Sensor for magnetic fields with Laplace force

Patent metadata

Field	Value
Publication number	US-9562789-B2
Application number	US-201314408176-A
Country	US
Kind code	B2
Filing date	Jun 14, 2013
Priority date	Jun 15, 2012
Publication date	Feb 7, 2017
Grant date	Feb 7, 2017

Abstract

A magnetic field sensor comprises a substrate and a moving part which is displaced when subjected to a Laplace force. There is a gauge for measuring the displacement of the moving part. There is a suspended lever that is rotationally displaced about an axis of rotation at right angles to the direction of displacement of the moving part. The lever is connected to the moving part to transmit displacement of the moving part to the lever to cause rotation of the lever about the axis of rotation. The lever is also connected to a first part of the gauge. The sensor comprises a hinge that connects the lever to the substrate. The hinge allows the rotation of the lever about its axis of rotation and is rigid to allow for a lever arm effect. The second part of the gauge is fixed with no degree of freedom to the substrate.

First claim

The invention claimed is:

1. A magnetic field sensor with Laplace force, comprising:
a substrate extending essentially in a plane called substrate plane,
at least one electrical conductor suitable for an electrical current to flow through, the electrical conductor comprising a moving part, suspended over the substrate, suitable for being displaced in a direction of displacement when it is subjected to a Laplace force,
mechanical links mechanically connecting the moving part to the substrate and electrically connecting the moving part to current power supply contact blocks arranged on the substrate,
at least one gauge suitable for measuring a physical quantity representative of the amplitude of the displacement of the moving part, the gauge comprising at least one first and one second parts,
a suspended lever that can be rotationally displaced about an axis of rotation at right angles to the direction of displacement of the moving part, the lever comprising a first and a second distinct attachment points, the first attachment point being mechanically connected to the moving part to transmit the displacement of the moving part to the lever in such a way as to drive the lever in rotation about the axis of rotation in response to a displacement of the moving part, and the second attachment point being directly mechanically connected to the first part of the gauge, wherein:
the sensor also comprises a hinge mechanically connecting the lever to the substrate, the hinge being distinct and separate from the mechanical links of the moving part and from the first and second attachment points, the hinge allowing the rotation of the lever about its axis of rotation, and
the lever is rigid to allow for a lever arm effect, and
the second part of the gauge is fixed with no degree of freedom to the substrate.

2. The sensor as claimed in claim 1 , in which the second attachment point is closer to the axis of rotation of the lever than the first attachment point, and the shortest distance between this second attachment point and the axis of rotation is less than a tenth of the length of the lever.

3. The sensor as claimed in claim 1 , in which the gauge is a suspended strain gauge, comprising, in addition to the first and second parts, a third part, positioned between the first and second parts, suspended over the substrate.

4. The sensor as claimed in claim 3 , in which the thickness of the third part is at least two times less than the thickness of the lever.

5. The sensor as claimed in claim 1 , in which the gauge comprises two armatures facing one another forming a capacitor, one of the armatures being secured to the substrate, while the other of the armatures is mechanically connected to the second attachment point of the lever in such a way as to be displaced relative to the other armature in response to a displacement of the lever.

6. The sensor as claimed in claim 1 , in which the gauge is a resonant gauge comprising:
at least one beam suspended between the second attachment point and the substrate,
an electrode suitable for causing the beam to vibrate,
another electrode or the same electrode for measuring the frequency of vibration of the beam.

7. The sensor as claimed in claim 1 , in which the sensor comprises at least two gauges positioned in such a way as to each measure a displacement of the lever, of opposite signs to the displacement measured by the other gauge.

8. The sensor as claimed in claim 1 , in which the weight of the lever is distributed on either side of its axis of rotation in such a way that the shortest distance between the axis of rotation of the lever and the center of gravity of the lever is less than 1% of the length of the lever.

9. The sensor as claimed in claim 8 , in which:
the sensor comprises at least one first and one second copies of said at least one electrical conductor, and
the axis of rotation of the lever is situated in the middle of the lever in the direction of its length,
the first attachment point is mechanically connected to the first copy of said at least one conductor, and
the lever comprises a third attachment point mechanically connected to the second copy of said at least one electrical conductor, the first and third attachment points being symmetrical to one another relative to the axis of rotation.

10. The sensor as claimed in claim 1 , in which:
the electrical conductor is rigid so as not to be deformed under the action of the Laplace force, and
the mechanical links are configured in meander fashion to allow the electrical conductor to be displaced when it is subjected to the same Laplace force.

11. The sensor as claimed in claim 1 , in which the moving part is mechanically connected to the first attachment point of the lever via a mechanical link in meander form arranged in such a way that the stiffness of this mechanical link in the direction of displacement of the moving part is at least five times greater than its stiffness in a direction orthogonal to this direction of displacement.

12. The sensor as claimed in claim 1 , in which the sensor comprises a plurality of electrical conductors positioned parallel to one another.

13. A method for using a magnetic field sensor with Laplace force, the method comprising:
deploying a magnetic field sensor comprising;
a substrate extending essentially in a plane called substrate plane,
at least one electrical conductor suitable for an electrical current to flow through, the electrical conductor comprising a moving part, suspended over the substrate, suitable for being displaced in a direction of displacement when it is subjected to a Laplace force,
mechanical links mechanically connecting the moving part to the substrate and electrically connecting the moving part to current power supply contact blocks arranged on the substrate,
at least one gauge suitable for measuring a physical quantity representative of the amplitude of the displacement of the moving part, the gauge comprising at least one first and one second parts,
a suspended lever that can be rotationally displaced about an axis of rotation at right angles to the direction of displacement of the moving part, the lever comprising a first and a second distinct attachment points, the first attachment point being mechanically connected to the moving part to transmit the displacement of the moving part to the lever in such a way as to drive the lever in rotation about the axis of rotation in response to a displacement of the moving part, and the second attachment point being directly mechanically connected to the first part of the gauge, wherein:
the sensor also comprises a hinge mechanically connecting the lever to the substrate, the hinge being distinct and separate from the mechanical links of the moving part and from the first and second attachment points, the hinge allowing the rotation of the lever about its axis of rotation, and
the lever is rigid to allow for a lever arm effect, and
the second part of the gauge is fixed with no degree of freedom to the substrate;

and subsequently performing the steps;
supplying the electrical conductor with an alternating current of fundamental frequency f A ,
acquiring the signal representative of the amplitude of the displacement of the moving part,
determining the measurement of the magnetic field only from the components of the acquired measurement signal having a frequency lying within the width at −3 dB of the resonance peak centered on the frequency f A in the power spectral density of the acquired signal,
determining a measurement of an acceleration in the direction of displacement of the electrical conductor only from the comp

Assignees

• Commissariat L Energie Atomique Et Aux Energies Alternatives

Inventors

• Philippe Robert
• Ettelt Dirk
• Walther Arnaud

Classifications

• G01R33/0286

  comprising microelectromechanical systems [MEMS] (MEMS devices in general B81B) · CPC title

• G01D5/12 Primary

  using electric or magnetic means (G01D5/06 takes precedence) · CPC title

• G01L1/00

  Measuring force or stress, in general (measuring force due to impact G01L5/00) · CPC title

• G01H11/00

  Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by detecting changes in electric or magnetic properties · CPC title

• G01R33/038

  using permanent magnets, e.g. balances, torsion devices · CPC title