression sensor for human motion detection including squeezing a golf ball.

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Anisotropic, Wrinkled, and Crack-Bridging Structure for Ultrasensitive, Highly Selective Multidirectional Strain Sensors

Nano-Micro Letters ◽

10.1007/s40820-021-00615-5 ◽

2021 ◽

Vol 13 (1) ◽

Author(s):

Heng Zhang ◽

Dan Liu ◽

Jeng-Hun Lee ◽

Haomin Chen ◽

Eunyoung Kim ◽

...

Keyword(s):

Rational Design ◽

Full Range ◽

Human Motion ◽

Strain Sensors ◽

Gauge Factor ◽

Wearable Electronics ◽

Trade Off ◽

Human Motion Detection ◽

Sensing Applications ◽

Anisotropic Structures

AbstractFlexible multidirectional strain sensors are crucial to accurately determining the complex strain states involved in emerging sensing applications. Although considerable efforts have been made to construct anisotropic structures for improved selective sensing capabilities, existing anisotropic sensors suffer from a trade-off between high sensitivity and high stretchability with acceptable linearity. Here, an ultrasensitive, highly selective multidirectional sensor is developed by rational design of functionally different anisotropic layers. The bilayer sensor consists of an aligned carbon nanotube (CNT) array assembled on top of a periodically wrinkled and cracked CNT–graphene oxide film. The transversely aligned CNT layer bridge the underlying longitudinal microcracks to effectively discourage their propagation even when highly stretched, leading to superior sensitivity with a gauge factor of 287.6 across a broad linear working range of up to 100% strain. The wrinkles generated through a pre-straining/releasing routine in the direction transverse to CNT alignment is responsible for exceptional selectivity of 6.3, to the benefit of accurate detection of loading directions by the multidirectional sensor. This work proposes a unique approach to leveraging the inherent merits of two cross-influential anisotropic structures to resolve the trade-off among sensitivity, selectivity, and stretchability, demonstrating promising applications in full-range, multi-axis human motion detection for wearable electronics and smart robotics.

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Flexible and wearable strain sensor based on electrospun carbon sponge/polydimethylsiloxane composite for human motion detection

RSC Advances ◽

10.1039/d0ra09070k ◽

2021 ◽

Vol 11 (7) ◽

pp. 4186-4193

Author(s):

He Gong ◽

Chuan Cai ◽

Hongjun Gu ◽

Qiushi Jiang ◽

Daming Zhang ◽

...

Keyword(s):

Motion Detection ◽

Strain Sensor ◽

Human Motion ◽

Gauge Factor ◽

Human Motion Detection ◽

Tensile Strains

Electrospun carbon sponge was used to measure tensile strains with a high gauge factor.

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Linearly Sensitive and Flexible Pressure Sensor Based on Porous Carbon Nanotube/Polydimethylsiloxane Composite Structure

Polymers ◽

10.3390/polym12071499 ◽

2020 ◽

Vol 12 (7) ◽

pp. 1499 ◽

Cited By ~ 1

Author(s):

Young Jung ◽

Kyung Kuk Jung ◽

Dong Hwan Kim ◽

Dong Hwa Kwak ◽

Jong Soo Ko

Keyword(s):

Carbon Nanotube ◽

Pressure Sensor ◽

Porous Carbon ◽

Composite Structure ◽

Low Cost ◽

Human Motion ◽

Mechanical And Electrical Properties ◽

Human Motion Detection ◽

Working Principle ◽

Flexible Pressure Sensor

We developed a simple, low-cost process to fabricate a flexible pressure sensor with linear sensitivity by using a porous carbon nanotube (CNT)/polydimethylsiloxane (PDMS) composite structure (CPCS). The working principle of this pressure sensor is based on the change in electrical resistance caused by the contact/non-contact of the CNT tip on the surface of the pores under pressure. The mechanical and electrical properties of the CPCSs could be quantitatively controlled by adjusting the concentration of CNTs. The fabricated flexible pressure sensor showed linear sensitivity and excellent performance with regard to repeatability, hysteresis, and reliability. Furthermore, we showed that the sensor could be applied for human motion detection, even when attached to curved surfaces.

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Near-Linear Responsive and Wide-Range Pressure and Stretch Sensor Based on Hierarchical Graphene-Based Structures via Solvent-Free Preparation

Polymers ◽

10.3390/polym12081814 ◽

2020 ◽

Vol 12 (8) ◽

pp. 1814 ◽

Cited By ~ 1

Author(s):

Jian Wang ◽

Ryuki Suzuki ◽

Kentaro Ogata ◽

Takuto Nakamura ◽

Aixue Dong ◽

...

Keyword(s):

Organic Solvents ◽

Large Strain ◽

Rapid Development ◽

Wearable Sensors ◽

Human Motion ◽

Solvent Free ◽

Gauge Factor ◽

Wearable Electronics ◽

Human Motion Detection ◽

Wide Range

Flexible and wearable electronics have huge potential applications in human motion detection, human–computer interaction, and context identification, which have promoted the rapid development of flexible sensors. So far the sensor manufacturing techniques are complex and require a large number of organic solvents, which are harmful not only to human health but also to the environment. Here, we propose a facile solvent-free preparation toward a flexible pressure and stretch sensor based on a hierarchical layer of graphene nanoplates. The resulting sensor exhibits many merits, including near-linear response, low strain detection limits to 0.1%, large strain gauge factor up to 36.2, and excellent cyclic stability withstanding more than 1000 cycles. Besides, the sensor has an extraordinary pressure range as large as 700 kPa. Compared to most of the reported graphene-based sensors, this work uses a completely environmental-friendly method that does not contain any organic solvents. Moreover, the sensor can practically realize the delicate detection of human body activity, speech recognition, and handwriting recognition, demonstrating a huge potential for wearable sensors.

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Practical and Durable Flexible Strain Sensors Based on Conductive Carbon Black and Silicone Blends for Large Scale Motion Monitoring Applications

Sensors ◽

10.3390/s19204553 ◽

2019 ◽

Vol 19 (20) ◽

pp. 4553 ◽

Cited By ~ 2

Author(s):

Yun Xia ◽

Qi Zhang ◽

Xue E. Wu ◽

Tim V. Kirk ◽

Xiao Dong Chen

Keyword(s):

Carbon Black ◽

Large Scale ◽

Low Cost ◽

Strain Range ◽

Human Motion ◽

Flexion Angle ◽

Gauge Factor ◽

Large Strains ◽

Human Motion Detection

Presented is a flexible capacitive strain sensor, based on the low cost materials silicone (PDMS) and carbon black (CB), that was fabricated by casting and curing of successive silicone layers—a central PDMS dielectric layer bounded by PDMS/CB blend electrodes and packaged by exterior PDMS films. It was effectively characterized for large flexion-angle motion wearable applications, with strain sensing properties assessed over large strains (50%) and variations in temperature and humidity. Additionally, suitability for monitoring large tissue deformation was established by integration with an in vitro digestive model. The capacitive gauge factor was approximately constant at 0.86 over these conditions for the linear strain range (3 to 47%). Durability was established from consistent relative capacitance changes over 10,000 strain cycles, with varying strain frequency and elongation up to 50%. Wearability and high flexion angle human motion detection were demonstrated by integration with an elbow band, with clear detection of motion ranges up 90°. The device’s simple structure and fabrication method, low-cost materials and robust performance, offer promise for expanding the availability of wearable sensor systems.

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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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Highly Sensitive and Stretchable c-MWCNTs/PPy Embedded Multidirectional Strain Sensor Based on Double Elastic Fabric for Human Motion Detection

Nanomaterials ◽

10.3390/nano11092333 ◽

2021 ◽

Vol 11 (9) ◽

pp. 2333

Author(s):

Huiying Shen ◽

Huizhen Ke ◽

Jingdong Feng ◽

Chenyu Jiang ◽

Qufu Wei ◽

...

Keyword(s):

Degrees Of Freedom ◽

Large Scale ◽

Strain Sensor ◽

High Sensitivity ◽

Human Motion ◽

Strain Sensors ◽

Gauge Factor ◽

Wearable Electronics ◽

Synovial Joint ◽

Human Motion Detection

Owing to the multi-dimensional complexity of human motions, traditional uniaxial strain sensors lack the accuracy in monitoring dynamic body motions working in different directions, thus multidirectional strain sensors with excellent electromechanical performance are urgently in need. Towards this goal, in this work, a stretchable biaxial strain sensor based on double elastic fabric (DEF) was developed by incorporating carboxylic multi-walled carbon nanotubes(c-MWCNTs) and polypyrrole (PPy) into fabric through simple, scalable soaking and adsorption-oxidizing methods. The fabricated DEF/c-MWCNTs/PPy strain sensor exhibited outstanding anisotropic strain sensing performance, including relatively high sensitivity with the maximum gauge factor (GF) of 5.2, good stretchability of over 80%, fast response time < 100 ms, favorable electromechanical stability, and durability for over 800 stretching–releasing cycles. Moreover, applications of DEF/c-MWCNTs/PPy strain sensor for wearable devices were also reported, which were used for detecting human subtle motions and dynamic large-scale motions. The unconventional applications of DEF/c-MWCNTs/PPy strain sensor were also demonstrated by monitoring complex multi-degrees-of-freedom synovial joint motions of human body, such as neck and shoulder movements, suggesting that such materials showed a great potential to be applied in wearable electronics and personal healthcare monitoring.

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Graphene/PVA buckypaper for strain sensing application

Scientific Reports ◽

10.1038/s41598-020-77139-2 ◽

2020 ◽

Vol 10 (1) ◽

Author(s):

Ahsan Mehmood ◽

N. M. Mubarak ◽

Mohammad Khalid ◽

Priyanka Jagadish ◽

Rashmi Walvekar ◽

...

Keyword(s):

Testing Machine ◽

Strain Range ◽

Industrial Applications ◽

Human Motion ◽

Gauge Factor ◽

Strain Sensing ◽

Tensile Testing Machine ◽

Sensor Applications ◽

Human Motion Detection ◽

Sensing Applications

AbstractStrain sensors in the form of buckypaper (BP) infiltrated with various polymers are considered a viable option for strain sensor applications such as structural health monitoring and human motion detection. Graphene has outstanding properties in terms of strength, heat and current conduction, optics, and many more. However, graphene in the form of BP has not been considered earlier for strain sensing applications. In this work, graphene-based BP infiltrated with polyvinyl alcohol (PVA) was synthesized by vacuum filtration technique and polymer intercalation. First, Graphene oxide (GO) was prepared via treatment with sulphuric acid and nitric acid. Whereas, to obtain high-quality BP, GO was sonicated in ethanol for 20 min with sonication intensity of 60%. FTIR studies confirmed the oxygenated groups on the surface of GO while the dispersion characteristics were validated using zeta potential analysis. The nanocomposite was synthesized by varying BP and PVA concentrations. Mechanical and electrical properties were measured using a computerized tensile testing machine, two probe method, and hall effect, respectively. The electrical conducting properties of the nanocomposites decreased with increasing PVA content; likewise, electron mobility also decreased while electrical resistance increased. The optimization study reports the highest mechanical properties such as tensile strength, Young’s Modulus, and elongation at break of 200.55 MPa, 6.59 GPa, and 6.79%, respectively. Finally, electrochemical testing in a strain range of ε ~ 4% also testifies superior strain sensing properties of 60 wt% graphene BP/PVA with a demonstration of repeatability, accuracy, and preciseness for five loading and unloading cycles with a gauge factor of 1.33. Thus, results prove the usefulness of the nanocomposite for commercial and industrial applications.

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Flexible Strain-Sensitive Silicone-CNT Sensor for Human Motion Detection

Bioengineering ◽

10.3390/bioengineering9010036 ◽

2022 ◽

Vol 9 (1) ◽

pp. 36

Author(s):

Natalia A. Demidenko ◽

Artem V. Kuksin ◽

Victoria V. Molodykh ◽

Evgeny S. Pyankov ◽

Levan P. Ichkitidze ◽

...

Keyword(s):

Laser Radiation ◽

Human Motion ◽

Gauge Factor ◽

Human Hand ◽

Human Motion Detection ◽

Multi Walled Carbon Nanotubes ◽

Sensor Signals ◽

Sensitive Sensor ◽

Sensitive Characteristics ◽

Walled Carbon Nanotubes

This article describes the manufacturing technology of biocompatible flexible strain-sensitive sensor based on Ecoflex silicone and multi-walled carbon nanotubes (MWCNT). The sensor demonstrates resistive behavior. Structural, electrical, and mechanical characteristics are compared. It is shown that laser radiation significantly reduces the resistance of the material. Through laser radiation, electrically conductive networks of MWCNT are formed in a silicone matrix. The developed sensor demonstrates highly sensitive characteristics: gauge factor at 100% elongation −4.9, gauge factor at 90° bending −0.9%/deg, stretchability up to 725%, tensile strength 0.7 MPa, modulus of elasticity at 100% 46 kPa, and the temperature coefficient of resistance in the range of 30–40 °С is −2 × 10−3. There is a linear sensor response (with 1 ms response time) with a low hysteresis of ≤3%. An electronic unit for reading and processing sensor signals based on the ATXMEGA8E5-AU microcontroller has been developed. The unit was set to operate the sensor in the range of electrical resistance 5–150 kOhm. The Bluetooth module made it possible to transfer the received data to a personal computer. Currently, in the field of wearable technologies and health monitoring, a vital need is the development of flexible sensors attached to the human body to track various indicators. By integrating the sensor with the joints of the human hand, effective movement sensing has been demonstrated.

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Flexible Strain Sensor Based on Carbon Black/Silver Nanoparticles Composite for Human Motion Detection

Materials ◽

10.3390/ma11101836 ◽

2018 ◽

Vol 11 (10) ◽

pp. 1836 ◽

Cited By ~ 19

Author(s):

Weiyi Zhang ◽

Qiang Liu ◽

Peng Chen

Keyword(s):

Silver Nanoparticles ◽

Carbon Black ◽

Motion Detection ◽

Thermoplastic Polyurethane ◽

Strain Sensor ◽

Human Motion ◽

Tunneling Effect ◽

Gauge Factor ◽

Human Motion Detection ◽

Flexible Strain Sensor

The demand for flexible and wearable electronic devices with excellent stretchability and sensitivity is increasing, especially for human motion detection. In this work, a simple, low-cost and convenient strategy has been employed to fabricate flexible strain sensor with a composite of carbon black and silver nanoparticles as sensing materials and thermoplastic polyurethane as matrix. The strain sensors thus prepared possesses high stretchability and good sensitivity (gauge factor of 21.12 at 100% tensile strain), excellent static (almost constant resistance variation under 50% strain for 600 s) and dynamic (100 cycles) stability. Compared with bare carbon black-based strain sensor, carbon black/silver nanoparticles composite-based strain sensor shows ~18 times improvement in sensitivity at 100% strain. In addition, we discuss the sensing mechanisms using the disconnection mechanism and tunneling effect which results in high sensitivity of the strain sensor. Due to its good strain-sensing performance, the developed strain sensor is promising in detecting various degrees of human motions such as finger bending, wrist rotation and elbow flexion.

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