Piezoresistive Sensor Research Articles

Tactile corpuscle-inspired piezoresistive sensors based on (3-aminopropyl) triethoxysilane-enhanced CNPs/carboxylated MWCNTs/cellulosic fiber composites for textile electronics

Recently, wearable electronic products and gadgets have developed quickly with the aim of catching up to or perhaps surpassing the ability of human skin to perceive information from the external world, such as pressure and strain. In this study, by first treating the cellulosic fiber (modal textile) substrate with (3-aminopropyl) triethoxysilane (APTES) and then covering it with conductive nanocomposites, a bionic corpuscle layer is produced. The sandwich structure of tactile corpuscle-inspired bionic (TCB) piezoresistive sensors created with the layer-by-layer (LBL) technology consists of a pressure-sensitive module (a bionic corpuscle), interdigital electrodes (a bionic sensory nerve), and a PU membrane (a bionic epidermis). The synergistic mechanism of hydrogen bond and coupling agent helps to improve the adhesive properties of conductive materials, and thus improve the pressure sensitive properties. The TCB sensor possesses favorable sensitivity (1.0005 kPa−1), a wide linear sensing range (1700 kPa), and a rapid response time (40 ms). The sensor is expected to be applied in a wide range of possible applications including human movement tracking, wearable detection system, and textile electronics.

Comparative analysis for strain response and life monitoring of composite using carbon-based nanosensors

Sensing technology based on carbon nanomaterials has become a very promising technology in the field of composite health monitoring, which requires high-sensitivity piezoresistive strain sensors to serve. In this study, two different carbon nano-sensors were used. Based on the traditional carbon nano-paper sensor, a flexible printed circuit and a polysulfone membrane were added to ensure the stability and sensitivity of the sensor. The conductive mechanism of adjacent carbon nanotubes (CNT) was analyzed. The electrical network model inside the carbon nanosensor was established, and its working mechanism during loading and unloading was described. The research mainly adopts three-point bending experiment. The deformation and failure of composite laminates containing two kinds of sensors under load experience low strain and high strain cyclic loading. Both sensors have the same response and stability as the load growth trend. Experiments show that the CNT-Paper sensor is suitable for long-term health monitoring of composite materials. The carbon nanotube-ultrafiltration membrane (CNT-UM) sensor is more sensitive to the cyclic monitoring of small strain.

Bending and Stretching‐Insensitive, Crosstalk‐Free, Flexible Pressure Sensor Arrays for Human‐Machine Interactions

AbstractAccurate data acquisition from flexible sensors placed on deformable 3D freeform surfaces is of critical importance for many applications, such as wearable electronics, human‐machine interfaces, and soft robotics. However, the mechanical coupling between the sensor and the deformable subject surface to bending and stretching deformations can significantly reduce the accuracy of the acquired data. This study combines a polyimide (PI) micropore isolation layer (PIL) and serpentine electrodes with a flexible piezoresistive sensor to mitigate the issue of mechanical coupling. As a mechanical buffer to distribute the external pressure and reduce the strain concentration, the PIL can avoid the bending interference for bending curvature up to 256 m−1, while maintaining a high sensitivity of S > 21.5 kPa−1. The serpentine electrode design further allows the sensor to reliably acquire data in the presence of stretching up to 45% without cross‐talk. The versatility of the developed sensor is demonstrated in several human‐machine interaction scenarios, including gesture recognition and motion detection. The design strategies on materials and structures from this study can also be applied for the development of other flexible sensors with high sensitivity and low deformation interference to avoid the mechanical coupling between the sensor and the deformable surface.

Bio‐Disintegrable Elastic Polymers for Stretchable Piezoresistive Strain Sensors

AbstractThe fast‐growing usage of electronics is creating large amounts of e‐waste (electronic waste), most of which are directly sent into landfills or incinerated as recycling is either impractical or too costly. Therefore, it is believed that degradable, environmentally friendly materials are the solution to this pressing issue. Herein, disintegrable, durable, and highly stretchable strain sensors are developed based on elastic thin films made of sodium carboxymethyl cellulose, glycerol, and polyvinyl alcohol. The polymer thin films show a failure strain up to ≈ 330% and low hysteresis (5.74% at the second cycle) when subjected to 50% cyclic strain, due to the formation of inter or intramolecular hydrogen bonds. Carbon nanofibers with Au thin film are deposited on the elastic thin film, resulting in highly stretchable piezoresistive strain sensors with a maximum gauge factor of 1.7. More interestingly, the as‐developed sensors can be completely broken down in hot water (at ≈ 95 °C) within ≈ 25 min, indicating their remarkable disintegrability. This unique characteristic is expected to contribute to environmental sustainability. The applications of the sensor for joint bending recognition as well as physiological sign measurement have been demonstrated.

Uniform Synthesis of Bilayer Hydrogen Substituted Graphdiyne for Flexible Piezoresistive Applications.

Graphdiyne (GDY) has garnered significant attention as a cutting-edge 2D material owing to its distinctive electronic, optoelectronic, and mechanical properties, including high mobility, direct bandgap, and remarkable flexibility. One of the key challenges hindering the implementation of this material in flexible applications is its large area and uniform synthesis. The facile growth of centimeter-scale bilayer hydrogen substituted graphdiyne (Bi-HsGDY) on germanium (Ge) substrate is achieved using a low-temperature chemical vapor deposition (CVD) method. This material's field effect transistors (FET) showcase a high carrier mobility of 52.6cm2V-1s-1 and an exceptionally low contact resistance of 10Ωµm. By transferring the as-grown Bi-HsGDY onto a flexible substrate, a long-distance piezoresistive strain sensor is demonstrated, which exhibits a remarkable gauge factor of 43.34 with a fast response time of ≈275ms. As a proof of concept, communication by means of Morse code is implemented using a Bi-HsGDY strain sensor. It is believed that these results are anticipated to open new horizons in realizing Bi-HsGDY for innovative flexible device applications.

Antibacterial highly sensitive eco-friendly wearable piezoresistive sensor for monitoring multiple physiological parameters

Recent progress in wearable biomedical devices has made real-time monitoring possible through non-invasive wearable strain sensors, which can transform physical or biological signals into electrical responses. This work has fabricated multifunctional wearable strain sensors by coating composites (SiE-µG) of electrochemically exfoliated micro-sized multi-layer graphene flakes (µG) and Silicone elastomer (SiE) onto stretchable textile-based orthopedic bandage having ZnO adhesive (SiE-µG@Bandage). The composite coated textile sensors exhibited a remarkable sensitivity of 18330, large stretchability of 35%, superior mechanical durability of 50000 cycles, minute detection limit of 0.04% strain, and fast response time of 400 and recovery time 900 ms. The SiE-µG@Bandage also showed antibacterial properties against Escherichia coli (E. coli) bacteria. Additionally, zinc oxide-based skin-friendly and non-toxic adhesive on the backside of the bandage allowed stable and conformal attachment with the skin. Owing to the above merits, the sensors have shown applicability in real-time monitoring of various physical activities, physiological signals, joint movements, yoga postures, and meditation. Furthermore, the relevance of the sensors in the man-machine interaction has been demonstrated via real-time monitoring of traffic signals by finger movements. Moreover, the exceptional performance and specific features of the SiE-µG@Bandage sensors have enabled their application as electronics skins in health care and preventive care.

Carbon nanotube/liquid metal hybrid coating-based flexible pressure piezoresistive sensors

This work prepared carbon nanotubes/liquid metal (CNT/LM) coating films on a PDMS/Ecoflex (PE) blend substrate with a proportion of 2:1. An ultraviolet laser was used to improve the bonding between CNT/LM and PE 2:1, resulting in the formation of a robust and innovative conductive layer. The interaction between CNT and LM droplets, coupled with laser treatment on the CNT/LM coating, led to a reduced liquid metal oxide layer. The CNT/LM solution demonstrated highly stable CNTs particles with the assistance of liquid metal. The result demonstrated that CNT-assisted liquid metal could improve the electrical resistance compared to the CNT-only layer. Furthermore, the PE/CNT/LM/PE fabricated sensor exhibited enhanced sensitivity and recoverability under lower and higher applied compressive strains with a gauge factor ranging from 20.6 (10 %) to 57 (30 %) and a relatively fast response time (70 ms). The PE/CNT/LM/PE sensor showed extremely high load-bearing capacity confirming the potential of PE 2:1 to bear the load without disrupting the electrical signal. The electromechanical properties confirmed the potential of PE/CNT/LM/PE in wearable electronics and various sensing characteristics.

Recycling of Flyash: Route toward high-performance, eco-friendly, and cost-effective flexible strain sensor via synergizing multi-walled carbon nanotubes

Along with the widespread utilization of wearable and portable electronics, the rise of sensitive flexible strain sensors with wide detection range, excellent stability and affordable costs emerges as a substantial crux of this domain. Herein, we present a convenient and scalable approach for constructing high-performance flexible piezoresistive strain sensor by rationally assembling Flyash/Multi-carbon nanotubes (MWCNTs) active sensing hybrids. Owing to the unique heterostructure of Flyash/MWCNTs wherein Flyash is anchored with MWCNTs via polydopamine, the active sensing hybrids accommodated by porous polyurethane enables a sophisticated conductive network and large tensile deformability, permitting outstanding gauge factor of 1379, wide strain detection range of 0–100 %, remarkable operation stability and durability. Furthermore, the feasibility of sensor in human motions monitoring is validated. For the first time, the synergy of Flyash and MWCNTs demonstrates effective in advancing the sensing performance of piezoresistive strain sensor, providing a new sight towards high-performance, eco-friendly, and cost-effective flexible strain sensor.

Ultrahigh strain-response conductive polyurethane foam for strain sensor and pressure control switches

Conductive polyurethane foams as piezoresistive sensors have attracted considerable attention due to their promising applications in a variety of fields. However, there is still a challenge in high response to the strain of the conductive polyurethane foam. In this work, we constructed the high strain-response conductive polyurethane foam by immersing reduced graphene oxide and sodium alginate into the polyurethane foam. The high sensitivity of polyurethane foam to mechanical deformation was due to the change in the stacking degree of reduced graphene oxide induced by the deformation of polyurethane foam. The introduction of sodium alginate ensured the open pore structure and quick recovery of polyurethane foam. The polyurethane foam could achieve a good recovery of stress (98%) and the self-recovery was almost near to 100% after 5 min. Moreover, the conductivity of the reduced graphene oxide-loaded polyurethane foam was 0.013 S/m at 20% strain and 0.115 S/m at 70% strain. The high current sensitivity ranged from 13 µA to 100 mA corresponding to the strain ranging from 1% to 70%. The brightness of LED lamps was highly sensitive to the change of compressive strain, and the conductive polyurethane foam could accurately monitor the signal (bending of foam and bending of the elbow). Therefore, the conductive polyurethane foam should have broad application in various fields, for example, pressure control switches and strain sensors.

Enhanced braille recognition based on piezoresistive and piezoelectric dual-mode tactile sensors

Human Tactile perception can be divided into pressure perception and slip perception according to the mode of contact. At present, however, tactile sensors can not have the same good performance as human pressure and slip perception. In this paper, a piezoresistive and piezoelectric dual-mode tactile sensing scheme is proposed based on human finger tactile skin structure. PVDF polymer is used as the sensitive material in piezoelectric layer, which has good dynamic response and high sensitivity. Graphene and carbon black are used as the sensitive material in piezoresistive layer, the array process is simple and high resolution can be achieved. The fast response of piezoelectric signal can be used to segment the piezoresistive signal and improve the recognition accuracy when the tactile sensor is used for slip sensing. At the same time, the piezoelectric layer can also reflect the velocity information and direction information. In recognition method, according to the feature that the continuous tactile signal has both temporal and spatial features in the process of sliding, CNN-LSTM is proposed in this paper. The tactile sensors is integrated into the robot arm to detect 20 kinds of braille. At the same speed and the same force, the recognition rate of bimodal braille recognition is 90.58%. In addition, the model can be well recognized at different speeds and sliding directions, and the recognition rate is 84.2%. Finally, the tactile sensor is wore on the index finger of human hand, the average recognition rate of touch braille is 77.5%, which shows that the algorithm has good robustness, and the speed of recognition is twice as fast as that of the normal blind. In the future, it can be applied to blind reading, surface detection, texture identification and other fields.

Piezoresistive relaxation and creep model of porous polymer nanocomposite supported by experimental data

Porous piezoresistive nanocomposites (PPNs), a blend of conductive nanomaterials and a porous polymer matrix, have garnered significant attention in the realm of flexible pressure sensors. The porous microstructure offers exceptional sensitivity and lightweight characteristics of these sensors, but it also introduces challenges such as relaxation and creep behaviors. Grounded in viscoelastic theory, this paper introduces a mathematical model that provides a quantitative analysis of the resistance-strain relationship of PPN-based piezoresistive sensors, considering both bulk resistance and contact resistance. To elucidate the relaxation and creep behaviors, the model incorporates the conformational change and the slip motion of the polymer macromolecules during the deformation. Utilizing the Adam optimization algorithm, the model can accurately depict the piezoresistive behavior of various PPNs (with different porosities and conductive nanomaterial contents) with a fitting accuracy exceeding 99%. Furthermore, we explored some atypical characteristics of the PPN-based sensor, such as the negative resistance-strain behavior and the overshooting of bulk resistance. This study sets a theoretical basis for the development of sensitive and stable PPN-based sensors.

Resent Researches and Applications on Piezoresistive Flexible Pressure Sensor

Recent developments in piezoresistive flexible pressure sensors have generated a lot of interest because of the possible uses across numerous industries. With a focus on improving sensor performance, this paper covers current developments in the area of piezoresistive flexible pressure sensors. Over the years, there has been a growing interest in improving the capabilities of these sensors, leading researchers to explore various avenues for enhancement. The review highlights two primary areas of research: the optimization of active materials and the enhancement of sensor structures. These areas are actively being investigated to achieve superior sensor performance and overall functionality. In addition to utilizing high-quality materials, optimizing the sensor’s structure is crucial for achieving improved sensitivity, accuracy, and stability. The review also explores the wide range of applications where pressure sensors have made significant contributions, including human motion monitoring, healthcare, and other domains. Flexible and highly sensitive pressure sensors have the potential to revolutionize several sectors and open up new opportunities.

A flexible piezoresistive strain sensor based on MXene/bacterial cellulose hydrogel with high mechanical strength for real-time monitoring of human motions

A piezoresistive hydrogel sensor composed of bacterial cellulose and MXene nanosheets shows real-time stress sensing abilities at different amplitudes of human motions and maintains its sensing ability underwater.

Flexible piezo-resistive strain sensors using all-polydimethylsiloxane based hybrid nanocomposites for wearable electronics.

We report flexible piezo-resistive strain sensors composed of silver nanoparticle (Ag NP), graphene nanoplatelet (GNP), and multi walled carbon nanotube (MWCNT)-based ternary conductive hybrid nanocomposites as an active sensing layer fabricated using a simple solution processing method on flexible polydimethylsiloxane (PDMS) substrates. The electrical characteristics have been studied in PDMS-based flexible devices having three different kinds of structures, namely Ag NPs/MWCNT/PDMS, GNP/PDMS and Ag NPs/GNP/PDMS. The microscopic analysis of the hybrid nanocomposites is undertaken using field emission scanning electron microscopy. The diameter of the CNTs is found to be in the range of 20-40 nm, whereas the length is determined to be 100-800 nm. The average diameter and length of the GNPs are observed to be 30-50 nm and 100-500 nm, respectively. The crystallite size of the silver nanoparticles in the Ag NPs/MWCNT/PDMS and Ag NPs/GNP/PDMS-based nanocomposites is determined to be 22.8 nm and 29.1 nm, respectively. The prepared sample of Ag NPs shows four distinct peaks in the X-ray diffraction pattern, which correspond to the (111), (200), (220), and (311) face-centered cubic (FCC) crystalline planes. Raman spectroscopy is undertaken to study the fundamental physical properties and chemical analysis of the nanocomposites. Ag NPs/GNP/PDMS-based sensors exhibit superior performance in terms of sensitivity, response and recovery time during breathing/unbreathing analysis. The large surface area of the Ag NPs and GNPs promotes uniform distribution of Ag NPs to fill into the porous GNP surface, thereby facilitating high contact area along with better electron transport in the Ag NPs/GNP/PDMS hybrid nanocomposite-based sensors. The gauge factor (GF), response and recovery time of the Ag NPs/GNP/PDMS hybrid nanocomposite-based sensors are determined to be 221, 130 ms and 119 ms, respectively. The ternary conductive nanocomposite-based sensors are free from the drawbacks of binary nanocomposite-based sensors where the high percolation threshold and poor mechanical behaviour lead to the degradation of the device performance.

Flexible wearable piezoresistive physical sensors with photothermal conversion and self-cleaning functions for human motion monitoring.

Flexible wearable sensors can mimic the sensing ability of the skin and transform deformation stimuli into monitorable electrical signals, making them favorable in the fields of personalized healthcare, human motion monitoring, and remote monitoring systems. Here, an innovative piezoresistive physical sensor based on fluorine-free superhydrophobic dodecyltrimethoxysilane/polypyrrole/carbon nanotube (DTMS/PPy/CNT) cotton fabrics (DPC-CFs) was assembled via an environmentally safe and simple dip-coating method. The flexible wearable sensor exhibits self-cleaning capability (high water contact angle of 158.3°), good electrical conductivity (45.43 S m-1), photo-thermal conversion (surface temperature up to 94.8 °C), rapid response/recovery time (60 ms/50 ms), and excellent stability (>2400 cycles), and was successfully applied to dynamic monitoring of a series of human activities such as wrist pulse, voice recognition, and finger bending. Furthermore, the development of the superhydrophobic piezoresistive physical sensor derived from biodegradable cotton fabrics means an important step forward in the evolution of wearable sensors, which not only provide better coverage of three-dimensional irregular surfaces to capture mechanical stimulation signals but also demonstrate better comfort, flexibility and versatility. It is foreseen that such sensors, which are fabricated by utilizing abundant renewable and biodegradable green raw materials, have a broad application prospect in the next generation of biomedical systems, fitness, and human-computer interactive devices.

High-performance flexible piezoresistive pressure sensor based on multi-layer interlocking microstructures

PDMS/CNT films with microdome arrays and porous TPU/MXene nanofibre films are assembled into high-performance piezoresistive pressure sensors, which greatly improve the sensitivity and stability of piezoresistive pressure sensors.

Optimizing the piezoresistive design on the microcantilever for enhancing stress sensing and temperature effects

This paper addresses the issue of volatile organic compounds (VOCs), hazardous materials commonly present in paints, perfumes, petroleum and oil refineries, and plastic products, which can lead to health hazards. The detection of these toxic compounds has been a compelling subject for researchers. In this study, a novel approach is presented, involving the design of a sensor for VOC determination using a piezoresistive microcantilever. Microcantilevers have gained significant attention in electrochemical applications due to their enhanced sensitivity. The research explores various design factors, such as length, thickness, and material selection, to optimize the sensor’s response. Specifically, reducing the cantilever’s thickness is considered to improve the deflection sensitivity. To enhance the sensitivity of the piezoresistive sensor, particular emphasis is placed on developing the piezoresistive sensing layer to effectively address stress-induced changes. Experimental investigations involve exploring different cantilever shapes and piezolayer configurations to achieve the desired optimized condition. Ultimately, the rectangular cantilever shape is reshaped into a U-shape, which demonstrates enhanced sensitivity, offering promising possibilities for VOC detection. This study presents valuable insights into the design and optimization of piezoresistive microcantilever sensors for efficient VOC detection, its temperature effects, and monitoring applications.

Three-dimensional Force Detection and Decoupling of a Flexible Tactile Sensor Array based on Porous Composite Piezoresistive Materials

Abstract Flexible piezoresistive sensor array has broad application prospects in human-computer interaction. However, due to the complexity of reality, it is difficult to balance flexibility and perceptual ability in the process of tactile perception. Presented herein is a 4 × 4 matrix of a piezoresistive tactile sensor (TS) that is both pliable and composed of a porous blend of multi-walled carbon nanotubes (MWCNTs) and polydimethylsiloxane (PDMS). This sensor matrix is endowed with characteristics like pliability, consistency, and acute sensitivity, which facilitate its adherence to various shaped surface profiles. It boasts a peak sensitivity of 0.6 kPa−1 and is capable of detecting pressures within a broad spectrum from 0 to 640 kPa. An in-depth examination has been undertaken to assess the TS array's response to pressure, encompassing aspects such as hysteresis and repeatability. In addition to this, a scanning system for the array has been constructed to promptly detect, digitize, and present the pressure applied. A neural network model for three-dimensional force decoupling has been established to analyze the real-time data emanating from the sensor matrix, thereby enabling the precise forecasting of the three-dimensional force exerted upon the array.

A cross-scale honeycomb architecture-based flexible piezoresistive sensor for multiscale pressure perception and fine-grained identification.

Trade-off between sensitivity and the pressure sensing range remains a great challenge for flexible pressure sensors. Micro-nano surface structure-based sensors usually show high sensitivity only in a limited pressure regime, while porous structure-based sensors possess a broad pressure-response range with sensitivity being sacrificed. Here, we report a design strategy based on a cross-scale architecture consisting of a microscale tip and macroscale base, which provides continuous deformation ability over a broad pressure regime (10-4-104 kPa). The cross-scale honeycomb architecture (CHA)-based piezoresistive sensor exhibits an excellent sensitivity over a wide pressure range (0.5 Pa-0.56 kPa: S1 ∼ 27.97 kPa-1; 0.56-20.40 kPa: S2 ∼ 2.30 kPa-1; 20.40-460 kPa: S3 ∼ 0.13 kPa-1). As a result, the CHA-based sensor shows multiscale pressure perception and fine-grained identification ability from 0.5 Pa to 40 MPa. Additionally, the cross-scale architecture will be a general structure to design other types of sensors for highly sensitive pressure perception in a wide pressure range and its unit size from microscale to macroscale is beneficial for large-scale preparation, compared with micro-nano surface structures or internal pores.

Lightweight, flexible, and conductive PEDOT:PSS coated polyimide nanofibrous aerogels for piezoresistive pressure sensor application

Conductive PEDOT:PSS-coated polyimide nanofibrous aerogels as piezoresistive pressure sensors.