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With the rapid development of intelligent wearable technology, multimodal tactile sensors capable of data acquisition, decoupling of intermixed signals, and information processing have attracted increasing attention. Herein, a decoupled temperature–pressure dual‐mode sensor is developed based on single‐walled carbon nanotubes (SWCNT) and poly(3,4‐ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) decorated porous melamine foam (MF), integrating with a deep learning algorithm to obtain a multimodal input terminal. Importantly, the synergistic effect of PEDOT:PSS and SWCNT facilitates the sensor with ideal decoupling capability and sensitivity toward both temperature (38.2 µV K−1) and pressure (10.8% kPa−1) based on the thermoelectric and piezoresistive effects, respectively. Besides, the low thermal conductivity and excellent compressibility of MF also endow it with the merits of a low‐temperature detection limit (0.03 K), fast pressure response (120 ms), and long‐term stability. Benefiting from the outstanding sensing characteristics, the assembled sensor array showcases good capacity for identifying spatial distribution of temperature and pressure signals. With the assistance of a deep learning algorithm, it displays high recognition accuracy of 99% and 98% corresponding to “touch” and “press” actions, respectively, and realizes the encrypted transmission of information and accurate identification of random input sequences, providing a promising strategy for the design of high‐accuracy multimodal sensing platform in human–machine interaction. [ABSTRACT FROM AUTHOR]

Hydraulic technology with smaller sizes and higher reliability trends, including fault prediction and intelligent control, requires high-performance temperature and pressure-integrated sensors. Current designs rely on planar wafer- or chip-level integration, which is limited by pressure range, chip size, and low reliability. We propose a small-size temperature/high-pressure integrated sensor via the flip-chip technique. The pressure and temperature units are arranged vertically, and the sensing signals of the two units are integrated into one plane through silicon vias and gold–gold bonding, reducing the lateral size and improving the efficiency of signal transmission. The flip-chip technique ensures a reliable electrical connection. A square diaphragm with rounded corners is designed and optimised with simulation to sense high pressure based on the piezoresistive effect. The temperature sensing unit with a thin-film platinum resistor measures temperature and provides back-end high-precision compensation, which will improve the precision of the pressure unit. The integrated chip is fabricated by MEMS technology and packaged to fabricate the extremely small integrated sensor. The integrated sensor is characterised, and the pressure sensor exhibits a sensitivity and sensitivity drift of 7.97 mV/MPa and −0.19% FS in the range of 0–20 MPa and −40 to 120 °C. The linearity, hysteresis, repeatability, accuracy, basic error, and zero-time drift are 0.16% FS, 0.04% FS, 0.06% FS, 0.18% FS, ±0.23% FS and 0.04% FS, respectively. The measurement error of the temperature sensor and temperature coefficient of resistance is less than ±1 °C and 3142.997 ppm/°C, respectively. The integrated sensor has broad applicability in fault diagnosis and safety monitoring of high-end equipment such as automobile detection, industrial equipment, and oil drilling platforms. [ABSTRACT FROM AUTHOR]

Based on the piezoresistive effect of nano conductive rubber, conductive silicone rubber composite pressure sensor was prepared using the matrix material silicone rubber, nano superconductive carbon black, silk fiber fabric, interdigital electrode, buffer polymer material and encapsulation mold by processes such as internal mixing, open mixing, vulcanization and encapsulating, and the conductive silicone rubber composite material with the optimal piezoresistive characteristics was prepared by optimizing the content of conductive filler in the silicone rubber matrix. Finally, the application performance of encapsulated pressure sensor on bridge support model was explored. The results showed that when mass faction of nano superconductive carbon black ■ was 6.11%, the conductive silicone rubber composite material reached the penetration threshold point and had the best piezoresistive characteristics; the conductive sensing composite material obtained by implanting silk fiber fabric into conductive silicone rubber was then combined with the flexible interdigital single-layer electrode and encapsulated to generate the pressure sensor with increased range, sensitive detection, and enhanced toughness; the pressure sensor had a good linear relationship between the pressure signal and the electrical signal, and could achieve pressure detection within the range of 0 to 40 MPa. In addition, the measured value of the pressure sensor in the bridge support model test were highly consistent with the theoretical value.

An outstanding event related to the understanding of the physics of mechanical sensors occurred and was announced in 1954, exactly seventy years ago. This event was the discovery of the piezoresistive effect, which led to the development of semiconductor strain gauges with a sensitivity much higher than that obtained before in conventional metallic strain gauges. In turn, this motivated the subsequent development of the earliest micromachined silicon devices and the corresponding MEMS devices. The science and technology related to sensors has experienced noteworthy advances in the last decades, but the piezoresistive effect is still the main physical phenomenon behind many mechanical sensors, both commercial and in research models. On this 70th anniversary, this tutorial aims to explain the operating principle, subtypes, input–output characteristics, and limitations of the three main types of mechanical sensor: strain gauges, capacitive sensors, and piezoelectric sensors. These three sensor technologies are also compared with each other, highlighting the main advantages and disadvantages of each one. [ABSTRACT FROM AUTHOR]

Effects of varying Mn and Ni concentrations on the structure and piezoresistive properties of CuMnNi films deposited by magnetron sputtering with a segmented target were investigated. An increase in the Ni content refines the CuNi film grains, inducing an increase in defects such as internal micropores and a decrease in film density. At the same time, the positive piezoresistive coefficient of the film changes to negative. When 17.5 at.% Ni was added, the negative piezoresistive coefficient of the CuNi film was −2.0 × 10−4 GPa−1. The doping of Ni has a weakening effect on the positive piezoresistive effect of the film. Adding Mn into Cu refines the film grains while increasing the film density. The surface roughness of the film decreases with the increase in Mn content. When the Mn content was 16.7 at.%, the piezoresistive coefficient reached the largest recorded value of 23.81 × 10−4 GPa−1, and the film exhibited excellent repeatability in multiple piezoresistive tests. After the CuMn film with 16.7 at.% Mn was annealed at 400 °C for 2 h, the film grains grew slightly and the film residual stress decreased. The optimization of the film structure can reduce the scattering of electrons during transportation. The piezoresistive coefficient of the film was further improved to 35.78 × 10−4 GPa−1. [ABSTRACT FROM AUTHOR]

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Sensing of both temperature and strain is crucial for various diagnostic and therapeutic purposes. Here, we present a novel hydrogel-based electronic skin (e-skin) capable of dual-mode sensing of temperature and strain. The thermocouple ion selected for this study is the iodine/triiodide (I−/I3−) redox couple, which is a common component in everyday disinfectants. By leveraging the thermoelectric conversion in conjunction with the inherent piezoresistive effect of a gel electrolyte, self-powered sensing is achieved by utilizing the temperature difference between the human body and the external environment. The composite hydrogels synthesized from polyvinyl alcohol (PVA) monomers using a simple freeze‒thaw method exhibit remarkable flexibility, extensibility, and adaptability to human tissue. The incorporation of zwitterions further augments the resistance of the hydrogel to dehydration and low temperatures, allowing maintenance of more than 90% of its weight after 48 h in the air. Given its robust thermal current response, the hydrogel was encapsulated and then integrated onto various areas of the human body, including the cheeks, fingers, and elbows. Furthermore, the detection of the head-down state and the monitoring of foot movements demonstrate the promising application of the hydrogel in supervising the neck posture of sedentary office workers and the activity status. The successful demonstration of self-powered on-body temperature and strain sensing opens up new possibilities for wearable intelligent electronics and robotics. [ABSTRACT FROM AUTHOR]

Multifunctional wearable sensors have gained significant popularity in recent years for point of care diagnosis, tackling the myriad of obstacles faced in coping with health-related issues. However, complex fabrication, lack of biocompatibility, non-reusability, and accuracy limit their widespread use. In this work, we report a clean-room-free fabrication of molybdenum diselenide (MoSe2) interspersed with polyvinyl alcohol (PVA) based multifunctional device for in situ and non-invasive high-fidelity human gesture recognition, pulse rate monitoring, and skin hydration sensing. Detailed morphological characterization studies reveal the formation of a rhombohedral structure for MoSe2 nanoflakes stacked vertically to form a micro flower structure. Group synaptic activity of neurons results in a subtle electrical impulse, which, in turn, generates an electric field that is detected by the as-fabricated MoSe2/PVA device when attached to the forehead and interfaced to Open Brain-Computer Interface platform-based Cyton biosensing board. The device is also used as an ultrasensitive pressure sensor for arterial pulse pressure monitoring. This detection mechanism of the multifunctional sensor can be attributed to the piezoresistive effect of MoSe2 nanoparticles, wherein the dipoles reorient to form an internal polarization upon detection of physiological information. The strategy employed here paves the way toward replacing wet electrodes in conventional electroencephalogram (EEG)/electrocardiogram (ECG) measurements that result in skin abrasion and signal quality degradation with low-cost, reliable, skin-friendly, wearable MoSe2/PVA dry electrodes for rapid assessment. [ABSTRACT FROM AUTHOR]

Sputter-deposited thin films of pure chromium and of chromium with small amounts of nitrogen are characterized regarding their electrical resistivity and strain dependence, i.e., piezoresistivity. They show a temperature dependent piezoresistive effect with gauge factors ranging approximately from 10 to 20. Related to this effect, they exhibit signs of a paramagnetic–antiferromagnetic transition at temperatures of 420 K and higher. For characterization, resistivity is measured at different strain levels: in a bending setup with a fixed radius and in a four-point bending system with reference strain gauges. Several parameter series of the sputter deposition of pure Cr films show that the higher gauge factor is correlated to a higher temperature coefficient of resistivity (TCR). The addition of nitrogen extends the range of TCR toward negative values, with gauge factors still in the same range as pure Cr. A Cr–N strain gauge is characterized and shows a linear, low-hysteresis strain–resistivity effect as well as a relatively large transverse sensitivity. Resistivity and gauge factor of one Cr and one Cr–N sample are measured from room temperature up to 600 K. These films have a resistivity anomaly indicating an antiferromagnetic ordering temperature T N that is much higher than in bulk Cr. The gauge factor has a maximum near T N and falls to small values at higher temperatures. The results indicate that the piezoresistivity of Cr and Cr-rich films is coupled to their spin-density wave (SDW) antiferromagnetism. Since the SDW state is known to be tunable through alloying, internal stress, and crystallinity, it appears that piezoresistivity can be influenced by these parameters as well. [ABSTRACT FROM AUTHOR]

P-type silicon nanowires (SiNWs) have attracted significant attention for their potential in miniaturizing sensing devices, attributed to the observed giant piezoresistive (PZR) effects. However, the application of these advantageous PZR properties of SiNWs to microelectromechanical systems (MEMS) has been hindered by unclear noise levels and complicated fabrication methods. Additionally, several previous reports of anomalous PZR effects, such as doping-type inversion in hydrogen fluoride (HF)-treated p-type SiNWs, have introduced further complexities. Consequently, addressing these unclear challenges is necessary to effectively utilize the PZR effects of SiNWs for MEMS sensing applications. In this paper, the primary causes of uncertain noises and resistance levels in HF-treated p-SiNWs and their dependence on surface effects were analyzed to optimize NW parameters. SiNWs were fabricated using a suitable MEMS fabrication method, and their noises with PZR effects were measured and compared. The results indicated that SiNWs with abnormal PZR characteristics were worse in signal-to-noise ratio (SNR) than those with bulk PZR properties attributed to the significant noise increments from the depletion effects. Based on the NW experiment and additional mechanical analyses, suitable SiNW conditions for MEMS sensing unit were optimized and selected. A miniaturized 3-axis accelerometer utilizing the optimized SiNW was developed and tested. The experimental results showed that the developed accelerometer successfully reduced the total area of the sensor structure by 35.4% when compared to commercial capacitive accelerometers while maintaining competitive performance. This result was achieved without relying on the giant or anomalous PZR effects.

Conductive aerogel is a material with excellent electrical conductivity and unique three-dimensional nano-network structure, formed by doping conductive fillers into the aerogel, or directly through conductive substances such as conductive polymer. In addition, it has the advantages of high porosity, high specific surface area, low density, excellent flexibility and low cost. The purpose of this review is to summarize the research status of conductive aerogels to open up new ideas for scientific research in related fields for readers. Firstly, we summarize the assembly strategies of conductive aerogel. The assembly process includes preparation and drying of the gel. In addition, the aging process is involved. Secondly, we review its conduction mechanism. Then, the effects of pressure, temperature and humidity on the properties of conductive aerogels are summarized. Notably, conductive aerogel has piezoresistive effect because of its elasticity and compressibility. Finally, based on the properties of conductive aerogels and their advantages in electrical conductivity, we summarize the applications of conductive aerogels in supercapacitor, electrocatalysis, sensors and electromagnetic interference shielding. This review summarizes the current development and application of conductive aerogel in recent years, which provides strong support for the future development of conductive aerogel. [ABSTRACT FROM AUTHOR]

The strain induced piezoelectric and piezoresistive effects have been regarded as promising methods to regulate the photoelectric properties of two-dimensional transition metal dichalcogenides. However, the distinction between the influence of piezoelectric and piezoresistive effects on devices is ambiguous. Here, piezo-phototronic photodetectors based on monolayer WS2 were fabricated to investigate the competitive behavior of the piezoelectric and piezoresistive effects. We have shown that the piezoresistive effect dominates the photocurrent enhancement through narrowing the bandgap under small strain. With increasing strain, the influence of piezoelectric effect became more and more obvious, and it dominated the photo-induced carrier transport behavior through polarization charges accumulated at the metal–semiconductor contact interface when the strain exceeded 0.78%. Under the strain condition, the modulation of strain on photocurrent reached as high as 1400%. [ABSTRACT FROM AUTHOR]

Magnetorheological elastomers (MREs) are a category of smart materials composed of a magnetic powder dispersed in an elastomeric matrix. They are characterized by the ability to change their mechanical properties when an external magnetic field is applied, called magnetorheological (MR) effect. When a conductive filler is added to a magnetorheological elastomer, the resulting hybrid filler composite showcases both MR and piezoresistive effects. For such a reason, these composites are referred to as self‐sensing magnetorheological elastomers. In this case, the synthesized self‐sensing magnetorheological elastomers are based on styrene‐based thermoplastic elastomers (TPS), carbonyl iron particles (CIP), and carbon black (CB). The hybrid filler concept using various coated CIP and constant CB content showed that above 25 vol.% CIP the resistivity increased rapidly. This work proposes the first case of a 3D printable self‐sensing magnetorheological elastomer and cyclic mechanical compression and tensile mode analysis at high deformation (up to 20% and 10%, respectively). The results showcase a magnetoresistive change of up to 68% and a piezoresistive change of up to 42% and 98% in compression and tension, respectively. In addition, the magnetostriction of the self‐sensing samples has been characterized to be 3.6% and 5.6% in the case of CIP 15 and 30 vol.%, respectively. [ABSTRACT FROM AUTHOR]

This article presents research on biodegradable stretch sensors produced using biological material. This sensor uses a piezoresistive effect to indicate stretch, which can be used for force measurement. In this work, an attempt was made to develop the composition of a sensitive material and to design a sensor. The biodegradable base was made from a κ-carrageenan compound mixed with Fe2O3 microparticles and glycerol. The influence of the weight fraction and iron oxide microparticles on the tensile strength and Young's modulus was experimentally investigated. Tensile test specimens consisted of 10–25% iron oxide microparticles of various sizes. The results showed that increasing the mass fraction of the reinforcement improved the Young's modulus compared to the pure sample and decreased the elongation percentage. The GF of the developed films varies from 0.67 to 10.47 depending on composition. In this paper, it was shown that the incorporation of appropriate amounts of Fe2O3 microparticles into κ-carrageenan can achieve dramatic improvements in mechanical properties, resulting in elongation of up to 10%. The developed sensors were experimentally tested, and their sensitivity, stability, and range were determined. Finally, conclusions were drawn on the results obtained. [ABSTRACT FROM AUTHOR]

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]

A self‐powered and sustainable traffic monitoring system is highly required for future urban development. Herein, self‐healable piezoresistive sensors and triboelectric nanogenerators (TENGs) are constructed by in situ polymerization of polyvinyl alcohol‐polyacrylamide double network hydrogel in the presence of sodium alginate and tannic acid‐modified cellulose nanocrystals (denoted as PPC) for all‐weather self‐powered intelligent traffic monitoring applications. Because of hydrogen bonding and boron ester bonding, the resultant PPC‐based strain sensor can rapidly self‐heal and restore its sensing ability within 1 min with a self‐healing efficiency of 97.4%. Based on piezoresistive effect, the ions in sodium alginate endow the PPC‐based strain sensor with a relatively high gauge factor of 8.39, which can monitor the motion and fatigue of drivers. Based on triboelectrification effect, the PPC‐based TENG sensor can detect instantaneous vehicle speed, judge traffic accident liability, evaluate vehicle weight, and alert the driver to prevent accidents caused by drowsy driving. After partially replacing water in the PPC with glycerin, the resulting PPC‐based TENG sensor exhibits stable performance at temperatures ranging from ‐30 to 40 °C, ensuring its all‐weather monitoring ability. The all‐weather and self‐powered intelligent traffic monitoring system is promising for ensuring the security of future cities. [ABSTRACT FROM AUTHOR]

[Display omitted] • Bi-induced t/o-Bi 2 WO 6 phase transition led to formation of Bi 2 WO 6 homojunction. • PDA and Bi 2 WO 6 homojunction nanoclusters were synthesized by template method. • The coexistence of two phases enhances the piezoelectric polarization of Bi 2 WO 6. • The excellent conductivity of PDA polymer unit extend charge transfer path. • Efficient carrier separation and migration synergistically stimulate piezocatalysis. Piezocatalytic technology with controllable generation of reactive oxygen species (ROS) is emerging in wastewater treatment. This study employed the synergetic regulation of functional surface and phase interface modification to effectively accelerate redox reaction in piezocatalytic process. We anchored the conductive polydopamine (PDA) onto Bi 2 WO 6 (BWO) using template method, in which a small amount of Bi precipitation to induce partial phase transition of BWO from tetragonal to orthorhombic (t/o) in virtue of simple calcination. ROS traceability studies have identified the synergistic relationship between charge separation and transfer. Polarization in two-phase coexistence is intimately modulated by the orthorhombic relative central cation displacement. The orthorhombic phase with large electric dipole moment significantly promotes the generation of piezoresistive effect of intrinsic tetragonal BWO and optimizes the charge distribution. PDA further overcomes the obstruction of carrier migration at the phases interface to accelerate the generation rate of free radicals. Consequently, the superior rhodamine B (RhB) piezocatalytic degradation rate of 0.10 and 0.32 min−1 were delivered by t/o-BWO and t/o-BWO@PDA, respectively. This work reveals a feasible polarization enhancement strategy for the phase coexistence, and flexibly introduces the in-situ synthesized economical polymer conductive unit into the piezocatalysts. [ABSTRACT FROM AUTHOR]

Flexible sensing technologies that play a pivotal role in endowing robots with detection capabilities and monitoring their motions are impulsively desired for intelligent robotics systems. However, integrating and constructing reliable and sustainable flexible sensors with multifunctionality for robots remains an everlasting challenge. Herein, an entirely intrinsic self‐healing, stretchable, and attachable multimodal sensor is developed that can be conformally integrated with soft robots to identify diverse signals. The dynamic bonds cross‐linked networks including the insulating polymer and conductive hydrogel with good comprehensive performances are designed to fabricate the sensor with prolonged lifespan and improved reliability. Benefiting from the self‐adhesiveness of the hydrogel, strong interfacial bonding can be formed on various surfaces, which promotes the conformable integration of the sensor with robots. Due to the ionic transportation mechanism, the sensor can detect strain and temperature based on piezoresistive and thermoresistive effect, respectively. Moreover, the sensor can work in triboelectric mode to achieve self‐powered sensing. Various information can be identified from the electrical signals generated by the sensor, including hand gestures, soft robot crawling motions, a message of code, the temperature of objects, and the type of materials, holding great promise in the fields of environmental detection, wearable devices, human‐machine interfacing, and robotics. [ABSTRACT FROM AUTHOR]

In pressure sensors, four piezoresistors connected in a Wheatstone bridge are often provided with a voltage varying between 5 and 10 V. Unfortunately, this voltage is a source of drifts created by electric heating. This study focuses on the internal heating and piezoresistive effect of piezoresistors represented by the variation of their resistivity. To do this, we use the finite difference method (FDM) to solve the heat transfer equation, taking into account the conduction in Cartesian coordinates for the variable regime. We examine how the temperature affects the piezoresistivity in these sensors when the potential is applied. In this case, the variation of the temperature has been calculated as a function of applied voltage, as well as for the operating time of the sensor. Furthermore, the evolution of resistivity over time was determined for several geometric properties of the membrane using the mobility model. This was established for different doping levels. Additionally, the change in resistivity due to the application of voltage was evaluated. It was observed that resistivity is greatly affected by the temperature rise produced by the applied voltage when the device is actuated for a prolonged time. Consequently, this results in drifting in the output response of the sensor. [ABSTRACT FROM AUTHOR]

The surface fluctuaton pressure test of high-speed train is always accompanied by vibration of train body. Aiming at the acceleration-induced effects of pressure sensor, an experimental system for acceleration-induced effect of piezoresistive pressure sensor based on air storage tank is built. The dynamic model of piezoresistive pressure sensor under vibration load and pressure load is analyzed. Combined with the test, the corresponding transfer function model is obtained by using instrumental variable(IV) method and system identification theory(SIT). A digital compensation strategy for acceleration-induced effects was designed on the basis of this model. [ABSTRACT FROM AUTHOR]

In order to solve the problem of falling detection for the elderly living alone, a low-cost fabric pressure sensing array and pressure distribution detection system are designed. Several silver plated conductive yarns were arranged on the front side of the fabric substrate at intervals along the warp direction, while another group of several silver plated conductive yarns were arranged above the first group at intervals along the weft direction. Pressure sensing units were printed at the intersection of two groups of silver plated conductive yarns. The electromechanical properties of the sensing unit was experimentally tested. A pressure distribution detection system based on the sensing array was designed using Arduino microcontroller unit and multiplexers to measure the resistances of all the sensing units in the array to obtain the distributed pressure value. The results show that the resistance of the sensing unit which exhibits a significant piezoresistive effect decreases exponentially as the pressure increases. The sensing unit the maximum measurable pressure of which can be 25 kPa has reliable electromechanical stability. The pressure distribution can be detected by the sensing array, which will lay a foundation for the subsequent detection of the fall of elderly people. [ABSTRACT FROM AUTHOR]

Abstract 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.

An outstanding event related to the understanding of the physics of mechanical sensors occurred and was announced in 1954, exactly seventy years ago. This event was the discovery of the piezoresistive effect, which led to the development of semiconductor strain gauges with a sensitivity much higher than that obtained before in conventional metallic strain gauges. In turn, this motivated the subsequent development of the earliest micromachined silicon devices and the corresponding MEMS devices. The science and technology related to sensors has experienced noteworthy advances in the last decades, but the piezoresistive effect is still the main physical phenomenon behind many mechanical sensors, both commercial and in research models. On this 70th anniversary, this tutorial aims to explain the operating principle, subtypes, input–output characteristics, and limitations of the three main types of mechanical sensor: strain gauges, capacitive sensors, and piezoelectric sensors. These three sensor technologies are also compared with each other, highlighting the main advantages and disadvantages of each one.

Polymers mixed with conductive fillers hold significant potential for use in stretchable and wearable sensor devices. Enhancing the piezoresistive effect and mechanical stability is critical for these devices. To explore the changes in the electrical resistance under high strains, typically unachievable in single-layer composites, bi-layer structures were fabricated from carbon nanotubes (CNTs) and EcoFlex composites to see unobservable strain regions. Spherical types of non-conductive fillers composed of polystyrene and conductive filler, coated with Ni and Au on non-conductive fillers, were used as secondary fillers to improve the piezoresistive sensitivity of composites, and their respective impact on the conductive network was compared. The electrical and mechanical properties were examined in the static state to understand the impact of these secondary fillers. The changes in the electrical resistance under 100% and 300% tensile strain, and their dependence on the inherent electrical properties of the secondary fillers, were also investigated. Single-layer CNT composites proved incapable of withstanding 300% strain, whereas the bi-layer structures proved resilient. By implementing cyclic stretching tests, contrary to non-conductive fillers, reduced piezoresistive influence of the conductive secondary filler under extreme strain conditions could be observed. [ABSTRACT FROM AUTHOR]

The fundamental properties of two-dimensional α1-MA2Z4 (M = Mg, Ca, Sr; A = Al; Z = S, Se) monolayers have been systematically investigated based on the first principles calculations. Our results show that the α1-MA2Z4 monolayers have mixed ionic-covalent bonding character. The structural stability analyses reveal that all structures are dynamically stable and sustain stability below 800 K. All α1-MA2Z4 monolayers exhibit semiconducting property. The suitable bandgaps and the band edges alignment strides the redox potentials of water splitting, having potential as the candidates of the photocatalyst. All structures are predicted to possess isotropic electron-dominated mobility, which increases from 340.79 to 591.84 cm2 s−1 V−1 with the increase in atomic number of the alkaline-earth metal and chalcogen group. Further imposing the strain along the armchair direction, the electron mobility of α1-MA2Z4 can be enhanced to ∼103 cm2 V−1 s−1, especially the electron mobility of α1-MgA2S4 even increases to ∼2 × 103 cm2 V−1 s−1. The increased electron mobility indicates the reduced resistivity, which shows that the α1-MA2Z4 monolayers possess a remarked piezoresistive effect. The outstanding properties indicate that the α1-MA2Z4 is promising in photocatalysis and flexible electronics fields. [ABSTRACT FROM AUTHOR]

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]

Owing to excellent performance and a simple mechanism, stretchable piezoresistive strain sensors have been applied to human skin for monitoring physical activities, physiological activities, etc. However, it is still a challenge to simultaneously realize highly sensitive and stretchable piezoresistive strain sensors with high optical transparency. This study reports a transparent and stretchable piezoresistive strain sensor with 2D surface buckling by fabricating ultrathin indium tin oxide (ITO) film on the biaxially pre‐stretched polyacrylate (VHB) elastomer followed by pre‐stretch releasing. To the authors' knowledge, semiconductors are applied for a stretchable piezoresistive strain sensor for the first time. Furthermore, this strain sensor exhibits a high sensitivity of 569, a high transparency of 88% and a high biaxial stretchability of 110% at the same time. This device demonstrates the good long‐term stability over 500 stretching–relaxing cycles. The high sensitivity can be mainly attributed to the piezoresistive effect of the semiconductor where carrier mobility and the resulting resistivity can be significantly changed by the strain. The strain sensors attached to human skin are used to monitor many human motions such as chewing, swallowing, breathing, and walking. ITO‐based strain sensors pave the way toward the development of highly stretchable and sensitive wearable electronics. [ABSTRACT FROM AUTHOR]

In this study, we investigated the capacitive effect and the electromagnetic coupling on the measurement chain induced by impact experiments with a gas gun or powder gun. Reduced bandwidth and noise were noticed on experimental signals. Rogowski coil measurements were added on the cables to characterize the electromagnetic coupling. The perturbation currents on the cables were quantified depending on the configuration. The gauge, the transmission line and the conditioning system were modeled. The calculations reproduced the electrical wave arrival time, the transmission line transfer impedance and the conditioning system transfer impedance; and the bandwidth limitation has been displayed. A capacitive effect with the piezoresistive manganin gauge embedded into the sample was identified, depending on the experimental setup. [ABSTRACT FROM AUTHOR]

The piezoresistive effect of carbon fibers has been successfully applied to monitor or assess the stress–strain state of carbon fiber–reinforced polymers (CFRPs). There are insufficient studies on the piezoresistive effect of carbon fabric–reinforced cementitious matrices (CFRCMs). However, the influence of mortar infiltration cannot be ignored. In this study, the piezoresistive effects of dry carbon fiber bundles, CFRP bundles, and CFRCM bundles were compared. The condition of contacting filaments was observed by electron microscopy. Before loading, the epoxy resin had little effect on the contact, and the mortar separated many contacting filaments. Therefore, the CFRP bundles and dry carbon fiber bundles have similar initial resistances, while the CFRCM bundles have a larger initial resistance. During tension, the contact ratio of CFRCM bundles decreases due to mortar infiltration, and it improves the sensitivity to tensile fracture. However, this infiltration is nonuniform, which can only affect the piezoresistive effect of the sleeve layer. Almost every core filament can contact the surrounding filaments, and the contribution of core filaments to the piezoresistive effect is negligible. The result shows that the relative resistance change of the CFRCM in the failure stage is smaller than that of the CFRP, and the curves are more discrete. [ABSTRACT FROM AUTHOR]

The piezoresistive effect is characterized by the change in the resistivity of a material relative to mechanical forces exerted on it. Such materials can be used as pressure sensors and are among the most important components for micro-electro mechanical system applications. To date, most research on the piezoresistive effect has been directed toward cubic crystalline materials such as Si; however, the prospective non-cubic materials, such as SiC, are known to have exciting and promising properties. SiC exhibits high-temperature robustness and is chemically stable. It is expected that these properties can be applied to a variety of applications. These materials fall in the category of hexagonal crystalline systems, and it is difficult to evaluate the piezoresistive properties of such materials. In this study, we discuss the piezoresistive mobility model that corresponds to both the cubic and the hexagonal crystalline systems. This mobility model is derived from the empirical fitting of the Gauge Factor (G F) values using the longitudinal and the transverse piezoresistive coefficients and the material-unique fitting parameters. Our proposed method has been implemented in the original device simulator and has been evaluated with respect to both Si and SiC materials. This report shows the well-matched G F values and suggests that the proposed piezoresistive effect model can be implemented in device simulation modeling. [ABSTRACT FROM AUTHOR]

Significant attention has been paid to developing highly flexible and highly stretchable strain sensors due to the increasing demand for wearable devices such as motion-capturing devices and health-monitoring devices. Especially, carbon nanotube (CNT) network-based elastomeric sensors have been studied extensively for their unique strong piezoresistive response under large deformation. Despite its importance for the facile design of sensors, the effect of length and volume fraction of CNT on the piezoresistivity over a large strain range has not been fully uncovered. In this study, by combining coarse-grained molecular statics (CGMS) simulations and efficient percolation network analysis, we investigate the piezoresistive response of the CNT network for a wide range of the length and volume fraction and visualized the CNT network topology to understand the mechanism behind the piezoresistivity response. Based on the set of calculations, we obtain the design map of stretchability and sensitivity for the CNT-elastomer nanocomposite sensors over a wide range of design parameters of CNT, which can be used to fabricate the strain sensor with a desired performance.

In this study, a MoSe2/Ti3C2Tx nanohybrid-based fabricated flexible physical sensor demonstrates an elevated pressure sensitivity of 14.70 kPa−1 and a highly robust nature withstanding up to ∼2500 cycles. The fabricated pressure sensor's underlying transduction mechanism is elucidated by exploiting the inherent piezoresistive effect and the variation of the Schottky barrier height unveiled by the MoSe2/Ti3C2Tx interface with the assistance of comprehensive band structures that are appreciated by ultraviolet photoelectron spectroscopy. Also, sensors were employed as a 7 × 7 sensor matrix with a large area for tactile sensing and incorporated onto the volunteer hand to determine the artificial skin application. [ABSTRACT FROM AUTHOR]

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Carbon fibers and corresponding composites are being widely used in strengthening and repairing existing reinforced concrete structures. The piezoresistive effect of carbon fibers can be applied to self-monitor its stress and damage. However, rare piezoresistive models can be found in the literature considering the mesoscopic mechanism and material randomness of carbon fiber bundles to quantify the piezoresistive effect. The piezoresistive effect of carbon fiber bundles is mainly affected by the elastic deformation, breakage, and contact of filaments. In this paper, according to the analysis of these factors, a dynamic random equivalent parallel circuit model was established to quantify the piezoresistive effect of carbon fiber bundles during tension. With tensile results of 54 carbon fiber bundles, the uncertainties of filaments, such as the initial breakage, tensile breakage and contact change, were analyzed and their probability distributions were determined. The strength of filaments is subject to the Weibull distribution. Kolmogorov–Smirnov (K–S) test results show that the initial breakage ratio obeys a truncated lognormal distribution and the relative contact ratio change obeys a truncated normal distribution. Then Monte Carlo simulations were used to calculate the electrical resistance of carbon fiber bundles during tension. Comparing the simulated resistance with that of 15 verifying specimens, this piezoresistive model and calculation method is reliable and valid. [ABSTRACT FROM AUTHOR]

2D materials are promising nanomaterials for future applications due to their predominant quantum effects and unique properties in optics, electrics, magnetics, and mechanics. However, explorations in unique properties and potential applications of novel 2D materials have been hampered by synthesis and their stability under ambient conditions. Recently, in the graphene, 2D β‐CuI is observed experimentally under ambient conditions. Here, it is shown that this 2D β‐CuI@graphene possesses unexpected piezoresistive effect and room‐temperature ferromagnetism. Moreover, this 2D β‐CuI crystal is likely to be stable in a wide range of temperature, that is, below 900 K. Theoretical studies reveal that the unexpected piezoresistive effect is mainly attributable to the convergence of the electrons on Cu and I atoms to the Fermi level with increasing strain. There is a magnetic moment that is ≈0.97 μB on the edge of β‐CuI nanocrystal created by an iodine vacancy, which is considered the origin of such strong room‐temperature ferromagnetism. Clearly, the 2D β‐CuI@graphene provides a promising nanomaterial in the nano‐sensors with low power consumption pressure and magnetic nano‐devices with a size down to atomic scale. The discovery in the present work will evoke various new 2D nanomaterials with novel properties in nanotechnology, biotechnology, sensor materials, and technologies. [ABSTRACT FROM AUTHOR]

Microelectromechanical system (MEMS) pressure sensors based on silicon are widely used and offer the benefits of miniaturization and high precision. However, they cannot easily withstand high temperatures exceeding 150 °C because of intrinsic material limits. Herein, we proposed and executed a systematic and full-process study of SiC-based MEMS pressure sensors that operate stably from −50 to 300 °C. First, to explore the nonlinear piezoresistive effect, the temperature coefficient of resistance (TCR) values of 4H-SiC piezoresistors were obtained from −50 to 500 °C. A conductivity variation model based on scattering theory was established to reveal the nonlinear variation mechanism. Then, a piezoresistive pressure sensor based on 4H-SiC was designed and fabricated. The sensor shows good output sensitivity (3.38 mV/V/MPa), accuracy (0.56% FS) and low temperature coefficient of sensitivity (TCS) (−0.067% FS/°C) in the range of −50 to 300 °C. In addition, the survivability of the sensor chip in extreme environments was demonstrated by its anti-corrosion capability in H2SO4 and NaOH solutions and its radiation tolerance under 5 W X-rays. Accordingly, the sensor developed in this work has high potential to measure pressure in high-temperature and extreme environments such as are faced in geothermal energy extraction, deep well drilling, aeroengines and gas turbines. [ABSTRACT FROM AUTHOR]

A wearable and stretchable strain sensor with a gauge factor above 23 was prepared using a simple and effective technique. Conducting nanocomposite strands were prepared from styrene-b-(ethylene-co-butylene)-b-styrene triblock copolymer (SEBS) and carbon black (CB) through a solvent-processing method that uses a syringe pump. This novel nanocomposite preparation technique is a straightforward and cost-effective process and is reported in the literature for the first time. The work included two stages: the flexible nanocomposite preparation stage and the piezoresistive sensor stage. Depending on its molecular structure, the thermoelastic polymer SEBS is highly resilient to stress and strain. The main aim of this work is to fabricate a highly flexible and piezoresistive nanocomposite fibre/strand. Among the prepared composites, a composite corresponding to a composition just above the percolation threshold was selected to prepare the strain sensor, which exhibited good flexibility and conductivity and a large piezoresistive effect that was linearly dependent on the applied strain. The prepared nanocomposite sensor was stitched onto a sports T-shirt. Commercially available knee and elbow sleeves were also purchased, and the nanocomposite SEBS/CB strands were sewn separately on the two sleeves. The results showed a high sensitivity of the sensing element in the case of breathing activity (normal breathing, a 35% change, and deep breathing at 135%, respectively). In the case of knee and elbow movements, simultaneous measurements were performed and found that the sensor was able to detect movement cycles during walking. [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]

Wearable sensors integrating multiple functionalities are highly desirable in artificial wearable devices, which are of great significance in the field of biomedical research and for human–computer interactions. However, it is still a great challenge to simultaneously perceive multiple external stimuli such as pressure and temperature with one single sensor. Combining the piezoresistive effect with the negative temperature coefficient of resistance, in this paper, we report on a pressure–temperature dual-parameter sensor composed of a polydimethylsiloxane film, carbon nanotube sponge, and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate). The proposed multifunctional sensor can stably monitor pressure signals with a high sensitivity of 16 kPa−1, has a range of up to 2.5 kPa, and also has a fast response time. Meanwhile, the sensor can also respond to temperature changes with an ultrahigh sensitivity rate of 0.84% °C−1 in the range of 20 °C to 80 °C. To validate the applicability of our sensor in practical environments, we conducted real-scene tests, which revealed its capability for monitoring = human motion signals while simultaneously sensing external temperature stimuli, reflecting its great application prospects for electronic wearable devices. [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.)

In-situ formed free carbon nanodomain is an unique feature of polymer-derived ceramics (PDCs), which plays a significant role to affect the properties of PDCs, especially for the electoral property and piezoresistivity. In this study we report an enhanced piezoresistive properties of amorphous silicon carbonitrides (SiCN) ceramics derived by divinylbenzene (DVB)-modified polysilazane. Microstructure analysis indicated that the free carbon phase in SiCN ceramics is gradually increasing in order degree and concentration with increasing content of DVB. The average spacing between the conducting particles decreases with increasing concentration of free carbon, resulting in an enhanced internal electric field. The effects of DVB concentration on the piezoresistive properties of SiCN ceramics are also discussed, finding that the DVB has a significant effect on the piezoresistive properties. [ABSTRACT FROM AUTHOR]

Microelectromechanical systems (MEMS) thermal-piezoresistive resonator (TPRs) and thermal-piezoresistive oscillator (TPO) use thermal actuation and realize feedback through the piezoresistive effect. They have the advantages of simple manufacturing, high resolution, and low feedthrough. In particular, the piezoresistive effect can be used to realize thermal pumping to extract energy from a power supply and transmit it to the resonance structure. This can significantly improve the effective quality factor of the resonator and even realize spontaneous high-frequency oscillations, which has attracted significant interest from researchers. The combination of self-sustained oscillation with high quality factors of TPRs can perform various sensing applications and give excellent performance. This article provides a detailed introduction to the working principles of TPRs and thermal pumps and discusses methods to optimize their performance. Then, the manufacturing technologies of TPRs are summarized. Finally, applications of the resonators in sensing mass, magnetic fields, and displacement are reviewed. [ABSTRACT FROM AUTHOR]

This work presents an automated three‐point bending apparatus that can be used to study strain engineering and straintronics in 2D materials. This work benchmarks the system by reporting reproducible strain tuned micro‐reflectance, Raman, and photoluminescence spectra for monolayer molybdenum disulfide (MoS2). These results are in good agreement with reported literature using conventional bending apparatus. This work further utilizes the system to automate strain investigations of straintronic devices by measuring the piezoresistive effect and the strain effect on photoresponse in an MoS2 electrical device. The details of the construction of the straightforward system are given and it is anticipated that it can be easily implemented for study of strain engineering and straintronics in a wide variety of 2D material systems. [ABSTRACT FROM AUTHOR]

Abstract: In view of the problems of large volume, high energy consumption and difficult maintenance of electric field measurement sensors in existing power systems, non-contact miniature electric field sensors have become a hot topic in current research. In this paper, a MEMS miniature electric field measurement sensor model based on the principle of piezoelectric-piezoresistive coupling is constructed, and the sensor structure is optimized by analyzing the steady-state characteristics of the piezoelectric material and semiconductor membrane of the sensor. The input and output characteristics of the sensor were tested. The test results show that the sensor has excellent mechanical strain capacity, and the output voltage of the sensor has a linear relationship with the electric field strength, thus verifying the feasibility of the sensor measurement in the electric field. The research results will provide some reference for the development of contactless coupled sensors.

Piezoresistive effect is crucial in a pressure sensor design. Therefore, a theoretical model that can accurately predict the gauge factor (GF) of graphene pressure sensors should be designed. In this study, the function relationship between the relative change in resistance and the strain was established using the Fermi velocity as the intermediate variable. A theoretical model that can be used for various substrates was established after considering the anisotropic properties of graphene and the principle of action of pressure sensors. Tests on the graphene pressure sensor device fabricated using semiconductor technology revealed that the GF [GF = (ΔR/R)/ε] of the device was 1.14, which was within the theoretical prediction range (1.06–2.08). Furthermore, the reported Poisson's ratio values of various substrates were substituted into the calculation formula of the GF. The results revealed that the predicted value was highly consistent with the experimental test results. This result indicated that the theoretical model suitable for predicting the GF of graphene pressure sensors with various substrates is universal. This theory can provide theoretical guidance for the development of high-sensitivity graphene pressure sensors. [ABSTRACT FROM AUTHOR]

The effect of surface potential on the carrier mobility and piezoresistance of coreâ€"shell silicon carbide nanowires (SiC NWs) was investigated to realize small and sensitive SiC-microelectromechanical systems sensors. The p-type cubic crystalline SiC (3C-SiC) NWs were synthesized via the vaporâ€"liquidâ€"solid method and coated with silicon dioxide (SiO2) or aluminum oxide (Al2O3) dielectric shells to form coreâ€"shell structured NWs with different surface potentials. Four-point bending devices (FBDs) with a field-effect transistor (FET) configuration integrating a single coreâ€"shell 3C-SiC NW as the FET channel were fabricated to apply an additional electric field and strain to the coreâ€"shell 3C-SiC NWs. The fixed oxide charge densities of the SiO2 and Al2O3 shells showed positive and negative values, respectively, which were equivalent to electric fields of the order of several hundred thousand volt per centimeter in absolute values. In the coreâ€"shell 3C-SiC NWs with originally low impurity concentrations, the electric field induced by the fixed oxide charge of the shells can determine not only the electrical conduction but also the charge carriers in the NWs. Bending tests using the FBDs showed that the piezoresistive effect of the SiO2-coated NW was almost the same as that of the as-grown 3C-SiC NW reported previously, regardless of the gate voltage, whereas that of the Al2O3-coated NW was considerably enhanced at negative gate voltages. The enhancement of the piezoresistive effect was attributed to the piezo-pinch effect, which was more pronounced in the NW, where the carrier density at the coreâ€"shell interface is enhanced by the electric field of the dielectric. [ABSTRACT FROM AUTHOR]