Tactile Pressure Research Articles

Artificially Intelligent Tactile Ferroelectric Skin.

Lightweight and flexible tactile learning machines can simultaneously detect, synaptically memorize, and subsequently learn from external stimuli acquired from the skin. This type of technology holds great interest due to its potential applications in emerging wearable and human‐interactive artificially intelligent neuromorphic electronics. In this study, an integrated artificially intelligent tactile learning electronic skin (e‐skin) based on arrays of ferroelectric‐gate field‐effect transistors with dome‐shape tactile top‐gates, which can simultaneously sense and learn from a variety of tactile information, is introduced. To test the e‐skin, tactile pressure is applied to a dome‐shaped top‐gate that measures ferroelectric remnant polarization in a gate insulator. This results in analog conductance modulation that is dependent upon both the number and magnitude of input pressure‐spikes, thus mimicking diverse tactile and essential synaptic functions. Specifically, the device exhibits excellent cycling stability between long‐term potentiation and depression over the course of 10 000 continuous input pulses. Additionally, it has a low variability of only 3.18%, resulting in high‐performance and robust tactile perception learning. The 4 × 4 device array is also able to recognize different handwritten patterns using 2‐dimensional spatial learning and recognition, and this is successfully demonstrated with a high degree accuracy of 99.66%, even after considering 10% noise.

Development of Fully Flexible Tactile Pressure Sensor with Bilayer Interlaced Bumps for Robotic Grasping Applications.

Flexible tactile sensors have been utilized in intelligent robotics for human-machine interaction and healthcare monitoring. The relatively low flexibility, unbalanced sensitivity and sensing range of the tactile sensors are hindering the accurate tactile information perception during robotic hand grasping of different objects. This paper developed a fully flexible tactile pressure sensor, using the flexible graphene and silver composites as the sensing element and stretchable electrodes, respectively. As for the structural design of the tactile sensor, the proposed bilayer interlaced bumps can be used to convert external pressure into the stretching of graphene composites. The fabricated tactile sensor exhibits a high sensing performance, including relatively high sensitivity (up to 3.40% kPa−1), wide sensing range (200 kPa), good dynamic response, and considerable repeatability. Then, the tactile sensor has been integrated with the robotic hand finger, and the grasping results have indicated the capability of using the tactile sensor to detect the distributed pressure during grasping applications. The grasping motions, properties of the objects can be further analyzed through the acquired tactile information in time and spatial domains, demonstrating the potential applications of the tactile sensor in intelligent robotics and human-machine interfaces.

Very Thin, Macroscale, Flexible, Tactile Pressure Sensor Sheet.

In artificial intelligence and deep learning applications, data collection from a variety of objects is of great interest. One way to support such data collection is to use very thin, mechanically flexible sensor sheets, which can cover an object without altering the original shape. This study proposes a thin, macroscale, flexible, tactile pressure sensor array fabricated by a simple process for economical device applications. Using laser-induced graphene, a transfer process, and a printing method, a relatively stable, reliable, macroscale, thin (∼300 μm), flexible, tactile pressure sensor is realized. The detectable pressure range is about tens to hundreds of kPa. Then, as a proof-of-concept, the uniformity, sensitivity, repeatability, object mapping, finger pressure distribution, and pressure mapping are demonstrated under bending conditions. Although many flexible, tactile pressure sensors have been reported, the proposed structure has the potential for macroscale, thin, flexible, tactile pressure sensor sheets because of the simple and easy fabrication process.

Ultrasoft Liquid Metal Elastomer Foams with Positive and Negative Piezopermittivity for Tactile Sensing

AbstractSoft, capacitive tactile (pressure) sensors are important for applications including human–machine interfaces, soft robots, and electronic skins. Such capacitors consist of two electrodes separated by a soft dielectric. Pressing the capacitor brings the electrodes closer together and thereby increases capacitance. Thus, sensitivity to a given force is maximized by using dielectric materials that are soft and have a high dielectric constant, yet such properties are often in conflict with each other. Here, a liquid metal elastomer foam (LMEF) is introduced that is extremely soft (elastic modulus 7.8 kPa), highly compressible (70% strain), and has a high permittivity. Compressing the LMEF displaces the air in the foam structure, increasing the permittivity over a large range (5.6–11.7). This is called “positive piezopermittivity.” Interestingly, it is discovered that the permittivity of such materials decreases (“negative piezopermittivity”) when compressed to large strain due to the geometric deformation of the liquid metal droplets. This mechanism is theoretically confirmed via electromagnetic theory, and finite element simulation. Using these materials, a soft tactile sensor with high sensitivity, high initial capacitance, and large capacitance change is demonstrated. In addition, a tactile sensor powered wirelessly (from 3 m away) with high power conversion efficiency (84%) is demonstrated.

Investigation of complete life cycle and species identification of a digenean gill parasite <i>Centrocestus</i> sp. infesting Koi carp (<i>Cyprinus carpio</i> Linnaeus, 1758) using morphology and morphometric characters

This study was done to describe the morphology and morphometric characters of the life cycle stages of the digenean gill parasite, Centrocestus sp. that infests Koi carp (Cyprinus carpio) at Rambadagalle and Ginigathhena ornamental fish breeding centres of Sri Lanka and to identify the species of the parasite. The snail, Melanoides tuberculata (Muller, 1774) that inhabited the earthen ponds with Koi carps were induced to shed cercariae and 45 days old Koi carps were experimentally infested by them. The infected fish with mature metacercariae were fed to chicks (Gallus gallus) and eggs of the parasite released with faeces and adult stages of the parasite developed in the intestine were recovered. After keeping the eggs in water for several days ciliated miracidia were observed by application of tactile pressure. Infested snails were dissected and the morphometric characters of sporocyst and redia stages were recorded. The eggs were operculated, oval shaped, yellowish brown in colour with lattice design on the shell surface. The ciliated miracidi, was the infective stage to snails. The sporocyst was sac like and the redia was tubular and curved. The cercaria had an oral and a ventral sucker, two eye spots and a tail. The encysted metacercaria was oval in shape with ‘X-shaped excretory bladder’. Excysted metacercaria was elongated and narrower at the anterior end being similar to adults. The adult worm was small and oral sucker was surrounded by 32 circumoral spines arranged in two alternated rows. Acetabulum located in the middle of the body. The excretory bladder opened to a terminal excretory pore. The morphology and morphometric characters of the life cycle stages of the Centrocestus sp. that infests Koi carp at Rambadagalle and Ginigathhena ornamental fish breeding centres were compared with published literature and the parasite was identified as Centrocestus formosanus (Nishigori, 1924), which has not been documented in Sri Lanka earlier.

Plant‐Based Biodegradable Capacitive Tactile Pressure Sensor Using Flexible and Transparent Leaf Skeletons as Electrodes and Flower Petal as Dielectric Layer

AbstractIn biomedical sciences, there is demand for electronic skins with highly sensitive tactile sensors, having applications in patient monitoring, human–machine interfaces, and on‐body sensors. In clinical applications, it would be especially beneficial if the sensors would be disposable. Here, an all plant‐material‐based biodegradable capacitive tactile pressure sensor for disposable electronic skins is reported. Silver‐nanowire‐coated leaf skeletons are used as breathable and flexible electrodes while freeze‐dried rose petals are used as the dielectric layer. The leaf skeleton electrodes have a rough fractal‐like architecture, which provides good adhesion to the silver nanowires and maintains interconnections between the silver nanowires when the electrodes are bent. The electrodes display low constant resistance up to curvature of 800 m−1. The rose petal dielectric layer has a multiscale 3D cell wall microstructure, which compresses elastically when subjected to pressure. The fabricated sensor can respond to pressures ranging from 0.007 to at least 60 kPa, with a maximum sensitivity of ≈0.08 kPa−1. The signal is stable for at least 5000 pressure cycles, after an initial break‐in period. Owing to the all biomaterial constituents, the sensor is biodegradable under aqueous conditions. The sensor is successfully applied as an e‐skin in touch sensing and gesture monitoring.

(Invited) Multi-Functional Flexible Sensor Sheets

Flexible and stretchable electronics are now widely studied for a next class of electric devices replaced from the silicon-based conventional inflexible devices. In particular, multi-functional e-skins can contribute to the applications for wearable healthcare devices and Internet of Things (IoT) concepts. For healthcare application, chemical information such as pH, glucose, sodium ion, and potassium ion levels are very important to monitor as well as physical information including activity, temperature, heartbeat, and electrocardiogram (ECG) signals. Furthermore, simultaneous multiple condition monitoring of physical and chemical information is a next class of wearable devices for convenient and safe human life. To realize the multi-functional flexible sensor system platforms, in this talk, flexible physical and chemical sensor sheets using mainly inorganic nanomaterials will be discussed by proposing low-cost, macroscale, and multi-functional material systems. Especially, human-interactive flexible sensors to detect human motion and health conditions are mainly introduced. After understanding the fundamental properties and mechanism of the flexible sensors such as a strain sensor, a temperature sensor, an ultraviolet sensor, a tactile pressure sensor, and a chemical sensor, integrated device applications with several sensors on a flexible film are demonstrated as proof-of-concepts for multi-functional e-skins. Although a lot of researches and developments are still required for practical application, these studies may help to open a door for the next step of flexible electronics.

Light or Deep Pressure: Medical Staff Members Differ Extensively in Their Tactile Stimulation During Preterm Apnea.

Background: Even though tactile stimulation is common practice to terminate preterm apnea, the style and intensity of these interventions is not specified during theoretical or practical training and has never been clinically evaluated.Objective: The present study was designed to analyze the various modes of tactile stimulation used to terminate preterm apnea and measure the pressure intensity and frequency of these stimulations.Methods: A model with the size and weight of an actual preterm infant was equipped with sensor technology to measure stimulation pressure and frequency of tactile stimulation. Additionally a camera system was used to record hand positions and stimulation modes. Seventy medical staff members took part in the experiment.Results: We found extreme between subjects differences in stimulation pressure that could not be explained by professional experience but, to a degree, depended on apnea intensity. Pressures ranged from 11.11 to 226.87 mbar during low intensity apnea and from 9.89 to 428.15 mbar during high intensity apnea. The majority of participants used rhythmic stimulation movements with a mean frequency of ~1 Hz. Different modes (rubbing, squeezing, tickling, and tapping) and finger positions were used.Conclusion: Medical staff members intuitively adjust their tactile stimulation pressure depending on the premature infants' apnea intensity. However, mean pressure values varied greatly between subjects, with similar pressure ranges for low and high intensity apnea. The question remains which pressure intensities are necessary or sufficient for the task. It is reasonable to assume that some stimulation types may be more effective in rapidly terminating an apneic event.

One-structure-based multi-effects coupled nanogenerators for flexible and self-powered multi-functional coupled sensor systems

The simultaneous monitoring of multi-physical signals is essential for future sensor systems, but is currently only realized by integrating a variety of sensor types into a single device. However, the ability to use a single sensor structure that shares common electrodes can provide a route to multi-functional sensing while also decreasing device size and increasing spatial resolution. Here we report a ferroelectric barium titanate film-based multi-effect coupled nanogenerator for scavenging light, mechanical, and thermal energies to realize a self-powered multi-functional coupled sensor system without using any external power source. The coupled nanogenerator exhibits a strong coupling enhancement with detection sensitivities of 0.42 nA/(mW/cm2) during illumination by 405 nm light, 1.43 nA/kPa for pressure detection, and −8.85 nA/K for temperature sensing, where both the light and pressure sensing performances have the highest sensitivities during a cooling temperature variation of ~19.5 K and the largest temperature detection sensitivity can be achieved during strong light illumination of 83.2 mW/cm2. Moreover, the coupled nanogenerator array can be integrated into flexible forms for tactile pressure, temperature, and light sensors, and enabling coupled sensing for the development of electronic skins.

Wrist flexible heart pulse sensor integrated with a soft pump and a pneumatic balloon membrane

To monitor health and diagnose disease in the early stage, future healthcare standards will likely include the continuous monitoring of various vital data. One approach to collect such information is a wearable and flexible device, which detects information from the skin surface. An important dataset is heart pulse information. Herein a method to monitor the detailed pulse signal from a wrist stably and reliably is proposed. Specifically, a soft pneumatic balloon operated by a soft pump applies the appropriate pressure over a tactile sensor onto the radial artery of the wrist to detect detailed heart pulse waves. The soft pump, pneumatic balloon, and flexible tactile pressure sensor are characterized as a fundamental study. Additionally, a proof-of-concept of this integrated device platform is demonstrated by monitoring the heart pulse from a wrist with and without the soft pump functions.

Monitoring of Particle Crushing under One-Dimensional Loading

Abstract A modified one-dimensional testing apparatus that incorporates a bender–extender element system and tactile pressure sensors was developed for the monitoring of particle crushing. The apparatus was tested using five types of glass beads with different particle sizes. The compressional shear wave velocities and their ratio were evaluated with respect to the porosity to establish the microstructural evolution of the granular material. The results showed that the bender–extender element system functioned excellently under high-pressure one-dimensional compression, with the shear wave velocity ratio increasing with increasing loading stress up to 7 MPa and thereafter decreasing. The loading stress of 7 MPa was thus considered the breakage stress of the glass beads, as also reflected by a sharp increase in strain. The glass beads subsequently entered Stage 2 of the crushing process, characterized by significant crushing. Arching of the particle assembly was also clearly observed, and this was enhanced by an increase in the roughness of the side plates of the container. An empirical equation for evaluating the arching was derived. The microstructural evolution and macro behavior of the glass beads under the constrained boundary condition and high compression pressure were found to be analogous to those of the crushing of high-porosity sandstone.

A Novel Capacitance-Based In-Situ Pressure Sensor for Wearable Compression Garments.

This paper pertains to the development & evaluation of a dielectric electroactive polymer-based tactile pressure sensor and its circuitry. The evaluations conceived target the sensor’s use case as an in-situ measurement device assessing load conditions imposed by compression garments in either static form or dynamic pulsations. Several testing protocols are described to evaluate and characterize the sensor’s effectiveness for static and dynamic response such as repeatability, linearity, dynamic effectiveness, hysteresis effects of the sensor under static conditions, sensitivity to measurement surface curvature and temperature and humidity effects. Compared to pneumatic sensors in similar physiological applications, this sensor presents several significant advantages including better spatial resolution, compact packaging, manufacturability for smaller footprints and overall simplicity for use in array configurations. The sampling rates and sensitivity are also less prone to variability compared to pneumatic pressure sensors. The presented sensor has a high sampling rate of 285 Hz that can further assist with the physiological applications targeted for improved cardiac performance. An average error of ± 5.0 mmHg with a frequency of 1–2 Hz over a range of 0 to 120 mmHg was achieved when tested cyclically.

Consolidation behavior and elastic wave characteristics of lime-treated dredged mud with vacuum preloading

Recent advances in the preloading technologies and detection technologies used to measure different soil properties (e.g., settlement, drainage, shear strength, elastic wave velocity, and degree of consolidation) have provided a new opportunity to refine and improve soil treatment methods. In this study, a series of tests were conducted using a remolded dredged slurry sample containing different lime contents (0%, 2%, 4%, and 8%) and a modified vacuum preloading device with a porometer, bending element, and tactile pressure sensor. The consolidation behavior of samples with and without lime was determined. The effects of different lime contents on the consolidation properties were studied for the whole samples and at different depths. The optimum lime content of the dredged slurry sample under vacuum preloading conditions was determined by comparing the consolidation efficiencies (CEs). In addition, a one-dimensional surcharge preloading experiment was conducted on dredged slurry samples under incremental preloading (0–100 kPa, 100–200 kPa, and 200–400 kPa). Even though numerous soil consolidation properties differed according to preloading conditions, the optimum lime content based on the consolidation efficiency (CE) was consistently found to be 4%.

Mechanoluminescent, Air-Dielectric MoS2 Transistors as Active-Matrix Pressure Sensors for Wide Detection Ranges from Footsteps to Cellular Motions.

Tactile pressure sensors as flexible bioelectronic devices have been regarded as the key component for recently emerging applications in electronic skins, health-monitoring devices, or human-machine interfaces. However, their narrow range of sensible pressure and their difficulty in forming high integrations represent major limitations for various potential applications. Herein, we report fully integrated, active-matrix arrays of pressure-sensitive MoS2 transistors with mechanoluminescent layers and air dielectrics for wide detectable range from footsteps to cellular motions. The inclusion of mechanoluminescent materials as well as air spaces can increase the sensitivity significantly over entire pressure regimes. In addition, the high integration capability of these active-matrix sensory circuitries can enhance their spatial resolution to the level sufficient to analyze the pressure distribution in a single cardiomyocyte. We envision that these wide-range pressure sensors will provide a new strategy toward next-generation electronics at biomachine interfaces to monitor various mechanical and biological phenomena at single-cell resolution.

Flexible Pressure Sensors with Wide Linearity Range and High Sensitivity Based on Selective Laser Sintering 3D Printing

AbstractTo achieve practical applications of flexible pressure sensors, good performance and scalable manufacturing processes are both desired. Here, flexible pressure sensors with excellent performance are fabricated via selective laser sintering (SLS). Having benefitted from the irregular microstructures generated in the powder sintering process, the sensors exhibit high sensitivity of 55 kPa−1 in a wide linearity range of 100 kPa, and they maintain decent sensitivity (>10 kPa−1) over a high‐pressure range (100–400 kPa), which is among the best results for flexible pressure sensors. The working mechanism of the sensor is finely revealed combining in situ observations and electrical simulations. The results demonstrate that electrical saturation (due to parasitic resistance) greatly affects the linearity range except for the geometric saturation of the microstructure. As a proof of concept, tactile, pulse, muscle stiffness, and plantar pressure tests are performed. The fast and stable responses of the sensor show its great potential for electronic skin, human–machine interface, and healthcare monitoring. Besides its excellent performance, the fabrication processes via SLS are compatible with fab‐scale production and flexible customization, which pave new paths for the mass manufacturing and diversified applications of flexible pressure sensors in the future.

A flexible capacitive sensor based on the electrospun PVDF nanofiber membrane with carbon nanotubes

Flexible pressure sensors have been increasingly recognized over the past several decades, but there is still a challenge to fabricate them with a superb sensitivity and large sensing range. In this paper, a flexible capacitive pressure sensor based on the electrospun polyvinylidene fluoride (PVDF) nanofiber membrane with carbon nanotubes (CNTs) was developed to measure the pressure. The electrospinning CNT-PVDF nanofiber membrane can overcomes the limitations of the traditional solution-dip-coating for adhering conductive materials to the porous surface. The microstructure and characterization of the CNT-PVDF nanofiber membrane were analyzed by SEM, AFM and FTIR. By increasing the permittivity and decreasing the Young's modulus of the CNT-PVDF dielectric layer, the capacitive sensor exhibits high sensitivity (∼0.99/kPa), fast response (∼29 ms) and excellent cyclic loading/unloading stability (＞1000 cycles). Moreover, experiments were also conducted to investigate influence of the thickness and bending radius of the sensor as well as temperature and humidity of the environment. In addition, a 3 × 3 sensor network attached on the hand was used to measure the spatial distribution and magnitude of tactile pressure. The proposed sensor has great potential for application in soft robotics and electronic skin.

(Invited) Multi-Functional Flexible Physical and Chemical Sensor Sheets

Mechanically flexible and stretchable devices have been attracted much attention for a next class of electronics such as flexible photovoltaics, flexible displays, and wearable electronics. In particular, multiple sensors for potential applications such as wearable healthcare devices and Internet of Things (IoT) concepts are one of the most important components for moving forward to building the flexible sensor system platform. For healthcare application, chemical information such as pH, glucose, sodium ion, and pattaisum ion levles are very important to monitor as well as physical information such as activity, skin temperature, heartbeat, and electrocardiogram (ECG) signals. Furthermore, simultaneous multiple condition monitoring including physical and chemical information is a next class of wearable devices for convienient and safe human life. To address these challenges, in this talk, flexible physical and chemical sensor sheets using mainly inorganic nanomaterials will be introduced by proposing low-cost, macroscale, and multi-functional device integrations. Especially human-interactive flexible sensors to detect human motion, health condition, and room environment information are mainly discussed. In addition to the fundamental sensor characteristics of a strain sensor, a temperature sensor, an ultraviolet sensor, a tactile pressure sensor, and a chemical sensor, integrated device applications with several sensors on a flexible film are demonstrated as proof-of-concepts for multi-functional flexible healthcare sensor sheets. Although a lot of investigations and developments are still required for practical application as products, these studies may help to open a door for the next step of flexible electronics.

Is sensory processing associated with prematurity, motor and cognitive development at 12 months of age?

BackgroundPrematurity may be a risk factor for sensory processing difficulties. Limited research has investigated sensory processing in preterm infants in their first year of life, when sensory processing dysfunctions are more subtle and difficult to detect. AimsThe aims of this study were to investigate the association between prematurity and sensory processing and the associations between sensory processing and motor and cognitive development in infants at 12 months of age. Study designCross-sectional study. Subjects45 infants allocated in two groups: control (37–41 weeks' gestation) and preterm (<34 weeks' gestation). Outcome measuresSensory processing was assessed with the Test of Sensory Functions in Infants (TSFI). Motor and cognitive development was assessed with the Bayley Scales of Infant and Toddler Development, Third Edition (Bayley-III). ResultsPreterm group was associated with significant decrease in TSFI's total (p < 0.01), reactivity to deep tactile pressure (p = 0.02) and vestibular stimulation reactivity (p = 0.03) scores. Bayley-III motor score was positive associated with TFSI score on ocular-motor control domain (p = 0.03). Bayley-III cognitive score and TSFI scores were not significantly associated. ConclusionsPrematurity negatively interferes with sensory processing, especially in tactile and vestibular domains, and better sensory processing in ocular-motor control contributes to better motor performance at 12 months of age. It is important to consider sensory processing in early developmental evaluation and interventions to promote better developmental outcomes in preterm infants.

Fingerprint‐Inspired Conducting Hierarchical Wrinkles for Energy‐Harvesting E‐Skin

AbstractIn the field of bionics, sophisticated and multifunctional electronic skins with a mechanosensing function that are inspired by nature are developed. Here, an energy‐harvesting electronic skin (energy‐E‐skin), i.e., a pressure sensor with energy‐harvesting functions is demonstrated, based on fingerprint‐inspired conducting hierarchical wrinkles. The conducting hierarchical wrinkles, fabricated via 2D stretching and subsequent Ar plasma treatment, are composed of polydimethylsiloxane (PDMS) wrinkles as the primary microstructure and embedded Ag nanowires (AgNWs) as the secondary nanostructure. The structure and resistance of the conducting hierarchical wrinkles are deterministically controlled by varying the stretching direction, Ar plasma power, and treatment time. This hierarchical‐wrinkle‐based conductor successfully harvests mechanical energy via contact electrification and electrostatic induction and also realizes self‐powered pressure sensing. The energy‐E‐skin delivers an average output power of 3.5 mW with an open‐circuit voltage of 300 V and a short‐circuit current of 35 µA; this power is sufficient to drive commercial light‐emitting diodes and portable electronic devices. The hierarchical‐wrinkle‐based conductor is also utilized as a self‐powered tactile pressure sensor with a sensitivity of 1.187 mV Pa‐1 in both contact‐separation mode and the single‐electrode mode. The proposed energy‐E‐skin has great potential for use as a next‐generation multifunctional artificial skin, self‐powered human–machine interface, wearable thin‐film power source, and so on.

Time-lapsed shear-wave velocity (Vs) tomographic images and stress in sand surrounding displacement pile during setup

This study reports model pile tests designed to characterize the underlying mechanisms of driven pile setup in dry sand by means of stress measurement with the tactile pressure sensors and spatio-temporal, shear-wave velocity (Vs) distributions using an automated high-speed tomographic imaging system. The pile-load test results demonstrate a distinct increase in the pile shaft resistance after pile setup. The measured stress and Vs in the soil surrounding the pile suggest the increase in the radial effective stress during pile loading [Formula: see text], as a result of the aging-induced stiffness increase, is the dominant mechanism of pile setup. The spatio-temporal evolution of Vs distributions reveals that during initial aging (before pile installation), Vs is similar at any distance to the pile shaft and exhibits a similar aging rate S0 in terms of stiffness increases. After pile installation, the soil exhibits a higher aging rate S1. In addition, the ratio S1/S0 decreases with increasing distance from the pile shaft. A lower initial Vs and a higher aging rate S1 are also observed for the measurements at the three sensing layers of different depths, suggesting that more soils disturbed by pile installation tend to recover at a relative higher aging rate.