Pressure Sensor For Applications Research Articles

Research on the Application of Flexible Pressure Sensors in Wearable Devices

The potential applications of transparent, adaptable electronic devices in the human body are driving up demand for them. For flexible and wearable electronics, such as medical surveillance devices and artificial skin, pressure sensing is mandatory. The flexibility and sensitivity of pressure sensors have advanced recently owing to developments in material and device structure. Moreover, their low manufacturing costs enable widespread implementation, leading to promising application prospects. The sensors utilize different materials and structures, including capacitive pressure sensors with ionically charged CFMs, magnetic particle-infused carbon sponges, CNT-PDMS composites, and MoSe2/MWNT combinations. These sensors offer advantages such as high sensitivity, wide pressure-detecting ranges, optical transparency, and energy efficiency. They can detect both large and subtle human movements, from walking and finger bending to breathing and eye blinking. The fabrication methods range from simple and cost-effective processes to more complex techniques like photolithography. Many of the sensors incorporate carbon nanotubes (CNTs) in various forms, exploiting their excellent electrical properties. The review highlights the potential of these sensors for healthcare monitoring, clinical diagnosis, and integration into wearable electronics, emphasizing their flexibility, biocompatibility, and ability to provide real-time, non-invasive measurements of physiological signals. Moreover, their low manufacturing costs enable widespread implementation, leading to promising application prospects.

Application of nanocomposite pressure sensors in health monitoring

Application of nanocomposite pressure sensors in health monitoring

Highly compressible lamellar graphene/cellulose/sodium alginate aerogel via bidirectional freeze-drying for flexible pressure sensor.

Graphene exhibits exceptional electrical properties, and aerogels made from it demonstrate high sensitivity when used in sensors. However, traditional graphene aerogels have poor biocompatibility and sustainability, posing potential environmental and health risks. Moreover, the stacking of their internal structures results in low compressive strength and fatigue resistance, which limits their further applications. In this study, green and sustainable cellulose nanofibers/sodium alginate/reduced graphene oxide aerogels (BCSRA) were synthesized, featuring a well-defined lamellar structure and a fiber cross-linked network, employing techniques such as bidirectional freeze-drying, ionic cross-linking, and thermal annealing. The unique internal architecture of BCSRA results in a compressive strength of up to 64.55 kPa at 70 % compression deformation and an extremely low density of merely 7.21 mg/cm3. Furthermore, BCSRA displays outstanding fatigue resistance, maintaining 82.17 % of its stress after 100 compression cycles at 70 % compressive strain and 86.99 % after 1000 cycles at 50 % compressive strain. Remarkably, when utilized as a flexible pressure sensor, BCSRA achieves a sensitivity of 5.71 kPa-1 and endures over 2200 cycles at 40 % compression, all while ensuring consistent electrical signal output. These properties underscore its significant potential for application in wearable flexible pressure sensors, capable of detecting various human movements.

An Investigation into High-Accuracy and Energy-Efficient Novel Capacitive MEMS for Tire Pressure Sensor Application.

Tire pressure monitoring systems (TPMSs) are essential for maintaining driving safety by continuously monitoring critical tire parameters, such as pressure and temperature, in real time during vehicle operation. Among these parameters, tire pressure is the most significant, necessitating the use of highly precise, cost-effective, and energy-efficient sensing technologies. With the rapid advancements in micro-electro-mechanical system (MEMS) technology, modern automotive sensing and monitoring systems increasingly rely on MEMS sensors due to their compact size, low cost, and low power consumption. This study presents a novel high-precision capacitive pressure sensor based on a capacitive micromachined ultrasonic transducer (CMUT) structure and a silicon-silicon direct bonding process. The proposed design offers exceptional performance with high accuracy, ultra-low power consumption, and reduced production costs, making it an optimal solution for enhancing the precision and efficiency of TPMS. Leveraging its low power requirements, capacitive sensing technology emerges as a superior choice for energy-efficient systems in the automotive industry.

Flexible pressure sensor with metallic reinforcement and graphene nanowalls for wearable electronics device

In recent years, flexible pressure sensors have been seen widespread adoption in various fields such as electronic skin, smart wearables, and human-computer interaction systems. Owing to the electrical conductivity and adaptability to flexible substrates, vertical graphene nanowalls (VGNs) have recently been recognized as promising materials for pressure-sensing applications. Our study presented the synthesis of high-quality VGNs via plasma enhanced chemical vapor deposition and the incorporation of a metal layer by electron beam evaporation, forming a stacked structure of VGNs/Metal/VGNs. Metal nanoparticles attached to the edges and surfaces of graphene nanosheets can alter the charge transport paths within the material to enhance the responsiveness of the sensor. This layered structure effectively fulfilled the requirements of flexible pressure sensors, exhibiting high sensitivity (40.15 kPa-1), low response time (88 ms), and short recovery time (97 ms). The pressure sensitivity remained intact even after 1000 bending cycles. Additionally, the factors contributing to the impressive pressure-sensing performance of this composite were found and its capability to detect human pulse and finger flexion signals was demonstrated, making it a promising candidate for applications of wearable electronics devices.

Strain-induced bandgap engineering in 2D ψ-graphene materials: a first-principles study.

High mechanical strength, excellent thermal and electrical conductivity, and tunable properties make two-dimensional (2D) materials attractive for various applications. However, the metallic nature of these materials restricts their applications in specific domains. Strain engineering is a versatile technique to tailor the distribution of energy levels, including bandgap opening between the energy bands. ψ-Graphene is a newly predicted 2D nanosheet of carbon atoms arranged in 5,6,7-membered rings. The half and fully hydrogenated (hydrogen-functionalized) forms of ψ-graphene are called ψ-graphone and ψ-graphane. Like ψ-graphene, ψ-graphone has a zero bandgap, but ψ-graphane is a wide-bandgap semiconductor. In this study, we have applied in-plane and out-of-plane biaxial strain on pristine and hydrogenated ψ-graphene. We have obtained a bandgap opening (200 meV) in ψ-graphene at 14% in-plane strain, while ψ-graphone loses its zero-bandgap nature at very low values of applied strain (both +1% and -1%). In contrast, fully hydrogenated ψ-graphene remains unchanged under the influence of mechanical strain, preserving its initial characteristic of having a direct bandgap. This behavior offers opportunities for these materials in various vital applications in photodetectors, solar cells, LEDs, pressure and strain sensors, energy storage, and quantum computing. The mechanical strain tolerance of pristine and fully hydrogenated ψ-graphene is observed to be -17% to +17%, while for ψ-graphone, it lies within the strain span of -16% to +16%.

Electrospun Poly(vinylidene fluoride) Nanocomposites with Ionic Liquid Functionalized Graphene Nanoplatelets by a Noncovalent Method for Piezoresistive Pressure Sensor Applications.

Piezoresistive pressure sensors have been prepared by the electrospinning of poly(vinylidene fluoride) (PVDF) containing graphene nanoplatelets (GNP) functionalized using 1-butyl-3-methylimidazolium trifluoromethanesulfonate (BMIM(OTf)) ionic liquid (IL). Optical microscopy demonstrated that the functionalized GNP powder presented particles with a smaller lateral size. The obtained mats were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, differential scanning calorimetry, electrical resistivity using two and four probes, and electromechanical testing with up to 32 load-unload cycles. Functionalization with BMIM(OTf) resulted in a higher PVDF electroactive phase. Electrospun mats obtained without the IL displayed a signal comparable to noise, while mats obtained with the BMIM(OTf) functionalized GNP displayed a clear signal, indicating that the IL helped with the dispersion of GNP on the PVDF matrix. Electrospun mats containing 1.0%m functionalized GNP presented the best performance among the evaluated samples, presenting low hysteresis and a lower distribution of the read values especially in the working range of 0 to 250 kPa. The piezoresistive behavior of the sample was tested under 32 load-unload cycles, remaining stable. Higher ranges of axial load resulted in the rupture of the fibers and swift degradation of the piezoresistive signal under a high number of cycles. A simple load cell was assembled to demonstrate the capacity of the membranes to act as piezoresistive compressive sensors capable of detecting the pressing of a human finger and differentiating between applied weights.

Rapid-response, low-detection-limit, positive-negative air pressure sensing: GaN chips integrated with hydrophobic PDMS films

Despite the importance of positive and negative pressure sensing in numerous domains, the availability of a single sensing unit adept at handling this dual task remains highly limited. This study introduces a compact optical device capable of swiftly and precisely detecting positive and negative pressures ranging from −35 kPa to 35 kPa. The GaN chip, which serves as a core component of the device, is monolithically integrated with light-emitting and light-detecting elements. By combining a deformable PDMS film coated with a hydrophobic layer, the chip can respond to changes in optical reflectance induced by pressure fluctuations. The integrated sensing device has low detection limits of 4.3 Pa and −7.8 Pa and fast response times of 0.14 s and 0.22 s for positive and negative pressure variations, respectively. The device also demonstrates adaptability in capturing distinct human breathing patterns. The proposed device, characterized by its compactness, responsiveness, and ease of operation, holds promise for a variety of pressure-sensing applications.

Effect of boron doping levels on the piezoresistive properties of boron-doped diamond films prepared by HFCVD

The exceptional piezoresistive properties of boron-doped diamond (BDD) films render them highly promising for pressure sensor applications. These properties are closely associated with the doping concentration, crystal structure, and substrate material. In this study, BDD films with varying boron concentrations (B/C = 500–8000 ppm) were fabricated on silicon and diamond substrates using hot-filament chemical vapor deposition (HFCVD) equipment. The relationship between surface grain characteristics, grain boundaries, and gauge factor (GF) of BDD films deposited on different substrates was systematically examined. The concentration of boron doping significantly influenced the surface morphology, electrical resistivity, and GF of the BDD films. The grain size of BDD films initially increased as the boron doping concentration was raised from 500 ppm to 2000 ppm; however, it subsequently decreased when the boron doping content exceeded 2000 ppm. Moreover, we found that the piezoresistive impact of a BDD film is strongly correlated to its grain size; larger grain sizes result in higher GF values. Notably, compared to those on silicon substrates, the BDD films deposited on diamond substrates exhibited superior piezoresistive characteristics. Specifically at a doping concentration of 2000 ppm, a GF as high as 284 was achieved for the BDD film on a diamond substrate compared to only 140 for that on a silicon substrate.

Correlation of residual stress on piezoresistive properties of boron-doped diamond films

To investigate the influence of residual stress on the piezoresistive behavior of boron-doped diamond (BDD) films, BDD films with varying doping concentrations were synthesized using a hot-filament chemical vapor deposition (HFCVD) system on silicon and diamond substrates. The relationship between the surface morphology, structural composition, resistivity, and piezoresistive properties of BDD electrodes was examined, along with an in-depth analysis of the impact of boron doping level on these properties. The microstructure and bonding state of the BDD films were characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM), and Raman spectroscopy. The piezoresistive properties of the BDD films were evaluated employing a cantilever beam bending method. Our findings demonstrate that the level of boron doping not only affects resistivity but also directly influences residual stress in BDD films, both factors having an impact on their piezoresistive properties. Despite significantly larger grain sizes observed in BDD films grown on diamond substrates compared to those grown on silicon substrates at identical boron doping concentrations, they exhibit consistent variations in residual stress and gauge factor (GF) values. With increasing doping levels, the absolute residual stress decreases initially before increasing again; moreover, at 2000 ppm doping level, it transitions from compressive to tensile stress. The GF value is closely associated with both the magnitude and type of residual stress. By utilizing a doping concentration of 2000 ppm for growth on diamond substrates, we achieved a peak GF value of 257 for BDD films which highlights their promising potential for pressure sensor applications.

Preparation of aerogels with SBS@rGO structure by Pickering emulsion method for innovative applications in pressure sensors

Pressure sensors based on graphene conductive fillers show great promise for application in the field of smart wearable devices. The SBS@rGO structured aerogel sensors covered herein were prepared by the Pickering emulsion method based on a solution of styrene-butadiene-styrene (SBS) and reduced graphene oxide (rGO) dispersion. The mechanical properties of SBS@rGO aerogel were tested with 100 independent loading-unloading cycles in a graded compressive strain range of 10–40 %. The results indicate that the SBS@rGO aerogel have fast and slightly destructive resilience after unloading at low compressive strains (ε ≤ 30 %). Moreover, the presence of rGO endowed SBS@rGO with pressure sensing properties such as high electrical conductivity (2.294 S/m), high sensitivity (0.016 kPa−1 at 6.36–100 kPa), short signal response time (60 ms) and recovery time (30 ms). The SBS@rGO pressure sensors were integrated into shoe soles to simulate walking scenes, whose response signals had excellent reproducibility and could be differentiated according to three different walking states. The potential and feasibility of SBS@rGO aerogel as wearable flexible pressure sensors has been demonstrated.

Graphene‐Based Pressure Sensor Application in Non‐Invasive Pulse Wave Velocity Continuous Estimation

Graphene‐Based Pressure Sensor Application in Non‐Invasive Pulse Wave Velocity Continuous Estimation

Flexible and transparent leaf-vein electrodes fabricated by liquid film rupture self-assembly AgNWs for application of heaters and pressure sensors

The leaf veins with hierarchically interconnected network structures have great potential as self-assembly templates for transparent and flexible electrodes. In this paper, a liquid membrane ruptured assisted AgNWs self-assembly method was adopted to obtain conductive veins, which show a low sheet resistance of 3.6Ω/□ and a high transparency of 79 % at a minimal materials waste. The figure of merit of conductive veins was as high as 433Ω-1 and can be further increased by increasing the number of soaking because the light transmittance is nearly immune to the AgNWs layer number. The veins maintained a good electrical conductivity even after bending 10,000 times at a 2 mm radius of curvature and exhibited a good corrosion resistance under harsh conditions. Heaters based on the conductive veins are shown as application examples. A high temperature of 104 °C was achieved at a low voltage of 2 V, which is enough to heat cold water. They still have good heating properties even in the bending state or tensile state. Furthermore, pressure sensors based on the conductive veins were fabricated as examples of wearable devices. The sensor exhibits a high sensitivity of 3.8 kPa−1 in the low-pressure range (0–15 kPa) and 17.4 kPa−1 in the high pressure range (15–50.96 kPa). It can monitor human actions such as finger bending, finger taping, throat swallowing and wrist pulse in real-time, which has promising potential for motion monitoring and information encryption applications.

AgNPs/CNTs modified nonwoven fabric for PET-based flexible interdigitated electrodes in pressure sensor applications

Intelligent wearable sensing technology plays a pivotal role in the era of the Internet of Things and artificial intelligence, especially for human–machine interaction, physiological monitoring, and intelligent robotics. However, achieving a wide sensing range, high sensitivity, and ultra-long durability in pressure sensors while maintaining a simple and cost-effective fabrication remains challenging. This study presents a novel pressure sensor using silver nanoparticles (AgNPs) and carbon nanotubes (CNTs) modified nonwoven fabric for polyethylene terephthalate (PET) flexible interdigitated electrodes (IDEs). A low-cost spray-coating method was employed to deposit AgNPs/CNTs onto nonwoven fabric as the sensing layer, which was then combined with PET-based IDEs and encapsulated using polyimide (PI) film. The resulting piezoresistive sensor exhibits an extensive sensing range up to 90 kPa, high sensitivity up to 20 kPa−1 within 0–2 kPa, rapid response/recovery times (48 ms/44 ms), and outstanding repeatability over 6000 cycles. It can be assembled into an electronic skin tactile sensor array for mapping tactile size and orientation, and integrated into clothing for real-time monitoring of physiological signals like pulse, heartbeat, and grasp force. This work proposes a novel approach for developing wearable, highly sensitive, and wide-ranging pressure sensors, showing potential for multifunctional applications in next-generation artificial electronic skin, personal health monitoring, intelligent robotics, and human–machine interaction.

Enhancing self-induced polarization of PVDF-based triboelectric film by P-doped g-C3N4 for ultrasensitive triboelectric pressure sensors

Progress in wearable energy devices has reached the point of popularity over a few decades, as reflected by the rise of numerous sensors and storage devices driven by the urgent need for Internet of Things (IoT) applications. Triboelectric sensor (TES), on the basis of triboelectric nanogenerators (TENGs), exhibits high sensitivity and stability for pressure detection. Maximizing the sensitivity of the TES hinges upon the triboelectric layer selection capable of harnessing triboelectrification and electrostatic induction. Among them, PVDF has gained attention owing to its exceptional flexibility and tribo-negativity. However, the multiphase of pristine PVDF poses challenges, limiting its potential for TES with higher sensitivity. Tackling this issue, herein, we introduced phosphorus-doped graphitic carbon nitride (PCN) into the PVDF films to achieve self-induced polarization to enhance the sensitivity of the triboelectric pressure sensor. Through a controlled annealing temperature, phosphorus atoms are incorporated into the g-C3N4 (CN) matrix, enhancing the electronegativity of PVDF/PCN composite film while inducing a polarized β crystal phase in PVDF, thereby enabling greater attraction of positive charges. Consequently, the triboelectric output with PVDF/PCN composite film exhibited a significant improvement compared to the pristine PVDF film, achieving over a 100 V increment and the ability to power more than 100 LEDs. Furthermore, for the pressure-sensing applications, the TES with flexible PVDF/PCN triboelectric film exhibits a pressure sensitivity of 1.48 V/kPa, which shows a threefold increase in sensitivity compared to the pristine PVDF film (0.51 V/kPa), suggesting their great potential in self-powered wearable pressure sensors.

Innovative fabrication of ultrasensitive and durable graphene fiber aerogel for flexible pressure sensors

Elastic graphene aerogels have promising applications in flexible pressure sensors. However, it is still difficult to prepare graphene aerogels with high sensitivity and reliable mechanical stability due to the challenge in structural regulation. This study proposes an innovative method for preparing graphene aerogel by combining wet-electrospinning and freeze-drying. The resultant is a cotton-like 3D graphene fiber aerogel (GFA) with soft exterior but firm essence. The aerogel assembled of randomly stacked 1D graphene fiber, exhibiting softness and low compressive strength, thus ensuring the highly sensitive. Furthermore, this graphene fiber possessing strong mechanical properties after high-temperature thermal annealing, guarantees the fatigue resistance and elasticity of the aerogel. Therefore, the assembled GFA-based pressure sensor is ultrasensitive with a high sensitivity of 18.55 kPa−1 and a low detection limit of 2 Pa. Additionally, it has a rapid response time of 2 ms and maintains good stability even after 3000 cycles. The exceptional properties of GFA suggest its immense potential for application in human health monitoring and motion detection. In addition, the wet-electrospinning preparation of GFA provides a new strategy for the fabrication of graphene aerogels.

Pushing Pressure Detection Sensitivity to New Limits by Modulus-Tunable Mechanism.

Only microstructures are used to improve the sensitivity of iontronic pressure sensors. By modulating the compressive modulus, a breakthrough in the sensitivity of the iontronic pressure sensor is achieved. Furthermore, it allows for programmatic tailoring of sensor performance according to the requirements of different applications. Such a new strategy pushes the sensitivity up to a record-high of 25548.24kPa-1 and expands the linear pressure range from 15 to 127kPa. Additionally, the sensor demonstrates excellent mechanical stability over 10000 compression-release cycles. Based on this, a well-controlled robotic hand that precisely tracks the pressure behavior inside a balloon to autonomously regulate the gripping angle is developed. This paves the way for the application of iontronic pressure sensors in precise sensing scenarios.

Highly Sensitive Biomimetic Crack Pressure Sensor with Selective Frequency Response.

High-sensitivity sensors in practical applications face the issue of environmental noise interference, requiring additional noise reduction circuits or filtering algorithms to improve the signal-to-noise ratio (SNR). To address this issue, this study proposes a biomimetic crack pressure sensor with selective frequency response based on hydrogel dampers. The core of this research is to construct a biomimetic crack pressure sensor with selective frequency response using the high-pass filtering characteristics of gelatin-chitosan hydrogels. This design, inspired by the slit sensilla and stratum corneum structure of spider legs, delves into the material properties and principles of hydrogel dampers, exploring their application in biomimetic crack pressure sensors, including parameter selection, structural design, and performance optimization. By delving into the nuanced characteristics and working principles of hydrogel dampers, their integration in biomimetic crack pressure sensors is examined, focusing on aspects like parameter selection, structural engineering, and performance enhancement to selectively sieve out low-frequency noise and transmit target vibrational signals. Experimental results demonstrate that this innovative sensor, while suppressing low-frequency vibration signals, can selectively detect high-frequency signals with high sensitivity. At different vibration frequencies, the relative change in resistance exceeds 200%, and the sensor sensitivity is 7 × 104 kPa-1. Furthermore, this sensor was applied to human voice detection, and the corresponding results verified its frequency-selective performance evidently. This study not only proposes a new design for pressure sensors but also offers fresh insights into the application of biomimetic crack pressure sensors in intricate environments.

Additively Manufactured Stress-strain Dependant Frequency Reconfigurable Antenna for Pressure Sensor Applications

A novel additive-manufactured antenna for stretchable sensor application is designed, simulated and measured. The fully transparent antenna has air as a substrate and a conductive aluminium metal sheet as a patch. The layers are defined with thin Thermo Poly Urethane (TPU) material, as its flexible/stretchable property doesn't disturb the actual property of air. The air substrate is locked within the flexible TPU with a thickness of 200 microns, and the conducting patch is also dimensioned with the 3D printing method. The stretchable antenna is fabricated with 3D printing technology, considered a dielectric medium, and the conducting medium is a conducting aluminium sheet. Re-configurability is achieved with the pressure level applied over the air–substrate antenna. Hence, the minimal change in shape changes the dielectric constant, thus changing the antenna parameter and radiation pattern. The antenna achieves improved size and performance with a gain of 7.2 dB, a directivity of 7.574 dB, a radiation efficiency of 95.67 %, and a 12:509 front-to-back ratio. The fabricated antenna is tested for its resonant characteristics and radiation properties. This reconfigurable antenna can be used for various applications, including Wireless Local Area Network (WLAN) communication.

Single-Crystalline LiNbO₃ Film-Based Piezoelectric Sensors for Ultra-Precision Pressure-Sensing Applications

Single-Crystalline LiNbO₃ Film-Based Piezoelectric Sensors for Ultra-Precision Pressure-Sensing Applications