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Full-Text Articles in Aerospace Engineering
Measurements Of The Longitudinal Wave Speed In Thin Materials Using A Wideband Pvdf Transducer, Kwang Yul Kim, Wei Zou, Stephen D. Holland, Wolfgang Sachse
Measurements Of The Longitudinal Wave Speed In Thin Materials Using A Wideband Pvdf Transducer, Kwang Yul Kim, Wei Zou, Stephen D. Holland, Wolfgang Sachse
Stephen D. Holland
A flat transducer was constructed, using a 9-mm-thick PVDF (polyvinylidene fluoride) film for generation and detection of high-frequency ultrasonic waves, and used for measurements of the phase velocity of longitudinal waves traveling along the thickness direction in a very thin material. The transducer has a useful wideband frequency characteristic extending from 10 MHz to over 150 MHz. Measurements of the phase velocity of the longitudinal waves are carried out using a 0.212-mm-thick glass slide and a 0.102-mm-thick stainless-steel shim, using water as a coupling medium. The thickness limit for this measurement appears to be approximately 20 mm. The phase velocity …
A Time-Resolved Method For Nonlinear Acoustic Measurement, Stephen D. Holland
A Time-Resolved Method For Nonlinear Acoustic Measurement, Stephen D. Holland
Stephen D. Holland
We describe a time-resolved method for measuring nonlinear ultrasonic phenomena. Conventional approaches to the measurement of nonlinear phenomena utilize narrowband measurements of harmonic generation. These measurements are fundamentally narrowband and hence have poor time resolution. In contrast, our method utilizes a series of narrowband bursts that can be combined to form a composite time-resolved broadband impulse. Simultaneous time resolution and harmonic isolation are thereby obtained. The composite impulse can then be used to perform time-resolved measurements of weakly nonlinear phenomena. Such time-resolved measurements have the potential to dramatically improve the capability and performance of nondestructive testing systems that use acoustic …
A Time-Resolved Method For Nonlinear Ultrasonic Measurements, Stephen D. Holland, Wolfgang Sachse
A Time-Resolved Method For Nonlinear Ultrasonic Measurements, Stephen D. Holland, Wolfgang Sachse
Stephen D. Holland
We describe a time-resolved method for measuring nonlinear ultrasonic phenomena. Current approaches rely on a narrowband measurement of harmonic generation to identify and characterize nonlinearity. Concomitant with these techniques is poor time resolution. We address this limitation with a hybrid narrowband/broadband approach that provides simultaneous time resolution and harmonic isolation for the measurement of weak nonlinearites. We discuss applications and present demonstrative results showing harmonic generation both in water and at a dry contact aluminum-aluminum interface.
Determination Of Plate Source, Detector Separation From One Signal, Stephen D. Holland, Tadej Kosel, Richard Weaver, Wolfgang Sachse
Determination Of Plate Source, Detector Separation From One Signal, Stephen D. Holland, Tadej Kosel, Richard Weaver, Wolfgang Sachse
Stephen D. Holland
We address the problem of locating a transient source, such as an acoustic emission source, in a plate. We apply time-frequency analysis to the signals detected at a receiver. These highly dispersive and complex waveforms are measured for source-receiver separations ranging from 40 to 180 plate thicknesses and at frequencies such that ten to twenty Rayleigh-Lamb branches are included. Re-assigned, smoothed, pseudo-Wigner-Ville distributions are generated that exhibit the expected sharp ridges in the time-frequency plane, lying along the predicted frequency-time-of-arrival relations. The source-receiver separation can be determined from such plots.