A soft magnetic fiber paired with machine-knitted coils lets one textile unit switch among charging, motion sensing, and tactile feedback across wearable prototypes.
Paper: Machine-knitted magnetoactive textiles for wireless charging, biomechanical sensing, and haptic feedback. Image Credit: b.asia / Shutterstock
*Important notice: This news reports on an unedited version of an accepted paper and is awaiting final editing. Therefore, the paper should not be regarded as conclusive or treated as established information.
Scientists are increasingly developing electronic textiles that add functional components to flexible garments while keeping bulky hardware out of the textile itself.
A study reported in the journal npj Flexible Electronics introduced machine-knitted magnetoactive textiles that combine wireless power transfer, biomechanical sensing, and tactile feedback in a single textile structure.
The approach uses soft magnetic fibers and digitally machine-knitted electromagnets to integrate these functions into a single textile transducer, enabling soft, interactive garments that combine electronic functions with the flexibility of conventional textiles.
Challenges in Wearable Electronics
Wearable electronics aim to monitor and support everyday physical activities without restricting natural body movement. The researchers focused on three functions: wireless power transfer, biomechanical sensing, and localized tactile feedback.
Traditionally, specialized components and separate manufacturing steps have provided these functions. Adding such components to soft fabrics can increase bulk, weight, and rigidity, reducing flexibility and comfort.
Machine knitting, digital embroidery, and fiber-making can add conductive or magnetic materials to textiles, but prior systems have generally relied on separate structures or fabrication steps for each function. This can complicate manufacturing and limit wearability.
Design and Fabrication of Magnetoactive Textiles
The researchers developed a magnetoactive transducer by combining soft magnetic elastomer fibers with electromagnetic coils. Electromagnetic induction provides wireless power transfer and motion sensing, while alternating currents produce localized electromagnetic forces that vibrate the permanent-magnet fiber for tactile feedback.
The flexible magnetic fibers were fabricated by mixing liquid silicone elastomer with neodymium-iron-boron (NdFeB) magnetic microparticles.
A planetary mixer blended the materials, then the mixture was transferred into a syringe mounted on a 3D printing platform.
After curing for 12 hours at room temperature, the fibers were folded at their midpoint and exposed to an axial pulsed magnetic field. When unfolded, the two distal ends shared one magnetic polarity, while the central region had the opposite polarity.
The electromagnetic coils were produced using a computerized flatbed knitting machine programmed with dedicated textile design software. The machine routed three spools of 34-AWG copper Litz wire through one yarn feeder and treated the bundle as a single composite wire.
A double-bed jacquard knitting structure placed the conductive bundle on one side of the textile, while non-conductive acrylic yarn formed a stabilizing soft backing on the other side.
Custom stacked printed circuit boards controlled the different operating modes. The two-board control system used conventional electronic components to handle rectification, signal processing, mode switching, and haptic actuation. Relays switched a textile unit between wireless charging, sensing, and tactile feedback in 0.01 seconds (10 milliseconds). The modes operate sequentially, not simultaneously.
Transient signals also affected sensing for about 0.43 seconds on average after high-current tactile actuation.
Performance Evaluation of Magnetoactive Structures
Material characterization showed that an 88.9 wt% particle loading produced a magnetic flux density of 83.7 mT in a 1.5 mm-diameter composite fiber. At this particle concentration, the elastomer retained a strain at break of 214.7 ± 33% and a Young's modulus of 5.3 ± 2 kPa, giving it the mechanical compliance needed for wearable textiles.
The researchers examined the balance between electromagnetic performance and heat generation. Bundling three 34-AWG copper Litz wires produced strong electromagnetic fields while keeping the temperature below 36 °C under a continuous current of 1 A.
Knitting tests found that a structure with eight rows of loops (known as courses) and two columns (known as wales) balanced inductive sensing, wireless power transfer efficiency, and haptic output.
The magnetoactive textile generated a maximum open-circuit voltage of 8 V and delivered stable charging power of about 0.2 W to a 7.4 V two-cell battery pack after a roughly 100-second stabilization period using a 1 MHz transmitter. Bench testing showed sensitivity to magnetic fiber oscillations from 0.01 to 3,000 Hz. The garment demonstrations measured lower-frequency body movements such as finger tapping and wrist motion.
For tactile feedback, current pulses produced a peak fiber displacement of 1.1 mm at 40 Hz and a maximum vibrotactile force of 4.2 mN at 80 Hz. The sensing response remained stable over 80,000 vibration cycles and after machine washing, while haptic output remained stable over 1,500 actuation cycles.
Proof-of-Concept Wearable Applications
The researchers demonstrated the textile system in three wearable applications.
First, they developed a necklace-like smart choker worn over the larynx to detect vocal fold vibrations while reducing interference from ambient noise. A random forest model classified the skin-conducted signals into 15 interaction commands, covering phone functions, document navigation, and smart lighting controls. The garment delivered short vibration pulses to confirm command detection.
Second, a glove designed for rehabilitation exercises incorporated five sensing units along the fingers to monitor individual tapping exercises. The system identified the active finger, estimated tapping speed, and delivered tactile feedback when tapping speed fell below a target.
Third, the researchers developed a tubular forearm sleeve to track wrist movements during musical instrument practice. The sleeve measured wrist motion during violin vibrato and delivered tactile patterns when the player's vibrato tempo differed from the target rhythm.
The choker data came from one 28-year-old male participant, and the sleeve data came from one 25-year-old male participant. These demonstrations establish technical feasibility rather than broad clinical or user validation.
Study Scope and Outlook for Interactive Wearable Textiles
The findings show that three core functions can share a single machine-knitted textile structure, using one transducer rather than separate textile elements for each task. This design reduces the need for separate textile components while retaining a soft garment form. The complete system still requires a battery and rigid control electronics, including a stacked two-board printed circuit board.
The authors describe the architecture as a basis for future textile-based wearable devices. The three prototype garments show how the same design can be adapted to different garment shapes and uses. The demonstrated applications cover voice-based human-machine interaction, finger dexterity training, and musical skill practice. Broader uses will require further testing and validation.
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