High-sensitivity Pressure Sensor Research Articles

High sensitive pressure sensors based on multiple coating technique**Project supported by the National Key Research and Development Program of China (Grant No. 2016YFB0400603) and the National Natural Science Foundation of China (Grant No. 61804012).

A multi-coating technique of reduced graphene oxide (RGO) was proposed to increase the sensitivity of paper-based pressure sensors. The maximum sensitivity of 17.6 kPa−1 under the 1.4 kPa was achieved. The electrical sensing mechanism is attributed to the percolation effect. Such paper pressure sensors were applied to monitor the motor vibration, which indicates the potential of mechanical flaw detection by analyzing the waveform difference.

Flexible pressure sensors with a highly pressure- and strain-sensitive layer based on nitroxyl radical-grafted hollow carbon spheres.

The spherical structure of hollow carbon spheres (HCSs) makes their contact resistance and tunnel resistance extremely sensitive to the distance between them, which can be used as a conductive filler for high-sensitivity pressure sensors. Compared with one- and two-dimensional carbon-based materials, HCSs require a higher filling concentration for constructing an effective conductive network due to their average conductivity, which affects the mechanical properties of the sensor. In a single-electron system, electrons are transferred by hopping between the nitroxyl radical monomers and when the distance between the monomers is shortened, the electron transfer rate of nitroxyl radical compounds can be increased, thus further improving their conductivity. In this work, a composite of nitroxyl radical-modified hollow carbon spheres (HCS-g-NO˙) and polydimethylsiloxane (PDMS) polymer is introduced, and the resistivity of HCS-g-NO˙ is about one magnitude lower than that of HCSs at the same filling concentration. A flexible piezoresistive sensor with HCS-g-NO˙@PDMS as the sensitive layer coated on the PET electrode is presented, in which the spacing between HCS-g-NO˙ changes, causing changes in the contact and tunnel resistances in the sensitive layer when mechanical stresses are applied. The sensor achieved a piezoresistive response of -0.55 kPa-1 and the tensile response of 211 , and a sensor array of nine pixels was successfully demonstrated; thus, it can be used as a high sensitivity pressure and strain sensor.

Design and simulation of a high sensitive stripped-shaped piezoresistive pressure sensor

This paper deals with the design and simulation of a stripped-shaped piezoresistive pressure sensor. The sensor is based on the Wheatstone bridge configuration. The piezoresistive effect is a change in the electrical resistivity of a semiconductor or metal when mechanical strain is applied. For designing the sensor, piezoresistors are placed in series on each side of the square. The number of the piezoresistor arms is varied in two proposed designs where the sensitivity and the operable pressure range are analyzed with their characteristics. The COMSOL Multiphysics software is used for this work. The simulated sensitivity is about 7.736 mV/V/MPa over the range of pressure from 0 to 5 MPa. The simulated result reveals that the sensitivity significantly depends on the placement of the resistors, combination of the materials, shape of diaphragm, and size of diaphragm.

Mechanical-force-induced non-local collective ferroelastic switching in epitaxial lead-titanate thin films

Ferroelastic switching in ferroelectric/multiferroic oxides plays a crucial role in determining their dielectric, piezoelectric, and magnetoelectric properties. In thin films of these materials, however, substrate clamping is generally thought to limit the electric-field- or mechanical-force-driven responses to the local scale. Here, we report mechanical-force-induced large-area, non-local, collective ferroelastic domain switching in PbTiO3 epitaxial thin films by tuning the misfit-strain to be near a phase boundary wherein c/a and a1/a2 nanodomains coexist. Phenomenological models suggest that the collective, c-a-c-a ferroelastic switching arises from the small potential barrier between the degenerate domain structures, and the large anisotropy of a and c domains, which collectively generates much larger response and large-area domain propagation. Large-area, non-local response under small stimuli, unlike traditional local response to external field, provides an opportunity of unique response to local stimuli, which has potential for use in high-sensitivity pressure sensors and switches.

A High Sensitive Flexible Pressure Sensor Designed by Silver Nanowires Embedded in Polyimide (AgNW-PI).

Silver nanowires (AgNW) have excellent electrical conductivity, transparency, and flexing endurance, and are broadly used in flexible electrodes and flexible sensors. This study mixed the silver nanowires and polyimide (PI) polymer using an in situ synthesis method, effectively reducing the problem of silver nanowires falling off the substrate. The selective wet etching method was firstly used to process the surface of AgNW-PI films, greatly enhancing the surface conductivity of AgNW-PI films. A flexible pressure sensor with high sensitivity was designed with two face-to-face AgNW-PI ultrathin layers. The experimental results show that our sensor presented a high sensitivity of about 1.3294 kPa−1 under a pressure of about 600 Pa, and when pressure continued to increase, the sensitivity decreased rapidly and reached saturation. Our flexible pressure sensor has the properties of low cost, high sensitivity, excellent repeatability, durability, and can detect various types of mechanical forces which could be utilized for flexible electronics.

A Universal high accuracy wearable pulse monitoring system via high sensitivity and large linearity graphene pressure sensor

Long-term accurate pulse monitoring can provide much physiological parameter information in a non-invasive way. A versatile pressure sensor with high sensitivity over a wide linear range (up to 10 kPa) is thus especially desired for this purpose. However, the trade-off between linearity region and sensitivity has not been well balanced. Despite micro/nanostructure morphologies, our simulation and mechanism analyses found that a thinner structure and better conductivity property of the sensing layer contribute to a larger linearity range and higher sensitivity, respectively. However, these two properties are often difficult to achieve simultaneously in one traditional material. Herein, a novel material design strategy is developed to fabricate a self-assembled graphene sensing film, in which the conductivity and thickness can be well balanced. As a result, our sensor exhibits unprecedented comprehensive properties with both high sensitivity (1875.53 kPa−1) and wide linear detection range (0–40 kPa). The sensor is also endowed with good stability and high peak signal-noise ratio (78 dB). Taking advantages of these performances, a universal high accuracy wireless and wearable pulse monitoring system was built. This platform first provides the subtle arterial pulse signal information even under the interference of strong body movement in real-time (during running or cycling), which could not have been realized before. This wearable system is expected to provide more rich and accurate information for personalized diagnostic applications in the future.

Direct write of a flexible high-sensitivity pressure sensor with fast response for electronic skins

Abstract External tactile force/pressure sensing, as a vital function of electronic skins, is very important to robots in non-structured environments, intelligent prosthesis of the disabilities for baby care or daily life and medical cares, etc. Despite of great advance of pressure sensors for medium pressure (10–100 kPa), to achieve high sensitivity, good pressure resolution and fast response in electronic skins for applications in biomedicine, artificial prosthetics, personal health monitoring and robotics remains challengeable. Here we direct-wrote graphene nanoplatelets (GNPs) using Weissenberg effect on a PDMS substrate to fabricate a flexible pressure sensor with high pressure sensitivities about 6.56 MPa−1 and 0.335 kPa−1 respectively under the pressure less than 65 kPa and around 100 kPa. Minimum pressure change of ca. 14 Pa to the placement or removal of a tiny item can be detected. It is characterized to be of faster response/recovery speed (ca. 171 ms/110 ms), better repeatability and cycling stability, compared with most reported flexible medium-pressure sensor. The pressure electronic skin demonstrates good performance in its applications including pulse sensing on wrist and fingertip grabbing, indicating its greatly potential sensor candidate for electronic skins.

High Temperature Sensitivity Pressure Sensors Based on Filter Paper as a Mold

As an item commonly used in daily life, filter paper could be used as a mold to easily produce sensitive, efficient, stable and commercially valuable pressure sensors. The PDMS film prepared by the filter paper mold is completely coated by SWCNTs and encapsulated by a polyethylene (PE) film to obtain a high temperature sensitivity pressure sensors (TSPS). The TSPS is sensitive between 0 Pa and 0.84 kPa pressure ranges, it is sensitivity reached at 29.94 KPa−1. The TSPS had high sensitivity for identifying low pressures (33.4 × 10−6 N), and long-lasting stability over 5,500 pressure dynamic cycles. In addition, sensors made by this method can measure temperature changes under static pressure. TSPS has good temperature sensing performance, which showed sensitivity of 0.277%/°C under 261.8 Pa pressure and 0.251%/°C under 1231.8 Pa pressure. Pressure and temperature sensors have been successfully applied to a variety of real life scenarios, which indicates that they have the potential to be applied to human life.

Skin-inspired flexible and high-sensitivity pressure sensors based on rGO films with continuous-gradient wrinkles.

Flexible electronic devices have received more and more attention. In particular, for pressure sensors, traditional methods for improving sensing performances are mostly based on the construction of microstructured templates. However, it still remains significantly challenging to conveniently fabricate thin-film sensors which possess flexibility, high sensitivity and location detection ability. Inspired by the microstructure of the human skin surface, herein, a new pressure sensor with a hierarchical structure and gradient reduced graphene oxide (rGO) wrinkles is reported. Benefiting from the skin-like structure, the pressure sensor demonstrates outstanding sensitivity, reaching 178 kPa-1; it can also detect pressure as small as 42 Pa. Furthermore, the concept of designing and constructing a gradient structure has been applied to achieve position detection, which is expected to find practical applications in human motion detection.

Fabrication of enhanced dielectric PVDF nanocomposite based on the conjugated synergistic effect of ionic liquid and graphene

In recent years, due to its excellent dielectric property in polymers, polyvinylidene fluoride (PVDF) has been widely used to prepare polymer based electrical device and manufacture flexible sensors, transducers and energy harvesters. However, compared with some inorganic materials, the finite dielectric property of PVDF still limited its application as piezoelectric material in high-sensitivity pressure sensors for detecting dynamic signals. In this report, we prepared a high dielectric flexible material based on PVDF compositing with graphene and ionic liquid (IL, 1-butyl-3-methylimidazolium hexafluorophosphate). The introduction of IL improves the dispersion of graphene in nanocomposite matrix, and the conjugated synergistic effect of IL and graphene enhance the dielectric property of PVDF nanocomposite. IL can help to improve the interfacial polarization effect between graphene and PVDF matrix, and increase the content of β phase due to the ion-dipolar interaction between the -CF2 of the polymer backbone and imidazolium cation. Meanwhile, the uniform dispersion of graphene in PVDF can promote the formation of tiny graphene microcapacitor structure in matrix, which is significant in improvement of dielectric and electrical properties of PVDF nanocomposite. The nanocomposite with the concentration of 2.0 wt% graphene and 2.0 wt% ionic liquid has the best dielectric property in our work, the dielectric constant of nanocomposite is nearly 6 times higher than that of pure PVDF. In addition, the dielectric loss is less than 0.2 when the frequency between 104-106Hz, which is acceptable in applications.

A film bulk acoustic resonator pressure sensor based on lateral field excitation

A high-sensitive thickness shear mode film bulk acoustic resonator pressure sensor based on lateral field excitation is designed with its structure simulated in environment of air and liquids. A finite element model of film bulk acoustic resonator pressure sensor structure is established to obtain frequency variation under different pressure conditions by parameter sweep method when the multi-physics fields are added to the model. The results of simulation show that the pressure sensor’s resonance frequency is 2.114 GHz and pressure sensitivity is 1200 Hz/kPa in air. In liquid environment, film bulk acoustic resonator pressure sensor displays a pressure sensitivity of 325 Hz/kPa in ethanol, 475 Hz/kPa in deionized water, and 612.5 Hz/kPa in glycerol. This film bulk acoustic resonator pressure sensor has been proved to be highly sensitive both in air and liquid environment and has the potential to be used in biomedical applications.

Ultrahigh-Sensitivity Piezoresistive Pressure Sensors for Detection of Tiny Pressure.

High-sensitivity pressure sensors are crucial for the ultrasensitive touch technology and E-skin, especially at the tiny-pressure range below 100 Pa. However, it is highly challenging to substantially promote sensitivity beyond the current level at several to 200 kPa-1 and to improve the detection limit lower than 0.1 Pa, which is significant for the development of pressure sensors toward ultrasensitive and highly precise detection. Here, we develop an efficient strategy to greatly improve the sensitivity near to 2000 kPa-1 using short-channel coplanar device structure and sharp microstructure, which is systematically proposed for the first time and rationalized by the mathematic calculation and analysis. Significantly, benefiting from the ultrahigh sensitivity, the detection limit is improved to be as small as 0.075 Pa. The sensitivity and detection limit are both superior to the current levels and far surpass the function of human skin. Furthermore, the sensor shows fast response time (50 μs), excellent reproducibility and stability, and low power consumption. Remarkably, the sensor shows excellent detection capacity in the tiny-pressure range, including light-emitting diode switching with a pressure of 7 Pa, ringtone (2-20 Pa) recognition, and ultrasensitive (0.1 Pa) electronic glove. This work represents a performance and strategic progress in the field of pressure sensing.

P‐138: A High Sensitive Resistive Pressure Sensor with NH4HCO3‐induced Porous Structure Active Layer

A facile approach to achieve high sensitive piezoresistive pressure sensor is proposed. By introducing NH4HCO3 to produce porous structures in the PSR‐layer (Pressure sensor rubber), sensor shows high flexibility and elasticity. The resistance increases with external stress. Sensitivity reaches 0.8kPa‐1 under the pressure of 0–25kPa, with high linearity and stability.

Design and Analysis of MEMS based Piezoresistive Pressure sensor for Sensitivity Enhancement

This paper reported novel high sensitivity and linear 0-1MPa piezoresistive pressure sensor for environmental applications. The proposed work as two different structures of membrane (square and rectangular) having the similar surface area and thickness has been studied. The design and analyzed pressure sensor parameters such as stress, deflection and sensitivity are obtained by using INTELLISUITE 8.8v. The simulated sensor showed a sensitivity of 6.8×10-12 for 7µm thickness, 18.5×10-12 for 5µm thickness and 84.2×10-12 for 3µm thicknessof square membrane is prepared through the finite element tool. This deflection change providesthe validate of the pressure in that atmosphere. Finally, we observed that the best deflection obtained from square membrane and maximum stress output reactions are obtained fromthe rectangular membranewith the pressure range from 0.1 MPa to 1MPa and also maximum deformation of 84 μm for 3 µm thickness, 18.55µm for 5µm thickness and 6.9µm for 7µm thickness. The effect of these studies can be used to improve the sensitivity of these devices.

A new approach for ultrahigh-performance piezoresistive sensor based on wrinkled PPy film with electrospun PVA nanowires as spacer

Pressure sensor with high sensitivity is desirable for it's vast application in fields like wearable electronics and human-machine interface. Here, we report a simple but rarely investigated approach to fabricate amazing high sensitivity pressure sensors by using PVA nanowires as spacer between active materials. On one hand, Polyvinyl Alcohol (PVA) nanowire (PVANW) serves as contact spacer between polypyrrole (PPy) film and PET/ITO sheet, where the electrical transportation between PPy film and PET/ITO sheet can be altered with different density of PVANW; on the other hand, the electroplating-obtained PPy film with intrinsic wrinkled and fluffy structure, shows various electrical conductivities under various external pressures. By virtue of these two traits, the PPy-PVANW-PET/ITO (PPPI) sensor distinguishes itself with superior performances of ultrahigh sensitivity (109.9kPa−1, 0–0.17kPa; 228.5kPa−1, 0.5–2kPa; 11.9kPa−1, 5–9kPa), low detection limit (2.97Pa) and good stability (10,000 loading-unloading cycles). The excellent advantages of the sensor make it a promising candidate in today's pressure sensor industry, and the fabrication procedure of PPPI sensor also provides a simple method to improve the performance of pressure sensors.

High-sensitivity pressure sensor based on fiber Mach–Zehnder interferometer

In this paper we propose and experimentally demonstrate an optical fiber structure sensor based on a Mach–Zehnder interferometer for pressure measurement. The fiber sensor is composed of a single-mode-no-core-single-mode structure, a section of capillary pure silica tube and refractive index matching fluid (RIMF). As the pressure decreases, the sealed air in the tube expands and the liquid level of the RIMF increases, which causes a wavelength shift of the interferometer. The measurement of the pressure variation can thus be achieved by monitoring the wavelength shift. The experimental results agree well with the numerical simulation, and a maximum pressure sensitivity of 266.6 nm is achieved experimentally. Furthermore, the proposed fiber sensor has the potential to obtain higher sensitivity by enlarging the length of the air cavity.

Structural Engineering for High Sensitivity, Ultrathin Pressure Sensors Based on Wrinkled Graphene and Anodic Aluminum Oxide Membrane.

Nature-motivated pressure sensors have been greatly important components integrated into flexible electronics and applied in artificial intelligence. Here, we report a high sensitivity, ultrathin, and transparent pressure sensor based on wrinkled graphene prepared by a facile liquid-phase shrink method. Two pieces of wrinkled graphene are face to face assembled into a pressure sensor, in which a porous anodic aluminum oxide (AAO) membrane with the thickness of only 200 nm was used to insulate the two layers of graphene. The pressure sensor exhibits ultrahigh operating sensitivity (6.92 kPa-1), resulting from the insulation in its inactive state and conduction under compression. Formation of current pathways is attributed to the contact of graphene wrinkles through the pores of AAO membrane. In addition, the pressure sensor is also an on/off and energy saving device, due to the complete isolation between the two graphene layers when the sensor is not subjected to any pressure. We believe that our high-performance pressure sensor is an ideal candidate for integration in flexible electronics, but also paves the way for other 2D materials to be involved in the fabrication of pressure sensors.

High-pressure carbon dioxide adsorption kinetics of potassium-modified hydrotalcite at elevated temperature

A method for characterizing the high-pressure CO2 adsorption kinetics of potassium-modified hydrotalcite at elevated temperatures based on a modified static bed is proposed. The pressure drop of the adsorption tube with time was measured by a series of high-sensitivity pressure sensors to calculate the CO2 adsorption curves of the adsorbent. The concept of a hot/cold spot is introduced to eliminate the temperature deviation caused by the dead volume of the pipelines and the temperature disproportion in the tubes. As compared to conventional characterization methods such as thermal gravimetric analysis and fixed bed testing, the proposed method avoids the displacement effect, making it possible to obtain actual adsorption curves above atmospheric pressure. The effect of adsorption temperature (300–450°C) and CO2 partial pressure (0.1–2MPa) and a reversible adsorption isotherm with 30min adsorption/30min desorption, as well as desorption performance under vacuum, were investigated. The adsorption/desorption curves of hydrotalcite increased linearly with the logarithm of the adsorption time in almost all tested conditions. The CO2 uptake reached approximately 0.7 of the total adsorption capacity in less than 0.1min of adsorption time and exceeded 0.9 after 5min. A simple one-step kinetic model based on Elovich-type equations is built to describe the adsorption behavior of hydrotalcite at CO2 partial pressures above atmospheric pressure.

Simulation of capacitive pressure sensor based on microelectromechanical systems technology

This paper proposes a very high sensitivity pressure sensor with a novel technique for temperature compensation. The proposed technique employs a geometrical method for self-compensation of Young’s modulus reduction due to temperature increase, where a stronger spring with much larger length and width is anchored. According to the connection of the suspension spring to the larger spring, in higher temperatures, the large spring experiences more length increase, which in turn increases the stiffness of the suspension spring and, consequently, could compensates the Young’s modulus reduction. Simulation results verify that the temperature variation related error in the compensated sensor is less than 0.66% of full-scale under 260 ℃ of temperature range, which shows considerable improvement in comparison with literature. The total consumed area is about 0.033 mm2 with the sensitivity of 290 × 10−6 K−1.

Capacitive pressure sensing with suspended graphene-polymer heterostructure membranes.

We describe the fabrication and characterisation of a capacitive pressure sensor formed by an ultra-thin graphene-polymer heterostructure membrane spanning a large array of micro-cavities each up to 30 μm in diameter with 100% yield. Sensors covering an area of just 1 mm2 show reproducible pressure transduction under static and dynamic loading up to pressures of 250 kPa. The measured capacitance change in response to pressure is in good agreement with calculations. Further, we demonstrate high-sensitivity pressure sensors by applying a novel strained membrane transfer and optimising the sensor architecture. This method enables suspended structures with less than 50 nm of air dielectric gap, giving a pressure sensitivity of 123 aF Pa-1 mm-2 over a pressure range of 0 to 100 kPa.