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The ability to achieve real‐time movement visualization in piezoresistive sensors remains a challenge. A visual piezoresistive sensor to perceive the intensity of mechanical stimuli and visible spatial location information is designed based on the mechanoluminescence material CaZnOS: Mn. The linearity, detection range, sensitivity, and stability of the sensor are tested, and the sensing mechanism of the sensor is discussed, and the relationship between force, resistance, and light intensity is established. A 5 × 5 sensor array is prepared to realize the visual detection of dynamic force trajectory, and combined with a convolutional neural network and random forest algorithm, the human writing number and pressure characteristics are recognized, and the writing path and handwriting of the robot arm are controlled by multi‐feature input. The experimental results show that the machine learning algorithm is very reliable with an accuracy of 98.33% for digit recognition and 97.21% for identity recognition. The visual piezoresistive pressure sensor provides a new idea for the visualization of flexible pressure and promotes the development of flexible sensors towards integration and intelligence. [ABSTRACT FROM AUTHOR]

Highlights Glass fabric‐reinforced composites (GFRC) and other revolutionary engineered materials find extensive application in the aerospace, construction, and automobile sectors. It is challenging to predict damage under real‐time stresses due to the anisotropic behavior of composite materials. This study presents the development of a glass textile‐based multifunctional composite sensor and demonstrates its application as a change in resistance or gauge factor in structural health monitoring (SHM) systems. This sensor is coated with reduced graphene oxide (rGO) nanomaterial. Its electrical resistance is evaluated by examining the concentration of nanoparticles and varying geometrical parameters. A three‐point bending method assessed the piezoresistive behavior of the integrated sensor in the GFRC. The impact of sensor width and relative placements in the material's thickness direction within the composite samples is evaluated. Cyclic flexural testing was also performed to demonstrate real‐world applications. The research concludes that it can be utilized as a damage assessment technique for GFRC. The developed sensor can be used to provide an electrically conductive path or as a resistor in the field of E‐textiles. The developed piezoresistive sensor has the flexibility to be used as a multifunctional sensor for multiple purposes, such as force, torque, weight, pressure, flow, acceleration sensors, etc. Glass textile‐based multifunctional materials are reported as strain‐monitoring sensors. Tailored sensor resistance could be achieved through rGO current conduction paths. Glass textile‐based sensors could potentially be used in the field of E‐textile. [ABSTRACT FROM AUTHOR]

In this article, we have chosen to explore the performance of the piezoresistive accelerometer, favoured for its comparative advantages over other accelerometers. Our approach includes modelling this accelerometer according to the law of motion and validating the model through simulation tests and experimental trials. With this approach, we can determine the optimal damping rate and frequency range for the piezoresistive accelerometer, the optimisation of these parameters is crucial to maximise the performance of the accelerometer in various operating conditions, ensuring high sensitivity and fast response while minimising distortions or errors in the collected data. These optimal values of damping rate and frequency range guarantee precise and reliable accelerometer measurements. This paper provides a comprehensive overview of sensor design principles and signal processing methods from a theoretical standpoint. Beginning with sensor design, we delve into the foundational aspects of transduction principles, emphasising the conversion of physical quantities into electrical signals. The selection and optimisation of sensing elements are explored, highlighting material properties, geometrical considerations, and packaging strategies to ensure sensitivity, linearity, and robustness. [ABSTRACT FROM AUTHOR]

The second most common cause of blindness in the world is glaucoma. A key glaucoma indicator that can be monitored to treat the condition is intraocular pressure (IOP). A contact lens with a piezoresistive sensor to detect IOP continuously and non-invasively is proposed in this work. Two different contact lenses were fabricated, one with a sensing material made of carbon conductive paste and the other with graphene conductive paste. A screen-printing technique, which is a simple and inexpensive thin film-based technology was used for the fabrication of contact lenses. The fabricated contact lenses were tested for their transparency, waterproofing, ohmic contact, and sensitivity toward temperature. Results indicated that carbon conductive contact lens exhibited a sensitivity of 62.575 Ω/mmHg with a linear correlation coefficient of r2 = 0.948. Conversely, the graphene conductive contact lens demonstrated a sensitivity of 44.43 Ω/mmHg with a linear correlation coefficient of r2 = 0.974. The fabricated contact lenses complied with the fundamental requirements for contact lenses by being flexible, thin, and wrapped in a biocompatible material with high transparency. [ABSTRACT FROM AUTHOR]

A MEMS piezoresistive sensor for measuring accelerations greater than 100,000 g (about 106 m/s2) is described in this work. To enhance the performance of the sensor, specifically widening its measurement range and natural frequency, a cross-beam construction with a center block was devised, and a Wheatstone bridge was formed by placing four piezoresistors at the ends of the fixed beams to convert acceleration into electricity. The location of the varistor was determined using the finite element approach, which yielded the optimal sensitivity. Additionally, a reliable Pt-Ti-Pt-Au electrode was designed to solve the issue of the electrode failing under high impact and enhancing the stability of the ohmic contact. The accelerometer was fabricated using MEMS technology, and the experiment with a Hopkinson pressure bar and hammering was conducted, and the bias stability was measured. It had a sensitivity of 1.06 μV/g with good linearity. The simulated natural frequency was 633 kHz The test result revealed that the accelerometer can successfully measure an acceleration of 100,000 g. [ABSTRACT FROM AUTHOR]

Integrating 1D nanomaterials into 3D arrays or hierarchical structures is crucial to unlocking their complete potential in functional applications. This work highlights the significant influence of pH variations on the morphological evolution of three-dimensional zinc oxide foams (ZOFs) at relatively low temperatures, leading to the formation of diverse structures with varying aspect ratios and dimensions. Our findings underscore the role of alkaline conditions in fostering the evolution of dandelion-like 1D nanostructures, attributed to the intricate interplays of reaction kinetics and Ostwald ripening processes. Furthermore, the ZOF demonstrates potential applications in self-cleaning, oil/water separation, and human motion sensing. The ZOF is optimized to exhibit superhydrophobicity (water contact angle = 153 ± 2°) showcasing self-cleaning ability and enhanced oil–water separation performance following surface functionalization. The ZOF exhibits exceptional oil adsorption capacity (10–55 g/g) and superior stability, making it suitable for oil–water separation. Furthermore, our investigations showcase the biocompatibility and practical applicability in oil–water separation, both on surface and underwater, highlighting its efficacy in environmental remediation scenarios. Transitioning to wearable sensing, ZOF exhibits outstanding mechanical (compression strength increases by more than 130%) and piezoresistive characteristics (gauge factor = 1.036), precisely capturing a broad spectrum of human movements and tactile stimuli with rapid response times (∼60 ms). Furthermore, ZOF exhibits stability over 10,000 continuous tapping cycles, indicating the material's ability to maintain its piezoresistive properties over extended use. Overall, the multifaceted functionalities and versatility of the ZOF make it a promising material for environmental remediation, sensor technology, and human–machine interfaces. [ABSTRACT FROM AUTHOR]

Sustainability, safety and service life expansion in the construction sector have gained a lot of scientific and technological interest during the last few decades. In this direction, the synthesis and characterization of smart cementitious composites with tailored properties combining mechanical integrity and self-sensing capabilities have been in the spotlight for quite some time now. The key property for the determination of self-sensing behavior is the electrical resistivity and, more specifically, the determination of reversible changes in the electrical resistivity with applied stress, which is known as piezoresistivity. In this study, the mechanical and piezoresistive properties of mortars reinforced with carbon nanotubes (CNTs) and carbon micro-fibers (CMFs) are determined. Silica fume and a polymer with polyalkylene glycol graft chains were used as dispersant agents for the incorporation of the CNTs and CMFs into the cement paste. The mechanical properties of the mortar composites were investigated with respect to their flexural and compressive strength. A four-probe method was used for the estimation of their piezoresistive response. The test outcomes revealed that the combination of the dispersant agents along with a low content of CNTs and CMFs by weight of cement (bwoc) results in the production of a stronger mortar with enhanced mechanical performance and durability. More specifically, there was an increase in flexural and compressive strength of up to 38% and 88%, respectively. Moreover, mortar composites loaded with 0.4% CMF bwoc and 0.05% CNTs bwoc revealed a smooth and reversible change in electrical resistivity vs. compression loading—with unloading comprising a strong indication of self-sensing behavior. This work aims to accelerate progress in the field of material development with structural sensing and electrical actuation via providing a deeper insight into the correlation among cementitious composite preparation, admixture dispersion quality, cementitious composite microstructure and mechanical and self-sensing properties. [ABSTRACT FROM AUTHOR]

Touch serves as an important medium for human–environment interaction. The piezoresistive tactile sensor has attracted much attention due to its convenient technology, simple principle, and convenient signal acquisition and analysis. In this paper, conductive beads-on-string polyvinyl alcohol (PVA)/polyaniline doped with dodecyl benzene sulfonic acid (PANI-DBSA) nanofibers were fabricated via the electrospinning technique. Due to the special nanostructure of PVA-coated PANI-DBSA, the tactile sensor presented a wide measuring range of 12 Pa–121 kPa and appreciable sensitivity of 8.576 kPa−1 at 12 Pa~484 Pa. In addition, the response time and recovery time of the sensor were approximately 500 ms, demonstrating promising prospects in the field of tactile sensing for active upper limb prostheses. [ABSTRACT FROM AUTHOR]

Ensuring quality control by identifying issues such as nutrient deficiencies and pest infestations helps in crop yield estimation for effective planning and resource management. However, the development of sensors for real-time continuous monitoring of fruit growth in an open environment has been a challenge. Herein, we propose a hydrophobic and stretchable piezoresistive sensor to monitor real-time fruit growth using graphene–silicone-based screen-printable paste (GSiCP) remotely. Graphene has been synthesized with a green approach utilizing an electrochemical exfoliation process, wherein no hazardous or strong acids were employed. The synthesized graphene has been characterized using X-ray (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Raman spectroscopy, and dynamic light scattering. The developed (GSiCP) sensors have shown a high sensitivity, stretchability, and cyclic durability of 2050, 125%, and 5000 cycles, respectively. The sensors show an exceptional minimal detection limit of 0.04%, which shows the capability of monitoring the slowest fruit growth. The GSiCP sensors have been used to monitor on-field the continuous real-time growth of fruit (brinjal) for 15 days using the Internet of Things (IoT). Further, the impact of an excess amount of fertilizer (urea) on fruit growth and plants has been investigated. Owing to the sensor's merits, GSiCP sensors have shown applicability in monitoring physiological signals (radial artery pulse rate) and physical activities. [ABSTRACT FROM AUTHOR]

Three-dimensional flexible piezoresistive porous sensors are of interest in health diagnosis and wearable devices. In this study, conductive porous sensors with complex triply periodic minimal surface (TPMS) structures were fabricated using the 3D printed sacrificial mold and enhancement of MWCNTs. A new curing routine by the self-resistance electric heating was implemented. The porous sensors were designed with different pore sizes and unit cell types of the TPMS (Diamond (D), Gyroid (G), and I-WP (I)). The impact of pore characteristics and the hybrid fabrication technique on the compressive properties and piezoresistive response of the developed porous sensors was studied. The results indicate that the porous sensors cured by the self-resistance electric heating could render a uniform temperature distribution in the composites and reduce the voids in the walls, exhibiting a higher elastic modulus and a better piezoresistive response. Among these specimens, the specimen with the D-based structure cured by self-resistance electric heating showed the highest responsive strain (61%), with a corresponding resistance response value of 0.97, which increased by 10.26% compared to the specimen heated by the external heat sources. This study provides a new perspective on design and fabrication of porous materials with piezoresistive functionalities, particularly in the realm of flexible and portable piezoresistive sensors. [ABSTRACT FROM AUTHOR]

The development of a high-performance, low-cost, and simply fabricated flexible three-dimensional (3D) force sensor is essential for the future development of electronic skins suitable for the detection of normal and shear forces for several human motions. In this study, a sandwich-structured flexible 3D force tactile sensor based on a polyethylene-carbon composite material (velostat) is presented. The sensor has a large measuring range, namely, 0–12 N in the direction of the normal force and 0–2.6 N in the direction of the shear force. For normal forces, the sensitivity is 0.775 N−1 at 0–1 N, 0.107 N−1 between 1 and 3 N, and 0.003 N−1 at 3 N and above. For shear forces, the measured sensitivity is 0.122 and 0.12 N−1 in x- and y-directions, respectively. Additionally, the sensor exhibits good repeatability and stability after 2500 cycles of loading and releasing. The response and recovery times of the sensor are as fast as 40 and 80 ms, respectively. Furthermore, we prepared a glove-like sensor array. When grasping the object using the tactile glove, the information about the force applied to the sensing unit can be transmitted through a wireless system in real-time and displayed on a personal computer (PC). The prepared flexible 3D force sensor shows broad application prospects in the field of smart wearable devices. [ABSTRACT FROM AUTHOR]

Enhancing the piezoresistivity of polymer‐derived silicon oxycarbide ceramics (SiOCPDC) is of great interest in the advancement of highly sensitive pressure/load sensor technology for use in harsh and extreme working conditions. However, a facile, low cost, and scalable approach to fabricate highly piezoresistive SiOCPDC below 1400 °C still remains a great challenge. Here, the fabrication and enhancement of piezoresistive properties of SiOCPDC reinforced with β‐SiC nanopowders (SiCNP) through masked stereolithography‐based 3D‐printing and subsequent pyrolysis at 1100 °C are demonstrated. The presence of free carbon in SiCNP augments high piezoresistivity in the fabricated SiCNP‐SiOCPDC composites even at lower pyrolysis temperatures. A gauge factor (GF) in the range of 4385–5630 and 6129–8987 with 0.25 and 0.50 wt% of SiCNP, respectively is demonstrated, for an applied pressure range of 0.5–5 MPa at ambient working conditions. The reported GF is significantly higher compared to those of any existing SiOCPDC materials. This rapid and facile fabrication route with significantly enhanced piezoresistive properties makes the 3D‐printed SiCNP‐SiOCPDC composite a promising high‐performance material for the detection of pressure/load in demanding applications. Also, the overall robustness in mechanical properties and load‐bearing capability ensures its long‐term stability and makes it suitable for challenging and severe environment applications. [ABSTRACT FROM AUTHOR]

The flexible pressure sensor has been credited for leading performance including higher sensitivity, faster response/recovery, wider detection range and higher mechanical durability, thus driving the development of novel sensing materials enabled by new processing technologies. Using atomic layer infiltration, Pt nanocrystals with dimensions on the order of a few nanometers can be infiltrated into the compressible lamellar structure of Ti3C2Tx MXene, allowing a modulation of its interlayer spacing, electrical conductivity and piezoresistive property. The flexible piezoresistive sensor is further developed from the Pt-infiltrated MXene on a paper substrate. It is demonstrated that Pt infiltration leads to a significant enhancement of the pressure-sensing performance of the sensor, including increase of sensitivity from 0.08 ​kPa−1 to 0.5 ​kPa−1, extension of detection limit from 5 ​kPa to 9 ​kPa, decrease of response time from 200 ​ms to 20 ​ms, and reduction of recovery time from 230 ​ms to 50 ​ms. The mechanical durability of the flexible sensor is also improved, with the piezoresistive performance stable over 1000 cycles of flexure fatigue. The atomic layer infiltration process offers new possibilities for the structure modification of MXene for advanced sensor applications.

In this work, the flexible piezoresistive films were synthesized through in-situ dispersing perovskite MASnBrI 2 nanocrystals (NCs) into the elastic thermoplastic polyurethanes (TPU) substrate. Then, the flexible piezoresistive sensors were fabricated by sandwiching the NCs/TPU nanocomposite layer between interdigitated Ag electrodes. The piezoresistive behavior was attributed to the perovskite NCs which were distributed uniformly inside the TPU film. Specifically, it manifests as the change in electron cloud density of perovskite NCs under a pressure. The sensor made with a NCs/TPU composite membrane shows a pressure sensitivity of 0.796 kPa−1 over a wide linear range of 0∼0.7 kPa, an ultralow detect limitation of 0.2 Pa, a rapid response/recover time of 400 ms/370 ms and a good bending ability (90°). Additionally, the strain sensor also shows excellent performance in detecting the respiratory airflow, wrist pulse and finger joint curvature. We believe that this work might open up new opportunities for flexible strain sensors in the areas such as health monitoring, human-computer interaction, and smart electronic wearables. [ABSTRACT FROM AUTHOR]

This paper presents a ceramic stress sensor with the dimension of a coin, able to measure the compressive force (stress) applied to its two round faces. The sensor is designed and engineered to be embedded inside concrete or masonry structures, like bridges or buildings. It provides good accuracy, robustness, and simplicity of use at potentially low cost for large-scale applications in civil structures. Moreover, it can be calibrated temperature compensated, and it is inherently hermetic, ensuring the protection of sensitive elements from the external environment. It is, therefore, suitable for operating in harsh and dirty environments like civil constructions. The sensor directly measures the internal stress of the structure, exploiting the piezo resistivity of thick film ink based on ruthenium oxide. It is insensitive with respect to the stiffness of the embedding material and the variation of the surrounding material properties like concrete hardening, shrinkage, and creep as it decouples the two components of stress. [ABSTRACT FROM AUTHOR]

With a constantly growing percentage of the population having access to high‐quality healthcare facilities, preventable pathogenic illnesses have been nearly eradicated in the developed parts of the world, which has led to a significant rise in the average human life expectancy over the last few decades. In such a highly developed world, age‐related illnesses will lead to an immense burden on healthcare providers. Remote health monitoring enabled by wearable sensors will play a significant role in the growth and evolution of Health 3.0 by providing intimate and valuable information to healthcare providers regarding the progression of disease in patients with critical life‐altering conditions. Especially, in the case of people suffering from neurodegenerative disorders, inexpensive and user‐friendly wearable sensors can enable physiotherapists monitor real‐time physiological parameters to design patient‐specific treatment plans. This review provides a comprehensive overview of the recent advances and emerging trends at the convergence of biomimicry and nanomaterial sensors, with a specific focus on wearable skin‐inspired mechanical sensors for applications in IoT‐enabled human physiological parameters monitoring. Skin‐inspired wearable mechanical sensors with relevance to the most common types of sensing mechanisms including piezoresistive, piezocapacitive, and triboelectric sensing are discussed along with their current challenges and possible future opportunities. [ABSTRACT FROM AUTHOR]

Monolayers of graphene oxide, assembled into densely packed sheets at an immiscible hexane/water interface, form transparent conducting films on polydimethylsiloxane membranes after reduction in hydroiodic acid (HI) vapor to reduced graphene oxide (rGO). Prestraining and relaxing the membranes introduces cracks in the rGO film. Subsequent straining opens these cracks and induces piezoresistivity, enabling their application as transparent strain gauges. The sensitivity and strain range of these gauges is controlled by the cracked film structure that is determined by the reducing conditions used in manufacture. Reduction for 30 s in HI vapor leads to an array of parallel cracks that do not individually span the membrane. These cracks do not extend on subsequent straining, leading to a gauge with a usable strain range >0.2 and gauge factor (GF) at low strains ranging from 20 to 100, depending on the prestrain applied. The GF reduces with increasing applied strain and asymptotes to about 3, for all prestrains. Reduction for 60 s leads to cracks spanning the entire membrane and an increased film resistance but a highly sensitive strain gauge, with GF ranging from 800 to 16,000. However, the usable strain range reduces to <0.01. A simple equivalent resistor model is proposed to describe the behavior of both gauge types. The gauges show a repeatable and stable response with loading frequencies >1 kHz and have been used to detect human body strains in a simple e-skin demonstration. [ABSTRACT FROM AUTHOR]

A MEMS piezoresistive sensor for measuring accelerations greater than 100,000 g (about 106 m/s2) is described in this work. To enhance the performance of the sensor, specifically widening its measurement range and natural frequency, a cross-beam construction with a center block was devised, and a Wheatstone bridge was formed by placing four piezoresistors at the ends of the fixed beams to convert acceleration into electricity. The location of the varistor was determined using the finite element approach, which yielded the optimal sensitivity. Additionally, a reliable Pt-Ti-Pt-Au electrode was designed to solve the issue of the electrode failing under high impact and enhancing the stability of the ohmic contact. The accelerometer was fabricated using MEMS technology, and the experiment with a Hopkinson pressure bar and hammering was conducted, and the bias stability was measured. It had a sensitivity of 1.06 μV/g with good linearity. The simulated natural frequency was 633 kHz The test result revealed that the accelerometer can successfully measure an acceleration of 100,000 g.

Sustainability, safety and service life expansion in the construction sector have gained a lot of scientific and technological interest during the last few decades. In this direction, the synthesis and characterization of smart cementitious composites with tailored properties combining mechanical integrity and self-sensing capabilities have been in the spotlight for quite some time now. The key property for the determination of self-sensing behavior is the electrical resistivity and, more specifically, the determination of reversible changes in the electrical resistivity with applied stress, which is known as piezoresistivity. In this study, the mechanical and piezoresistive properties of mortars reinforced with carbon nanotubes (CNTs) and carbon micro-fibers (CMFs) are determined. Silica fume and a polymer with polyalkylene glycol graft chains were used as dispersant agents for the incorporation of the CNTs and CMFs into the cement paste. The mechanical properties of the mortar composites were investigated with respect to their flexural and compressive strength. A four-probe method was used for the estimation of their piezoresistive response. The test outcomes revealed that the combination of the dispersant agents along with a low content of CNTs and CMFs by weight of cement (bwoc) results in the production of a stronger mortar with enhanced mechanical performance and durability. More specifically, there was an increase in flexural and compressive strength of up to 38% and 88%, respectively. Moreover, mortar composites loaded with 0.4% CMF bwoc and 0.05% CNTs bwoc revealed a smooth and reversible change in electrical resistivity vs. compression loading—with unloading comprising a strong indication of self-sensing behavior. This work aims to accelerate progress in the field of material development with structural sensing and electrical actuation via providing a deeper insight into the correlation among cementitious composite preparation, admixture dispersion quality, cementitious composite microstructure and mechanical and self-sensing properties.

Abstract With a constantly growing percentage of the population having access to high‐quality healthcare facilities, preventable pathogenic illnesses have been nearly eradicated in the developed parts of the world, which has led to a significant rise in the average human life expectancy over the last few decades. In such a highly developed world, age‐related illnesses will lead to an immense burden on healthcare providers. Remote health monitoring enabled by wearable sensors will play a significant role in the growth and evolution of Health 3.0 by providing intimate and valuable information to healthcare providers regarding the progression of disease in patients with critical life‐altering conditions. Especially, in the case of people suffering from neurodegenerative disorders, inexpensive and user‐friendly wearable sensors can enable physiotherapists monitor real‐time physiological parameters to design patient‐specific treatment plans. This review provides a comprehensive overview of the recent advances and emerging trends at the convergence of biomimicry and nanomaterial sensors, with a specific focus on wearable skin‐inspired mechanical sensors for applications in IoT‐enabled human physiological parameters monitoring. Skin‐inspired wearable mechanical sensors with relevance to the most common types of sensing mechanisms including piezoresistive, piezocapacitive, and triboelectric sensing are discussed along with their current challenges and possible future opportunities.

Small, low-power, and inexpensive marine depth sensors are of interest for a myriad of applications from maritime security to environmental monitoring. Recently, laser-induced graphene (LIG) piezoresistive pressure sensors have been proposed given their rapid fabrication and large dynamic range. In this work, the practicality of LIG integration into fieldable deep ocean (1 km) depth sensors in bulk is explored. Initially, a design of experiments (DOEs) approach evaluated laser engraver fabrication parameters such as line length, line width, laser speed, and laser power on resultant resistances of LIG traces. Next, uniaxial compression and thermal testing at relevant ocean pressures up to 10.3 MPa and temperatures between 0 and 25 °C evaluated the piezoresistive response of replicate sensors and determined the individual characterization of each, which is necessary. Additionally, bare LIG sensors showed larger resistance changes with temperature (ΔR ≈ 30 kΩ) than pressure (ΔR ≈ 1–15 kΩ), indicating that conformal coatings are required to both thermally insulate and electrically isolate traces from surrounding seawater. Sensors encapsulated with two dip-coated layers of 5 wt% polydimethylsiloxane (PDMS) silicone and submerged in water baths from 0 to 25 °C showed significant thermal dampening (ΔR ≈ 0.3 kΩ), indicating a path forward for the continued development of LIG/PDMS composite structures. This work presents both the promises and limitations of LIG piezoresistive depth sensors and recommends further research to validate this platform for global deployment. [ABSTRACT FROM AUTHOR]

In this paper, a knittle pressure sensor was designed and fabricated by coating graphene/Polyvinylidene Fluoride nanocomposite on the knitted polyester substrate. The coating was carried out by a dip-coating method in a nanocomposite solution. The microstructure, surface properties and electrical properties of coated layers were investigated. The sensors were tested under the application of different pressures, and the corresponding sensor signals were analyzed in terms of resistance change. It was observed that the change in resistance was 55% kPa−1 with a sensitivity limit of 0.25 kPa. The sensor model was created and simulated using COMSOL Multiphysics software, and the model data were favorably compared with the experimental results. This investigation suggests that graphene-based nanocomposites can be used in knittle pressure sensor applications. [ABSTRACT FROM AUTHOR]

Stockouts constitute a major challenge in the retail industry. Stockouts are caused by errors related to manual stockkeeping and by the misplacement of items on shelves. Such errors account for up to 4% of lost sales. Real-time inventory management systems for misplaced items or missing stock detection in retail stores are limited. Accordingly, a conductive polymer-based interactive shelving system for real-time inventory management is developed. The system comprises an 80 × 48 sensor array fabricated by screen-printing a piezoresistive carbon-based conductive polymer layer onto gold interdigitated electrodes deposited on a flexible substrate. Each sensing pixel has dimensions of 5 mm × 5 mm and a sensing area of 4 mm × 4 mm. The sensor mat can detect the shape and weight features of stockkeeping units (SKUs), which can then be analyzed by a TensorFlow model for SKU identification. The developed system is characterized for functional resistance range, uniformity, repeatability, and durability. The accuracy of SKU identification achieved using shape features only and the accuracy of SKU identification achieved using both shape and weight features is 95% and 99.2%, respectively. The key novelty of the work is the development of a deep learning-embedded interactive smart shelving system for retail inventory management by using the shape and weight features of SKU. Also, the developed system helps to detect the SKU if they are stacked one over the other. Furthermore, multiple sensor mats implemented on various shelves in a retail store can be modularized and integrated for monitoring under the control of a single PC. Accordingly, the proposed retail inventory tracking system can facilitate the development of automated "humanless" shops. [ABSTRACT FROM AUTHOR]

Carbon nanotube (CNT) has numerous unique properties that may benefit creating new sensor technologies. CNT is intensely interested in sensing applications due to their exceptional mechanical strength, high Young's modulus, and high current density. In this work, the design and simulation of a carbon nanotube on a circular substrate-based piezoresistive pressure sensor were studied. Single and multi-walled carbon nanotubes were utilized to evaluate the best sensitivity and time response. The effect of changing pressure on displacement, current density, and von Mises stress was investigated using a single carbon nanotube (CNT) and an array of CNTs. It was noticed that as the pressure increased, there was also an increase in displacement, current density, and von Mises stress. The sensitivity achieved by SWCNTs was 1.428 × 10−11 μA\Pa, while for MWCNTs, it was 7.5 × 10−12 μA\Pa and the rise time range was 0.18 to 0.1 s, while for the pressure tested range was from 50 to 150 kPa. Additionally, the influence of varying diameters on the resistance of SWCNT and MWCNTs was discussed. This design has established diameter limits ranging from 1 to 4 nm. It has been discovered that increasing the diameter results in a decrease in the energy bandgap from 0.426 to 0.10 eV and reduces resistance from 2143 to 543 kΩ at zero strain. [ABSTRACT FROM AUTHOR]

MXenes are a new family of two-dimensional (2D) nanomaterials. They are inorganic compounds of metal carbides/nitrides/carbonitrides. Titanium carbide MXene (Ti 3 C 2 -MXene) was the first 2D nanomaterial reported in the MXene family in 2011. Owing to the good physical properties of Ti 3 C 2 -MXenes (e.g., conductivity, hydrophilicity, film-forming ability, elasticity) various applications in wearable sensors, energy harvesters, supercapacitors, electronic devices, etc., have been demonstrated. This paper presents the development of a piezoresistive Ti 3 C 2 -MXene sensor followed by experimental investigations of its dynamic response behavior when subjected to structural impacts. For the experimental investigations, an inclined ball impact test setup is constructed. Stainless steel balls of different masses and radii are used to apply repeatable impacts on a vertical cantilever plate. The Ti 3 C 2 -MXene sensor is attached to this cantilever plate along with a commercial piezoceramic sensor, and their responses for the structural impacts are compared. It is observed from the experiments that the average response times of the Ti 3 C 2 -MXene sensor and piezoceramic sensor are 1.28 ± 0.24 μ s and 31.19 ± 24.61 μ s, respectively. The fast response time of the Ti 3 C 2 -MXene sensor makes it a promising candidate for monitoring structural impacts. [ABSTRACT FROM AUTHOR]

The environmental impact of plastic waste has had a profound effect on our livelihoods and there is a need for future plastic‐based epidermal electronics to trend toward more sustainable approaches. Infusing graphene into the culinary process of seaweed spherification produces core‐shell, food‐based nanocomposites with properties exhibiting a remarkably high degree of tunability. Unusually, mechanical, electrical, and electromechanical metrics all became decoupled from one another, allowing for each to be individually tuned. This leads to the formation of a general electromechanical model which presents a universal electronic blueprint for enhanced performances. Through this model, performance optimization and system miniaturization are enabled, with gauge factors (G) >108 for capsule diameters (D) ≈290 µm and produced at a record rate of >100 samples per second. When coalesced into quasi‐2D planar networks, microcapsules form the basis of discrete, recyclable electronic smart skins with areal independent sensitives for muscular, breathing, pulse, and blood pressure measurements in real‐time. [ABSTRACT FROM AUTHOR]

Compliant sensors have drawn considerable interests in human–robot interactions. However, it is still challenging to obtain reliable and reproducible performance at reduced costs, especially for scaled‐up sensing applications. This work investigates the piezoresistive performance of a low‐cost, scalable sensor, which is made by spray coating exfoliated graphite natural rubber latex composites (EG/latex) over an elastomeric substrate. The EG/latex sensor provides a uniform distribution in the sheet resistance (variation below 4%) over a large 10 cm × 10 cm area. The stabilized piezoresistive response under cyclic tests is found highly related to both the filler concentration and the strain region. The 8 wt% and the 10 wt% sensors show nonlinear piezoresistive response, while the 25 wt% sensor exhibits the best linearity with a high gauge factor (7.6) and the lowest hysteresis (0.043) under a maximum strain of 60%. The distinct piezoresistive behavior is found attributed to the different levels of microbreakage under the applied strain. Scalable sensing performance is demonstrated on a hand‐size glove spray‐coated with 25 wt% EG/latex. Effective localization of contacts over the continuous sensing glove is achieved via the technique of electrical impedance tomography, validating the potential of the cost‐competitive EG/latex sensor for scalable sensing applications. [ABSTRACT FROM AUTHOR]

Touch serves as an important medium for human–environment interaction. The piezoresistive tactile sensor has attracted much attention due to its convenient technology, simple principle, and convenient signal acquisition and analysis. In this paper, conductive beads-on-string polyvinyl alcohol (PVA)/polyaniline doped with dodecyl benzene sulfonic acid (PANI-DBSA) nanofibers were fabricated via the electrospinning technique. Due to the special nanostructure of PVA-coated PANI-DBSA, the tactile sensor presented a wide measuring range of 12 Pa–121 kPa and appreciable sensitivity of 8.576 kPa−1 at 12 Pa~484 Pa. In addition, the response time and recovery time of the sensor were approximately 500 ms, demonstrating promising prospects in the field of tactile sensing for active upper limb prostheses.

The development of a high-performance, low-cost, and simply fabricated flexible three-dimensional (3D) force sensor is essential for the future development of electronic skins suitable for the detection of normal and shear forces for several human motions. In this study, a sandwich-structured flexible 3D force tactile sensor based on a polyethylene-carbon composite material (velostat) is presented. The sensor has a large measuring range, namely, 0–12 N in the direction of the normal force and 0–2.6 N in the direction of the shear force. For normal forces, the sensitivity is 0.775 N−1 at 0–1 N, 0.107 N−1 between 1 and 3 N, and 0.003 N−1 at 3 N and above. For shear forces, the measured sensitivity is 0.122 and 0.12 N−1 in x- and y-directions, respectively. Additionally, the sensor exhibits good repeatability and stability after 2500 cycles of loading and releasing. The response and recovery times of the sensor are as fast as 40 and 80 ms, respectively. Furthermore, we prepared a glove-like sensor array. When grasping the object using the tactile glove, the information about the force applied to the sensing unit can be transmitted through a wireless system in real-time and displayed on a personal computer (PC). The prepared flexible 3D force sensor shows broad application prospects in the field of smart wearable devices.

Three-dimensional flexible piezoresistive porous sensors are of interest in health diagnosis and wearable devices. In this study, conductive porous sensors with complex triply periodic minimal surface (TPMS) structures were fabricated using the 3D printed sacrificial mold and enhancement of MWCNTs. A new curing routine by the self-resistance electric heating was implemented. The porous sensors were designed with different pore sizes and unit cell types of the TPMS (Diamond (D), Gyroid (G), and I-WP (I)). The impact of pore characteristics and the hybrid fabrication technique on the compressive properties and piezoresistive response of the developed porous sensors was studied. The results indicate that the porous sensors cured by the self-resistance electric heating could render a uniform temperature distribution in the composites and reduce the voids in the walls, exhibiting a higher elastic modulus and a better piezoresistive response. Among these specimens, the specimen with the D-based structure cured by self-resistance electric heating showed the highest responsive strain (61%), with a corresponding resistance response value of 0.97, which increased by 10.26% compared to the specimen heated by the external heat sources. This study provides a new perspective on design and fabrication of porous materials with piezoresistive functionalities, particularly in the realm of flexible and portable piezoresistive sensors.

The composites with multiple types of nano-carbon fillers have better electrical conductivity and piezoresistive properties as compared with composites with a single type of nano-carbon fillers. As previously reported, the nano-carbon fillers with various aspect ratios, such as carbon nanotube (CNT) and carbon black (CB), have synergistic enhanced effects on the piezoresistive performance of composite sensors. However, most of the works that have been reported are experimental investigations. The efficient and usable numerical simulation investigation needs to be further developed. In this study, based on an integrated 3D statistical resistor network model, a numerical simulation model was created to calculate the piezoresistive behavior of the CNT/CB/ Polyvinylidene Fluoride (PVDF) composite. This model also takes into account the tunneling effect between nearby nano-fillers. It is found from numerical simulation results that the piezoresistive sensitivity of composite simulation cells can be influenced by the fraction of CNT and CB. In the case that the CNT content is 0.073 wt.%, the best force-electrical piezoresistive sensitivity can be achieved when the CB loading is up to 0.2 wt.%. To verify the validity of the simulation model, the previous experimental investigation results are also compared. The experimental results confirm the validity of the model. The investigation is valuable and can be utilized to design a strain sensor for this nano-composite with increased sensitivity. [ABSTRACT FROM AUTHOR]

The longstanding demands for micropressure detection in commercial and industrial applications have led to the rapid development of relevant sensors. As a type of long-term favored device based on microelectromechanical system technology, the piezoresistive micropressure sensor has become a powerful measuring platform owing to its simple operational principle, favorable sensitivity and accuracy, mature fabrication, and low cost. Structural engineering in the sensing diaphragm and piezoresistor serves as a core issue in the construction of the micropressure sensor and undertakes the task of promoting the overall performance for the device. This paper focuses on the representative structural engineering in the development of the piezoresistive micropressure sensor, largely concerning the trade-off between measurement sensitivity and nonlinearity. Functional elements on the top and bottom layers of the diaphragm are summarized, and the influences of the shapes and arrangements of the piezoresistors are also discussed. The addition of new materials endows the research with possible solutions for applications in harsh environments. A prediction for future tends is presented, including emerging advances in materials science and micromachining techniques that will help the sensor become a stronger participant for the upcoming sensor epoch. [ABSTRACT FROM AUTHOR]

Metal core piezoelectric fiber (MPF) with excellent dynamic force response performance is a promising coaxial fiber, but its application in numerous occasions requiring simultaneous detecting of static and dynamic forces is limited due to its inability to detect static forces. To overcome this problem, this paper proposes a novel double-layer electrowetting-aided spinning to produce a metal-core piezoelectric piezoresistive composite fiber (MPPCF). The MPPCF is composed of seven layers from inside to outside including a metal core, a polyimide (PI) layer, a poly(vinylidene-trifluoro-ethylene) (P(VDF-TrFE)) layer, a poly(chloro-p-xylylene) (Parylene C) layer, a middle sliver paste layer, a multi-walled carbon nanotubes (MWCNT)-polyurethane (PU) layer and an outside silver paste layer. The results show that MPPCF with good coaxial structure and surface morphology can be prepared by this technology. After testing, the MPCCF is sensitive to the dynamic force excited by vibration and the static force caused by bending. [ABSTRACT FROM AUTHOR]

Frequently, early detection of a malignant condition prevents most premature deaths. In this paper, three new designs are proposed for the microcantilever-based biosensor to detect carcinoembryonic antigen (CEA) tumor biomarkers. CEA is used for several types of human cancers, e.g., lung cancer, pancreatic cancer, breast cancer, ovarian cancer, and gastric cancer, particularly colorectal cancer. The proposed models are designed and the finite element method (FEM) analysis of these biosensors is performed using a COMSOL 5.4 Multiphysics (commercial package) software. Various analyses and comparisons are carried out by utilizing the designs in terms of displacement as well as piezo-resistive output due to an increase in mass of CEA adsorbed onto the surface of the cantilever beam, which is stimulated by applying a pressure range of 0 to 0.2 Pa on to the surface of a cantilever beam. A simulation is performed with the proposed designs by experimenting with different materials for better deflection results. Regarding the results obtained, Design 3, made with Kynar710, gives the highest total deflection of 0.7328 μm. However, a piezo-resistive readout technique is utilized to get the output in mV, and for that, p-silicon (single-crystal, lightly doped) material is used, respectively. Next, 5V is applied to the terminals of the piezo-resistive circuit. Based on the input applied pressure and output mV, the Design 3 made with Kynar710 gives a better sensitivity of 0.13089 [mV/V/Pa] compared to other designs made with other materials. [ABSTRACT FROM AUTHOR]

By virtue of their wide applications in transportation, healthcare, smart home, and security, development of sensors detecting mechanical stimuli, which are many force types (pressure, shear, bending, tensile, and flexure) is an attractive research direction for promoting the advancement of science and technology. Sensing capabilities of various force types based on structural design, which combine unique structure and materials, have emerged as a highly promising field due to their various industrial applications in wearable devices, artificial skin, and Internet of Things (IoT). In this review, we focus on various sensors detecting one or two mechanical stimuli and their structure, materials, and applications. In addition, for multiforce sensing, sensing mechanism are discussed regarding responses in external stimuli such as piezoresistive, piezoelectric, and capacitance phenomena. Lastly, the prospects and challenges of sensors for multiforce sensing are discussed and summarized, along with research that has emerged. [ABSTRACT FROM AUTHOR]

It is necessary to recognize the human knee movement for patients with knee joint pain (arthritis) and also in patients' under-recovery. Pressure variation around the knee joint is considered as a piece of vital information to address the problems in knee joint. Wearable sensors are the generally appropriate procedure for this. In this work, sensing mechanism are arranged in a suitable patella package using CNF (Carbon Nano Fiber) and TPU (Thermoplastic Polyurethane) based nanocomposite piezo-resistive (20% w/w) sensor film with bulk resistivity of 192Ω-cm. It is further tested for its suitability for monitoring the change in the resistance due to pressure variation during knee movement. The reliability of voltage variation under rehashed compressive stacking lab experiments shows significant usage for this piezoresistive film. Hence, it can be effectively utilized for signal acquisition application for knee movement monitoring in the arthritis patients. [ABSTRACT FROM AUTHOR]

Magneto-sensitive elastomer (MSE) samples were fabricated by dispersing carbonyl iron particles into a rubber matrix. Velostat, which can be regarded as a pressure-sensitive material with piezoresistive properties, and the prepared MSE were selected to design a composite structure, referred to as a magnetic field detection unit (MFDU). The magneto-induced properties of the MFDU were investigated by using a self-built experimental system, and the effect of the constant and dynamic magnetic fields were studied. This MFDU can generate an output voltage signal in response to the magneto-induced resistance using an external DC power supply. It was found that the relationship between the normal force of the MSE and the magnetic field, and the resistance of Velostat can be changed by the magneto-induced normal force in the MFDU. The experimental results also proved that the output voltage of the MFDU is almost linearly dependent on the constant magnetic field and exhibits loading and unloading hysteretic time of about 20 ms and 40 ms, respectively, for the magnetic-induced output under a step magnetic field. Moreover, the obvious frequency-dependent output amplitude was observed under a pulsed magnetic field, and the possible mechanism for the magneto-sensitive performance of the MFDU was proposed and analyzed. The MFDU exhibited a stable response and good magneto-sensitive performance, which provides an approach for detecting external magnetic field. [ABSTRACT FROM AUTHOR]

Polymeric foams, embedded with nano-scale conductive particles, have previously been shown to display quasi-piezoelectric (QPE) properties; i.e., they produce a voltage in response to rapid deformation. This behavior has been utilized to sense impact and vibration in foam components, such as in sports padding and vibration-isolating pads. However, a detailed characterization of the sensing behavior has not been undertaken. Furthermore, the potential for sensing quasi-static deformation in the same material has not been explored. This paper provides new insights into these self-sensing foams by characterizing voltage response vs frequency of deformation. The correlation between temperature and voltage response is also quantified. Furthermore, a new sensing functionality is observed, in the form of a piezoresistive response to quasi-static deformation. The piezoresistive characteristics are quantified for both in-plane and through-thickness resistance configurations. The new functionality greatly enhances the potential applications for the foam, for example, as insoles that can characterize ground reaction force and pressure during dynamic and/or quasi-static circumstances, or as seat cushioning that can sense pressure and impact. [ABSTRACT FROM AUTHOR]

To improve the shock-resistance of piezoresistive high-g accelerometer, we propose a design of piezoresistive high-g accelerometer. The accelerometer employs special-shaped proof masses system with a cross gap. Four tiny sensing beams are bonded above the cross gap. The expression of the deformation, natural frequency and damping is deduced, and the structural parameters are optimized. The accelerometer structure is simulated and verified by finite element method (FEM) simulation. The results show that the range of the accelerometer can reach 200,000 g, the natural frequency is 453.6 kHz, and the cross-axis sensitivity of X-axis and Y-axis is 0.25% and 0.11%, respectively, which can apply to the measurement of high shock. Contrastively, the crossaxis sensitivity of X-axis and Y-axis is respectively, reduced by 93.2% and 96.9%. The sensitivity of our accelerometer is 0.88 µV/g. It is of great value for the application of piezoresistive high-g accelerometer with high shock-resistance. [ABSTRACT FROM AUTHOR]

The substrate impurities scattering will lead to unstable temperature-sensitive behavior and poor linearity in graphene temperature sensors. And this can be weakened by suspending the graphene structure. Herein, we report a graphene temperature sensing structure, with suspended graphene membranes fabricated on the cavity and non-cavity SiO2/Si substrate, using monolayer, few-layer, and multilayer graphene. The results show that the sensor provides direct electrical readout from temperature to resistance transduction by the nano piezoresistive effect in graphene. And the cavity structure can weaken the substrate impurity scattering and thermal resistance effect, which results in better sensitivity and wide-range temperature sensing. In addition, monolayer graphene is almost no temperature sensitivity. And the few-layer graphene temperature sensitivity, lower than that of the multilayer graphene cavity structure (3.50%/°C), is 1.07%/°C. This work demonstrates that piezoresistive in suspended graphene membranes can effectively enhance the sensitivity and widen the temperature sensor range in NEMS temperature sensors. [ABSTRACT FROM AUTHOR]

Piezoresistive pressure sensors have transformed biomedical applications, enabling precise diagnostics and monitoring. This concise review explores the fundamental principles, key components, and fabrication techniques of piezoresistive pressure sensors, focusing on critical performance metrics such as sensitivity, accuracy, and response time. Biomedical design challenges, including biocompatibility and long-term stability, are examined, offering insights into solutions for optimal sensor integration. In diverse biomedical applications, piezoresistive pressure sensors play pivotal roles, from blood pressure monitoring to implantable medical devices. The paper emphasizes their versatility in enhancing patient care through continuous and accurate monitoring. Looking forward, the review discusses emerging trends and potential research directions, positioning piezoresistive pressure sensors as central contributors to the future of biomedical technology, promising improved patient outcomes and advanced healthcare delivery through precise and continuous monitoring.

This paper presents a ceramic stress sensor with the dimension of a coin, able to measure the compressive force (stress) applied to its two round faces. The sensor is designed and engineered to be embedded inside concrete or masonry structures, like bridges or buildings. It provides good accuracy, robustness, and simplicity of use at potentially low cost for large-scale applications in civil structures. Moreover, it can be calibrated temperature compensated, and it is inherently hermetic, ensuring the protection of sensitive elements from the external environment. It is, therefore, suitable for operating in harsh and dirty environments like civil constructions. The sensor directly measures the internal stress of the structure, exploiting the piezo resistivity of thick film ink based on ruthenium oxide. It is insensitive with respect to the stiffness of the embedding material and the variation of the surrounding material properties like concrete hardening, shrinkage, and creep as it decouples the two components of stress.

The use of fiber-reinforced composite materials has widely spread in various sectors, including aerospace, defense, and civil industry. The assessment of these heterogeneous material systems is important for safer and risk-free applications and has contributed to the need for self-sensing composites. This work is focused on the development of piezoresistive composites, the prediction of their performance and structural health monitoring (SHM). Additionally, this work unpacks the complexity of carbon nanotubes (CNTs) micro-fabrication and the development of piezoresistive and electromagnetic (EM) waves detection electrodes. Scanning electron microscopy (SEM) was used to characterize the CNTs structure and morphologies. The manufactured CNTs were incorporated in epoxy systems to fabricate glass fiber reinforced polymer (GFRP)-CNTs smart composites with piezoresistive properties. The detection of micro-damage onset and its progression was carried out in mode I, to evaluate the sensitivity of the smart composites to damage development. The change in electrical conductivity of the nanotubes-reinforced composite systems due to localized mechanical strains enabled crack propagation detection. The relationship between crack propagation, fracture toughness, and electrical resistivity of the smart composite was analyzed.

Abstract Precise sensing of pressure is essential for various mechanical and electrical systems. The recent emergence of flexible pressure sensors has enabled novel applications, such as human–machine interfaces, soft robotics, and wearable devices. Specifically, the piezoresistive sensing scheme is widely adapted for flexible pressure sensors as it is simple and exhibits outstanding measurement sensitivity and stability. The sensing properties of piezoresistive pressure sensors mainly depends on the materials and contact morphologies at the interface. This paper proposes a flexible pressure sensor based on multi-height microstructures in which the measurement sensitivity and detection range are tunable. Such tunability is due to the sequential contact of micropyramids with different heights. The multi-height micropyramid structured PDMS layer with stamp-coated multi-walled carbon nanotubes (MWCNTs) acts as a conductive active layer and a gold interdigitated electrode (IDE) patterned polyimide (PI) layer works as the bottom electrode. The fabricated sensor exhibits a sensitivity of 0.19 kPa−1, a fast response speed of 20 ms, and a detection range of up to 100 kPa. The sensor is applied to a robotic gripper for object recognition and integrated into a shoe to track walking motions.

Pressure sensors are widely employed in various fields from biomedical to aerospace engineering. Each field requires pressure sensors with specific sensitivity, response time, recovery time, durability, and detection limit. However, developing pressure sensors that meet the increasing demands of high mechanical strength and sensitive electrical responsiveness influencing reliability and accuracy still remains challenging. Herein, a highly robust and resilient piezoresistive sensor was developed by combining elongated amyloid fibrils (eAFs) aerogel made of a self-assembly protein of α-synuclein, which provided stable porous 3D interconnected network and thus increased surface area, and multi-walled carbon nanotube (MWCNT) as a reinforcement material for improved mechanical and electrical properties. Owing to the integration between eAFs aerogel and MWCNT, the MWCNT-embedded eAFs aerogel exhibited augmentation in mechanical strength and resiliency depending on the amount of MWCNT introduced. Additionally, the MWCNT-embedded eAFs aerogel showed piezoresistive properties with stable pressure sensing capability toward human motions, airflow, and underwater pressure. It is, therefore, suggested that the pressure sensor fabricated with the eAFs aerogel containing MWCNT could be utilized in diverse areas including wearable device and artificial skin development. [Display omitted] • MWCNTs were uniformly embedded into the eAFs aerogel due to the high adsorption property of the eAFs aerogel. • The fabricated MWCNT-embedded eAFs aerogel exhibited high mechanical strength of robustness and resilience • The fabricated MWCNT-embedded eAFs aerogel exhibited stable and sensitive piezoresistive sensing property. • Pressure sensor exhibited dexterous performance on precisely recognizing different pressure levels. [ABSTRACT FROM AUTHOR]