Transducer

• US 5,962,788 A
• Filed: 01/31/1997
• Issued: 10/05/1999
• Est. Priority Date: 08/18/1994
• Status: Expired due to Fees

• Current Assignee: BTG International Limited (Boston Scientific Corporation)
• Original Assignee: BTG International Limited (Boston Scientific Corporation)
• Inventors: Fawcett, John Neville
• Primary Examiner(s): Williams, Hezron
• Assistant Examiner(s): MOLLER, RICHARD ALAN
• Application Number:
  US08/791,731
• Time in Patent Office: 977 Days
• Field of Search: 73/514.01, 73/514.32, 73/514.36, 73/514.38, 73/514.17, 73/514.018, 73/514.21, 73/862.381, 73/862.61
• US Class Current: 73/514.36
• CPC Class Codes: G01P 15/0802 Details
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01P 15/131 with electrostatic counterbalancing means
• CPC Class Codes: G01P 15/18 in two or more dimensions

Abstract

A force transducer in which a deflectable seismic mass is supported on a frame by support means is disclosed. The seismic mass at rest includes a plane and when the seismic mass is deflected by any force the mass always retains the plane parallel to the rest position. Any deflection of the seismic mass is purely topographically translational movement with no rotational movement allowed. The invention allows three identical structures to be etched onto a flat semiconductor wafer and yet can be used to determine accelerations in three perpendicular directions. As the structures deflect, the surfaces of their seismic masses always remain parallel to the wafer surface. This enables measurement of the deflection to be made easily, for example by depositing electrodes on the surfaces of the seismic masses and fixed surfaces (such as deflection stops) and measuring the change in capacitance between the electrodes. Cross coupling effects will be negligible since each transducer is stiff in all directions except the sensitive direction.

Claims

1. A transducer comprising a deflectable seismic mass supported on a frame by support structure, said seismic mass having a surface, a plane of said surface being disposed in a first orientation when said seismic mass is disposed in a rest position wherein the support structure comprises a plurality of parallel beams each extending at an angle α

relative to said plane of said surface whereby when the seismic mass is deflected by a force, irrespective of a direction of the force, the plane of said surface will be disposed in an orientation substantially parallel to said first orientation.

2. A transducer as claimed in claim 1 wherein the seismic mass deflects along a single axis, said single axis being oriented in a direction that is substantially perpendicular to a plane of a surface of a said support beam when said seismic mass is disposed in the rest position.

3. A transducer as claimed in claim 2 characterised in that the parallel beams are stiff in directions perpendicular to said single axis.

4. A transducer as claimed in claim 2 characterised in that the transducer includes a a deflecting surface of the seismic mass having an inner electrode and a fixed surface parallel to said deflecting surface and having an outer electrode, said inner and outer electrodes having a capacitance which changes when the seismic mass is deflected.

5. A transducer as claimed in claim 4 characterised in that the transducer includes actuators, responsive to the change in capacitance, which counteract the deflection of the mass.

6. An transducer as claimed in claim 1 wherein the transducer includes null members, vibrating at a natural frequency, which prevent the deflection of the mass and are subjected to compressive and tensile loads when a force is applied to the mass, thereby causing or permitting a change in the frequency of the vibration.

7. A multi-directional transducer comprising at least two transducers, each said transducer comprising:

a deflectable seismic mass supported on a frame by support structure, said seismic mass having a surface, a plane of said surface being disposed in a first orientation when said seismic mass is disposed in a rest position, wherein the support structure comprises a plurality of parallel beams each extending at an angle α

relative to said plane of said surface whereby when the seismic mass is deflected by a force, irrespective of a direction of the force, the plane of said surface will be disposed in an orientation substantially parallel to said first orientation,

wherein the seismic mass of each said transducer deflects along a single axis, and

wherein the transducers are arranged such that said axes of deflection are not parallel to one another.

8. A multi-directional transducer as claimed in claim 7, each transducer including a second plane which is parallel to said surface of said seismic mass and intersects all parallel support beams thereof wherein the second planes of each seismic mass are parallel to one another.

9. A multi-directional transducer as claimed in claim 8, wherein the second planes of each seismic mass remain parallel when deflected by a force irrespective of a direction thereof.

10. A multi-directional transducer as claimed in claim 8, wherein each said second plane is parallel to said plane of said surface and at rest the second planes of each seismic mass are coplanar.

11. A multi-directional transducer as claimed in claim 7, wherein there are three transducers and the transducers are arranged such that said axes of deflection are mutually orthogonal.

12. A method of manufacturing a transducer comprising:

providing a substrate for defining a frame;

forming a deflectable seismic mass and a support structure for supporting said seismic mass on said frame, said seismic mass having a surface, a plane of said surface being disposed in a first orientation when said seismic mass is disposed in a rest position,

said step of forming a support structure comprising forming a plurality of parallel beams to extend between said seismic mass and said frame, each said parallel beam extending at an angle α

relative to said plane of said surface,

whereby when the seismic mass is deflected by a force, irrespective of a direction of the force, the plane of said surface will be disposed in an orientation substantially parallel to said first orientation.

13. A method of manufacturing a transducer as claimed in claim 12, wherein the transducer is manufactured from a single crystal of semiconductor material.

14. A method of manufacturing a transducer as claimed in claim 13 wherein the single crystal of semiconductor material is etched using anisotropic etching.

15. A method of manufacturing a transducer as claimed in claim 13 wherein the single crystal of semiconductor material is etched using isotropic etching.

16. A single axis accelerometer including a force transducer comprising:

a deflectable seismic mass supported on a frame by support structure, said seismic mass having a surface, a plane of said surface being disposed in a first orientation when said seismic mass is disposed in a rest position, wherein the support structure comprises a plurality of parallel beams each extending at an angle α

relative to said plane of said surface whereby when the seismic mass is deflected by a force, irrespective of a direction of the force, the plane of said surface will be disposed in an orientation substantially parallel to said first orientation.

17. A three dimensional accelerometer including three force transducers each comprising:

a deflect able seismic mass supported on a frame by support structure, said seismic mass having a surface, a plane of said surface being disposed in a first orientation when said seismic mass is disposed in a rest position, wherein the support structure comprises a plurality of parallel beams each extending at an angle α

relative to said plane of said surface whereby when the seismic mass is deflected by a force, irrespective of a direction of the force, the plane of said surface will be disposed in an orientation substantially parallel to said first orientation.