How to Make Intelligent Carbon-Fiber Composites

Recently, we told you about a method for combining the 3D printing of a plastic airplane wing with printed 3D electronics , including antennas. The technique could be used to print conformal electronics inside structures. Now the Fraunhofer Institute for Integrated Circuits (IIS) in Germany has demonstrated the ability to embed radio frequency identification (RFID) tags with ultra-thin antennas inside components made of carbon-fiber-reinforced composites, such as aircraft wings. The technique may also be adaptable to composite structural health monitoring.

RFID is a wireless communications technology most commonly used for identifying objects in non-line-of-sight applications. It can replace bar codes for inventory management, track items during manufacturing, prevent counterfeiting, or control access to certain areas of a plant. It can be used to access data like serial numbers stored on chips or tags. Hundreds of RFID chips can be read by a single reader. Combined with sensors, chips acting as transponders can form data collection networks. The range is very short -- 15 meters (using UHF frequencies) is considered a long distance in RFID networks for logistics and production applications.

It might not occur to everyone to embed RFID or other wireless chips in carbon-fiber composites. For one thing, these composites can be conductive and can damp signals at commonly used frequencies such as LF, HF, and UHF. Also, composite manufacturing is usually done at temperatures and pressures that might crush the chips, though the transponders are fairly resistant to mechanical stress. But scientists at the Fraunhofer IIS say they have overcome these problems by working with several industry partners.

The three frequencies work well with glass fibers, but carbon fibers interfered with the chips' signal transmission, especially at UHF frequencies higher than 868MHz. The researchers designed transponders that can withstand typical manufacturing conditions (such as pressures of up to 10 bars and temperatures as high as 180C) and thus can be incorporated into aircraft components. The transponders measure only a few square millimeters, and the antenna is thin enough to be embedded in composites while being protected by a thin layer of fibers.

The researchers developed the first prototypes with the RFID transponder manufacturer Schreiner LogiData. These include a UHF transponder, an LF sensor for wireless temperature measurement during manufacturing, and an antenna for LF, HF, and UHF transponders. This will make it possible to embed RFID tags in aircraft composite components during manufacturing.

In the newer, parallel SmartFiber project sponsored by the European Union, RFID is being used to transmit data to a network of fiber-optic sensors, with the whole thing embedded in fiber-reinforced composites. The goal is to develop a millimeter-scale structural health monitoring system that can be embedded in the composites employed in structures such as satellites, airplanes, bridges, boat hulls, propellers, wind turbine blades, and oil and gas wells.

The SmartFiber website says the network is fully embedded in the composite material and will be demonstrated in a working production environment. The system will generate an ongoing record about the composite structures to make it easier for technicians to monitor their health and decide when they need

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