Ultra-broadband microwave absorber and high-performance pressure sensor based on aramid nanofiber,polypyrrole and nickel porous aerogel

Electronic devices have become ubiquitous in our daily lives,leading to a surge in the use of microwave absorbers and wearable sensor devices across various sectors.A prime example of this trend is the aramid nanofibers/polypyrrole/nickel(APN)aerogels,which serve dual roles as both microwave absorbers and pressure sensors.In this work,we focused on the preparation of aramid nanofibers/polypyrrole(AP15)aerogels,where the mass ratio of aramid nanofibers to pyrrole was 1:5.We employed the oxidative polymerization method for the preparation process.Following this,nickel was thermally evaporated onto the surface of the AP15 aerogels,resulting in the creation of an ultralight(9.35 mg·cm^(-3)).This aerogel exhibited a porous structure.The introduction of nickel into the aerogel aimed to enhance magnetic loss and adjust impedance matching,thereby improving electromagnetic wave absorption performance.The minimum reflection loss value achieved was-48.7 dB,and the maximum effective absorption bandwidth spanned 8.42 GHz with a thickness of 2.9 mm.These impressive metrics can be attributed to the three-dimensional network porous structure of the aerogel and perfect impedance matching.Moreover,the use of aramid nanofibers and a three-dimensional hole structure endowed the APN aerogels with good insulation,flame-retardant properties,and compression resilience.Even under a compression strain of 50%,the aerogel maintained its resilience over 500 cycles.The incorporation of polypyrrole and nickel particles further enhanced the conductivity of the aerogel.Consequently,the final APN aerogel sensor demonstrated high sensitivity(10.78 kPa-1)and thermal stability.In conclusion,the APN aerogels hold significant promise as ultra-broadband microwave absorbers and pressure sensors.

Flexible capacitive pressure sensor based on interdigital electrodes with porous microneedle arrays for physiological signal monitoring

Flexible pressure sensors have many potential applications in the monitoring of physiological signals because of their good biocompatibil-ity and wearability.However,their relatively low sensitivity,linearity,and stability have hindered their large-scale commercial application.Herein,aflexible capacitive pressure sensor based on an interdigital electrode structure with two porous microneedle arrays(MNAs)is pro-posed.The porous substrate that constitutes the MNA is a mixed product of polydimethylsiloxane and NaHCO3.Due to its porous and interdigital structure,the maximum sensitivity(0.07 kPa-1)of a porous MNA-based pressure sensor was found to be seven times higher than that of an imporous MNA pressure sensor,and it was much greater than that of aflat pressure sensor without a porous MNA structure.Finite-element analysis showed that the interdigital MNA structure can greatly increase the strain and improve the sensitivity of the sen-sor.In addition,the porous MNA-based pressure sensor was found to have good stability over 1500 loading cycles as a result of its bilayer parylene-enhanced conductive electrode structure.Most importantly,it was found that the sensor could accurately monitor the motion of afinger,wrist joint,arm,face,abdomen,eye,and Adam’s apple.Furthermore,preliminary semantic recognition was achieved by monitoring the movement of the Adam’s apple.Finally,multiple pressure sensors were integrated into a 33 array to detect a spatial pressure distribu-×tion.Compared to the sensors reported in previous works,the interdigital electrode structure presented in this work improves sensitivity and stability by modifying the electrode layer rather than the dielectric layer.

Flexible polydimethylsiloxane pressure sensor with micro-pyramid structures and embedded silver nanowires:A novel application in urinary flow measurement

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.

Blade-Coated Porous 3D Carbon Composite Electrodes Coupled with Multiscale Interfaces for Highly Sensitive All-Paper Pressure Sensors

Flexible and wearable pressure sensors hold immense promise for health monitoring,covering disease detection and postoperative rehabilitation.Developing pressure sensors with high sensitivity,wide detection range,and cost-effectiveness is paramount.By leveraging paper for its sustainability,biocompatibility,and inherent porous structure,herein,a solution-processed all-paper resistive pressure sensor is designed with outstanding performance.A ternary composite paste,comprising a compressible 3D carbon skeleton,conductive polymer poly(3,4-ethylene dioxythiophene):poly(styrenesulfonate),and cohesive carbon nanotubes,is blade-coated on paper and naturally dried to form the porous composite electrode with hierachical micro-and nano-structured surface.Combined with screen-printed Cu electrodes in submillimeter finger widths on rough paper,this creates a multiscale hierarchical contact interface between electrodes,significantly enhancing sensitivity(1014 kPa-1)and expanding the detection range(up to 300 kPa)of as-resulted all-paper pressure sensor with low detection limit and power consumption.Its versatility ranges from subtle wrist pulses,robust finger taps,to large-area spatial force detection,highlighting its intricate submillimetermicrometer-nanometer hierarchical interface and nanometer porosity in the composite electrode.Ultimately,this all-paper resistive pressure sensor,with its superior sensing capabilities,large-scale fabrication potential,and cost-effectiveness,paves the way for next-generation wearable electronics,ushering in an era of advanced,sustainable technological solutions.

Flexible piezoresistive pressure sensor based on a graphene-carbon nanotube-polydimethylsiloxane composite

Flexible sensors are used widely in wearable devices, specifically flexible piezoresistive sensors, which are common and easy to manipulate.However, fabricating such sensors is expensive and complex, so proposed here is a simple fabrication approach involving a sensor containing microstructures replicated from a sandpaper template onto which polydimethylsiloxane containing a mixture of graphene and carbon nanotubes is spin coated. The surface morphologies of three versions of the sensor made using different grades of sandpaper are observed, and the corresponding pressure sensitivities and linearity and hysteresis characteristics are assessed and analyzed. The results show that the sensor made using 80-mesh sandpaper has the best sensing performance. Its sensitivity is 0.341 kPa-1in the loading range of 0–1.6 kPa, it responds to small external loading of 100 Pa with a resistance change of 10%, its loading and unloading response times are 0.126 and 0.2 s, respectively,and its hysteresis characteristic is ~7%, indicating that the sensor has high sensitivity, fast response, and good stability. Thus, the presented piezoresistive sensor is promising for practical applications in flexible wearable electronics.

Nanocellulose-Assisted Construction of Multifunctional MXene-Based Aerogels with Engineering Biomimetic Texture for Pressure Sensor and Compressible Electrode

Multifunctional architecture with intriguing structural design is highly desired for realizing the promising performances in wearable sensors and flexible energy storage devices.Cellulose nanofiber(CNF)is employed for assisting in building conductive,hyperelastic,and ultralight Ti_(3)C_(2)T_(x)MXene hybrid aerogels with oriented tracheid-like texture.The biomimetic hybrid aerogels are constructed by a facile bidirectional freezing strategy with CNF,carbon nanotube(CNT),and MXene based on synergistic electrostatic interaction and hydrogen bonding.Entangled CNF and CNT“mortars”bonded with MXene“bricks”of the tracheid structure produce good interfacial binding,and superior mechanical strength(up to 80%compressibility and extraordinary fatigue resistance of 1000 cycles at 50%strain).Benefiting from the biomimetic texture,CNF/CNT/MXene aerogel shows ultralow density of 7.48 mg cm^(-3)and excellent electrical conductivity(~2400 S m^(-1)).Used as pressure sensors,such aerogels exhibit appealing sensitivity performance with the linear sensitivity up to 817.3 kPa^(-1),which affords their application in monitoring body surface information and detecting human motion.Furthermore,the aerogels can also act as electrode materials of compressive solid-state supercapacitors that reveal satisfactory electrochemical performance(849.2 mF cm^(-2)at 0.8 mA cm^(-2))and superior long cycle compression performance(88%after 10,000 cycles at a compressive strain of 30%).

MXene-based flexible pressure sensor with piezoresistive properties significantly enhanced by atomic layer infiltration

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.

Self-healing Au/PVDF-HFP composite ionic gel for flexible underwater pressure sensor

Ionic gels can be potentially used in wearable devices owing to their high humidity resistance and non-volatility.However,the applicability of existing ionic gel pressure sensors is limited by their low sensitivity.Therefore,it is very import-ant to develop an ionic gel pressure sensor with high sensitivity and a wide pressure detection range without sacrificing mechan-ical stretchability and self-healing ability.Herein,we report an effective strategy for developing pressure sensors based on ion-ic gel composites consisting of high-molecular-weight polymers,ionic liquids,and Au nanoparticles.The resulting capacitive pressure sensors exhibit high pressure sensitivity,fast response,and excellent self-healing properties.The sensors composed of highly hydrophobic polymers and ionic liquids can be used to track underwater movements,demonstrating broad application prospects in human motion state monitoring and underwater mechanical operations.

Dynamic compensation and its application of shock wave pressure sensor

In order to correct the test error caused by the dynamic characteristics of pressure sensor and avoid the influence of the error of sensor＇s dynamic model on compensation results,a dynamic compensation method of the pressure sensor is presented,which is based on quantum-behaved particle swarm optimization（QPSO）algorithm and the mean square error（MSE）.By using this method,the inverse model of the sensor is built and optimized and then the coefficients of the optimal compensator are got.This method is verified by the dynamic calibration with shock tube and the dynamic characteristics of the sensor before and after compensation are analyzed in time domain and frequency domain.The results show that the working bandwidth of the sensor is extended effectively.This method can reduce dynamic measuring error and improve test accuracy in actual measurement experiments.

Silver Nanowire Electrodes: Conductivity Improvement Without Post-treatment and Application in Capacitive Pressure Sensors

Transparent electrode based on silver nanowires(Ag NWs) emerges as an outstanding alternative of indium tin oxide film especially for flexible electronics. However, the conductivity of Ag NWs transparent electrode is still dramatically limited by the contact resistance between nanowires at high transmittance. Polyvinylpyrrolidone(PVP) layer adsorbed on the nanowire surface acts as an electrically insulating barrier at wire–wire junctions, and some devastating post-treatment methods are proposed to reduce or eliminate PVP layer, which usually limit the application of the substrates susceptible to heat or pressure and burden the fabrication with high-cost, time-consuming, or inefficient processes. In this work, a simple and rapid pre-treatment washing method was proposed to reduce the thickness of PVP layer from 13.19 to0.96 nm and improve the contact between wires. Ag NW electrodes with sheet resistances of 15.6 and 204 X sq-1have been achieved at transmittances of 90 and 97.5 %, respectively. This method avoided any post-treatments and popularized the application of high-performance Ag NW transparent electrode on more substrates. The improved Ag NWs were successfully employed in a capacitive pressure sensor with high transparency, sensitivity, and reproducibility.

Morphological Engineering of Sensing Materials for Flexible Pressure Sensors and Artificial Intelligence Applications

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.

On the Temperature Profile of the Thermally Excited Resonant Silicon Micro Structural Pressure Sensor

According to the sensing structure of a practical silicon resonant pressure micro sensor whose preliminary sensing unit is a square silicon diaphragm and the final sensing unit is a silicon beam resonator, its operating mechanism is analyzed. The thermal resistor acts as the excited unit, and the piezoresistive unit acts as the detector, for the above micro sensor. By using the amplitude and phase conditions, the self exciting closed loop system is investigated based on the operating mechanism for the abov...

Highly Sensitive Pseudocapacitive Iontronic Pressure Sensor with Broad Sensing Range

Flexible pressure sensors are unprecedentedly studied on monitoring human physical activities and robotics.Simultaneously,improving the response sensitivity and sensing range of flexible pressure sensors is a great challenge,which hinders the devices’practical application.Targeting this obstacle,we developed a Ti_(3)C_(2)T_(x)-derived iontronic pressure sensor(TIPS)by taking the advantages of the high intercalation pseudocapacitance under high pressure and rationally designed structural configuration.TIPS achieved an ultrahigh sen-sitivity(S_(min)>200 kPa^(−1),S_(max)>45,000 kPa^(−1))in a broad sensing range of over 1.4 MPa and low limit of detection of 20 Pa as well as stable long-term working durability for 10,000 cycles.The practical application of TIPS in physical activity monitoring and flexible robot manifested its versatile potential.This study provides a demonstration for exploring pseudocapacitive materials for building flexible iontronic sensors with ultrahigh sensitivity and sensing range to advance the development of high-performance wearable electronics.

An Optical Pressure Sensor Based on MEMS

An optical fiber pressure sensor has been developed for the measurement in human body.The sensing element is possessed of a membrane structure,which is fabricated by micromachining.The fabrication process includes anisotropic wet etching on the silicon wafer.For the transmitting source and signal light,a multimode optical fiber 50/125 μm (core/clad)in diameter was used.The intensity of the light reflected back into the fiber varies with the membrane deflection,which is s function of pressure.The deflection of the membrane by applied pressure can be mathematically described.

Artificial Tactile Sense Technique for Predicting Beef Tenderness Based on FS Pressure Sensor

We present a rapid system for predicting beef tenderness by mimicking the human tactile sense. The detection system includes a FS pressure sensor, a power supply conversion circuit, a signal amplifier and a box in which the sample is mounted. A sample of raw Longissimus dorsi (LD) muscle is placed in the measuring box; then a rod connected to the pressure sensor is pressed into the beef sample to a given depth; the reaction force of the beef sample is measured and used to predict the tenderness. Sensory evaluation and Warner-Bratzler Shear Force (WBSF) evaluation of samples from the same LD muscle are used for comparison. The new detection system agrees with established procedure 95% of the time, and the time to test a sample is less than 5 minutes.

High-Porosity Foam-Based Iontronic Pressure Sensor with Superhigh Sensitivity of 9280 kPa^(-1)

Flexible pressure sensors with high sensitivity are desired in the fields of electronic skins,human-machine interfaces,and health monitoring.Employing ionic soft materials with microstructured architectures in the functional layer is an effective way that can enhance the amplitude of capacitance signal due to generated electron double layer and thus improve the sensitivity of capacitive-type pressure sensors.However,the requirement of specific apparatus and the complex fabrication process to build such microstructures lead to high cost and low productivity.Here,we report a simple strategy that uses open-cell polyurethane foams with high porosity as a continuous three-dimensional network skeleton to load with ionic liquid in a one-step soak process,serving as the ionic layer in iontronic pressure sensors.The high porosity(95.4%) of PU-IL composite foam shows a pretty low Young's modulus of 3.4 kPa and good compressibility.A superhigh maximum sensitivity of 9,280 kPa^(-1) in the pressure regime and a high pressure resolution of 0.125% are observed in this foam-based pressure sensor.The device also exhibits remarkable mechanical stability over 5,000 compression-release or bending-release cycles.Such high porosity of composite structure provides a simple,cost-effective and scalable way to fabricate super sensitive pressure sensor,which has prominent capability in applications of water wave detection,underwater vibration sensing,and mechanical fault monitoring.

Wireless contactless pressure measurement of an LC passive pressure sensor with a novel antenna for high-temperature applications

In this paper, a novel antenna is proposed for high-temperature testing, which can make the high-temperature pressure characteristics of a wireless passive ceramic pressure sensor demonstrated at up to a temperature of 600℃. The design parameters of the antenna are similar to those of the sensor, which will increase the coupling strength between the sensor and testing antenna. The antenna is fabricated in thick film integrated technology, and the properties of the alumina ceramic and silver ensure the feasibility of the antenna in high-temperature environments. The sensor, coupled with the ceramic antenna, is investigated using a high-temperature pressure testing platform. The experimental measurement results show that the pressure signal in a harsh environment can be detected by the frequency diversity of the sensor.

THICKNESS-SHEAR VIBRATION OF CIRCULAR CRYSTAL PLATE IN CYLINDRICAL SHELL AS PRESSURE SENSOR

Based on the theory for small fields superposed on relatively larger fields in an electroelastic body, a theoretical analysis is performed on a circular plate thicknessshear crystal resonator sealed in a circular cylindrical shell for pressure measurement. A simple expression is obtained for pressure induced frequency shifts in the resonator, which is examined for design optimization. Numerical results show that the frequency shifts depend linearly on the pressure, and that or a smaller thickness ratio of the crystal plate a pressure sensor with a softer outer shell to the outer shell has higher sensitivity.

Carbon nanotube cuprous oxide composite based pressure sensors

In this paper, we present the design, the fabrication, and the experimental results of carbon nanotube （CNT） and Cu20 composite based pressure sensors. The pressed tablets of the CNT Cu20 composite are fabricated at a pressure of 353 MPa. The diameters of the multiwalled nanotubes （MWNTs） are between 10 nm and 30 nm. The sizes of the Cu20 micro particles are in the range of 3-4 μm. The average diameter and the average thickness of the pressed tablets are 10 mm and 4.0 mm, respectively. In order to make low resistance electric contacts, the two sides of the pressed tablet are covered by silver pastes. The direct current resistance of the pressure sensor decreases by 3.3 times as the pressure increases up to 37 kN/m^2. The simulation result of the resistance-pressure relationship is in good agreement with the experimental result within a variation of ±2%.

Highly Sensitive Flexible Pressure Sensors based on Graphene/Graphene Scrolls Multilayer Hybrid Films

In recent years,flexible pressure sensors have attracted much attention owing to their potential applications in motion detection and wearable electronics.As a result,important innovations have been reported in both conductive materials and the underlying substrates,which are the two crucial components of a pressure sensor.1D materials like nanowires are being widely used as the conductive materials in flexible pressure sensors,but such sensors usually exhibit low performances mainly due to the lack of strong interfacial interactions between the substrates and 1D materials.In this paper,we report the use of graphene/graphene scrolls hybrid multilayers films as the conductive material and a microstructured polydimethylsiloxane substrate using Epipremnum aureum leaf as the template to fabricate highly sensitive pressure sensors.The 2D structure of graphene allows to strongly anchor the scrolls to ensure the improved adhesion between the highly conductive hybrid films and the patterned substrate.We attribute the increased sensitivity(3.5 k Pa^-1),fast response time(<50 ms),and the good reproducibility during 1000 loading-unloading cycles of the pressure sensor to the synergistic effect between the 1D scrolls and 2D graphene films.Test results demonstrate that these sensors are promising for electronic skins and motion detection applications.