Fabrication Of Pressure Sensor Research Articles

An E-Textile Respiration Sensing System for NICU Monitoring: Design and Validation.

The world is witnessing a rising number of preterm infants who are at significant risk of medical conditions. These infants require continuous care in Neonatal Intensive Care Units (NICU). Medical parameters are continuously monitored in premature infants in the NICU using a set of wired, sticky electrodes attached to the body. Medical adhesives used on the electrodes can be harmful to the baby, causing skin injuries, discomfort, and irritation. In addition, respiration rate (RR) monitoring in the NICU faces challenges of accuracy and clinical quality because RR is extracted from electrocardiogram (ECG). This research paper presents a design and validation of a smart textile pressure sensor system that addresses the existing challenges of medical monitoring in NICU. We designed two e-textile, piezoresistive pressure sensors made of Velostat for noninvasive RR monitoring; one was hand-stitched on a mattress topper material, and the other was embroidered on a denim fabric using an industrial embroidery machine. We developed a data acquisition system for validation experiments conducted on a high-fidelity, programmable NICU baby mannequin. We designed a signal processing pipeline to convert raw time-series signals into parameters including RR, rise and fall time, and comparison metrics. The results of the experiments showed that the relative accuracies of hand-stitched sensors were 98.68 (top sensor) and 98.07 (bottom sensor), while the accuracies of embroidered sensors were 99.37 (left sensor) and 99.39 (right sensor) for the 60 BrPM test case. The presented prototype system shows promising results and demands more research on textile design, human factors, and human experimentation.

Sensing Social Behavior With Smart Trousers

Nonverbal signals play an important role in social interaction. Body orientation, posture, hand, and leg movements all contribute to successful communication, though research has typically focused on cues transmitted from the torso alone. Here, we explore lower body movements and address two issues. First, the empirical question of what social signals they provide. Second, the technical question of how these movements could be sensed unintrusively and in situations where traditional methods prove challenging. To approach these issues, we propose a soft, wearable sensing system for clothing. Bespoke “smart” trousers with embedded textile pressure sensors are designed and deployed in seated, multiparty conversations. Using simple machine learning techniques and evaluating individual and community models, our results show that it is possible to distinguish basic conversational states. With the trousers picking up speaking, listening, and laughing, they present an appropriate modality to ubiquitously sense human behavior.

Breathable Ti3C2Tx MXene/Protein Nanocomposites for Ultrasensitive Medical Pressure Sensor with Degradability in Solvents.

Flexible, breathable, and degradable pressure sensors with excellent sensing performance are drawing tremendous attention for various practical applications in wearable artificial skins, healthcare monitoring, and artificial intelligence due to their flexibility, breathability, lightweight, decreased electronic rubbish, and environmentally friendly impact. However, traditional plastic or elastomer substrates with impermeability, uncomfortableness, mechanical mismatches, and nondegradability greatly restricted their practical applications. Therefore, the fabrication of such pressure sensors with high flexibility, facile degradability, and breathability is still a critical challenge and highly desired. Herein, we present a wearable, breathable, degradable, and highly sensitive MXene/protein nanocomposites-based pressure sensor. The fabricated MXene/protein-based pressure sensor is assembled from a breathable conductive MXene coated silk fibroin nanofiber (MXene-SF) membrane and a silk fibroin nanofiber membrane patterned with a MXene ink-printed (MXene ink-SF) interdigitated electrode, which can serve as the sensing layer and the electrode layer, respectively. The assembled pressure sensor exhibits a wide sensing range (up to 39.3 kPa), high sensitivity (298.4 kPa-1 for 1.4-15.7 kPa; 171.9 kPa-1 for 15.7-39.3 kPa), fast response/recovery time (7/16 ms), reliable breathability, excellent cycling stability over 10 000 cycles, good biocompatibility, and robust degradability. Furthermore, it shows great sensing performance in monitoring human psychological signals, acting as an artificial skin for the quantitative illustration of pressure distribution, and wireless biomonitoring in real time. Considering the biodegradable and breathable features, the sensor may become promising to find potential applications in smart electronic skins, human motion detection, disease diagnosis, and human-machine interaction.

Experimental study on the movement characteristics of pedestrians under sudden contact forces

In crowd disasters, collision among pedestrians is one of the main causes of crushing and trampling. However, in most controlled experiments, there is little physical contact among pedestrians, and microscopic human behaviors are less studied. Therefore, a series of controlled experiments where physical contact occurred were conducted to study the microscopic dynamics of a single pedestrian’s movement process and the transmission of impulse between two pedestrians. The impulse can be extracted from a flexible fabric pressure sensor that covers the pedestrian’s back. In the single-pedestrian experiment, the body postures and behaviors are analyzed. It is found that the impulse release distance increases as the impulse increases and the numerical linear relation is established to show the trend. The polynomial relation in the movement process is adopted and the numerical relations between speed, move distance and exerted impulse are established. In the two-pedestrian experiment, the transmission of impulse is studied. The transmission coefficient increases first and then decreases as the distance increases and the numerical rational relation is adopted to show the trend. The transmitted impulse increases as the exerted impulse increases in each distance and the numerical exponential relation is adopted. These equations can be used to study the impulse transmitted along the queue. The findings in this study can help us to understand pedestrian collision evacuation dynamics in a high-density crowd. Eventually, they could be used to assess the risk levels in local crowds and prevent crowd disasters involving trampling.

(Invited) Fabric Pressure Sensors for Longitudinal Monitoring of Human Motion in Natural Environments

Apparel with embedded self-powered sensors can revolutionize human behavior monitoring by leveraging everyday clothing as the sensing substrate. The key is to inconspicuously integrate sensing elements and portable power sources into garments while maintaining the weight, feel, comfort, function and ruggedness of familiar clothes and fabrics. We use reactive vapor coating to transform commonly-available, mass-produced fabrics, threads or premade garments into comfortably-wearable electronic devices by directly coating them with uniform and conformal films of electronically-active conjugated polymers. By carefully choosing the repeat unit structure of the polymer coating, we access a number of fiber- or fabric-based circuit components, including resistors, depletion-mode transistors, diodes, thermistors, and pseudocapacitors. Further, vapor-deposited electronic polymer films are notably wash- and wear-stable and withstand mechanically-demanding textile manufacturing routines, enabling us to use sewing, weaving, knitting or embroidery procedures to create self-powered garment sensors. We will describe our efforts in monitoring heartrate, breathing, joint motion/flexibility, gait and sleep posture using loose-fitting garments.

Recent Progress in Development of Wearable Pressure Sensors Derived from Biological Materials.

This review summarizes recent progress in the use of biological materials (biomaterials) in wearable pressure sensors. Biomaterials are abundant, sustainable, biocompatible, and biodegradable. Especially, many have sophisticated hierarchical structure and biological characteristics, which are attractive candidates for facile and ecologically-benign fabrication of wearable pressure sensors that are biocompatible, biodegradable, and highly sensitivity. The biomaterials and structures that use them in wearable pressure sensors that exploit sensing mechanisms such as piezoelectric, triboelectric, piezoresistive and capacitive effects are present. Finally, remaining impediments are discussed to use of biomaterials in wearable pressure sensors.

Advance on flexible pressure sensors based on metal and carbonaceous nanomaterial

As an indispensable and prevailing kind of flexible sensors, pressure sensors have been extensively used in the field of flexible electronics. To enhance the performance and broaden the applications of flexible pressure sensors, emerging nanomaterials with excellent electromechanical properties have been explored and developed over recent years. Herein, the latest progresses in flexible pressure sensors based on metal and carbonaceous nanomaterial are reviewed in this paper. Firstly, fundamental considerations of pressure sensors including transduction principles, evaluation parameters and nano-micro structures are presented. Furthermore, flexible pressure sensors based on carbonaceous nanomaterials, transition metal carbides and carbonitrides (Mxene), along with metal nanomaterials are reviewed and classified by different transduction principles. At last, a number of applications on electronic skin (E-skin) involving metal and carbonaceous nanomaterial-based flexible pressure sensors are introduced, including pressure distribution sensing, force direction detection, multifunctional sensing and system integration. • Latest progresses on flexible pressure sensors based on metal and carbonaceous nanomaterials are reviewed elaborately. • Fundamental consideration, device structure, and E-skin application of nanomaterial-based pressure sensors are summarized. • This review should have considerable reference value for design, fabrication and development of flexible pressure sensors.

Fabrication of Pressure Sensor Using Electrospinning Method for Robotic Tactile Sensing Application.

Tactile sensors are widely used by the robotics industries over decades to measure force or pressure produced by external stimuli. Piezoelectric-based pressure sensors have intensively been investigated as promising candidates for tactile sensing applications. In contrast, piezoelectric-based pressure sensors are expensive due to their high cost of manufacturing and expensive base materials. Recently, an effect similar to the piezoelectric effect has been identified in non-piezoelectric polymers such as poly(d,l-lactic acid (PDLLA), poly(methyl methacrylate) (PMMA) and polystyrene. Hence investigations were conducted on alternative materials to find their suitability. In this article, we used inexpensive atactic polystyrene (aPS) as the base polymer and fabricated functional fibers using an electrospinning method. Fiber morphologies were studied using a field-emission scanning electron microscope and proposed a unique pressure sensor fabrication method. A fabricated pressure sensor was subjected to different pressures and corresponding electrical and mechanical characteristics were analyzed. An open circuit voltage of 3.1 V was generated at 19.9 kPa applied pressure, followed by an integral output charge (ΔQ), which was measured to calculate the average apparent piezoelectric constant dapp and was found to be 12.9 ± 1.8 pC N−1. A fabricated pressure sensor was attached to a commercially available robotic arm to mimic the tactile sensing.

Amalgamation‐Assisted Lithography: Amalgamation‐Assisted Control of Profile of Liquid Metal for the Fabrication of Microfluidic Mixer and Wearable Pressure Sensor (Adv. Mater. Interfaces 10/2021)

In article number 2100038, Sheng Yan and co-workers present a simple and straightforward amalgamation-assisted method for creating liquid metal droplets and microdomes with highly controllable sizes. The microdome can generate the vortices, enhancing the flow mixing inside the microfluidic channel. Besides, the microdomes are patterned on the surface of stretchable conductive composites to develop a flexible and sensitive pressure sensor.

Highly Sensitive Porous PDMS-Based Capacitive Pressure Sensors Fabricated on Fabric Platform for Wearable Applications.

A novel porous polydimethylsiloxane (PDMS)-based capacitive pressure sensor was fabricated by optimizing the dielectric layer porosity for wide-range pressure sensing applications in the sports field. The pressure sensor consists of a porous PDMS dielectric layer and two fabric-based conductive electrodes. The porous PDMS dielectric layer was fabricated by introducing nitric acid (HNO3) into a mixture of PDMS and sodium hydrogen bicarbonate (NaHCO3) to facilitate the liberation of carbon dioxide (CO2) gas, which induces the creation of porous microstructures within the PDMS dielectric layer. Nine different pressure sensors (PS1, PS2,..., PS9) were fabricated in which the porosity (pore size, thickness) and dielectric constant of the PDMS dielectric layers were varied by changing the curing temperature, the mixing proportions of the HNO3/PDMS concentration, and the PDMS mixing ratio. The response of the fabricated pressure sensors was investigated for the applied pressures ranging from 0 to 1000 kPa. A relative capacitance change of ∼100, ∼323, and ∼485% was obtained by increasing the curing temperature from 110 to 140 to 170 °C, respectively. Similarly, a relative capacitance change of ∼170, ∼282, and ∼323% was obtained by increasing the HNO3/PDMS concentration from 10 to 15 to 20%, respectively. In addition, a relative capacitance change of ∼94, ∼323, and ∼460% was obtained by increasing the PDMS elastomer base/curing agent ratio from 5:1 to 10:1 to 15:1, respectively. PS9 exhibited the highest sensitivity over a wide pressure sensing range (low-pressure ranges (<50 Pa), 0.3 kPa-1; high-pressure ranges (0.2-1 MPa), 3.2 MPa-1). From the results, it was observed that the pressure sensors with dielectric layers prepared at relatively higher curing temperatures, higher HNO3 concentrations, and higher PDMS ratios resulted in increased porosity and provided the highest sensitivity. As an application demonstrator, a wearable fit cap was developed using an array of 16 pressure sensors for measuring and mapping the applied pressures on a player's head while wearing a helmet. The pressure mapping aids in observing and understanding the proper fit of the helmet in sports applications.

Design and Fabrication of a New Wearable Pressure Sensor for Blood Pressure Monitoring.

In recent years, research into the field of materials for flexible sensors and fabrication techniques directed towards wearable devices has helped to raise awareness of the need for new sensors with healthcare applicability. Our goal was to create a wearable flexible pressure sensor that could be integrated into a clinically approved blood pressure monitoring device. The sensor is built from a microfluidic channel encapsulated between two polymer layers, one layer being covered by metal transducers and the other being a flexible membrane containing the microfluidic channel, which also acts as a sealant for the structure. The applied external pressure deforms the channel, causing changes in resistance to the microfluidic layer. Electrical characterization has been performed in 5 different configurations, using alternating current (AC) and (DC) direct current measurements. The AC measurements for the fabricated pressure sensor resulted in impedance values at tens of hundreds of kOhm. Our sensor proved to have a high sensitivity for pressure values between 0 and 150 mm Hg, being subjected to repeatable external forces. The novelty presented in our work consists in the unique technological flow for the fabrication of the flexible wearable pressure sensor. The proposed miniaturized pressure sensor will ensure flexibility, low production cost and ease of use. It is made of very sensitive microfluidic elements and biocompatible materials and can be integrated into a wearable cuffless device for continuous blood pressure monitoring.

Fabrication of capacitive pressure sensor with extraordinary sensitivity and wide sensing range using PAM/BIS/GO nanocomposite hydrogel and conductive fabric

Herein, a flexible and robust hydrogel, polyacrylamide hydrogel containing graphene oxide and N, N-isopropyl di-acrylamide, was developed through a novel in-situ synthesis procedure. A high-sensitive capacitive pressure sensor was then fabricated through an assembly of the hydrogel wrapped by an insulated ultra-thin polyethylene film as the primary dielectric, and two soft-plated woven fabrics as conductive layers. The nanocomposite (NC) hydrogel displayed superior strength and resilience that the breaking strength and elongation at break are close to 45 kPa and 2110%, and a 50% cyclic compressive strain for 50 times along with a compressive strength of 84.17 kPa was exhibited, implying NC-hydrogel was ideal. The sensitivity of the as-made capacitive pressure sensor reached incredibly up to 2.6; the sensing range was available from 0 ~ 80%. Consequently, this conductive pressure sensor is profoundly high-potential for capturing some slight limbs' movements and strain in response to even the slightest amounts of pressure.

Flexible M-Tooth Hybrid Micro-Structure-Based Capacitive Pressure Sensor With High Sensitivity and Wide Sensing Range

A novel flexible capacitive pressure sensor based on hybrid micro-structured (HM) polydimethylsiloxane (PDMS) dielectric layer was developed. The HM-PDMS with M-tooth structured patterns was fabricated using a laser engraved acrylic master mold. The top and bottom electrodes were fabricated by depositing silver (Ag) on flexible polyethylene terephthalate (PET) substrate using additive screen-printing process. The pressure sensor was assembled by sandwiching two HM-PDMS based dielectric layers between the top and bottom electrodes. The capability of the developed pressure sensor to detect a wide range of pressure was investigated by applying varying pressure from 0 to 1 kPa, 1 to 10 kPa, and 10 kPa to 40 kPa. A sensitivity of 51.36% kPa-1, 8.37% kPa-1, and 2.46% kPa-1 was obtained for the pressure ranges of 0 to 1 kPa, 1 to 10 kPa, and 10 to 40 kPa, respectively. The capacitive pressure sensor response, hysteresis, and repeatability of the fabricated pressure sensor is investigated and presented in this paper. To demonstrate the wide sensing range of the pressure sensor, the sensor was attached to face mask for breath monitoring applications that require low pressure sensing of ~20 Pa, and to the hand glove for fingertip pressure monitoring applications that require relatively high pressure sensing of ~3 kPa.

Amalgamation‐Assisted Control of Profile of Liquid Metal for the Fabrication of Microfluidic Mixer and Wearable Pressure Sensor

AbstractThe presence of microdomes can significantly increase the surface roughness, contact area, and deformability of materials, which have been adopted in many fields including microfluidics, wearable devices, and microanalysis systems. However, the shape of liquid metal (LM) droplet is defined by the density and surface energy, which has very limited room to tune. In this work, a simple, low‐cost method to effectively control the profile of LM using the masked amalgamation is presented. The LM amalgamates the masked copper surface to create the complex microdomes with various aspect ratios, sizes, profiles, and structures. The concave dome replicated from the LM mold has been demonstrated to enhance the microfluidic mixing performance. With a pattern transfer technique, the microconvex domes can be patterned on the surface of stretchable conductive composites to develop a flexible and sensitive pressure sensor. This sensor exhibits a fast response time, a wide working range, and an enhanced sensitivity for detecting small strains. As such, the fabricated microdomes exhibit a great potential to enable the fabrication of high‐performance sensors, microfluidic platforms, and micro total analysis systems.

High-performance textile piezoelectric pressure sensor with novel structural hierarchy based on ZnO nanorods array for wearable application

With the increasing demand for smart wearable clothing, the textile piezoelectric pressure sensor (T-PEPS) that can harvest mechanical energy directly has attracted significant attention. However, the current challenge of T-PEPS lies in remaining the outstanding output performance without compromising its wearing comfort. Here, a novel structural hierarchy T-PEPS based on the single-crystalline ZnO nanorods are designed. The T-PEPS is constructed with three layers mode consisting of a polyvinylidene fluoride (PVDF) membrane, the top and bottom layers of conductive rGO polyester (PET) fabrics with self-orientation ZnO nanorods. As a result, the as-fabricated T-PEPS shows low detection limit up to 8.71 Pa, high output voltage to 11.47 V and superior mechanical stability. The sensitivity of the sensor is 0.62 V·kPa−1 in the pressure range of 0–2.25 kPa. Meanwhile, the T-PEPS is employed to detect human movements such as bending/relaxation motion of the wrist, bending/stretching motion of each finger. It is demonstrated that the T-PEPS can be up-scaled to promote the application of wearable sensor platforms and self-powered devices.

Reliable sensors based on graphene textile with negative resistance variation in three dimensions

The weft-knitted reduced graphene oxide (r-GO) textile that is made up of many conductive r-GO coated fibers was successfully prepared dependent on the electrospray deposition technique. Interestingly, the r-GO textile presents negative resistance variation not only in axial direction as the pressure increases but also in transverse direction as the lateral stretch increases which makes it has the advantage to fabricate the reliable sensors based on strain-resistance effect. The transverse-strain and pressure sensors based on the r-GO textiles all show the excellent sensing characteristics such as high sensitivity, reliability, and good durability, etc. The maximum gauge factors (GF) of the transverse-sensor are 27.1 and 153.5 in the x- and y-direction, respectively. And the practical detection range can up to 40% in the x-direction and 35% in the y-direction, respectively. The r-GO textile pressure sensor also shows high sensitivity for a broad pressure range that with a GF up to 716.8 kPa−1 for less than 4.5 kPa region and still has more sensitive pressure sensing characteristics even the pressure goes up to 14 kPa. Based on those good performances of r-GO textile sensors, its potential applications in human body states monitoring have been studied.

Highly sensitive, flexible, green synthesized graphene/biomass aerogels for pressure sensing application

With the advent of the Internet-of-Things (IoT) age, flexible sensors are highly desired in various intelligent systems. However, most of them are based on petrochemical materials and the inevitable use of toxic chemicals during their manufacturing, which may lead to potential damage to human health. Herein, we report a green and facile strategy to fabricate pressure sensors based on bacteria cellulose and caffeic acid-reduced graphene oxide (rGO) composite aerogel. Benefiting from the three-dimensional (3D) hierarchical porous structure (a porosity of ~98.9%), the pressure aerogel sensor exhibits integrated performance of high sensitivity (13.89 kPa−1), ultralow limit of detection (47.2 Pa), and fast response (120 ms), thus clearly detecting subtle strain and monitoring human physical motions. Remarkably, the aerogel possesses excellent reproducibility in 1000 cycles of pressure loading-unloading. Hence, the strategy of using natural resources to fabricate flexible functional materials is highly possible to apply in flexible electronics field.

Wearable pressure sensor based on MXene/single-wall carbon nanotube film with crumpled structure for broad-range measurements

High-performance flexible pressure sensors are attracting great interest owing to their potential applications for electronic skins, human–machine interfaces, and biomedical diagnostics. However, there remain significant challenges for the fabrication of low-cost and high-sensitivity sensors. Here, we report the preparation of Ti3C2T x MXene/single-wall carbon nanotube (SWNT) composite films through vacuum-assisted filtration followed by thermal shrinkage. SWNTs can effectively prevent MXenes from stacking and improve the electrical performance of the films. The films are used as a flexible piezoresistive sensor for pressures ranging from 33 Pa to 130 kPa. And experimental test results indicate that the fabricated pressure sensors have high sensitivity (116.15 kPa−1 below 40 kPa and 12.7 kPa−1 at 40–130 kPa), a fast response time of 13 ms, and long-term stability over 6000 periods. The sensor can be used to monitor human physiological signals, such as finger movements, voice detection, and wrist pulse in real-time. Moreover, a 4 × 4 sensor array was successfully applied in the pressure distribution mapping of different objects, indicating that the pressure sensor can be applied in electronic skin, medical devices, and other wearable devices.

Design and development of GMR based low range pressure sensor for medical ventilator application

In this report, we present a thermally compensated low range magnetic pressure sensor. The fabricated sensor consists of a corrugated stainless steel (SS) diaphragm, a permanent magnet, a giant magnetoresistance (GMR) sensor, and a signal conditioning unit. The diaphragm with a permanent magnet produces a magnetic field which changes under the exposure of external pressure. The GMR sensor is placed asymmetrically with reference to the cylindrical axis of a magnet, which results in an output voltage proportional to external pressure. Simulations were performed to optimize the design having a linear output with higher sensitivity of the order of 14.97 μV/V/mbar, which is close to the experimentally measured value of 13 μV/V/mbar at room temperature. The sensor prototypes were fabricated in pressure ranges: ± 30 and ± 70 mbar. The fabricated pressure sensor prototypes were tested in different temperature ranges and calibrated for offset, linearity, and thermal variations using a commercial sensor signal conditioner. The performance of the calibrated sensors was evaluated at different temperatures and over an extended period. Furthermore, the performance of the sensor was experimentally evaluated in an indigenously developed medical ventilator, and compared with an existing commercial MEMS pressure sensor for a longer duration. The performance of the prototype sensor was found to be equivalent with an accuracy of ±0.1 mbar for an operation in the range of ± 30 mbar.

DAid pressure socks system: Performance evaluation

BackgroundPlantar pressure measurement has been proven to produce crucial information for gait analysis. Socks with integrated textile pressure sensors are a promising tool for non-obtrusive plantar pressure acquisition and monitoring. Research questionCan the DAid Pressure Socks System be employed for the measurement of plantar pressure and temporal parameters during walking? MethodPlantar pressure measurement was acquired simultaneously by the DAid Pressure Socks System (DPSS) and Pedar® insole measurement system for a normal walking gait of 17 volunteers. The measurement from both systems was processed and gait temporal parameters were calculated. The calculated temporal parameters included stride time, step time, stance time, swing time, single support time, double support time, and cadence. The Intraclass Correlation Coefficient (ICC) was calculated to evaluate the agreement between the plantar pressure measurement and temporal parameters obtained from both systems. ResultsFor plantar pressure measurement, excellent agreement (ICC > 0.90) was achieved in approximately 23 % cases, while in roughly 37 %, 27 %, and 13 % cases the agreement was good (ICC > 0.75), moderate (ICC > 0.50), and poor (ICC < 0.50), respectively. The mean relative differences (as a percentage) between the temporal parameter values calculated from the measurement of both systems were 0.80 % (stride time), 3.06 % (step time), 3.15 % (stance time), 5.08 % (swing time / opposite single support time), 14.47 % (double support time), and 0.78 % (cadence). SignificanceThe ICC result calculated for the plantar pressure measurement indicated a reasonable agreement between both systems. Additionally, the relatively low mean difference was observed for 5 out of 6 calculated temporal gait parameters. Consequently, the presented DPSS could be considered as a substitute for the commercial gait analysis tools for applications that do not require great accuracy of the absolute plantar pressure measurement.