Microwave NDE of Aircraft Composite Structures A Modern Approach to Inspection of Aviation and Aerospace Composites

7. Basic Principles, Health & Safety The voltage supplied to the transducer is quite low, on the order of 5-10 Volts, DC. Power output of the transducer is on the order of a few milli-watts. There is no radiation warning required to comply with US, EU and other international Health Standards. Microwave energy is non-ionizing so no radiation health issues.

8. Microwave NDE – Basic Principles A non-conductive (dielectric) specimen is bathed in electromagnetic energy in the 5-50 GHz frequency range. Some fraction of the impinging energy is reflected or transmitted at each interface of differing dielectric constant (Snell’s Law). All reflections are superimposed with a portion of the outgoing beam to create a detector voltage. The voltage is sampled across the specimen and an image is created.

9. Basic Principles, cont. Transducer frequency is constant. No time of flight or other time domain relationships are employed. Typical image data point density is on the order of 250,000 per square foot. Very small defects, on the order of several thousandths of an inch can be detected.

11. System Hardware Overview Data acquisition and imaging computer Electronics Module Microwave Transducer

12. Microwaves are created in the transducer assembly. Two detectors are employed, staggered in the “Z” dimension, such that maximum probability of detection is obtained for any defect throughout the thickness of the specimen. Detector voltages are amplified, sampled, converted to digital values and matched to X and Y locations in the electronics module. These (X,Y,Detector Voltage) data sets are saved in digital data files and displayed on the system laptop computer.

13. Microwave equipment is fitted to either commercially available X-Y scanners or designed as an integral part of a purpose-built custom system. Laboratory scanning is performed on a scanning table, permitting very high X-Y resolution (typically < 0.05 mm). Field fixtures include right-circular-cylindrical pipe scanners (for which X is Circumferential and Y is Axial, or vice versa) or Cartesian X-Y scanner, held in place with suction cups or the like. Position can be obtained using infra-red (IR) diode tracking within an IR camera frame. This X,Y method is demonstrated on a military radome later in the presentation

19. Inspection Results – Helicopter Manufacturing

20. Inspection Results – Helicopter Rotor

21. Inspection Results – Helicopter Rotor

22. Inspection Results – US Military Aircraft Radome

23. Inspection Results – Aircraft Radome

24. Inspection Results – Aircraft Radome

25. Inspection Results – Impact Aircraft Radome Hand Scan

26. Inspection Results Pre-Impact Aircraft Radome Hand Scan

27. Inspection Results Post-Impact Aircraft Radome Hand Scan

29. Summary Modern aircraft are increasingly being manufactured using strong, light composite materials. These materials present challenges to traditional NDE methods Microwave scanning can provide good results when searching for interlaminar as well as deep structural defects in composite components. Microwave scanning is effective on new, modern composite forms, including honeycomb composites and ceramic matrix composites Flaws like delaminations, fluid intrusion and mechanical damage can be detected, imaged and monitored over time. Microwave scanning can be manual or fully automated. Microwave scanning is non-contact, requires no couplant and requires access to only one side of the part.

30. Questions?