| Description |
xii, 94 leaves : illustrations (some color) ; 29 cm |
| Summary |
"The depth of damage to metal surfaces is a particularly useful, sought after, and difficult to obtain piece of information, and is used to guide repair decisions. For this investigation such damage is represented as rectangular slots (cracks) or cylindrical pits. Several millimeter wave methods are presented to evaluate depth. The quarter-wavelength resonant response of cracks, excited by a probing rectangular waveguide, allows evaluation of depth using the phase of reflection coefficient. A theoretical derivation is also supplied, modeling the system as the junction of two rectangular waveguides, the probing waveguide and the crack. If the crack is filled with a dielectric material, shallower cracks may be evaluated and the magnitude of reflection coefficient may be used instead of phase. This approach has the advantage of low sensitivity to crack width and probe position, but has some limitations in the minimum depth and the smallest openings which can be evaluated. The depth of pits and shorter cracks may be evaluated using the phase in a non-resonant approach, by comparison with reference curves. A dielectric slab-loaded waveguide probe is also developed which theoretically would allow measurement of smaller damages, of both opening and depth, as a resonance perturbation. Sensitivity to very small damage is apparent, but high sensitivity to probe position is also evident. Extensive simulation results are presented for each approach, with supporting measurements. Evaluation of the depth of filled cracks, using the quarter-wavelength resonance approach, is, in particular, demonstrated in measurements for depths from 0.7- 2.7 mm for three frequency bands and three filling materials"--Abstract, leaf iii. |
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