Flexible Sensor Sheet Research Articles

(Invited) Wireless Healthcare Flexible Sensor System

Daily continuous health condition monitoring is now of great interests using multi-functional flexible sensors. In particular, vital signals from skin are the most convenient way to measure continuously data collections during daily life. For this purpose, flexible sensor sheets allow it to detect multiple information from skin precisely due to conformable covering over skin surface. To realize this platform, multiple developments including flexible sensors, wireless system, and edge system to analyse huge size of datasets are required. In this talk, I introduce a wireless multiple sensor sheet with real-time data analyses on a smartphone as an edge system. The system has a function to display real-time analysed results on a smartphone to notify the users about their conditions.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.

A Fully Printed Flexible Sensor Sheet for Simultaneous Proximity–Pressure–Temperature Detection

A Fully Printed Flexible Sensor Sheet for Simultaneous Proximity–Pressure–Temperature Detection

(Invited) Wireless Healthcare Flexible Sensor System with Comfortable and Precise Monitoring

Daily continuous health condition monitoring is now of great interests using multi-functional flexible sensors. In particular, vital signals from skin are the most convenient way to measure continuously data collections during daily life. For this purpose, flexible sensor sheets allow it to detect multiple information from skin precisely due to conformable covering over skin surface. To realize this platform, multiple developments including flexible sensors, wireless system, and potential application are required. In this talk, I introduce a wireless multiple sensor sheet system with multiple printed flexible sensors such as skin perspiration, respiration, electrocardiogram etc. The system makes a feedback alarm if abnormal human condition signals are detected. Furthermore, to monitor the vital signals precisely and comfortably even under activity such as walking and running, device architecture is also discussed.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.

(Invited, Digital Presentation) Heterogeneously Integrated Nanomaterial-Based Multimodal Flexible Sensor Sheets

Human interaction is of great interests for a next class of human society to realize convenient, comfortable, and safe life. For this purpose, multimodal sensing is one of the most important functionalities. Furthermore, without sacrificing the original shape change or uncomfortability to attach or wear the sensor systems onto the targeted surface, respectively, ultrathin and mechanically flexible sensor is required. To address these requirements together, one potential material system is inorganic nanomaterials, which allows it to achieve a variety of material integrated formation on a film and mechanical flexibility due to ultra-small dimensions with high performance. However, the challenges to utilize the nanomaterials for the practical flexible device applications are still remained such as scalability, long-time stability, and multi-functional integrations. In my group, we are trying to develop the heterogeneously integrated nanomaterial-based sensors on flexible films to overcome all challenges to move forward to building the new sensor platforms.In this talk, as the progress on our research activity to contribute the flexible sensor community and IoT applications, multimodal flexible sensors using mainly nanomaterials formed by solution-based and laser-induced methods are discussed for wearable healthcare/medical applications. In addition to the flexible sensors, wireless system and signal processing for the feedback alarm function when the abnormal signal is detected are introduced as the potential flexible sensor application. In particular, electrocardiogram (ECG), skin temperature, and skin humidity flexible sensors and their integration on a flexible film are explained by using fundamental characteristics.This study focuses on the heterogeneously integrated multimodal flexible sensors for the application of remote healthcare applications. Although additional functional sensors and systems to realize more useful and convenient home-use healthcare system is required, the approaches may contribute the further developments to open a next class of electronics for IoT.

(Invited) Multimodal Flexible Sensor System with Wireless Feedback Alarm Function

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 sensor sheets can contribute to the applications for Internet of Things concepts applied to infrastructure, vehicles, plants, and human owing to macroscale and conformable covering onto curved and soft surfaces. One of the interesting approaches to use the flexible sensor sheet is a healthcare and medical application to monitor vital signals from skin surface. Because of soft and flexible sensor system, it can be attached onto skin conformally and comfortably, resulting in that more vital signals can be detected unlike conventional wearable watch-based devices. In this 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 by integrating with wireless and signal processing circuit systems.To realize the multi-functional flexible sensor system platforms, in this talk, multimodal flexible physical and chemical sensor sheets will be discussed by developing low-cost and macroscale fabrication methods. Especially, ECG, respiration, perspiration, skin temperature, and human activity are monitored by using the developed sensor system. After understanding the fundamental properties and mechanism of the flexible sensors, integrated device applications with several sensors on a flexible film are demonstrated as proof-of-concepts for multi-functional e-skins. Finally, wireless and feedback alarm system integrated with the multimodal flexible sensor sheet are briefly discussed.

A Fully Printed Flexible Sensor Sheet for Simultaneous Proximity–Pressure–Temperature Detection

AbstractFlexible multimodal sensors are an indispensable part of Internet of Things for human–machine interfaces, health monitoring, and soft robots. Despite tremendous research efforts dedicated to high sensitivity, flexibility, and multifunctionality, these merits are conventionally accompanied with sophisticated fabrications that hinder practical applications. Herein, a fully printed flexible trimodal sensor sheet containing 4 × 4 pressure sensor units, 2 × 2 temperature sensor units, and 1 proximity sensor unit is proposed. Its elaborate structure featured by a trifunctional bottom electrode layer effectively extends the functionality of this sensor sheet as well as maintains facile fabrication. The heterogeneous sensor units in this multifunctional device are rationally integrated to suppress crosstalk and mutual interference while keeping a compact configuration. Moreover, the integration of all functionalities enables a dual‐level detection capability, where proximity perception at the upper level can detect the event of interest to wake up temperature and pressure perceptions at the lower level. This provides a solution to free densely distributed sensor networks from a long‐term operation, thereby saving power consumption. The fully printable multimodal sensor sheet shows potentials for low‐cost macroscale flexible electronics.

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.

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

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.

(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.

Textile‐Based Flexible Tactile Force Sensor Sheet

AbstractThe next generation of electronics will include human‐interactive flexible sensor sheets to monitor health. One approach is to realize practical macroscale low‐cost sensor arrays to monitor pressure distribution and health conditions without directly attaching a device onto the body. However, practical requirements such as reliability, scalability, and washability are not often discussed as most studies focus on the sensing sensitivity and validations. This study demonstrates an all textile‐based tactile force sensor sheet that covers the above requirements. By considering the device design and materials, high reliability/repeatability (≈250 000 cycles at ≈5 kPa) and washability are realized. These are important factors for practical applications for human‐interactive macroscale sensor sheets. In addition to the fundamental characteristics, pressure distribution mapping and respiration rate monitoring are confirmed by placing the sensor sheets on a bed, chair, and floor.

A flexible giant magnetoresistive device for sensing strain direction

Miniaturized strain sensors are of value in a variety of areas, including wearable devices and structural health monitoring. Strain gauges based on magnetoresistance effects have previously been developed and offer potential advantages over conventional devices. However, these approaches have so far focused on sensing only the magnitude of the strain. Here, we show that a flexible giant magnetoresistive device can be used to detect the direction of strain in a material. Our trilayer devices, which are fabricated on a flexible substrate, consist of a strain-sensitive ferromagnetic cobalt layer and a strain-insensitive ferromagnetic permalloy (NiFe) layer, separated by a non-magnetic copper layer. We also show that the strain-sensitive and strain-insensitive layers can be made from a single ferromagnetic material by engineering the magnetoelastic properties of cobalt layers. Our integration of spintronics and flexible electronics could lead to the development of a flexible sensor sheet capable of mapping local strain directions. The direction of strain in a material can be detected using flexible giant magnetoresistive devices that consist of a strain-sensitive free layer and a strain-insensitive pinned layer.

Flexible sensor sheet for real-time pressure monitoring in artificial knee joint during total knee arthroplasty.

As described in this paper, we propose a sheet-type pressure sensor to support assistive technology for artificial knee joint replacement. The proposed pressure sensor consists of two sheets: an electrode sheet with metal wiring and a flexible polymer-based insulating layer on 80 μm polyimide film, as well as a pressure-sensitive conductive sheet that can function as a pressure-to-resistance sensor. We developed a 5 cm × 7 cm pressure sensor sheet with 116 sensing points. The multiple sensing sheet is expected to monitor the pressure distribution in an artificial knee joint during total knee arthroplasty to improve patients' quality of life.

(Invited) Multi-Functional Flexible Healthcare Sesnors and Integrated Circuits

The concepts of trillion sensor network and Internet of Things (IoT) require a variety of sensors that can be economically attached on any surfaces. To address this requirement, printed flexible electronics is one of solutions to integrate multifunctional macro-scale sensor networks without increasing fabrication cost compared to the Si-based sensors. To show a proof-of-concept of the printed and flexible devices, in this talk, a printed multi-functional flexible healthcare patch will be presented. The device contains a temperature sensor, a electrocardiogram sensor, an acceleration sensor, and an ultraviolet sensor on a flexible plastic substrate, which are fabricated by all printing methods. Especially, inorganic nanomaterials mixed with organic materials were used to achieve the high performance, air-stability, and mechanical flexibility. Furthermore, for the future flexible signal processing circuits, digital and analog circuits will be also demonstrated. It should be noted that those circuits are still fabricated by using a standard semiconductor lithography technique due to difficulity of material integration using printing methods. Those multi-fuctional sensors and flexible circuits are successfully demonstrated as the first proof-of-concepts. Although more developments to realize printed fully flexible device systems are required, we believe that the demonstrations of the macro-scale flexible sensor sheets may contribute to move forward to realizing the next generation electronics.

Development of a Polymer-Based Flexible Sensor Sheet Using Electric Capacitance (A New Structure Achieving Both High Precision and High Resolution)

Development of a Polymer-Based Flexible Sensor Sheet Using Electric Capacitance (A New Structure Achieving Both High Precision and High Resolution)

機能性ゴムを応用した柔軟センサの開発

機能性ゴムを応用した柔軟センサの開発