Pressure Sensor Research Articles

Thiol Coordination Softens Liquid Metal Particles To Improve On-Demand Conductivity.

Achieving tunable rupturing of eutectic gallium indium (EGaIn) particles holds great significance in flexible electronic applications, particularly pressure sensors. We tune the mechanosensitivity of EGaIn particles by preparing them in toluene with thiol surfactants and demonstrate an improvement over typical preparations in ethanol. We observe, across multiple length scales, that thiol surfactants and the nonpolar solvent synergistically reduce the applied stress requirements for electromechanical actuation. At the nanoscale, dodecanethiol and propanethiol in toluene suppress gallium oxide growth, as characterized by transmission electron microscopy and X-ray photoelectron spectroscopy. Quantitative AFM imaging produces force-indentation curves and height images, while conductive AFM measures current while probing individual EGaIn particles. As the applied force increases, thiolated particles demonstrate intensified softening, rupturing, and stress-induced electrical activation at forces 40% lower than those for bare particles in ethanol. To confirm that thiolation facilitates rupturing at the macroscale, a laser is used to ablate samples of EGaIn particles. Scanning electron microscopy and resistance measurements across macroscopic samples confirm that thiolated EGaIn particles coalesce to exhibit electrical activation at 0.1 W. Particles prepared in ethanol, however, require 3 times higher laser power to demonstrate a similar behavior. This unique collection of advanced techniques demonstrates that our particle synthesis conditions can facilitate on-demand functionality to benefit electronic applications.

Biodegradable polylactic acid emulsion ink based on carbon nanotubes and silver for printed pressure sensors

Investigating biodegradable and biocompatible materials for electronic applications can lead to tangible outcomes such as developing green-electronic devices and reducing the amount of e-waste. The proposed emulsion-based conducting ink formulation takes into consideration circular economy and green principles throughout the entire process, from the selection of materials to the production process. The ink is formulated using the biopolymer polylactic acid dissolved in a sustainable solvent mixed with water, along with conductive carbon nanotubes (CNTs) and silver flakes as fillers. Hybrid conductive fillers can lower the percolation threshold of the ink and the production costs, while maintaining excellent electrical properties. The coating formed after the deposition of the ink, undergoes isothermal treatment at different temperatures and durations to improve its adhesion and electrical properties. The coating’s performance was evaluated by creating an eight-finger interdigitated sensor using a Voltera PCB printer. The sensor demonstrates exceptional performance when exposed to various loading and unloading pressures within the 0.2–500.0 kPa range. The results show a consistent correlation between the change in electrical resistance and the stress caused by the applied load. The ink is biodegradable in marine environments, which helps avoiding its accumulation in the ecosystem over time.

Design and performance simulation of silica microdisk cavity optical pressure sensor

Design and performance simulation of silica microdisk cavity optical pressure sensor

Enhanced 3D indoor position estimation from smartphone’s inbuilt IMU and pressure sensor via hybrid approach

Enhanced 3D indoor position estimation from smartphone’s inbuilt IMU and pressure sensor via hybrid approach

Polyurethane-Encapsulated Biomass Films Based on MXene@Loofah Sponge for Piezoresistive Pressure Sensor Applications

Multifunctional wearable electronic sensors exhibit significant potential for applications in health management, motion tracking, intelligent healthcare, etc. In this study, we developed a novel assembly method for a polymeric silver nanowire (Ag NW)/transition metal carbide/nitride (MXene) @Loofah device using a facile solution dip-coating technique. During the pretreatment phase, the loofah was conditioned with polydiallyldimethylammonium chloride (PDAC), promoting the self-assembly of MXene layers and bolstering device stability. Then, the Ag NWs/MXene@Loofah was packaged with polyurethane to form a piezoresistive pressure sensor, which demonstrated superior pressure-sensing capabilities and was adept at registering movements of human joints and even subtle pulses. The design strategy presents a novel and rational approach to developing efficient pressure sensors.

The Effect of Arm Movements on the Dynamics of the Wheelchair Frame during Manual Wheelchair Actuation and Propulsion

Wheelchair propulsion and actuation are influenced by the moving masses of the wheelchair user; however, the extent of this effect is still unclear. The main evidence of this effect is that the speed of the wheelchair frame continues to increase after the end of the push phase. The wheelchair’s speed was measured using IMUs and the duration of the push period was recorded using miniaturised pressure sensors attached to the driver’s middle fingers. The velocity and acceleration were determined for various average stroke cycle speeds to determine the speed dependency of the acceleration. The wheelchair was then mounted on a force plate to measure the inertial forces of the hands moving back and forth. The aerodynamic drag and rolling resistance forces were determined from coast-down experiments. Based on the measured forces, the behaviour of the force and velocity profiles was finally modelled by gradually reducing the mass of the arms and thus their inertial force. The results showed that the wheelchair is accelerated throughout the push phase (except for a temporary deceleration in the middle of the push phase at higher velocities), and that this acceleration continues well after the push phase. In the second half of the recovery phase, the wheelchair decelerates. The horizontal inertial forces measured on the force plate are predominantly negative in the push phase and in the second half of the recovery phase, and positive in the first half of the push phase, and their impulse is zero due to the conservation of momentum. Modelling the wheelchair with moving masses showed that reducing the horizontal inertial forces has no effect on the driver’s propulsive force but reduces the velocity fluctuations. The main conclusion of this research is that the wheelchair user’s power should be calculated only from the pure propulsive force that is required in the push phase to overcome the dissipative forces and that enables the gain or loss in speed per stroke cycle, but not directly from the measured velocity.

A Sensorized 3D-Printed Knee Test Rig for Preliminary Experimental Validation of Patellar Tracking and Contact Simulation

Experimental validation of computational simulations is important because it provides empirical evidence to verify the accuracy and reliability of the simulated results. This validation ensures that the simulation accurately represents real-world phenomena, increasing confidence in the model’s predictive capabilities and its applicability to practical scenarios. The use of musculoskeletal models in orthopedic surgery allows for objective prediction of postoperative function and optimization of results for each patient. To ensure that simulations are trustworthy and can be used for predictive purposes, comparing simulation results with experimental data is crucial. Although progress has been made in obtaining 3D bone geometry and estimating contact forces, validation of these predictions has been limited due to the lack of direct in vivo measurements and the economic and ethical constraints associated with available alternatives. In this study, an existing commercial surgical training station was transformed into a sensorized test bench to replicate a knee subject to a total knee replacement. The original knee inserts of the training station were replaced with personalized 3D-printed bones incorporating their corresponding implants, and multiple sensors with their respective supports were added. The recorded movement of the patella was used in combination with the forces recorded by the pressure sensor and the load cells, to validate the results obtained from the simulation, which was performed by means of a multibody dynamics formulation implemented in a custom-developed library. The utilization of 3D-printed models and sensors facilitated cost-effective and replicable experimental validation of computational simulations, thereby advancing orthopedic surgery while circumventing ethical concerns.

Design and demonstration of a sensing network for full-scale wind pressure measurements on buildings

There is a need for full-scale wind pressure measurements to evaluate the accuracy of peak wind load estimates from wind tunnel measurements, numerical simulations, or building codes. The objective of this study was to design a sensing network for obtaining long-term records of fluctuating wind pressures, and to demonstrate the network’s potential through deployment. A custom data-logger using the BMP388 absolute pressure sensor, which can measure pressure coefficients within ±0.1 at a wind speed of 10 m/s, was designed. The accuracy of the measured statistics was established through comparison with a standard differential sensor in a wind tunnel experiment. A network of 10 motes was deployed on the sloped roof of the 184 m tall Space Needle, obtaining over 1000 h of fluctuating pressure data. The measurements reveal a windward separation region with strong dependency of the approach wind turbulence on the pressure statistics, but positive skewness limits the peak values. The skewness becomes negative near the edge of a second, leeward separation region, resulting in peak factors up to 2.6 times larger than the code-prescribed value of 3.4. The results demonstrate that long-term full-scale measurements provide valuable insight into peak wind pressures and their dependence on approach wind characteristics.

Flexible piezoelectric pressure sensor based on BaTiO3-CNT/RTV composite film with filter paper microstructures for monitoring hand motions

Flexible piezoelectric sensors are widely used in various applications such as physiological signal monitoring and human-computer interaction. The present study introduces a BaTiO3-CNT/RTV piezoelectric sensor fabricated using a filter paper template. It incorporates micro-scale fiber stacking and a 1% CNT doping in the microstructure, resulting in a notable enhancement of sensor sensitivity, increasing it from 0.07 V N−1 to 0.69 V N−1, representing an almost tenfold improvement. Furthermore, the study investigates the influence of affecting factors like the flexible substrate of the sensing film, thickness, and mass fractions of various materials on the output voltage. The sensor exhibits superior characteristics such as good repeatability under 5000 cyclic loads, high elongation at break, fast response (80 ms) and recovery times (90 ms), and good linearity. It also demonstrates outstanding sensitivity (12 mV/10°) when monitoring different finger bending states, enabling real-time, sensitive, and reliable hand motion tracking. This sensor holds promising prospects for future developments in the fields of intelligent grasping and sign language translation.

Sensitivity enhanced flexible capacitive pressure sensor microstructure optimization for biomedical applications

Abstract This paper explores the design and optimization of Flexible Capacitive Pressure Sensors (FCPS) using microfabrication technology for applications in the emerging field of flexible electronics, with a particular focus on measuring bio-signals characterized by lower pressure ranges. Sensitivity, a critical parameter for effective FCPS performance, is investigated through a comprehensive series of simulation analyses employing finite element modeling. The study involves varying geometrical and mechanical parameters that influence FCPS performance, individually adjusting each parameter while keeping others constant. Microstructures such as cuboids, truncated pyramids with an aspect ratio of 0.5, cylinders, pyramids, and cones are modeled on the dielectric material surface. The parameters considered include inter-space, base length, height, and elastic modulus, to enhance FCPS sensitivity and linearity. Among the different shapes modeled, the cone exhibits the highest sensitivity, followed by the pyramid structure. Comparative analysis indicates that the cone and pyramid shapes demonstrate 15- and 10-times higher sensitivity, respectively, compared to the cuboid structure under an applied pressure of 10 Pa. Simulation results suggest that sensitivity can be finely tuned, with higher inter-space and microstructure height, as well as lower base length and Young's modulus of the dielectric material, contributing to increased sensitivity. However, it is noted that these conditions may lead to decreased capacitance in the absence of applied pressure due to air occupation relative to the dielectric material. The findings are further compared with existing literature, and the FCPS response analysis provides valuable insights for the future design of FCPS, particularly in the context of biomedical applications requiring precise low-pressure signal measurements. This research contributes to advancing the understanding of FCPS performance optimization and lays the groundwork for the development of sensors with enhanced sensitivity for bio-medical applications.

A dual‐range Janus‐structure pressure sensor with broad detection range and high resolution combining triboelectricity and piezoelectricity

AbstractEnabling pressure sensors with high resolution and a broad detection range is of paramount importance yet challenging due to the limitations of each known sensing method. Overlying different sensing mechanisms to achieve complementary functions is a promising approach, but it often leads to increased device thickness, crosstalk signals and complex signal channel management. Herein, we present a dual‐functional conformable pressure sensor that adopts a Janus thin film layout, enabling simultaneous piezoelectric and triboelectric signal detection capabilities between just one electrode pair, showing a most compact device configuration. Notably, despite its thin thickness (~80 μm for a packaged device), it exhibits a broad‐range detection capability with high signal resolution and fast response time, demonstrating a distinct signal‐relay characteristic corresponding to piezoelectricity and triboelectricity. Despite the slimness and simple structure, it shows an impressive signal resolution of 0.93 V·kPa−1 in the range of 0.1–140 kPa and 0.05 V·kPa−1 in the range of 140–380 kPa. Moreover, the device fabrication can be combined with the kirigami method to improve fitting to joint surfaces. This work introduces an innovative paradigm for designing advanced pressure sensing mechanisms, enabling a single device that can meet diverse application scenarios through its simplicity, slim layout, conformable, and self‐powered characteristics to adapt to multiple scenarios.image

A Rational Design of Bio-Derived Disulfide CANs for Wearable Capacitive Pressure Sensor.

Classic approaches to integrate flexible capacitive sensor performance are to on-demand microstructing dielectric layers and to adjust dielectric material compositions via the introduction of insoluble carbon additives (to increase sensitivity) or dynamic interactions (to achieve self-healing). However, the sensor's enhanced performances often come with the increased material complexity, discouraging its circular economy. Herein, we introduce a new intrinsic self-healable, closed-loop recyclable dielectric layer material, a fully nature-derived dynamic covalent poly(disulfide) decorated with rich H bonding and metal-catechol complexations. The polymer network possesses a mechanically ductile character with an Arrhenius-like dependent viscoelasticity. The assembled capacitive pressure sensor is able to achieve a sensitivity up to 9.26 kPa-1, fast response/recovery times of 32/24ms, and could deliver consistent signals of continuous consecutive cycles even after being self-healed or closed-loop recycled for real-time detection of human motions. This is expected to be of high interest for current capacitive sensing research to move towards a life-like, high performance and circular economy direction. This article is protected by copyright. All rights reserved.

Pt/Zn-TCPP Nanozyme-Based Flexible Immunoassay for Dual-Mode Pressure-Temperature Monitoring of Low-Abundance Proteins.

Pressure and temperature, as common physical parameters, are important for monitoring human health. In contrast, single-mode monitoring is prone to causing experimental errors. Herein, we innovatively designed a dual-mode flexible sensing platform based on a platinum/zinc-meso-tetrakis(4-carboxyphenyl)porphyrin (Pt/Zn-TCPP) nanozyme for the quantitative monitoring of carcinoembryonic antigen (CEA) in biological fluids with pressure and temperature readouts. The Pt/Zn-TCPP nanozyme with catalytic and photothermal efficiencies was synthesized by means of integrating photosensitizers into porous materials. The flexible sensing system after the antigen-antibody reaction recognized the pressure using a flexible skin-like pressure sensor with a digital multimeter readout, whereas the temperature was acquired via the photoheat conversion system of the Pt/Zn-TCPP nanozyme under 808 nm near-infrared (NIR) irradiation using a portable NIR imaging camera on a smartphone. Meanwhile, the dual-mode flexible sensing system was carried out on a homemade three-dimensional (3D)-printed device. Results revealed that the developed dual-mode immunosensing platform could exhibit good pressure and temperature responses within the dynamic range of 0.5-100 ng mL-1 CEA with the detection limits of 0.24 and 0.13 ng mL-1, respectively. In addition, the pressure and temperature were sensed simultaneously without crosstalk interference. Importantly, the dual-mode flexible immunosensing system can effectively avoid false alarms during the measurement, thus providing great potential for simple and low-cost development for point-of-care testing.

Anti-Oxidized Self-Assembly of Multilayered F-Mene/MXene/TPU Composite with Improved Environmental Stability and Pressure Sensing Performances

MXenes, as emerging 2D sensing materials for next-generation electronics, have attracted tremendous attention owing to their extraordinary electrical conductivity, mechanical strength, and flexibility. However, challenges remain due to the weak stability in the oxygen environment and nonnegligible aggregation of layered MXenes, which severely affect the durability and sensing performances of the corresponding MXene-based pressure sensors, respectively. Here, in this work, we propose an easy-to-fabricate self-assembly strategy to prepare multilayered MXene composite films, where the first layer MXene is hydrogen-bond self-assembled on the electrospun thermoplastic urethane (TPU) fibers surface and the anti-oxidized functionalized-MXene (f-MXene) is subsequently adhered on the MXene layer by spontaneous electrostatic attraction. Remarkably, the f-MXene surface is functionalized with silanization reagents to form a hydrophobic protective layer, thus preventing the oxidation of the MXene-based pressure sensor during service. Simultaneously, the electrostatic self-assembled MXene and f-MXene successfully avoid the invalid stacking of MXene, leading to an improved pressure sensitivity. Moreover, the adopted electrospinning method can facilitate cyclic self-assembly and the formation of a hierarchical micro-nano porous structure of the multilayered f-MXene/MXene/TPU (M-fM2T) composite. The gradient pores can generate changes in the conductive pathways within a wide loading range, broadening the pressure detection range of the as-proposed multilayered f-MXene/MXene/TPU piezoresistive sensor (M-fM2TPS). Experimentally, these novel features endow our M-fM2TPS with an outstanding maximum sensitivity of 40.31 kPa−1 and an extensive sensing range of up to 120 kPa. Additionally, our M-fM2TPS exhibits excellent anti-oxidized properties for environmental stability and mechanical reliability for long-term use, which shows only ~0.8% fractional resistance changes after being placed in a natural environment for over 30 days and provides a reproducible loading–unloading pressure measurement for more than 1000 cycles. As a proof of concept, the M-fM2TPS is deployed to monitor human movements and radial artery pulse. Our anti-oxidized self-assembly strategy of multilayered MXene is expected to guide the future investigation of MXene-based advanced sensors with commercial values.

Observing And Characterizing Infragravity Waves Through Different Sampling Devices: A Case-Study Off The Belgian Coast

Infragravity waves are surface waves with relatively longer periods in comparison to periods of the spectrum-dominant gravity waves. They are characterized by oscillations between 20 and 300 seconds (0.0033 Hz < f < 0.05 Hz), amplitudes that range from a few millimeters to tens of centimeters, and wavelengths of kilometers (Munk, 1950; Holman and Bowen, 1982; Ardhuin et al., 2014). Their forcing is linked to, amongst others, nonlinear interaction between sea swell waves, varying wave heights causing the breaking point of the waves to vary with height, and height variation of incoming waves (Bertin et al., 2018). Infragravity waves play an important role in coastal dynamics (Svendsen, 2005) and have been reported to trigger nearshore hazards such as beach and dune erosion (de Vries et al. 2008; Roelvink et al., 2009), development of seiches in harbors (Melito et al., 2006; Cuomo and Guza, 2017), wave-driven coastal inundation (Gent, 2001; Stockdon et al., 2006), and ice shelves collapsing (Bromirski et al., 2010). Therefore, revealing infragravity wave characteristics is of utmost importance to understand their potential to generate hazards in a certain region, especially at sites strongly influenced by human occupation and activities. Their consideration in coastal safety planning can avoid damages, as several locations have already experienced in the past (Yamanaka et al., 2019). Implementing optimal sampling strategies for observing and characterizing infragravity waves might be challenging. By nature, these waves are hard to measure accurately due to their low amplitude. Their evolving characteristics in an environment marked by pronounced bathymetric features, such as the sand bank systems off the Belgian coast, add a degree of complexity that requires testing of different approaches, and at different sites. Within this context, this work first revisits observational approaches, instrumentation, logistics, and sampling techniques that have been used to study this phenomenon on the Belgian Coast. The advantages, challenges and limitations of different approaches are discussed, and best practices for collecting high-quality data in the field are addressed. To do so, this study explores multi-sensor in situ deployments conducted at four selected sites off the Belgian coast (Figure 1) (Nieuwpoort, Raversijde (inshore and offshore Stroombank), and Trapegeer) within the context of the “Influence of infragravity sea waves during storms on the hydro- and morphodynamic processes along hybrid soft-hard coastal defence structures with a shallow foreshore” project, an FWO-funded initiative being conducted in collaboration between UGent, VLIZ, and KULeuven and with support of Agency for Coastal and Maritime Services (AMDK). More specifically, field observations were conducted using multipurpose mooring frames equipped both with (i) Acoustic Doppler Current Profiles (ADCPs) to sample pressure (0.1% FS), current, and sea surface elevation through acoustic surface tracking and (ii) high-accuracy quartz pressure sensors (accuracy 0.01 % FS). Both ADCPs and pressure sensors were set to measure continuously at 4 Hz being, therefore, able to capture both infra- and gravity waves. Furthermore, the moorings were collocated with standard wave buoys from AMDK. Data was collected continuously for about 3 months, covering storm and calm wave conditions. Finally, the measurements from ADCPs (pressure and acoustic) and pressure sensors were compared and used to derive the infragravity wave characteristics, as well as cross-validated against wave buoy data.

A Novel Hollow Graphene/Polydimethylsiloxane Composite for Pressure Sensors with High Sensitivity and Superhydrophobicity.

Flexible pressure sensors have attracted great interest as they play an important role in various fields such as health monitoring and human-machine interactions. The design of the pressure sensors still faces challenges in achieving a high sensitivity for a wide sensing range, and the interference of water restricts the applications of the sensors. Herein, we developed a graphene-polydimethylsiloxane film combining a hierarchical surface with nanowrinkles on it and a hollow structure. The microstructure design of the composite can be facilely controlled to improve the sensing and hydrophobic performance by tailoring the microsphere building units. Attributed to the irregular surface and hollow structure of the sensing layer, the optimized sensor exhibits a superior sensitivity of 1085 kPa-1 in a 50 kPa linear range. For practical applications, the nanowrinkles on the surface of the microspheres and the polymer coating endow the composite with waterproof properties. Inspired by the dual receptors of the skin, two designed microstructured films can simply integrate into one with double-sided microstructures. The sensing performance and the water-repellence property allow the sensor to detect physiological signals under both ambient and underwater conditions. Furthermore, underwater stimuli detection and communication are demonstrated. This method of fabricating a flexible sensor shows great potential in wearable and robotic fields.

Recent Advances in Ferroelectret Fabrication, Performance Optimization and Applications.

The growing demand for wearable devices has sparked a significant interest in ferroelectret films. They possess flexibility and exceptional piezoelectric properties due to strong macroscopic-dipoles formed by charges trapped at the interface of their internal cavities. This review of ferroelectrets focuses on the latest progress in fabrication techniques for high temperature resistant ferroelectrets with regular and engineered cavities, strategies for optimizing their piezoelectric performance, and novel applications. The charging mechanisms of bipolar and unipolar ferroelectrets with closed and open-cavity structures are explained first. Next, the preparation and piezoelectric behavior of ferroelectret films with closed, open and regular cavity structures using various materials are discussed. Three widely used models for predicting the piezoelectric coefficients (d33) are outlined. Methods for enhancing the piezoelectric performance such as optimized cavity design, utilization of fabric electrodes, injection of additional ions, application of DC bias voltage and synergy of foam structure and ferroelectric effect are illustrated. A variety of applications of ferroelectret films in acoustic devices, wearable monitors, pressure sensors and energy harvesters are presented. Finally, the future development trends of ferroelectrets towards fabrication and performance optimization are summarized along with its potential for integration with intelligent systems and large-scale preparation. This article is protected by copyright. All rights reserved.

Design, fabrication, and evaluation of a novel highly sensitive tuning fork pressure sensor for precise liquid level measurement

This article investigates the under-explored potential of utilizing a thin stainless-steel diaphragm coupled with a quartz tuning fork sensor for liquid depth measurements. The focus is on monitoring molten salt fluid levels in nuclear reactors and concentrated solar power systems. Addressing a literature gap, the research explores cantilever-type configurations of a double-ended quartz tuning fork resonator, with a no-load resonance frequency of 17.37 kHz, on thin stainless-steel diaphragms for fluid depth measurement at room temperature. As the fluid depth increases, hydro-static pressure acting on a 20 μm diaphragm causes deflection, bending a tuning fork. The resulting change in resonance frequency correlates with fluid depth. Experimental setups assess the tuning fork’s sensitivity to strain and bending, revealing strain sensitivity of 7.83 Hz/μ strain (450.78 ppm/μ strain) and bending sensitivity of 0.09 Hz/μm (5.18 ppm/μm). The pressure sensor assembly, tested in a water tank, exhibits a sensitivity of −0.28 Hz/mm (−16.12 ppm/mm) in a single cantilever-type configuration. Despite a limited linear range, it effectively measures water depth changes as small as 0.7 mm. Exploring a double cantilever-type configuration yields a sensitivity of 0.07 Hz/mm (4.03 ppm/mm) with a broader linear range. The article discusses the reasons for opposite sensitivity and highlights the advantages of each configuration. Beyond molten salt level monitoring, the technology’s applications may extend to fluid depth and pressure measurements in industrial and domestic settings.

Bioinspired Suspended Sensing Membrane Array with Modulable Wedged-Conductive Channels for Crosstalk-Free and High-Resolution Detection.

High spatial-resolution detection is essential for biomedical applications and human-machine interaction. However, as the sensor array density increases, the miniaturization will lead to interference between adjacent units and deterioration in sensing performance. Here, inspired by the cochlea's sensing structure, a high-density flexible pressure sensor array featuring with suspended sensing membrane with sensitivity-enhanced customized channels is presented for crosstalk-free and high-resolution detection. By imitating the basilar membrane attached to spiral ligaments, a sensing membrane is fixed onto a high-stiffness substrate with cavities, forming a stable braced isolation to provide an excellent crosstalk-free capability (crosstalk coefficient: 47.24dB) with high-density integration (100 units within 1 cm2). Similar to the opening of ion channels in hair cells, the wedge-type expansion of the embedded cracks introduced by stress concentration structures enables a high sensitivity (0.19 kPa-1) and a large measuring range (400kPa). Finally, it demonstrates promising applications in distributed displays and the condition monitoring of medical-surgical intubation.

Characteristic Changes of the Stance-Phase Plantar Pressure Curve When Walking Uphill and Downhill: Cross-Sectional Study.

Monitoring of gait patterns by insoles is popular to study behavior and activity in the daily life of people and throughout the rehabilitation process of patients. Live data analyses may improve personalized prevention and treatment regimens, as well as rehabilitation. The M-shaped plantar pressure curve during the stance phase is mainly defined by the loading and unloading slope, 2 maxima, 1 minimum, as well as the force during defined periods. When monitoring gait continuously, walking uphill or downhill could affect this curve in characteristic ways. For walking on a slope, typical changes in the stance phase curve measured by insoles were hypothesized. In total, 40 healthy participants of both sexes were fitted with individually calibrated insoles with 16 pressure sensors each and a recording frequency of 100 Hz. Participants walked on a treadmill at 4 km/h for 1 minute in each of the following slopes: -20%, -15%, -10%, -5%, 0%, 5%, 10%, 15%, and 20%. Raw data were exported for analyses. A custom-developed data platform was used for data processing and parameter calculation, including step detection, data transformation, and normalization for time by natural cubic spline interpolation and force (proportion of body weight). To identify the time-axis positions of the desired maxima and minimum among the available extremum candidates in each step, a Gaussian filter was applied (σ=3, kernel size 7). Inconclusive extremum candidates were further processed by screening for time plausibility, maximum or minimum pool filtering, and monotony. Several parameters that describe the curve trajectory were computed for each step. The normal distribution of data was tested by the Kolmogorov-Smirnov and Shapiro-Wilk tests. Data were normally distributed. An analysis of variance with the gait parameters as dependent and slope as independent variables revealed significant changes related to the slope for the following parameters of the stance phase curve: the mean force during loading and unloading, the 2 maxima and the minimum, as well as the loading and unloading slope (all P<.001). A simultaneous increase in the loading slope, the first maximum and the mean loading force combined with a decrease in the mean unloading force, the second maximum, and the unloading slope is characteristic for downhill walking. The opposite represents uphill walking. The minimum had its peak at horizontal walking and values dropped when walking uphill and downhill alike. It is therefore not a suitable parameter to distinguish between uphill and downhill walking. While patient-related factors, such as anthropometrics, injury, or disease shape the stance phase curve on a longer-term scale, walking on slopes leads to temporary and characteristic short-term changes in the curve trajectory.