Electricity: measuring and testing – Of geophysical surface or subsurface in situ – For small object detection or location
Patent
1979-07-09
1981-10-06
Strecker, Gerard R.
Electricity: measuring and testing
Of geophysical surface or subsurface in situ
For small object detection or location
G01V 311
Patent
active
042938163
ABSTRACT:
A search loop for a metal detector is described having a magnetic flux feedback coil whose magnetic flux opposes that of the transmit coil to provide a balanced loop. The balanced loop is thereby nulled and produces no output signal on the receive coil when such loop is positioned in air remote from the ground and no metal object is present. The transmit coil, the feedback coil and the receive coil are supported coplanar with each other and the feedback coil is supported on the receive coil so that it is concentric therewith. As a result of supporting the feedback coil on the receive coil, there is no relative movement between these two coils due to temperature changes or mechanical stress. Such movement tends to produce false output signals in the receive coil. In the preferred embodiment the feedback coil and the transmit coil are circular and are positioned concentric with a surrounding circular transmit coil. In one embodiment an electrostatic shield is provided between the feedback coil and the receive coil to reduce capacitive coupling. The balanced loop of the present invention can provide a balanced magnetic flux region within the receive coil even though it is not exactly concentric with the transmit coil so the loop is less expensive to manufacture but is capable of high sensitivity and good pinpointing of a target.
REFERENCES:
patent: 2451596 (1948-10-01), Wheeler
patent: 3108220 (1963-10-01), Ruddock
patent: 3549985 (1970-12-01), Penland
patent: 3882374 (1975-05-01), McDaniel
patent: 4024468 (1977-05-01), Hirschi
patent: 4030026 (1977-06-01), Payne
Garrett, Chas., "Successful Coin Hunting;" Ram Publishing Co.; Copyright 1974, pp. 171-173, 189-192.
Strecker Gerard R.
White's Electronics, Inc.
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