| 摘要 |
A system for the non-contact inspection and characterization of an object in which wideband (40kHz to approximately 2MHz) air/gas coupled ultrasonic transducers are used. The system of the present invention enables a single set of transducers to be used in an inspection/defect detection arrangement to characterize materials having a wide range of through-thickness, and other resonances. For example, the through-thickness fundamental resonance of 11mm thick plywood is 44kHz, 723kHz for 2mm thick carbon fibre, and 1.47kHz for 0.75mm thick polystyrene, all of which are measurable in the same system. The system is used in a method to characterize a defect by being able to operate at or near the resonant frequency of the normal material and at or near the resonant frequency of the material in a defect region to improve the accuracy of detecting specific types of defects including inclusions, material thinning, delamination and pitting by monitoring changes of various attributes (e.g. amplitude, frequency) of the detected output signal. The system of the present invention can also be combined with laser or EMAT systems, where the means for generating ultrasonic vibrations in the object is a laser or EMAT and in pulse-echo arrangements in which a single wideband air-coupled transducer is used as the source and as the receiver/detector of ultrasound.
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