arXiv subjects

Yoshihiro Kawahara

Publications and source records attributed to Yoshihiro Kawahara.

At least 19 recordsLinked to original sources

arXiv2026

Patched-Wall Quasistatic Cavity Resonators for 3-D Wireless Power Transfer

Traditional wireless power transfer (WPT) systems are largely limited to 1-D charging pads or 2-D charging surfaces and therefore do not support a truly ubiquitous device-powering experience. Although room-scale WPT based on multimode quasistatic cavity resonance (QSCR) has demonstrated full-volume coverage by leveraging multiple resonant modes, existing high-coverage implementations require obstructive internal conductive structures, such as a central pole. Here, we present a new structure, termed the patched-wall QSCR, that eliminates such internal obstructions while preserving full-volume coverage. By using conductive wall segments interconnected by capacitors, the proposed structure supports two complementary resonant modes that cover both the peripheral and central regions without obstructions within the charging volume. Electromagnetic simulations show that, by selectively exciting these two resonant modes, the proposed structure achieves a minimum power-transfer efficiency of 48.1% throughout the evaluated interior volume of a 54m^3 enclosure while preserving an unobstructed charging space.

physics.app-ph↗

arXiv2026

Hierarchical resonators for localized charging in room-scale magnetoquasistatic wireless power systems

Magnetoquasistatic wireless power transfer can deliver substantial power to mobile devices over near-field links. Room-scale implementations, such as quasistatic cavity resonators, extend this capability over large enclosed volumes, but their efficiency drops sharply for centimeter-scale or misoriented receivers because the magnetic field is spatially broad and weakly coupled to small coils. Here, we introduce hierarchical resonators that act as selectively activated relays within a room-scale quasistatic cavity resonator, coupling to the ambient magnetic field and re-emitting a stronger local field near a target receiver. This architecture enables localized power delivery to miniature devices without requiring global reshaping of the room-scale cavity mode. Experimentally, the hierarchical link improves power transfer efficiency by more than two orders of magnitude relative to direct room-scale transfer and delivers up to 500 mW of DC power to a 15 mm receiver. We further demonstrate selective multi-relay operation and field reorientation for furniture-embedded charging scenarios. These results establish a scalable route to reconfigurable wireless power delivery for miniature and batteryless devices in room-scale environments.

physics.app-ph↗

arXiv2026

JSL-DC: A Word-Level Japanese Sign Language Dataset with Linguist-Derived Descriptions for Distinguishing Confusable Signs

Effective sign language (SL) acquisition is crucial for deaf children, yet 95% are born to hearing parents who often lack proficiency in SL. SL recognition can power learning tools to help parents communicate with their children. However, Japanese Sign Language (JSL) lacks large-scale, multi-signer datasets, hindering the development of models that can generalize to new users. To address this gap, we introduce JSL-DC, the largest JSL dataset by video count, comprising 36.7K videos from 19 signers. The entire process was Deaf-centric: the lexicon comprising 270 JSL words was selected by Deaf and Coda linguists to facilitate parent-child communication, all participants were Deaf individuals who use JSL daily, and the data underwent a two-stage review process involving Deaf linguists. Moreover, we provide linguist-derived descriptions for distinguishing confusable signs. We demonstrate that the proposed model inspired by the descriptions outperforms state-of-the-art recognition methods by 9.8% on the confusable subset. The dataset, along with its linguistic description that inspires new models, will be released under a CC-BY 4.0 license to accelerate research in SL recognition.

cs.CV↗

arXiv2026

picoRing dual: ultralow-power bimanual ring controllers for everyday AR

Advances in smart eyewear, such as AR glasses and HMDs, bring digital information into outdoor and public situations. However, traditional handheld controllers for hand interactions remain too bulky and socially awkward for these everyday contexts, failing to match the portability and subtlety required for mobile use. Ring-based input controllers offer a reliable finger-sensing solution; however, continuous operation with a tiny, battery-constrained ring remains challenging. Here, we present picoRing dual, an ultra-low-power bimanual interface with a pair of ring-wristbands based on inductive coupling. Unlike the original picoRing mouse limited to uni-manual tens of bps slow trackball interaction, picoRing dual uses a stable NFC-based ring-to-wristband link to capture fast index-finger motions and thumb-to-index microgestures at approximately 1.4 kbps. By tuning the ring's coil geometry, our system achieves stable NFC against finger bending while complying with NFC's ultra-low power profile. Therefore, picoRing dual with approximately 0.86 mW on the ring side can last approximately 100 continuous hours on a single charge of the ring's 20 mAh battery. picoRing dual has the potential to offer ubiquitous finger input for everyday AR interaction.

cs.HC↗

arXiv2026

Machine-knittable, Magnetically-Plug-n-Play E-Textile Prototyping

Electronic textiles (e-textiles) integrated with wearable sensors are essential for daily motion monitoring and long-term physiological sensing. For example, capturing optimal kinematic or bio-signals requires aligning sensors with specific anatomical parts, which vary significantly across individuals and application scenarios. This necessity for personalization makes e-textile prototyping inherently iterative, however current fabrication methods, such as manual conductive stitching, rely on permanent bonds that restrict rapid adjustment. This paper introduces Plug-n-play e-knit, a machine-knittable e-textile prototyping platform that enables repeatable, quick adjustment of sensor positions across garments. First, to cover the large area of the textile for prototyping, we use industrial digital knitting of conductive yarn to integrate power and communication buses directly into the large-scale textile. Then, to ensure plug-n-play attachment to the textile, we employ soft-magnetic connectors that enable sensors to be repeatedly plugged into the wiring without damaging the fabric. Furthermore, our LED-positioning system enables the automatic identification and localization of each sensor node. We demonstrate the platform's capabilities through forearm movement calibration and position-aware temperature mapping.

cs.HC↗

arXiv2026

TopoStyle: Supporting Iterative Design with Generative AI for 2.5D Topology Optimization

Topology optimization(TO) is widely used in engineering because of its ability to save material and optimize structural performance. Although prior work has explored 2D human-centered design tool for TO, the results are often limited in variety and offer weak customizability. Meanwhile, due to the high computational and time costs of TO, researchers have attempted to address these issues using generative AI; however, such methods often provide limited interactivity. In addition, topology optimization in many cases needs to balance structural performance and aesthetic qualities through iterative design, a perspective that has rarely been emphasized in traditional TO. We present TopoStyle, an iterative design tool for 2.5D topology optimization using a 2D diffusion model. We explore two interaction methods. The first exports 3D parts to a graphical interface for hand-drawn interaction. The second enables direct interaction within 3D modeling software using points. Our tool also supports the use of masks to apply topology optimization to specific regions, allowing users to address customized design needs. We compare and evaluate both performance and interaction methods, and investigate how TopoStyle can balance performance and aesthetics while improving design efficiency through customization and iterative design. Finally, we demonstrate the application scenarios of TopoStyle through several design cases.

cs.HC↗

arXiv2026

3D-Printing Water-Soluble Channels Filled with Liquid Metal for Recyclable and Cuttable Wireless Power Sheet

A recyclable and cuttable wireless power transfer (WPT) sheet is proposed, enabled by H-tree wiring and water-soluble channels filled with liquid metal (LM). Conventional 2D WPT systems lose their functionality when physically damaged or modified. The H-tree wiring pattern maintains the operation of the remaining coils even after the outer region of the sheet is cut away. The LM can be recovered by dissolving 3D-printed polyvinyl alcohol (PVA) channels in water. The sheet dimensions were experimentally optimized, and a Q-factor over 55 was achieved at 6.78 MHz. The sheet maintained its bending stiffness and electrical resistance during 100 bending cycles. After four dissolution-refabrication cycles, 98 percent of the LM was recovered with stable electrical properties. The WPT sheet can be integrated into everyday objects and enables long-term, continuous operation of surrounding electronic devices, contributing to IoT applications and ambient computing.

cs.HC↗

arXiv2026

A Passive Elastic-Folding Mechanism for Stackable Airdrop Sensors

Air-dispersed sensor networks deployed from aerial robotic systems (e.g., UAVs) provide a low-cost approach to wide-area environmental monitoring. However, existing methods often rely on active actuators for mid-air shape or trajectory control, increasing both power consumption and system cost. Here, we introduce a passive elastic-folding hinge mechanism that transforms sensors from a flat, stackable form into a three-dimensional structure upon release. Hinges are fabricated by laminating commercial sheet materials with rigid printed circuit boards (PCBs) and programming fold angles through a single oven-heating step, enabling scalable production without specialized equipment. Our geometric model links laminate geometry, hinge mechanics, and resulting fold angle, providing a predictive design methodology for target configurations. Laboratory tests confirmed fold angles between 10 degrees and 100 degrees, with a standard deviation of 4 degrees and high repeatability. Field trials further demonstrated reliable data collection and LoRa transmission during dispersion, while the Horizontal Wind Model (HWM)-based trajectory simulations indicated strong potential for wide-area sensing exceeding 10 km.

cs.RO↗

arXiv2026

Sketch2Topo: Using Hand-Drawn Inputs for Diffusion-Based Topology Optimization

Topology optimization (TO) is employed in engineering to optimize structural performance while maximizing material efficiency. However, traditional TO methods incur significant computational and time costs. Although research has leveraged generative AI to predict TO outcomes and validated feasibility and accuracy, existing approaches still suffer from limited customizability and impose a high cognitive load on users. Furthermore, balancing structural performance with aesthetic attributes remains a persistent challenge. We developed Sketch2Topo, which augments a diffusion-based TO model with image-to-image generation and image editing capabilities. With Sketch2Topo, users can use sketching to customize geometries and specify physical constraints. The tool also supports mask input, enabling users to perform TO on selected regions only, thereby supporting higher levels of customization. We summarize the workflow and details of the tool and conduct a brief quantitative evaluation. Finally, we explore application scenarios and discuss how hand-drawn input improves usability while balancing functionality and aesthetics.

cs.HC↗

arXiv2026

Body-scale NFC for wearables: human-centric body-scale NFC networking for ultra-low-power wearable devices (Demo of UTokyo Kawahara Lab 2025)

Near Field Communication (NFC) is a promising technology for ultra-low-power wearables, yet its short communication range limits its use to narrow-area, point-to-point interactions. We propose a body-scale NFC networking system that extends NFC coverage around the body, enabling surface-to-multipoint communication with distributed NFC sensor tags. This demonstration introduces two key technologies: Meander NFC and picoRing NFC. First, Meander NFC expands a clothing-based NFC networking area up to body scale while enabling a stable readout of small NFC tags occupying 1% of the coverage area. Meander NFC uses a meander coil which creates a spatially confined inductive field along the textile surface, ensuring robust coupling with small tags while preventing undesired electromagnetic body coupling. Second, picoRing NFC solves the weak inductive coupling caused by distance and size mismatches. By leveraging middle-range NFC and coil optimization, picoRing NFC extends the communication range to connect these disparate nodes between the ring and wristband.

cs.NI↗

arXiv2025

Magnetic field estimation using Gaussian process regression for interactive wireless power system design

Wireless power transfer (WPT) with coupled resonators offers a promising solution for the seamless powering of electronic devices. Interactive design approaches that visualize the magnetic field and power transfer efficiency based on system geometry adjustments can facilitate the understanding and exploration of the behavior of these systems for dynamic applications. However, typical electromagnetic field simulation methods, such as the Method of Moments (MoM), require significant computational resources, limiting the rate at which computation can be performed for acceptable interactivity. Furthermore, the system's sensitivity to positional and geometrical changes necessitates a large number of simulations, and structures such as ferromagnetic shields further complicate these simulations. Here, we introduce a machine learning approach using Gaussian Process Regression (GPR), demonstrating for the first time the rapid estimation of the entire magnetic field and power transfer efficiency for near-field coupled systems. To achieve quick and accurate estimation, we develop 3D adaptive grid systems and an active learning strategy to effectively capture the nonlinear interactions between complex system geometries and magnetic fields. By training a regression model, our approach achieves magnetic field computation with sub-second latency and with an average error of less than 6% when validated against independent electromagnetic simulation results.

physics.app-ph↗

arXiv2025

OriStitch: A Machine Embroidery Workflow to Turn Existing Fabrics into Self-Folding 3D Textiles

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 existing materials (e.g., leather, woven fabric, and denim). We present the design of specific embroidered hinges that fully close under exposure to heat. We discuss the stitch pattern design, thread and fabric selection, and heating conditions. To allow users to create 3D textiles using our hinges, we create a tool to convert 3D meshes to 2D stitch patterns automatically, as well as an end-to-end fabrication and actuation workflow. To validate this workflow, we designed and fabricated a cap (303 hinges), a handbag (338 hinges), and a cover for an organically shaped vase (140 hinges). In technical evaluation, we found that our tool successfully converted 23/28 models (textures and volumetric objects) found in related papers. We also demonstrate the folding performance across different materials (suede leather, cork, Neoprene, and felt).

cs.HC↗

arXiv2025

Ultra-low-power ring-based wireless tinymouse

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 lifespan frequently disrupts users' mouse use with the need for frequent charging. This paper presents picoRing mouse, enabling a continuous ring-based mouse interaction with ultra-low-powered ring-to-wristband wireless communication. picoRing mouse employs a coil-based impedance sensing named semi-passive inductive telemetry, allowing a wristband coil to capture a unique frequency response of a nearby ring coil via a sensitive inductive coupling between the coils. The ring coil converts the corresponding user's mouse input into the unique frequency response via an up to 449 uW mouse-driven modulation system. Therefore, the continuous use of picoRing mouse can last approximately 600 (8hrs use/day)-1000 (4hrs use/day) hours on a single charge of a 27 mAh battery while supporting subtle thumb-to-index scrolling and pressing interactions in real-world wearable computing situations.

cs.HC↗

arXiv2025

Full-body WPT: wireless powering with meandered e-textiles

We present Full-body WPT, wireless power networking around the human body using a meandered textile coil. Unlike traditional inductive systems that emit strong fields into the deep tissue inside the body, the meander coil enables localized generation of strong magnetic field constrained to the skin surface, even when scaled to the size of the human body. Such localized inductive system enhances both safety and efficiency of wireless power around the body. Furthermore, the use of low-loss conductive yarn achieve energy-efficient and lightweight design. We analyze the performance of our design through simulations and experimental prototypes, demonstrating high power transfer efficiency and adaptability to user movement and posture. Our system provides a safe and efficient distributed power network using meandered textile coils integrated into wearable materials, highlighting the potential of body-centric wireless power networking as a foundational layer for ubiquitous health monitoring, augmented reality, and human-machine interaction systems.

cs.HC↗

arXiv2025

Wireless charging and readout via textile coil for continuous full-body wearable computing

The growing use of wearable devices for activity tracking, healthcare, and haptics faces challenges due to the bulkiness and short lifespan of batteries. Integration of a textile-based wireless charging and readout system into everyday clothing can enable seamless power supply and data collection around the body. However, expanding such system to cover the entire body is challenging, as it increases electromagnetic interference with the body, degrading the performance of wireless system. This article introduces a meandered textile coil designed for body-scale, efficient wireless charging and readout. The meander coil can confine a strong inductive field near the body surface, ensuring W-class safe charging and sensitive readout with uW-class low power. Moreover, its zigzag design is simple enough for mass production on industrial knitting machines. Therefore, the body-scale meander coil can continuously operate battery-free wearable devices across the body, leading to ubiquitous deployment of continuous full-body wearable computing into everyday clothing.

cs.HC↗

arXiv2025

Full-body NFC: body-scale near-field sensor networks with machine-knittable meandered e-textiles

Wireless body networks comprising battery-free on-body sensors and textile-based wireless readers can enable daily health monitoring and activity tracking by continuously monitoring physiological signals across the body. However, previous textile-based wireless networks made of coils or antennas have limited the data and power transmission area because covering the whole body results in undesirable levels of electromagnetic interactions with the body, degrading the scalability, power consumption, and data rate. Here, we report Full-body NFC, digitally-knitted electronic textiles based on a twin meander coil design that enables body-scale near-field communication (NFC) with battery-free sensor tags arbitrarily placed around the body. Full-body NFC features i) a meander coil that enhances the magnetic field intensity on the body's surface while suppressing undesired interactions with deep tissues, in addition to ii) paired identical coil structure that enables highly-sensitive and motion-robust NFC using a differential architecture. Additionally, industrial digital knitting machines loaded with conductive yarn allow the integration of the Full-body NFC system into daily garments supporting approximately $70-80\%$ large-scale NFC-enabled area of the body. We demonstrate Full-body NFC could achieve mW-class energy-efficient near-field sensor networks with hundreds of kbps-class NFC battery-free sensor tags occupying less than $0.3\%$ of the coverage area under severe body movements.

cs.HC↗

arXiv2025

Joint-repositionable Inner-wireless Planar Snake Robot

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, inner-wireless snake robot that enables multi-joint-like locomotion using a low-powered underactuated mechanism. The snake robot, consisting of a series of flexible passive links, can dynamically change its joint coupling configuration by repositioning motor-driven joint units along rack gears inside the robot. Additionally, a soft robot skin wirelessly powers the internal joint units, avoiding the risk of wire tangling and disconnection caused by the movable joint units. The combination of the joint-repositionable mechanism and the wireless-charging-enabled soft skin achieves a high degree of bending, along with a lightweight structure of 1.3 kg and energy-efficient wireless power transmission of 7.6 watts.

cs.RO↗

arXiv2025

Demo of picoRing mouse: an ultra-low-powered wireless mouse ring with ring-to-wristband coil-based impedance sensing

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 enabling continuous ring-based mouse interaction with ultra-low-powered ring-to-wristband wireless communication through a coil-based impedance sensing method called semi-passive inductive telemetry. This allows a wristband coil to capture a unique frequency response of a nearby ring coil via sensitive inductive coupling, converting the user's mouse input into the unique frequency response via an 820 uW mouse-driven modulation module. Thus, the continuous use of picoRing mouse can potentially last over 92 hours on a single charge of a 20 mAh battery while supporting subtle scrolling and pressing interactions.

cs.HC↗