# US 10,310,030 B2 · Method for automatically recognising a magnetic object

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- Number: US 10,310,030 B2
- Document ID: US10310030B2
- Status: Granted
- Kind: B2
- Application number: 14/773,509
- Filed: 2014-02-26
- Published: 2016-01-21
- Granted: 2019-06-04
- Earliest claimed: 2013-03-08
- Assignees: Commissariat A L'energie Atomique Et Aux Energies Alternatives
- Applicants: Commissariat à l'énergie atomique et aux énergies alternatives
- Inventors: Tristan Hautson; Rabeb Aloui; Saifeddine Aloui; Timothée Jobert
- Web page: https://patentgrep.com/patent/US10310030B2

## CPC

- G01R 33/12: Measuring magnetic properties of articles or specimens of solids or fluids (involving magnetic resonance G01R33/20)
- G01R 33/0094: {Sensor arrays}
- G01R 33/0206: {Three-component magnetometers}
- G01R 33/10: Plotting field distribution {; Measuring field distribution}
- G01V 3/081: {the magnetic field is produced by the objects or geological structures (characterised by the method of magnetic field measurement G01R33/00)}
- G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12)
- G01V: GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS (means for indicating the location of accidentally buried, e.g. snow-buried, persons A63B29/02)

## Abstract

A method for recognizing a magnetic object includes holding the object immobile in front of an array of N (where N is >five) tri-axial magnetometers (Mij) linked with no degree of freedom. There is a fixed distance between two consecutive magnetometers less than the maximum separation between the magnetic parts of the magnetic object furthest away from one another. The method includes measuring by each magnetometer a vector bi,m of which each coordinate represents the value of the magnetic field projected onto a respective measurement axis of the magnetometer, and a union of vectors bi,m forming a measured magnetic signature Sm, where the index “i” is an identifier of the magnetometer. The method includes computing of a deviation E between the magnetic signature Sm and a prerecorded magnetic signature SRef of a known magnetic object. The method includes comparing E to a predetermined threshold and recognizing the magnetic object.

## Claims

### Claim 1

A non-abstract method comprising implementing an improvement in technology, wherein said technology is the technology of magnetometers, wherein said improvement comprises a method of using an array of magnetometers to recognize a relationship between a first object and a second object, said first and second objects each being secured to a corresponding one of a plurality of parts—wherein each of said parts is capable of distorting the field lines of the Earth's magnetic field, wherein said plurality of parts comprises a first part and a second part, wherein said array comprises at least five tri-axial magnetometers, wherein said at least five tri-axial magnetometers comprise consecutive tri-axial magnetometers that are separated by a fixed distance, wherein implementing said improvement comprises executing a process that includes holding said first object at a predetermined position against said array and computing a deviation between a measurement and a reference, wherein said measurement is a measurement of at least fifteen norms along said array of magnetometers, wherein said norms are measured while said first object is thus held against said array, wherein said reference is a reference based on at least fifteen corresponding norms that would have been obtained by said array had said second object been held against said array at said predetermined position, wherein each of said norms is a norm of a projection of a magnetic field along an axis of one of said tri-axial magnetometers, wherein said process further comprises determining a relationship between said deviation and a predetermined threshold, and based on said relationship, selecting an action from the group consisting of recognizing that said first object corresponds to said second object and recognizing that said first object does not correspond to said second object, wherein said plurality of parts comprises a third part that is fixed to said first object, wherein a separation between said first and third parts is a maximum separation between any two parts on said first object, wherein said maximum separation is twice said fixed distance between said magnetometers.

### Claim 2 (depends on 1)

The method of claim 1, wherein, for at least four magnetometers of the array of magnetometers, the shortest distance between the magnetometers and the magnetic object is less than dmax, dmax being equal to [μ0m/4πσ10(SNR/20)]1/3, where: σ is the standard deviation of the noise of the magnetometer, μ0 is the permeability of the vacuum, m is the magnetic moment of the magnetic object, and SNR is a constant equal to 6.02 db.

### Claim 3 (depends on 1)

The method of claim 1, wherein, for at least four magnetometers of the array of magnetometers, the shortest distance between the magnetometers and the magnetic object is less than 50 cm.

### Claim 4 (depends on 1)

The method of claim 1, wherein holding said first object at a predetermined position against said array comprises holding the magnetic object in a predetermined position in front of the array of magnetometers in which the fixed distance between two immediately consecutive magnetometers is at least half the maximum separation between two magnetic parts of the magnetic object furthest away from one another.

### Claim 5 (depends on 1)

The method of claim 1, wherein the array of magnetometers comprises magnetometers distributed along at least two non-parallel directions.

### Claim 6 (depends on 1)

The method of claim 1, wherein selecting an action comprises recognizing that said first object does not correspond to said second object.

### Claim 7 (depends on 1)

The method of claim 1, wherein selecting an action comprises recognizing that said first object corresponds to said second object.

### Claim 8 (depends on 1)

The method of claim 1, wherein said plurality of parts comprises a third part, said method further comprising selecting said first object to be a frame of a cell phone, selecting said first part to be a microphone secured to said frame, and selecting said third part to be a speaker secured to said frame.

### Claim 9 (depends on 1)

The method of claim 1, wherein holding said first object at a predetermined position against said array comprises placing said first object within an outline of said first object.

### Claim 10 (depends on 1)

The method of claim 1, wherein holding said first object at a predetermined position against said array comprises placing said first object within a recess shaped like said first object.

### Claim 11 (depends on 1)

The method of claim 1, wherein there exists a first dipole moment associated with said first object, wherein said magnetometers are characterized by a noise level having a variance, wherein there exists a cube that has a volume that is proportional to a ratio of said dipole moment to said variance, wherein, while said first object is held, there exists a plurality of distances, each of which is a distance between a magnetometer and said first object, wherein holding said first object comprises causing said first object to be a location such that at least four distances from said plurality of distances is less than a maximum distance, and wherein said maximum distance is selected based on a length of an edge of said cube.

### Claim 12 (depends on 11)

The method of claim 11, further comprising increasing said distance in response to an increase in said dipole moment.

### Claim 13 (depends on 11)

The method of claim 11, further comprising decreasing said distance in response to an increase in said variance.

### Claim 14 (depends on 1)

The method of claim 1, wherein computing a deviation comprises causing one of a translation or rotation of at least one of said measurement and said reference so as to minimize said deviation.

### Claim 15 (depends on 1)

The method of claim 1, wherein said first object comprises a permanent magnet.

### Claim 16

A non-abstract apparatus for implementing an improvement in the technology of recognizing a relationship between first and second objects, said first and second objects each being secured to a corresponding one of a plurality of parts, wherein each of said parts is capable of distorting the field lines of the Earth's magnetic field, wherein said plurality of parts comprises a first part, a second part, and a third part, wherein said third part is fixed to said first object, said apparatus comprising an array of non-abstract magnetometers, said array comprising at least five tri-axial non-abstract magnetometers that are linked mechanically to one another with no degree of freedom to maintain a fixed distance between each of the magnetometers, wherein a separation between said first and third parts is a maximum separation between any two parts on said first object, wherein said maximum separation is twice said fixed distance between each of the magnetometers, and a processing unit programmed to compute a deviation between a measurement and a reference when said first object is held at a predetermined first position against said array, wherein said measurement is a measurement of at least fifteen norms along said array of magnetometers, wherein said norms are measured while said first object is thus held against said array, wherein said reference is a reference based on at least fifteen corresponding norms that would have been obtained by said array had said second object been held against said array at said predetermined position, wherein each of said norms is a norm of a projection of a magnetic field along an axis of one of said tri-axial magnetometers, wherein said processor is further configured to determine a relationship between said deviation and a predetermined threshold, and based on said relationship, to select an action from the group consisting of recognizing that said first object corresponds to said second object and recognizing that said first object does not correspond to said second object.

### Claim 17 (depends on 16)

The apparatus of claim 16, further comprising a device for holding the first object in a predetermined position, the device being at least suitable for indicating, to a human being, the predetermined position in which the first object, which is to be recognized, must be placed.

### Claim 18

A manufacture comprising a tangible and non-transitory information storage medium comprising instructions for causing an electronic computer to compute a deviation, wherein said electronic computer is a constituent of an apparatus for recognizing a relationship between first and second objects, said first and second objects each being secured to a corresponding one of a plurality of parts, wherein each of said parts is capable of distorting the field lines of the Earth's magnetic field, wherein said plurality of parts comprises a first part, a second part, and a third part, wherein said third part is fixed to said first object, wherein said apparatus comprises, in addition to said electronic computer, an array of non-abstract magnetometers, said array comprising at least five tri-axial non-abstract magnetometers that are linked mechanically to one another with no degree of freedom to maintain a fixed distance between each of the magnetometers, wherein a separation between said first and third parts is a maximum separation between any two parts on said first object, wherein said maximum separation is twice said fixed distance between each of the magnetometers, and wherein said instructions, when executed by said electronic computer, cause said electronic computer to compute said deviation between a measurement and a reference when said first object is held at a predetermined first position against said array, wherein said measurement is a measurement of at least fifteen norms along said array of magnetometers, wherein said norms are measured while said first object is thus held against said array, wherein said reference is a reference based on at least fifteen corresponding norms that would have been obtained by said array had said second object been held against said array at said predetermined position, wherein each of said norms is a norm of a projection of a magnetic field along an axis of one of said tri-axial magnetometers, wherein said instructions further comprise instructions for causing said electronic computer to determine a relationship between said deviation and a predetermined threshold and based on said relationship, to select an action from the group consisting of recognizing that said first object corresponds to said second object and recognizing that said first object does not correspond to said second object.