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Electromagnetic Acoustic Resonance Spectrometer

IP.com Disclosure Number: IPCOM000039378D
Original Publication Date: 1987-May-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 2 page(s) / 46K

Publishing Venue

IBM

Related People

Tam, AC: AUTHOR

Abstract

Described here is a new technique and apparatus for nondestructive evaluation (NDE) of a mechanical assembly containing one or more ferromagnetic elements. This technique is called "Electromagnetic Acoustic Resonance Spectrometry" (EMARS), because it relies on the use of an electromagnetic field that is scanned in frequency to seek out mechanical resonances in a mechanical assembly; the positions and the widths provide a "fingerprinting" information on the size and shape and structural and material properties of the assembly. The word "spectrometry" is used here (as is common in the field of optics) to indicate that the frequency of the sinusoidal variation of the field is scanned to obtain acoustic resonance line positions and shapes. An embodiment is indicated in the figure.

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Electromagnetic Acoustic Resonance Spectrometer

Described here is a new technique and apparatus for nondestructive evaluation (NDE) of a mechanical assembly containing one or more ferromagnetic elements. This technique is called "Electromagnetic Acoustic Resonance Spectrometry" (EMARS), because it relies on the use of an electromagnetic field that is scanned in frequency to seek out mechanical resonances in a mechanical assembly; the positions and the widths provide a "fingerprinting" information on the size and shape and structural and material properties of the assembly. The word "spectrometry" is used here (as is common in the field of optics) to indicate that the frequency of the sinusoidal variation of the field is scanned to obtain acoustic resonance line positions and shapes. An embodiment is indicated in the figure. A simple high-frequency electromagnet with high spatial resolution was made by wrapping 50 turns of thin formvarcoated copper wire onto a ferromagnetic rod (e.g., steel rod) to enhance and localize the field. The output from a sweep oscillator (producing 20 V peak-to-peak sinusoidal oscillations of frequency f scannable from 0.1 to 10 MHz) was connected to the copper coil and also to a frequency counter to measure the instantaneous frequency (if the scanning time is long compared to the integration time of the counter). The sample used in the present demonstration was a porous ferromagnetic object of approximate dimensions 3x5x22 mm but with large surface pores and protrusions. It was in acoustical contact with an ultrasonic transducer of the lead- zirconate-titanate type that had frequency response up to a few MHz. The transducer output was amplified by 26 dB and displaye...