Yoshihiro Kawahara

• PhD
• Professor (Associate) at The University of Tokyo

Wireless mouse rings offer subtle, reliable pointing interactions for wearable computing platforms. However, the small battery below 27 mAh in the miniature rings restricts the ring's continuous lifespan to just 1-10 hours, because current low-powered wireless communication such as BLE is power-consuming for ring's continuous use. The ring's short...

The monitoring of indoor HVAC data is critical in smart buildings to optimize energy use and maintain thermal comfort. Conventional stationary sensor systems face challenges in capturing data from elevated or diverse spatial points, limiting their ability to provide comprehensive volumetric data. These systems also lack adaptability to dynamic envi...

The powering range of wireless power transfer (WPT) systems is typically confined to areas close to the transmitter. Shape-reconfigurable two-dimensional (2-D) relay resonator arrays have been developed to extend this range, offering greater deployment flexibility. However, these arrays encounter challenges due to cross-coupling among adjacent reso...

Wireless power transfer has the potential to seamlessly power electronic systems, such as electric vehicles, industrial robots, and mobile devices. However, the leakage magnetic field is a critical bottleneck that limits the transferable power level, and heavy ferromagnetic shields are needed for transferring large amounts of power. In this paper,...

Magnetoquasistatic wireless power transfer can be used to charge and power electronic devices such as smartphones and small home appliances. However, existing coil-based transmitters, which are composed of wire conductors, have a limited range. Here we show that multimode quasistatic cavity resonance can provide room-scale wireless power transfer....

Wireless mouse rings offer subtle, reliable pointing interactions for wearable computing platforms, but the small battery below 27 mAh in the miniature rings restricts the ring's continuous lifespan to just 1-2 hours due to the power consumption of current low-powered wireless communication like BLE. However, the picoRing mouse addresses this by en...

Bio-inspired multi-joint snake robots offer the advantages of terrain adaptability due to their limbless structure and high flexibility. However, a series of dozens of motor units in typical multiple-joint snake robots results in a heavy body structure and hundreds of watts of high power consumption. This paper presents a joint-repositionable, inne...

Prototyping electronic textile (e-textile) involves embedding electronic components into fabrics to develop smart clothing with specific functionalities. However, this process is still challenging since the complicated wiring setup is required during experimental phases. This paper presents plug-n-play e-knit, a large-scale, repositionable e-textil...

OriStitch is a computational fabrication workflow to turn existing flat fabrics into self-folding 3D structures. Users turn fabrics into self-folding sheets by machine embroidering functional threads in specific patterns on fabrics, and then apply heat to deform the structure into a target 3D structure. OriStitch is compatible with a range of exist...

Hot-desking offices, where users move to seats according to their preferences, have garnered attention for the efficient use of office space and cost-saving benefits, highlighting the need for an effective seat recommendation system. Traditional systems focus on specific parameters such as temperature or illuminance; however, user preferences vary...

Objective To investigate if cartilage conduction (CC) rerouting devices are noninferior to air-conduction (AC) rerouting devices for single-sided deafness (SSD) patients by measuring objective and subjective performance using speech-in-noise tests that resemble a realistic hearing environment, sound localization tests, and standardized questionnair...

Analyzing trajectory data within buildings provides valuable insights for enhancing environmental design and habitability. To gain a comprehensive understanding of how architectural structures affect human behavior, it is necessary to collect extensive spatial-temporal trajectory data from various building types. Therefore, we need methods that can...

This letter presents trimmed aperture corner reflectors (CRs) for assigning angle selectivity to chipless radio frequency identification (RFID) tags. This angle selectivity can benefit the landmark use of CR-based tags by exhibiting different signals in each direction, which enables infrastructure-to-device communication with rich context. The key...

We propose Inkjet 4D Print, a self-folding fabrication method of 3D origami tessellations by printing 2D patterns on both sides of a heat-shrinkable base sheet, using a commercialized inkjet ultraviolet (UV) printer. Compared to the previous folding-based 4D printing approach using fused deposition modeling (FDM) 3D printers [An et al. 2018], our m...

The indoor crowd density monitoring system using BLE beacons is one of the effective ways to prevent overcrowded indoor situations. The indoor crowd density monitoring system consists of a mobile application at the user's side and the beacon sensor network as the infrastructure. Since the performance of crowd density monitoring highly depends on ho...

Wireless power transfer has the potential to seamlessly power electronic systems, such as electric vehicles, industrial robots, and mobile devices. However, the leakage magnetic field is a critical bottleneck that limits the transferable power level, and heavy ferromagnetic shields are needed for transferring large amounts of power. In this paper,...

Jamming grippers can grasp objects of various shapes with simple control. However, grasping fragile objects is challenging, as a secure grasp requires firm pressing, which can potentially damage delicate objects. Thus, it is important to achieve an appropriate pressing distance for damage-free grasping. Consequently, the detection of the deformatio...

Conventional model theories are not suitable to control soft-bodied robots as deformable materials present rapidly changing behaviors. Neuromorphic electronics are now entering the field of robotics, demonstrating that a highly integrated device can mimic the fundamental properties of a sensory synaptic system, including learning and proprioception...

Soft-bodied animals move by using the anisotropic friction between their body and the environment. Inspired by these bodily structures, we propose a wriggle soft-bodied robot with an anisotropic frictional skin to support its locomotion. We combine soft and rigid materials in 3D printers to make different patterns of frictional anisotropy. We build...

Wearable haptic displays can provide haptic information while allowing for free body movement. Among these haptic displays, pneumatic haptic displays have the advantages of flexibility and lightweight; however, they require bulky air tubes and a heavy air compressor. To solve this problem, we propose a wearable haptic display that uses a liquid-to-...

Wireless power transfer technology has seen steady advances in recent years, yet seamlessly charging devices within large volumes of space remains challenging. Although quasi-static cavity resonators have recently demonstrated safe wireless power transfer at room-scale sizes at significant power levels, previous work investigated this concept using...

Energy-efficient and unconstrained wearable sensing platforms are essential for ubiquitous healthcare and activity monitoring applications. This paper presents Twin Meander Coil for wirelessly connecting battery-free on-body sensors to a textile-based reader knitted into clothing. This connection is based on passive inductive telemetry (PIT), where...

Pneumatic actuators have been applied to wearable haptic devices owing to their lightweight. However, the pneumatic actuators require an air compressor and air valves. Thus, the resulting systems are large and heavy. We have studied a haptic display using a liquid-to-gas phase change actuator. The actuator is composed of a thin plastic pouch contai...

Insects have acquired various types of wings over their course of evolution and have become the most successful terrestrial animals. Consequently, the essence of their excellent environmental adaptability and locomotive ability should be clarified; a simple and versatile method to artificially reproduce the complex structure and various functions o...

The need for cable connection with soft robotic systems suppresses the benefits granted by their softness and flexibility. Such systems can be untethered by equipping batteries or by relying on non-electrical actuation mechanisms. However, these approaches cannot simultaneously support long-term and intelligent operations. This research examines a...

Wireless power transfer via magnetic resonance coupling offers the prospect of autonomously charging connected devices. Previous work demonstrated that the system deployment can be facilitated by “routing” power on 2-D relay resonator arrays, using the multi-hop phenomenon. Power propagates through untethered relay resonators in such systems, and t...

Magnetoquasistatic wireless power transfer can be used to charge and power electronic devices such as smartphones and small home appliances. However, existing coil-based transmitters, which are composed of wire conductors, have a limited range. Here we show that multimode quasistatic cavity resonance can provide room-scale wireless power transfer....

Inflatables are safe and lightweight structures even at the human scale. Inflatable robots are expected to be applied to physical human-robot interaction (pHRI). Although active joint mechanisms are essential for developing inflatable robots, the existing mechanisms are complex in structure and it is difficult to integrate actuators, which diminish...

In the present study, we propose a largely deformable and miniaturized soft actuator that is made by an elastic rubber bladder (called a pouch) with a low-boiling-point liquid. When the temperature of the low-boiling-point liquid reaches 34 $^{\circ }$ C, the liquid inside the pouch evaporates, and the whole structure inflates. Thanks to the prop...

Widespread research is being conducted on computational materials. The challenge for the realization of computational materials is how to weave computers into everyday objects consisting of various shapes and form factors. One idea to achieve this vision is to build physical computational particles that can cooperatively communicate among others an...

In recent years, soft robots have been attracting interest because of their potential for new application fields. Among soft actuators for soft robots, liquid-to-gas phase change actuators have the advantage of structural simplicity. However, the actuators require an external heater to vaporize a low boiling point liquid inside the actuator. The he...

In this paper, we investigate a multitone simultaneous wireless information and power transfer (SWIPT) based modulation scheme for battery-less Internet of Things (IoT) nodes that works in the ultra high frequency (UHF) region. The conventional SWIPT system is assumed to have power-consuming communication modules. Having such modules on to the IoT...

Personal mobility devices (PMDs) are gaining ground as a modern form of transportation that can seamlessly connect the first and the last miles to public transportation. The batteries installed in these devices are currently charged via wires, which enforce unnecessary charging mainly done by humans and exposed electrodes that limit durability in o...

We propose a 3D-printed interface, CAPath, in which conductive contact points are in a grid layout. This structure allows not only specific inputs (e.g., scrolling or pinching) but also general 2D inputs and gestures that fully leverage the "touch surface." We provide the requirements to fabricate the interface and implement a designing system to g...

We present the first demonstration of a battery-free untethered wirelessly powered sub-gram jumping robot on an insect-scale. In order to operate the insect-sized robot autonomously, the limitation in battery use emphasizes the need for a wireless power transmission system as an onboard power solution. We designed a wireless power transmission syst...

Despite the recent growth in popularity of personal mobility devices (e.g., e-scooters and e-skateboards), they still suffer from limited safety and narrow design form factors, due to their rigid structures. On the other hand, inflatable interfaces studied in human-computer interaction can achieve large volume change by simple inflation/deflation....

Caterpillars do not process skeleton inside its body; instead, they utilize the environment, e.g., branches, to maintain the posture against gravity. This strategy is also beneficial for soft-bodied robotic artifacts, which allows us to simplify the body and control design. This paper presents a soft-bodied crawling robot able to locomote in an ups...

Hydrogel glucose sensors with boronic acid-based fluorescence intensity theoretically hold promise to improve in vivo continuous glucose monitoring (CGM) by facilitating long-lasting accuracy. However, these sensors generally degrade after implantation and the fluorescence intensity decreases immediately over time. Herein, we describe a hydrogel gl...

We envision "Soft Mobility," which is a new type of personal mobility made of soft, lightweight, and inflatable materials. A soft body enables safer user interactions with pedestrians and drivers; the lightweight and inflatable properties allow the users to easily carry it as a "portable device," by deflating, folding, and packing it into, for exam...

As robots become more complex, small, and sophisticated, the cost and effort necessary for “wiring” become critical; the complex wiring makes the fabrication costly and necessitates care about space and stiffness of wires, which can inhibit the deformation of soft bodied robots. The concept of power bus, which powers, controls, and monitors multipl...

This paper models and analyzes the power efficiency of wireless power transfer systems with arbitrary load impedances using passive two-port network parameters. In this formulation, two novel indices--the load resistance optimization factor and the load reactance optimization factor--are defined and introduced to indicate the deviation of the load...

Caregivers hug their infants to express affection and joy. However, it remains unknown how infants react to being hugged. Here we examined heart rate responses in first-year infants during a hug, hold, and tight hug from parents. Infants older than four months showed an increased R-R interval (RRI) during a hug, indicating reduced heart rates and p...

Conventional planar pneumatic actuators have not been able to make the most of their thin, lightweight, and flexible nature due to tubes and pumps inevitably connected to them. In this article, we build upon our prior work and propose Liquid Pouch Motors, a family of printable soft actuators that consist of one or more gas-tight bladders (called po...

Wireless power transfer (WPT) has the significant potential for soft-bodied continuum robots to extend the operational time limitlessly and reduce weight. However, rigid power receiver coils, widely used in WPT, hinder the continuum deformation of the robot, and as a result, the function realization using the continuum deformation (e.g., locomotion...

Untethered control of soft-bodied robots is attractive for interactions in a variety of unstructured and dynamic environments. However, soft robotics systems are currently limited in terms of wireless, selective, and scalable control of multiple actuators. Therefore, we propose a method to wirelessly drive multiple soft actuators by laser projectio...

Energy harvesting (EH) technologies are useful for the semi-permanent operation of wireless sensor networks, especially, for agricultural monitoring as the networks need to be installed in large areas where power supply is unavailable. In this paper, we propose a battery-free soil-monitoring sensor for agriculture, which leverages the temperature d...