Pressure-sensitive Materials Research Articles

Electrical resistance and self-sensing properties of pressure-sensitive materials with graphite filler in Kuralon fiber concrete

Abstract This study aimed to investigate conductivity behavior of concrete containing graphite and its sensitivity to the effects of pressure. Graphite powder was added to concrete to replace partial cement (4 wt.%, 8 wt.%, 12 wt.%, and 16 wt.%) as conductive fillers with a water-to-cementitious ratio of 0.45. Specimens with 0.5 vol.% Kuralon fibers were treated to enhance the performance of self-sensing properties to investigate the influence of graphite and fiber contents on electrical resistivities. The relationship between the axial load and changes in resistivity was determined using cyclic loading tests, indicating the existence and development of internal cracking in concrete. The results indicated that the compressive strength presented a linear decline proportional to the addition of graphite. Specimens with 8% graphite reached the lower bound of self-sensing properties, and with an increase in the amount of graphite, resistivity gradually decreased. In the cyclic loading tests, specimens containing >8% graphite were able to better reflect the relationship between loading and resistivity. Kuralon fibers in concrete had further improvement in resistance and self-sensing properties. In inclusion, the mixture with 8% graphite provided the best self-sensing properties to warn for preventing the effects of cracking, as well as achieved better mechanical properties.

Flexible piezoresistive sensor based on surface modified dishcloth fibers for wearable electronics device

With potential application for health monitoring and images of the interface between machine and human, flexible pressure sensors have attracted more and more attention. However, both the complex manufacturing process and the expensive electroconductive materials limit their wide distribution in practice. Here, we propose a flexible pressure sensor based on carbonizing the dishcloth fibers coated with zeolitic imidazolate framework-67 nanosheets (ZIF-67 @CD), which exhibits a high sensitivity of 3.10 kPa-1, a wide range detection of 0–470 kPa, a low detection limit of 1 Pa, and an excellent stability of 5500 cycles. Meanwhile, the flexible sensor array also shows excellent flexibility and compatibility, which can pave the way for detecting weak airstream, wrist pulses, sound, bending, swallowing, and other real-time signals with greater precision. More importantly, the pressure-sensitive material for this pressure sensor is prepared by a simple process with low material cost, which demonstrates its potential application in the next generation of low-cost flexible electronics.

Ti3C2Tx MXene-Based Flexible Piezoresistive Physical Sensors.

MXenes have received increasing attention due to their two-dimensional layered structure, high conductivity, hydrophilicity, and large specific surface area. Because of these distinctive advantages, MXenes are considered as very competitive pressure-sensitive materials in applications of flexible piezoresistive sensors. This work reviews the preparation methods, basic properties, and assembly methods of MXenes and their recent developments in piezoresistive sensor applications. The recent developments of MXene-based flexible piezoresistive sensors can be categorized into one-dimensional fibrous, two-dimensional planar, and three-dimensional sensors according to their various structures. The trends of multifunctional integration of MXene-based pressure sensors are also summarized. Finally, we end this review by describing the opportunities and challenges for MXene-based pressure sensors and the great prospects of MXenes in the field of pressure sensor applications.

Application of Carbon Nanocomposite Sensing and Functional Magnetic Nanomaterial in the Sports Industry and Its Biosecurity Research

Nanomaterial science is a particularly important research field in modern science and technology, which has attracted wide attention and research from all walks of life since its inception and has formed a relatively perfect category of science and technology. The purpose of this paper is to explore the application of carbon nanocomposite sensing and functional magnetic nanomaterial in the sports industry and their biosecurity research. This paper first discusses the research progress of nanocomposite in biosecurity and concludes that chemical modification can reduce the negative biological effects of nanomaterial, then puts forward the research methods on nanocomposite in the sports industry, and then selects nanosilver composites to explore and study the effects of different particle sizes and concentrations on the antibacterial properties of Aspergillus and test and characterize the properties of nanocomposite. The stability of nanocomposite modification electrodes is also explored. The results show that nanosilver has excellent bactericidal effects on both AF293 and Gra04. In particular, 8.08 × 10−5 mol/L and 4.03 × 10−5 mol/L nanosilver has a bacteriological rate of 100%, indicating that the growth of all fungal spores can be completely inhibited, and when the content of 10 wt% is found, the thermal conductivity of PHBE‐MWNT pressure‐sensitive composite materials is achieved 0.6975 W/(m‐K), 1.8 times the MWNT pressure‐sensitive glue, higher than the pure pressure‐sensitive glue about 255%.

High-Sensitivity Flexible Pressure Sensor-Based 3D CNTs Sponge for Human-Computer Interaction.

Researchers are showing an increasing interest in high-performance flexible pressure sensors owing to their potential uses in wearable electronics, bionic skin, and human–machine interactions, etc. However, the vast majority of these flexible pressure sensors require extensive nano-architectural design, which both complicates their manufacturing and is time-consuming. Thus, a low-cost technology which can be applied on a large scale is highly desirable for the manufacture of flexible pressure-sensitive materials that have a high sensitivity over a wide range of pressures. This work is based on the use of a three-dimensional elastic porous carbon nanotubes (CNTs) sponge as the conductive layer to fabricate a novel flexible piezoresistive sensor. The synthesis of a CNTs sponge was achieved by chemical vapor deposition, the basic underlying principle governing the sensing behavior of the CNTs sponge-based pressure sensor and was illustrated by employing in situ scanning electron microscopy. The CNTs sponge-based sensor has a quick response time of ~105 ms, a high sensitivity extending across a broad pressure range (less than 10 kPa for 809 kPa−1) and possesses an outstanding permanence over 4000 cycles. Furthermore, a 16-pixel wireless sensor system was designed and a series of applications have been demonstrated. Its potential applications in the visualizing pressure distribution and an example of human–machine communication were also demonstrated.

High-sensitivity tactile sensor based on Ti2C-PDMS sponge for wireless human–computer interaction

Tremendous attention has been paid to high-performance flexible tactile sensors owing to their potential applications in bionic skin, wearable electronics, the Internet of Things, etc. However, the majority of pressure sensors require an intricately designed nanostructure requiring a high-cost complex manufacturing process. Therefore, the high-throughput and low-cost technology to produce high-sensitivity, flexible, pressure-sensitive materials with a large responding range is urgently needed. Herein, a novel flexible piezoresistive tactile sensor is fabricated based on the Ti2C-PDMS sponge as the conductive elastomer. The sensor exhibits a high sensitivity of 279 kPa−1 in a wide pressure range (0–34.4 kPa). The response time is as fast as 0.45 s with excellent durability over 4,000 cycles. Moreover, a 16-pixel wireless sensor system is fabricated and a series of applications have been demonstrated, including real-time force perception and pressure morphology feedback, which promote the potential applications in the visualizing of pressure distribution, human–machine communication and wearable devices.

Correlation of Global Quantities at Material Characterization of Pressure-Sensitive Materials Using Sharp Indentation Testing

Correlation of sharp indentation problems is examined theoretically and numerically. The analysis focuses on elastic-plastic pressure-sensitive materials and especially the case when the local plastic zone is so large that elastic effects on the mean contact pressure will be small or negligible as is the case for engineering metals and alloys. The results from the theoretical analysis indicate that the effect from pressure-sensitivity and plastic strain-hardening are separable at correlation of hardness values. This is confirmed using finite element methods and closed-form formulas are presented representing a pressure-sensitive counterpart to the Tabor formula at von Mises plasticity. The situation for the relative contact area is more complicated as also discussed.

Influence of Elastic Modulus of Matrix on Conductivity of VGCF Dispersed in Plastic Matrix

Pressure-sensitive conductive material is used for various pressure sensors consists of a polymer nanocomposite with carbon nanotubes (VGCF). And the resistance in it were changed by adding applied load. Recently, carbon nanotubes (VGCF) has drawn attention as a function filler that imparts various functions to a resin, including electrical properties. In polycarbonate (PC) composite with VGCF, the resistance decreases with increase in applied load. And increase of the addition amount of VGCF was enhanced the mechanical properties and electronic properties. In addition, this conclusion suggested that strain of PC/VGCF caused reducing the resistance. Therefore, changing matrix is predictably effective on electrical properties in pressure-conductive materials. In the present study, we used various matrix had different elastic modulus. The addition amount of VGCF was 12.5% volume rate. We made silicone/VGCF and polyethylene (PE)/VGCF and polycarbonate (PC)/VGCF by twin screw extruder and injection moldings. To clarify the influence of elastic modulus of matrix on conductivity of VGCF dispersed plastic matrix composites. The experimental results showed that conductive property of pressure-sensitive conductive materials is related to elastic modulus of them.

A Battery-Free, Chipless, Highly Sensitive LC Pressure Sensor Tag Using PEDOT: PSS and Melamine Foam

We have designed and developed a compact, contactless, chipless, high frequency wireless passive LC pressure sensor tag capable of measuring pressure from 0 Pa to 60 kPa. The LC pressure sensor tag design consists of a parallel combination of a planar inductor and a pressure sensitive interdigitated capacitor (IDC). The readout or signal detection and signal processing system combines a Colpitts oscillator, different electronic circuits, and a microcontroller-based signal processing unit. Operation of the sensor is based on mutual coupling of the inductor of the LC pressure sensor tag and the oscillation coil of the Colpitts oscillator. The pressure sensitive IDC consists of interdigitated electrodes and a melamine foam containing poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) as an elastic pressure sensitive dielectric material. When pressure is applied to the LC pressure sensor tag, the capacitance of the IDC sensing element changes, which changes the resonance frequency. Because the LC pressure tag and the inductor of the oscillator are inductively coupled, the frequency of oscillation of the Colpitts oscillator changes. The LC pressure sensor has a highly sensitive sensing response of 762.65 Hz/kPa and a linear sensing performance over a wide measurement range, with a correlation coefficient ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{R}^{\sf 2}$ </tex-math></inline-formula> ) of 0.997. The LC pressure sensor tag is lightweight, highly sensitive, inexpensive to fabricate, and has good repeatability and stability values in the percentage of 2.8 and 1.1, respectively.

Hydrostatic pressure effects on a one-dimensional defective phononic crystal comprising a polymer material

In this research, the hydrostatic pressure effects on the transmission spectra of a one-dimensional (1D) defective phononic crystal (PnC) are calculated and studied. The transmission spectra of the defective PnC are calculated based on the transfer matrix method (TMM). To measure the hydrostatic pressure efficiently, a pressure-sensitive material such as Poly (methyl methacrylate) (PMMA) is proposed as a defect layer. Thereby, the proposed PnC structure is designed from silicon (Si) and tungsten (W) according to the configuration [(Si/W)2 PMMA (Si/W)2]. The numerical results show the appearance of a localized resonant mode through the transmission spectra. A wide pressure range from 0 GPa to 10 GPa is considered on the PnC transmission spectra and the localized resonant mode as well. Remarkably, any increase in the hydrostatic pressure value resulted in the displacement of the resonant mode towards the higher frequencies with a significant increase in its intensity as well. The effect of the PMMA thickness on the number of resonant modes is studied as well. Moreover, the proposed PnC design showed high performance for hydrostatic pressure sensing represented by the high sensitivity and Q-factor values of 556,300 Hz/GPa and 3660, respectively. We expect this design to attract the researchers' attention to hydrostatic pressure influences that may affect different PnC designs and applications.

53‐5: Late‐News Paper: a‐IGZO TFT Based Active Matrix Pressure Sensor by Integrating ZnO Nanowires as Sensing Unit

In this paper, we demonstrated an amorphous indium‐gallium‐zinc‐oxide thin film transistors (a‐IGZO TFTs) based active matrix touch sensor array by integrating ZnO nanowires (NWs) as pressure sensitive materials. ZnO NWs servicing as a piezoelectric material shown superior mechanical‐electric transition performance as well as excellent compatibility with TFT process. The ZnO NWs were connected with switching TFT in series. When a pressure was applied on sensor unit, the deformation of ZnO NWs would induce change of resistance or metal‐semiconductor barrier height between ZnO NWs and contact metal, thus the current following through pressure unit would change. By using this method, we accurately mapped pressure change in a region of 1.4cm*1.4cm2. The demonstration in this work gave a possible solution for integrating pressure sensor in display panel in future applications.

Ultracomfortable Hierarchical Nanonetwork for Highly Sensitive Pressure Sensor.

Skin sensors are of paramount importance for flexible wearable electronics, which are active in medical diagnosis and healthcare monitoring. Ultrahigh sensitivity, large measuring range, and high skin conformability are highly desirable for skin sensors. Here, an ultrathin flexible piezoresistive sensor with high sensitivity and wide detection range is reported based on hierarchical nanonetwork structured pressure-sensitive material and nanonetwork electrodes. The hierarchical nanonetwork material is composed of silver nanowires (Ag NWs), graphene (GR), and polyamide nanofibers (PANFs). Among them, Ag NWs are evenly interspersed in a PANFs network, forming conductive pathways. Also, GR acts as bridges of crossed Ag NWs. The hierarchical nanonetwork structure and GR bridges of the pressure-sensitive material enable the ultrahigh sensitivity for the pressure sensor. More specifically, the sensitivity of 134 kPa-1 (0-1.5 kPa) and the low detection of 3.7 Pa are achieved for the pressure sensor. Besides, the nanofibers act as a backbone, which provides effective protection for Ag NWs and GR as pressure is applied. Hence, the pressure sensor possesses an excellent durability (>8000 cycles) and wide detection range (>75 kPa). Additionally, ultrathin property (7 μm) and nanonetwork structure provide high skin conformability for the pressure sensor. These superior performances lay a foundation for the application of pressure sensors in physiological signal monitoring and pressure spatial distribution detection.

Additive manufacturing of smart insole by direct printing of pressure sensitive material

3D printing technology is gaining attention as one of the key technologies that will lead the fourth industrial revolution. In addition, the field of application is from trial production to mass production of products. However, in many cases, the application area is limited to the geometrical shape building of products. This paper shows an example of application technology for manufacturing the smart insole by applying 3D printing technology for the purpose of giving various functions as well as making geometric shape. In the production of smart insole, 3D printing technology is applied to direct printing of pressure sensitive sensor and highly conductive wire as well as flexible insole object itself. The materials used in the production of flexible products, conductors and sensor are different, and in order to produce the sensor by 3D printing, suitable materials have been directly manufactured and used. This paper shows that the 3D printing technology can be directly applied to the manufacturing of multi functional products through the above manufacturing process as well as the experimental results after the actual production.

Sugar-templated conductive polyurethane-polypyrrole sponges for wide-range force sensing

Porous conductive polyurethane (PU) sponges were prepared by combining a sugar-templated fabrication of porous polyurethane elastomer and the in-situ polymerization of pyrrole inside the sponges. The conductive sponges had a uniform porous structure similar to the sugar cube templates and a unique micro-wrinkled structure of polypyrrole (PPy). Moreover, the conductive sponges exhibited good mechanical properties and electrical conductivity by the combination of elastomeric PU and conductive PPy, which make the conductive PPy-PU sponges as good candidates for pressure and strain sensitive materials. It was shown that a single PPy-PU conductive sponge was not only sensitive to large forces, but also sensitive to the tiny deformation by small forces such as 0.1 N, thus realizing a wide-range detection of pressure forces from 0.1 N to 200 N. Furthermore, the detection range could be further enlarged to more than 800 N by assembling a sponge array. A PPy-PU sponge matrix was also designed and showed potential application in multi-site position detection. These sugar-templated conductive sponges may find application for sensors in human physiological movement and intelligent monitoring.

Predictive control of 2D spatial thermal dose delivery in atmospheric pressure plasma jets

Atmospheric pressure plasma jets (APPJs) are unique devices for processing of heat and pressure sensitive (bio)materials. However, operational challenges of APPJs such as run-to-run variability in dynamics and sensitivity to disturbances can complicate safe and reliable delivery of the spatially distributed cumulative effects of plasma, or plasma dose, to complex surfaces. This paper presents a hierarchical feedback control strategy based on model predictive control for regulating the spatial thermal dose delivery to a surface. Closed-loop control experiments demonstrate the effectiveness of the proposed control strategy in drastically improving the spatial uniformity of thermal dose delivery in the presence of step changes in the jet tip-to-surface distance as well as abrupt changes in the substrate type. The proposed feedback control strategy shows promise for improving the reliability and effectiveness of spatially uniform treatment of complex surfaces in medical and materials processing applications of APPJs.

Inkjet Printing of Polyacrylic Acid-Coated Silver Nanoparticle Ink onto Paper with Sub-100 Micron Pixel Size

Printed electronics (PE) technology shows huge promise for the realisation of low-cost and flexible electronics, with the ability to pattern heat- or pressure-sensitive materials. In future developments of the PE market, the ability to produce highly conductive, high-resolution patterns using low-cost and roll-to-roll processes, such as inkjet printing, is a critical technology component for the fabrication of printed electronics and displays. Here, we demonstrate inkjet printing of polyacrylic acid (PAA) capped silver nanoparticle dispersions onto paper for high-conductivity electronic interconnects. We characterise the resulting print quality, feature geometry and electrical performance of inkjet patterned features and demonstrate the high-resolution printing, sub-100 micron feature size, of silver nanoparticle materials onto flexible paper substrate. Printed onto photo-paper, these materials then undergo chemically triggered sintering on exposure to chloride contained in the paper. We investigated the effect of substrate temperature on the properties of printed silver material from room temperature to 50 °C. At room temperature, the resistivity of single layer printed features, of average thickness of 500 nm and width 85 µm, was found to be 2.17 × 10−7 Ω·m or 13 times resistivity of bulk silver (RBS). The resistivity initially decreased with an increase in material thickness, when achieved by overprinting successive layers or by decreasing print pitch, and a resistivity of around 10 times RBS was observed after overprinting two times at pitch 75 µm and with single pass print pitch of between 60 and 80 µm, resulting in line thickness up to 920 nm. On further increases in thickness the resistivity increased and reached 27 times RBS at print pitch of 15 µm. On moderate heating of the substrate to 50 °C, more compact silver nanoparticle films were formed, reducing thickness to 200 nm from a single pass print, and lower material resistivity approaching five times RBS was achieved.

A flexible and highly pressure-sensitive PDMS sponge based on silver nanoparticles decorated reduced graphene oxide composite

Flexible pressure sensors have a wide range of applications in wearable electronics and human-machine interfacing. A flexible and highly pressure-sensitive sensor was fabricated with silver nanoparticles (Ag NPs) decorated-reduced graphene oxide composites (Ag/rGO) filling into the PDMS sponge. The Ag/rGO composites were synthesized by one-step chemical reduction method that Ag NPs were tightly and uniformly coated on the surface of reduced graphene oxide nanosheets. Then Ag/rGO composites filled PDMS sponge (Ag/rGO-PDMS) was prepared through a dip-drying method as pressure sensitive materials. The Ag NPs coated on the surface of graphene nanosheets improved the conductivity of the Ag/rGO composites and reduced the contact resistance of graphene nanosheets. The graphene nanosheets could enhance the flexible stability and facilitate the electron transport in Ag/rGO-PDMS. The Ag/rGO-PDMS sponge with optimized GO to Ag weight ratio showed maximum pressure sensitivity of 8.86 kPa−1 which enhanced twenty-two times compared with that of pure rGO filled PDMS sponge (0.40 kPa−1). The flexible Ag/rGO-PDMS sponge with high pressure sensitivity could be used for detection of different kinds of mechanical forces (pressing, bending and twisting) and radial artery blood pulses in real-time.

High sensitive applied load measurement using optical fiber tapered-loop probe with SPR effect

A new tapered-loop fiber structure with Au film was designed for applied load detection in this work. Surface Plasmon Resonance (SPR) effect was applied to the physical parameter detection for the first time. The effective incidence angle of fiber loop was changed by pressure-stress, and then the characteristic wavelength was expected to drift. FEM analysis determined the mapping relationship between loading field and SPR effect based on the established theoretical model. The calculation results guided the preparation of a physical probe. Pressure-sensitive material package and diaphragm type encapsulation composed the sensing substrate. This optimized probe had an excellent linearity and good sensitivity of 1.473 nm/kPa within the loading range of 0–20 kPa. Under repetitive experiments, the maximum error got 0.29 nm in uplink curve and 0.4 nm in downlink curve. The upper limit of probe detection got 100 KPa. It had a high resolution in the linear region, which was conducive to perceive a micro-pressure. Compared with bare fiber structure, this combined probe showed high repeatability and mechanical stability that had a great practical potential.

Fabrication of highly pressure-sensitive, hydrophobic, and flexible 3D carbon nanofiber networks by electrospinning for human physiological signal monitoring.

Three-dimensional (3D) porous nanostructure materials have promising applications in pressure sensors or other situations. However, the low sensing sensitivity of these materials restricts precise detection of physiological signals, and it is still a challenge to manufacture highly pressure-sensitive materials, which simultaneously possess other versatile properties. Herein, a simple and cost-efficient strategy is proposed to fabricate versatile 3D carbon nanofiber networks (CNFNs) with superior pressure-sensitivity through electrospinning and thermal treatment. The pressure sensitivity of the CNFNs is 1.41 kPa-1, which is much higher than that of similar 3D porous materials. Unlike traditional carbonaceous materials, the CNFNs exhibit excellent flexibility, stable resilience, and super compressibility (>95%), because of the nano-reinforce of Al2O3. Benefiting from the robust mechanical and piezoresistive properties of the CNFNs, a pressure sensor designed with the CNFNs is able to monitor human physiological signals, such as phonation, pulse, respiration and human activities. An arch-array platform for direction identification of tangential forces and an artificial electronic skin bioinspired by human's hairy skin have been ingeniously designed. The CNFNs also present other versatile characteristics as well, including ultralight density, hydrophobicity, low thermal conductivity, and low infrared emissivity. Therefore, the CNFNs have promising potential in a wide range of applications.

개선된 압력감응제가 적용된 곡면유연촉각센서의 적층제작

A tactile sensor is a device that collects pressure information from its environment. However, the sensors mimicking a human’s sensory system have not been sufficiently developed for practical application. It is noted that planar flexible tactile sensors have sufficient elasticity and flexibility for attachment to non-planar surfaces. But, they are subjected to an initial strain when attached to a non-planar surface. Therefore an additional calibration process is required. In this study, the fabrication process of a non-planar flexible tactile sensor is proposed, using a direct writing technology as well as an additive manufacturing technology. A curved elastic sensor body was fabricated using mold by the use of a layer-by-layer process. Moreover, the pressure sensitive material which is composed of MWCNTs and PDMA, was dispensed using a direct writing technology. The non-planar flexible tactile sensor was fabricated and tested in terms of an external pressure.