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In the area of flexible electronics, pressure sensors are a widely utilized variety of flexible electronics that are both indispensable and prevalent. The importance of pressure sensors in various fields is currently increasing, leading to the exploration of materials with unique structural and piezoelectric properties. Perovskite-based materials are ideal for use as flexible pressure sensors (FPSs) due to their flexibility, chemical composition, strain tolerance, high piezoelectric and piezoresistive properties, and potential integration with other technologies. This article presents a comprehensive study of perovskite-based materials used in FPSs and discusses their components, performance, and applications in detecting human movement, electronic skin, and wireless monitoring. This work also discusses challenges like material instability, durability, and toxicity, the limited widespread application due to environmental factors and toxicity concerns, and complex fabrication and future directions for perovskite-based FPSs, providing valuable insights for researchers in structural health monitoring, physical health monitoring, and industrial applications. [ABSTRACT FROM AUTHOR]

Flexible pressure sensors are lightweight and highly sensitive, making them suitable for use in small portable devices to achieve precise measurements of tiny forces. This article introduces a low-cost and easy-fabrication strategy for piezoresistive flexible pressure sensors. By embedding silver nanowires into a polydimethylsiloxane layer with micro-pyramids on its surface, a flexible pressure sensor is created that can detect low pressure (17.3 Pa) with fast response (<20 ms) and high sensitivity (69.6 mA kPa−1). Furthermore, the pressure sensor exhibits a sensitive and stable response to a small amount of water flowing on its surface. On this basis, the flexible pressure sensor is innovatively combined with a micro-rotor to fabricate a novel urinary flow-rate meter (uroflowmeter), and results from a simulated human urination experiment show that the uroflowmeter accurately captured all the essential shape characteristics that were present in the pump-simulated urination curves. Looking ahead, this research provides a new reference for using flexible pressure sensors in urinary flow-rate monitoring. ARTICLE HIGHLIGHTS: • A flexible pressure sensor is presented based on a micro-pyramid array and silver nanowires and with low detection limit, high sensitivity, and fast response. • The sensor responds accurately and stably to human pulse signals and rapidly changing cyclic loads. • The sensor can accurately and sensitively detect dynamic water flow passing over its upper surface, and the uroflowmeter designed using it has considerably high detection accuracy. [ABSTRACT FROM AUTHOR]

The wide range of pressure detection and the exceptional linearity are essential performance parameters for flexible pressure sensors, enabling them to adapt to diverse scenarios and acquire information accurately. However, currently available "ultra‐wide range" piezoresistive sensors lack an optimal solution that effectively balances sensing properties, device thickness, and process cost. This study proposes a distinctive approach by introducing a Janus conductive structure assembled with dual resistive sensitive layers. The design allows for a pressure‐induced staged transformation of the current transport path, effectively mitigating variations and saturation in sensor resistance over a wide pressure range. The resulting piezoresistive sensor demonstrates an unprecedented detection range of 0–3800 kPa, showcasing remarkable sensitivity of 4.11 kPa−1 and outstanding linearity of 99.9% within the range of 0–1000 kPa. Additionally, the sensor boasts a thickness of only ≈200 µm, made possible through the utilization of a cellulose nanofibers material matrix. These performance achievements stand at the forefront when compared to existing reports. This research explores the potential applications of these sensors and extended arrays in the domains of human health and motion monitoring. It investigates their utility in gait analysis for assisted posture correction, as well as in the assessment and rehabilitation of gait instability. [ABSTRACT FROM AUTHOR]

This paper reports the designing and testing, as well as the processing and testing, of a flexible piezoresistive sensor for pressure-sensing applications, utilizing a composite film of graphene/polyvinylidene fluoride (Gr/PVDF). Graphene serves as the conductive matrix, while PVDF acts as both the binder and a flexible polymer matrix. The composite film was fabricated using the solution casting technique on a flexible polyethylene substrate. We investigated the impact of post-infrared annealing on the pressure response of the Gr/PVDF films. The experimental results indicated that the films IR-annealed for 2 min exhibited improved pressure sensitivity compared with the as-deposited films. The stability and durability of the sensors were assessed through the application of pressure over more than 1000 cycles. The mechanical properties of the films were examined using a universal tensile testing machine (UTM) for scenarios both with and without infrared light annealing. Raman spectroscopy was employed to analyze the quality and characteristics of the prepared nanocomposites. This study enhances our understanding of the interplay between the Gr/PVDF composite, the IR annealing effect, and the hysteresis effect in the pressure-sensing mechanism, thereby improving the piezoresistance of the Gr/PVDF nanocomposite through the infrared annealing process. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Materials Engineering / Cailiao Gongcheng is the property of Journal of Materials Engineering Editorial Office 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.)

Artificial skins or flexible pressure sensors that mimic human cutaneous mechanoreceptors transduce tactile stimuli to quantitative electrical signals. Conventional trial-and-error designs for such devices follow a forward structure-to-property routine, which is usually time-consuming and determines one possible solution in one run. Data-driven inverse design can precisely target desired functions while showing far higher productivity, however, it is still absent for flexible pressure sensors because of the difficulties in acquiring a large amount of data. Here, we report a property-to-structure inverse design of flexible pressure sensors, exhibiting a significantly greater efficiency than the conventional routine. We use a reduced-order model that analytically constrains the design scope and an iterative "jumping-selection" method together with a surrogate model that enhances data screening. As an exemplary scenario, hundreds of solutions that overcome the intrinsic signal saturation have been predicted by the inverse method, validating for a variety of material systems. The success in property design on multiple indicators demonstrates that the proposed inverse design is an efficient and powerful tool to target multifarious applications of flexible pressure sensors, which can potentially advance the fields of intelligent robots, advanced healthcare, and human-machine interfaces. [ABSTRACT FROM AUTHOR]

Flexible capacitive pressure sensors play a crucial role in wearable electronics and robotics. However, their susceptibility to environmental noise poses challenges to sensing precision. To mitigate the impact of environmental influences, a sensor capable of producing signals orders of magnitudes larger than the noise becomes essential. One straightforward method to enhance capacitance values involves reducing the thickness of the dielectric layer. Yet, when this reduction reaches nanometer scale, the dielectric layer may become mechanically vulnerable and more importantly, their charge storage capability is compromised due to electron tunneling. To address these challenges, here the naturally formed alumina (Al2O3) on aluminum (Al) surface is employed as a stable and ultra‐thin dielectric layer. Simultaneously, the Schottky effect at the Al‐Al2O3‐carbon black (CB) interface is harnessed to prevent electron tunneling. These strategies collectively yielded a large unit‐area capacitance (UAC) of 50 nF cm−2 and demonstrated high electrical and environmental stability. Furthermore, hollow hemispherical microstructures are incorporated at the interface, resulting in a flexible pressure sensor with high sensitivity (8.6 kPa−1) and a linear response up to 50 kPa. With its simple two‐layer structure, this sensor can be seamlessly integrated in situ and offers commercial‐grade resolution at mN‐level for monitoring human biomechanical signals. [ABSTRACT FROM AUTHOR]

Flexible pressure sensors can be attached to the human skin to sense external pressure signals， and have the characteristics of wide sensing range， short response time， high sensitivity， and durability. Therefore， they are widely used in the fields of electronic skin and human-computer interaction. Flexible pressure sensors are usually composed of flexible substrates， active materials and conductive electrodes. Among them， one or more of the active materials form a sensing material by compounding with a flexible substrate， and its deformation under external excitation will cause changes in parameters such as resistance， thereby achieving sensing function.In addition， by introducing microstructure， the compressibility and sensitivity to small pressure of the sensing material can be increased， and its sensing performance can be improved. In this paper， the research progress in flexible pressure sensors doped with carbon-based， metal-based， and black phosphorus-based active materials on film and fabric substrates was reviewed. The preparation methods， electromechanical properties and application scenarios of different sensors were discussed， and the advantages and disadvantages of various sensors were summarized. On this basis， the research on how to achieve wide-range pressure detection， commercialization， non-toxicity of the production process and long-term biocompatibility experiments of smart wearable flexible pressure sensors in the future is prospected.

AbstractAlthough MXene sheets are highly conductive, it is still challenging to prepare MXene complex functional materials for flexible electronics by simple and effective methods. In 3D printing, especially direct ink writing (DIW), different materials are used to create complex 3D shapes by formulating inks with controlled rheological properties. Herein, a printable MXene ink is developed, exhibiting good rheological properties, to print different complex shapes, and potentially manufacture electronic devices such as sensors. Then, we fabricated a highly sensitive hierarchical structure MXene composite materials composed of two layers of bionic micro-spine microstructure and network structure, formed by 3D printing and freeze casting. The obtained MXene composite materials exhibit good pressuring sensing properties with a sensitivity of 17.5 kPa−1, a fast response time (

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Bioinspired microdevices have made significant strides in various applications including human motion and health detection. However, facile and highly efficient fabrication approach of flexible pressure sensors remains a great challenge. Herein, inspired by the gecko's foot structure, a flexible pressure sensor with microdomes structure is fabricated by tip‐assisted on‐demand electrohydrodynamic jet (EHD‐jet) printing method. Ascribed to the interlocking electrodes with microdome structure, 3D deformation rates are substantially enlarged. When the microdromes structure is under pressure, the resistivity of carbon nanotubes film coated on the surface of microdomes structure will change remarkably. By using the combined effect of assisted tip and ring focusing electrode, the influence and constraints on microstructure fabrication caused by substrate material and morphology are minimized. The desired uniform structures can be adjusted rapidly by changing the printing parameters and liquid properties. High length‐height ratio (0.64) of microdomes enhances sensitivity, with minimum detection limit is 2 Pa and response time is 40 ms. Finally, the bionic flexible sensor indicated excellent performance in capable of detecting pressure, sound vibrations and human motion. This work presents a new method for high‐efficiency fabrication micro‐nano patterns for flexible sensors inspired, which could be used in wearable tech and health monitoring. [ABSTRACT FROM AUTHOR]

A high-performance flexible pressure sensor is one of the most important components of electronic skin, which can endow artificial devices with human-like capabilities. However, the electronic skin usually relies on the arrays of sensors to simultaneously obtain both pressure magnitude and position, making the data processing time-consuming, tedious, and error-prone. Here, a novel continuous pressure positioning sensor (PPS) with flexible multilayer structures based on a combinatorial bionic strategy is designed and fabricated. This PPS is composed of the pressure sensing layer (PSL) and the pressure positioning layer (PPL). The PSL exhibits high sensitivity (18.87 kPa-1) owing to the bionic crack structures. Based on the connection/disconnection of the upper and lower conductive layers, this PPL exhibits excellent positioning properties with excellent resolution (≈35 µm). More importantly, due to stable signal change and synchronization of signals between the two functional layers (>21 pa), this PPS can recognize the type of signal. Applications of the PPS for pressure monitoring, tire safety monitoring, lunar rover road condition monitoring, and emotional communication in human-computer interaction are further demonstrated to measure magnitude, position, and recognition of pressure signals. So, it will have broad application prospects in fields such as pressure detection and human-computer interaction. [ABSTRACT FROM AUTHOR]

Wearable electronic devices are portable gadgets worn either directly on the body or embedded in clothing or accessories. They offer functionalities across several domains such as medical health, outdoor sports, video and audio entertainment. Advancements in science and technology have led to electronic components being combined with flexible substrates, facilitating the development of wearable electronics in a more flexible and lightweight direction. This is beneficial to enhancing individuals’ quality of life. Flexible wearable technology offers significant advantages such as flexibility, easy deformation, and good biological adaptability. However, there are also issues such as low sensitivity, limited detection range, and weak reliability resulting from environmental interference. The flexible pressure sensor plays a significant role in pressure detection within these devices. Therefore, the key to the development of flexible wearable devices lies in the advancement of flexible pressure sensors with outstanding performance. Flexible pressure sensors merge the suppleness of wearable materials with the electrical activity of electronic components, and can be attached to irregular surfaces to efficiently detect the pressure on the surface of objects. The selection of substrates and conductive materials will have a direct impact on the sensing performance of the flexible pressure sensor. Silk is a biological material with a lengthy history, possessing exceptional tensile strength and toughness, biocompatibility, biodegradability, and effortless processing, making it an ideal material for flexible sensors. Based on the features of silk processing and molding, it can be categorized into natural silk-based materials, regenerated silk protein materials, and silk primary fibers and aggregates. Consequently, in this study, three types of silk materials including silk fabric, flat silk cocoon, and electrospun silk fibroin film are selected as flexible substrates to develop the flexible sensors. Polyaniline (PANI), a unique conductive polymer, exhibits electrical conductivity when acid-doped and oxidized; however, it lacks conductivity when either completely oxidized or completely reduced. The gas-liquid interface polymerization process restricts the synthesis of PANI to the two-phase interface, ensuring controlled reaction degree to prevent over-oxidization of aniline. Additionally, it prevents secondary growth, resulting in PANI that exhibits uniform morphology. Herein, on the basis of the above analysis, the gas-liquid interface polymerization method was utilized to achieve in-situ growth of PANI on silk fabric, flat silk cocoon, and electrospun silk fibroin film, prepare a flexible substrate with PANI as an active conductive substance and assemble it into a flexible pressure sensor, so as to explore the changes in the properties of silk materials before and after the gas-liquid interface polymerization and the performance of the flexible pressure sensor based on silk. This study presents a novel approach and theoretical foundation for creating wearable electronic devices with optimal performance, safety, dependability, and effortless portability. The study demonstrates that among the three types of silk-based flexible pressure sensors, the SFP sensor has the largest pressure sensing range（16.27-504.79 kPa）, the tensile deformation can reach 20%, while the sensitivity is only 0.001 29 kPa-1. The sensitivity of the ESFP sensor is the highest(0.013 76 kPa-1), but the tensile deformation ability is poor, only being 2.3%. The pressure detection sensitivity of the SFCP sensor is slightly higher than that of the SFP sensor, reaching 0.001 34 kPa-1, and the linear detection range is 9.8-87.6 kPa. The developed silk-based flexible pressure sensor has a good application prospect in the field of motion detection, but it still requires external power supply, which will limit the flexibility and convenience of wearable devices. Therefore, the future research direction can be to combine the silk-based flexible pressure sensor developed in this study with self-powered devices and develop an integrated intelligent detection system. This can provide a broader perspective for intelligent pressure detection. [ABSTRACT FROM AUTHOR]

When sensors were fabricated without a conductive layer, metal wires or pin headers were mainly used to receive the electrical signals from the sensor material. By fabricating the conductive layer, the degree of freedom in sensor design is increased and geometrically complex shapes can be manufactured. In this study, we built the electrical circuit for the flexible pressure sensor by arranging the multi-walled carbon nanotubes/polydimethylsiloxane composite and the conductive layer made from silver paste. That is, using DIW technology, the sensor material and conductive layer were formed into a series circuit and a parallel circuit, respectively, and the change in electrical resistance according to pressure was measured. As a result of experiments based on pressure, when the two materials were configured in a series circuit, they responded quickly to pressure at 35 ms. The changed resistance remained stable while pressure was applied. Consequently, the developed series circuit flexible pressure sensor demonstrates potential for applications involving instantaneous force or steadily increasing pressure measurement. [ABSTRACT FROM AUTHOR]

Piezoelectric nanogenerator (PENG) produces stable electrical signals in response to external mechanical stimuli and holds promise in the fields of flexible sensors and smart wearable devices. In practice, a high‐performance PENG with a straightforward structure and exceptional reliability is deeply desired. This study optimally synthesizes piezoelectric composites comprising polyvinylidene fluoride (PVDF) incorporated with barium titanate (BTO) nanoparticles (NPs) and fabricated a PENG with heightened sensitivity by using the electrospinning technique. The polar β‐phase content of the dual‐optimized BTO‐PVDF (barium titanate and polyvinylidene fluoride) electrospun fiber reaches up to 82.39%. In the bending mode, it achieves a remarkable maximum open‐circuit voltage of 19.152 V, a transferred charge of 8.058 nC, and an output voltage per unit area of 2.128 V cm−2. Under vertical pressure conditions, the BP‐PENG exhibits an impressive voltage of 12.361 V while the force is 2.156 N, demonstrating a notable pressure sensing sensitivity of 5.159 V kPa−1, with an excellent linear relationship. Furthermore, the BP‐PENG displays sensitive sensing features in monitoring hand movements. The sensitive response and high performance make it promising for applications in human motion monitoring and smart wearable devices. [ABSTRACT FROM AUTHOR]

Copyright of Journal of the Beijing Institute of Fashion Technology (Natural Science Edition) is the property of Beijing Institute of Fashion Technology 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.)

Flexible pressure sensor is widely used in fields such as healthcare, intelligent prosthetics, and patient rehabilitation. However, how to ensure high sensitivity of the sensor while having a wide detection range remains a challenge. In order to address this challenge, a flexible pressure sensor with a wide detection range based on capacitive‐piezoresistive dual mode conversion is proposed. By manufacturing circular through‐holes on the dielectric layer of the sensor, the microstructure of the upper and lower electrode layers can achieve non‐contact and contact switching under different pressures through the through holes. This means that the sensor remains in capacitive mode at low pressure and then in piezoresistive mode at high pressure. By cleverly combining the two modes, the measurement range can reach 2 000 kPa and high sensitivity can be maintained during mode switching. In addition, its production process is simple, the cost is low, and it has a fast response time (120 ms) and good repeatability stability. The experimental results indicate that the sensor can achieve ideal performance in proximity detection, human behavior monitoring, and ultra high‐pressure detection, and has broad application prospects in providing a more powerful human‐computer interaction interface and expanding more comprehensive health monitoring. [ABSTRACT FROM AUTHOR]

Liquid metal (LM) eutectic gallium–indium (EGaIn) possesses the ductility of a polymer and the conductivity of metal materials, making it a promising material for flexible electronics. Fabricating LM-based circuits is challenging because of the large surface tension of EGaIn. However, the circuit can be fabricated on various substrates using an additive printing process based on the principle of ultrasonic resonance. To improve the wettability between the LM and a substrate material, LM nanoparticles/carbon nanotubes (LMP/CNT) composite nano-ink was prepared, which has excellent colloidal stability and biocompatibility. A conductive circuit was realized by attaching CNTs to LMPs for imparting intrinsic electrical conductivity. Subsequently, flexible polydimethylsiloxane (PDMS) was used as the substrate, and a flexible pressure sensor with a response time of 103 ms was produced. This study introduces fabrication strategies for a flexible pressure sensor based on LMP/CNT composite nano-ink and additive printing processes, providing enormous possibilities for the application of LM in the field of printed electronics. [ABSTRACT FROM AUTHOR]

Shapeable and flexible pressure sensors with superior mechanical and electrical properties are of major interest as they can be employed in a wide range of applications. In this regard, elastomer‐based composites incorporating carbon nanomaterials in the insulating matrix embody an appealing solution for designing flexible pressure sensors with specific properties. In this study, PDMS chains of different molecular weight were successfully functionalized with benzoxazine moieties in order to thermally cure them without adding a second component, nor a catalyst or an initiator. These precursors were then blended with 1 weight percent of multi‐walled carbon nanotubes (CNTs) using an ultrasound probe, which induced a transition from a liquid‐like to a gel‐like behavior as CNTs generate an interconnected network within the matrix. After curing, the resulting nanocomposites exhibit mechanical and electrical properties making them highly promising materials for pressure‐sensing applications. [ABSTRACT FROM AUTHOR]

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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.)

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

Flexible pressure sensors have attracted wide attention due to their applications to electronic skin, health monitoring, and human-machine interaction. However, the tradeoff between their high sensitivity and wide response range remains a challenge. Inspired by human skin, we select commercial silicon carbide sandpaper as a template to fabricate carbon nanotube (CNT)/polydimethylsiloxane (PDMS) composite film with a hierarchical structured surface (h-CNT/PDMS) through solution blending and blade coating and then assemble the h-CNT/PDMS composite film with interdigitated electrodes and polyurethane (PU) scotch tape to obtain an h-CNT/PDMS-based flexible pressure sensor. Based on in-situ optical images and finite element analysis, the significant compressive contact effect between the hierarchical structured surface of h-CNT/PDMS and the interdigitated electrode leads to enhanced pressure sensitivity and a wider response range (0.1661 ​kPa−1, 0.4574 ​kPa−1 and 0.0989 ​kPa−1 in the pressure range of 0–18 ​kPa, 18–133 ​kPa and 133–300 ​kPa) compared with planar CNT/PDMS composite film (0.0066 ​kPa−1 in the pressure range of 0–240 ​kPa). The prepared pressure sensor displays rapid response/recovery time, excellent stability, durability, and stable response to different loading modes (bending and torsion). In addition, our pressure sensor can be utilized to accurately monitor and discriminate various stimuli ranging from human motions to pressure magnitude and spatial distribution. This study supplies important guidance for the fabrication of flexible pressure sensors with superior sensing performance in next-generation wearable electronic devices.

In the area of flexible electronics, pressure sensors are a widely utilized variety of flexible electronics that are both indispensable and prevalent. The importance of pressure sensors in various fields is currently increasing, leading to the exploration of materials with unique structural and piezoelectric properties. Perovskite-based materials are ideal for use as flexible pressure sensors (FPSs) due to their flexibility, chemical composition, strain tolerance, high piezoelectric and piezoresistive properties, and potential integration with other technologies. This article presents a comprehensive study of perovskite-based materials used in FPSs and discusses their components, performance, and applications in detecting human movement, electronic skin, and wireless monitoring. This work also discusses challenges like material instability, durability, and toxicity, the limited widespread application due to environmental factors and toxicity concerns, and complex fabrication and future directions for perovskite-based FPSs, providing valuable insights for researchers in structural health monitoring, physical health monitoring, and industrial applications.

This paper reports the designing and testing, as well as the processing and testing, of a flexible piezoresistive sensor for pressure-sensing applications, utilizing a composite film of graphene/polyvinylidene fluoride (Gr/PVDF). Graphene serves as the conductive matrix, while PVDF acts as both the binder and a flexible polymer matrix. The composite film was fabricated using the solution casting technique on a flexible polyethylene substrate. We investigated the impact of post-infrared annealing on the pressure response of the Gr/PVDF films. The experimental results indicated that the films IR-annealed for 2 min exhibited improved pressure sensitivity compared with the as-deposited films. The stability and durability of the sensors were assessed through the application of pressure over more than 1000 cycles. The mechanical properties of the films were examined using a universal tensile testing machine (UTM) for scenarios both with and without infrared light annealing. Raman spectroscopy was employed to analyze the quality and characteristics of the prepared nanocomposites. This study enhances our understanding of the interplay between the Gr/PVDF composite, the IR annealing effect, and the hysteresis effect in the pressure-sensing mechanism, thereby improving the piezoresistance of the Gr/PVDF nanocomposite through the infrared annealing process.

Flexible pressure sensor plays a crucial role in wearable devices since it converts the physical signals of human motions into electrical signals. Among various pressure sensors, foam-based pressure sensors received great attention due to their excellent flexibility, low weight, and pressure resistance. However, the sensitivity of the foam-based pressure sensor is still not large enough, and the sensing range is also urged to be further improved. Herein, we proposed a high-performance foam-based pressure sensor composed of polydimethylsiloxane (PDMS), multi-walled carbon nanotubes (MWCNT), and nanofibers (FIBER). The PDMS/FIBER@MWCNT foam-based pressure sensor possessed outstanding sensitivity up to 4.07 kPa− 1 and a wide sensing range of 0–70 kPa. The pressure sensor also presented excellent linearity during 0–20 kPa and 20–70 kPa, respectively. And 2000 cyclic compression tests shown good cyclic stability. Meanwhile, the pressure sensor worked efficiently in monitoring subtle and large human motions, such as finger bending, wrist bending, throat vocal signals, and various pressures. In addition, the pressure sensor owned significant discrimination and high efficiency against different pressure, which is beneficial in human complex motion monitoring and signal analysis of wearable devices. Consequently, the PDMS/FIBER@MWCNT foam-based pressure sensor may possess promising prospects and potential in the applications of artificial electrical skin and wearable devices. [ABSTRACT FROM AUTHOR]

MXene-based films have been intensively explored for construction of piezoresistive flexible pressure sensors owing to their excellent mechanical and electrical properties. High pressure sensitivity relies on pre-molding a flexible substrate, or regulating the micromorphology of MXene sheets, to obtain a micro-structured surface. However, the two avenues usually require complicated and time-consuming microfabrication or wet chemical processing, and are limited to non-adjustable topographic-electrical (topo-electro) properties. Herein, we propose a lithographic printing inspired in-situ transfer (LIPIT) strategy to fabricate MXene-ink films (MIFs). In LIPIT, MIFs not only inherit ridge-and-valley microstructure from paper substrate, but also achieve localized topo-electro tunability by programming ink-writing patterns and cycles. The MIF-based flexible pressure sensor with periodical topo-electro gradient exhibits remarkably boosted sensitivity in a wide sensing range (low detection limit of 0.29 Pa and working range of 100 kPa). The MIF sensor demonstrates versatile applicability in both subtle and vigorous pressure-sensing fields, ranging from pulse wave extraction and machine learning-assisted surface texture recognition to piano-training glove (PT-glove) for piano learning. The LIPIT is quick, low-cost, and compatible with free ink/substrate combinations, which promises a versatile toolbox for designing functional MXene films with tailored morphological-mechanical-electrical properties for extended application scenarios. [ABSTRACT FROM AUTHOR]

At present, flexible pressure-sensitive materials generally have problems with weak adhesion and poor wear resistance, which easily result in friction failure when used for plantar pressure detection. In this study, a flexible pressure sensor with the advantages of a wide detection range, fast recovery, and good abrasive resistance was designed and prepared based on the screen printing process. The pressure-sensitive unit with a structural size of 5 mm× 8 mm was a functional material system due to the use of graphene and epoxy resin. The influence of the different mass ratios of the graphene and epoxy resin on the sensing properties was also studied. The test results showed that when the mass ratio of graphene to epoxy resin was 1:4, the response time and recovery time of the sensing unit were 40.8 ms and 3.7 ms, respectively, and the pressure detection range was 2.5–500 kPa. The sensor can detect dynamic pressure at 0.5 Hz, 1 Hz, 2 Hz, 10 Hz, and 20 Hz and can withstand 11,000 cycles of bending. In addition, adhesion tests showed that the high viscosity of the epoxy helped to improve the interlayer bond between the pressure-sensitive materials and the flexible substrate, which makes it more suitable for plantar pressure detection environments, where friction is common. [ABSTRACT FROM AUTHOR]

In designing a flexible microfluidic-based pressure sensor, the microchannel plays an important role in maximizing the sensor's performance. Similarly, the material used for the sensor's membrane is crucial in achieving optimal performance. This study presents an analytical analysis and FEA simulation of the membrane and microchannel of the flexible pressure sensor, aimed at optimizing it design and material selection. Different types of materials, including two commonly used polymers, Polyimide (PI) and Polydimethylsiloxane (PDMS) were evaluated. Moreover, different designs of the microchannel, including single-channel, double-channel, and triple-channel, were analyzed. The applied pressure, width of the microchannel, and length of the microchannel were varied to study the normalized resistance of the microchannel and maximize the performance of the pressure sensor. The results showed that the triple-channel design produced the highest normalized resistance. To achieve maximum performance, it is found that using a membrane with a large area facing the applied pressure was optimal in terms of dimensions. In conclusion, optimizing the microchannel and membrane design and material selection is crucial in improving the overall performance of flexible microfluidic-based pressure sensors.

Noninvasive measurement of arterial pulse provides information about the heart condition through the evaluation of primary hemodynamic parameters such as blood pressure (BP), pulse rate (PR), and pulse regularity. Moreover, BP is one of the most important biomarkers of cardiovascular disease, mainly hypertension. To prevent this, accurate measurement of BP becomes necessary. Currently, flexible pressure sensors have drawn a lot of interest due to their prospective applications in wearable devices for healthcare monitoring. We have collected the human oscillometric pulse by a polymer-based flexible capacitive pressure sensor and calculated the BP as well as PR using the maximum amplitude algorithm. The results are compared with a pre-calibrated oscillometric BP monitor available in the market. Based on the error criteria, the device followed the universal standard. In addition, the flexibility and high accuracy of the device result in the assessment of the possible medical applications, including abnormal pulse rates such as tachycardia or bradycardia and irregular heart rhythm such as cardiac arrhythmia.

Flexible pressure sensors play an important role in the field of monitoring, owing to their inherent safety and the fact that they are embedded at the material level. Capacitive pressure sensors have been proven to be quite versatile, with the ability to change the sensitivity and monitoring range by modifying the pore structure of the dielectric layer (elastic modulus). In this paper, capacitive pressure sensors are devised, comprising hierarchical porous polydimethylsiloxane. Due to the inherent hollow and hierarchical micropore structure, the capacitive pressure sensor allows operation at a wider pressure range (~1000 kPa) while maintaining sensitivity (6.33 MPa−1) in the range of 0–300 kPa. Subsequently, the capacitance output model of the sensor is optimized, which provides an overall approximation of the experimental values for the sensor performance. Additionally, the signal response of the "break up the whole into parts" (by analysis of the whole sensor in parts) is simulated and outputted by the finite element analysis. The simplified analysis model provides a good understanding of the relationship between the local pressure and the signal response of the pressure sensor. For practical applications, seal monitoring and rubber wheel pressure array system are tested, and the proposed sensor shows sufficient potential for application in large deformation elastomer products. [ABSTRACT FROM AUTHOR]

In recent years, laser engraving has received widespread attention as a convenient, efficient, and programmable method which has enabled high-quality porous graphene to be obtained from various precursors. Laser engraving is often used to fabricate the dielectric layer with a microstructure for capacitive pressure sensors; however, the usual choice of electrodes remains poorly flexible metal electrodes, which greatly limit the overall flexibility of the sensors. In this work, we propose a flexible capacitive pressure sensor made entirely of thermoplastic polyurethane (TPU) and laser-induced graphene (LIG) derived from wood. The capacitive pressure sensor consisted of a flexible LIG/TPU electrode (LTE), an LIG/TPU electrode with a microhole array, and a dielectric layer of TPU with microcone array molded from a laser-engraved hole array on wood, which provided high sensitivity (0.11 kPa−1), an ultrawide pressure detection range (20 Pa to 1.4 MPa), a fast response (~300 ms), and good stability (>4000 cycles, at 0–35 kPa). We believe that our research makes a significant contribution to the literature, because the easy availability of the materials derived from wood and the overall consistent flexibility meet the requirements of flexible electronic devices. [ABSTRACT FROM AUTHOR]

With the advent of the internet of things and artificial intelligence, flexible and portable pressure sensors have shown great application potential in human-computer interaction, personalized medicine and other fields. By comparison with traditional inorganic materials, flexible polymeric materials conformable to the human body are more suitable for the fabrication of wearable pressure sensors. Given the consumption of a huge amount of flexible wearable electronics in near future, it is necessary to turn their attention to biodegradable polymers for the fabrication of flexible pressure sensors toward the development requirement of green and sustainable electronics. In this paper, the structure and properties of silk fibroin (SF) are introduced, and the source and research progress of the piezoelectric properties of SF are systematically discussed. In addition, this paper summarizes the advance in the studies on SF-based capacitive, resistive, triboelectric, and piezoelectric sensors reported in recent years, and focuses on their fabrication methods and applications. Finally, this paper also puts forward the future development trend of high-efficiency fabrication and corresponding application of SF-based piezoelectric sensors. It offers new insights into the design and fabrication of green and biodegradable bioelectronics for in vitro and in vivo sensing applications.

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In order to improve sensitivity, reliability and sustainability of the flexible wearable pressure sensor based on fabric, silver nanowires interdigital electrode was designed and fabricated by direct writing technology and used as the bottom electrode. Silver nano wire conductive fabric was prepared by soaking technology and used as piezoresistive layer. A piezoresistive flexible fabric pressure sensor was assembled by the bottom electrode and piezoresistive layer, its related properties were tested. The results showed that the current of pressure sensing fabric was increased linearly with the increase of applied voltage under different pressures. The pressure sensing fabric had better sensing stability and reproducibility, better response performance and high sensitivity to external force. The flexible fabric pressure sensor achieved excellent switching ratio at low voltage of 0. 1 V and had fast response performance at 5 g weight pressure. It is considered that the flexible pressure sensor has potential application value in wearable controller and motion detection. [ABSTRACT FROM AUTHOR]

Flexible pressure sensors are widely applied in tactile perception, fingerprint recognition, medical monitoring, human–machine interfaces, and the Internet of Things. Among them, flexible capacitive pressure sensors have the advantages of low energy consumption, slight signal drift, and high response repeatability. However, current research on flexible capacitive pressure sensors focuses on optimizing the dielectric layer for improved sensitivity and pressure response range. Moreover, complicated and time-consuming fabrication methods are commonly applied to generate microstructure dielectric layers. Here, we propose a rapid and straightforward fabrication approach to prototyping flexible capacitive pressure sensors based on porous electrodes. Laser-induced graphene (LIG) is produced on both sides of the polyimide paper, resulting in paired compressible electrodes with 3D porous structures. When the elastic LIG electrodes are compressed, the effective electrode area, the relative distance between electrodes, and the dielectric property vary accordingly, thereby generating a sensitive pressure sensor in a relatively large working range (0–9.6 kPa). The sensitivity of the sensor is up to 7.71%/kPa−1, and it can detect pressure as small as 10 Pa. The simple and robust structure allows the sensor to produce quick and repeatable responses. Our pressure sensor exhibits broad potential in practical applications in health monitoring, given its outstanding comprehensive performance combined with its simple and quick fabrication method. [ABSTRACT FROM AUTHOR]

Designing stretchable and skin-conformal self-powered sensors for intelligent sensing and posture recognition is challenging. Here, based on a multi-force mixing and vulcanization process, as well as synergistically piezoelectricity of BaTiO3 and polyacrylonitrile, an all-in-one, stretchable, and self-powered elastomer-based piezo-pressure sensor (ASPS) with high sensitivity is reported. The ASPS presents excellent sensitivity (0.93 V/104 Pa of voltage and 4.92 nA/104 Pa of current at a pressure of 10–200 kPa) and high durability (over 10,000 cycles). Moreover, the ASPS exhibits a wide measurement range, good linearity, rapid response time, and stable frequency response. All components were fabricated using silicone, affording satisfactory skin-conformality for sensing postures. Through cooperation with a homemade circuit and artificial intelligence algorithm, an information processing strategy was proposed to realize intelligent sensing and recognition. The home-made circuit achieves the acquisition and wireless transmission of ASPS signals (transmission distance up to 50 m), and the algorithm realizes the classification and identification of ASPS signals (accuracy up to 99.5%). This study proposes not only a novel fabrication method for developing self-powered sensors, but also a new information processing strategy for intelligent sensing and recognition, which offers significant application potential in human—machine interaction, physiological analysis, and medical research. [ABSTRACT FROM AUTHOR]

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The use of flexible pressure sensors has significantly advanced and improved human life. However, several issues are hindering their applicability such as the difficulty to achieve high sensitivity over a wide pressure measurement range. Herein, a one-step foaming method and hydrothermal approach were used to fabricate a three-dimensional conductive porous foam comprising polyurethane, carbon nanotube, and polyaniline. The sensor exhibits excellent electrical conductivity due to its cellular foam structure, while its high durability enables a large response output across an extremely broad range (0–30 000 kPa). The sensor also exhibits exceptional stability over 1000 loading/unloading cycles, a fast response time of 80 ms, and high sensitivity of 0.019 53 kPa−1 (0–200 kPa), 0.126 48 kPa−1 (200–5000 kPa), and 0.038 85 kPa−1 (5000–30 000 kPa). Furthermore, rational material selection and structural design allows the sensor to monitor low- to high-signal stimuli, thereby providing a reference for the design of other large-scale sensors. [ABSTRACT FROM AUTHOR]

Abstract As an indispensable branch of wearable electronics, flexible pressure sensors are gaining tremendous attention due to their extensive applications in health monitoring, human –machine interaction, artificial intelligence, the internet of things, and other fields. In recent years, highly flexible and wearable pressure sensors have been developed using various materials/structures and transduction mechanisms. Morphological engineering of sensing materials at the nanometer and micrometer scales is crucial to obtaining superior sensor performance. This review focuses on the rapid development of morphological engineering technologies for flexible pressure sensors. We discuss different architectures and morphological designs of sensing materials to achieve high performance, including high sensitivity, broad working range, stable sensing, low hysteresis, high transparency, and directional or selective sensing. Additionally, the general fabrication techniques are summarized, including self-assembly, patterning, and auxiliary synthesis methods. Furthermore, we present the emerging applications of high-performing microengineered pressure sensors in healthcare, smart homes, digital sports, security monitoring, and machine learning-enabled computational sensing platform. Finally, the potential challenges and prospects for the future developments of pressure sensors are discussed comprehensively.