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 piezoresistiveflexible pressure sensors.By embedding silver nanowires into a polydimethylsiloxane layer with micro-pyramids on its surface,aflexible pressure sensor is created that can detect low pressure(17.3 Pa)with fast response ms)and high sensitivity(69.6 mA(<20 kPa-1).Furthermore,the pressure sensor exhibits a sensitive and stable response to a small amount of waterflowing on its surface.On this basis,theflexible pressure sensor is innovatively combined with a micro-rotor to fabricate a novel urinaryflow-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 usingflexible pressure sensors in urinaryflow-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.

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%).

Bioinspired flexible piezoresistive sensor for high-sensitivity detection of broad pressure range

The human skin has the ability to sense tactile touch and a great range of pressures.Therefore,in prosthetic or robotic systems,it is necessary to prepare pressure sensors with high sensitivity in a wide measurement range to provide human-like tactile sensation.Herein,we developed a flexible piezoresistive pressure sensor that is highly sensitive in a broad pressure range by using lotus leaf micropatterned polydimethylsiloxane and multilayer superposition.By superposing four layers of micropatterned constructive substrates,the multilayer piezoresistive pressure sensor achieves a broad pressure range of 312 kPa,a high sensitivity of 2.525 kPa^(−1),a low limit of detection(LOD)of<12 Pa,and a fast response time of 45 ms.Compared with the traditional flexible pressure sensor,the pressure range of this sensor can be increased by at least an order of magnitude.The flexible piezoresistive pressure sensor also shows high robustness:after testing for at least 1000 cycles,it shows no sign of fatigue.More importantly,these sensors can be potentially applied in various human motion detection scenarios,including tiny pulse monitoring,throat vibration detection,and large under-feet pressure sensing.The proposed fabrication strategy may guide the design of other kinds of multifunctional sensors to improve the detection performance.

A personalized electronic textile for ultrasensitive pressure sensing enabled by biocompatible MXene/ PEDOT:PSS composite

Flexible,breathable,and highly sensitive pressure sensors have increasingly become a focal point of interest due to their pivotal role in healthcare monitoring,advanced electronic skin applications,and disease diagnosis.However,traditional methods,involving elastomer film-based substrates or encapsulation techniques,often fall short due to mechanical mismatches,discomfort,lack of breathability,and limitations in sensing abilities.Consequently,there is a pressing need,yet it remains a significant challenge to create pressure sensors that are not only highly breathable,flexible,and comfortable but also sensitive,durable,and biocompatible.Herein,we present a biocompatible and breathable fabric-based pressure sensor,using nonwoven fabrics as both the sensing electrode(coated with MXene/poly(3,4-ethylenedioxythiophene):polystyrene sulfonate[PEDOT:PSS])and the interdigitated electrode(printed with MXene pattern)via a scalable spray-coating and screen-coating technique.The resultant device exhibits commendable air permeability,biocompatibility,and pressure sensing performance,including a remarkable sensitivity(754.5 kPa^(−1)),rapid response/recovery time(180/110 ms),and robust cycling stability.Furthermore,the integration of PEDOT:PSS plays a crucial role in protecting the MXene nanosheets from oxidation,significantly enhancing the device's long-term durability.These outstanding features make this sensor highly suitable for applications in fullrange human activities detection and disease diagnosis.Our study underscores the promising future of flexible pressure sensors in the realm of intelligent wearable electronics,setting a new benchmark for the industry.

A triboelectric nanogenerator based on a spiral rotating shaft for efficient marine energy harvesting of the hydrostatic pressure differential

Equipment used in underwater sensing and exploration typically relies on cables or batteries for energy supply,resulting in a limited and inconvenient energy supply and marine environmental pollution that hinder the sustainable development of distributed ocean sensing networks.Here,we design a deep-sea differential-pressure triboelectric nanogenerator(DP-TENG)based on a spiral shaft drive using modified polymer materials to harness the hydrostatic pressure gradient energy at varying ocean depths to power underwater equipment.The spiral shaft structure converts a single compression into multiple rotations of the TENG rotor,achieving efficient conversion of differential pressure energy.The multi-pair electrode design enables the DP-TENG to generate a peak current of 61.7μA,the instantaneous current density can reach 0.69μA cm^(-2),and the output performance can be improved by optimizing the spiral angle of the shaft.The DP-TENG can charge a 33μF capacitor to 17.5 V within five working cycles.It can also power a digital calculator and light up 116 commercial power light-emitting diodes,demonstrating excellent output capability.With its simple structure,low production cost,and small form factor,the DP-TENG can be seamlessly integrated with underwater vehicles.The results hold broad prospects for underwater blue energy harvesting and are expected to contribute to the development of self-powered equipment toward emerging“smart ocean”and blue economy applications.

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.

A bellow pressure fiber optic sensor for static ice pressure measurements

Static ice pressure affects safe operation of hydraulic structures. However, current detection methods are hindered by the following limitations： poor real-time performance and errors owing to the partial pressure of the surrounding wall on traditional electrical resistance strain bellow pressure sensors. We developed a fiber optic sensor with a special pressure bellow to monitor the static ice pressure on hydraulic structures and used the sensor to measure static pressure in laboratory ice growth and melting tests from -30℃ to 5℃. The sensor resolution is 0.02 kPa and its sensitivity is 2.74 × 10-4/kPa. The experiments suggest that the static ice pressure peaks twice during ice growth and melting. The first peak appears when the ice temperature drops to -15℃ owing to the liquid water to solid ice transition. The second peak appears at 0℃ owing to the thermal expansion of the ice during ice melting. The novel fiber optic sensor exhibits stable performance, high resolution, and high sensitivity and it can be used to monitor the static ice pressure during ice growth and melting.

Advancing the pressure sensing performance of conductive CNT/PDMS composite film by constructing a hierarchical-structured surface

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.

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.

Non-destructive Evaluation of Composite Pressure Vessel by Using FBG Sensors

In recent years, advanced composite structures are used extensively in many industries such as aerospace, aircraft, automobile, pipeline and civil engineering. Reliability and safety are crucial requirements posed by them to the advanced composite structures be- cause of their harsh working conditions. Therefore, as a very important measure, structural health monitoring （SHM） in-service is deft- nitely demanded for ensuring their safe working in-situ. In this paper, fiber Bragg grating （FBG） sensors are surface-mounted on the hoop and in the axial directions of a FRP pressure vessel to monitor the strain status during its pressurization. The experimental results show that the FBG sensors could be used to monitor the strain development and determine the ultimate failure strain of the composite pressure vessel.

Application and analysis of functionally graded piezoelectrical rotating cylinder as mechanical sensor subjected to pressure and thermal loads

The exact thermoelastic analysis of a functionally graded piezoelectrical （FGP） rotating cylinder is investigated analytically. The cylinder is subjected to a com- bination of electrical, thermal, and mechanical loads simultaneously. The structure is a simplified model of a rotational sensor or actuator. The basic governing differential equation of the system is obtained by using the energy method. A novel term, named as the additional energy, is introduced to exact the evaluation of the energy functional. The solution to the governing differential equation is presented for two types of boundary conditions including free rotating and rotating cylinders exposed to the inner pressure. The effect of the angular velocity is investigated on the radial distribution of various components. The mentioned structure can be considered as a sensor for measuring the angular velocity of the cylinder subjected to the pressure and temperature. The obtained results indicate that the electrical potential is proportional to the angular velocity.

State-of-the-art and recent developments in micro/nanoscale pressure sensors for smart wearable devices and health monitoring systems

Small-sized,low-cost,and high-sensitivity sensors are required for pressure-sensing applications because of their critical role in consumer electronics,automotive applications,and industrial environments.Thus,micro/nanoscale pressure sensors based on micro/nanofabrication and micro/nanoelectromechanical system technologies have emerged as a promising class of pressure sensors on account of their remarkable miniaturization and performance.These sensors have recently been developed to feature multifunctionality and applicability to novel scenarios,such as smart wearable devices and health monitoring systems.In this review,we summarize the major sensing principles used in micro/nanoscale pressure sensors and discuss recent progress in the development of four major categories of these sensors,namely,novel material-based,flexible,implantable,and selfpowered pressure sensors.

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...

Pressure effects in AlAs/Inx Ga1-xAs/GaAs resonant tunnelling diodes for application in micromachined sensors

This paper reports the current-voltage characteristics of [001]-oriented AlAs/InxGa1-xAs/GaAs resonant tunnelling diodes （RTDs） as a function of uniaxial external stress applied parallel to the [110] and the [1^-10] orientations, and the output characteristics of the GaAs pressure sensor based on the pressure effect on the RTDs. Under [110] stress, the resonance peak voltages of the RTDs shift to more positive voltages. For [1^-10] stress, the peaks shift toward more negative voltages. The resonance peak voltage is linearly dependent on the [110] and [1^-0] stresses and the linear sensitivities are up to 0.69 mV/MPa, -0.69 mV/MPa respectively. For the pressure sensor, the linear sensitivity is up to 0.37 mV/kPa.