Pulse field metal detector with spaced, dual coil transmitter and receiver systems

• US 4,605,898 A
• Filed: 06/27/1985
• Issued: 08/12/1986
• Est. Priority Date: 11/06/1981
• Status: Expired due to Term

• Current Assignee: Metorex Security Products, Inc. (OSI Systems Incorporated)
• Original Assignee: Outokumpu Oyj
• Inventors: Aittoniemi, Kari T. J., Kiuru, Erkki S., Savolainen, Kalevi, Lappalainen, Aatu V. K.
• Primary Examiner(s): Strecker, Gerard R.
• Application Number:
  US06/750,054
• Time in Patent Office: 411 Days
• Field of Search: 324/226, 324/232, 324/239, 324/243, 340/551, 340/552, 340/572
• US Class Current: 324/232
• CPC Class Codes: G01V 3/104 using several coupled or uncoupled coils G01V3/101 takes precedence

Abstract

The apparatus of the invention comprises at least two transmitter coils (3) and a respective number of receiver coils (4). The transmitter coils (3) and the respective receiver coils (4) are placed in a crosswise position with respect to each other so that the primary fields created by the transmitter coils (3) are divergent.

Claims

1. An apparatus for detecting metal objects, the said apparatus comprising a transmitter coil system and a receiver coil system spaced and separated from said transmitter coil system to allow the passage of objects to be detected between the two systems, the transmitter coil system consisting of at least two coils for creating divergent primary fields which change their direction and size according to their location, which primary fields in turn create eddy currents in an object moving within the said primary fields, whereafter the secondary field created in the object induces a signal in the receiver coil system, as well as means for amplifying and processing the signal, wherein the transmitter coil system is formed of at least two planar coils, each planar coil comprising a plurality of planar loops extending in a given direction and encompassing a predetermined area, said planar coils being juxtaposed, one on top of the other, so as to lie substantially within the same plane in said predetermined area, with the loops of one of said coils being in mirror image relationship with respect to the loops of the other of said coils so that the magnetic fields created by the coils are divergent and that the receiver coil system is also comprised of the same number of coils as the transmitter coil system which coils are placed with respect to each other in a similar relationship to that of the coils of the transmitter coil system, means for alternately energizing said at least two transmitter coils, and means synchronized with said energizing means for alternately sampling signals induced in said receiver coils and feeding said sampled signals to said means for amplifying and processing the signal.

2. The apparatus of claim 1, wherein the transmitter and receiver coil systems are essentially identical in shape.

3. The apparatus of claim 1, wherein the transmitter and receiver coil systems have essentially identical windings.

4. The apparatus of any one of the above claims, wherein the eddy currents induced by the separate transmitter coils are each measured by a receiver coil which is in a position corresponding to the transmitter coil in question.

5. The apparatus of any one of the claims 1 through 3, wherein a timer is used for controlling both the transmitter coils and the receiver coils.