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[Display omitted] Flexible electronics have introduced new challenges for efficient human–machine interactions. Hydrogels have emerged as prominent materials for electronic wearable applications due to their exceptional mechanical deformability and lightweight characteristics combined in some cases with conductive properties, and softness. Additionally, bio-interphases require multisensory response to stress, strain, temperature, and self-healing capacity. To mimic these properties, this work developed interpenetrated hydrogel networks composed of chitosan (CHI) and polyacrylic acid (PAA), combined with Fe (III) ions and varying amounts of NMBA (0–0.25 %), to achieve tailored conductivity (0.8–2.5 mS/cm), self-healing, self-standing and mechanical properties (E = 11.7–110 Pa and fracture strain = 64.9–1923 %) suitable for strain sensor applications. The results revealed a significant influence of the restrictive effect on the mobility of uncrosslinked chain segments, caused by Fe ions and NMBA, on the piezoresistance (GF 2.1–1.3) and self-healing capability of the gels. Interestingly, a transparent/turbid transition, driven by microphase separation that is characteristic of systems with high dynamic interactions, was encountered for the first time in these hydrogels. This transition was analyzed in relation to external temperature, water content, pH, and the influence of Fe ions and NMBA. The simultaneous sensitivity of these materials to temperature and pH, along with their piezoresistive and self-healing behaviour, can be highly valuable for multifunctional sensors in a wide range of applications. [ABSTRACT FROM AUTHOR]

Piezoresistive sensors composed of nickel nanostrands, nickel-coated carbon fibers, and silicone can be used to measure large physical deflections but exhibit viscoelastic properties and creep, leading to a complex and nonlinear electrical response that is difficult to interpret. This study considers the impact of modifying the geometry and architecture of the sensors on their mechanical and electrical performance. Varying the sensor thickness leads to potentially significant differences in conductive fiber alignment, while adding external layers of pure silicone provides elastic support for the sensors, potentially reducing their extreme viscoelastic nature. The impact of such modifications on both mechanical and electrical behavior was assessed by analyzing strain to failure, the magnitude of hysteresis with cycling, the repeatability of the electro-mechanical response, the strain level at which resistance begins to monotonically decrease, and the drift in electrical response with cycling. The results indicate that thicker single-layer sensors have less electrical drift. Sensors with a multilayered architecture exhibit several improvements in behavior, such as increasing the range of the monotonic region by approximately 52%. These improvements become more significant as the thickness of the pure silicone layers increases. [ABSTRACT FROM AUTHOR]

Strain engineering is a widely used technique for enhancing the mobility of charge carriers in semiconductors, but its effect is not fully understood. In this work, we perform first-principles calculations to explore the variations of the mobility of electrons and holes in silicon upon deformation by uniaxial strain up to 2% in the [100] crystal direction. We compute the π11 and π12 electron piezoresistances based on the low-strain change of resistivity with temperature in the range 200 K to 400 K, in excellent agreement with experiment. We also predict them for holes which were only measured at room temperature. Remarkably, for electrons in the transverse direction, we predict a minimum room-temperature mobility about 1200 cm2 V−1 s−1 at 0.3% uniaxial tensile strain while we observe a monotonous increase of the longitudinal transport, reaching a value of 2200 cm2 V−1 s−1 at high strain. We confirm these findings experimentally using four-point bending measurements, establishing the reliability of our first-principles calculations. For holes, we find that the transport is almost unaffected by strain up to 0.3% uniaxial tensile strain and then rises significantly, more than doubling at 2% strain. Our findings open new perspectives to boost the mobility by applying a stress in the [100] direction. This is particularly interesting for holes for which shear strain was thought for a long time to be the only way to enhance the mobility. [ABSTRACT FROM AUTHOR]

Flexible pressure sensors have attracted much attention because of their application prospects in wearable devices, electronic skin, and health monitoring. However, it is still difficult to obtain pressure sensors with excellent performance simply and efficiently. Indium tin oxide (ITO) is a widely used transparent conductive material, and polyvinyl alcohol (PVA) is an elastic insulating material with the advantages of easy processing and stable mechanical properties. ITO nano‐crystalline particles are dispersed into PVA polymers to form an ITO nanocrystalline‐PVA composite film with good electrical conductivity as a piezorestoresistive material, fabricating a pressure sensor with excellent performance. The pressure sensor possesses superior sensitivity (641.15 kPa−1), wide detection range (0–80 kPa), fast response time (10.93 ms), and recovery time (8.05 ms), and excellent stability (more than 1500 cycles). The pressure sensor shows excellent performance in a variety of applications, such as pulse testing, speech recognition, and detection of various joint movements of the human body (such as knees, fingers, elbows, etc.). The sensor has application prospects in health monitoring and motion perception. [ABSTRACT FROM AUTHOR]

The development of flexible piezoresistive sensors has increasingly attracted widespread attention due to their various potential applications in wearable devices, human–machine interfaces, and health monitoring systems. Developing high‐performance sensors that can accurately monitor movement and human health monitoring is very necessary. This study uses silver nanoparticles, MXene, and polypyrrole to prepare conductive fabrics based on various fabrics through layer‐by‐layer encapsulation. Finally, conductive fabrics with different layers were encapsulated to prepare a multilayer fiber sensor. Next, the series piezoresistive performance of sensors made of different fabric materials and sensors with different layers were tested. The experimental results show that the sensor prepared has the best performance when the selected fabric material is mulberry silk and the number of layers of the fabric is five. After testing, the sensitivity of the sensor is 4.9029 at low strain and 0.7901 at high strain. Moreover, it exhibits good stability during 1600 compression‐release cycles and temperatures range from −20 to 60°C. The designed sensor performs well in motion and human physiological signal monitoring. This study provides new ideas and references for the design and research of multilayer fiber sensors. [ABSTRACT FROM AUTHOR]

Abstract Measurements of low‐frequency physiological signals, such as heart rate and pulse waves, play an essential role in biomedical applications for the early diagnosis of abnormal cardiovascular activities. Recent advances in flexible mechanical electronics represent a novel concept of miniaturized, wearable sensors for heart rate measurement that can be used in ambulatory environments. However, most mechanical sensors require the sensing element to be placed directly on the skin surface, which can lead to performance degradation or device damage due to significant skin deformation or external forces from skin‐object interactions. This work addresses this challenge by developing soft, stretchable mechano‐acoustic sensing platforms where all sensing components are not directly subjected to skin movement or deformation. Instead, this design allows cardiovascular pulse waves to propagate through a hollow, flexible microchannel, to vibrate the piezoresistive sensing element. Experimental studies demonstrate a complete wireless sensing system capable of detecting pulse waves and heart rates, with results consistent with those of commercially available devices. The proposed sensing concept allows for the develop of other wireless and flexible sensing systems such as a flexible air‐channel pad for detecting swallowing patterns from users’ laryngeal movements, facilitating a non‐invasive and remote platform for potential monitoring, and assessment of dysphagia.

Atomically thin two-dimensional materials, such as graphene, exhibit extreme high-pressure sensitivity compared to the commercially used pressure sensors due to their high surface-to-volume ratio and excellent mechanical properties. The smaller piezoresistance of graphene across different transport regimes limits its pressure sensitivity compared to other two-dimensional materials. Using membrane theory and the thin-film adhesivity model, we show miniaturization as a means to enhance the overall performance of graphene pressure sensors. Our findings reveal that ballistic graphene can be configured to measure ultra-high pressure (≈ 10 9 Pa) with many-fold high-pressure sensitivity than other contemporary two-dimensional materials. Based on these findings, we propose an array of ballistic graphene sensors with extreme high-pressure sensitivity and ultra-high-pressure range that will find applications in next-generation nano-electro-mechanical system pressure sensors. The performance parameters of the array sensors can be further enhanced by reducing the size of graphene membranes and increasing the number of sensors in the array. The methodology developed in this paper can be used to explore similar applications using other two-dimensional materials. [ABSTRACT FROM AUTHOR]

A force plate is mainly used in biomechanics; it aims to measure the ground reaction force in a person's walking or standing position. In this study, a large-area force mat of the piezoresistance sensing type was developed, and a deep-learning-based weight measurement calibration method was applied to solve the problem in which measurements are not normalized because of physical limitations in hardware and signal processing. The test set was composed of the values measured at each point by weight and the value of the center of the pressure variable, and the measured value was predicted using a deep neural network (DNN) regression model. The calibration verification results show that the average weight errors range from a minimum of 0.06% to a maximum of 3.334%. This is simpler than the previous method, which directly measures the ratio of the resistance value to the measured weight of each sensor and derives an equation. [ABSTRACT FROM AUTHOR]

This study discusses the effect of stress on 4H-silicon carbide (4H-SiC) power diodes using numerical simulations. Two power diodes were evaluated; namely, a 600 V PiN diode and 1.8 kV junction barrier Schottky (JBS) diode. Stress changes the carrier mobilities in the material of the PiN diode of a bipolar diode; that is, the mobility is enhanced by the piezoresistive effect, which minimizes the on-resistance or leakage current. The simulation results demonstrate that compressive stress can have a positive effect on the device operation, particularly in p$^+$-substrate power diodes. Regarding the JBS diode, the GPa-order tensile stress positively effects both forward and reverse characteristics. A cantilever structure is suitable for JBS diodes, and press-pack packaging for PiN diodes can enhance the device characteristics.

Piezoresistance, the change of electrical resistance due to applied mechanical strain, has been characterized for films in tension or bending. However, measuring the compressive piezoresistance of films remains a challenge because the in-plane compression often results in macroscopic buckling and kinking, leading to localization of strain. Here, we overcame this issue via a newly developed method to calculate the compressive piezoresistance of films by measuring the change of resistance in situ under tensile and bending stresses. A linear fit was applied to the experimental tensile piezoresistive response and a quadratic fit was applied to the bending piezoresistive response. The experimental bending response was mathematically decomposed into its tensile and compressive components. The compressive response was then isolated by subtracting the tensile response from the bending response. In this study, the method is applied to reduced graphene oxide (rGO) film specimens. For rGO films, the compressive piezoresistance was found to be much greater than the tensile piezoresistance. Scanning electron microscope images revealed that extensive damage occurred on the compressive side of the bending specimen, resulting in a large increase in resistivity. We anticipate that our study will be adapted to applications that require mechanically reliable, flexible, and highly conductive materials, such as flexible electronics and structural energy and power. [ABSTRACT FROM AUTHOR]

Wearable devices for gait measurement are devices worn on the body to measure the gait of the wearers. During gait measurement, several parameters are measured and the choice of parameters is influenced by the application and by extension the gait index. Two approaches have been adopted in this research. One is the provision of an overview of wearable devices for gait measurement with a bias towards textile-based “soft” smart wearable systems using information from varied academic sources and databases. The second approach is to map out key scientific research trends within the wearable device classes using the Web of Science database. The focus is to make a case for textile-based gait measurement devices and systems while exploring the key determinants of wearable gait sensor placements and application efficiency. These soft smart wearable systems describe flexible material sensor-based systems which have their sensing mechanisms based on material deformation after being subjected to stress or pressure. This study could therefore serve as an apt reference for the development of soft smart wearable gait measurement systems as it throws light on the various soft wearable gait measurement applications, the bottlenecks in soft wearable device design, opportunities for developing new devices and the merit that soft gait analysis systems possess over their hard gait measurement counterparts.

Accurate and fast breath monitoring is of great importance for various healthcare applications, for example, medical diagnoses, studying sleep apnea, and early detection of physiological disorders. Devices meant for such applications tend to be uncomfortable for the subject (patient) and pricey. Therefore, there is a need for a cost-effective, lightweight, small-dimensional, and non-invasive device whose presence does not interfere with the observed signals. This paper reports on the fabrication of a highly sensitive human respiratory sensor based on silicon nanowires (SiNWs) fabricated by a top-down method of metal-assisted chemical-etching (MACE). Besides other important factors, reducing the final cost of the sensor is of paramount importance. One of the factors that increases the final price of the sensors is using gold (Au) electrodes. Herein, we investigate the sensor's response using aluminum (Al) electrodes as a cost-effective alternative, considering the fact that the electrode's work function is crucial in electronic device design, impacting device electronic properties and electron transport efficiency at the electrode–semiconductor interface. Therefore a comparison is made between SiNWs breath sensors made from both p-type and n-type silicon to investigate the effect of the dopant and electrode type on the SiNWs respiratory sensing functionality. A distinct directional variation was observed in the sample's response with Au and Al electrodes. Finally, performing a qualitative study revealed that the electrical resistance across the SiNWs renders greater sensitivity to breath than to dry air pressure. No definitive research demonstrating the mechanism behind these effects exists, thus prompting our study to investigate the underlying process. [ABSTRACT FROM AUTHOR]

Nanoscale electro-mechanical systems (NEMS) displaying piezoresistance offer unique measurement opportunities at the sub-cellular level, in detectors and sensors, and in emerging generations of integrated electronic devices. Here, we show a single-molecule NEMS piezoresistor that operates utilising constitutional and conformational isomerisation of individual diaryl-bullvalene molecules and can be switched at 850 Hz. Observations are made using scanning tunnelling microscopy break junction (STMBJ) techniques to characterise piezoresistance, combined with blinking (current-time) experiments that follow single-molecule reactions in real time. A kinetic Monte Carlo methodology (KMC) is developed to simulate isomerisation on the experimental timescale, parameterised using density-functional theory (DFT) combined with non-equilibrium Green's function (NEGF) calculations. Results indicate that piezoresistance is controlled by both constitutional and conformational isomerisation, occurring at rates that are either fast (equilibrium) or slow (non-equilibrium) compared to the experimental timescale. Two different types of STMBJ traces are observed, one typical of traditional experiments that are interpreted in terms of intramolecular isomerisation occurring on stable tipped-shaped metal-contact junctions, and another attributed to arise from junction‒interface restructuring induced by bullvalene isomerisation. The quest for miniaturisation of electromechanical nanosystems requires the use of single molecules as active components. Here, the authors develop a piezoresistor based on a single bullvalene molecule that changes its shape by a Cope rearrangement. [ABSTRACT FROM AUTHOR]

The geotechnical monitoring of tailings dams combined with a suitable application of geophysical electrical methods can improve their structure evaluation, allowing several correlations between direct analyses and the resistivity anomaly pattern. Considering this synergy, twenty-three electrical resistivity sections (ERT) were acquired along the beach, abutments, and central part of a dam, totalizing 10,776 m of dataset. After the interpretation of each ERT section, comparing the anomaly ranges with the water level meters measurements, three resistivity zones were defined: Zones of low resistivity (<64 ohm-m), correlated to regions of high humidity; zones of high resistivity (> 357 ohm-m), interpreted as dry zones, and regions with intermediate resistivity values, located between these limits. The groundwater surface generated from the interpretation of the electrical resistivity dataset and the groundwater surface acquired from the water level gauges were almost coincident. On the right abutment, the conductive anomalies showed remarkable continuity, suggesting a high moisture content in this region with strong gradients (200 mV) directed towards the zone of low resistivity values identified in the sections. The analysis showed a robust correlation of the ERT data with localized physical geotechnical measurements, valuable for monitoring dam integrity, overseeing the structure's response to climate and operational changes, and ultimately mitigating the risks of failure. The results of this study support the adoption of a seasonal 4D electrical resistivity survey as an effective tool to monitor and manage surface and high humidity zones, key indicators of dam integrity throughout the entire structure. [ABSTRACT FROM AUTHOR]

This paper addresses semiconductor piezoresistive materials selection in MEMS engineering design. From the practical engineering point of view, it is important to understand piezoresistance properties of semiconductors even if less accuracy under feasibility design phase. However, piezoresistance is frequently analyzed based on first principle electronic band structure simulations by sophisticate physicists. Practical engineers not familiar with this simulation cannot directly apply useful information derived from the result of simulation. This paper provides practical prediction method for piezoresistance based on electronic band parameters obtained from the state‐of‐the‐art solid‐state physics. It is demonstrated that the crucial parameters which control the p‐type shear piezoresistance coefficient π44 in diamond and zinc‐blend single crystals are the inverse of square of bond length in unit cell atom, the square root of valence light hole mass, and the shear elastic compliance coefficient S44. [ABSTRACT FROM AUTHOR]

The piezoresistance of carbon nanotube (CNT)-coated microfibers is examined using diametric compression. Diverse CNT forest morphologies were studied by changing the CNT length, diameter, and areal density via synthesis time and fiber surface treatment prior to CNT synthesis. Large-diameter (30–60 nm) and relatively low-density CNTs were synthesized on as-received glass fibers. Small-diameter (5–30 nm) and-high density CNTs were synthesized on glass fibers coated with 10 nm of alumina. The CNT length was controlled by adjusting synthesis time. Electromechanical compression was performed by measuring the electrical resistance in the axial direction during diametric compression. Gauge factors exceeding three were measured for small-diameter (<25 μm) coated fibers, corresponding to as much as 35% resistance change per micrometer of compression. The gauge factor for high-density, small-diameter CNT forests was generally greater than those for low-density, large-diameter forests. A finite element simulation shows that the piezoresistive response originates from both the contact resistance and intrinsic resistance of the forest itself. The change in contact and intrinsic resistance are balanced for relatively short CNT forests, while the response is dominated by CNT electrode contact resistance for taller CNT forests. These results are expected to guide the design of piezoresistive flow and tactile sensors. [ABSTRACT FROM AUTHOR]

Piezoresistive nanocomposites are an important class of materials that allow the production of very sensitive strain sensors. Herein, a new class of piezoresistive nanocomposites prepared by mixing different types of 2D nanosheets is explored. In this way, three distinct types of nanocomposite are produced by mixing conducting and insulating nanosheets (graphene, Gr and boron nitride, BN), conducting and semiconducting nanosheets (graphene and tungsten diselenide, WSe2 or tungsten disulfide, WS2) as well as mixing two different types of conducting nanosheets (graphene and silver, Ag). For each nanocomposite type, a different dependence of composite conductivity on filler volume fraction is observed although all behaviors can be fully described by percolation theory. In addition, each composite type shows different piezoresistive properties. Interestingly, while the conductor insulator composites show the standard monotonic relationship between gauge factor and conductivity, both conductor:semi‐conductor and conductor:conductor composites show very unusual behavior, in each case displaying a peak engage factor at the percolation threshold. In each case, percolation theory is used to develop simple equations for gauge factor as a function of both volume fraction and conductivity that fully describes all experimental data. This work expands the understanding of piezoresistive nanocomposites and provides a platform for the engineering of high‐performance strain sensors. [ABSTRACT FROM AUTHOR]

In this study, an electrostatic force-driven on-chip tester consisting of a mass with four guided cantilever beams was employed to extract the process-related bending stiffness and piezoresistive coefficient in-situ for the first time. The tester was manufactured using the standard bulk silicon piezoresistance process of Peking University, and was tested on-chip without additional handling. In order to reduce the deviation from process effects, the process-related bending stiffness was first extracted as an intermediate value, namely, 3590.74 N/m, which is 1.66% lower than the theoretical value. Then, the value was used to extract the piezoresistive coefficient using a finite element method (FEM) simulation. The extracted piezoresistive coefficient was 9.851 × 10−10 Pa−1, which essentially matched the average piezoresistive coefficient of the computational model based on the doping profile we first proposed. Compared with traditional extraction methods, such as the four-point bending method, this test method is on-chip, achieving automatic loading and precise control of the driving force, so it has high reliability and repeatability. Because the tester is manufactured together with the MEMS device, it has the potential to be used for process quality evaluation and monitoring on MEMS sensor production lines. [ABSTRACT FROM AUTHOR]

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In the automotive, aerospace, biomedical, and home appliance industries, piezoresistive pressure sensors were among the earliest MEMS products created. Piezoresistive microcantilever sensor is one of the promising mechanical microsensors that have been around for many years. Microcantilevers are mechanical stress sensors that are being developed as physical chemical, and biological sensors. The piezoresistive transduction mechanism is a common transduction process for pressure sensors. This piezoresistive pressure sensor design has improved tremendously over the last decade, beginning with the development of piezoresistance in silicon and continuing with the most recent piezoresistive pressure sensor materials. This paper provides cantilever designs with rectangle, T-shape, E shape, and U shape stress concentration areas to increase the surface-stress sensitivity of piezoresistive micro cantilevers. Differential stress at the surface to the beam of the cantilever causes the bending of cantilever. Silicon dioxide material are used for the cantilever substrates, while p-doped silicon is used for the piezoresistor. COMSOL software is used to get the sensor design and analysis parameters such as stress, deflection, and sensitivity.

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]

The in situ strain/stress detection of hot components in harsh environments remains a challenging task. In this study, graphene/SiCN (G-SiCN) thin-film strain gauges (TFSGs) were fabricated on alumina substrates by direct ink writing (DIW). The percolation model and the piezoresistive effect of G-SiCN composites were systematically studied. On this basis, a TFSG with high conductivity (0.1 S/cm) and high sensitivity (gauge factor (GF) 9.9) of ceramic matrix conductive composites was fabricated. The graphene/SiCN TFSG has excellent static and dynamic strain response at room temperature. Subsequently, the strain dynamic test was conducted at 400 °C, and there was no attenuation of the GF, so as to verify the high-temperature performance of the G-SiCN TFSG. Therefore, G-SiCN TFSGs provide an effective approach for the measurement of the in situ static and dynamic strain of hot components in high-temperature environments. [ABSTRACT FROM AUTHOR]

Electronic nematicity, the breaking of the crystal lattice rotational symmetry by the electronic fluid, is a fascinating quantum state of matter. In this work, using electronic transport under strain we investigate the electronic nematicity of BaNi2(As1−xPx)2, a candidate system for charge-induced nematicity. We report a large B1g elastoresistance coefficient that is maximized at the tetragonal-to-orthorhombic transition temperature, that slightly precedes the first-order triclinic transition. An hysteretic behavior is observed in the resistance versus strain sweeps and interpreted as the pinning of orthorhombic domains. Remarkably, the elastoresistance only onsets together with a strong enhancement of the incommensurate charge density wave of the material, strongly suggesting that this electronic instability is uniaxial in nature and drive the orthorhombic transition. The absence of sizeable elastoresistance above this electronic phase clearly contrasts dynamic and static electronic nematicity. Finally, the elastoresistance temperature dependence that strongly differs from the Curie-Weiss form of iron-based superconductors reveals major differences for the respective coupling of electronic nematicity to the lattice. Our results uncover an extremely strain-sensitive platform to study electronic anisotropy induced by a charge-density-wave instability. [ABSTRACT FROM AUTHOR]

Herein, a novel in-plane dual-axis micro-electro-mechanical system piezoresistive accelerometer was proposed based on theoretical and simulation analyses. Its self-support piezoresistive beam (SPB) possessed the features of force amplification and axial deformation to obtain high sensitivity. To clarify the influence of structural dimensions on the performance of the accelerometer and the pure axial-deformation condition of the SPB, a theoretical model was established to analyze mechanical behavior. The theoretical results were in well accordance with the simulation ones, displaying a maximum relative error of less than 10%. The theoretical and simulation results suggested that the accelerometer with thin and long support/hinge beams possesses a higher sensitivity but a lower frequency. However, the sensitivity and natural frequency increased simultaneously before the distance between SPB and support beam $D$ reached a certain value. The simulated longitudinal stress of SPB achieved the average value of 32.473 MPa, and the first-order natural frequency was nearly 13.6 kHz. Furthermore, the fabricated accelerometer was tested in a simple packaging case. The experimental results demonstrated that the proposed accelerometer had a measuring sensitivity of 0.198 mV/g/V with a maximum non-linearity of 1.00% FS and a resonant frequency of 12.93 kHz. The cross sensitivities were 11.93 and $15.97~\mu \text{V}$ /g/5V in the $y$ and $z$ axes, respectively, which were 1.21% and 1.61% of the prime-axis sensitivity. The zero offset with varying temperatures was 0.00296%/°C, and the zero drift in the long-term static stability test was 0.02 mV. All the results above revealed the promising application potential of the proposed accelerometer in vibration detection in the high-speed rotating spindle of machine tools. [2022-0057] [ABSTRACT FROM AUTHOR]

The measurement of high electric field is widely used in applications such as power grid, electrical equipment, space launch, petroleum industry, and meteorological monitoring. Traditional electric field measurement methods, such as field mills, are bulky and cause electric field distortion. In this article, we presented a trampoline-shaped microelectric field sensor (E-sensor) based on microelectromechanical system (MEMS). The micro E-sensor uses the effect of electrostatic induction, which generates force that drives the vibration of a piezoresistive film and converts the electric field into a differential voltage signal. The presented E-sensor can measure both ac and dc high electric fields with relatively high resolution and wide range. Through experimental measurement, the device exhibits an ac resolution of 172 V/m/Hz1/2 and a linear measurable electric field range of 312 V/m to over 700 kV/m. The presented E-sensor has good performance with mm-level size and low cost, which could be mass produced for broad applications. [ABSTRACT FROM AUTHOR]

This study investigates the piezoresistive (self-sensing) properties of short stainless-steel fiber-reinforced mortar under varying temperature conditions. Different reinforced mortars were produced by varying fiber and aggregate content. First, Electrical Impedance Spectroscopy (EIS) measurements were used to characterize the electrical properties of the mortar specimens. EIS measurements were performed at temperatures of 24 °C, 35 °C, and 50 °C. Second, to investigate the self-sensing capacity of the different composites, the fractional changes of electrical impedance at 1 kHz were monitored under two conditions: temperature variation alone (cooling down from 35 °C or 50 °C to room temperature), and temperature variation combined with cyclic compressive loading (up to 5 MPa). The results of the former were used to compensate for the effect of temperature variations in the latter. Both temperature and mechanical loading produced meaningful variations in the electrical impedance and piezoresistivity of the investigated composites. Conclusions are drawn with respect to the stress and temperature sensitivity of the composites. The real and imaginary parts of the electrical impedance of the mortar produced with the highest fiber volume fraction (0.01%) and higher aggregate content (volume fraction of 60%) were distinctly sensitive to temperature and stress, which suggests the possibility of using the same composite as a stress and temperature sensor. [ABSTRACT FROM AUTHOR]

Flexible pressure sensors with high sensitivity, low cost, lightweight, and convenience are of significance in the field of human movement monitoring and sensing. This article demonstrated a piezoresistive pressure sensor prepared by layer-by-layer (LbL) self-assembly of MXene and carbon black (CB) on a polyurethane (PU) sponge. The electronegativity of MXene and the electropositive of CB enable them to combine more stably. The assembled sensor achieves reliable repeatability (over 3700 cycle testing), high sensitivity (−5.26 kPa $^{-{1}}$), wide sensing range (0–240 kPa), acceptable response time (300/300 ms), and good reproducibility under various pressures. MXene and CB greatly increase the electrical conductivity and measurement range of the piezoresistive sensors. The existence of microcracks allows the sensor to sensitively capture micropressure signals, such as human radial artery pulse and respiration. In addition, the large-area conductive framework permits the sensor to maintain high responsiveness over a huge strain range and to distinguish various degrees of human movement. Furthermore, the sensor has shown excellent performance in controlling smart devices through external pressure as a human–machine interface. The pressure sensor based on LbL self-assembled MXene/CB on a PU sponge has potential applications in motion signal detection, artificial intelligence, and other fields. [ABSTRACT FROM AUTHOR]

In this article, a methodology for wireless and passive pressure measurement systems has been presented based on the principle of inductive-capacitive (LC) sensing. In the proposed method, two flexible carbon composite materials: Velostat and carbon conductive foam have been chosen as the pressure sensing element. Both the materials have the property of piezoresistivity and show the change in resistivity with applied pressure. In the designed sensor, the LC circuit has been modified into an LCR tank circuit with a variable resistor as a sensing element. During the measurement, pressure has been monitored and measured using a reader coil, connected with the impedance analyzer. The change in resistance in Velostat or conductive foam with applied pressure, changes the input impedance, quality factor, and resonance frequency. The proposed measurement system has shown an innovative technique based on an LC pressure measurement system with a resistive sensing element. Both the sensing materials have been taken separately and individual experiments have been performed. The method has been tested and evaluated experimentally, which also analyzes the two carbon-composite-based materials for this type of wireless pressure sensor. [ABSTRACT FROM AUTHOR]

Bolted joints play important roles in ensuring the integrity of composite structures. Information obtained through structural health monitoring (SHM) can be used to determine the health condition of composite bolted joints. However, integrating monitoring sensors with the composite bolted joints is an extremely challenging problem. In this study, a nanocomposite piezoresistive sensor made of carbon black (CB) and polyvinyl pyrrolidone (PVP) is applied to the composite bolted joints looseness monitoring. The change in the mass fraction of CB particles leads to different resistance values, which are measured to analyze the conductive property of the sensor. The mechanical properties of the sensor are demonstrated under pressure loading with different mass fractions of CB particles. The nanocomposite piezoresistive sensor is integrated with the carbon fiber reinforced plastics (CFRP) single-lap bolted joints, and the optimized electrode layout is presented by comparing the change of resistance and the sensitivity. The state of CFRP bolted joints looseness is represented by the change of relative resistance with different torques. The experimental results show that the CB/PVP nanocomposite piezoresistive sensor has great potential in SHM to realize the integration of the sensor and life-cycle monitoring of composite bolted joints. [ABSTRACT FROM AUTHOR]

Antioverload high-range accelerometer is playing an increasingly important role in the field of hard target penetration testing, and the demand of higher accuracy and higher range accelerometers is growing consequently. Therefore, a novel accelerometer with a new structure of membrane island is proposed in this article, while the measurement range is significantly improved to 200 000 g. The design is mainly based on the finite-element method. In general, the membrane-island structured piezoresistive accelerometer is formed of a four-clamped membrane that carries a piezoresistor at the four ends. The four piezoresistors form a Wheatstone bridge. Then, based on the Timoshenko plate and shell theory, a mathematical stiffness model of the four-clamped membrane is established. The detailed parameters of the sensor are carried out by the finite-element analysis (FEA) and optimization, and it has a maximum stress of 26.8 MPa and a maximum displacement of $0.208~\mu \text{m}$ when applying an input acceleration of 200 000 g. Finally, the sensitivity test, antioverload test, and dynamic test of three membrane-island structured prototypes are carried out, and their sensitivities are 0.579, 0.505, and $0.532~\mu \text{V}$ /g, respectively; the passband with 5% dynamic error is 14.9, 16.5, and 15.8 kHz, respectively. The accelerometer has an antioverload capability of 250 000 g, which is verified by the Hopkinson bar. The test results show that this membrane-island structured accelerometer has both good antioverload capability and high accuracy. [ABSTRACT FROM AUTHOR]

This study examined the temperature-related piezoresistance issues of p-type doped 3C-silicon carbide (3C-SiC) materials. Previously, we proposed piezoresistance temperature models that describe phenomena based on the ionization energies of materials oriented for high-temperature operations. This study aimed to determine the ionization energy as a function of the aluminum doping concentration of 3C-SiC. However, at the low-temperature region a drastic decrease in the piezoresistive coefficient was observed, and it was predicted to occur when materials possessing large impurity ionization energy are used under negative thermal strained conditions. This phenomenon is in contrast to the conventional piezoresistance factor $P(N,T)$ that is based on narrow band-gap materials such as silicon or germanium; thus, it provides new insights into low-temperature piezoresistance phenomena.

In this paper, a first-order average temperature coefficient of resistance ( TC R ave ) calculation model is established and analyzed based on the distribution of piezoresistive doping concentration in bulk silicon. Furthermore, by extracting the experimental results of the first-order TC R ave of multiple research groups and combining the first-order TCR ave calculation model, the new mobility model in the concentration range of piezoresistance (1 Ă— 1018â€"1 Ă— 1020 at cmâˆ'3) is obtained by fitting. The first-order TC R ave of five implantation concentrations under the same process is tested. The results show that the error between the first-order TC R ave obtained based on the new mobility calculation model and the test results is within 5%. However, the first-order TC R ave based on the Arora mobility model has a deviation of 104.6% under the implantation condition of 3.75 Ă— 1015 at cmâˆ'2. At the same time, the effects of different annealing temperatures and time on the first-order TC R ave at the implantation concentration of 8.5 Ă— 1013 at cmâˆ'2 are compared. The results show that a higher annealing temperature or longer annealing time is not conducive to reducing the first-order TC R ave , but the difference is small. [ABSTRACT FROM AUTHOR]

For pressure sensors, high sensitivity and broad effective sensing range are often incompatible. To balance the relationship between them, herein, a flexible pressure sensor employing 3-D porous MXene/reduced graphene oxide (MXene/rGO) hybrid foam as piezoresistive sensing material is developed by an efficient hydrothermal synthesis and a novel reduction method of flash instantaneous irradiation. Compared with conventional reduction methods, this instantaneous reduction process can effectively maintain MXene nanoflakes in tightly interconnected rGO sheets, resulting in robust mechanical elasticity and high conductivity of the proposed MXene/rGO hybrid foam. On account of the 3-D porous skeleton structure of MXene/rGO hybrid foam, the proposed pressure sensor presents a high sensitivity up to 3.75 kPa−1, a broad sensing range from 0 to 28 kPa, an ultralow detectable limit down to 1.5 Pa, rapid dynamic response/recovery times with 20/40 ms, a low hysteresis of 2.95%, as well as a strong stability for over 2000 Hz. Notably, the flexible pressure sensor possesses the superior function of precisely detecting some subtle human activities (pulse, vocalization, breathing, etc.) and large joints (knee, finger, elbow, wrist, etc.) movements in real time. Besides, a matrix pressure array of $4\times $ 4 pixels has been exploited for multipoint recognition. [ABSTRACT FROM AUTHOR]

The research toward high-performing pressure sensors has been going on for more than two decades, with the goal of improving key parameters, namely the high gauge factor (GF) and device stability for future applications. In the present work, the piezoresistivity of the polycrystalline molybdenum disulfide (MoS2) is harnessed for pressure sensing applications with very low noise levels. The fabricated microelectromechanical systems (MEMS) pressure sensor exhibits a high GF of ~92 with pressure sensitivity of ~ $0.46 \mu \text{A}$ /Pa and a low nonlinearity of ~12% in the applied pressure range 0–20 kPa. This exceptional performance is explained based on fluctuation-induced tunneling in the polycrystalline MoS2-based pressure sensor. The tunneling barrier between two grains gets modified with the application of external pressure. Furthermore, the noise analysis of the fabricated MEMS pressure sensor shows that the noise level gets altered with the applied stress due to the modified barrier potential. [ABSTRACT FROM AUTHOR]

Silicon nanowires (SiNWs) are known to exhibit a large piezoresistance (PZR) effect, making them suitable for various sensing applications. Here, we report the results of a PZR investigation on randomly distributed and interconnected vertical silicon nanowire arrays as a pressure sensor. The samples were produced from p-type (100) Si wafers using a silver catalyzed top-down etching process. The piezoresistance response of these SiNW arrays was analyzed by measuring their I-V characteristics under applied uniaxial as well as isostatic pressure. The interconnected SiNWs exhibit increased mechanical stability in comparison with separated or periodic nanowires. The repeatability of the fabrication process and statistical distribution of measurements were also tested on several samples from different batches. A sensing resolution down to roughly 1 m pressure was observed with uniaxial force application, and more than two orders of magnitude resistance variation were determined for isostatic pressure below atmospheric pressure. [ABSTRACT FROM AUTHOR]

Silicon piezoresistive sensors have been widely used for many applications in recent decades. Monocrystalline silicon resistors are realized using an ion-implantation or a thermal diffusion process with a Gaussian or complementary error function profile. However, over the years, most researchers have neglected the doping concentration profile of the piezoresistor in the modeling stages resulting in erroneous responses that are far removed from experimental results of fabricated resistive sensors. In the present work, we propose a simulation approach to accurately estimate the piezoresistance of thermally diffused resistors with a non-uniform doping profile. We have modeled the diffused resistor as a parallel combination of several small slices, each having a unique piezoresistive coefficient. Three different slicing strategies were investigated to evaluate the impact of the piezoresistive coefficients, the electrical resistivity of the resistor slices, and the stress profile across the thickness of the resistor embedded in an accelerometer device. The cumulative impact of these parameters on the sensor’s overall sensitivity is evaluated. Further, we have also studied the influence of the accelerometer’s flexure thickness on the sensor’s sensitivity. It is observed from the simulation results that one of the slicing strategies with more slices at the surface of the resistor results in less than 1% error compared to the experimental results of an accelerometer device with a 60 µ m flexure thickness. [ABSTRACT FROM AUTHOR]

Elastic and plastic molecular crystals that exhibit electrical conductivity have attracted much attention. Flexible molecular semiconductors exhibiting significant piezoresistivity can be utilized in mechanical sensors in which the application of silicon-based semiconductors is difficult. In this study, we prepared a simple stress–strain measuring apparatus that can be combined with electric measuring instruments. The electric resistivity of the organic semiconductive crystal of Q(TCNQ)2 (Q+ = quinolinium) was measured during the stress–strain test. A large increase in resistivity was observed during the bending of the Q(TCNQ)2 crystal. The coefficient of the resistivity change against strain was much larger than that of the general strain gauge comprising metallic alloys, where the elastic limit was considerably larger than that of the strain gauge fabricated using silicon-based semiconductors. The large resistivity change was described using a tight-binding model with simple material mechanics. [ABSTRACT FROM AUTHOR]

The hydrostatic pressure effect on the resistivity and magnetization of the narrow band gap manganite Sm0.7-xLaxSr0.3MnO3 (x=0, 0.1) systems has been investigated. At ambient pressure measurements, the parent compound Sm0.7Sr0.3MnO3 showed a ferromagnetic-insulating nature, whereas the 10% La-doped compound Sm0.6La0.1Sr0.3MnO3 showed a ferromagnetic-metallic nature. Furthermore, both samples showed a spin-reorientation transition (TSR) below Curie temperature, which originated from the Mn sublattice and was supported by an antiferromagnetic Sm(4f)-Mn(3d) interaction. Both samples exhibited a normal and inverse magnetocaloric effect as a result of these two different magnetic transitions. Magnetization measurements on Sm0.7Sr0.3MnO3 under pressure did not show an appreciable change in the Curie temperature, but enhanced TSR, whereas an insulator-metallic transition was observed during resistivity measurements under pressure. On the other hand, for Sm0.6La0.1Sr0.3MnO3, TC increased and TSR reduced upon the application of pressure. The metallic nature which is observed at ambient pressure resistivity measurement was further enhanced with 97% of piezoresistance. The pressure did not change the normal magnetocaloric effect of Sm0.7Sr0.3MnO3, but increased it in Sm0.6La0.1Sr0.3MnO3. However, there was not much change in the inverse magnetocaloric effect of both compounds. These studies were analyzed based on the pressure effect on the activation energy and scattering interaction factors. [ABSTRACT FROM AUTHOR]

The inconsistency of symmetry relationships in nonlinear piezoresistance coefficients, which is a long-standing puzzle, is resolved by taking into account the complex relations between piezoresistance coefficients and piezoconductance coefficients. The procedure to obtain correct nonlinear piezoresistance coefficients in theory according to the coordinate transformations of tensors is suggested. [ABSTRACT FROM AUTHOR]

This work demonstrates the design, implementation, and experimental results of a low-cost disposable flexible sensor system capable of both impact localization and measurement. The proposed flexible sensor structure utilizes a special series of Bristol paper as the main fabrication material, which is coated with electric paint graphite paste and silver paste. The implemented sensor system uses a planar absolute encoder-like sensing topology to locate the impact and has a low-cost and quick manufacturing process. The size of the structure is ${210}\times {18}.{56}$ mm with a thickness of approximately 340 $\mu \text{m}$. It has an electronic read-out consisting of three identical Wheatstone bridge circuits and instrumentation amplifiers for each bit. It can detect the external forces in the range of 0.6N to 12N with a spatial resolution of 2.4 cm and 0.55 cm in horizontal and vertical axes, respectively. The proposed sensor structure is tested in a series of experiments using a robotic setup consisted of a pantograph mechanism and a direct drive linear motor. The experiments illustrate the results with measurement sensitivity as small as 1N and proper fatigue resilience against repetitive loads. [ABSTRACT FROM AUTHOR]

The tactile sensing capabilities of human hands are essential in daily activities. Simultaneously perceiving normal and shear forces via the mechanoreceptors integrated into the hands allow us humans to achieve daily tasks like grasping delicate objects. In this paper, we design and fabricate a biomimetic tactile sensor with skin-like heterogeneity that perceives normal and shear contact forces simultaneously. It mimics the multilayered structure of mechanoreceptors in human skin by combining an extrinsic layer (piezoresistive sensors) and an intrinsic layer (a Hall sensor) so that it can perform estimation of contact force directions, locations, and joint-level torque. By integrating our sensors, a robotic gripper can obtain contact force feedback at the fingertips; accordingly, robots can perform challenging tasks, such as using tweezers and grasping eggs. This insightful sensor design can be customized and applied in different areas of robotics and provide them with heterogeneous force sensing, potentially supporting robotics in acquiring skin-like tactile feedback. [ABSTRACT FROM AUTHOR]

Continuous strain measurement on fibre-reinforced structures demands mechanical sensors with superior fatigue resistance. Shape-memory alloy wires are predestined for strain sensors utilising their strong piezo-resistance. Calibration of these sensors is necessary in order to extract mechanical data. Therefore, four-point bending of glass-fibre reinforced plastic specimens with applied strain sensors and an optical reference measuring system is used to calibrate and compare shape-memory alloy sensors and standard strain gauges. The gauge factor and its standard deviation is successfully measured by this calibration method. Shape-memory alloy sensors show strain-dependent gauge factor whilst standard strain gauges show a constant strain sensitivity, both with a narrow stochastic distribution. Shape-memory alloy mechanical sensors are reliable to determine strain of fibre-reinforced structures. This offers the possibility to use them in structural health monitoring applications of such structures. Consequently, the four-point bending calibration using glass-fibre reinforced specimens represents a suitable possibility for calibration of strain sensors exposed to higher strain amplitudes. [ABSTRACT FROM AUTHOR]

In this study, the chip-package interaction is analyzed by means of stress sensors with electrical simulation being initially carried out to optimize the stress sensor model. The analysis includes determination of piezoresistive coefficients along with a systematic characterization approach, starting with wafer-level measurements and finalizing with package-level measurements. Final validation is carried out using a ceramic package, where the electrical measurements fully confirm the results from mechanical simulations and thus verify the suggested proof-of-concept. Besides obtaining valuable information on the piezoresistive coefficients and validating the evaluation approach, this study also generates a guideline: in a phenomenological manner we show which mechanisms and effects need to be taken into account to provide reliable evaluation of stress distribution in a semiconductor package by using stress sensors. [ABSTRACT FROM AUTHOR]

Three types of piezoresistive pressure sensors were designed and fabricated using different process technologies incorporating standard diffused piezoresistors, and oxide isolated polysilicon or single crystal silicon piezoresistors. The performance of these sensors up to an elevated temperature of 200°C and pressure of 140 bar was investigated by measuring the variation of sensitivity, offset voltage and hysteresis. At room temperature, the diffused piezoresistor based pressure sensor demonstrated sensitivity of 0.147 mV/V/bar and it was observed to operate up to the maximum temperature of 100 °C. The oxide isolated single crystal silicon piezoresistor and polysilicon piezoresistor based pressure sensors showed sensitivities of 0.211 mV/V/bar and 0.308 mV/V/bar respectively at room temperatures. These sensors could be operated up to the measured temperature of 200 °C without any failure. All types of sensors showed decreased sensitivities with temperature. With respect to the sensitivity at room temperature, the sensor with diffused piezoresistors exhibited 13% decrease of sensitivity at 100 °C. For oxide isolated single crystal silicon or poly silicon piezoresistors, the decrease in the sensitivity at 200 °C was 19.5% and 9.0% respectively y. At elevated temperatures of 200 °C, the sensors with oxide isolated polysilicon piezoresistors demonstrated the best performance in terms of lowest decrease of sensitivity, and variation of offset voltage and hysteresis. [ABSTRACT FROM AUTHOR]

In this paper, a mechanical-electrical-process integrated model of the piezoresistive pressure sensor sensitivity is established for the first time, and the nonlinearity is analyzed from two aspects of bridge arm resistance and piezoresistive stress difference. Furthermore, a new peninsula structure diaphragm (NPSD) piezoresistive differential pressure sensor is proposed. By creating stress concentration areas and adding the cross beam-circular boss structure, within the pressure range of 0–5 kPa, the sensitivity of the sensor measured by the experiment reaches 22.7 mV/kPa, and the nonlinearity is only 0.11%FSO (full-scale output). In addition, it has been proved theoretically and experimentally that the SiO2/Si3N4 passivation film seriously affects the zero output voltage of the sensor, and causes the nonlinearity of 1.22% FSO. At the same time, compared with several typical structures, the pressure sensor proposed has the advantages of high sensitivity, low nonlinearity and small diaphragm. [2021-0206] [ABSTRACT FROM AUTHOR]

Simultaneous or concurrent multiplexing techniques with orthogonal sequences have been used to extend the channel capacity of tactile sensor systems. Typically, dynamic sensor signals violate the orthogonality requirement; as such, parallel multiplexing of driving signals should be strictly constrained in industrial practices. This makes it difficult to improve the signal-to-noise ratio of nonstatic targets in high-order multiplexing. This article proposes a sliding-windowed and compensated multiplexing technique to address the fundamental problems in concurrent multiplexing and improve its applicability. Two construction methods for palindromic sequences were developed to reduce multiplexing errors, based on conventional orthogonal matrices. Then, the orthogonal sequences were expanded to consecutive signal samples within a limited signal window. This increases the received signal and reduces the output latency of data acquisition. Further reduction of residual errors in the expanded signal samples was achieved via the postprocessing filter. The proposed method is scalable in order to conform to system requirements in terms of responsiveness, signal errors, and design complexity. Hardware implementation was successfully demonstrated by concurrently stimulating a 16 × 10 piezoresistive tactile panel. In the experiments, 70–88% of concurrent multiplexing errors were removed. [ABSTRACT FROM AUTHOR]

Various 2D functional materials were studied to evaluate their suitability for a variety of applications, such as energy storage devices, electronic devices, sensors, etc. Among many sensors, pressure sensors are widely used in healthcare, automobiles, industrial automation, and robotic electronic skin applications, etc. Pressure sensors work on different principles. Among them, the piezoresistance principle is more relevant for 2D materials-based pressure sensors. Among many 2D materials classes, MXenes are the latest materials which have been studied for different applications in the past few years. MXenes exhibit a piezoresistance effect by a reduced lattice interlayer distance, enhanced surface contact area, and increased strain under applied pressure. In the past few years, many researchers have studied MXene-based resistance pressure sensors (RPSs) for a variety of applications in healthcare. Here, a review of the recent literature on vital signs (heart rate, blood pressure, respiration rate) monitoring, and body language analysis by MXene-based RPSs is systematically reported. Vital signs give information about the homeostasis status of the human body. Further, various synthesis methods for different MXenes and their composites functional materials preparation, sensor fabrication geometries, such as sensors with and without a spacer layer, and matrix array sensors have been reported. The MXenes and their composite-based RPSs vital signs monitoring performances are also compared with other 2D graphene materials, for a quick understanding. [ABSTRACT FROM AUTHOR]