Electro-magnetic desensitizer

Claim 3

A deactivating apparatus for magnetizing a magnetically responsive marker of an electronic article surveillance system, said system comprising means for producing within an interrogation zone an alternating magnetic field for interrogating a said marker and means for producing an appropriate alarm signal when a characteristic response produced by an activated marker in said zone is detected, said marker comprising at least one magnetizable element which, when magnetized, causes a different response to be produced than that resulting when the magnetizable element is unmagnetized, said deactivating apparatus comprising a) electronic article surveillance system simulation means comprising a wave generatior (1), a coil (2) for generating a first magnetic field corresponding to that produced by said system for interrogating said marker, within which first field said marker may be positioned, means (8, 16) for detecting the response from the marker and for producing an active marker signal in the event the response corresponds with the characteristic response required by the system to produce a said alarm signal, b) means (3) for generating within said coil a second magnetic field identified by its flux density, and for applying said second field to said magnetizable element to change the magnetic state thereof, thereby altering said response, and c) means (9) for applying a said first magnetic field to said marker, detecting the response therefrom and means (20) for producing a deactivated marker signal when said altered response is detected, said apparatus being characterized by electronic switch means (13, 15) responsive to said active marker signal for automatically and gradually applying current through a rectifier means (12) directly from a source of alternating electrical power to said coil to gradually build up said second magnetic field, which is directionally constant, means (14) for sensing the current in said coil, electronic evaluator means (17) for responding when said sensed current reaches a current level at which the intensity of said second magnetic field corresponds to that level at which said characteristic response will be altered, and electronic control means (18) for automatically opening said switch means (13, 15) to disconnect the source of alternating electrical power from the coil when the intensity of said second magnetic field is sufficient to alter said response.

Claim 4

A deactivating apparatus for magnetizing a magnetically responsive marker of an electronic article surveillance system, said system comprising means for producing within an interrogation zone an alternating magnetic field for interrogating a said marker and means for producing an appropriate alarm signal when a characteristic response produced by an activated marker in said zone is detected, said marker comprising at least one magnetizable element which, when magnetized, causes a different response to be produced than that resulting when the magnetizable element is unmagnetized, said deactivating apparatus comprising a) electronic article surveillance system simulation means comprising a wave generatior (1), a coil (2) for generating a first magnetic field corresponding to that produced by said system for interrogating said marker, within which first field said marker may be positioned, means (8, 16) for detecting the response from the marker and for producing an active marker signal in the event the response corresponds with the characteristic response required by the system to produce a said alarm signal, b) means (3) for generating within said coil a second magnetic field identified by its flux density, and for applying said second field to said magnetizable element to change the magnetic state thereof, thereby altering said response, and c) means (9) for applying a said first magnetic field to said marker, detecting the response therefrom and means (20) for producing a deactivated marker signal when said altered response is detected, said apparatus being characterized by electronic switch means (13, 15) responsive to said active marker signal for automatically and gradually applying current through a rectifier means (12) directly from a source of alternating electrical power to said coil to gradually build up said second magnetic field, which is directionally constant, means (14) for sensing the current in said coil, electronic evaluator means (17) for responding when said sensed current reaches a current level at which the intensity of said second magnetic field corresponds to that level at which said characteristic response will be altered, and electronic control means (18) for automatically opening said switch means (13, 15) to disconnect the source of alternating electrical power from the coil when the intensity of said second magnetic field is sufficient to alter said response.

Claim 5

An apparatus according to claim 2, wherein said wave generator (1) generates a substantially sinusoidal first magnetic field.

Claim 6

An apparatus as in claim 3, characterized in that both terminals of said coil (2) are connected through impedance matching and decoupling capacitors (11) to said wave generator (1), and in that said switch means (13) prevents current from said wave generator from being short-circuited.

Claim 7

An apparatus according to claim 2, further including a yoke (5) of ferromagnetic material proximate to said coil and wherein said rectifier means comprises a full wave bridge rectifier (12) connected directly to said source of electrical power and short-circuiting said coil, with said current sensing means (14) and a portion (13) of said electronic switch means being connected in series in said short-circuit.

Claim 8

An apparatus as in claim 5, characterized by said yoke (5) being configured to create a relatively wide air gap, with the yoke (5) and coil (2) being adapted to be mounted underneath a table top (6).

Claim 9

An apparatus as in claim 5, characterized by said yoke (5) having a substantially U-shaped configuration such that the magnetic flux density required for deactivating the magnetic marker is provided outside of said U-shaped configuration.

Claim 10

An apparatus as in claim 2, characterized by the magnetic flux density required for deactivating the magnetic marker being built up by a plurality of rectified voltage pulses from the source of electrical power.

Claim 11

An apparatus as in claim 2, characterized by said current sensing means being set to respond to a maximum current level corresponding to a magnetic flux density amounting to three times the magnetic flux density required for deactivation.

Claim 12

An apparatus according to claim 2, characterized in that said current sensing means is set to respond to a maximum current level corresponding to a magnetic flux density in the range of 300 to 1000 G (30-100 mT (milli-Tesla)).

Claim 13

An apparatus as in claim 2; characterized by a yoke (5) proximate to said coil (2) consisting of a relatively low coercive force material.