Device for reading information magnetically coded on a carrier

Claim 1

A device for reading information magnetically coded on a carrier having precoded information and adapted to be passed successively in front of a magnetizing device for magnetizing the information and a magnetic transducer device for detecting the magnetized information, comprising: a magnetizing device having at least one magnetic layer said magnetic layer containing a succession of adjoining zones of lengths d 1 and d 2 , the length d 2 being much greater than d 1 and the magnetic inductions in the zones being of opposite sense; a magnetic transducer device having at least one magneto-resistive member for detecting the information and a magneto-resistive compensating member, said compensating member being disposed close to the magneto-resistive detecting member at a distance such that it is subject to the same interference fields as the detecting member while not being subject to the magnetic leakage field of the magnetized information as it passes in front of the transducer, and the voltages developed across the detecting and compensating members in response to the effect of the interference fields being substantially equal.

Claim 2

A device for reading information magnetically coded on a carrier having precoded information and adapted to be passed successively in front of a magnetizing device for magnetizing the information and a magnetic transducer device for detecting the magnetized information, comprising: a magnetizing device having at least one magnetic layer said magnetic layer containing a succession of adjoining zones of lengths d 1 and d 2 , the length d 2 being much greater than d 1 and the magnetic inductions in the zones being of opposite sense; a magnetic transducer device having at least one magneto-resistive member for detecting the information and a magneto-resistive compensating member, said compensating member being disposed close to the magneto-resistive detecting member at a distance such that it is subject to the same interference fields as the detecting member while not being subject to the magnetic leakage field of the magnetized information as it passes in front of the transducer, and the voltages developed across the detecting and compensating members in response to the effect of the interference fields being substantially equal.

Claim 4

A device according to claims 1 or 2 wherein the magnetizing device is arranged in such a way that its edge closest to the said magneto-resistive members is at a distance of δ from the latter such that its leakage field Hpol polarizes the magneto-resistive members by causing their axes of easy magnetization to rotate through an angle θ of between 0 and 90°.

Claim 7

A device according to claims 1 or 2 wherein the magnetizing and magnetic transducer devices are arranged on the same insulating substrate.

Claim 8

A device according to claims 1 or 2 wherein the magnetic layer has a high coercive field.

Claim 9

A device according to claims 1 or 2 wherein the magnetic induction in the shorter zones is positive and is equal to the residual induction of the magnetic layer.

Claim 10

A device according to claims 1 or 2 wherein the magnetic induction in the longer zones is negative and equal to the residual induction of the magnetic layer.

Claim 11

A device according to claims 1 or 2 where the detecting and compensating members have the same co-efficient of magneto-resistance.

Claim 14

A device for reading information magnetically coded on a carrier having precoded information and adapted to be passed successively in front of a magnetizing device for magnetizing the information and a magnetic transducer device for detecting the magnetized information, comprising: a magnetizing device having at least one magnetic layer said magnetic layer containing a succession of adjoining zones of lengths d 1 and d 2 , the length d 2 being much greater than d 1 and the magnetic inductions in the zones being of opposite sense; a magnetic transducer device having at least one magneto-resistive member of anisotropic magnetic material for detecting the information and a magneto-resistive compensating member of anisotropic material, said compensating member being disposed close to the magneto-resistive detecting member at a distance such that it is subject to the same interference fields as the detecting member while not being subject to the magnetic leakage field of the magnetized information as it passes in front of the transducer, the voltages developed across the detecting and compensating members in response to the effect of the interference fields being substantially equal, and said magnetizing device being disposed on the same insulating substrate as the magnetic transducer and being arranged such that its edge closest to the said magneto-resistive members is at a distance of δ from the latter such that its leakage field Hpol polarizes the magneto-resistive members by causing their axes of easy magnetization to rotate through an angle θ of between 0 and 90°.

Claim 15

A device for reading information magnetically coded on a carrier having precoded information and adapted to be passed successively in front of a magnetizing device for magnetizing the information and a magnetic transducer device for detecting the magnetized information, comprising: a magnetizing device having at least one magnetic layer said magnetic layer containing a succession of adjoining zones of lengths d 1 and d 2 , the length d 2 being much greater than d 1 and the magnetic inductions in the zones being of opposite sense; a magnetic transducer device having at least one magneto-resistive member of anisotropic magnetic material for detecting the information and a magneto-resistive compensating member of anisotropic material, said compensating member being disposed close to the magneto-resistive detecting member at a distance such that it is subject to the same interference fields as the detecting member while not being subject to the magnetic leakage field of the magnetized information as it passes in front of the transducer, the voltages developed across the detecting and compensating members in response to the effect of the interference fields being substantially equal, and said magnetizing device being disposed on the same insulating substrate as the magnetic transducer and being arranged such that its edge closest to the said magneto-resistive members is at a distance of δ from the latter such that its leakage field Hpol polarizes the magneto-resistive members by causing their axes of easy magnetization to rotate through an angle θ of between 0 and 90°.