The algorithm for the piezoresistance coefficients of p-type polysilicon

In order to improve the piezoresistance theory of polysilicon, based on the tunneling piezoresistance model, using the mechanisms of approximate valence band equation and shifts of the hole transfer and hole con- duction mass by stress, a novel algorithm for the piezoresistance coefficients of p-type polysilicon is presented. It proposes three fundamental piezoresistance coefficients π11,π12 and π44 of the grain neutral and grain boundary regions, separately. With those piezoresistance coefficients, the gauge factors of the p-type polysilicon nanofilm and the p-type common polysilicon film are calculated, and then the plots of the gauge factor as a function of doping concentration are given, which are consistent with the experimental results.

Composite silicone rubber of high piezoresistance repeatability filled with nanoparticles

The ruthenium oxide nanoparticles with size less than 20 nm were fabricated by annealing the metallic ruthenium nanoparticles in air,which were synthesized by using the thermal reduction in the polyol solution.The rutile structure of the ruthenium oxide was proved by using transmission electron microscopy(TEM)and X-ray photoelectron spectroscopy(XPS).The oxide has good electron conductivity. The surface of the ruthenium oxide was modified by a vinyl silane coupling agent.The assembling of the silane to the oxide surface was proved by Infrared(IR)absorption spectroscopy.By mixing the nanoparticles with poly(methylvinylsiloxane)(PMVS)silicone rubber,a composite filled with dispersive conducting phase was fabricated.The temperature dependent conductivity shows that the electron transportation through composite is mainly dominated by tunneling.The measurement of piezoresistance shows that the composite at low strain has high piezoresistance repeatability.The 3D reconstruction images of the composite filled with carbon black or ruthenium oxide show that the aggregation of the nanoparticles differs much for two composites.The narrow distribution range of the particle size was thought to be the main factor for the high piezoresistance recurrence.

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 timeconsuming.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 Ti_(3)C_(2)-MXene film as an intermediate conductive filler,and the few-layer Ti_(3)C_(2)-MXene nanosheetbased 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.

METHOD FOR MEASURING RESISTANCE OF METALS IN DIAMOND ANVIL CELL AND THE MEASUREMENT OF PIEZORESISTANCE COEFFICIENT OF MANCANIN

With an experimental method developed for measuring the electrical resistance of met-als in diamond anvil cell （DAC）, we measured the pressure dependence of resistance ofmanganin up to 18.5 GPa. The relationship between the resistance of manganin and thepressure is linear below 13 GPa. Another linear relationship is obtained in the range of 13-18.5 GPa. A "turning point" of linear relation is formed at 13 GPa. The piezoresistancecoefficient of manganin measured is 0.024 GPa1 below 13 GPa, which is in good agreementwith those given in literature. A new resistance-pressure relation is obtained in the rangeof 13～18.5 GPa. with the piezoresistance coefficient of 0.020 GPa-1.

A novel algorithmic method for piezoresistance calculation

A novel algorithmic method, based on the different stress distribution on the surface of thin film in an SOI microstructure, is put forward to calculate the value of the silicon piezoresistance on the sensitive film. In the proposed method, we take the Ritz method as an initial theoretical model to calculate the rate of piezoresistance ΔR/R through an integral （the closed area Ω where the surface piezoresistance of the film lies as the integral area and the product of stress σ and piezoresistive coefficient π as the integral object） and compare the theoretical values with the experimental results. Compared with the traditional method, this novel calculation method is more accurate when applied to calculating the value of the silicon piezoresistance on the sensitive film of an SOI pieoresistive pressure sensor.

Highly Ordered Thermoplastic Polyurethane/Aramid Nanofiber Conductive Foams Modulated by Kevlar Polyanion for Piezoresistive Sensing and Electromagnetic Interference Shielding

Highly ordered and uniformly porous structure of conductive foams is a vital issue for various functional purposes such as piezoresistive sensing and electromagnetic interference(EMI) shielding. With the aids of Kevlar polyanionic chains, thermoplastic polyurethane(TPU) foams reinforced by aramid nanofibers(ANF) with adjustable pore-size distribution were successfully obtained via a nonsolvent-induced phase separation. In this regard, the most outstanding result is the in situ formation of ANF in TPU foams after protonation of Kevlar polyanion during the NIPS process. Furthermore, in situ growth of copper nanoparticles(Cu NPs) on TPU/ANF foams was performed according to the electroless deposition by using the tiny amount of pre-blended Ti_(3)C_(2)T_(x) MXene as reducing agents. Particularly, the existence of Cu NPs layers significantly promoted the storage modulus in 2,932% increments, and the well-designed TPU/ANF/Ti_(3)C_(2)T_(x) MXene(PAM-Cu) composite foams showed distinguished compressive cycle stability. Taking virtues of the highly ordered and elastic porous architectures, the PAM-Cu foams were utilized as piezoresistive sensor exhibiting board compressive interval of 0–344.5 kPa(50% strain) with good sensitivity at 0.46 kPa^(-1). Meanwhile,the PAM-Cu foams displayed remarkable EMI shielding effectiveness at 79.09 dB in X band. This work provides an ideal strategy to fabricate highly ordered TPU foams with outstanding elastic recovery and excellent EMI shielding performance, which can be used as a promising candidate in integration of satisfactory piezoresistive sensor and EMI shielding applications for human–machine interfaces.

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.

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.

Recent progress in graphene-based wearable piezoresistive sensors:From 1D to 3D device geometries

Electronic skin and flexible wearable devices have attracted tremendous attention in the fields of human-machine interaction,energy storage,and intelligent robots.As a prevailing flexible pressure sensor with high performance,the piezoresistive sensor is believed to be one of the fundamental components of intelligent tactile skin.Furthermore,graphene can be used as a building block for highly flexible and wearable piezoresistive sensors owing to its light weight,high electrical conductivity,and excellent mechanical.This review provides a comprehensive summary of recent advances in graphene-based piezoresistive sensors,which we systematically classify as various configurations including one-dimensional fiber,two-dimensional thin film,and threedimensional foam geometries,followed by examples of practical applications for health monitoring,human motion sensing,multifunctional sensing,and system integration.We also present the sensing mechanisms and evaluation parameters of piezoresistive sensors.This review delivers broad insights on existing graphene-based piezoresistive sensors and challenges for the future generation of high-performance,multifunctional sensors in various applications.

Multifunctional characteristics of 3D printed polymer nanocomposites under monotonic and cyclic compression

This study presents the multifunctional characteristics of multi-walled carbon nanotube(MWCNT)/polypropylene random copolymer(PPR) composites enabled via fused filament fabrication(FFF) under monotonic and quasi-static cyclic compression. Utilizing in-house MWCNT-engineered PPR filament feedstocks, both bulk and cellular composites were realized. The morphological features of nanocomposites were examined via scanning electron microscopy, which reveals that MWCNTs are uniformly dispersed. The uniformly dispersed MWCNTs forms an electrically conductive network within the PPR matrix, and the resulting nanocomposite shows good electrical conductivity(~10^(-1)S/cm), improved mechanical performance(modulus increases by 125% and compressive strength increases by 25% for 8 wt% MWCNT loading) and pronounced piezoresistive response(gauge factor of 27.9-8.5 for bulk samples)under compression. The influence of strain rate on the piezoresistive response of bulk samples(4 wt% of MWCNT) under compression was also measured. Under repeated cyclic compression(2% constant strain amplitude), the nanocomposite exhibited stable piezoresistive performance up to 100 cycles. The piezoresistive response under repeated cyclic loading with increasing strain amplitude of was also assessed.The gauge factor of BCC and FCC cellular composites(4 wt% of MWCNT) with a relative density of 30%was observed to be 46.4 and 30.2 respectively, under compression. The higher sensitivity of the BCC plate-lattice could be attributed to its higher degree of stretching-dominated deformation behavior than the FCC plate-lattice, which exhibits bending-dominated behavior. The 3D printed cellular PPR/MWCNT composites structures were found to show excellent piezoresistive self-sensing characteristics and open new avenues for in situ structural health monitoring in various applications.

A novel micro-accelerometer with adjustable sensitivity based on resonant tunnelling diodes

Resonant tunnelling diodes （RTDs） have negative differential resistance effect, and the current-voltage characteristics change as a function of external stress, which is regarded as mesc-piezoresistance effect of RTDs. In this paper, a novel micro-accelerometer based on AlAs/GaAs/In0.1Ga0.9As/GaAs/AlAs RTDs is designed and fabricated to be a four-beam-mass structure, and an RTD-Wheatstone bridge measurement system is established to test the basic properties of this novel accelerometer. According to the experimental results, the sensitivity of the RTD based micro-accelerometer is adjustable within a range of 3 orders when the bias voltage of the sensor changes. The largest sensitivity of this RTD based miero-accelerometer is 560.2025 mV/g which is about 10 times larger than that of silicon based micro piezoresistive accelerometer, while the smallest one is 1.49135 mV/g.

Mechanical Yielding and Strength Behaviour of OFHC Copper in Planar Shock Waves

It is necessary to study the validation of strength models under planar shock loading in view of the fact that strength models for metals obtained at moderate strain rates are often used in the numerical simulations of shock wave phenomena. The variations of longitudinal stress, transverse stress and yield strength of oxygen-free high conductance （OFHC） copper with time under planar shock loading are obtained by using the manganin stress gauges and compared with the predicted results by the constructed seven constitutive models based on Y/G=constant and on G/B=constant （Y the yield strength, G the shear modulus, B the bulk modulus）, respectively. It seems that the pressure, density, temperature and plastic strain dependence of the yield strength for OFHC copper under planar shock loading is essential to the constitutive description.

正交异性材料的压阻特性(英文)

阐述和证明了正交异性材料主方向的压阻特性：（１）压阻效应只与正应变／正应力有关，而与剪切应变／剪切应力无关；（２）压导系数与压阻系数间存在下列关系ηｉｋｋ＝－（γｉ）－２ξｉｋｋ＝－（ρｉ）２ξｉｋｋλｉｋｋ＝－（γｉ）－２χｉｋｋ＝－（ρｉｉ）２χｉｉｋｋ（３）由正交异性单层构成的层合板的电特性呈整体正交异性。

Nanosensitive Silicon Microprobes for Mechanical Detection and Measurements

Nanosensitive mechanical microprobes with CMOS transistors, inverters, inverters cascades and ring oscillators, integrated on the thin silicon cantilevers are presented. Mechanical stress shifts linear, steep switching fragment of the inverters’ electrical characteristics. Microprobes were fabricated with use of the standard CMOS technology (3.5 μm design rules, one level polysilicon gate and one level of the metal interconnections) and relief MEMS technique. Control of the silicon cantilever thickness was satisfactory in the range above the few micrometers. Several computer simulations were done to analyze and optimize transistors location on the cantilever, in respect to the mechanical stress distribution. Results of the microprobes electromechanical tests confirm high deflection sensitivity 1.2 - 1.8 mV/nm and force sensitivity 2.0 - 2.4 mV/nN, both in nano ranges. Microprobes, with the ring oscillators revealed sensitivities 5 - 8 Hz/nm. These microprobes seem to be appropriate for applications in precise chemical and biochemical sensing.

Flexible Tactile Electronic Skin Sensor with 3D Force Detection Based on Porous CNTs/PDMS Nanocomposites

Flexible tactile sensors have broad applications in human physiological monitoring,robotic operation and human-machine interaction.However,the research of wearable and flexible tactile sensors with high sensitivity,wide sensing range and ability to detect three-dimensional(3D)force is still very challenging.Herein,a flexible tactile electronic skin sensor based on carbon nanotubes(CNTs)/polydimethylsiloxane(PDMS)nanocomposites is presented for 3D contact force detection.The 3D forces were acquired from combination of four specially designed cells in a sensing element.Contributed from the double-sided rough porous structure and specific surface morphology of nanocomposites,the piezoresistive sensor possesses high sensitivity of 12.1 kPa?1 within the range of 600 Pa and 0.68 kPa?1 in the regime exceeding 1 kPa for normal pressure,as well as 59.9 N?1 in the scope of<0.05 N and>2.3 N?1 in the region of<0.6 N for tangential force with ultra-low response time of 3.1 ms.In addition,multi-functional detection in human body monitoring was employed with single sensing cell and the sensor array was integrated into a robotic arm for objects grasping control,indicating the capacities in intelligent robot applications.

Self-monitoring Application of Asphalt Concrete Containing Graphite and Carbon Fibers

The self-monitoring application of asphalt concrete containing graphite and carbon fibers using indirect tensile test and wheel rolling test were introduced. The experiment results indicate that this kind of pitch-based composite is effective for strain/stress self-monitoring. In the indirect tensile test, for a completely conductive asphalt concrete specimen, the piezoresistivity was very weak and slightly positive, which meant the resistivity increase with the increment of tensile strain at all stress/strain amplitudes, with the gage factor as high as 6. The strain self-sensing ability was superior in the case of higher graphite content. However, when the conductive concrete was embedded into common asphalt concrete specimen as a partial structure function, the piezoresistivity was positive at all stress/strain amplitudes and with the gage factor of 13, which was much higher than that of completely conductive specimen. Thus, the strain self-sensing ability was superior when conductive asphalt concrete was taken in as a partial structure function. In the wheel-rolling test, the piezoresistivity was highly positive. At any stress amplitude, the piezoresistivity was strong, with the gage factor as high as 100, which was higher for a stress amplitude of 0.7 MPa than that of 0.5 MPa.

Flexible Waterproof Piezoresistive Pressure Sensors with Wide Linear Working Range Based on Conductive Fabrics

Developing flexible sensors with high working performance holds intense interest for diverse applications in leveraging the Internet-of-things(IoT)infrastructures.For flexible piezoresistive sensors,traditionally most efforts are focused on tailoring the sensing materials to enhance the contact resistance variation for improving the sensitivity and working range,and it,however,remains challenging to simultaneously achieve flexible sensor with a linear working range over a high-pressure region(>100 kPa)and keep a reliable sensitivity.Herein,we devised a laserengraved silver-coated fabric as"soft"sensor electrode material to markedly advance the flexible sensor's linear working range to a level of 800 kPa with a high sensitivity of 6.4 kPa^-1 yet a fast response time of only 4 ms as well as long-time durability,which was rarely reported before.The integrated sensor successfully routed the wireless signal of pulse rate to the portable smartphone,further demonstrating its potential as a reliable electronic.Along with the rationally building the electrode instead of merely focusing on sensing materials capable of significantly improving the sensor's performance,we expect that this design concept and sensor system could potentially pave the way for developing more advanced wearable electronics in the future.

Laser direct writing and characterizations of flexible piezoresistive sensors with microstructures

Functional materials with high viscosity and solid materials have received more and more attentions in flexible pressure sensors,which are inadequate in the most used molding method.Herein,laser direct writing(LDW)method is proposed to fabricate flexible piezoresistive sensors with microstructures on PDMS/MWCNTs composites with an 8%MWCNTs mass fraction.By controlling laser energy,microstructures with different geometries can be obtained,which significantly impacts the performances of the sensors.Subsequently,curved microcones with excellent performance are fabricated under parameters of f=40 kHz and v=150 mm·s^(-1).The sensor exhibits continuous multi-linear sensitivity,ultrahigh original sensitivity of 21.80%kPa^(-1),wide detection range of over 20 kPa,response/recovery time of~100 ms and good cycle stability for more than 1000 times.Besides,obvious resistance variation can be observed when tiny pressure(a peanut of 30 Pa)is applied.Finally,the flexible piezoresistive sensor can be applied for LED brightness controlling,pulse detection and voice recognition.

Piezoresistivity in Carbon Fiber Reinforced Cement Based Composites

The results of some interesting investigation on the piezoresistivity of carbon fiber reinforced cement based composites (CFRC) are presented with the prospect of developing a new nondestructive testing method to assess the integrity of the composite. The addition of short carbon fibers to cement-based mortar or concrete improves the structural performance and at the same time significantly decreases the bulk electrical resistivity. This makes CFRC responsive to the smart behavior by measuring the resistance change with uniaxial pressure. The piezoresistivity of CFRC under different stress was studied, at the same time the damage occurring inner specimens was detected by acoustic emission as well. Test results show that there exists a marking pressure dependence of the conductivity in CFRC, in which the so-called negative pressure coefficient of resistive (NPCR) and positive pressure coefficient of resistive (PPCR) are observed under low and high pressure. Under constant pressures, time-dependent resistivity is an outstanding characteristic for the composites, which is defined as resistance creep. The breakdown and rebuild-up process of conductive network under pressure may be responsible for the pressure dependence of resistivity.

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.