High-performance Flexible Pressure Sensors Research Articles

Flexible Nanofiber Pressure Sensors with Hydrophobic Properties for Wearable Electronics

In recent years, flexible pressure sensors have received considerable attention for their potential applications in health monitoring and human–machine interfaces. However, the development of flexible pressure sensors with excellent sensitivity performance and a variety of advantageous characteristics remains a significant challenge. In this paper, a high-performance flexible piezoresistive pressure sensor, BC/ZnO, is developed with a sensitive element consisting of bacterial cellulose (BC) nanofibrous aerogel modified by ZnO nanorods. The BC/ZnO pressure sensor exhibits excellent mechanical and hydrophobic properties, as well as a high sensitivity of −15.93 kPa−1 and a wide range of detection pressure (0.3–20 kPa), fast response (300 ms), and good cyclic durability (>1000). Furthermore, the sensor exhibits excellent sensing performance in real-time monitoring of a wide range of human behaviors, including mass movements and subtle physiological signals.

Ecofriendly and high-performance flexible pressure sensor derived from natural plant materials for intelligent audible and silent speech recognition

Flexible pressure sensors (FPSs) are widely used in human–computer interaction (HCI) and medical diagnoses, but their further development faces several challenges. Integrating artificial intelligence (AI) with FPSs is indispensable for advancing the cognitive capabilities of HCI systems, but the FPS must also be ecofriendly, cost-effective, and high-performance to meet the demands of environmental protection and sustainable development. Here, a biodegradable capacitive FPS is presented that is fabricated from natural plant materials (i.e., cornstarch and lignocellulose) while exhibiting remarkable attributes such as high sensitivity (2.427 kPa−1 at 0–2 kPa), rapid response/recovery time (20/24 ms), extremely low detection limit (∼10 Pa), outstanding stability (> 6000 fatigue tests), excellent biocompatibility (survival rate exceeding 99 % in cell viability assays), and prominent biodegradability (complete degradation within 24 h). Prepared sensors were integrated with optimized AI algorithms, embedded systems, and wireless transmission technologies to develop a dual-functional (i.e., audible and silent) speech recognition system that achieved recognition rates exceeding 95 %. The developed sensor is expected to play a crucial role in future HCI and medical assistance applications.

In-situ graft fibrous PPy@PEI enables sensitive and all-seasoned crack monitoring for ancient architectures based on flexible pressure sensors

The non-destructive, real-time, and automatic monitoring for the development of cracks in ancient architectures is crucial to the preservation of precious ancient heritages. Here, light-weight crack sensing constructed with ultra-thin and high-performance flexible pressure sensors is proposed to fulfill this demand. The signal drift and poor reversibility commonly observed in widely-reported sensors based on elastomer matrix, which originates from the creep and relaxation behaviors, are addressed using piezoresistive polypyrrole-grafted polyetherimide fibers. The corresponding flexible piezoresistive sensors exhibit great sensitivity (9.45 kPa−1 in 0 ∼ 1 kPa and 3.48 kPa−1 in 3 ∼ 10 kPa), outstanding static stability (5.13 % signal drift after 48 h under 1 kPa), dynamic durability (4.72 % degradation after ∼30,000 cycles) and excellent robustness across an ultra-wide temperature range of −70 ∼ 150 ℃. Based on this highly reliable pressure sensor, the proposed non-destructive crack sensors integrated into an Internet of Things (IoT) platform display outstanding stability during their service in the Forbidden City. By virtue of the low energy consumption, one lithium battery can power the monitoring system for more than one year.

Highly sensitive flexible graphene pressure sensor based on indocalamus leaves’ microstructure

In recent years, high-performance flexible pressure sensors have attracted much attention due to their important application potential in intelligent robotics, wearable electronics, and electronic skin. Here, a wearable pressure sensor with high sensitivity in a large useable range is demonstrated. By utilizing indocalamus leaf as a template, the sensing layer of the sensor was prepared in the form of Graphene films with a bionic composite microstructure. Due to the hierarchical deformation of bionic composite microstructure, the sensor demonstrates high sensitivity and wide detection range at the same time. The sensitivity of sensor is 4.56 kPa−1 (5 Pa-20 kPa), 1.87 kPa−1 (20 Pa-100 kPa) and 0.70 kPa−1 (100 kPa-250 kPa). Therefore, it is not only sensitive to slight pressure as low as 5 Pa but also has a detection limit up to 250 kPa. At the same time, sensor has a short response time of 130 ms. After 1000 pressure cycles, the current change rate of the sensor can still reach 90% of the original. Meanwhile, the flexible pressure sensor could be used for monitoring human physiological signals, such as wrist pulse, voice recognition, and human activities, which shows a broad application prospect.

High Sensitivity and Wide Linear Range Flexible Piezoresistive Pressure Sensor with Microspheres as Spacers for Pronunciation Recognition.

Flexible piezoresistive pressure sensors have received great popularity in flexible electronics due to their simple structure and promising applications in health monitoring and artificial intelligence. However, the contradiction between sensitivity and detection range limits the application of the sensors in the medium-pressure regime. Here, a flexible piezoresistive pressure sensor is fabricated by combining a hierarchical spinous microstructure sensitive layer and a periodic microsphere array spacer. The sensor achieves high sensitivity (39.1 kPa-1) and outstanding linearity (0.99, R2 coefficient) in a medium-pressure regime, as well as a wide range of detection (100 Pa-160.0 kPa), high detection precision (<0.63‰ full scale), and excellent durability (>5000 cycles). The mechanism of the microsphere array spacer in improving sensitivity and detection range was revealed through finite element analysis. Furthermore, the sensors have been utilized to detect muscle and joint movements, spatial pressure distributions, and throat movements during pronouncing words. By means of a full-connect artificial neural network for machine learning, the sensor's output of different pronounced words can be precisely distinguished and classified with an overall accuracy of 96.0%. Overall, the high-performance flexible pressure sensor based on a microsphere array spacer has great potential in health monitoring, human-machine interface, and artificial intelligence of medium-pressure regime.

Porous nanofibers and micro-pyramid structures array for high-performance flexible pressure sensors

Flexible pressure sensors have attracted extensive research interest as smart wearable devices’ core components. However, developing flexible pressure sensors with high sensitivity and wide pressure detection range remains a great challenge. Utilizing electrospinning and mould transfer technology, this paper presents a novel ‘sandwich’ flexible pressure sensor composed of a sensitive layer of poly (lactic acid) (PLA) porous nanofiber network film and electrodes made of polydimethylsiloxane (PDMS) micro-pyramid structure array film. Through ultrasonic treatment, carbon black particles penetrate into the PLA porous nanofiber film, which effectively enhances the conductivity of the PLA film. Due to the complex conductive pathways formed by the ultra-high specific surface area of the PLA porous nanofibers and the three-dimensional amplification structure of the PDMS micro-pyramid arrays, the sensor has a high sensitivity of 54.06 kPa−1, a wide detection range of 0–56 kPa, an ultra-low detection limit of 2.5 Pa and excellent durability (10000 cycles). Impressively, the sensor is able to accurately monitor various physiological activities of the human body in real time, which is believed to be a strong impetus for the development of the next generation of wearable products.

A High-Performance Flexible Capacitive Pressure Sensor With 3-D Printed Hemispherical Graded Microstructures

A High-Performance Flexible Capacitive Pressure Sensor With 3-D Printed Hemispherical Graded Microstructures

High-Sensitivity and Wide-Range Flexible Ionic Piezocapacitive Pressure Sensors with Porous Hemisphere Array Electrodes.

The development of high-performance flexible pressure sensors with porous hierarchical microstructures is limited by the complex and time-consuming preparation processes of porous hierarchical microstructures. In this study, a simple modified heat curing process was first proposed to achieve one-step preparation of porous hemispherical microstructures on a polydimethylsiloxane (PDMS) substrate. In this process, a laser-prepared template was used to form surface microstructures on PDMS film. Meanwhile, the thermal decomposition of glucose monohydrate additive during heat curing of PDMS led to the formation of porous structures within PDMS film. Further, based on the obtained PDMS/CNTs electrodes with porous hemisphere array and ionic polymer dielectric layers, high-performance ionic piezocapacitive sensors were realized. Under the synergistic effect of the low-stiffness porous hemisphere microstructure and the electric double layer of the ionic polymer film, the sensor based on an ionic polymer film with a 1:0.75 ratio of P(VDF-HFP):[EMIM][TFSI] not only achieves a sensitivity of up to 106.27 kPa-1 below 3 kPa, but also has a wide measurement range of over 400 kPa, which has obvious advantages in existing flexible piezocapacitive sensors. The rapid response time of 110 s and the good stability of 2300 cycles of the sensor further elucidate its practicality. The application of the sensor in pulse monitoring, speech recognition, and detection of multiple dynamic loads verifies its excellent sensing performance. In short, the proposed heat curing process can simultaneously form porous structures and surface microstructures on PDMS films, greatly simplifying the preparation process of porous hierarchical microstructures and providing a simple and feasible way to obtain high-performance flexible pressure sensors.

Synergistic advancements in high-performance flexible capacitive pressure sensors: structural modifications, AI integration, and diverse applications.

The development of flexible pressure sensors for monitoring human motion and physiological signals has attracted extensive scientific research. However, achieving low monitoring limits, a wide detection range, large bending stresses, and excellent mechanical stability simultaneously remains a serious challenge. With the aim of developing a high-performance capacitive pressure sensor (CPS), this paper introduces the successful preparation of a single-walled carbon nanotube (SWNT)/polydimethylsiloxane (S-PDMS) composite dielectric with a foam-like structure (high permittivity and low elasticity modulus) and MXene/SWNT (S-MXene) composite film electrodes with a micro-crumpled structure. The above structurally modified CPS (SMCPS) demonstrated an excellent response output during pressure loading, achieving a wide pressure detection range (up to 700 kPa), a low detection limit (16.55 Pa), fast response/recovery characteristics (48/60 ms), enhanced sensitivity across a wide pressure range, long-term stability under repeated heavy loading and unloading (40 kPa, >2000 cycles), and reliable performance under various temperature and humidity conditions. The SMCPS demonstrated a precise and stable capacitive response in monitoring subtle physiological signals and detecting motion, owing to its unique electrode structure. The flexible device was integrated with an Internet of Things module to create a smart glove system that enables real-time tracking of dynamic gestures. This system demonstrates exceptional performance in gesture recognition and prediction with artificial intelligence analysis, highlighting the potential of the SMCPS in human-machine interface applications.

Microstructured Polyelectrolyte Elastomer-Based Ionotronic Sensors with High Sensitivities and Excellent Stability for Artificial Skins.

High-performance flexible pressure sensors are highly demanded for artificial tactile sensing. Using ionic conductors as the dielectric layer has enabled ionotronic pressure sensors with high sensitivities owing to giant capacitance of the electric double layer (EDL) formed at the ionic conductor/electronic conductor interface. However, conventional ionotronic sensors suffer from leakage, which greatly hinders long-term stability and practical applications. Herein, a leakage-free polyelectrolyte elastomer as the dielectric layer for ionotronic sensors is synthesized. The mechanical and electrical properties of the polyelectrolyte elastomer are optimized, a micropyramid array is constructed, and it is used as the dielectric layer for an ionotronic pressure sensor with marked performances. The obtained sensor exhibits a sensitivity of 69.6 kPa-1 , a high upper detecting limit on the order of 1MPa, a fast response/recovery speed of ≈6ms, and excellent stability under both static and dynamic loads. Notably, the sensor retains a high sensitivity of 4.96 kPa-1 at 500kPa, and its broad sensing range within high-pressure realm enables a brand-new coding strategy. The applications of the sensor as a wearable keyboard and a quasicontinuous controller for a robotic arm are demonstrated. Durable and highly sensitive ionotronic sensors potentialize high-performance artificial skins for soft robots, human-machine interfaces, and beyond.

Biomimetic nanofiber-iongel composites for flexible pressure sensors with broad range and ultra-high sensitivity

To achieve high-performance flexible pressure sensors, it is imperative to develop biomimetic devices that mimic the functional structure and sensing mechanism of human skin. Nevertheless, the creation of skin-like sensors with both ultra-high sensitivity and broad response range poses a formidable challenge. Drawing inspiration from the tactile sensing mechanisms and hierarchical structure of human skin, we engineered a nanofiber-iongel (NFIG) composite with internally graded stiffness characteristics and surface semi-embedded microstructures through the application of electrostatic spinning and droplet injection methods. The gel mimics the layered nanofiber structure of human skin, along with its ion-sensing mechanism, and comprises an ion gel infused with highly elastic PVDF-HFP nanofibers. This study explores the impact of Young's modulus and external pressure on unit capacitance, and it establishes a fiber-gel composite model to assess how the fibers influence sensor performance, encompassing ion fluxes, displacements, and alterations in electric potential. These findings reveal that the utilization of high-modulus materials enhances ion mobility, decreases the double electrical layer thickness, and augments pressure resistance. Based on these discoveries, we engineered the NFIG sensor, which exhibits ultra-high sensitivity (>10,000 kPa−1), a wide pressure range (∼1000 kPa), and exceptional stability (over 5000 cycles). Furthermore, this sensor is versatile, finding utility in a range of human monitoring contexts, array configurations, and even skateboard monitoring, thereby substantiating its promise in the fields of human-computer interaction and sports health.

Electrically Conductive AgNPs/TPU-Electrospun Fibers with Hierarchical Microstructures by a One-Step Method for a High-Performance Flexible Pressure Sensor

Electrically Conductive AgNPs/TPU-Electrospun Fibers with Hierarchical Microstructures by a One-Step Method for a High-Performance Flexible Pressure Sensor

Nonlinearity synergy: An elegant strategy for realizing high-sensitivity and wide-linear-range pressure sensing

Flexible pressure sensors are indispensable components in various applications such as intelligent robots and wearable devices, whereas developing flexible pressure sensors with both high sensitivity and wide linear range remains a great challenge. Here, we present an elegant strategy to address this challenge by taking advantage of a pyramidal carbon foam array as the sensing layer and an elastomer spacer as the stiffness regulator, realizing an unprecedentedly high sensitivity of 24.6 kPa−1 and an ultra-wide linear range of 1.4 MPa together. Such a wide range of linearity is attributed to the synergy between the nonlinear piezoresistivity of the sensing layer and the nonlinear elasticity of the stiffness regulator. The great application potential of our sensor in robotic manipulation, healthcare monitoring, and human-machine interface is demonstrated. Our design strategy can be extended to the other types of flexible sensors calling for both high sensitivity and wide-range linearity, facilitating the development of high-performance flexible pressure sensors for intelligent robotics and wearable devices.

High performance flexible PVDF film pressure sensor fabricated by femtosecond laser

Flexible pressure sensors have shown great potential for applications in detection and medical fields due to their unique piezoelectricity and high sensitivity. In this paper, micro-nano-perforated structures with different periods and diameters are fabricated on the polyester (PET) films by femtosecond laser direct writing (FsLDW), and then the perforated structures are embossed on polyvinylidene fluoride (PVDF) films to form sensors with circular truncated cone (CTC) structures. The effect of period and diameter on the sensitivity of the sensor is studied numerically and experimentally. The results show that the high sensitivity of 8.98 mV/KPa can be achieved in a PVDF film pressure sensor with a period of 50 μm and a diameter of 30 μm, which is about 10.9 times that of the structureless sensor. This work not only provide a fast fabricated method for the pressure sensor based on the femtosecond laser and hot embossing, but also has potential applications in the detection of the micro-signals.

High sensitivity and wide range flexible piezoresistive sensor based on petal-shaped MOF-derived NiCo-NPC

Due to the advantages of high porosity, excellent conductivity, and tunable morphology, carbonized metal-organic framework (C-MOF) is expected to become an ideal material for constructing high-performance flexible pressure sensor. Herein, to achieving the suitable morphology of C-MOF for piezoresistive sensors, a rapid thermal process (RTP) was used for carbonization of NiCo-MOF, and the petal-shaped NiCo alloy nanoparticles/nanoporous carbon composites (NiCo-NPCs) were obtained. Compared with NiCo-NPCs carbonized by common thermal process (CTP), NiCo-NPCs carbonized by RTP exhibit a modified morphology with smaller particle size and larger most frequent pore diameter. Due to the modified morphology, the piezoresistive sensor with RTP-carbonized NiCo-NPCs has a high sensitivity of 62.13 kPa–1 at 0–3 kPa, which is 3.46 times higher than that of the sensor with CTP-carbonized NiCo-NPCs. Meanwhile, the sensor shows an ultra-wide range of 1000 kPa, excellent cycle stability (>4000 cycles), and fast response/recovery time of 25/44 ms. Furthermore, the application of the sensor in dynamic loading test, airflow monitoring, voice recognition, and gesture detection demonstrates its great application prospects. In short, this work investigates the application of carbonized NiCo-MOFs in flexible pressure sensors, and provides a new strategy to improve the performance of piezoresistive sensors with porous carbon derived from MOFs.

Fully sprayed MXene-based high-performance flexible piezoresistive sensor for image recognition

High-performance flexible pressure sensors provide comprehensive tactile perception and are applied in human activity monitoring, soft robotics, medical treatment, and human-computer interface. However, these flexible pressure sensors require extensive nano-architectural design and complicated manufacturing and are time-consuming. Herein, a highly sensitive, flexible piezoresistive tactile sensor is designed and fabricated, consisting of three main parts: the randomly distributed microstructure on T-ZnOw/PDMS film as a top substrate, multilayer Ti3C2-MXene film as an intermediate conductive filler, and the few-layer Ti3C2-MXene nanosheet-based interdigital electrodes as the bottom substrate. The MXene-based piezoresistive sensor with randomly distributed microstructure exhibits a high sensitivity over a broad pressure range (less than 10 ​kPa for 175 ​kPa−1) and possesses an out-standing permanence of up to 5000 cycles. Moreover, a 16-pixel sensor array is designed, and its potential applications in visualizing pressure distribution and an example of tactile feedback are demonstrated. This fully sprayed MXene-based pressure sensor, with high sensitivity and excellent durability, can be widely used in, electronic skin, intelligent robots, and many other emerging technologies.

Lithographic printing inspired in-situ transfer of MXene-based films with localized topo-electro tunability for high-performance flexible pressure sensors

Lithographic printing inspired in-situ transfer of MXene-based films with localized topo-electro tunability for high-performance flexible pressure sensors

Rapid Fabrication of High-Performance Flexible Pressure Sensors Using Laser Pyrolysis Direct Writing.

The fabrication of flexible pressure sensors with low cost, high scalability, and easy fabrication is an essential driving force in developing flexible electronics, especially for high-performance sensors that require precise surface microstructures. However, optimizing complex fabrication processes and expensive microfabrication methods remains a significant challenge. In this study, we introduce a laser pyrolysis direct writing technology that enables rapid and efficient fabrication of high-performance flexible pressure sensors with a micro-truncated pyramid array. The pressure sensor demonstrates exceptional sensitivities, with the values of 3132.0, 322.5, and 27.8 kPa-1 in the pressure ranges of 0-0.5, 0.5-3.5, and 3.5-10 kPa, respectively. Furthermore, the sensor exhibits rapid response times (loading: 22 ms, unloading: 18 ms) and exceptional reliability, enduring over 3000 pressure loading and unloading cycles. Moreover, the pressure sensor can be easily integrated into a sensor array for spatial pressure distribution detection. The laser pyrolysis direct writing technology introduced in this study presents a highly efficient and promising approach to designing and fabricating high-performance flexible pressure sensors utilizing micro-structured polymer substrates.

High-performance flexible pressure sensor based on ordered double-level nanopillar array films: Design, development, and modeling

To improve the sensitivity and broaden the range of flexible pressure sensors, we proposed a high-performance flexible pressure sensor based on ordered double-level nanopillar array films. In this work, polypyrrole/multi-walled carbon nanotube/polyurethane (PPy/MWCNT/PU) conductive films with double-level nanopillar array microstructures were prepared by continuously adjusting the oxidation and pore expansion parameters of a porous anodic alumina template (AAO), where the high pillar height was 1243.0 ± 7.0 nm, and the low pillar height was 868.0 ± 4.70 nm. We studied the influence of the structural characteristics of ordered double-level nanopillar array conductive films and a flexible pressure sensor on the sensing performance using finite element simulations, the establishment of sensing mechanism, and sensor performance measurements. The results showed that the pressure was positively correlated with the change rate of strain and the surface microstructure contact area of the ordered double-level nanopillar array films. The sensor sensitivity reached 208.353 kPa−1, and its range was extended by 267%. In addition, the sensor, which could monitor vocalization, drinking pulse and finger movements, could be used in a wide range of applications, including wearable medical monitoring and smart sign language textiles.

A Flexible Piezocapacitive Pressure Sensor with Microsphere-Array Electrodes.

Flexible pressure sensors that emulate the sensation and characteristics of natural skins are of great importance in wearable medical devices, intelligent robots, and human-machine interfaces. The microstructure of the pressure-sensitive layer plays a significant role in the sensor's overall performance. However, microstructures usually require complex and costly processes such as photolithography or chemical etching for fabrication. This paper proposes a novel approach that combines self-assembled technology to prepare a high-performance flexible capacitive pressure sensor with a microsphere-array gold electrode and a nanofiber nonwoven dielectric material. When subjected to pressure, the microsphere structures of the gold electrode deform via compressing the medium layer, leading to a significant increase in the relative area between the electrodes and a corresponding change in the thickness of the medium layer, as simulated in COMSOL simulations and experiments, which presents high sensitivity (1.807 kPa-1). The developed sensor demonstrates excellent performance in detecting signals such as slight object deformations and human finger bending.