3-axis angular accelerometer
Angular accelerometers are described, as are systems employing such accelerometers. The angular accelerometers may include a proof mass and rotational acceleration detection beams directed toward the center of the proof mass. The angular accelerometers may include sensing capabilities for angular acceleration about three orthogonal axes. The sensing regions for angular acceleration about one of the three axes may be positioned radially closer to the center of the proof mass than the sensing regions for angular acceleration about the other two axes. The proof mass may be connected to the substrate though one or more anchors.
1. An apparatus for angular acceleration detection, comprising:
a proof mass having an outer edge bounding a first area, an inner edge disposed within the first area and bounding a second area smaller than the first area, and a center disposed within the second area;
an anchor connected to a substrate; and
a tether coupling the proof mass to the anchor, the tether being symmetric with respect to a plane that passes through the center of the proof mass and is substantially perpendicular to the substrate, the tether comprising:
first, second and third beams positioned on a first side of the plane, wherein the first and second beams are substantially parallel to the plane and are connected to each other by the third beam, the third beam being angled relative to the plane;
fourth, fifth and sixth beams positioned on a second side of the plane opposite the first side, wherein the fourth and fifth beams are substantially parallel to the plane and are connected to each other by the sixth beam, the sixth beam being angled relative to the plane; and
a seventh beam disposed between the first beam and the fourth beam and having an end directly attached to the inner edge of the proof mass;
the proof mass further comprising a plurality of free-end beams having fixed ends fixed to the inner edge of the proof mass, the free-end beams further having free ends positioned closer to the center of the proof mass than the fixed ends.
2. The apparatus of claim 1 , wherein the proof mass is shaped as a rectangle.
3. The apparatus of claim 1 , wherein the anchor is disposed closer to the center of the proof mass than the plurality of free-end beams.
4. The apparatus of claim 3 , further comprising an electrode connected to the substrate and adjacent a first free-end beam of the plurality of free-end beams, and configured to generate a detection signal in response to a movement of the free-end beam.
5. The apparatus of claim 4 , wherein the electrode is a first electrode and the detection signal is a first detection signal, the apparatus further comprising a second electrode connected to the substrate, the second electrode being adjacent the first free-end beam and opposite the first electrode, and configured to generate a second detection signal, opposite the first detection signal, in response to the movement of the first free-end beam.
6. The apparatus of claim 4 , wherein the electrode is a first electrode, the detection signal is a first detection signal and the movement is a first movement about a first axis, the apparatus further comprising a second electrode disposed on the substrate and configured to generate a second detection signal in response to a second movement of the proof mass about a second axis, perpendicular to the first axis.
7. The apparatus of claim 6 , further comprising a third electrode disposed on the substrate and configured to generate a third detection signal in response to a third movement of the proof mass about a third axis, perpendicular to the first axis and the second axis.
8. The apparatus of claim 7 , wherein a point of the inner edge of the proof mass that is disposed closest to the at least one anchor is disposed at a first radial distance from the at least one anchor, the first radial distance being less than a second radial distance between the second electrode and the at least one anchor, and the first radial distance being less than a third radial distance between the third electrode and the at least one anchor.
9. The apparatus of claim 1 , wherein the plurality of free-end beams having fixed ends fixed to the inner edge of the proof mass extend radially toward the center of the proof mass.
10. The apparatus of claim 1 , wherein the anchor is connected to the center of the proof mass.
11. The apparatus of claim 1 , wherein the third beam is substantially perpendicular to each of the first and second beams.
12. The apparatus of claim 11 , wherein the sixth beam is substantially perpendicular to each of the fourth and fifth beams.
13. The apparatus of claim 1 , wherein the seventh beam is substantially parallel to the first and fourth beams.
14. The apparatus of claim 1 , wherein the seventh beam lies substantially in the plane.
15. The apparatus of claim 1 , wherein the seventh beam comprises a plurality of holes.
16. The apparatus of claim 1 , wherein the tether is configured to reject torsion of the proof mass responsive to linear acceleration.
17. The apparatus of claim 1 , wherein the proof mass and the tether lie substantially in a same plane.
18. The apparatus of claim 1 , further comprising a stopper for limiting motion of the proof mass.
19. The apparatus of claim 18 , wherein the stopper comprises a protrusion formed on the outer edge of the proof mass.
20. The apparatus of claim 18 , wherein the stopper is positioned in the second area.