Accelerometer without proof mass

• US 6,666,088 B2
• Filed: 05/04/2001
• Issued: 12/23/2003
• Est. Priority Date: 06/26/1996
• Status: Expired due to Term

• Current Assignee: Simon Fraser University
• Original Assignee: Simon Fraser University
• Inventors: Leung, Albert M.
• Primary Examiner(s): Williams, Hezron
• Assistant Examiner(s): BELLAMY, TAMIKO D
• Application Number:
  US09/848,000
• Publication Number:
  US 20020007674A1
• Time in Patent Office: 963 Days
• Field of Search: 735/140.9, 735/140.8, 735/045, 735/040.6, 735/040.7, 736/54, 280/735, 188/181.A
• US Class Current: 73/488
• CPC Class Codes: G01F 1/6845 Micromachined devices
• CPC Class Codes: G01P 15/00 Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration
• CPC Class Codes: G01P 15/008 by using thermal pick-up
• CPC Class Codes: G01P 15/0802 Details
• CPC Class Codes: G01P 15/12 by alteration of electrical resistance G01P15/0897, G01P15/105 take precedence
• CPC Class Codes: G01P 15/18 in two or more dimensions
• CPC Class Codes: G01P 21/00 Testing or calibrating of apparatus or devices covered by the preceding groups

Abstract

An accelerometer has a substrate with a cavity therein, a heater extending over the cavity, and a pair of temperature sensitive elements each spaced apart from the heater a distance of 75-400 microns also extending over the cavity. On passing an electrical current through the heater a symmetrical temperature distribution is set up on both sides of the heater. On acceleration, this distribution moves and by measuring the temperature as sensed by the pair of temperature sensitive elements the acceleration that caused the shift can be calculated.

Claims

1. An accelerometer, comprising:

(a) a substrate having an open space therein;

(b) a primary heater extending across said open space;

(c) a pair of temperature sensitive elements extending across said open space, said temperature sensitive elements being located on opposite sides of said primary heater and each spaced apart from said heater by a distance of 75 to 400 microns; and

(d) a non-solid heat transfer medium surrounding said primary heater and said temperature sensitive elements.

2. An accelerometer according to claim 1, wherein said temperature sensitive elements are parallel to and equidistant from and located on opposite sides of said primary heater.

3. An accelerometer according to claim 1, including an electrical conductor connectable to an external source of power operative to conduct electric current through said heater so as to develop a symmetrical temperature gradient extending outwardly from said heater on either side thereof.

4. An accelerometer according to claim 1, including a bridge circuit operative to measure the differential resistance of said temperature sensitive elements.

5. An accelerometer according to claim 1, wherein said primary heater and said temperature sensitive elements are coated with silicon dioxide.

6. An accelerometer according to claim 1, including a pair of auxiliary heaters symmetrically disposed on either side of and spaced from said primary heater.

7. An accelerometer according to claim 1, including

(a) a conductor connectable to an external source of power and operative to conduct current through said primary heater so as to develop a symmetrical temperature gradient in the air surrounding said primary heater in which the air temperature lowers in a direction away from said primary heater; and

(b) a bridge circuit operative to measure the differential resistance of said temperature sensitive elements and relating that to acceleration in a direction transverse to said temperature sensitive elements and along the surface of said substrate.

8. An accelerometer according to claim 7, wherein said primary heater and said sensors are polysilicon.

9. An accelerometer according to claim 6, wherein said auxiliary heaters are intermediate said temperature sensitive elements and said primary heater.

10. An accelerometer according to claim 9, including conductive lines coupled to said auxiliary heaters and to an external source of power and operative to permit independent changing of current through each of said auxiliary heaters.

11. An accelerometer according to claim 1, wherein said temperature sensing elements are thermopiles,

said thermopiles arranged linearly and substantially parallel to a first direction and located at two positions equidistant from and on either side of said primary heater,

each one of said thermopiles being operative to produce an electrical potential proportional to the temperature at one of said two positions.

12. An accelerometer according to claim 11, wherein said thermopiles are electrically connected in series and with opposite polarity, such that the electrical potential produced across the combination of both thermopiles is proportional to the difference in temperature between said two positions.

13. An accelerometer according to claim 11, which further comprises a conductive path coupled to said thermopiles and to an external meter for permitting measuring the electrical potential produced by said thermopiles and relating that to acceleration in a second direction transverse to said temperature sensitive elements and along a surface of said substrate.

14. An accelerometer according to claim 11, including a differential amplifier coupled to said thermopiles and providing an output for measuring the electrical potential produced by said thermopiles.

15. An accelerometer according to claim 11, wherein each of said thermopiles is comprised of a plurality of thermocouples,

each of said thermocouples being made out of a first material and a second material, which first and second materials form a thermocouple junction in a location where they are joined,

each of said thermocouple junctions operative to produce an electrical potential proportional to the temperature at said thermocouple junction,

said plurality of thermocouple junctions being physically arranged in a linear pattern and electrically coupled in series so as to form an array of thermocouple junctions.

16. An accelerometer according to claim 9, wherein said heater is coated with a dielectric.

17. An accelerometer according to claim 16, wherein said dielectric is silicon dioxide.