Two-axis, single output magnetic field sensing antenna

• US 20020093331A1
• Filed: 01/03/2002
• Published: 07/18/2002
• Est. Priority Date: 02/08/2000
• Status: Active Grant

• Current Assignee: Xyz Microsystems, LLC
• Original Assignee: Concorde Microsystems, Inc. (Siemens AG)
• Inventors: Rochelle, James M.
• Granted Patent: US 6,538,617 B2
• Time in Patent Office: Days
• US Class Current: 324/247
• CPC Class Codes: G08B 21/0263 System arrangements wherein the object is to detect the direction in which child or item is located

Abstract

A passive, non-multiplexed, two-axis antenna for sensing time-varying magnetic fields of a particular carrier frequency at a second point in space as produced by a electromagnetic field generator located at a first point in space. The antenna has a particular sensitive plane and produces a single output signal having amplitude proportionally related to the magnitude of the incident magnetic field'"'"'s vector projection onto the antenna'"'"'s sensitive plane. If the phase of the magnetic field is known, then the antenna'"'"'s signal is processed to obtain the incident magnetic field'"'"'s vector components. The antenna enables the realization of two- or three-axis magnetic field receivers with reduced signal processing complexity, cost and power requirements.

Claims

1. An antenna assembly for sensing a time-varying magnetic field having a predetermined frequency, comprising:

a first element having a sensing axis producing an amplitude response to the magnetic field and a transverse axis orthogonal to said sensing axis, said first element including at least one inductor; and

a second element in electrical communication with said first element, said second element having a sensing axis producing an amplitude response to the magnetic field and a transverse axis orthogonal to said sensing axis, said second element sensing axis being orthogonal to said first element sensing axis, either of said first element sensing axis and said first element transverse axis being co-linear with said second element transverse axis, said second element including at least one inductor.

2. The antenna assembly of claim 1 wherein each said first element and said second element have common amplitude response characteristics.

3. The antenna assembly of claim 1 wherein each of said first element and said second element produce an amplitude response which is proportional to a magnetic field direction vector sensed by each of said first element and said second element.

4. The antenna assembly of claim 1 wherein each of said first element and said second element define a transduction scaling factor, said first element transduction scaling factor being equal to said second element transduction scaling factor offset by a time domain phase difference of approximately 90 degrees.

5. The antenna assembly of claim 1 wherein said first element and said second element are serially connected producing an antenna assembly having a single pair of output leads.

6. The antenna assembly of claim 1 wherein each of said first element and said second element is a parallel LCR circuit, including at least one inductor, at least one resistor, and at least one capacitor.

7. The antenna assembly of claim 6 wherein each of said first at least one element inductor and said second element inductor have equivalent inductance.

8. The antenna assembly of claim 1 wherein each of said first element and said second element include an inductor having a magnetic core with a small loss tangent at a predetermined output frequency.

9. The antenna assembly of claim 1 each of said first element and said second element having a quality factor in the range of approximately 4 to approximately 8.

10. The antenna assembly of claim 1 wherein said first element transverse axis is co-linear with said second element transverse axis.

11. The antenna assembly of claim 1 wherein said antenna assembly is disposed within an enclosure, said first element including a plurality of inductors serially connected and disposed along two opposing edges of said enclosure, each of said first element plurality of inductors being oriented parallel to each other, said second element including a plurality of inductors serially connected and disposed along two opposing edges of said enclosure, each of said second element plurality of inductors being oriented parallel to each other and orthogonal to each of said first element plurality of inductors.

12. The antenna assembly of claim 1 wherein said first element sensing axis is co-linear with said second element transverse axis.

13. The antenna assembly of claim 12 said first element being physically separated from said second element by a predetermined distance thereby reducing the inductive coupling therebetween.

14. The antenna assembly of claim 13 wherein one said first element and said second element define a largest dimension, said predetermined distance being greater than approximately four times said largest dimension.

15. The antenna assembly of claim 1 further comprising a shield, said shield being a partially conductive enclosure having a sheet resistivity chosen to selectively attenuate an electric field relative to the magnetic field, said shield enclosing said first element and said second element.

16. The antenna assembly of claim 15 wherein said shield sheet resistivity is in a range of approximately tens of ohms per square for a carrier frequency within a frequency range of approximately tens of kilohertz.

17. The antenna assembly of claim 15 wherein said antenna assembly includes a high-impedance lead and a low-impedance lead, said shield electrically connected to said low-impedance lead and insulated from said high-impedance lead.