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Browse Prior Art Database

Mapping an AC Magnetic Field

IP.com Disclosure Number: IPCOM000091171D
Original Publication Date: 1969-Nov-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 39K

Publishing Venue

IBM

Related People

Thornley, RFM: AUTHOR

Abstract

The apparatus in drawing 1 shows a technique for obtaining a series of maps when a magnetic head is driven by an AC signal. Each map in the series is associated with a different phase of the AC drive signal.

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Mapping an AC Magnetic Field

The apparatus in drawing 1 shows a technique for obtaining a series of maps when a magnetic head is driven by an AC signal. Each map in the series is associated with a different phase of the AC drive signal.

The electron beam of an electron beam microscope is directed past the gap of magnetic head 10 and strikes a two-dimensional grid 12. When the electron beam strikes grid 12, it causes secondary emission of electrons from such grid. These electrons are picked up by detector 14 and converted into a signal which is amplified by amplifier 16. This signal can be passed by gate 18 to cathode ray tube 20 to control the intensity of the display.

The scanning in tube 20 is coordinated with the scanning of the electron beam. If there is no signal applied to head 10, an image of grid 12 appears on the screen of tube 20. When head 10 is excited, the field of head 10 deflects the electron beam and distorts the image of grid 12 as displayed on tube 20. For a given excitation of head 10, the field produced by such head is shown on tube 20 as a distortion of grid 12.

To obtain a series of maps for AC excitation of head 10, a sampling technique is used to gate the signal from amplifier 16 to tube 20. The AC excitation for head 10 originates at oscillator 22. The AC signal is applied to driver 24 which drives head 10 according to the AC signal. The AC signal is also applied to phase shifter 26. The latter is adjustable to vary the amount of phase by...