Kenichiro Kanao

Fully Printed Flexible Fingerprint-like Three-Axis Tactile and Slip Force and Temperature Sensors for Artificial Skin

A three-axis tactile force sensor that determines the touch and slip/friction force may advance artificial skin and robotic applications by fully imitating human skin. The ability to detect slip/friction and tactile forces simultaneously allows unknown objects to be held in robotic applications. However, the functionalities of flexible devices have been limited to a tactile force in one direction due to difficulties fabricating devices on flexible substrates. Here we demonstrate a fully printed fingerprint-like three-axis tactile force and temperature sensor for artificial skin applications. To achieve economic macroscale devices, these sensors are fabricated and integrated using only printing methods. Strain engineering enables the strain distribution to be detected upon applying a slip/friction force. By reading the strain difference at four integrated force sensors for a pixel, both the tactile and slip/friction forces can be analyzed simultaneously. As a proof of concept, the high sensitivity and selectivity for both force and temperature are demonstrated using a 3×3 array artificial skin that senses tactile, slip/friction, and temperature. Multifunctional sensing components for a flexible device are important advances for both practical applications and basic research in flexible electronics.

Highly selective flexible tactile strain and temperature sensors against substrate bending for an artificial skin

Flexible devices can conformally cover any surfaces and interact with different stimuli such as human touch. Although a flexible tactile sensor has been reported as an artificial skin application, distinguishing between a tactile force and strain due to substrate bending remains challenging. Here we report a highly selective tactile force sensor against bending on the basis of strain engineering by fabricating a cantilever structure. The proposed device achieves a 4–23 times improvement in selectivity compared to conventional pressure sensitive rubber. As a proof-of-concept for e-skin, an array composed of highly selective tactile force sensors and temperature sensors is successfully demonstrated to imitate human skin.

Air Ambient-Operated pNIPAM-Based Flexible Actuators Stimulated by Human Body Temperature and Sunlight

Harnessing a natural power source such as the human body temperature or sunlight should realize ultimate low-power devices. In particular, macroscale and flexible actuators that do not require an artificial power source have tremendous potential. Here we propose and demonstrate electrically powerless polymer-based actuators operated at ambient conditions using a packaging technique in which the stimulating power source is produced by heat from the human body or sunlight. The actuating angle, force, and reliability are discussed as functions of temperature and exposure to sunlight. Furthermore, a wearable device platform and a smart curtain actuated by the temperature of human skin and sunlight, respectively, are demonstrated as the first proof-of-concepts. These nature-powered actuators should realize a new class of ultimate low-power devices.

An all-solution-processed tactile memory flexible device integrated with a NiO ReRAM

Flexible electronics have great potential as the next class of macroscale multi-sensing devices capable of collecting a variety of information from diverse surfaces. A platform to integrate different electric components on a flexible substrate for macroscale electronics without increasing device fabrication costs needs to be explored. To address this requirement, we demonstrate an all-solution-processed tactile touch memory flexible device integrated with a NiO ReRAM, a tactile touch sensor, and resistors. The function of the solution-processed NiO ReRAM is attributed to a threshold switching mechanism due to the charge trap in the NiO film and the trap-controlled space-charge-limited current. In terms of device operations, the NiO ReRAM is mechanically stable with an on/off current ratio more than 103 while bending the substrate with a radius up to 6.1 mm. As a proof-of-concept for device applications, a tactile touch memory device, which has functions of writing and erasing tactile touch information by applying a tactile touch and SET/RESET voltage, respectively, is successfully operated. The results are promising to advance all-solution-based macroscale flexible electronics.

Human-interactive multi-functional electronic wallpaper integrated with sensors and memory

The internet of things concept has promoted research on human-interactive electronics for wearable devices and robotic applications. One interesting application is wallpaper to monitor a room environment and to act as an electronic message board. To demonstrate the potenital of electronic wallpaper (e-wallpaper), this study prepares a flexible nonvolatile floating gate random access memory (FGRAM) array integrated with a tactile touch sensor array as the message board. Additionally, a temperature sensor array is also laminated to monitor the room temperature. Besides the mechanical flexibility, the fundamental properties of flexible FGRAMs, including the tunneling dielectric thickness, program voltage, and program time dependencies, are characterized. Finally, e-wallpaper is demonstrated as a first proof-of-concept to show a possible platform for future macroscale flexible electronics.

Flexible and high selective pressure sensitive rubber for tactile sensing

This study proposes and demonstrates a multi-layered pillar-like, carbon black (CB)/polydimethylsiloxane (PDMS)-based pressure sensor embedded in silicone rubbers to realize high selectivity of tactile pressure against bending of substrate based on a strain engineering. This device is fabricated by all solution-based process that is eventually applied to all-printing technique. Furthermore, as the first proof-of-concept, real-time tactile sensing is demonstrated for several applications such as wearable devices and robotic artificial skin (e-skin). This finding and demonstration eventually can be applied to the low-cost, high precise tactile sensor that can be conformally covered over any surfaces.

All solution-processed flexible memory integrated with tactile sensor

This study demonstrates a tactile pressure-memorized functional flexible device integrated with a tactile pressure sensor and a resistive random access memory (ReRAM) using all solution-based fabrication process toward low-cost and macroscale flexible electronics. Solution-processed NiO ReRAM shows a stable switching operation with >3 orders-ON/OFF resistance ratio without being affected by bending of the substrate up to 5.6 mm radius. As the first proof-of-concept, carbon black (CB) and polydimethylsiloxane (PDMS)-based tactile pressure sensor is integrated with the ReRAM. The integrated device can successfully memorize tactile information by ReRAM. This demonstration eventually allows us to apply for flexible human-interactive tactile array devices by memorizing tactile or other sensing information.

Printable flexible tactile pressure and temperature sensors with high selectivity against bending

Flexible electronics are of great interest in a future electric device such as artificial electronic devices. Especially, artificial electronic skin (e-skin) is widely studied by developing a tactile pressure sensor on a flexible substrate. However, conventional flexible tactile sensors also detect the bending of substrate without applying a tactile pressure, and that is the one of bottlenecks to realize stable operation of a flexible device. This study demonstrates the high selectivity of tactile pressure and temperature sensors against bending based on strain engineering. To achieve high selectivity, a cantilever type strain sensor in a flexible substrate is developed. In addition, the temperature sensor is also mechanically stable. It should be worth to note that these sensors are fabricated by a fully printing method using a screen printer. This finding and demonstration eventually allow us to apply the flexible devices on versatile surfaces with accurate sensing.

Electrical powerless, thermal and optical responsive polymer-based actuator

This study demonstrates thermal and optical responsive actuator operated by skin temperature and sunlight without using electrical power supply. Different types of thermal and optical responsive actuators have been reported to date. However, actuator stimulated by both skin temperature and sunlight has yet to be demonstrated, although these are a high potential as the next class of power sources for devices. To realize an actuation using these stimuli, we propose to use a mixture of poly(N-isopropylacrylamide) (pNIPAM) as a thermal actuation material and carbon nanotubes (CNTs) as a light absorber to convert into heat on a polyethylene terephthalate (PET) substrate. By considering a packaging technique of the pNIPAM film, a human body temperature-and the sunlight-stimulated actuator is successfully demonstrated in air ambient.

Flexible, printed tactle, friction, and temperature sensor array for artificial skin

This paper describes printed, flexible, tactile, friction, and temperature sensors for the applications of an artificial electronic skin (e-skin). Conventional e-skin reported previously does not have the capability to detect friction in addition to tactile and temperature that allows us to imitate human functionalities and hold an object without dropping and/or breaking. This is due to difficulty of device fabrication on a flexible substrate. Furthermore, a printing technique is required to realize macroscale and low-cost flexible devices for the practical application. Here, we address these two challenges by arranging the structure of devices and developing the inks and printing technique.