Magnetic field detector with a resiliently mounted electrical coil

• US 5,424,642 A
• Filed: 09/22/1993
• Issued: 06/13/1995
• Est. Priority Date: 09/29/1992
• Status: Expired due to Term

• Current Assignee: Pacesetter AB (Abbott Laboratories)
• Original Assignee: Siemens AG
• Inventors: Ekwall, Christer
• Primary Examiner(s): Snow, Walter E.
• Application Number:
  US08/124,453
• Time in Patent Office: 629 Days
• Field of Search: 324/244, 324/256, 324/257, 324/260
• US Class Current: 324/256
• CPC Class Codes: A61B 5/055 involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
• CPC Class Codes: A61B 5/06 Devices, other than using radiation, for detecting or locating foreign bodies for removing same A61B17/50 ; determining position of probes within or on the body of the patient
• CPC Class Codes: A61N 1/36542 controlled by body motion, e.g. acceleration
• CPC Class Codes: G01R 33/038 using permanent magnets, e.g. balances, torsion devices

Abstract

A magnetic field detector, particularly for implantable medical apparatuses, has a coil mounted at the free end of a resilient member fixed at its opposite end portion, and a detecting device for detecting, as a measure of a magnetic field, the movement of the coil in the field when fed with an electric current from a controllable current source. The resilient member is bent to form at least two shanks interconnected at one end. The coil is mounted at the free end of one of the shanks and the resilient member is fixed at the free end portion of the other shank.

Claims

1. A magnetic field detector comprising:

an electrical coil;

a resilient member, separate from said coil, on which said coil is mounted, said resilient member being bent to form two shanks which are interconnected by a bend at one end of said resilient member, each shank having a free end, and said coil being mounted at the free end of one of the shanks, and means for rigidly fixing said resilient member at a region of the free end of the other shank for causing said resilient member to vibrate as a whole upon displacement of said coil;

means for feeding said coil with a controllable electrical current; and

means for detecting movement of said resilient member caused by displacement of said coil in the presence of a magnetic field, when said coil is fed with said electrical current, as a measure of said magnetic field.

5. A detector as claimed in claim 1 wherein said means for detecting comprises:

a light source;

a light reflector fixed to said coil for co-movement therewith for producing a reflected light beam; and

means for recording movement of said reflected light beam caused by movement of said coil.

7. A detector as claimed in claim 1 wherein said means for detecting comprises:

a variable capacitance having one stationary plate and one plate mechanically coupled to said coil for co-movement therewith; and

means for detecting variations in the capacitance of said variable capacitance caused by movement of said coil.

8. A detector as claimed in claim 1 wherein said means for feeding said coil with an electrical current comprises means for supplying current pulses to said coil.

9. A detector as claimed in claim 8 wherein said means for supplying current pulses comprises means for supplying square pulses to said coil through a capacitor.

10. A detector as claimed in claim 9 wherein the combination of said coil and said means for resiliently supporting said coil has a natural mechanical resonant frequency, wherein said coil has an inductance, and wherein said capacitor has a capacitance selected for producing an electrical resonant frequency in combination with said inductance of said coil substantially equal to said mechanical resonant frequency.

11. A detector as claimed in claim 8 wherein said means for supplying current pulses further includes means for supplying an adjustable d.c. current to said coil in addition to said current pulses.

12. A detector as claimed in claim 1 wherein said coil has a ferrite core.

2. A detector as claimed in claim I wherein said means for detecting comprises a piezoelectric element applied to said resilient member covering said bend, and generating an electrical signal representative of deformation of said member caused by movement of said coil in said magnetic field.

3. A detector as claimed in claim 2 wherein said resilient member has a U-shape, and wherein said coil is mounted inside the U-shape of said resilient member.

4. A detector as claimed in claim 2 wherein said resilient member has a U-shape, and wherein said piezoelectric element comprises a sheet of piezoelectric material covering an outer side of said U-shaped resilient member over said bend.

6. A detector as claimed in claim I wherein said means for detecting comprises:

a reflector fixed to said coil for co-movement therewith;

a monochromatic light source which directs an incoming light beam toward said reflector for producing a reflected light beam; and

means disposed between said monochromatic light source and said reflector for recording an interference pattern produced by said incoming and reflected light beams, said interference pattern representing movement of said coil.