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Soft strain sensors can accurately monitor the deformation of irregular and dynamic surfaces. However, traditional thin‐film strain sensors are generally not direction‐specific, and the sensor becomes unpredictable when stretched in different directions simultaneously. Here, a soft 1D strain sensor is reported that is only sensitive to axial deformation by rolling up a thin‐film strain sensor based on liquid metals (LM) and thermoplastic polyurethane (TPU) elastomer. The sensitivity of the 1D sensor can be regulated by rolling the 2D sensor at different angles. The 1D strain sensors have a large strain measuring range (>100%), high strain resolution (0.5%), fast responsiveness (<40 ms), and high reproducibility (over 2000 cycles), which are expected to adapt to various application scenarios with different sensitivity requirements. In addition, 1D strain sensors with different sensitivities can be braided into a three‐strand braid to provide measurements with three different sensitivities at the same time. [ABSTRACT FROM AUTHOR]

Non-contact and full-field strain mapping captures strain across an entire surface, providing a complete two-dimensional (2D) strain distribution without attachment to sensors. It is an essential technique with wide-ranging applications across various industries, significantly contributing to experimental mechanics and structural health monitoring. Although there have been reviews that focus on specific methods, such as interferometric techniques or carbon nanotube-based strain sensors, a comprehensive comparison that evaluates these diverse methods together is lacking. This paper addresses this gap by focusing on strain mapping techniques specifically used in experimental mechanics and structural health monitoring. The fundamental principles of each method are illustrated with specific applications. Their performance characteristics are compared and analyzed to highlight strengths and limitations. The review concludes by discussing future challenges in strain mapping, providing insights into potential advancements and developments in this critical field. [ABSTRACT FROM AUTHOR]

Flexible strain sensors are of great significance in health monitoring, wearable electronic devices, intelligent robot sensing, and other fields. Most of the reported works focus on the enhancement of sensitivity or working range, while linearity is ignored and exhibits strong nonlinearity. Conflict among performances remains a serious challenge for the development of flexible strain sensors. Herein, inspired by the architecture of butterfly's wings, a strain sensor with double conductive layers and wrinkles/holes structures is proposed. The fabricated sensor shows a high linearity of >0.98 over a full working strain range of 120%, and a linearity of up to 0.999 within a strain range of 0%–30%. Apart from that, the sensor also presents a sensitivity of 8.28, high stability over 40 000 cycles when subjected to a full‐scale strain, as well as a water contact angle of >167.4°. Meanwhile, strains as low as 0.075% can be identified, while a maximum frequency of 40 Hz can be responded to for the sensor. It is demonstrated that the sensor is capable of enabling flexible grippers to sense and monitor the motions of underwater vehicles, indicating its greater potential for diverse applications, such as human–machine interaction, marine environmental protection, and biological research. [ABSTRACT FROM AUTHOR]

A robust strain sensor is demonstrated based on a microfiber Mach–Zehnder interferometer (MMZI) encapsulated by the polymer polydimethylsiloxane (PDMS). Benefiting from the low Young's modulus of PDMS, both a robust structure and high sensitivity can be realized based on three different encapsulations. In the experiment, the proposed sensors are fabricated and tested with strain sensitivities ranging from −20.95 pm/με to 127.00 pm/με within the wavelength range of 1200–1650 nm. Compared with the bare MMZI sensor, at least one order of magnitude higher sensitivity is reached. To further evaluate the performance of the sensor, the dependences of sensitivity on probing wavelength and the different types and quantities of polymers used in encapsulation are discussed. Results show that the sensitivity of the sensor will increase with the probing wavelength. The type and quantity of polymer used are also very critical to sensitivity. Additionally, a response time of 24.72 ms can be reached. Good recoverability and repeatability of the sensor are also demonstrated by repeated experiments. The strain sensor demonstrated here shows the advantages of simple fabrication, robust structure, high and tunable sensitivity, fast response, good recoverability and repeatability. [ABSTRACT FROM AUTHOR]

Fiber‐based multimodal sensors with electrical/optical signals are highly desired for next‐generation wearable electronics. Despite the remarkable progress in this area, achieving large‐scale knittable, washable, and self‐healing performance in fiber‐based multimodal sensors simultaneously remains a great challenge. Here, a smart fiber capable of exhibiting piezoresistive/luminescent properties based on an H‐bonding connected multilayered core–shell nanostructure is developed. The core principle of this design involves constructing strong interfacial interactions between the fiber layers, which results in a sensor with high sensitivity (gauge factor = 12383500), exceptional water resistance, and robust self‐healing properties (tensile strength 30.9 MPa, healing efficiency 72.9%). Unlike traditional fiber‐based sensors where elaborate nanostructures are prone to shedding during knitting, this strategy enables the fiber sensors with excellent knittability to be patterned in the fabric, improving both optical and electrical sensitivities. This work is anticipated to make a significant contribution to the further development of wearable electronic products and visual human–computer interaction electronic devices. [ABSTRACT FROM AUTHOR]

With favorable properties of stretchability, stitchability, and potential to be woven into a fabric, thread-based sensors have gained considerable interest for wearable devices for smart and connected health applications. To facilitate wearable applications, an easy and reliable way to fabricate these thread-based sensors with good performance and consistency is the key while manufacturing these smart threads. In this paper, we propose an automated thread-coating system that can fabricate thread-based strain sensors with controlled parameters. The platform uses integrated sensors for controlled manufacturing of the threads in a highly compact structure that consists of an innovative tension sensor and a closed-loop thermal management system. Using this new system, a sample thread with a gauge factor of 1.47 and tension sensitivity of 32.64 K Ω /N is prepared. Compared with hand-coated thread, the machine-fabricated thread shows much better sensitivity and consistency. The prepared strain sensor is made into a respiration sensor patch and a limb motion patch to demonstrate its application. [ABSTRACT FROM AUTHOR]

Highly performance flexible strain sensor is a crucial component for wearable devices, human‐machine interfaces, and e‐skins. However, the sensitivity of the strain sensor is highly limited by the strain range for large destruction of the conductive network. Here the quasi‐1D conductive network (QCN) is proposed for the design of an ultra‐sensitive strain sensor. The orientation of the conductive particles can effectively reduce the number of redundant percolative pathways in the conductive composites. The maximum sensitivity will reach the upper limit when the whole composite remains only "one" percolation pathway. Besides, the QCN structure can also confine the tunnel electron spread through the rigid inclusions which significantly enlarges the strain‐resistance effect along the tensile direction. The strain sensor exhibits state‐of‐art performance including large gauge factor (862227), fast response time (24 ms), good durability (cycled 1000 times), and multi‐mechanical sensing ability (compression, bending, shearing, air flow vibration, etc.). Finally, the QCN sensor can be exploited to realize the human‐machine interface (HMI) application of acoustic signal recognition (instrument calibration) and spectrum restoration (voice parsing). [ABSTRACT FROM AUTHOR]

The application of gel wearable sensors in aquatic environments is very promising, however, the preparation of underwater gel sensors with excellent anti‐swelling properties and sensing performance remains a great challenge. In this paper, a solvent exchange strategy is proposed to fabricate an anti‐swelling gel, in which the hydrophobic segments are induced to gather and microphase separation occurs inside the gel. The prepared gel possesses excellent anti‐swelling performance (swelling ratio of 4.79%), good mechanical properties (tensile strain of 712%), high sensitivity (GF = 1.07), and high linearity (R2 = 0.998, 0 to 70% strain range). Moreover, it can achieve high stability (more than 90 days) and fatigue resistance (1000 cycles at 50% strain) as an underwater sensor. Therefore, the designed underwater gel strain sensors can be utilized for monitoring human motion information, underwater distress and smart alarms, revealing the great potential application in the field of underwater strain sensors. [ABSTRACT FROM AUTHOR]

Purpose: This paper aims to provide a new method to study and improve the dynamic characteristics of the four-column resistance strain force sensor through the elastomer structure design and optimization. Design/methodology/approach: Based on the mechanism analysis method, the authors first present a dynamic characteristic model of the four-column resistance strain force sensors' elastomer. Then, the authors verified and modified the model according to the Solidworks finite element simulation results. Finally, the authors designed and optimized two types of four-column elastomers based on the dynamic characteristic model and verified the improvement of sensor dynamic performance through a hammer knock dynamic experiment. Findings: The Solidworks finite element simulation and hammer knock dynamic experiment results show that the relative error of the model is less than 10%, which confirms the accuracy of the model. The dynamic performance of the sensors based on the model can be improved by more than 30%, which is a great improvement in sensor dynamic performance. Originality/value: The authors first present a dynamic characteristic model of the four-column elastomer and optimize the four-column sensors successfully based on the mechanism analysis method. And a new method to study and improve the dynamic characteristics of the resistance is provided. [ABSTRACT FROM AUTHOR]

We demonstrated the feasibility of obtaining a low-cost, flexible strain sensor by spraying a conductive thin layer of MWCNT's over an S-pattern embedded within a PDMS matrix. The final composite conforms a dog bone-shaped tensile specimen intended to measure the strain associated with a human wrist extension movement. Our sensor works with a combination of different mechanisms, such as piezoresistivity and tunneling, which depend on the level and repetitions of loads applied to the sensor. According to the reported elongation ratios, these sensors can detect large strains, up to 40%, for several uniaxial loading-unloading cycles. This makes them useful for human skin strain measurements. [ABSTRACT FROM AUTHOR]

Conventional optical fiber temperature/strain sensors often have to make compromises between the resolution and the dynamic range. Here we present a new method that meets the measurement requirements for both high resolution and large dynamic range. A high-quality optical fiber Fabry-Perot Interferometer (FPI) constructed using a pair of chirped fiber Bragg gratings is employed as the sensor and a dual-mode direct spectrum interrogation method is proposed to identify the small drift of external temperature or strain. As a proof-of-concept illustration, a temperature resolution of 0.2 °C within 30–130 °C is demonstrated. For strain sensing, the resolution can be 10 µε within 0–1000 µε. The measurement resolution can be improved further by routinely increasing the reflectivity of the CFBG and the cavity length and the sensor can also be mass-produced. This new sensing schema not only resolves the conflict between the resolution and the dynamic range of fiber-optic temperature/strain sensors but can also be extended to other sensors and measurands. [ABSTRACT FROM AUTHOR]

Many studies on flexible strain and pressure sensors have been reported due to growing interest in wearable devices for healthcare purposes. Here, we present flexible pressure and strain (motion) sensors prepared with only graphene oxide (GO) and commercial silk fabrics and yarns. The pressure sensors were fabricated by simply dipping the silk fabric into GO solution followed by applying a thermal treatment at 400 °C to obtain reduced GO (rGO). The pressure sensors were made from rGO-coated fabrics, which were stacked in three, five, and seven layers. A super-sensitivity of 2.58 × 103 kPa−1 at low pressure was observed in the seven-layer pressure sensor. The strain sensors were obtained from rGO-coated twisted silk yarns whose gauge factor was 0.307. Although this value is small or comparable to the values for other sensors, it is appropriate for motion sensing. The results of this study show a cost-effective and simple method for the fabrication of pressure and motion sensors with commercial silk and GO. [ABSTRACT FROM AUTHOR]

In recent years, there has been growing interest in the development of metal-free, environmentally friendly, and cost-effective biopolymer-based piezoelectric strain sensors (bio-PSSs) for flexible applications. In this study, we have developed a bio-PSS based on pure deoxyribonucleic acid (DNA) and curcumin materials in a thin-film form and studied its strain-induced current-voltage characteristics based on piezoelectric phenomena. The bio-PSS exhibited flexibility under varying compressive and tensile loads. Notably, the sensor achieved a strain gauge factor of 407 at an applied compressive strain of −0.027%, which is 8.67 times greater than that of traditional metal strain gauges. Furthermore, the flexible bio-PSS demonstrated a rapid response under a compressive strain of −0.08%. Our findings suggest that the proposed flexible bio-PSS holds significant promise as a motion sensor, addressing the demand for environmentally safe, wearable, and flexible strain sensor applications. [ABSTRACT FROM AUTHOR]

This research has developed a fabricating process of thin‐strain sensor by utilizing wafer‐level‐packaging (WLP) techniques. The thickness of sensor makes thinner, its performance is able to highly increase. However, the thinner sensor was fragile, and so it was difficult to handle in post processes. Thus, a thin sensor with lid by utilizing WLP techniques, which is tough to break even when handled, is proposed in this research. More than 250‐µm‐deep grooves were fabricated around the lid by deep reactive ion etching. After the lid substrate was bonded on the sensor substrate with a resin, the sensor and lid substrates were respectively polished to 50 and 200 µm thickness. The lids were released along the grooves, and the 50‐µm‐thick strain sensors were able to be fabricated by utilizing WLP techniques. This sensor was used as a diaphragm to measure pressure. The sensors were assembled on a stainless steel housing without breakage. The performance of the developed sensor was almost showed with a conventional pressure sensor. [ABSTRACT FROM AUTHOR]

Bio‐compatible strain sensors are indispensable for human monitoring devices, requiring a delicate balance of robustness, flexibility, and sensitivity. However, achieving these attributes concurrently remains a formidable challenge. This article presents a pioneering approach to fabricate three‐dimensional flexible strain sensors using laser‐induced graphene (LIG) on polyimide (PI) substrates. Through a one‐step laser direct writing (LDW) technique, durable LIG/CuSO4 composites with closed‐pore porous structures are synthesized. The integration of copper sulfate within the closed‐cell architecture of LIG establishes a resilient conducting pathway, enhancing sensitivity to deformation under tensile stress. The resulting sensor exhibits exceptional performance in monitoring a wide range of human movements, from vigorous activities to subtle oscillations and physiological signals. Notably, the sensor boasts a remarkable sensing range of up to 25% strain, coupled with a high sensitivity characterized by a gauge factor of approximately 597. Rapid response times of 175 ms and quick recovery times of 200 ms further underscore its efficiency. Moreover, the sensor demonstrates outstanding stability and durability, maintaining consistent performance over 5600 cyclic experiments. This innovative approach represents a significant advancement in bio‐compatible strain sensor technology, offering a versatile solution for diverse monitoring applications. [ABSTRACT FROM AUTHOR]

This paper comprehensively reviews sensors and sensing devices developed or/and proposed so far utilizing two smart materials: electrorheological fluids (ERFs) and magnetorheological materials (MRMs) whose rheological characteristics such as stiffness and damping can be controlled by external stimuli; an electrical voltage for ERFs and a magnetic field for MRMs, respectively. In this review article, the MRMs are classified into magnetorheological fluids (MRF), magnetorheological elastomers (MRE) and magnetorheological plastomers (MRP). To easily understand the history of sensing research using these two smart materials, the order of this review article is organized in a chronological manner of ERF sensors, MRF sensors, MRE sensors and MRP sensors. Among many sensors fabricated from each smart material, one or two sensors or sensing devices are adopted to discuss the sensing configuration, working principle and specifications such as accuracy and sensitivity. Some sensors adopted in this article include force sensors, tactile devices, strain sensors, wearable bending sensors, magnetometers, display devices and flux measurement sensors. After briefly describing what has been reviewed in a conclusion, several challenging future works, which should be undertaken for the practical applications of sensors or/and sensing devices, are discussed in terms of response time and new technologies integrating with artificial intelligence neural networks in which several parameters affecting the sensor signals can be precisely and optimally tuned. It is sure that this review article is very helpful to potential readers who are interested in creative sensors using not only the proposed smart materials but also different types of smart materials such as shape memory alloys and active polymers. [ABSTRACT FROM AUTHOR]

Screen sensors are the most commonly used human-machine interfaces in our everyday life, which have been extensively applied in personal electronics like cellphones. Touchless screen sensors are attracting growing interest due to their distinct advantages of high interaction freedom, comfortability, and hand hygiene. However, the material compositions of current touchless screen sensors are rigid and fragile, hardly meeting the needs of wearable and stretchable on-skin electronics development. Additionally, these touchless screen sensors are also restricted by high power consumption, limited gesture types of recognition, and the requirement of light conditions. Here, we report a stretchable on-skin touchless screen sensor (OTSS) enabled by an ionic hydrogel-based triboelectric nanogenerator (TENG). Compared with current touchless screen sensors, the OTSS is stretchable, self-powered, and competent to recognize diverse gestures by making use of charges naturally carried on fingers without the need of sufficient light conditions. An on-skin noncontact screen operating system is further demonstrated on the basis of the OTSS, which could unlock a cellphone interface in touchless operation mode on the human skin. This work for the first time introduces the on-skin touchless concept to screen sensors and offers a direction to develop new-generation screen sensors for future cellphones and personal electronics. [ABSTRACT FROM AUTHOR]

With the rapid advancement of modern technology, flexible and wearable electronics, particularly electromechanical sensors, have gained considerable attention for motion‐based applications in medical health monitoring and artificial intelligence. Correspondingly, extensive efforts have been dedicated to enhancing their performance and practicality. Electromechanical sensors based on functional composites and structures accurately detect and monitor the body, generating the corresponding output signals. However, there are several limitations in manufacturing composite sensors, such as the selection and combination of functional materials, geometrical structures, constructed conductive pathways, stability of output signals, and operational lifetime. Thus, this review summarizes notable trends in the electromechanical sensors using functional composites and structures. This also provides an overview of different types of electromechanical pressure and strain sensors, exploring their operational mechanisms regarding triboelectricity, piezoelectricity, piezocapacitance, and piezoresistivity. The unique characteristics of functional materials, including conductive polymers, nanostructured metals, and carbon nanomaterials and composites, are analyzed alongside various design concepts for highly flexible and stretchable sensors. Furthermore, potential applications concerning human motion and human–machine interfaces are also recommended. Additionally, several future outlooks are reviewed for insights into future prospects and strategies. Thus, this review can assist readers in understanding current electromechanical devices more accurately. [ABSTRACT FROM AUTHOR]

With the development of society, the demand for smart coatings is increasing. The development of flexible strain sensors using block copolymer self-assembled ionic gel materials provides a promising method for promoting the development of smart coatings. The ionic liquid in the ionic part of the material is crucial for the performance of the sensor. In this study, the structural changes within FDA/dEAN (self-assembly of acrylated Pluronic F127 (F127-DA) in partially deuterated ethylammonium nitrate (dEAN)) triblock copolymer ionic gel during uniaxial tensile flow were characterized using an in situ SAXS technique. The results revealed that the characteristics of the responses of the ionic gel to strain resistance were intricately linked to the evolution of its microstructure during the tensile process. At low levels of strain, the face-centered cubic lattice arrangement of the micelles tended to remain unchanged. However, when subjected to higher strains, the molecular chains aligned along the stretching direction, resulting in a more ordered structure with reduced entropy. This alignment led to significant disruption in bridging structures within the material. Furthermore, this research explored the impact of the stretching rate on the relaxation process. It was observed that higher stretching rates led to decreases in the average relaxation time, indicating rate dependence in the microstructure's behavior. These findings provide valuable insights into the behavior and performance of flexible strain sensors based on ionic gel materials in smart coatings. [ABSTRACT FROM AUTHOR]

Dexterity and perceptual abilities of the hand are crucial in virtual reality (VR) interactions. This necessitates haptic gloves capable of accurately measuring finger movements and ensuring comfort, a challenging combination that demands both high sensitivity and stretchability. A flexible sensor fabricated from semi‐solid material CNTs‐Inkpad composed of carbon nanotubes (CNTs) mixed with silica gel is proposed and its real‐time response can be achieved by controlling the ratio. Its semi‐solid form harnesses CNTs' high conductivity and sensitivity, avoiding structural cracking in solid CNTs during extensive stretching, thus the semi‐solid form can adapt to various hand gestures. This mechanism enables the CNTs‐Inkpad to function as strain sensors with high gauge factors (GF = 16.99) and high extensibility (350%). By integrating ten CNTs‐Inkpad sensors and five vibrators, a thin and lightweight haptic glove is developed with high sensitivity and stretchability. The glove enables collaborative measurement of all finger joints required for typical gestures in VR interactions, suitable for motion detection and haptic feedback. [ABSTRACT FROM AUTHOR]

This study describes a novel stretchable and very sensitive strain gauge enabled by laser‐joining carbon nanotubes, resulting in unique architectures forming macroscopic web networks. The stiffness of the resistive strain sensor created by laser material patterning is reduced significantly, from 1.5824 to 0.142 kN m−1, corresponding to a change in laser power from 0 to 0.436 W. Many benefits of laser‐based bonding include precise and flexible local pattern production with minimal energy impact on the flexible substrate. Furthermore, the maximum Gauge factor of the sensor exhibits diverse trends with different strains, generating values of GF = 12.8 for strains less than 2.5% and GF = 165 for strains greater than 2.5% during extension‐retraction cycles. These disparities are the result of a dynamic fight between network degradation and regeneration. [ABSTRACT FROM AUTHOR]

Bolt looseness may occur on wind turbine (WT) blades exposed to operational and environmental variability conditions, which sometimes can cause catastrophic consequences. Therefore, it is necessary to monitor the loosening state of WT blade root bolts. In order to solve this problem, this paper proposes a method to monitor the looseness of blade root bolts using the sensors installed on the WT blade. An experimental platform was first built by installing acceleration and strain sensors for monitoring bolt looseness. Through the physical experiment of blade root bolts' looseness, the response data of blade sensors is then obtained under different bolt looseness numbers and degrees. Afterwards, the sensor signal of the blade root bolts is analyzed in time domain, frequency domain, and time‐frequency domain, and the sensitivity features of various signals are extracted. So the eigenvalue category as the input of the state discrimination model was determined. The LightGBM (light gradient boosting machine) classification algorithm was applied to identify different bolt looseness states for the multi‐domain features. The impact of different combinations of sensor categories and quantities as the data source on the identification results is discussed, and a reference for the selection of sensors is provided. The proposed method can discriminate four bolt states at an accuracy of around 99.8% using 5‐fold cross‐validation. [ABSTRACT FROM AUTHOR]

The one-dimensional hollow cylindrical carbon nanotube nanostructure has been crucial in advancing nanotechnology since its discovery. Carbon nanotubes have been utilized in technical fields both in their pristine form and as nanocomposites. They have been combined with various conductive and non-conductive matrices based on specific end goals. In sensing technology, remarkable progress has been made in the development of multifunctional carbon nanotube nanocomposites. Common matrices used in this context include conjugated polymers such as poly(3,4-ethylenedioxythiophene): polystyrene sulfonic acid, polyaniline, etc., along with thermoplastics like polyamide, polyurethane, etc. Within these matrices, carbon nanotubes can establish a percolation network for electron or charge transport and can also create interfacial interactions to enhance compatibility, stability, and durability. The sensing capabilities of the resulting carbon nanotube nanocomposites are influenced by their interactions with the analyte, whether it be gases/ions, biomolecules, or motion. As a result, nanocomposites have been employed in the creation of effective gas sensors, strain sensors, and biosensors. The performance of carbon nanotube sensors has been evaluated based on factors such as sensitivity, selectivity, detection limit, reproducibility, and responses to analytes. [ABSTRACT FROM AUTHOR]

Flexible paper-based force sensors have garnered significant attention for their important potential applications in healthcare wearables, portable electronics, etc. However, most studies have only used paper as the flexible substrate for sensors, not fully exploiting the potential of paper's micro-nanostructure for sensing. This article proposes a novel approach where paper serves both as the sensitive element and the flexible substrate of force sensors. Under external mechanical forces, the micro-nanostructure of the conductive-treated paper will change, leading to significant changes in the related electrical output and thus enabling sensing. To demonstrate the feasibility and universality of this new method, the article takes paper-based capacitive pressure sensors and paper-based resistive strain sensors as examples, detailing their fabrication processes, constructing sensing principle models based on the micro-nanostructure of paper materials, and testing their main sensing performance. For the capacitive paper-based pressure sensor, it achieves a high sensitivity of 1.623 kPa−1, a fast response time of 240 ms, and a minimum pressure resolution of 4.1 Pa. As for the resistive paper-based strain sensor, it achieves a high sensitivity of 72 and a fast response time of 300 ms. The proposed new method offers advantages such as high sensitivity, simplicity in the fabrication process, environmental friendliness, and cost-effectiveness, providing new insights into the research of flexible force sensors. [ABSTRACT FROM AUTHOR]

Physical sensors have emerged as a promising technology for real‐time healthcare monitoring, which tracks various physical signals from the human body. Accurate acquisition of these physical signals from biological tissue requires excellent electrical conductivity and long‐term durability of the sensors under complex mechanical deformation. Conductive polymers, combining the advantages of conventional polymers and organic conductors, are considered ideal conductive materials for healthcare physical sensors due to their intrinsic conductive network, tunable mechanical properties, and easy processing. Doping engineering has been proposed as an effective approach to enhance the sensitivity, lower the detection limit, and widen the operational range of sensors based on conductive polymers. This approach enables the introduction of dopants into conductive polymers to adjust and control the microstructure and energy levels of conductive polymers, thereby optimizing their mechanical and conductivity properties. This review article provides a comprehensive overview of doping engineering methods to improve the physical properties of conductive polymers and highlights their applications in the field of healthcare physical sensors, including temperature sensors, strain sensors, stress sensors, and electrophysiological sensing. Additionally, the challenges and opportunities associated with conductive polymer‐based physical sensors in healthcare monitoring are discussed. [ABSTRACT FROM AUTHOR]

In this post-Moore era, on-chip components have transitioned into the "more Moore" and "more than Moore" technology routes. Serving as the foundational point and data source for all intelligent devices, sensors are undergoing development for multifunctionality, systematization, and integration. However, the current micro/nano multifunctional sensor fabrication technology is not sufficiently advanced to meet the requirements of practical applications. In this study, we prepared high-precision microwire arrays as multifunctional microsensors. This microsensor exhibited a highly sensitive response to humidity and bending strain. It has a sensitivity of up to 8520% and response time as low as 0.9/3.5 s (response/recovery) over a wide range of humidity variations from 23% to 97%. In the bending strain range of −0.4–0.4%, the microsensor exhibits a gauge factor of up to 267. This multifunctional microsensor has the potential for use in integrated intelligent devices. [ABSTRACT FROM AUTHOR]

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Two‐dimensional transition metal dichalcogenides (TMDs) are needed in high‐performance piezoresistive sensors due to their strong strain‐induced bandgap modification and thereby large gauge factors. However, integrating a conventional high‐temperature chemical vapor deposition (CVD)‐grown TMD with a flexible substrate necessitates a transfer process that inevitably degrades the sensing properties of the TMDs and increases the overall fabrication complexity. We present a high‐performance piezoresistive strain sensor that employs large‐area PdSe2 films grown directly on polyimide (PI) substrates via plasma‐assisted selenization of a sputtered Pd film. The reliable strain transfer from the substrate to the PdSe2 film ensures an outstanding strain‐sensing capability of the sensor. Specifically, the sensors have a gauge factor of up to −315 ± 2.1, a response time under 25 ms, a detection limit of 8 × 10−6, and an exceptional stability of over 104 loading–unloading cycles. By attaching the sensors to the skin surface, we demonstrate their application for measuring physiological parameters in health care monitoring, including motion, voice, and arterial pulse vibration. Furthermore, using the PdSe2 film sensor combined with deep learning technology, we achieved intelligent recognition of artery temperature from arterial pulse signals with only a 2% difference between predicted and actual temperatures. The excellent sensing performance, together with the advantages of low‐temperature fabrication and simple device structure, make the PdSe2 film sensor promising for wearable electronics and health care sensing systems. [ABSTRACT FROM AUTHOR]

Individuals living with cognitive impairments are faced with unique challenges in completing important activities of daily living such as dressing. In this paper, we present the first socially assistive robot-wearable sensors system to provide dressing assistance through social human-robot interactions. A novel robot-wearable architecture has been developed to recognize and classify user dressing actions and provide personalized prompts and feedback. Our system uses smart clothing with embedded strain sensors to estimate the user’s actions, which are then classified into different dressing steps. Our assistive robot uses a MAXQ hierarchical learning method to learn appropriate assistive behaviors to aid a user with the sequence of dressing steps. Experiments conducted validated the performance of our robot-wearable system in identifying and effectively responding to a variety of user states and dressing step actions. Furthermore, a robot demonstration study with stakeholders found that overall, they had positive perceptions and attitudes towards the socially assistive robot-wearable system, in particular with respect to its usefulness with the intended user population. [ABSTRACT FROM AUTHOR]

The sensitivity of randomly distributed multi-walled carbon nanotube (MWCNT)/polymer nanocomposite sensors has been extensively investigated, while that of aligned nanocomposite sensors is to be explored. In this paper, a novel hybrid computational scheme is presented for the transversely isotropic sensing behaviors of aligned MWCNT/polymer nanocomposite sensors combining micromechanics and finite element simulations. Specifically, the strain-dependent tunneling effect and multi-scale simulation of underlying heterogeneous microstructures are analyzed cooperatively to quantitatively illustrate the electromechanical coupling phenomenon of strain sensors. First, the effective elastic and electric properties of coated MWCNT with the weak interface connection are calculated by the Mori–Tanaka method on the microscopic scale. Then, the mesoscopic representative volume element (RVE) is established by coated MWCNTs as inclusions and polymer as the matrix. The tunneling effect and electric damage process are implemented with a proposed strain-dependent tunneling distance. Next, the macroscopic strain sensing behaviors of homogenized RVEs are evaluated with finite element simulations. The predicted resistance change ratio and sensitivity of aligned MWCNT/polymer nanocomposite sensors are both consistent with the experimental data over a wide loading range. This research has demonstrated the high sensing performance of aligned MWCNT/polymer nanocomposite sensors along the preferred direction. [ABSTRACT FROM AUTHOR]

Polyampholytes are a specific type of zwitterionic materials composed of monomers with both positive and negative charges. These materials can be synthesized through various methods, such as free radical, anionic, or cationic polymerization, or by modifying existing polymers through postpolymerization processes. Polyampholytes possess unique properties that make them attractive for a wide range of applications, particularly in sensor technology. They can undergo conformational changes in response to external stimuli like pH variations, temperature fluctuations, or changes in salt concentration. These properties have led to their application in biosensors, salt and ion sensors, pH sensors, fluorescence‐based sensors, strain sensors, and thermosensitive sensors. It is worth noting that in some cases polyampholytes can respond to multiple stimuli simultaneously. Overall, polyampholytes are drawing great attention for their excellent mechanical properties including self‐healing, high toughness, and fatigue resistance. Thus, this review is focused on advances that are made to develop polyampholyte polymer‐based sensors in different applications. [ABSTRACT FROM AUTHOR]

In this paper, a midband interrogation system for Fiber Bragg Grating (FBG) sensors is presented and its numerical demonstration is reported. The midband interrogation system is based on a finite reflection filter with automatic correction. The filter is used to interrogate the FBG sensors. The strain FBG sensors were used to demonstrate the effectiveness of the proposed systems. The results demonstrate that the proposed system of interrogation has a great resolution (±1 pm) with good stability. [ABSTRACT FROM AUTHOR]

High-aspect-ratio carbon nanotubes can be directly mixed into polymers to create piezoresistive polymers. Reducing the cross-sensitivity and creating unidirectional sensitive sensors can be achieved by aligning the nanotubes before they are cured in the polymer layer. This research presents and characterises this alignment of carbon nanotubes inside polydimethylsiloxane and gives the corresponding strain sensor results. The influence on the alignment method, as well as the field strength, frequency and time is shown. An analytical model is created to investigate the sensor's behaviour and determine the effect of electron-tunnelling in the sensor. A numerical model gives insight into the necessary applied field strength, frequency and time to facilitate alignment in viscous liquids. The experimental data show a two-phase piezoresistive response; first, a linear strain response, after which the more dominant electron-tunnelling piezoresistive phase starts with high gauge factors up to k ≈ 4500 in the preferential direction, depending on the carbon nanotube concentration. Gauge factors in the orthogonal direction remain low (k ≈ 22). Finally, the dynamic stability of the sensors is proven by exposing the sensors to a cyclic strain. Small initial drifts are observed but appear to stabilise after several cycles. [ABSTRACT FROM AUTHOR]

Grand challenges exist in the fabrication of robust skin electronics that are resistant to water interference, which can play vital roles in healthcare and lifesaving in activities such as showering, surfing, and swift water rescue. Particularly, dynamic water impingement is very destructive to skin electronics by causing device–skin delamination and sensing malfunctions. Herein, an anemone‐inspired self‐adhesive epidermal sensor with superior ability to resist water interference in various aquatic environments is developed. The epidermal sensor consists of a strain sensing layer composed of interconnected graphene flakes wrapped in ultrathin Ecoflex and a self‐adhesive layer composed of semi‐crosslinked polydimethylsiloxane, which is named as an adhesive graphene encapsulated in Ecoflex (a‐G@E) sensor. The a‐G@E sensor can conformally and stably attach on the skin under the synergy effect of the ultrathin thickness and the self‐adhesive layer. Remarkably, it can maintain a highly stable device–skin interface even under extreme aquatic conditions such as intense water impingement (up to 4 m s−1). As examples, this study demonstrates its applications in transmitting information, controlling robotics underwater, and tracking swimming modes of a fish. It is believed that the a‐G@E sensor can play a unique role in health‐care, sports‐monitoring, and human–machine interactions, especially for aquatic scenarios. [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]

Performance degradation and even loss of function due to mechanical stiffening caused by internal water evaporation and/or freezing significantly limit the application of hydrogel‐based electronics. Herein, a high‐performance liquid‐free electronic skin (e‐skin) is assembled based on the dry poly(ethylene glycol)‐based gel and conductive Ti3C2 MXenes that is successfully applied in wearable strain sensors. The fabricated liquid‐free e‐skin exhibits superior mechanical performance, broad sensing ranges (>1000%), good temperature adaptability, and durable environmental stability. Without extra sealed packaging, the e‐skin sensor maintains remarkable cycling stability and retains 98.5% conductivity at room temperature after 6 months. Furthermore, the liquid‐free e‐skin sensors are utilized to provide individuals with proper guidance on body alignment and posture awareness, fostering the development and maintenance of correct exercise techniques, thus mitigating the likelihood of sports‐related injuries. This work provides a novel liquid‐free electron‐conductive electronic integrated with adhesiveness, stretchability, self‐healabilitiy, and antifreezing, which can meet wide application needs from artificial skins to smart interfaces. [ABSTRACT FROM AUTHOR]

Structural health monitoring (SHM) is crucial for ensuring operational safety in applications like pipelines, tanks, aircraft, ships, and vehicles. Traditional embedded sensors have limitations due to expense and potential structural damage. A novel technology using radio frequency identification devices (RFID) offers wireless transmission of highly sensitive strain measurement data. The system features a thin, flexible sensor based on an inductance‐capacitance (LC) circuit with a parallel‐plate capacitance sensing unit. By incorporating tailored cracks in the capacitor electrodes, the sensor's capacitor electrodes become highly piezoresistive, modifying electromagnetic wave penetration. This unconventional change in capacitance shifts the resonance frequency, resulting in a wireless strain sensor with a gauge factor of 50 for strains under 1%. The frequency shift is passively detected through an external readout system using simple frequency sweeping. This wire‐free, power‐free design allows easy integration into composites without compromising structural integrity. Experimental results demonstrate the cracked wireless strain sensor's ability to detect small strains within composites. This technology offers a cost‐effective, non‐destructive solution for accurate structural health monitoring. [ABSTRACT FROM AUTHOR]

The urgent need for flexible strain sensors that are both aesthetic and functional is addressed, given the rapid development of smart wearable technology and the improvement of material level. To achieve this, silver-plated yarns based on nylon and nylon wrapped spandex were directly knitted into the sensor using cross-knit intarsia and plating technology. Five samples, with varying percentages of loops and tuck loops, were designed. The results indicated that the sensor demonstrated a GF of 2.80 kPa−1 at the Lx-axis and 3.67 kPa−1 at the Ly-axis, showing good repeatability during 1000 cycles of stretch/release. Moreover, it exhibited fast responsiveness, enabling it to discriminate between different rates of stretch. The sensor's potential for application in wearable smart medical monitoring was demonstrated by its ability to be embedded in garments for joint motion monitoring. These findings collectively suggest that the designed knitted strain sensor holds promising potential for use in the field of wearable smart medical monitoring. [ABSTRACT FROM AUTHOR]

Flexible self‐adhesive hydrogel sensors are attracting considerable concerns in recent years. However, creating a self‐adhesive hydrogel sensor with excellent mechanical properties remains to be challenging. Herein, a double‐sided self‐adhesive hydrogel capable of strain sensor with high strength is demonstrated by penetration strategy. The middle poly(acrylic acid)‐polyacrylamide/Fe3+ (PAA–PAM/Fe3+) tough layer endows the double‐sided self‐adhesive hydrogel with high mechanical properties, while the bilateral poly[2‐(methacryloyloxy) ethyl]dimethyl‐(3‐sulfopropyl)ammonium hydroxide‐polyacrylamide (PSBMA–PAM) adhesive layers are used to ensure excellent adhesiveness on diverse substrates. The tough layer of the double‐sided self‐adhesive hydrogel sensor shows a strong interface bonding force against the adhesive layer. The double‐sided self‐adhesive hydrogel sensor enables excellent adhesiveness on diverse substrates. More importantly, it can accurately detect different strains and human motions as a self‐adhesive hydrogel strain sensor. This work manifests a new route of structural design to develop a self‐adhesive hydrogel sensor with excellent mechanical properties that is suitable for a wide range of applications. [ABSTRACT FROM AUTHOR]

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Soft strain sensors pose great potential for emerging human–machine interfaces. However, their real-world applications have been limited due to challenges such as low reproducibility, susceptibility to environmental noise, and short lifetimes, which are attributed to nanotechnologies, including microfabrication techniques. In this study, we present a computer vision-based optical strain (CVOS) sensor system that integrates computer vision with streamlined microfabrication techniques to overcome these challenges and facilitate real-time multiaxial strain mapping. The proposed CVOS sensor consists of an easily fabricated soft silicone substrate with micro-markers and a tiny camera for highly sensitive marker detection. Real-time multiaxial strain mapping allows for measuring and distinguishing complex multi-directional strain patterns, providing the proposed CVOS sensor with higher scalability. Our results indicate that the proposed CVOS sensor is a promising approach for the development of highly sensitive and versatile human–machine interfaces that can operate long-term under real-world conditions. [ABSTRACT FROM AUTHOR]

To realize continuously and stably work in a "moist/hot environment", flexible electronics with excellent humid resistance, anti-swelling, and detection sensitivity are demanding. Herein, a solvent-resistant and temperature-ultrasensitive hydrogel sensor was prepared by combining MXene and quaternized chitosan (QCS) with the binary polymer chain. The strong electrostatic interaction between the QCS chain and the poly(acrylic acid) (PAA) network endows the hydrogel stability against solvent erosion, high temperature, and high humidity. The strong dynamic interaction between MXene and polymer matrix significantly improves the mechanical properties and sensing (strain and temperature) sensitivity of the hydrogel. The hydrogel strain sensor exhibits a high gauge factor (5.53), temperature/humidity tolerance (equilibrium swelling ratio of 2.5% at 80 °C), and excellent cycle stability, which could achieve a remote and accurate perception of complex human motion and environment fluctuation under aquatic conditions. Moreover, the hydrogel sensor exhibits impressive thermal response sensitivity (−3.183%/°C), ultrashort response time (< 2.53 s), and a low detection limit (< 0.5 °C) in a wide temperature range, which is applied as an indicator of the body surface and ambient temperature. In short, this study broadens the application scenarios of hydrogels in persistent extreme thermal and wet environments. [ABSTRACT FROM AUTHOR]

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This study investigated the innovative use of magnetoelastic sensors to detect the formation of single cracks in cement beams under bending vibrations. The detection method involved monitoring changes in the bending mode spectrum when a crack was introduced. The sensors, functioning as strain sensors, were placed on the beams, and their signals were detected non-invasively using a nearby detection coil. The beams were simply supported, and mechanical impulse excitation was applied. The recorded spectra displayed three distinct peaks representing different bending modes. The sensitivity for crack detection was determined to be a 24% change in the sensing signal for every 1% decrease in beam volume due to the crack. Factors influencing the spectra were investigated, including pre-annealing of the sensors, which improved the detection signal. The choice of beam support material was also explored, revealing that steel yielded better results than wood. Overall, the experiments demonstrated that magnetoelastic sensors enabled the detection of small cracks and provided qualitative information about their location. [ABSTRACT FROM AUTHOR]

We present a high-performance flexible bending strain sensor for directional motion detection of human hands and soft robotic grippers. The sensor was fabricated using a printable porous conductive composite composed of polydimethylsiloxane (PDMS) and carbon black (CB). The utilization of a deep eutectic solvent (DES) in the ink formulation induced a phase segregation between the CB and PDMS and led to a porous structure inside the printed films after being vapored. This simple and spontaneously formed conductive architecture provided superior directional bend-sensing characteristics compared to conventional random composites. The resulting flexible bending sensors displayed high bidirectional sensitivity (gauge factor of 45.6 under compressive bending and 35.2 under tensile bending), negligible hysteresis, good linearity (>0.99), and excellent bending durability (over 10,000 cycles). The multifunctional applications of these sensors, including human motion detection, object-shape monitoring, and robotic perceptions, are demonstrated as a proof-of-concept. [ABSTRACT FROM AUTHOR]

Stretchable display has become emerging technology as the next‐generation form‐factor of flexible and rollable displays. Especially, advanced form of stretchable organic light‐emitting diode (OLED) display plays an increasingly central role in wearable healthcare applications. The stretchability of OLED display platform enable conformal to the curvature of the human body. Therefore, stretchability and the pixel density remain key requirements for the development of highly stretchable OLED display. Here, we report rational structural design for highly stretchable OLED panel with biophysical sensors embedded for healthcare applications. The island and stretchable bridges enable stretchability over 20%. Moreover, stretchable temperature and strain sensors embedded in panel provide new approach toward wearable healthcare applications. [ABSTRACT FROM AUTHOR]

Currently, an urgent need in the field of wearable electronics is the development of flexible sensors that can be attached to the human body to monitor various physiological indicators and movements. In this work, we propose a method for forming an electrically conductive network of multi-walled carbon nanotubes (MWCNT) in a matrix of silicone elastomer to make stretchable sensors sensitive to mechanical strain. The electrical conductivity and sensitivity characteristics of the sensor were improved by using laser exposure, through the effect of forming strong carbon nanotube (CNT) networks. The initial electrical resistance of the sensors obtained using laser technology was ~3 kOhm (in the absence of deformation) at a low concentration of nanotubes of 3 wt% in composition. For comparison, in a similar manufacturing process, but without laser exposure, the active material had significantly higher values of electrical resistance, which was ~19 kOhm in this case. The laser-fabricated sensors have a high tensile sensitivity (gauge factor ~10), linearity of >0.97, a low hysteresis of 2.4%, tensile strength of 963 kPa, and a fast strain response of 1 ms. The low Young's modulus values of ~47 kPa and the high electrical and sensitivity characteristics of the sensors made it possible to fabricate a smart gesture recognition sensor system based on them, with a recognition accuracy of ~94%. Data reading and visualization were performed using the developed electronic unit based on the ATXMEGA8E5-AU microcontroller and software. The obtained results open great prospects for the application of flexible CNT sensors in intelligent wearable devices (IWDs) for medical and industrial applications. [ABSTRACT FROM AUTHOR]

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In this study, we introduce a novel design for a three-dimensional (3D) controller, which incorporates the omni-purpose stretchable strain sensor (OPSS sensor). This sensor exhibits both remarkable sensitivity, with a gauge factor of approximately 30, and an extensive working range, accommodating strain up to 150%, thereby enabling accurate 3D motion sensing. The 3D controller is structured such that its triaxial motion can be discerned independently along the X, Y, and Z axes by quantifying the deformation of the controller through multiple OPSS sensors affixed to its surface. To ensure precise and real-time 3D motion sensing, a machine learning-based data analysis technique was implemented for the effective interpretation of the multiple sensor signals. The outcomes reveal that the resistance-based sensors successfully and accurately track the 3D controller's motion. We believe that this innovative design holds the potential to augment the performance of 3D motion sensing devices across a diverse range of applications, encompassing gaming, virtual reality, and robotics. [ABSTRACT FROM AUTHOR]