Ultrasonic Transducers for Materials Testing and Their Characterization

Ultrasonic sensors

Partial discharge (PD) location in transformers is very important, and many methods that have been brought forward in past decades have a limitation theoretically, namely, they cannot locate multiple PDs in electrical equipment. In this paper, a new PD location method based on UHF and ultrasonic-phased arrays receiving theory has been presented, which has a possibility to locate multiple PDs. According to the method, a phased-ultrasonic receiving-planar array sensor that possesses 16 x 16 elements is designed; and, based on the phased-array theory, the characteristics of the plane sensor are studied. The laboratory experimental tests on the plane sensor element indicates that it has a good performance within the frequency band of the main ultrasonic energy produced by PD in transformer oil. Location tests are conducted on one or two piezoelectric ultrasonic sources in oil, which are both simulated as PD sources and triggered by an electrical pulse whose front is considered as a time benchmark in the locating algorithm. The test results show locations to one and two PDs can be realized in a single measurement, which lays a foundation for locating PDs in a power transformer in service

Phased-ultrasonic receiving-planar array transducer for partial discharge location in transformer

The authors describe a data acquisition system to determine the frequency spectrum between 500 KHz and 3 MHz of the initial acoustic emission. They measured the transfer function of the piezoelectric transducer and of the specimen for their results using a computer. They present an application of this device to the study of the emission of a low-carbon steel.

A spectrum analysis of acoustic emission

Dana la Partie I, un modele de source ďemisson acoustique a ete developpe Dane cette seconde partie, le modele de source est exploite pour ľinterpretation a la fois de ľemission continue et de ľemission par salves Ľemission acoustique est detectee par des capteura piezoelectriques a large bande de frequence, qui sont decrita Dens le cas de ľemission continue, associee a la deformation plastique homogene, ľanalyse spectrale du signal conduit a une mesure du temps de vol moyen des dislocations Pour des solutions solides Al–Mg, le franchiasement thermiquement active ďobstacles est mis en evidence; le temps de vol des dislocations diminue globalement si la temperature de deformation est plus elevee et si la teneur en Mg est plus faible Dana le caa de ľemission par salves, observee pendant la traction de ľalliage 2024 T361, des exemples de signaux enregistres sont donnes Ces signaux contiennent des echos qui sont analyses : ils proviennent de reflexions et conversions de modes dens ľeprouvette e

F. Lakestani

Papers

Broadening the bandwidth of piezoelectric transducers by means of transmission lines