Ultrasensitive Pressure Sensors Research Articles

Bioinspired and bristled microparticles for ultrasensitive pressure and strain sensors

Biological sensory organelles are often structurally optimized for high sensitivity. Tactile hairs or bristles are ubiquitous mechanosensory organelles in insects. The bristle features a tapering spine that not only serves as a lever arm to promote signal transduction, but also a clever design to protect it from mechanical breaking. A hierarchical distribution over the body further improves the signal detection from all directions. We mimic these features by using synthetic zinc oxide microparticles, each having spherically-distributed, high-aspect-ratio, and high-density nanostructured spines resembling biological bristles. Sensors based on thin films assembled from these microparticles achieve static-pressure detection down to 0.015 Pa, sensitivity up to 121 kPa−1, and a strain gauge factor >104, showing supreme overall performance. Other properties including a robust cyclability >2000, fast response time ~7 ms, and low-temperature synthesis compatible to various integrations further indicate the potential of this sensor technology in applying to wearable technologies and human interfaces.

Transcatheter Self‐Powered Ultrasensitive Endocardial Pressure Sensor

AbstractChanges in endocardial pressure (EP) have important clinical significance for heart failure patients with impaired cardiac function. As a vital parameter for evaluating cardiac function, EP is commonly monitored by invasive and expensive cardiac catheterization, which is not feasible for long‐term and continuous data collection. In this work, a miniaturized, flexible, and self‐powered endocardial pressure sensor (SEPS) based on triboelectric nanogenerator (TENG), which is integrated with a surgical catheter for minimally invasive implantation, is reported. In a porcine model, SEPS is implanted into the left ventricle and the left atrium. The SEPS has a good response both in low‐ and high‐pressure environments. The SEPS achieves the ultrasensitivity, real‐time monitoring, and mechanical stability in vivo. An excellent linearity (R 2 = 0.997) with a sensitivity of 1.195 mV mmHg−1 is obtained. Furthermore, cardiac arrhythmias such as ventricular fibrillation and ventricular premature contraction can also be detected by SEPS. The device may promote the development of miniature implantable medical sensors for monitoring and diagnosis of cardiovascular diseases.

Ultrasensitive Wearable Pressure Sensors Assembled by Surface-Patterned Polyolefin Elastomer Nanofiber Membrane Interpenetrated with Silver Nanowires.

Wearable pressure sensors with ultrahigh sensitivity and flexibility have garnered tremendous attention because of their abilities to mimic the human somatosensory system and perceive surrounding pressure distribution. Herein, an ultrasensitive pressure sensor was fabricated with surface-patterned nanofibrous membranes (SPNMs) via a facile replica method from available plain-weaved nylon textiles. The SPNMs were composed of internal three-dimensional interpenetrating polyolefin elastomer nanofibers and silver nanowires (Ag NWs). The effects of the geometry of surface patterns and the density of the Ag NW network on the sensing performance of the assembled pressure sensor were systematically investigated. The results indicated that clavate groove-shaped surface patterns improved the sensitivity and a larger groove spacing contributed to higher sensitivities, whereas denser Ag NWs would reduce the sensing performance. The optimal pressure sensor assembled with SPNMs-45 and a Ag NW fraction of 3.8% showed high sensitivity (19.4 kPa-1) below the pressure of 2.76 kPa, a low detection limit (<1.6 Pa), fast response (30 and 42 ms), as well as excellent durability. These outstanding performances demonstrated its promising potential for wearable electronic applications, like detecting the spatial pressure distribution and monitoring human muscle motions.

Polyelectrolyte Dielectrics for Flexible Low‐Voltage Organic Thin‐Film Transistors in Highly Sensitive Pressure Sensing

AbstractOrganic thin‐film transistors (OTFTs) can provide an effective platform to develop flexible pressure sensors in wearable electronics due to their good signal amplification function. However, it is particularly difficult to realize OTFT‐based pressure sensors with both low‐voltage operation and high sensitivity. Here, controllable polyelectrolyte composites based on poly(ethylene glycol) (PEG) and polyacrylic acid (PAA) are developed as a type of high‐capacitance dielectrics for flexible OTFTs and ultrasensitive pressure sensors with sub‐1 V operation. Flexible OTFTs using the PAA:PEG dielectrics show good universality and greatly enhanced electrical performance under a much smaller operating voltage of −0.7 V than those with a pristine PAA dielectric. The low‐voltage OTFTs also exhibit excellent flexibility and bending stability under various bending radii and long cycles. Flexible OTFT‐based pressure sensors with low‐voltage operation and superhigh sensitivity are demonstrated by using a suspended semiconductor/dielectric/gate structure in combination with the PAA:PEG dielectric. The sensors deliver a record high sensitivity of 452.7 kPa−1 under a low‐voltage of −0.7 V, and excellent operating stability over 5000 cycles. The OTFT sensors can be built into a wearable sensor array for spatial pressure mapping, which shows a bright potential in flexible electronics such as wearable devices and smart skins.

3D Printing: Rational Design of Ultrasensitive Pressure Sensors by Tailoring Microscopic Features (Adv. Mater. Interfaces 18/2018)

Ultrasensitive resistive pressure sensors are developed by using an additive manufacturing technique (3D printing) to create contacting surfaces with different microstructure features. These new sensors' performance is highly tunable by adjusting the surface topographic features. More details can be found in article number 1800403 by Shuhua Peng, Chun H. Wang, and co-workers.

Bionic Fish-Scale Surface Structures Fabricated via Air/Water Interface for Flexible and Ultrasensitive Pressure Sensors.

In recent years, wearable and flexible sensors have attracted considerable research interest and effort owing to their broad application prospects in wearable devices, robotics, health monitoring, and so on. High-sensitivity and low-cost pressure sensors are the primary requirement in practical application. Herein, a convenient and low-cost process to fabricate a bionic fish-scale structure poly(dimethylsiloxane) (PDMS) film via air/water interfacial formation technique is presented. High-sensitivity flexible pressure sensors can be constructed by assembling conductive films of graphene nanosheets into a microstructured film. Thanks to the unique fish-scale structures of PDMS films, the prepared pressure sensor shows excellent performance with high sensitivity (-70.86% kPa-1). In addition, our pressure sensors can detect weak signals, such as wrist pulses, respiration, and voice vibrations. Moreover, the whole process of pressure sensor preparation is cost-effective, eco-friendly, and controllable. The results indicate that the prepared pressure sensor has a profitable and efficient advantage in future applications for monitoring human physiological signals and sensing subtle touch, which may broaden its potential applications in wearable devices.

Rational Design of Ultrasensitive Pressure Sensors by Tailoring Microscopic Features

AbstractWearable sensors are increasingly used in a wide range of applications such as tactile sensors and artificial skins for soft robotics, monitoring human motions for wellbeing and sports performance, and pressure control of compression garments for wound healing. In this work, an ultrasensitive resistive pressure sensor based on conductive polydimethylsiloxane (PDMS) thin films with different microstructures is presented. These microscopic features include micropyramids, micro‐semispheres, and micro‐semicylinders which are created by soft lithography replication of 3D printing templates. To enable piezoresistivity, a thin layer of carbon nanofibers (CNFs) is spray‐coated on the textured PDMS film. The resistance changes of the three microstructure designs under compression loading show that the micro‐semicylinder‐based sensor has the highest sensitivity of −3.6 kPa−1. Finite element modeling reveals that among the three designs, the micro‐semicylinders show the largest change in contact area under the same pressure, consistent with the experimental results that the largest resistance change under the same pressure. This sensor is capable of detecting pressure as low as 1.0 Pa. This 3D printing technology is a promising fabrication technique to design microstructured piezoresistive layers, paving the way to tailor sensor performance by engineering their microstructures and to produce ultrasensitive pressure sensors at low cost.

An ultrasensitive flexible pressure sensor for multimodal wearable electronic skins based on large-scale polystyrene ball@reduced graphene-oxide core–shell nanoparticles

In this study, we report the fabrication of a flexible film shaped resistive-type pressure sensor with high performance and versatile applications.

Direct Printing for Additive Patterning of Silver Nanowires for Stretchable Sensor and Display Applications

AbstractA unique direct printing method is developed to additively pattern silver nanowires (AgNWs) with length of up to ≈40 µm. Uniform and well‐defined AgNW features are printed on various substrates by optimizing a series of parameters including ink composition, printing speed, nozzle size, substrate temperature, and hydrophobicity of the substrate surface. The capability of directly printing such long AgNWs is essential for stretchable electronics applications where mechanical compliance is required as manifested by a systematic study comparing the electrical and electromechanical performance of printed AgNW features with different nanowire lengths. Such printed AgNWs are used to demonstrate biaxially stretchable conductors, ultrasensitive capacitive pressure sensor arrays, and stretchable electroluminescent displays, indicating their great potential for applications in low‐cost wearable electronics. This strategy is adaptable to other material platforms like semiconducting nanowires, which may offer a cost‐effective entry to various nanowire‐based mechanically compliant sensory and optoelectronic systems.

Piezoelectric ultra-sensitive aluminum nitride thin film on flexible aluminum substrate

Development of ultra-sensitive mechanical pressure sensors is required for various technological fields such as medical diagnosis and gas leakage. Aluminum nitride (AlN) thin films deposited by rf reactive sputtering on flexible aluminum substrates show a piezoelectric response to an ultra-small mechanical pressure in the scale of few Pa. This result is achieved only in the case where the residual average stress in the AlN film is close to zero. The deposition temperature determines the crystallographic orientation of the grains relative to the AlN film plane and consequently the type and magnitude of the residual stress in the film. Various sources of mechanical pressures were applied on the AlN films including a stream of air from a narrow diameter nozzle, sound waves in air and a piezoelectric actuator. In addition, a thermally induced pressure was tested. The scale of the applied mechanical pressures was calibrated and found to be in the range of few Pascals. The piezoelectric response of the AlN film is correlated with the mismatch of atomic arrangement at the AlN film/Al substrate interface.

2D Nanosheet Paint from Solvent-Exfoliated Bi2Te3 Ink

Embedding 2D layered materials into polymers and other materials as composites has resulted in the development of ultrasensitive pressure sensors, tunable conductive stretchable polymers, and thermoelectric coatings. As a wettable paint or ink, many 2D materials may be penciled, printed, or coated onto a range of surfaces for a variety of applications. However, the intrinsic conductive properties of painted coatings using 2D and layered materials are not completely understood, and conductive polymer additives may mask underlying properties such as directional conductivity. We report a process for making a paint from solvent-exfoliated Bi2Te3 into solution-dispersible 2D and few-layer (multiple quintuple) nanosheet inks, that form smooth, uniform paint blends at several concentrations of Bi2Te3. The individual solvent-exfoliated nanosheets are edge-coated by (poly)ethylene glycol to produce a paint, stable over extended period in solution. Electrical transport is found to be sensitive to aspect ratio, and ...

CVD growth of fingerprint-like patterned 3D graphene film for an ultrasensitive pressure sensor

With the rapid development of wearable devices, flexible pressure sensors with high sensitivity and wide workable range are highly desired. In nature, there are many well-adapted structures developed through natural selection, which inspired us for the design of biomimetic materials or devices. Particularly, human fingertip skin, where many epidermal ridges amplify external stimulations, might be a good example to imitate for highly sensitive sensors. In this work, based on unique chemical vapor depositions (CVD)-grown 3D graphene films that mimic the morphology of fingertip skin, we fabricated flexible pressure sensing membranes, which simultaneously showed a high sensitivity of 110 (kPa)−1 for 0–0.2 kPa and wide workable pressure range (up to 75 kPa). Hierarchical structured PDMS films molded from natural leaves were used as the supporting elastic films for the graphene films, which also contribute to the superior performance of the pressure sensors. The pressure sensor showed a low detection limit (0.2 Pa), fast response (< 30 ms), and excellent stability for more than 10,000 loading/unloading cycles. Based on these features, we demonstrated its applications in detecting tiny objects, sound, and human physiological signals, showing its potential in wearable electronics for health monitoring and human/machine interfaces.

Ultrasensitive Pressure Sensor Based on an Ultralight Sparkling Graphene Block.

Herein, we develop a supersensitive pressure sensor based on a fully air-bubbled ultralight graphene block through a simple sparkling strategy. The obtained sparkling graphene block (SGB) exhibits excellent elasticity even at 95% compressive strain and rebounds a steel ball with an ultrafast recovery speed (∼1085 mm s-1). Particularly, the SGB-based sensor reveals a record pressure sensitivity of 229.8 kPa-1, much higher than other graphene materials, because of the highly cavity-branched internal structure. Impressively, the pressure sensor can detect the extremely gentle pressures even beyond the real human skin and hence are promising for ultrasensitive sensing applications.

Ultra-sensitive Pressure sensor based on guided straight mechanical cracks

Recently, a mechanical crack-based strain sensor with high sensitivity was proposed by producing free cracks via bending metal coated film with a known curvature. To further enhance sensitivity and controllability, a guided crack formation is needed. Herein, we demonstrate such a ultra-sensitive sensor based on the guided formation of straight mechanical cracks. The sensor has patterned holes on the surface of the device, which concentrate the stress near patterned holes leading to generate uniform cracks connecting the holes throughout the surface. We found that such a guided straight crack formation resulted in an exponential dependence of the resistance against the strain, overriding known linear or power law dependences. Consequently, the sensors are highly sensitive to pressure (with a sensitivity of over 1 × 105 at pressures of 8–9.5 kPa range) as well as strain (with a gauge factor of over 2 × 106 at strains of 0–10% range). A new theoretical model for the guided crack system has been suggested to be in a good agreement with experiments. Durability and reproducibility have been also confirmed.

Ultrasensitive cellular fluorocarbon piezoelectret pressure sensor for self-powered human physiological monitoring

Flexible and wearable pressure sensors are of essential importance in developing artificial electronic skin (e-skin) for areas such as healthcare monitoring and clinical diagnosis. Here, we report an ultrasensitive cellular fluorocarbon piezoelectret pressure sensor (FPS) via a three-step hot-pressing method. By constructing micron-sized voids in the inner cell, and combination with outstanding charge storage ability of the fluorocarbon electrets, tremendous piezoelectric activity can be obtained. The flexible FPS showed advantages of remarkable sensitivity (7380pCN−1) in the subtle-pressure regime (<1kPa), fast response time (50ms), very low limit of detection (5Pa) as well as high stability (30,000 cycles). In addition, the flexible and self-powered FPS owns the capability for detecting human motions such as wrist stretching, cheek motion from open-bite-open, eyes blinking and chest respiration, respectively. It can be also used for monitoring human physiological signals such as radial artery pulse wave. By virtue of easy processability in large scale, light weight, and low cost, the FPS is especially suitable for mass production and flexible electronics, indicating their promising applications in artificial intelligence and mobile healthcare monitoring systems.

Ultrasensitive Pressure Detection of Few-Layer MoS2.

Ultrasensitive pressure sensors are constructed with few-layer MoS2 films. As-designed Fabry-Perot (F-P) sensors exhibit nearly synchronous pressure-deflection responses with a very high sensitivity (89.3 nm Pa-1 ), which is three orders of magnitude higher than those of conventional diaphragm materials (e.g., silica, silver films). This kind of F-P sensor may open up new avenues for 2D materials in biomedical and environmental applications.

Polymer Swelling Induced Conductive Wrinkles for an Ultrasensitive Pressure Sensor.

Deposition of particular layers of solid materials on a swelling polymer leads to the formation of functional wrinkles after the release of polymer strain. Unlike traditional mechanical stretching, polymer swelling could introduce uniform wrinkle structures on complex substrates as a result of isotropic polymer elongation. In this work, conductive silver wrinkles are grown on an elastomer by combining polymer swelling with electroless deposition. By adjusting the cross-linking ratio of polymer substrate or deposition time, the amplitude and wavelength of wrinkles can be tuned to meet demands for ultrasensitive pressure sensors. The detectable pressure limit is successfully reached below 1.0 Pa.

An ultra-sensitive and rapid response speed graphene pressure sensors for electronic skin and health monitoring

Design of pressure sensors with ultra-sensitivity, rapid response speed and long-term stability is a key procedure to fulfill high performance electronic skins. Herein, we report the fabrication of a self-assembled 3D films platform that combines a natural viscoelastic property material P(VDF-TrFe) with an electrically conductive material rGO for the first time. Notably, modular assembly of the rGO-encapsulated P(VDF-TrFe) nanofibers led to the fabrication of a highly sensitive pizeoresistive pressure sensor which exhibited high sensitivity (15.6kPa−1), low detection limit (1.2Pa) and working voltage (1V). The excellent long-term stability under 100,000 cycles and rapid response time of 5ms at 50Hz are particularly captivating. Besides, using the simple and versatile procedures, a framework to make integrated sensor array platforms easily can be used as highly sensitive electronic skins for mapping spatial pressure distribution, and monitoring the human physiological signals, including the real-time pulses and muscle movements.

Design of In Situ Poled Ce(3+)-Doped Electrospun PVDF/Graphene Composite Nanofibers for Fabrication of Nanopressure Sensor and Ultrasensitive Acoustic Nanogenerator.

We report an efficient, low-cost in situ poled fabrication strategy to construct a large area, highly sensitive, flexible pressure sensor by electrospun Ce(3+) doped PVDF/graphene composite nanofibers. The entire device fabrication process is scalable and enabling to large-area integration. It can able to detect imparting pressure as low as 2 Pa with high level of sensitivity. Furthermore, Ce(3+)-doped PVDF/graphene nanofiber based ultrasensitive pressure sensors can also be used as an effective nanogenerator as it generating an output voltage of 11 V with a current density ∼6 nA/cm(2) upon repetitive application of mechanical stress that could lit up 10 blue light emitting diodes (LEDs) instantaneously. Furthermore, to use it in environmental random vibrations (such as wind flow, water fall, transportation of vehicles, etc.), nanogenerator is integrated with musical vibration that exhibits to power up three blue LEDs instantly that promises as an ultrasensitive acoustic nanogenerator (ANG). The superior sensing properties in conjunction with mechanical flexibility, integrability, and robustness of nanofibers enabled real-time monitoring of sound waves as well as detection of different type of musical vibrations. Thus, ANG promises to use as an ultrasensitive pressure sensor, mechanical energy harvester, and effective power source for portable electronic and wearable devices.

Nanoparticle monolayer-based flexible strain gauge with ultrafast dynamic response for acoustic vibration detection

The relatively poor dynamic response of current flexible strain gauges has prevented their wide adoption in portable electronics. In this work, we present a greatly improved flexible strain gauge, where one strip of Au nanoparticle (NP) monolayer assembled on a polyethylene terephthalate film is utilized as the active unit. The proposed flexible gauge is capable of responding to applied stimuli without detectable hysteresis via electron tunneling between adjacent nanoparticles within the Au NP monolayer. Based on experimental quantification of the time and frequency domain dependence of the electrical resistance of the proposed strain gauge, acoustic vibrations in the frequency range of 1 to 20,000 Hz could be reliably detected. In addition to being used to measure musical tone, audible speech, and creature vocalization, as demonstrated in this study, the ultrafast dynamic response of this flexible strain gauge can be used in a wide range of applications, including miniaturized vibratory sensors, safe entrance guard management systems, and ultrasensitive pressure sensors.