Measuring and testing – Vibration – By mechanical waves
Patent
1995-07-27
1997-03-04
Chapman, John E.
Measuring and testing
Vibration
By mechanical waves
73 52, 73643, 73290V, G01N 2920
Patent
active
056081642
ABSTRACT:
An ultrasonic inspection technique using a specially designed electromagnetic acoustic transducer (EMAT) launches and receives longitudinal ultrasonic waves into a thin metal wall or thin metal foil seal of a container, causing it to vibrate and launch ultrasonic compressional waves into liquid contained therein. The contents of plastic containers having a metal foil seal forming one wall are easily inspected. The EMAT establishes a magnetic field in the surface of the metal parallel to the surface. Radio frequency (RF) eddy currents are also induced by the EMAT in the surface of the metal. A Lorentz force is generated in the metal surface according the vector product of J, the current density, and H, the magnetic field, and the force generated by the interaction of the perpendicular components of the magnetic field H and the eddy currents J is directed normally to the surface of the metal. This normal force oscillates with the frequency of the induced eddy currents creating ultrasonic compressional waves which propagate normal to the surface of the metal. In such thin-walled metal containers or thin metal foil seals, where the thickness of the metal is much shorter than the ultrasonic wavelength in the metal, the generation and reception process is analogous to the operation of a loudspeaker in air. In this application, the thin metal wall or foil acts as a membrane, with the Lorentz forces generated in the wall or foil causing the metal membrane to vibrate, generating ultrasonic waves in the liquid. Because the thin wall or foil is much more compliant than a thick piece of metal, much larger displacements are generated at the metal-liquid interface than for the thick-wall case, resulting in much larger signal amplitudes than in the thick-wall case.
REFERENCES:
patent: 2277037 (1942-03-01), Clark et al.
patent: 3357556 (1967-12-01), Martner et al.
patent: 3553636 (1971-01-01), Baird
patent: 3802252 (1974-04-01), Hayward et al.
patent: 3832885 (1974-09-01), Hayward et al.
patent: 3913383 (1975-10-01), Kreula et al.
patent: 4208915 (1980-06-01), Edwards
patent: 4384476 (1983-05-01), Black et al.
patent: 4399514 (1983-08-01), Hamasaki et al.
patent: 4821573 (1989-04-01), Nagata et al.
patent: 4848924 (1989-07-01), Nuspl et al.
patent: 5167157 (1992-12-01), Wertz et al.
patent: 5372042 (1994-12-01), Jarman et al.
Maxfield, B. W., A. Kuramoto & J. K. Hulbert, "Evaluating EMAT Designs for Selected Applications", Materials Evaluation, 45, Oct. 1987. pp. 1166-1183.
Thompson, R. B. & C. F. Vasile, "An elastic-wave ellipsometer for measurement of material property variations", Appl. Phys. Lett., 34(2), 15 Jan. 1979. pp. 128-130.
Chapman John E.
Edwards Robert J.
Marich Eric
The Babcock & Wilcox Company
LandOfFree
Electromagnetic acoustic transducer (EMAT) for ultrasonic inspec does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electromagnetic acoustic transducer (EMAT) for ultrasonic inspec, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electromagnetic acoustic transducer (EMAT) for ultrasonic inspec will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2147569