Device for selectively detecting different kinds and sizes of metals

Claim 2

A metal detecting station for detecting the movement of deliberately hidden ferrous or non-ferrous metal objects through said station comprising a transmitting coil and at least one receiving coil, said transmitting coil and said at least one receiving coil disposed in spaced relationship to each other, a signal generator connected to said transmitting coil for inducing an electromagnetic field in said at least one receiving coil, first means associated with said station for producing a fixed voltage output in said at least one receiving coil, second means in said station and associated with said first means in such a way that said second means operates only when said first means operates and induces a phase shift between the transmitting coil and said at least one receiving coil, said phase shift in a direction such that the metal-detecting station is sensitive to ferrour or non-ferrous metal objects passing through the station and sufficiently large to distort the electromagnetic field inside the metal-detecting station so that no likely combination of target-shape or target-orientation could pass through the station without disturbing the voltage in said receiving coil, and means associated with the station and connected to said at least one receiving coil for providing an indication of any voltage change in said at least one receiving coil caused by the passage of a metal object through the station.

Claim 3

The metal detecting station described in claim 1 wherein said fixed voltage output introduced into said at least one receiving coil is of sufficient magnitude to make the metal detecting station comparatively insensitive to the movement of metal objects through the station which are smaller than metal objects of interest.

Claim 4

A metal detecting station for detecting the movement of deliberately hidden ferrous or non-ferrous metal objects through the station which are greater than a predetermined size, said metal detecting station having an interior portion and at least one planar wall, said at least one planar wall formed from a plurality of layers, one of said layers formed from an insulating material and comprising a rigid support layer, at least one other layer formed from a thin ferrous sheet metal, means securing such ferrous sheet metal to said rigid support layer whereby said rigid support layer and ferrous sheet metal are generally coextensive and the ferrous sheet metal is rigidly supported thereby in a fixed position on said wall, said layer of ferrous sheet metal serving to shield the interior of said station from electromagnetic signals or magnetic influences caused by ferrous or non-ferrous metal objects moving by said wall outside said station, detecting means associated with this station for detecting the movement of objects through said station, said detecting means comprising a transmitting coil and at least one receiving coil, said transmitting coil and said at least one receiving coil in spaced relationship to each other, a signal generator connected to said transmitting coil for inducing an electromagnetic field in said at least one receiving coil, first means in said station for producing a fixed voltage output in said at least one receiving coil of sufficient magnitude to make the metal detecting station comparatively insensitive to metal objects substantially smaller than metal objects of interest to prevent spurious indications in the station caused by the movement of said tiny metal objects through the station, second means in said station and associated with said first means in such a way that said second means operates only when said first means operates and induces a phase shift between the transmitting coil and said at least one receiving coil in such a direction that the metal detecting station is sensitive to the movement of both ferrous and non-ferrous metal objects through the station and sufficiently large to distort the electromagnetic field inside the station so that no likely combination of target-shape or target-orientation could pass through the station without disturbing the voltage in said at least one receiving coil, and means associated with said station and connected to said at least one receiving coil for providing an indication of any voltage change in said at least one receiving coil caused by the passage of a metal object through the station.

Claim 5

A metal detecting station for detecting the movement of deliberately hidden ferrous or non-ferrous metal objects through the station which are greater than a predetermined size, said metal detecting station having an interior portion and at least one planar wall, said at least one planar wall formed from a plurality of layers, one of said layers formed from an insulating material and comprising a rigid support layer, at least one other layer formed from a thin ferrous sheet metal, means securing such ferrous sheet metal to said rigid support layer whereby said rigid support layer and ferrous sheet metal are generally coextensive and the ferrous sheet metal is rigidly supported thereby in a fixed position on said wall, said layer of ferrous sheet metal serving to shield the interior of said station from electromagnetic signals or magnetic influences caused by ferrous or non-ferrous metal objects moving by said wall outside said station, detecting means associated with this station for detecting the movement of objects through said station, said detecting means comprising a transmitting coil and at least one receiving coil, said transmitting coil and said at least one receiving coil in spaced relationship to each other, a signal generator connected to said transmitting coil for inducing an electromagnetic field in said at least one receiving coil, first means in said station for producing a fixed voltage output in said at least one receiving coil of sufficient magnitude to make the metal detecting station comparatively insensitive to metal objects substantially smaller than metal objects of interest to prevent spurious indications in the station caused by the movement of said tiny metal objects through the station, second means in said station and associated with said first means in such a way that said second means operates only when said first means operates and induces a phase shift between the transmitting coil and said at least one receiving coil in such a direction that the metal detecting station is sensitive to the movement of both ferrous and non-ferrous metal objects through the station and sufficiently large to distort the electromagnetic field inside the station so that no likely combination of target-shape or target-orientation could pass through the station without disturbing the voltage in said at least one receiving coil, and means associated with said station and connected to said at least one receiving coil for providing an indication of any voltage change in said at least one receiving coil caused by the passage of a metal object through the station.

Claim 6

A metal detecting station for detecting the movement of deliberately hidden ferrous or non-ferrous metal objects through the station which are greater than a predetermined size comprising a single turn transmitting coil and two single turn receiving coils disposed in spaced parallel relationship to each other on opposite sides of the transmitting coil and positioned so that objects passing through the station must pass through the coils, a signal generator connected to said transmitting coil for inducing an electromagnetic field in the receiving coils, first means associated with said station for producing a fixed voltage output in said receiving coils which is of sufficient magnitude to make the metal detecting station comparatively insensitive to metal objects substantially smaller than metal objects of interest to prevent the station from responding to the movement of tiny metal objects through the station, second means in said station and associated with said first means in such a way that said second means operates only when said first means operates to induce a phase shift between the transmitting coil and said receiving coil in such a direction that the metal detecting station is sensitive to both ferrous or non-ferrous metal objects passing through the station and sufficiently large to distort the electromagnetic field inside the station so that no likely combination of target-shape or target orientation could pass through the station without disturbing the voltage in said receiving coils, and means associated with said station and connected to said receiving coils for providing an indication of any voltage change in said receiving coils caused by the passage of metal objects of sufficient size through the station.

Claim 7

A metal detecting station for detecting the movement of deliberately hidden ferrous or non-ferrous metal objects through the station which are greater than a predetermined size comprising a single turn transmitting coil and two single turn receiving coils disposed in spaced parallel relationship to each other on opposite sides of the transmitting coil and positioned so that objects passing through the station must pass through the coils, a signal generator connected to said transmitting coil for inducing an electromagnetic field in the receiving coils, first means associated with said station for producing a fixed voltage output in said receiving coils which is of sufficient magnitude to make the metal detecting station comparatively insensitive to metal objects substantially smaller than metal objects of interest to prevent the station from responding to the movement of tiny metal objects through the station, second means in said station and associated with said first means in such a way that said second means operates only when said first means operates to induce a phase shift between the transmitting coil and said receiving coil in such a direction that the metal detecting station is sensitive to both ferrous or non-ferrous metal objects passing through the station and sufficiently large to distort the electromagnetic field inside the station so that no likely combination of target-shape or target orientation could pass through the station without disturbing the voltage in said receiving coils, and means associated with said station and connected to said receiving coils for providing an indication of any voltage change in said receiving coils caused by the passage of metal objects of sufficient size through the station.

Claim 8

A metal detecting station for detecting the movement of deliberately hidden ferrous and non-ferrous metal objects above a predetermined size through said station, said station having opposed ends, and detecting means therein for detecting the movement of ferrous or non-ferrous metal objects through the station, said detecting means comprising a single turn transmitting loop and two single turn receiving loops positioned in a spaced relationship to each other on each side of the transmitting loop and adjacent to said opposed ends of the station, an oscillator associated with said station, said oscillator including a transformer, the secondary coil of said transformer connected to said transmitting loop for inducing an electromagnetic field in said transmitting loop and serving both to determine the frequency of the oscillator and to match the impedance of the oscillator to the impedance of the single turn transmitting loop thereby permitting the transmitting loop to be formed from a single turn of wire, means connected to said receiving loops to tune said receiving loops to the frequency of the transmitting loops, first means associated with the station for producing a fixed voltage output in said receiving loops of sufficient magnitude to make the metal detecting station comparatively insensitive to metal objects substantially smaller than metal objects of interest to prevent the station from responding to the movement of said tiny metal objects through the station, second means in the station and associated with said first means in such a way that the second means operates only when said first means operates to induce a phase shift between the transmitting loop and said receiving loops, said phase shift directed so the metal detecting station is sensitive to both ferrous and non-ferrous metal objects passing through the station and sufficiently large to distort the electromagnetic field inside the station so that no likely combination of target-shape or target-orientation could pass through the station without disturbing the voltage on said receiving loops, voltage indicator associated with said station and connected to said receiving loops for providing an indication of any voltage change in said receiving loops caused by the passage of ferrous or non-ferrous metal objects through the station, said second means for providing said phase shift between the transmitting loop and said receiving loops comprising at least one wing loop mounted in a plane generally perpendicular to the planes of the transmitting and receiving loops and mounted between a receiving loop and said transmitting loop, said wing loop positioned generally transverse to a side of said transmitting and receiving loops, means connected to the said at least one wing loop and said oscillator for providing said at least one wing loop with current 90 degrees out of phase with respect to the current supplied to the transmitting loop whereby the current in the said at least one wing loop produces a magnetic field which changes the phase relationship between the voltage in the associated receiving loop and the voltage in the transmitting loop when the first means in the station produces said fixed voltage output in the receiving loops.

Claim 9

A metal detecting station for detecting the movement of deliberately hidden ferrous and non-ferrous metal objects above a predetermined size through said station, said station having opposed ends, and detecting means therein for detecting the movement of ferrous or non-ferrous metal objects through the station, said detecting means comprising a single turn transmitting loop and two single turn receiving loops positioned in a spaced relationship to each other on each side of the transmitting loop and adjacent to said opposed ends of the station, an oscillator associated with said station, said oscillator including a transformer, the secondary coil of said transformer connected to said transmitting loop for inducing an electromagnetic field in said transmitting loop and serving both to determine the frequency of the oscillator and to match the impedance of the oscillator to the impedance of the single turn transmitting loop thereby permitting the transmitting loop to be formed from a single turn of wire, means connected to said receiving loops to tune said receiving loops to the frequency of the transmitting loops, first means associated with the station for producing a fixed voltage output in said receiving loops of sufficient magnitude to make the metal detecting station comparatively insensitive to metal objects substantially smaller than metal objects of interest to prevent the station from responding to the movement of said tiny metal objects through the station, second means in the station and associated with said first means in such a way that the second means operates only when said first means operates to induce a phase shift between the transmitting loop and said receiving loops, said phase shift directed so the metal detecting station is sensitive to both ferrous and non-ferrous metal objects passing through the station and sufficiently large to distort the electromagnetic field inside the station so that no likely combination of target-shape or target-orientation could pass through the station without disturbing the voltage on said receiving loops, voltage indicator associated with said station and connected to said receiving loops for providing an indication of any voltage change in said receiving loops caused by the passage of ferrous or non-ferrous metal objects through the station, said second means for providing said phase shift between the transmitting loop and said receiving loops comprising at least one wing loop mounted in a plane generally perpendicular to the planes of the transmitting and receiving loops and mounted between a receiving loop and said transmitting loop, said wing loop positioned generally transverse to a side of said transmitting and receiving loops, means connected to the said at least one wing loop and said oscillator for providing said at least one wing loop with current 90 degrees out of phase with respect to the current supplied to the transmitting loop whereby the current in the said at least one wing loop produces a magnetic field which changes the phase relationship between the voltage in the associated receiving loop and the voltage in the transmitting loop when the first means in the station produces said fixed voltage output in the receiving loops.

Claim 10

The metal detecting station described in claim 5 wherein said first means for producing a fixed voltage output in said receiving loops comprises a piece of metal which is movably disposed near one receiving loop.

Claim 11

The metal detecting station described in claim 5 wherein said second means for producing a phase shift between the voltage in the transmitting loop and the voltage in the receiving loops comprises two single turn wire wing loops mounted in a plane generally perpendicular to the planes of the transmitting and receiving loops, each wing loop positioned near a receiving loop at one end or the other of said station and associated therewith, a multiple position switch associated with the station, one end of a wire in each wing loop connected to a terminal of the multiple position switch, said multiple position switch including a shaft mounted rotary arm connected to the oscillator and adapted to be electrically connected to one of the terminals of the multiple position switch to selectively energize an associated wing loop, said wires in each wing loop disposed so they extend in generally opposite directions from the center of the station to the opposed ends of the station whereby the direction of current flow through said wing loops with respect to the station can be reversed depending on which terminal the rotary arm of the multiple position switch is connected to, said rotary arm connected to the said oscillator in such a way that the current supplied to the wing loops is 90° out of phase with respect to the current supplied to the transmitting loop, whereby the current in the energized wing loop produces a magnetic field which changes the phase relationship between the voltage in the transmitting loop and the voltage in the receiving loop associated with the energized wing loop, in a direction such that the station responds to the movement of a ferrous or non-ferrous metal object of sufficient size passing through the station.

Claim 12

The metal detecting station described in claim 7, wherein said receiving loops are substantially identical and equidistant from the transmitting loop, on each side thereof, and wherein said first means comprises a sheet metal film, said fin connected to the shaft of the rotary arm of the multiple position switch, said shaft and fin positioned so that the fin is movable toward one or the other of the receiving loops depending on which terminal the rotary arm engages, said multiple position switch having a test terminal, said test terminal of the multiple position switch so positioned in the station that when the rotary arm is connected to the test terminal, neither wing loop is energized and the metal fin is equidistant from both receiving loops so that if no target is passing through the station the voltage output from the receiving loops is null whereby errors in assembly or shifts in the position of the transmitting and receiving loops and wing loops can be detected.

Claim 13

A metal detecting station for detecting hidden ferrous of non-ferrous metal objects carried by a person, said station having an interior portion with at least one wall, said wall formed from a rigid insulating material and comprising a support, at least one layer formed from sheet metal, means rigidly securing said sheet metal layer to said rigid support so it lies coextensive therewith whereby said planar layered wall shields the interior of the station from external magnetic or electromagnetic influences originating outside the station, said station having detecting means therein for detecting the movement of ferrous or non-ferrous metal objects moving through the station, said detecting means comprising a single turn transmitting loop and two single turn receiving loops positioned on each side of said transmitting loop in spaced relationship to each other and adjacent opposed ends of the station, an oscillator associated with said station, said oscillator including a transformer, the secondary coil of said transformer connected to said transmitting loop for inducing an electromagnetic field in said receiving loops and serving both to determine the frequency of the oscillator and to match the impedance of the oscillator to the impedance of the single turn transmitting loop, thereby permitting the transmitting loop to be formed from a single turn of wire, means connected to said receiving loops to tune said receiving loops to the frequency of said transmitting loop, said receiving loops connected together in phase opposition, a detecting meter adapted to be connected to said receiving loops to detect the voltage difference between them, first means in the station associated with one of said receiving loops for producing a fixed voltage output in said associated receiving loop whereby the detecting meter receives an output signal when no ferrous or non-ferrous target is moving through the station so it can discriminate between mechanical vibrations, affecting the meter, transient magnetic or electromagnetic disturbances in the station, and between ferrous or non-ferrous metal targets moving through the station, and second means for introducing a controlled phase shift between the voltage in the transmitting loop and the voltage in the receiving loops, said second means comprising at least one wire wing loop mounted in a plane generally perpendicular to the planes of the transmitting and receiving loops, and mounted between a receiving loop and the transmitting loop, said wing loop including at least spaced generally parallel wires positioned generally transverse to a side of said transmitting and receiving loops and including a connecting wire connected between said generally parallel wires, means connected between said wing loop and said oscillator for supplying the wing loop with current 90° out of phase with respect to the current supplied to the transmitting loop whereby the current in the wing loop produces a magnetic field which changes the phase relationship between the voltage in the transmitting loop and the receiving loop so that a metal object passing through the station disturbs the said fixed voltage and/or said phase relationship in the receiving loop.

Claim 14

A metal detecting station for detecting hidden ferrous of non-ferrous metal objects carried by a person, said station having an interior portion with at least one wall, said wall formed from a rigid insulating material and comprising a support, at least one layer formed from sheet metal, means rigidly securing said sheet metal layer to said rigid support so it lies coextensive therewith whereby said planar layered wall shields the interior of the station from external magnetic or electromagnetic influences originating outside the station, said station having detecting means therein for detecting the movement of ferrous or non-ferrous metal objects moving through the station, said detecting means comprising a single turn transmitting loop and two single turn receiving loops positioned on each side of said transmitting loop in spaced relationship to each other and adjacent opposed ends of the station, an oscillator associated with said station, said oscillator including a transformer, the secondary coil of said transformer connected to said transmitting loop for inducing an electromagnetic field in said receiving loops and serving both to determine the frequency of the oscillator and to match the impedance of the oscillator to the impedance of the single turn transmitting loop, thereby permitting the transmitting loop to be formed from a single turn of wire, means connected to said receiving loops to tune said receiving loops to the frequency of said transmitting loop, said receiving loops connected together in phase opposition, a detecting meter adapted to be connected to said receiving loops to detect the voltage difference between them, first means in the station associated with one of said receiving loops for producing a fixed voltage output in said associated receiving loop whereby the detecting meter receives an output signal when no ferrous or non-ferrous target is moving through the station so it can discriminate between mechanical vibrations, affecting the meter, transient magnetic or electromagnetic disturbances in the station, and between ferrous or non-ferrous metal targets moving through the station, and second means for introducing a controlled phase shift between the voltage in the transmitting loop and the voltage in the receiving loops, said second means comprising at least one wire wing loop mounted in a plane generally perpendicular to the planes of the transmitting and receiving loops, and mounted between a receiving loop and the transmitting loop, said wing loop including at least spaced generally parallel wires positioned generally transverse to a side of said transmitting and receiving loops and including a connecting wire connected between said generally parallel wires, means connected between said wing loop and said oscillator for supplying the wing loop with current 90° out of phase with respect to the current supplied to the transmitting loop whereby the current in the wing loop produces a magnetic field which changes the phase relationship between the voltage in the transmitting loop and the receiving loop so that a metal object passing through the station disturbs the said fixed voltage and/or said phase relationship in the receiving loop.

Claim 15

The metal detecting station described in claim 9 wherein said first means for producing fixed voltage in a receiving loop, is a piece of metal movably disposed near one receiving loop.

Claim 16

The metal detecting station described in claim 9 wherein said second means for introducing said controlled phase shift comprises two single turn wire wing loops mounted in a plane generally perpendicular to the planes of the transmitting and receiving loops, each wing loop positioned near a receiving loop at one end or the other of said station and associated therewith and comprising spaced parallel wires and a connecting wire connected between the parallel wires, a multiple position switch associated with the station, one end of a parallel wire in each wing loop connected to a terminal of the multiple position switch, said multiple position switch including a shaft mounted rotary arm connected to the oscillator and adapted to be electrically connected to one of the terminals of the multiple position switch to selectively energize one of the wing loops, said parallel wires in each wing loop disposed so they extend in opposite directions from the center of the station to the opposed ends of the station whereby the direction of current flow through said wing loops with respect to the station can be reversed depending on which terminal the rotary arm of the multiple position switch is connected to, said rotary arm connected to the said oscillator in such a way that the current supplied to the wing loops is 90° out of phase with respect to the current supplied to the transmitting loop, whereby the current in the energized wing loop produces a magnetic field which changes the phase relationship between the voltage in the transmitting loop and the voltage in the receiving loop associated with the energized wing loop so that a metal object passing through the station disturbs the said fixed voltage and/or said phase relationship in the associated receiving loop.

Claim 17

The metal detecting station described in claim 11 wherein the transmitting loop is positioned equidistant between the receiving loops and the receiving loops are identical and electrically connected together in phase opposition, and said first means for producing a fixed voltage in the receiving loop comprises a sheet metal fin, said fin connected to the shaft of the rotary arm of the multiple position switch, said shaft and fin positioned so that the fin is movable toward one or the other of the receiving loops depending on which terminal the rotary arm engaged, whereby said change in the phase relationship caused by the energized wing loop and said fixed voltage produced in the associated receiving loop by said metal fin are of such magnitude that no reasonably likely combination of target material and shape can move through the station without disturbing said fixed voltage and/or said phase relationship in said receiving loop, said multiple position switch having a test terminal, the test terminal of the multiple position switch so positioned in the station that when the rotary arm is connected to the test terminal, neither wing loop is energized and the metal fin is equidistant from both receiving loops so that if no target is passing through the station the voltage output from the receiving loops is null whereby errors in assembly or shifts in the position of the transmitting and receiving loops and wing loops can be detected.

Claim 18

The metal detecting station described in claim 9 wherein the detecting station comprises a base wall layered planar side walls and a layered planar top wall, all rigidly connected together, said station rectangular in cross-section, one layer of the planar side walls and top walls formed from a rigid insulating material, a second layer of said walls and said top walls formed from a planar sheet metal, a third layer of the side and top walls formed from another insulating support material, said layers of insulating material secured tightly together with said sheet metal mounted between so that the sheet metal is rigidly mounted between the insulating layers of the side walls and the top walls, whereby the interior of the metal detecting station is shielded from electromagnetic disturbances and influences caused by moving ferrous and non-ferrous metal objects outside the station.

Claim 19

The metal detecting station described in claim 13 wherein the plane of the transmitting and receiving loops is perpendicular to the plane of the side walls and top walls of the station and wherein said receiving loops are rectangular in shape and are generally co-extensive with the cross-section of the metal detecting station, said receiving loops mounted so the sides of the receiving loops are closely adjacent the side walls and top wall of the station.

Claim 20

The metal detecting station described in claim 14 including means for holding said single turn wire loops rigidly in said station.

Claim 21

The detecting station described in claim 15 wherein said means for holding said single turn wire loops rigidly in position in said station include strips formed from a suitable rigid insulating material, said strips rigidly mounted in the station against said walls and top wall, wire receiving grooves formed in said strips, said single turn loops mounted in the wire receiving grooves in said strips whereby said strips hold the single turn loops rigidly in the station, and in addition rigidly hold the sheet metal layers in position in the side walls and top wall.

Claim 22

The metal detecting station described in claim 16 including means associated with said metal detecting station for compensating the metal detecting station for the presence of massive ferrous or non-ferrous metal objects adjacent the station.

Claim 23

A metal detecting station for detecting the movement of deliberately hidden ferrous or non-ferrous metal objects greater than a predetermined size through said station, said station having an interior portion and at least one planar wall, said at least one planar wall formed from a plurality of layers, one of said layers formed from an insulating material and comprising a rigid support layer at least one layer formed from a thin ferrous sheet metal, means securing said ferrous sheet metal to said rigid support layer whereby said ferrous sheet metal is coextensive with said rigid support layer and is rigidly supported thereby in a fixed position on said wall, said layer of ferrous sheet metal serving to shield the interior of the station from electromagnetic signals or magnetic influences caused by ferrous or non-ferrous metal objects moving by said wall outside the station, detecting means in the station for detecting the movement of ferrous or non-ferrous metal objects moving through the station, said detecting means comprising a single turn transmitting coil and two single turn receiving coils disposed in space parallel relationship to each other on opposite sides of said transmitting coil and positioned so that objects passing through the station must pass through the coils, said single turn coils positioned so that they are each generally perpendicular to said at least one planar wall and shaped so that one side of said coil lies closely adjacent to said planar wall, a signal generator connected to said transmitting coil for inducing an electromagnetic field in said receiving coils, first means associated with a station for causing a fixed voltage output in said receiving coils of sufficient magnitude to make the metal detecting station comparatively insensitive to metal objects substantially smaller than metal objects of interest to prevent the station from responding to the movement of said tiny metal objects through the station, second means in said station and associated with said first means in such a way that said second means operates only when said first means operates, to produce a phase shift between the transmitting coil and said receiving coil in such a direction that the metal detecting station is sensitive to both ferrous and non-ferrous metal objects passing through the station, said phase shift being large enough to distort the electromagnetic field inside the station so that no likely combination of target-shape or target-orientation could pass through the station without disturbing the voltage on said receiving coils, and means associated with this station and connected to said receiving coils for producing an indication of any voltage change in said receiving coils caused by the passage of metal objects through the station.

Claim 24

A metal detecting station for detecting the movement of deliberately hidden ferrous or non-ferrous metal objects greater than a predetermined size through said station, said station having an interior portion and at least one planar wall, said at least one planar wall formed from a plurality of layers, one of said layers formed from an insulating material and comprising a rigid support layer at least one layer formed from a thin ferrous sheet metal, means securing said ferrous sheet metal to said rigid support layer whereby said ferrous sheet metal is coextensive with said rigid support layer and is rigidly supported thereby in a fixed position on said wall, said layer of ferrous sheet metal serving to shield the interior of the station from electromagnetic signals or magnetic influences caused by ferrous or non-ferrous metal objects moving by said wall outside the station, detecting means in the station for detecting the movement of ferrous or non-ferrous metal objects moving through the station, said detecting means comprising a single turn transmitting coil and two single turn receiving coils disposed in space parallel relationship to each other on opposite sides of said transmitting coil and positioned so that objects passing through the station must pass through the coils, said single turn coils positioned so that they are each generally perpendicular to said at least one planar wall and shaped so that one side of said coil lies closely adjacent to said planar wall, a signal generator connected to said transmitting coil for inducing an electromagnetic field in said receiving coils, first means associated with a station for causing a fixed voltage output in said receiving coils of sufficient magnitude to make the metal detecting station comparatively insensitive to metal objects substantially smaller than metal objects of interest to prevent the station from responding to the movement of said tiny metal objects through the station, second means in said station and associated with said first means in such a way that said second means operates only when said first means operates, to produce a phase shift between the transmitting coil and said receiving coil in such a direction that the metal detecting station is sensitive to both ferrous and non-ferrous metal objects passing through the station, said phase shift being large enough to distort the electromagnetic field inside the station so that no likely combination of target-shape or target-orientation could pass through the station without disturbing the voltage on said receiving coils, and means associated with this station and connected to said receiving coils for producing an indication of any voltage change in said receiving coils caused by the passage of metal objects through the station.

Claim 25

A metal detecting station, said station having an interior portion defined by at least spaced parallel planar side walls and a connecting planar top wall, all of said walls formed from a plurality of layers, one of said layers in each wall formed from an insulating material and comprising a rigid support layer, at least one other layer in each wall formed from a thin ferrous sheet metal, means securing said ferrous sheet metal to said rigid support layer whereby said ferrous sheet metal is coextensive with said rigid support layer and is rigidly supported thereby in a fixed position in said wall, said layers of sheet metal in the side walls and the top wall of the station serving to shield the interior of the station from electromagnetic signals or magnetic influences caused by ferrous or non-ferrous metallic objects moving by said wall outside the station, detecting means in the station for detecting the movement of ferrous or non-ferrous metal objects moving through the station, said detecting means comprising a single turn transmitting loop and two single turn receiving loops disposed and spaced parallel relationship to each other and positioned on opposite sides of the transmitting loop and positioned so that objects passing through the station must pass through the loops, each single turn loop positioned so it lies in a plane perpendicular to the planes of the planar side walls and the planar top wall and shaped so that one side of each loop lies closely adjacent to said planar side wall and one side of each loop lies closely adjacent to said planar top wall, a signal generator connected to said transmitting loop for inducing an electromagnetic field in the receiving loops, said signal generator comprising an oscillator including a transformer, the secondary coil of said transformer connected to said transmitting loop and serving to match the impedance of the oscillator to the impedance of a single turn transmitting loop, means connected to said receiving loops to tune said receiving loops to the frequency of the transmitting loop, said means including transformers for each of said receiving loops, first means associated with said station for producing a fixed voltage output in said receiving loops of sufficient magnitude to make the metal detecting station comparatively insensitive to the movement of tiny metal objects through the station, second means in said station and connected to said first means in such a way that it operates only when said first means operates to induce a phase shift between the transmitting loop and the receiving loops in such a direction that the metal detecting station is sensitive to both ferrous and non-ferrous metal objects passing through the station, said phase shift large enough to distort the electromagnetic field inside the metal detecting station so that no likely combination of target-shape or target-orientation could pass through the station without disturbing the voltage on said receiving loops, and means associated with this station and connected to said receiving loops for providing an indication of any voltage change in said receiving loops caused by the passage of metal objects of sufficient size through the station.

Claim 26

A metal detecting station, said station having an interior portion defined by at least spaced parallel planar side walls and a connecting planar top wall, all of said walls formed from a plurality of layers, one of said layers in each wall formed from an insulating material and comprising a rigid support layer, at least one other layer in each wall formed from a thin ferrous sheet metal, means securing said ferrous sheet metal to said rigid support layer whereby said ferrous sheet metal is coextensive with said rigid support layer and is rigidly supported thereby in a fixed position in said wall, said layers of sheet metal in the side walls and the top wall of the station serving to shield the interior of the station from electromagnetic signals or magnetic influences caused by ferrous or non-ferrous metallic objects moving by said wall outside the station, detecting means in the station for detecting the movement of ferrous or non-ferrous metal objects moving through the station, said detecting means comprising a single turn transmitting loop and two single turn receiving loops disposed and spaced parallel relationship to each other and positioned on opposite sides of the transmitting loop and positioned so that objects passing through the station must pass through the loops, each single turn loop positioned so it lies in a plane perpendicular to the planes of the planar side walls and the planar top wall and shaped so that one side of each loop lies closely adjacent to said planar side wall and one side of each loop lies closely adjacent to said planar top wall, a signal generator connected to said transmitting loop for inducing an electromagnetic field in the receiving loops, said signal generator comprising an oscillator including a transformer, the secondary coil of said transformer connected to said transmitting loop and serving to match the impedance of the oscillator to the impedance of a single turn transmitting loop, means connected to said receiving loops to tune said receiving loops to the frequency of the transmitting loop, said means including transformers for each of said receiving loops, first means associated with said station for producing a fixed voltage output in said receiving loops of sufficient magnitude to make the metal detecting station comparatively insensitive to the movement of tiny metal objects through the station, second means in said station and connected to said first means in such a way that it operates only when said first means operates to induce a phase shift between the transmitting loop and the receiving loops in such a direction that the metal detecting station is sensitive to both ferrous and non-ferrous metal objects passing through the station, said phase shift large enough to distort the electromagnetic field inside the metal detecting station so that no likely combination of target-shape or target-orientation could pass through the station without disturbing the voltage on said receiving loops, and means associated with this station and connected to said receiving loops for providing an indication of any voltage change in said receiving loops caused by the passage of metal objects of sufficient size through the station.

Claim 27

A metal detecting station for detecting the movement of deliberately hidden ferrous or non-ferrous metal objects greater than a predetermined size through the station, said station having opposed ends and detecting means therein for detecting the movement of ferrous or non-ferrous metal objects through the station, said detecting means comprising a single turn transmitting loop and two single turn receiving loops positioned on each side of the transmitting loop in spaced parallel relationship to each other and adjacent opposed ends of the station, an oscillator associated with the station, said oscillator including a transformer, the secondary coil of said transformer connected to said transmitting loop for inducing an electromagnetic field in said transmitting loop and serving both to determine the frequency of the oscillator and to match the impedance of the oscillator to the impedance of the single turn transmitting loop thereby permitting the loops to be formed from a single turn of wire, means connected to said receiving loops to tune said receiving loops to the frequency of the transmitting loop, first means in said station associated with the receiving loops for inducing a fixed voltage output in the receiving loops of sufficient magnitude to make the metal detecting station insensitive to metal objects substantially smaller than metal objects of interest to prevent the station from responding sufficiently to the movement of tiny metal objects through the station, second means in the station and connected to said first means in such a way that the second means operates only when said first means operates to induce a phase shift between the transmitting loop and said receiving loops, in such a direction that the metal-detecting station will be sensitive to both ferrous and non-ferrous metal objects passing through the station, said phase shift large enough to distort the electromagnetic field inside the station so that no likely combination of target-shape or target-orientation could pass through the station without disturbing the voltage on said receiving loops, and means associated with this station and connected to said receiving loops for providing an indication of any voltage change in said receiving loops caused by the passage of metal objects greater than a predetermined size through the station.

Claim 28

A metal detecting station for detecting the movement of deliberately hidden ferrous or non-ferrous metal objects greater than a predetermined size through the station, said station having opposed ends and detecting means therein for detecting the movement of ferrous or non-ferrous metal objects through the station, said detecting means comprising a single turn transmitting loop and two single turn receiving loops positioned on each side of the transmitting loop in spaced parallel relationship to each other and adjacent opposed ends of the station, an oscillator associated with the station, said oscillator including a transformer, the secondary coil of said transformer connected to said transmitting loop for inducing an electromagnetic field in said transmitting loop and serving both to determine the frequency of the oscillator and to match the impedance of the oscillator to the impedance of the single turn transmitting loop thereby permitting the loops to be formed from a single turn of wire, means connected to said receiving loops to tune said receiving loops to the frequency of the transmitting loop, first means in said station associated with the receiving loops for inducing a fixed voltage output in the receiving loops of sufficient magnitude to make the metal detecting station insensitive to metal objects substantially smaller than metal objects of interest to prevent the station from responding sufficiently to the movement of tiny metal objects through the station, second means in the station and connected to said first means in such a way that the second means operates only when said first means operates to induce a phase shift between the transmitting loop and said receiving loops, in such a direction that the metal-detecting station will be sensitive to both ferrous and non-ferrous metal objects passing through the station, said phase shift large enough to distort the electromagnetic field inside the station so that no likely combination of target-shape or target-orientation could pass through the station without disturbing the voltage on said receiving loops, and means associated with this station and connected to said receiving loops for providing an indication of any voltage change in said receiving loops caused by the passage of metal objects greater than a predetermined size through the station.

Claim 29

The metal detecting station described in claim 9 wherein the station has means therein for causing the voltage indicator associated with the station for providing an indication of any voltage change in the receiving loops to respond in separate ways dependant on the direction of motion of a metal object through the station.