Fiber optic seismic sensor based on MEMS cantilever

• US 7,684,051 B2
• Filed: 04/18/2007
• Issued: 03/23/2010
• Est. Priority Date: 04/18/2006
• Status: Active Grant

• Current Assignee: Halliburton Energy Services Incorporated (Halliburton Company)
• Original Assignee: Halliburton Energy Services Incorporated (Halliburton Company)
• Inventors: Needham, David B., Berthold, John W.
• Primary Examiner(s): Chowdhury; Tarifur
• Assistant Examiner(s): COOK, JONATHON
• Application Number:
  US11/787,965
• Publication Number:
  US 20080174781A1
• Time in Patent Office: 1,070 Days
• Field of Search: 356/480, 356/498, 356/501, 356/505, 356/506, 356/519
• US Class Current: 356/519
• CPC Class Codes: G01P 1/023 for acceleration measuring devices
• CPC Class Codes: G01P 15/08 with conversion into electric or magnetic values
• CPC Class Codes: G01P 15/093 by photoelectric pick-up
• CPC Class Codes: G01V 1/184 Multi-component geophones

Abstract

A dual cantilevered beam structure is attached to a silicon frame. An optical fiber extends from a borosilicate wafer bonded to the bottom of the frame. A second borosilicate wafer is bonded to the top of the frame. The bottom borosilicate wafer is bonded to the optical fiber with a bonding agent having an index of refraction between the refractive index of the fused silica optical fiber and the refractive index of the borosilicate wafer. In an embodiment, the bonding agent has a refractive index substantially similar to optical cement. Light is reflected into the optical fiber from the beam structure for measuring seismic changes.

Claims

1. An apparatus for measuring seismic movement comprising:

a sensor having;

a wafer;

a frame attached to said wafer;

a cantilevered mass pivotally connected to the frame, the cantilevered mass having two beams, on the same side of the cantilevered mass, for pivoting the cantilevered mass relative to the frame; and

a cavity located between the cantilevered mass and the wafer wherein the cantilevered mass is capable of moving to change the size of the cavity.

2. The apparatus of claim 1 further comprising:

a borosilicate lid attached to the beams, wherein said lid is attached to the beams such that the cantilevered mass is movable toward the lid.

3. The apparatus of claim 1 wherein the cantilevered mass is a solid body and further wherein the beams are integrally formed with the solid body.

4. The sensor of claim 1 wherein the beams are capable of moving with respect to the frame.

5. The sensor of claim 1 wherein the frame is a portion of an etched silicon wafer.

6. The sensor of claim 1 wherein the cantilever mass and the beams each have a uniform thickness.

7. The sensor or claim 1 where the wafer is borosilicate glass.

8. The apparatus of claim 1 further comprising:

a borosilicate wafer bonded to the frame, the borosilicate wafer having a partially reflective dielectric coating.

9. The apparatus of claim 8 further comprising:

an optical fiber bonded to the borosilicate wafer, the optical fiber capable of directing light toward the cavity and receiving light reflected from the cavity.

10. The sensor of claim 8 wherein the sensor measures light reflected from the cantilevered mass through the optical fiber to determine seismic movement and further wherein the cantilevered mass moves to change the light reflected from the cantilever mass.

11. The apparatus of claim 9 wherein the optical fiber and the borosilicate wafer are bonded with a bonding agent having an index of refraction midway between the refractive index of the optical fiber and the borosilicate wafer.

12. The sensor of claim 11 wherein the bonding agent is optical cement.

13. An apparatus for measuring seismic movement comprising:

a MEMS sensor having;

a frame;

a borosilicate wafer connected to said frame;

a cantilevered mass pivotally connected to said frame, said cantilevered mass movable with respect to said borosilicate wafer;

a pair of beams attached to the frame and supporting said cantilevered mass, wherein the beams are on the same side of the cantilevered mass; and

an optical fiber attached to the borosilicate wafer for directing light through said borosilicate wafer to said cantilevered mass and receiving light reflected from said cantilevered mass.

14. The apparatus of claim 13 further comprising:

a bonding agent adhering the optical fiber to the borosilicate wafer, the bonding agent having an index of refraction between the refractive index of the optical fiber and the refractive index of the borosilicate wafer.

15. The apparatus of claim 13 further comprising:

a packaging container enclosing the sensor, the container securing the sensor along a first axis.

16. The apparatus of claim 15 further comprising:

a plurality of sensors secured within the container, at least one sensor having a cantilevered mass and a pair of beams supporting said cantilevered mass wherein the cantilevered mass is movable to determine seismic movement.

17. The apparatus of claim 15 wherein the container secures a triad of sensors to measure seismic movement along three different axes.

18. The apparatus of claim 15 wherein the container is an octagonal structure.

19. The apparatus of claim 15 wherein the container is a hollow cube.

20. The apparatus of claim 15 wherein the width of the container is substantially equal to a width of one of the sensors.