Guided ultrasonic wave

Longitudinal Flaws by Guided Ultrasonic Waves," IEEE Trans. Sonics Ultrason. SU-23,1976, pp. 369-374. 

Inspection with Guided Ultrasonic Waves," Nuclear Engng. Des. Vol.102,1987, pp. 356-376. 

Ultrasonic transducers can excite various wave modes, eg, guided Lamb waves that may be suitable for specific apphcations (143). Ultrasonic excitation is also used to detect the so-called acoustic nonlinearity associated with defects, eg, in PMC (144,145). The combination of recording guided ultrasonic waves with numerical back-calculation of wave propagation for detecting indications of defects in PMC pipes also looks promising (146). Surface-bonded fiber optics can detect ultrasonic waves via interferometric techniques (147). Beyond frequencies of 1 GHz, ultrasonics is called acoustic microscopy, for details, the reader is referred to Reference 148. This technique can be applied to polymers or PMC (149), specifically to polymeric microelectronics packaging (150). 

Other ultrasonic techniques which show promise are oblique incidence waves (Pilarski et al, 1990) and Lamb waves (Bork and Challis 1995). Rose and co-workers (Puthillath and Rose 2010 Rose et al. 1996 Rose and Ditri 1992 Rose et al. 1995) have used guided ultrasonic waves to detect defects in adhesively bonded joints. 

The electrical field 3 is apphed across the PWAS thickness in the three directions. The prevalent piezoelectric coupling is between inplane strain in the one and two directions and out-of-plane electrical field in the three direction. At ultrasonic lie-quencies, PWAS can sense and excite guided Lamb waves traveling long distances along the thin-waU shell stmctures of aircraft and space vehicles (Figure 16.5). 

Acousto-ultrasonics [49] is a guided-wave pitch-catch method. The acousto part in the name reminds one of the reception of guided waves generated by the AE process at a propagating crack. The term ultrasonics infers that this is an active technique in which ultrasonic waves are generated by the transmitter thus this technique is different from the AE technique in that is just a passive technique. 

Ultrasonic waves (t5q)ically in the MHz range) can be excited by piezoelectric transducers coupled to the test object. Electromagnetic acoustic transducers (EMAT) (123) cannot be used for ultrasonics of polsrmers and PMC alternatives are discussed in Reference 124. The waves propagate and are scattered and attenuated in the material. The signal can be detected in either reflection or transmission mode (by the transducer emitting the ultrasonic pulse for reflection or by additional transducers at other locations in transmission). Acousto-ultrasonics (AU) (11) records low frequency guided waves (t5q)ically 30-500 kHz) emitted at another location to detect changes in the test objects, eg, in carbon-carbon... 

However, attention must be paid not only to application systems but also to the interaction between ultrasonic waves and drying chambers. The correct design of drying walls and the use of ultrasonic wave reflectors could guide, or even... 

Figure 15.9 Typical ultrasonic configurations, (a) TTU (b) PE (c) pitch catch and (d) guided waves.

Detection of delaminations has been tried by both traveling guided waves and by standing ultrasonic guided waves. In the former case, mode conversion and scatter at the delamination boundary modifies the traveling wave pattern. In the latter case, disbonds and delamination manifest high-frequency breathing modes that were not present in the pristine stmcture. 

Yan F, Royer RL, Rose JL. Ultrasonic guided wave imaging techniques in structural health monitoring. J Intell Mater Syst Struct 2010 21(3) 377—84. http //dx.doi.org/ 10.1177/1045389x09356026. 

Yu L, Giurgiutiu V. In situ 2-D piezoelectric wafer active sensors arrays for guided wave damage detection. Ultrasonics 2008 48(2) 117—34. http //dx.doi.0rg/lO.lOl6/ j.ultras.2007.10.008. 

Improved Performance of Guided Wave Ultrasonic Testing for Long Range Inspection of Pipelines using Multi-Channel Systems... 

Guided waves can exist in massive and hollow cylinders as well as in shell structures. In flat plates, ultrasonic guided waves travel as Lamb waves and as shear horizontal waves (SH). Lamb waves are vertically polarized while SH waves are horizontally polarized. Both, Lamb waves and SH-waves can be symmetric or antisymmetric with respect to the plate midplane [103]. 

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