April 26, 2012
Seeing Inside The Nose Of An Aircraft
Radio signals reach pilots on board an aircraft through the “radar dome“, the rounded nose of the aircraft. But if errors occur during the production of this “nose“, — tiny foreign particles, drops of water or air bubbles — this can impede radio traffic. In the future, a non-destructive testing system will identify just such imperfections during production. Researchers will be presenting the new testing system at the Control trade fair, May 8-11 in Stuttgart (Hall 1, stand 1502).
The planned arrival time, the request to land or the landing direction — this is the kind of information pilots discuss via radio with ground staff in the control tower. The nose of the aircraft, the “radar dome“, receives incoming radio signals and transmits radio signals sent by the pilot as well. It is made of a fiberglass composite. But if even tiniest imperfections arise during production — if, for instance, little foreign particles, drops of water or air bubbles become enclosed in the resin — over time they can cause fine cracks through which moisture can seep. This causes interference in radio traffic through the aircraft nose, introducing static into the signal.
Researchers have come up with another terahertz testing system as well, one that analyzes the thickness of layers — such as are found on aircraft and cars. “Our terahertz measuring system is one of the few robust enough for industrial use,“ according to Dr. Joachim Jonuscheit, deputy head of department at Fraunhofer IPM. Just like the system that checks aircraft noses, this one also consists of a rolling cabinet along with a transmitter and a receiver connected to the container by cables five meters long. This system works with very short terahertz pulses. Each pulse is partially reflected off of the interfaces of the layers: the surface of the first layer, the interface between layer one and two, and so on. The deeper the layer reflecting the pulses, the longer the pulses take to return to the detector. Using the time each pulse takes to make its way back to the detector, built-in software automatically calculates the thickness of the various layers.
The system℠s great advantage is its robustness. But how did researchers accomplish this? “First of all, we no longer shoot the laser that excites the system by open beam as typically used in terahertz systems; instead, we feed it through optical fibers. And secondly, we have fixed and arranged the optical elements to make them mechanically robust. We have also improved the manufacturing processes for the semiconductor components — the transmitters and detectors — to make the individual elements more resistant,“ Jonuscheit explains. At the Control trade fair, the researchers will demonstrate live measurements on multi-layered plastic films of varying thicknesses.
On the Net: