⚡ electrical engineering

Sustainable and Circular Wireless E-Textiles based on Modular Flexible Radio Frequency contactless Interposers

This paper presents a sustainable, modular wireless e-textile system utilizing contactless, capacitively coupled flexible interposers that enable high-performance gigabit data transmission and active RF circuit integration while supporting solvent-assisted recycling to significantly reduce environmental impact.

Original authors: Tasneem Khodair, Xiaochuan Fang, Benjamin King, Nikolas Bruce, Jeff Kettle, Mahmoud Wagih

Published 2026-09-14

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CC BY 4.0

Original authors: Tasneem Khodair, Xiaochuan Fang, Benjamin King, Nikolas Bruce, Jeff Kettle, Mahmoud Wagih

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine a world where the clothes we wear are not just fabric, but intelligent companions capable of monitoring our health, communicating with our devices, or even adapting to our environment. This vision relies on "smart textiles," or e-textiles, which blend the soft, flexible nature of cloth with the rigid, powerful chips found in our phones and computers. For years, engineers have struggled to marry these two very different materials. Traditional methods involve soldering hard electronic components directly onto soft fabric, a process that creates weak points prone to breaking when the garment stretches or bends. Furthermore, once these electronics are sewn into a shirt, they are nearly impossible to remove, meaning that when the clothing reaches the end of its life, the valuable chips are often discarded along with the fabric, contributing to a growing mountain of electronic waste. The challenge has been to create a connection that is strong enough to carry high-speed data, flexible enough to move with the body, and modular enough to be taken apart and reused.

A team of researchers at the University of Glasgow has developed a new approach that solves these problems without using any physical glue or solder. Instead of forcing a rigid circuit board onto a piece of cloth, they created a system where the two components simply sit on top of one another, touching but not connected. They call this a "contactless" interface. The electronic components are mounted on a thin, flexible circuit board, while the fabric is printed with special silver lines that act as pathways for signals. When the board is placed over the fabric, the two layers form a tiny capacitor—a device that can store electrical energy. This capacitor acts as a bridge, allowing radio signals to jump across the gap between the board and the fabric without ever needing a physical wire or a melted solder joint to connect them. It is a bit like holding two pieces of paper close together; even though they are not touching, a magnetic field can pass between them, but in this case, it is an electrical signal passing through the air gap.

The researchers tested this method to see if it could handle the fast data speeds required for modern wireless communication. They found that the connection was remarkably efficient, losing very little signal strength as it passed from the board to the fabric. They were able to send data at speeds of up to 3.6 gigabits per second, which is fast enough to stream high-definition video or support complex medical monitoring in real time. To prove the system was robust, they pushed it with high-power radio signals, similar to what a strong transmitter might use. Even when the system was running at high power, the temperature of the fabric barely rose, staying well below levels that would damage the material or hurt a wearer. They also built a complete wireless system, connecting these flexible circuits to a small antenna printed directly onto the cloth, and demonstrated that it could successfully send and receive signals through the air.

Perhaps the most significant aspect of this work is how it changes the life cycle of smart clothing. Because the electronic board is not permanently glued to the fabric, it can be easily removed when the garment is worn out. The researchers demonstrated a simple recycling process where they used a mild solvent and a little heat to soften the layer holding the board in place. This allowed them to peel the valuable electronic module off the old fabric without damaging it. They then took this recovered module and attached it to a fresh piece of cloth, and it worked just as well as a brand-new one. This means the expensive and energy-intensive electronic parts can be reused many times, while the fabric itself can be discarded or recycled separately.

By calculating the environmental impact of this process, the team showed that reusing the electronic modules significantly reduces the carbon footprint of making smart clothes. The energy and materials required to manufacture the chips are the largest contributors to the environmental cost of these devices. By keeping those chips in use for multiple generations of clothing, the researchers found that the global warming potential of each device drops by at least 23 percent with every reuse. This work does not just offer a new way to connect wires; it offers a new way to think about the future of wearable technology, one where high-performance electronics and sustainable fashion can coexist without compromising on either durability or the environment.

Technical Summary: Sustainable and Circular Wireless E-Textiles based on Modular Flexible Radio Frequency Contactless Interposers

Problem Statement
The integration of rigid Radio Frequency Integrated Circuits (RFICs) into flexible electronic textiles (e-textiles) presents significant challenges regarding electrical performance, reliability, and circularity. Conventional methods, such as direct soldering or conductive adhesives, often create mechanical failure points when the textile is stretched or bent, degrade RF performance at GHz frequencies due to parasitic inductances, and permanently bond high-value semiconductor components to disposable fabric substrates. This permanent bonding hinders the recovery of electronic components at the end-of-life (EoL), contributing to the growing global e-waste problem and preventing the realization of truly modular, repairable, and sustainable smart wearable systems.

Methodology
The authors propose a modular, contactless interposer architecture that bridges the gap between rigid surface-mount components and soft textile circuits without physical electrical contact. The core of the system is a Flexible Printed Circuit Board (FPCB) interposer that is capacitively coupled to screen-printed silver coplanar waveguide (CPW) traces laminated directly onto a textile substrate.

Fabrication: The textile substrate utilizes commercially available cotton covered with a 63 µm thermoplastic polyurethane (TPU) film. Silver CPW traces are created via screen-printing and heat-pressed onto the textile. The FPCB interposer, containing the RFICs, is laminated onto the textile using a secondary TPU layer.
Coupling Mechanism: The interface functions as a parallel-plate capacitor where the FPCB copper pads (ENIG plated) and the textile silver traces act as plates, with the FPCB's polyimide substrate (25 µm or 75 µm) serving as the dielectric. This creates a DC-blocking, AC-coupled transition.
Circularity Process: To enable recycling, a solvent-assisted delamination process is employed. Acetone is applied to the TPU encapsulation, followed by mild heat pressing (100°C), which softens the TPU and allows for the clean separation and recovery of the rigid FPCB interposer from the textile substrate.

Key Contributions and Results

High-Performance Contactless RF Transition:
- The capacitive interface achieves an insertion loss of less than 0.5 dB per transition at 1 GHz.
- The system supports broadband transmission with a reflection coefficient ( $|S_{11}|$ ) better than -10 dB and transmission coefficient ( $|S_{21}|$ ) better than -3 dB across the target operating bandwidth (up to 2 GHz, relevant for ISM bands).
- Time-domain analysis confirms distortion-free data transmission at rates up to 3.6 Gbps using Manchester encoding, validating the interface's suitability for high-speed wireless applications.
Active Circuit Integration and Power Handling:
- The architecture successfully integrates active components, including single-stage and cascaded two-stage RF Power Amplifiers (PAs).
- Measured gain and reverse isolation of the textile-integrated amplifiers closely match manufacturer datasheets and FPCB-only benchmarks, demonstrating that the contactless transition does not degrade active component performance.
- Thermal reliability was verified under continuous high-power conditions. A 5 W RF input resulted in a temperature rise of less than 20°C along the textile lines, and active modules operated safely with surface temperatures under 50°C, confirming no structural failure or performance degradation under thermal stress.
System-Level Wireless Demonstration:
- A complete active front-end was constructed, featuring a cascaded two-stage amplifier chain integrated with a screen-printed monopole antenna resonating at 815 MHz.
- Over-the-Air (OTA) measurements demonstrated a system gain difference of over 40 dB between ON and OFF states, confirming effective signal transmission and deep isolation.
Circularity and Environmental Impact:
- The delamination process successfully recovers the FPCB interposer with no measurable degradation in RF performance (gain and gain compression remain stable) compared to pristine samples.
- A comparative Life Cycle Assessment (LCA) revealed that while silicon ICs dominate the Global Warming Potential (GWP) of the system, the proposed modular approach significantly reduces environmental impact.
- By treating the textile as a sacrificial carrier and reusing the interposer, the study calculates at least a 23% reduction in GWP per recycling instance. The LCA indicates that the environmental cost of manufacturing a second device is reduced to the replacement of the screen-printed textile and the energy required for the recycling process.

Significance
The paper claims to present the first demonstration of broadband, contactless RF transitions directly integrated on textile substrates for smart textiles. By replacing solder joints and conductive adhesives with a capacitive coupling interface, the work establishes a scalable route toward high-performance, modular wireless e-textiles. The significance lies in addressing the critical trade-off between RF performance and mechanical flexibility while enabling a circular economy model where high-value electronic modules can be recovered and reused, thereby mitigating the environmental footprint of next-generation wearable electronics. The proposed approach aligns with industrial textile manufacturing processes, suggesting a viable pathway for future sustainable smart textile production.

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