Multifunctional Pressure Sensors Research Articles

Microchannel pressure sensor for continuous and real-time wearable gait monitoring

A highly sensitive and multi-functional pressure sensor capable of continuous pressure readings is greatly needed, particularly for precise gait pattern analysis. Here, we fabricate a sensitive and reliable pressure sensor by employing eutectic gallium indium (EGaIn) liquid metal as the sensing material and EcoFlex 00-30 silicone as the substrate, via a low-cost process. The device architecture features a microchannel, creating two independent sensing devices, and the mechanical properties of the substrate and sensing material contribute to high stretchability and flexibility, resulting in a sensitivity of 66.07 MPa−1 and a low measurement resolution of 0.056 kPa. The sensor detects applied pressure accurately and can distinguish pressure distribution across a wide area. We demonstrate high efficiency for monitoring human walking gait at various speeds when a single sensor is attached to the foot, and can differentiate between walking postures. This device has strong potential for clinical and rehabilitation applications in gait analysis.

Elastic Multifunctional Pressure Sensor Based on C–NiCoZn–O/CMF Composites for Polar Exploration

Elastic Multifunctional Pressure Sensor Based on C–NiCoZn–O/CMF Composites for Polar Exploration

Multifunctional starch-based double-network hydrogels as electronic skin

The realization of flexible pressure sensors that could mimic the perception functions of human skin (touch, temperature, and humidity) is important for development of electronic skin. However, the design and preparation of highly sensitive sensors for multifunctional sensing of pressure, temperature and humidity remains a challenge. Here, we first designed and prepared a flexible starch/polyacrylamide (PAM) double-network hydrogel, with additional introduction of Na+ and Cl− to further enhance the electrical properties. Subsequently, a multifunctional pressure sensor was fabricated by sandwiching a microstructured starch-based hydrogel into two flexible AgNWs electrodes. In the test run, the prepared sensor exhibited a high sensitivity of 48.35 kPa−1, a fast response time of 11 ms, and remarkable mechanical stability (>3000 cycles). Given the satisfactory performance for pressure sensing, we demonstrated the ability of the sensor to monitor various human dynamics. Moreover, the starch-based hydrogel was further developed as a flexible temperature and humidity sensor for its water absorption and swelling properties. In particular, the asynchrony of pressure, temperature and humidity strains (straining to stability at 11 ms, 2 s and 10 s, respectively) resulted in the automatic separation of different electrical signals. The intuitive interpretation of the data without involving complex parameter separation calculations allowed the starch-based hydrogels to be developed as an integrated, multifunctional sensor of pressure, temperature and humidity with high sensitivity and flexibility. The above properties suggest that the prepared bio-based hydrogels may provide a new solution for the prospect of green and multifunctional electronic skin development.

A superelastic SiOC@carbon ceramic spring for multifunctional pressure sensor in wide temperature range

With the flourishing development in space exploration and human motion detection, the wide-temperature flexible pressure sensors are urgently required in various complex application situations. One massive challenge of current available sensors is to enhance the oxidation resistance property, which is crucial for their applications in high-temperature environments. Herein, we fabricated a superelastic silicon oxycarbide @carbon (SiOC@C) ceramic spring, possessing a porous lamellar and spring-like structure. The spring-like structure tends to deform and absorb the energy under the external loads, and then the anisotropic lamellar structure can effectively and uniformly release the stress. The as-prepared SiOC@C spring exhibits excellent superelasticity, high compressibility (60%), and robustness (∼99.0% maximum stress retention after 1000 cycles at 50% compression). Meanwhile, the SiOC@C spring-derived sensor possesses a high sensitivity under low pressure (282.46 kPa−1 at < 1.3 kPa), a low detection limit (< 0.098 Pa) and a short response/recovery time (∼12 ms/4 ms). Moreover, benefiting from the high/low-temperature resistance of SiOC nanolayer coated on the carbon framework, the SiOC@C spring-based sensor can function properly at a wide temperature range from − 196 °C to 500 °C, showing the potential application in various fields of biomedical monitoring, space exploration, and automotive industries.

Fluorescent N-CQDs uniformly implanted into sponge-like PVDF-HFP piezoelectric film by facile two-step process for multifunctional pressure sensor

To meet the diversified demands for the booming intelligent systems, a multifunctional pressure sensor with two basic capabilities of ultraviolet excited fluorescence and force-electricity response has been proposed, and named as fluorescent pressure sensor (FPS). Carbon quantum dots (CQDs) are being rapidly developed as an reasonable photoluminescence materials. However, the CQDs were utilized in the solid-state film along with serious aggregation-induced quenching (AIQ). Here, we developed a two-step method instead of the typical one-step method to overcome the AIQ of the CQDs in the representative piezoelectric polymer. The sponge-like poly (vinylidene) fluoride-hexafluoropropylene (PVDF-HFP) film with high porosity formed based on nonsolvent-induced phase separation was selected as the host matrix of the guest nitrogen-doped CQDs (N-CQDs). The impressive bright blue fluorescence with enhanced intensity derived from the N-CQDs is successfully implanted into the obtained N-CQDs/PVDF-HFP piezoelectric hybrid film, attributing to two key factors: (i) the sponge-like matrix supported uniform distribution of the N-CQDs and (ii) the hydrogen bonding between the N-CQDs and the matrix chains. Meanwhile, the hybrid film used in the FPS still keeps a sensitivity of 92.7 mV N−1, thanks to the β piezoelectric phase formation in the matrix. Since the hybrid film based FPS has multiple features, such as ultraviolet excited fluorescence, force-electricity response, self-powered capability and flexibility, it will show a great potential in the intelligent systems used as the multifunctional sensor and energy harvester.

High-performance multifunctional piezoresistive/piezoelectric pressure sensor with thermochromic function for wearable monitoring

To meet the application of the pressure sensors in various conditions, a high-performance piezoresistive/piezoelectric (IOF) sensor with a thermochromic function has been designed and fabricated in this work, which consists of a color-changing piezoelectric film (BP) and a piezoresistive layer (FPM) laminated together. Benefiting from the reaction between the color-former and the developer in a temperature-dependent co-solvent, the thermochromic function in the IOF sensor can be achieved, showing from blue at 30 °C to white at 150 °C. Moreover, by introducing Bi0.5Na0.5TiO3 (BNT) piezoelectric material, the BP piezoelectric layer can provide 80 V output voltage, 1.398 V·kPa−1 sensitivity, and 30 ms response time, respectively. Electrical conductivity is imparted to the fabric through the introduction of MXene, and the FPM piezoresistive layer displays 0.835 kPa−1 sensitivity and 73 ms response time in a wide stress range of 0–300 kPa, respectively. When the IOF sensor is attracted to the human body and KN95 masks, it has good sensitivity to measure human behavior, breath airflow, and daily speaking signals, showing a promise to use in wearable monitoring. Summarily, the studied pressure sensor integrates the advantages of piezoresistive and piezoelectric sensors and may provide a new paradigm to develop multifunctional pressure sensors for wearable monitoring with temperature visualization.

Synergistic effect of carbon nanotubes and carbon black as nanofillers of silicone rubber pressure sensors

Pressure sensors based on nitrogen-doped bamboo-shaped carbon nanotubes (N-BCNT) and carbon black (CB) as nanofillers, polyurethane foam (PU) as supporting substrate, and silicone rubber (SR) as a matrix were prepared. Dip coating was used to coat PU with 0.44 wt% nanofiller, including different mixing ratios of N-BCNT and CB (5:5; 6:4; 7:3; 8:2; 9:1). Then, the coated PU is impregnated in SR to fill the pores. Due to the higher aspect ratio of the N-BCNT, it contributes more to improving the electrical conductivity in the composites, while the CB fills the smaller gaps. The prepared sensors were tested in various applications, and it was found that the optimal mixing ratio of nanofillers was 7:3 N-BCNT:CB. Thus, a multifunctional pressure sensor has been developed successfully with excellent flexibility and good resilience, suitable for motion detection and finger touch applications. The pressure sensor showed high sensitivity, and the ability to detect a wide range of pressures. The sensor exhibited success in a range of applications, paving the way for its potential use in various fields in the future, such as wearable devices, prosthetics, robotic devices, and medical devices.

Flexible multifunctional pressure sensors based on Cu-CAT@CNFN and ZnS:Cu/PDMS composite electrode films for visualization and quantification of human motion

Flexible multifunctional pressure sensors for human motion monitoring have recently attracted extensive attention. However, the preparation of a multifunctional sensor with wide coverage and high sensitivity to pressure detection remains a considerable challenge. Here, we design a flexible multifunctional pressure sensor consisting of Cu-catechol nanowire coated carbonized nanofiber networks (Cu-CAT@CNFN) sandwiched between two interlocking polydimethylsiloxane doped with ZnS:Cu (ZnS:Cu/PDMS) composite electrode films. Due to the pressure concentration between the interlock micromastoid arrays and the thicker pressure sensitive layer, the pressure sensors demonstrate a high sensitivity of 45.40 kPa−1, pressure detection coverage of 0 to 110 kPa, a response time of 0.166 s, outstanding cyclic stability of 5,000 cycles and visualization of the pressure. Furthermore, the pressure sensor can be used to detect pulses, wrist and elbow bending, and finger press. The excellent performance of the pressure sensor demonstrates its application potential in the next generation of wearable electronics.

Highly Compressible Elastic Aerogel Spring-Based Piezoionic Self-Powering Pressure Sensor for Multifunctional Wearable Electronics.

To meet the rapid development of wearable flexible electronics, the multifunctional integrations into singe device are in extreme demand. In this paper, we developed novel self-powering multifunctional pressure sensors and supercapacitor-integrated device based on highly elastic silver nanowires@reduced graphene aerogel, being conductive to reduce integration difficulties and device size. Serving as an energy device, it behaves with a prominent specific capacitance of 146.6 F g−1, and excellent rate capability even at 500 mV s−1. The fabricated sensor demonstrates an excellent sensitivity of 2.54 kPa−1 and superior pressure-sensing stability up to 1000 compressive cycles. Piezoionization effect is suggested to reveal the sensing mechanism. Our research provides a new research direction in designing the integration of self-driving wearable electronics.

Ultrasensitive and self-alarm pressure sensor based on laser-induced graphene and sea urchin-shaped Fe2O3 sandwiched structure

Flexible pressure sensors are widely used in wearable electronics. In recent years, it is still a challenge to prepare high-sensitivity and high-performance pressure sensors, though flexible pressure sensors have made significant progress. Therefore, a new sensor structure is designed in this study. This structure is composed of sea urchin-like Fe2O3 as a spacer layer, which is sandwiched between two laser-induced graphene (LIG)/polyimide (PI) films. Additionally, a flexible multifunctional sensing device with both health monitoring and alarm functions is prepared based on the excellent mechanical properties and thermal conductivity of LIG. Multifunctional sensing devices have high sensitivity, integrated monitoring, and alarm functions. Specifically, the sensitivity of the pressure sensor is 603 kPa−1 for the pressure ranges of 0–10 kPa. The pressure sensor possesses a working range of up to 200 kPa and good cycle stability (for over 3000 loading–unloading cycles). Furthermore, LIG is employed as a heater to realize the alarm function. In this work, the combination of high performance and simple methods provides an effective method for the development of the integration of multifunctional pressure sensors for wearable electronic devices.

3D Porous MXene Aerogel through Gas Foaming for Multifunctional Pressure Sensor

The development of smart wearable electronic devices puts forward higher requirements for future flexible electronics. The design of highly sensitive and high-performance flexible pressure sensors plays an important role in promoting the development of flexible electronic devices. Recently, MXenes with excellent properties have shown great potential in the field of flexible electronics. However, the easy-stacking inclination of nanomaterials limits the development of their excellent properties and the performance improvement of related pressure sensors. Traditional methods for constructing 3D porous structures have the disadvantages of complexity, long period, and difficulty of scalability. Here, the gas foaming strategy is adopted to rapidly construct 3D porous MXene aerogels. Combining the excellent surface properties of MXenes with the porous structure of aerogel, the prepared MXene aerogels are successfully used in high-performance multifunctional flexible pressure sensors with high sensitivity (306 kPa -1 ), wide detection range (2.3 Pa to 87.3 kPa), fast response time (35 ms), and ultrastability (&gt;20,000 cycles), as well as self-healing, waterproof, cold-resistant, and heat-resistant capabilities. MXene aerogel pressure sensors show great potential in harsh environment detection, behavior monitoring, equipment recovery, pressure array identification, remote monitoring, and human-computer interaction applications.

MXene/tissue paper composites for wearable pressure sensors and thermotherapy electronics

Multifunctional pressure sensors with diversified applications exhibited tremendous demand and great potential for commercialization. Herein, pressure sensors with high sensitivity were realized through efficient surface bonding of MXene materials with traditional tissue paper. The sensors exhibited a broad working range of 0-100 kPa with high sensitivity, fast response and recovery time of around 30 ms, excellent mechanical endurance without obvious fatigue over 2000 loading/unloading cycles as well as low detection limit of 0.89 Pa. Based on these excellent sensing properties, physiological signals of pressure sensors were evaluated including gesture, breath and pulse, further revealing the potential for commercial wearable electronics. Moreover, pressure regulation pattern of wearable thermotherapy electronics further demonstrated the intrinsic dominant electro-thermal properties of Ti3C2Tx. We anticipated that the Ti3C2Tx/tissue paper integrated pressure sensor would offer great contributes for developing smart wearable thermotherapy electronics to achieve motion detection and health protection in the future.

Wearable, Washable, and Highly Sensitive Piezoresistive Pressure Sensor Based on a 3D Sponge Network for Real-Time Monitoring Human Body Activities.

Wearable pressure sensors are highly desirable for monitoring human health and realizing a nice human-machine interaction. Herein, a chitosan/MXene/polyurethane-sponge/polyvinyl alcohol (CS/MXene/PU sponge/PVA)-based 3D pressure sensor is developed to simultaneously achieve wearability, washability, and high sensitivity in a wide region. In the force-sensitive layer of the sensor, MXene and CS are fully attached to the PU sponge to ensure that the composite sponge has remarkable conductivity and washability. Benefiting from the highly resistive PVA-nanowire spacer, the initial current of the sensor is reduced significantly so that the sensor exhibits extremely high sensitivity (84.9 kPa-1 for the less than 5 kPa region and 140.6 kPa-1 for the 5-22 kPa region). Moreover, the sensor has an excellent fast response time of 200 ms and a short recovery time of 30 ms, as well as non-attenuating durability over 5000 cycles. With the high sensitivity in a wide range, the sensor is capable of detecting multiple human and animal activities in real time, ranging from the large pressure of joint activities to a subtle pressure of pulse. Furthermore, the sensor also demonstrates the potential application in measuring pressure distribution. Overall, such a multifunctional pressure sensor can supply a new platform for the design and development of wearable health-monitoring equipment and an efficient human-machine interface.

Research progress of flexible wearable pressure sensors

Flexible pressure sensors with high sensitivity, high flexibility, lightness and easy integration have been extensively researched in the fields of electronic skin, wearable devices, medical diagnosis, physical health detection and artificial intelligence. This review summarizes the latest research progress of piezoresistive pressure sensors, capacitive pressure sensors, and piezoelectric pressure sensors. In addition, high-performance flexible pressure sensors designed for different application requirements such as self-powered pressure sensors, multifunctional pressure sensors, and self-healing pressure sensors are also discussed. After a comprehensive description of the latest flexible pressure sensors, we discussed the current challenges and potential prospects of flexible pressure sensors. Exploring new sensing mechanisms, seeking new functional materials, and developing novel integrated technologies for flexible devices will be the key direction in the sensor field in the future.

Ultrasensitive Thin-Film Pressure Sensors with a Broad Dynamic Response Range and Excellent Versatility Toward Pressure, Vibration, Bending, and Temperature

Flexible pressure sensors with high sensitivity and wide pressure response range are attracting considerable research interest for their potential applications as e-skins. Nowadays, it seems a dilemma to realize high-performance, multifunctional pressure sensors with cost-effective, scalable strategy, which can simplify wearable sensing systems without additional signal processing, enabling device miniaturization and low power consumption. Herein, pressure sensors with ultrahigh sensitivity and broad response pressure range are developed with a low-cost, facile method by combining strain-induced percolation behavior and contact area contributions. Due to their special surface structure and strain induced conductive network formation behavior, these unique pressure sensors exhibit wide sensing range of 1 Pa-500 kPa, ultra-high sensitivity (1×106 kPa-1and 3.1×104 kPa-1 in the pressure ranges of 1 Pa-20 kPa and 20-500 kPa, respectively), fast signal response (< 50 ms), low detect limit (1 Pa) and high stability over 500 loading/unloading cycles. These characteristics allow the devices work as e-skins to monitor human pulse signals and finger touch. Moreover, these sensors illustrate precise electrical response to mechanical vibration, bending and temperature stimuli, which afford the ability of detecting cell phone call-in vibration signals, joint bending and spatial pressure & temperature distributions, indicating promising applications in next-generation wearable, multifunctional e-skins.

Highly Wearable, Breathable, and Washable Sensing Textile for Human Motion and Pulse Monitoring.

At present, pressure sensor textiles are of great significance in the area of wearable electronics, especially for making smart or intelligent textiles. However, the design of these textile-based devices with sensitive ability, simple fabrication, and low cost is still challenging. In this study, we developed a triboelectric sensing textile constructed with core-shell yarns. Nylon filament and polytetrafluoroethylene filament were selected as the positive and negative layers, respectively, in the woven structure while the built-in helical stainless steel yarn was serving as the inner electrode layer. The sensitivity of the sensing textile can reach up to 1.33 V·kPa-1 and 0.32 V·kPa-1 in the pressure range of 1.95-3.13 kPa and 3.20-4.61 kPa, respectively. This sensing textile presented good mechanical stability and sensing capability even after 4200 cycles of continuous operation or after 4 h continuous water washing. Benefiting from the favorable merits of being highly flexible, breathable, lightweight, and even dyeable, the fabricated device was capable of being placed on any desired body parts for quantifying the dynamic human motions. It can be effectively used to measure and monitor various human movements associated with different joints, such as the hand, elbow, knee, and underarm. Moreover, the sensing textile was able to capture real-time pulse signals and reflect the current health status for human beings. This study affords an innovative and promising track for multifunctional pressure sensor textiles with wide applications in smart textiles and personalized healthcare.

Hierarchically Rough Structured and Self-Powered Pressure Sensor Textile for Motion Sensing and Pulse Monitoring.

Nowadays, real-time human motion sensing and pulse monitoring can provide significant basis for health assessment and medical diagnosis. Nevertheless, it is still a big challenge to design a lightweight, flexible, and energy-sustainable pressure sensor with high sensitivity and breathability. Here, we fabricated a triboelectric all-fiber structured pressure sensor via a facile electrospinning technique. The constructed sensor textile holds a composite structure made up of a polyvinylidene fluoride/Ag nanowire nanofibrous membrane (NFM), an ethyl cellulose NFM, and two layers of conductive fabrics. This wearable device with high shape adaptability exhibited excellent sensing capability because of the introduced hierarchically rough structure on the nanofibers. The sensitivity can reach up to 1.67 and 0.20 V·kPa-1 in the pressure range of 0-3 and 3-32 kPa, respectively. The fabricated sensor textile also showed a superior mechanical stability even after continuous operation of 7200 working cycles. This sensor textile was easily conformable on different desired body parts for dynamic motion sensing and real-time pulse monitoring. It can work in a self-powered manner to detect and quantify various human motions associated with joints, such as elbows, knees, and ankles. Additionally, it can be placed on the carotid artery to capture the pulse signals, serving as a reliable way to reflect the state of health. This work has great possibilities to promote the rapid advancement and broad applications of multifunctional pressure sensors and next-generation wearable electronics.

Seeing pressure in color based on integration of highly sensitive pressure sensor and emission tunable light emitting diode.

We demonstrate a highly sensitive, low-cost, environmental-friendly pressure sensor derived from a wool-based pressure sensor with wide pressure sensing range using wool bricks embedded with a Ag nano-wires. The easy fabrication and light weight allow portable and wearable device applications. Wth the integration of a light-emitting diode possessing multi-wavelength emission, we illustrate a hybrid multi-functional LED-integrated pressure sensor that is able to convert different applied pressures to light emission with different wavelengths. Due to the high sensitivity of the pressure sensor, the demonstration of acoustic signal detection has also been presented using sound of a metronome and a speaker playing a song. This multi-functional pressure sensor can be implemented to technologies such as smart lighting, health care, visible light communication (VLC), and other internet of things (IoT) applications.

A Flexible and Highly Sensitive Pressure Sensor Based on AgNWs/NRLF for Hand Motion Monitoring.

Flexible, highly sensitive, easy fabricating process, low-cost pressure sensors are the trend for flexible electronic devices. Inspired by the softness, comfortable, environmental friendliness and harmless of natural latex mattress, herein, we report an agile approach of constructing a flexible 3D-architectured conductive network by dip-coating silver nanowires (AgNWs) on the natural rubber latex foam (NRLF) substrate that provide the 3D micro-network structure as the skeleton. The variation of the contact transformed into the electrical signal among the conductive three-dimensional random networks during compressive deformation is the piezoresistive effect of AgNWs/NRLF pressure sensors. The resulting AgNWs/NRLF pressure sensors exhibit desirable electrical conductivity (0.45–0.50 S/m), excellent flexibility (58.57 kPa at 80% strain), good hydrophobicity (~128° at 5th dip-coated times) and outstanding repeatability. The AgNWs/NRLF sensors can be assembled on a glove to detect hand motion sensitively such as bending, touching and holding, show potential application such as artificial skin, human prostheses and health monitoring in multifunctional pressure sensors.

A Proposal of New Multifunctional Pressure Sensor Based on PVDF Films

In this paper, a new multifunctional pressure sensor based on polyvinylidene difluoride (PVDF) films is proposed. The proposed sensor consists of a pair of PVDF films with urethane gel. The electrical voltage (capacitance) and ultrasonic propagation time are simultaneously measured by a pair of PVDF films. In addition, the voltages generated on the PVDF film by the vibration and temperature change are also measured due to the piezoelectric and pyroelectric effects. When the object is loaded onto the proposed sensor, the pressure is measured by the change of propagation time because the thickness of the urethane gel changes. In addition, information about the object, such as the electrical properties and vibration and temperature change, is obtained by the measured capacitance and voltages. Therefore, it is possible to measure the pressure, the electrical property, temperature change, and vibration of the object with the proposed sensor. In this experiment, the fundamental properties of the proposed sensor-pressure (weight), electrical property, vibration, and temperature-were presented. As results, electrical voltage and propagation time were measured with the relative standard deviations (RSDs) of the 21% and 2% between 0 and 50 kg weights. Two types of vibrations-sinusoidal wave of 1 Hz and pulse wave of 1.2 Hz-were detected with the RSDs of 2% and 1%, respectively. In addition, the peak voltage generated by temperature change between 14°C and 40°C was approximately measured with the RSD of 26%.