Sensor Sheet Research Articles

Wireless and Flexible Skin Moisture and Temperature Sensor Sheets toward the Study of Thermoregulator Center (Adv. Healthcare Mater. 17/2021)

Flexible Humidity Sensors In article number 2100103 by Kuniharu Takei and co-workers, an integrated flexible humidity and temperature sensor system allows for the monitoring of physiological conditions from skin wetness and temperature, under different conditions, wirelessly. The results prove the possibility of the study of a real-time and continuous thermoregulatory center by wearing the deviceintegrated glove or attaching the sensor sheet system onto the skin.

Modulation of tongue motion and tongue pressure during liquid swallowing with different bolus volumes.

The tongue functions by modulating according to bolus volume when swallowing; however, associated tongue dynamics are unclear. We aimed to clarify how tongue motion and tongue pressure change with bolus volume during swallowing. Sixteen healthy volunteers (age 29.5±3.8years; 12males, 4 females) were recruited. Two electromagnetic articulography markers were attached, one each on the anterior and posterior parts of the tongue, to measure motion. A sensor sheet, with five pressure-sensitive points, was attached to the hard palate to measure tongue pressure. Participants were asked to swallow 3ml and 10ml of water. Motion trajectory, maximum velocity, vertical displacement just before contact with the hard palate, and maximum magnitude and duration of tongue pressure were analysed. Tongue rotation was observed in the sagittal plane; its rate of appearance was significantly higher when swallowing 3ml of water than when swallowing 10ml, and the rate of rotation at posterior part was significantly higher than at the anterior part. The maximum velocity and vertical displacement were significantly greater when swallowing 10ml of water than those when swallowing 3ml of water. There was no significant difference in either the maximum magnitude of tongue pressure or maximum duration of tongue pressure between 3ml and 10ml. Bolus volume influenced the pattern of tongue motion; however, there was no difference in tongue pressure.

Unconstrained Measurement of Heart Rate Considering Harmonics of Respiratory Signal Using Flexible Tactile Sensor Sheet

Measurement of the sleeping state is useful for monitoring the health of a person being nursed. The sleeping state can be estimated from biological information such as respiration rate, heart rate, body motion, and lying posture. A heart rate measurement method that considers the harmonics of a respiratory signal is described herein. The harmonics of respiratory signals for heart rate measurement has not been considered hitherto. An unconstrained method is proposed for measuring respiration, heart rate, and lying posture using a Smart Rubber sensor, which is a rubber-based flexible planar tactile sensor developed for this study. Respiration and heart rates are measured by applying frequency analysis to time-series data of body pressure. The harmonics of a respiratory signal serves as noise in heart rate measurement. Therefore, the heart rate measurement is improved by eliminating the effects of harmonics. The average frequency error of the heart rate measurement by our proposed method is 0.144 Hz. Experimental results show that our proposed method enhances the precision of heart rate measurement. Hence, this method enables the accurate measurement of the sleeping state.

Wireless and Flexible Skin Moisture and Temperature Sensor Sheets toward the Study of Thermoregulator Center.

A disorder in the thermoregulator center in a human body leads to some potential diseases such as fever and hyperthyroidism. To predict these diseases early, monitoring the health condition of the human body due to the influence of thermoregulation disorders is important. Although extensive works are performed on sweat-rate detection by constructing microfluidic channels, skin-moisture evaporation before sweating remains unknown. This work proposes a wireless and flexible sensor sheet to investigate the thermoregulatory responses of different people under cold stimulation and exercise by measuring the temperature and moisture variations on the finger skin. An integrated flexible sensor system consists of a ZnIn2 S4 nanosheet-based humidity sensor and carbon nanotube/SnO2 temperature sensor. The results exhibit distinct thermoregulation abilities of five volunteers. Interestingly, the sudden increase in finger moisture that results from the excitation by the sympathetic nerve is observed during the cold-stimulus test. Although further studies are required to predict the potential diseases resulted from thermoregulation disorders in human body, this study provides a possibility of continuous and real-time monitoring of thermoregulatory activities via skin moisture and temperature detection using a flexible sensor sheet.

Multimodal Wearable Sensor Sheet for Health-Related Chemical and Physical Monitoring.

Continuous multiple data health monitoring has high potential to detect abnormal conditions or early stages of diseases in the future. To monitor a continuous small vital signal, one of the promising architectures is an attachable flexible multimodal sensor system, which can detect multiple health conditions from the skin surface. Recent breakthroughs have realized continuous sweat chemicals or physical conditions using flexible sensors. However, multimodal sensor integration to monitor chemical and physical information simultaneously and precisely is still a challenge. In this study, we present a multimodal wearable sensor sheet, which allows us to monitor sweat glucose, electrocardiograms, and skin temperature. Furthermore, to prevent the accumulation of glucose on the sensor surface for precise monitoring, a fluidic channel is also integrated to refresh the sweat from the sensor surface, resulting in the precise measurement of chemical substances in real time. This multimodal and flexible sensor platform takes a significant step toward realizing wearable healthcare applications to diagnose the early stages of diseases in advance.

A new simpler approach to measure the strength of toe plantar flexion requiring no mechanical restraint with a light-weight device.

Conventionally, the strength of toe plantar flexion (STPF) is measured in a seated position, in which not only the target toe joints but also the knee and particularly ankle joints, are usually restrained. We have developed an approach for the measurement of STPF which does not involve restraint and considers the interactions of adjacent joints of the lower extremities. This study aimed to evaluate this new approach and comparing with the seated approach. A thin, light-weight, rigid plate was attached to the sole of the foot in order to immobilize the toe area. Participants were 13 healthy young women (mean age: 24 ± 4 years). For measurement of STPF with the new approach, participants were instructed to stand, raise the device-wearing leg slightly, plantar flex the ankle, and push the sensor sheet with the toes to exert STPF. The sensor sheet of the F-scan II system was inserted between the foot sole and the plate. For measurement with the seated approach, participants were instructed to sit and push the sensor with the toes. They were required to maintain the hip, knee, and ankle joints at 90°. The mean values of maximum STPF of the 13 participants obtained with each approach were compared. There was no significant difference in mean value of maximum STPF when the two approaches were compared (new: 59 ± 23 N, seated: 47 ± 33 N). The coefficient of variation of maximum STPF was smaller for data obtained with the new approach (new: 39%, seated: 70%). Our simple approach enables measurement of STPF without the need for the restraints that are required for the conventional seated approach. These results suggest that the new approach is a valid method for measurement of STPF.

Occlusal support and postural stability in children: An observational study.

The relationship between uneven occlusal contact and fall risk has been described in elderly participants; however, multiple confounding factors, such as systemic disease or deterioration in vestibular function, have not been well considered. This study aimed to investigate this relationship in pediatric participants at the age of approximately 9-12, where these confounding factors are absent and the replacement of primary molars by permanent ones generally occurs and transiently results in uneven occlusal contact. Sixty-five children (36 boys and 29 girls, mean age: 9.5 ± 1.5years) were enrolled in this study. Participants were asked whether they had experienced at least two falls within the past 1year. The occlusal contact area ratio was calculated by dividing the greater half (right or left dental arch) by the smaller half (the other half) with U-shaped pressure sensor sheet. The total length and rectangular area of the center of pressure while standing upright for 10s were measured with a stabilometer and used as postural sway parameters. The occlusal contact area ratio significantly correlated with the postural sway parameters. Comparison between those who had experienced the fall incidences and those who had not after propensity score matching that adjusts their overall physical function revealed that there were no significant differences in the postural sway parameters and occlusal contact area ratio regardless of the history of fall incidence. Uneven occlusal contact leads to an increase in postural sway in children; however, this may not be associated with fall incidence.

A Method for Improving Recognition of Lying Postures Using a Measured Signal Intensity of Respiration and Heartbeat by Flexible Tactile Sensor Sheet

A Method for Improving Recognition of Lying Postures Using a Measured Signal Intensity of Respiration and Heartbeat by Flexible Tactile Sensor Sheet

Unconstrained Measurement of Heart Rate Considering Harmonics of a Respiratory Signal by Flexible Tactile Sensor Sheet

Unconstrained Measurement of Heart Rate Considering Harmonics of a Respiratory Signal by Flexible Tactile Sensor Sheet

Development of a checklist to evaluate seat pressure mapping using a sensor sheet for elderly wheelchair users

Development of a checklist to evaluate seat pressure mapping using a sensor sheet for elderly wheelchair users

A Liquid Metal Based Multimodal Sensor and Haptic Feedback Device for Thermal and Tactile Sensation Generation in Virtual Reality

AbstractVirtual reality (VR) has been widely used for training, gaming, and entertainment, and the value of VR is continually increasing as a contact‐free technology. For an immersive VR experience, measuring finger movements and providing appropriate feedback to the hand are as important as visual information, given the necessity of the hands for activities in daily life. Thus, a hand‐worn VR device with motion sensors and haptic feedback is desirable. In this paper, a multimodal sensing and feedback glove is developed with soft, stretchable, lightweight, and compact sensor and heater sheets manufactured by direct ink writing (DIW) of liquid metal, eutectic gallium‐indium (eGaIn). In the sensor sheet, ten sensors and three vibrators are embedded to measure finger movements and provide vibro‐haptic feedback. The other heater sheet provides thermo‐haptic sensation in accurate and rapid manner via model‐based feedback control even under stretched conditions. The multimodal sensing and feedback glove allows users to feel the contact status and discriminate materials with different temperature. Performance of the proposed multimodal glove is verified under VR environments including touching and pushing two blocks of different materials and grabbing a heated metal ball submerged in hot water.

Coordination between lingual motion and pressure production during dipper/tipper type swallows.

Tongue motor biomechanics during swallowing was not fully elucidated due to the technical difficulty. To evaluate the relationship between tongue motion and tongue pressure production by simultaneously measuring tongue motion and tongue pressure during water swallowing. In 12 healthy male participants (mean age, 30.8±4.2years), tongue pressure and tongue motion trajectory during dipper- and tipper-type swallows of 3mL of water were measured using a sensor sheet system equipped with five sensing points and an electromagnetic articulography, respectively. The temporal correlation between motion of anterior/posterior tongue and tongue pressure production during swallowing was evaluated on the synchronised waveforms. In the dipper-type swallow, a similar up-and-down motion pattern in vertical direction was observed among all participants before tongue pressure production. Those motion patterns were common at the anterior and posterior tongue locations with a temporal difference in some segment of tongue motion. On the other hand, tongue directly attached to hard palate with temporal synchronicity between the anterior and posterior parts. In both types of swallow, a strong temporal correlation was found between the timing of tongue-palate contact and the Onset of tongue pressure by intra-class correlation coefficients. From the simultaneous measurement of tongue motion and tongue pressure production, the tongue motion pattern during water swallowing and the temporal correlation between tongue motion and tongue pressure production were elucidated.

Detachable Flexible ISFET‐Based pH Sensor Array with a Flexible Connector

AbstractFlexible sensors that can detect different types of stimuli simultaneously from any surface are attractive in many fields, including the Internet of Things. An important function of a flexible sensor sheet is multiple sensing without sacrificing mechanical flexibility, conformability, and device cost on the macroscale. This study proposes a macroscale detachable pH sensor array consisting of a disposable pH sensitive membrane sheet and a reusable flexible transistor array via a flexible electrical connector. Mechanical flexibility and stable electrical connection are realized by a soft Ag electrode and sticky polydimethylsiloxane/polyethylenimine layer for the connector. After laminating the two sheets, a fundamental study reveals a sensitivity of about 66.5 mV per pH. Although a small potential change in the pH membrane is observed as the temperature changes, the pH value can be monitored using the detachable flexible transistor‐based pH sensor sheet with a sufficient resolution. As a proof‐of‐concept for solution diffusion monitoring using the pH change, a 5 × 5 array sensor sheet is successfully demonstrated. The sensor array can measure the pH distribution with a different pH diffuses into a solution bath within a few seconds.

Wearable Flexible Sensor Sheets toward Continuous Healthcare Monitoring

Wearable Flexible Sensor Sheets toward Continuous Healthcare Monitoring

Ultrathin Highly Flexible Featherweight Ceramic Temperature Sensor Arrays.

We fabricated highly flexible Sr- and Ni-doped perovskite SmMnO3 thermistor film sensor arrays on an ultrathin (5 μm thick) and lightweight (21 mg) polyimide sheet for healthcare monitoring devices. The Ag nanowire and nanoparticle-impregnated carbon microcone array, which was prepared by precisely controlled surface laser carbonization of polyimide, showed sufficiently low resistance as a bottom electrode and good stability against sharp bending angles. The dot-shaped (diameter: 900 μm) perovskite thermistor film with a thickness of 900 nm was crystallized by pulsed ultraviolet laser irradiation of a precursor film printed with perovskite nanoparticle dispersion ink, and the film functioned well as the thermistor with a thermistor constant of 2820 K. The thermistor sensor sheet exhibited rapid responses to temperature variation and high stability in the temperature cycle tests over 1000 cycles between room temperature and 80 °C. The bending durability for a bending angle of 60° with a small bending radius (500 μm) was also high. During the bending test over 1000 cycles, the monitoring temperature variation was suppressed only within 0.1 °C. This ultrathin sensor array sheet can be mounted on surfaces with shape variations, and we used the sensor for real-time monitoring in healthcare to detect precise temperature variations on the human skin during physical exercise.

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.

Detection of swallowing disorders using a multiple channel surface electromyography sheet: A preliminary study

Background/purposeWe invented a sensor sheet with multiple electromyogram electrodes, which can be easily attached to the front of the neck, to evaluate surface electromyograms (sEMG) during swallowing function. In this paper, we evaluated sEMG in healthy volunteers and dysphagia patients using the sensor sheet and discussed its potential to evaluate swallowing function. Materials and methodsTen healthy volunteers (age, 29.5 ± 3.9 years) and 18 clinically diagnosed dysphagia patients (age, 67.8 ± 12.1 years) were included. The sensor sheet had four pairs of electrodes, and sEMG at the suprahyoid muscles (positions A and B) and the infrahyoid muscles (positions C and D) were recorded while swallowing water, thickened water, yogurt, and jelly; sEMG findings were compared between these positions. ResultsSignificant differences in the duration of muscle activity was observed when swallowing yogurt at position D and when swallowing jelly, thickened water, and water at position B (Mann–Whitney U test, p < 0.05). In healthy volunteers, muscle activation typically began from positions A or B to position D, whereas in dysphagia patients, it sometimes began from position D. ConclusionThere were significant differences in duration and sequence patterns of four sEMG activities between healthy young volunteers and dysphagia patients in the assessment using the sensor sheet, although some technical and scientific problems remained unresolved. These results indicate that swallowing function could be evaluated using the sensor sheet.

Measurement of Spatial Stability in Precision Grip.

The purpose of the protocol is to indirectly evaluate the direction of the finger force during manipulation of a handheld object based on the biomechanical relationships in which deviated force direction causes center of pressure (COP) replacement. To evaluate this, a thin, flexible, and high spatial resolution pressure sensor sheet is used. The system allows measurement of the COP trajectory in addition to the force amplitude and its temporal regulation. A series of experiments found that increased trajectory length reflected a sensorimotor deficit in stroke patients, and that decreased COP trajectory reflects a compensatory strategy to avoid an object slipping from the hand grip in the elderly. Moreover, the COP trajectory could also be decreased by dual task interference. This article describes the experimental procedure and discusses how finger COP contributes to an understanding of the physiology and pathophysiology of grasping.

(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.

Development of a Strain Sensor Matrix on Mobilized Flexible Substrate for the Imaging of Wind Pressure Distribution.

This paper presents a novel flexible sensor for monitoring wind pressure distribution. Based on the concept of “flexible mechatronics”, a suspended structure was incorporated into the matrix of a resistive-strain sensor in a plastic film to make the sensor mechanically movable against the wind. Screen printing and laser cutting were confirmed to be satisfactory methods for fabricating the proposed device structure. As a result, the visualization of wind pressure was successfully demonstrated by the fabricated sensor sheet and an imaging-display-creation software. The results of this study show that a mechanically functionalized substrate opens up new avenues for flexible electronics.