Graphene as a Piezoresistive Material in Strain Sensing Applications

High accuracy measurement of mechanical strain is critical and broadly practiced in several application areas including structural health monitoring, industrial process control, manufacturing, avionics and the automotive industry, to name a few. Strain sensors, otherwise known as strain gauges, are fueled by various nanomaterials, among which graphene has attracted great interest in recent years, due to its unique electro-mechanical characteristics. Graphene shows not only exceptional physical properties but also has remarkable mechanical properties, such as piezoresistivity, which makes it a perfect candidate for strain sensing applications. In the present review, we provide an in-depth overview of the latest studies focusing on graphene and its strain sensing mechanism along with various applications. We start by providing a description of the fundamental properties, synthesis techniques and characterization methods of graphene, and then build forward to the discussion of numerous types of graphene-based strain sensors with side-by-side tabular comparison in terms of figures-of-merit, including strain range and sensitivity, otherwise referred to as the gauge factor. We demonstrate the material synthesis, device fabrication and integration challenges for researchers to achieve both wide strain range and high sensitivity in graphene-based strain sensors. Last of all, several applications of graphene-based strain sensors for different purposes are described. All in all, the evolutionary process of graphene-based strain sensors in recent years, as well as the upcoming challenges and future directions for emerging studies are highlighted.

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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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Inkjet Printing of Highly Sensitive, Transparent, Flexible Linear Piezoresistive Strain Sensors

Coatings ◽

10.3390/coatings11010051 ◽

2021 ◽

Vol 11 (1) ◽

pp. 51

Author(s):

Ting-Kuo Kang

Keyword(s):

Thin Film ◽

Inkjet Printing ◽

Mechanical Strain ◽

Strain Range ◽

Phase Segregation ◽

Strain Sensors ◽

Tunneling Effect ◽

Gauge Factor ◽

Highly Sensitive ◽

Thin Film Resistors

Flexible strain sensors are fabricated by using a simple and low-cost inkjet printing technology of graphene-PEDOT:PSS (poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)) conductive ink. The inkjet-printed thin-film resistors on a polyethylene terephthalate (PET) substrate exhibit an excellent optical transmittance of about 90% over a visible wavelength range from 400 to 800 nm. While an external mechanical strain is applied to thin-film resistors as strain sensors, a gauge factor (GF) of the piezoresistive (PR) strain sensors can be evaluated. To improve the GF value of the PR strain sensors, a high resistive (HR) path caused by the phase segregation of the PEDOT:PSS polymer material is, for the first time, proposed to be perpendicular to the PR strain sensing direction. The increase in the GF with the increase in the HR number of the PR strain sensors without a marked hysteresis is found. The result can be explained by the tunneling effect with varied initial tunneling distances and tunneling barriers due to the increase in the number of HR. Finally, a high GF value of approximately 165 of three HR paths is obtained with a linear output signal at the strain range from 0% to 0.33%, further achieving for the inkjet printing of highly sensitive, transparent, and flexible linear PR strain sensors.

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Embedded 3D Printing of Highly Flexible Nanocomposites With Piezoresistive Sensing Capabilities

Volume 4: Advances in Aerospace Technology ◽

10.1115/imece2020-23173 ◽

2020 ◽

Author(s):

Blake Herren ◽

Mrinal C. Saha ◽

M. Cengiz Altan ◽

Yingtao Liu

Keyword(s):

3D Printing ◽

Human Skin ◽

Strain Sensor ◽

Strain Range ◽

High Sensitivity ◽

Curing Temperature ◽

Gauge Factor ◽

Strain Sensing ◽

Sensing Applications ◽

Human Joints

Abstract In recent years, highly flexible nanocomposite sensors have been developed for the detection of a variety of human body movements. To precisely detect the bending motions of human joints, the sensors must be able to conform well with the human skin and produce signals that effectively describe the amount of deformation applied to the material during bending. In this paper, a carbon nanotube-based piezoresistive strain sensor is developed via the direct ink writing based embedded 3D printing method. The optimum weight concentration range of carbon nanotubes in the nanocomposite inks, appropriate for embedded 3D printing, is identified. Samples with complex 2D and 3D geometries are printed to demonstrate the manufacturing capabilities of the embedded printing process. The sensitivity of the piezoresistive strain sensor is optimized by determining the ideal nanofiller concentration, curing temperature, and nozzle size to produce the highest gauge factor in a wide strain range. The piezoresistive and mechanical properties of the optimized sensors are fully characterized to verify the suitability for skin-attachable strain sensing applications. The developed sensors have a wide sensing range, high sensitivity, and minimal strain rate dependence. In addition, their low elasticity and high biocompatibility allow them to be comfortably bonded on the human skin.

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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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A Review: Carbon Nanotube-Based Piezoresistive Strain Sensors

Journal of Sensors ◽

10.1155/2012/652438 ◽

2012 ◽

Vol 2012 ◽

pp. 1-15 ◽

Cited By ~ 152

Author(s):

Waris Obitayo ◽

Tao Liu

Keyword(s):

Carbon Nanotubes ◽

Carbon Nanotube ◽

Composite Films ◽

Strain Sensors ◽

Voltage Response ◽

Strain Sensing ◽

Multiwalled Carbon ◽

Sensing Applications ◽

Mechanical Deformations ◽

Electrical Resistivities

The use of carbon nanotubes for piezoresistive strain sensors has acquired significant attention due to its unique electromechanical properties. In this comprehensive review paper, we discussed some important aspects of carbon nanotubes for strain sensing at both the nanoscale and macroscale. Carbon nanotubes undergo changes in their band structures when subjected to mechanical deformations. This phenomenon makes them applicable for strain sensing applications. This paper signifies the type of carbon nanotubes best suitable for piezoresistive strain sensors. The electrical resistivities of carbon nanotube thin film increase linearly with strain, making it an ideal material for a piezoresistive strain sensor. Carbon nanotube composite films, which are usually fabricated by mixing small amounts of single-walled or multiwalled carbon nanotubes with selected polymers, have shown promising characteristics of piezoresistive strain sensors. Studies also show that carbon nanotubes display a stable and predictable voltage response as a function of temperature.

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Optimization of 3D Printed Elastomeric Nanocomposites for Flexible Strain Sensing Applications

Volume 1: Advances in Aerospace Technology ◽

10.1115/imece2019-11467 ◽

2019 ◽

Author(s):

Mohammad Abshirini ◽

Mohammad Charara ◽

Mrinal C. Saha ◽

M. Cengiz Altan ◽

Yingtao Liu

Keyword(s):

3D Printing ◽

Strain Sensor ◽

Sensitive Strain ◽

Curing Temperature ◽

Gauge Factor ◽

Strain Sensing ◽

Sensing Applications ◽

Wide Range ◽

Load Rate ◽

3D Printed

Abstract Flexible and sensitive strain sensors can be utilized as wearable sensors and electronic devices in a wide range of applications, such as personal health monitoring, sports performance, and electronic skin. This paper presents the fabrication of a highly flexible and sensitive strain sensor by 3D printing an electrically conductive polydimethylsiloxane (PDMS)/multi-wall carbon nanotube (MWNT) nanocomposite on a PDMS substrate. To maximize the sensor’s gauge factor, the effects of MWNT concentration on the strain sensing function in nanocomposites are evaluated. Critical 3D printing and curing parameters, such as 3D printing nozzle diameter and nanocomposites curing temperature, are explored to achieve the highest piezoresistive response, showing that utilizing a smaller deposition nozzle size and higher curing temperature can result in a higher gauge factor. The optimized 3D printed nanocomposite sensor’s sensitivity is characterized under cyclic tensile loads at different maximum strains and loading rates. A linear piezoresistive response is observed up to 70% strain with an average gauge factor of 12, pointing to the sensor’s potential as a flexible strain sensor. In addition, the sensing function is almost independent of the applied load rate. The fabricated sensors are attached to a glove and used as a wearable sensor by detecting human finger and wrist motion. The results indicate that this 3D printed functional nanocomposite shows promise in a broad range of applications, including wearable and skin mounted sensors.

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Gold/Polyimide-Based Resistive Strain Sensors

Electronics ◽

10.3390/electronics8050565 ◽

2019 ◽

Vol 8 (5) ◽

pp. 565 ◽

Cited By ~ 5

Author(s):

Tao Han ◽

Anindya Nag ◽

Nasrin Afsarimanesh ◽

Fowzia Akhter ◽

Hangrui Liu ◽

...

Keyword(s):

Thin Film ◽

Industrial Applications ◽

Gold Layer ◽

Gauge Factor ◽

Strain Sensing ◽

Thin Film Sensors ◽

Pressure Mapping ◽

Sensing Applications ◽

The Cost ◽

Two Sides

This paper presents the fabrication and implementation of novel resistive sensors that were implemented for strain-sensing applications. Some of the critical factors for the development of resistive sensors are addressed in this paper, such as the cost of fabrication, the steps of the fabrication process which make it time-consuming to complete each prototype, and the inability to achieve optimised electrical and mechanical characteristics. The sensors were fabricated via magnetron sputtering of thin-film chromium and gold layer on the thin-film substrates at defined thicknesses. Sticky copper tapes were attached on the two sides of the sensor patches to form the electrodes. The operating principle of the fabricated sensors was based on the change in their responses with respect to the corresponding changes in their relative resistance as a function of the applied strain. The strain-induced characteristics of the patches were studied with different kinds of experiments, such as consecutive bending and pressure application. The sensors with 400 nm thickness of gold layer obtained a sensitivity of 0.0086 Ω/ppm for the pressure ranging between 0 and 400 kPa. The gauge factor of these sensors was between 4.9–6.6 for temperatures ranging between 25 °C and 55 °C. They were also used for tactile sensing to determine their potential as thin-film sensors for industrial applications, like in robotic and pressure-mapping applications. The results were promising in regards to the sensors’ controllable film thickness, easy operation, purity of the films and mechanically sound nature. These sensors can provide a podium to enhance the usage of resistive sensors on a higher scale to develop thin-film sensors for industrial applications.

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Printed Strain Sensors Based on an Intermittent Conductive Pattern Filled with Resistive Ink Droplets

Sensors ◽

10.3390/s20154181 ◽

2020 ◽

Vol 20 (15) ◽

pp. 4181 ◽

Cited By ~ 1

Author(s):

Daniel Zymelka ◽

Takahiro Yamashita ◽

Xiuru Sun ◽

Takeshi Kobayashi

Keyword(s):

Strain Range ◽

Functional Materials ◽

Cost Effective ◽

Hybrid Structure ◽

Strain Sensors ◽

Gauge Factor ◽

Strain Sensitivity ◽

Sensor Design ◽

Good Strain ◽

Single Droplets

In this study, we demonstrate a strain sensor fabricated as a hybrid structure of a conductive intermittent pattern with embedded single droplets of a functional resistive ink. The main feature of our proposed sensor design is that although the intermittent pattern comprises the majority of the entire sensor area, the strain sensitivity depends almost selectively on the resistive droplets. This opens up the possibility for fast and inexpensive evaluation of sensors manufactured from various functional materials. As the use of resistive ink was limited to single droplets deposition, the required ink amount needed to build a sensor can be considerably reduced. This makes the sensors cost-effective and simple for fabrication. In this study, our proposed sensor design was evaluated when a carbon-based ink was used as the resistive material incorporated into an intermittent structure made of silver. The developed strain sensors were tested during bending deformations demonstrating good strain sensitivity (gauge factor: 7.71) and no hysteresis within the investigated strain range.

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LASER Reduced Graphene on Flexible Substrate for Strain Sensing Applications: Temperature Effect on Gauge Factor

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.644.115 ◽

2015 ◽

Vol 644 ◽

pp. 115-119 ◽

Cited By ~ 4

Author(s):

Sahour Sayed ◽

Mohammed Gamil ◽

Ahmed M.R. Fath El-Bab ◽

Ahmed Abd El Moneim Abd Elmoneim

Keyword(s):

Low Cost ◽

Flexible Substrate ◽

Graphene Film ◽

Gauge Factor ◽

Strain Sensing ◽

Commercial Strain ◽

Sensing Applications ◽

Poly Ethylene Terephthalate ◽

Poly Ethylene ◽

The Stability

New technique is developed to synthesize graphene film on flexible substrate for strain sensing applications. A flexible graphene/Poly-ethylene Terephthalate (PET) strain sensor based on graphene piezoresistivity is produced by a new simple low cost technique. Graphene oxide film on PET substrate is reduced and patterned simultaneously using 2 Watt CO2LASER beam. The synthesized graphene film is characterized by XRD, FT-IR, SEM, and Raman techniques. Commercial strain gauges are used to predict experimentally the gauge factor (GF) of the graphene film at different values of applied strain. The stability of the graphene film and its GF are studied at different operating temperatures. The fabricated sensor showed high GF of 78 with great linearity and stability up to 60 °C.

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Ultrasensitive Strain Sensor Based on Pre-Generated Crack Networks Using Ag Nanoparticles/Single-Walled Carbon Nanotube (SWCNT) Hybrid Fillers and a Polyester Woven Elastic Band

Sensors ◽

10.3390/s21072531 ◽

2021 ◽

Vol 21 (7) ◽

pp. 2531

Author(s):

Yelin Ko ◽

Ji-seon Kim ◽

Chi Cuong Vu ◽

Jooyong Kim

Keyword(s):

High Performance ◽

Strain Sensor ◽

Strain Range ◽

Human Motion ◽

Strain Sensors ◽

Gauge Factor ◽

Elastic Band ◽

Practical Applications ◽

Single Walled Carbon ◽

Novel Strategy

Flexible strain sensors are receiving a great deal of interest owing to their prospective applications in monitoring various human activities. Among various efforts to enhance the sensitivity of strain sensors, pre-crack generation has been well explored for elastic polymers but rarely on textile substrates. Herein, a highly sensitive textile-based strain sensor was fabricated via a dip-coat-stretch approach: a polyester woven elastic band was dipped into ink containing single-walled carbon nanotubes coated with silver paste and pre-stretched to generate prebuilt cracks on the surface. Our sensor demonstrated outstanding sensitivity (a gauge factor of up to 3550 within a strain range of 1.5–5%), high stability and durability, and low hysteresis. The high performance of this sensor is attributable to the excellent elasticity and woven structure of the fabric substrate, effectively generating and propagating the prebuilt cracks. The strain sensor integrated into firefighting gloves detected detailed finger angles and cyclic finger motions, demonstrating its capability for subtle human motion monitoring. It is also noteworthy that this novel strategy is a very quick, straightforward, and scalable method of fabricating strain sensors, which is extremely beneficial for practical applications.

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