Structural damage in carbon fiber composites can now be detected and transmitted wirelessly using energy generated by the damage itself.
Study: From vibration to information: self-powered crack detection and wireless communication in carbon fiber reinforced piezoelectric nanocomposites. Image Credit: Yo_bie/Shutterstock.com
A recent publication in the International Journal of Smart and Nano Materials introduces a laminated composite that unites structural integrity, energy harvesting, and real-time sensing.
The material, a combination of potassium sodium niobate-epoxy (KNN-epoxy) and carbon fiber-reinforced polymer (CFRP), serves simultaneously as a load-bearing element and a self-sustaining sensing platform.
In practical terms, the composite can detect structural damage, convert mechanical vibrations into electrical energy, and wirelessly transmit data without reliance on external power. It offers a compelling solution to ongoing challenges in autonomous sensing systems, particularly for remote or maintenance-limited environments.
Why Piezoelectric Materials Matter
Piezoelectric materials are uniquely positioned to support self-powered sensor networks by converting mechanical energy, such as ambient vibration, into usable electrical signals. Among lead-free candidates, potassium sodium niobate (KNN) and barium titanate (BTO) are prominent, with KNN offering advantages for high-temperature applications due to its higher Curie point and improved thermal stability.
However, as performance demands increase, single-phase materials often prove insufficient. This has prompted growing interest in piezoelectric composites, which combine the electrical functionality of piezoelectric fillers with the mechanical robustness of engineered matrices.
Why Carbon Fiber-Reinforced Polymer (CFRP)?
CFRPs are widely used across aerospace, automotive, and infrastructure sectors due to their strength-to-weight ratio and chemical resistance. Importantly, the conductive nature of carbon fibers allows CFRP to act as both mechanical reinforcement and functional electrode. When integrated with a piezoelectric layer, CFRP-based composites become multifunctional systems capable of structural support, energy harvesting, and sensing.
To date, many such composites have been demonstrated in isolation, focusing on damage detection or energy harvesting alone. What remains largely underexplored is their integration into closed-loop, self-powered systems with wireless communication. And this is precisely the gap addressed in this study.
The Study
In this work, the research team fabricated a CFRP/KNN-epoxy composite where interlaminar cracks, typically seen as performance degradations, are instead leveraged as sensing features. The presence and progression of cracks affect the composite’s energy harvesting behavior, allowing electrical signals to serve as indicators of structural health.
Finite element analysis (FEA) and experimental results confirmed a quantitative correlation between crack length, electrical output, and energy harvesting performance. This relationship enables real-time assessment of damage severity through variations in harvested energy and signal transmission - effectively turning structural response into diagnostic data.
The composite was produced through a series of controlled steps:
- A semi-cured, woven CFRP prepreg was molded under 5?MPa pressure at 120?°C, improving fiber contact and electrical conductivity without compromising mechanical performance.
- KNN particles (30 % by volume, based on prior optimization studies) were mixed into epoxy using a planetary mixer, then blade-coated to 0.5?mm thickness and cured at 80?°C.
- Two CFRP layers were laminated over the KNN-epoxy layer with a 0.1?mm polytetrafluoroethylene (PTFE) film inserted to create a controlled pre-crack. The composite was trimmed and polished to final dimensions of 55?×?10?×?1?mm.
- A sputtered gold electrode and copper tape provided electrical contact, while Kapton tape ensured mechanical and electrical insulation.
The researchers then integrated the composite into an IoT-compatible system comprising:
- A wireless transmission unit
- Environmental sensors (humidity, barometric pressure, temperature)
- A standalone temperature sensor
- A 3-axis accelerometer
The system operates cyclically. Vibration-induced energy is harvested to charge a capacitor, which then powers the transmission of sensor data once a threshold is met. The result is a fully self-sufficient sensing platform, capable of remote monitoring without external power input.
Performance Overview
Overall the CFRP/KNN-epoxy composite demonstrated a piezoelectric charge constant (d33) of 7.8?pC/N and generated 13.6?V at its resonant frequency (262?Hz) under 0.05?mm displacement. It successfully powered seven LEDs and an IoT module.
To evaluate crack sensitivity, artificial interlaminar cracks of 5, 10, and 15?mm were introduced. The presence of damage correlated with:
- Decreasing voltage output and resonant frequency
- Slower capacitor charging rates
- Extended transmission intervals
This behavior enables the composite to infer the severity of structural damage based solely on energy harvesting characteristics without requiring direct visual or dimensional measurement.
Implications and Future Potential
By combining structural load-bearing capacity with sensing and power generation, this composite offers a viable path toward autonomous monitoring systems in aerospace, civil engineering, and industrial settings. It effectively translates vibration into information, offering real-time diagnostics with minimal infrastructure.
The broader implication means that materials need not be passive.
With the right design, they can contribute to the ongoing assessment of their own condition, improving safety, reducing maintenance demands, and enabling long-term operational insights.
Journal Reference
Sueda, Y. et al. (2026). From vibration to information: self-powered crack detection and wireless communication in carbon fiber reinforced piezoelectric nanocomposites. International Journal of Smart and Nano Materials, 1-17. DOI: 10.1080/19475411.2025.2610182, https://www.tandfonline.com/doi/full/10.1080/19475411.2025.2610182
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