Low-power shock and vibration sensors and methods of making sensors

• US 20080168840A1
• Filed: 01/12/2007
• Published: 07/17/2008
• Est. Priority Date: 01/12/2007
• Status: Active Grant

• Current Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Original Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Inventors: Delgado, Eladio Clemente, Seeley, Charles Erklin
• Granted Patent: US 8,443,672 B2
• Time in Patent Office: Days
• US Class Current: 73/649
• CPC Class Codes: G01H 11/08 using piezoelectric devices

Abstract

Sensors for monitoring shock or vibration of an object are provided. The sensors include a proof mass, at least piezoelectric device, and an electronic circuit connected to the piezoelectric device. The piezoelectric device generates a current when the proof mass imparts a force on the piezoelectric device in response to the proof mass being subjected to a transient acceleration when the object is subjected to a shock or vibration. The electronic circuit is at least partially controlled in response to the current generated from the piezoelectric device due to the shock or vibration. Embodiments of the sensor provide multi-axis sensing capabilities. Methods of making the sensors and flexible circuits are also provided.

Claims

1. A low-power sensor-for monitoring exposure of an object to a stimulus, the sensor comprising:

a proof mass;

at least one first piezoelectric device operable to generate a current when the proof mass imparts a force on the first piezoelectric device in response to the proof mass undergoing a transient acceleration when the object is subjected to a stimulus; and

a first electronic circuit connected to the first piezoelectric device, wherein the first electronic circuit is at least partially controlled in response to the current generated from the first piezoelectric device due to the stimulus.

2. The sensor of claim 1, wherein the proof mass and first piezoelectric device are inside of a rigid housing.

3. The sensor of claim 1, further comprising a first thrust plate in contact with a first surface of the proof mass and the first piezoelectric device.

4. The sensor of claim 1, wherein:

the proof mass comprises a plurality of planar second surfaces; and

the sensor comprises a plurality of low-friction surfaces, each low friction surface contacts a respective planar second surface of the proof mass.

5. The sensor of claim 4, wherein:

the low-friction surfaces are surfaces of a plurality of respective spheres; and

the sensor comprises a compliant material with a plurality of cavities, each of the spheres is held and rotatable within a respective one of the cavities.

6. The sensor of claim 1, wherein the first piezoelectric device comprises at least one lead zirconate titanate ceramic material or ferroelectric material.

7. The sensor of claim 1, wherein the first piezoelectric device comprises at least two layers of piezoelectric material.

8. The sensor of claim 1, further comprising:

at least one second piezoelectric device operable to generate a current when the proof mass imparts a force on the second piezoelectric device in response to the proof mass undergoing the transient acceleration, wherein the second piezoelectric device faces a surface of the proof mass opposite to a surface of the proof mass faced by the first piezoelectric device; and

a second electronic circuit connected to the second piezoelectric device, wherein the second electronic circuit is at least partially controlled in response to the current generated from the second piezoelectric device due to the stimulus.

9. The sensor of claim 1, wherein the first electronic circuit is operable to:

convert the magnitude of the current to a first voltage;

store the first voltage;

in real time, sense the current and determine whether the current exceeds a threshold current corresponding to a threshold transient acceleration;

when the current exceeds the threshold current, create a second voltage from the current produced by the stimulus, wherein the second voltage triggers an interrupt;

monitor the interrupt to determine the duration of the stimulus;

store a peak value of the first voltage proportional to the current generated by the stimulus; and

read the peak value of the first voltage and record the peak value and a time stamp in a memory.

10. The sensor of claim 9, wherein the first electronic circuit is further operable to determine the duration and frequency of the stimulus.

11. The sensor of claim 1, wherein the first electronic circuit comprises a power supply and is operable to draw a current of less than about 20 mA from the power supply when no transient acceleration is present.

12. The sensor of claim 11, wherein the first electronic circuit is operable to draw a current of less than about 10 μ

A from the power supply when no transient acceleration is present.

13. The sensor of claim 1, wherein the first electronic circuit comprises:

an event driven circuit operable to (i) convert the magnitude of the current to a first voltage, (ii) in real time, sense the current to determine whether the current exceeds a threshold current corresponding to a threshold transient acceleration, and (iii) when the current exceeds the threshold current, create a second voltage proportional to the current, wherein the second voltage triggers an interrupt;

a peak and hold unit operable to store a peak value of the first voltage proportional to the transient acceleration; and

a microcontroller operable to (i) monitor the interrupt to determine the duration of the stimulus and (ii) read the stored peak value of the first voltage and record the peak value and a time stamp in a memory.

14. The sensor of claim 13, wherein the microcontroller is operable to determine the duration and frequency of the transient acceleration.

15. A method of monitoring exposure of an object to a stimulus, comprising:

arranging the sensor according to claim 1 with respect to an object;

converting the magnitude of the current to a first voltage;

storing the first voltage;

in real time, sensing the current and determining whether the current exceeds a threshold current corresponding to a threshold transient acceleration;

when the current exceeds the threshold current, creating a second voltage from the current produced by the stimulus, wherein the second voltage triggers an interrupt;

monitoring the interrupt to determine the duration of the stimulus;

storing a peak value of the first voltage proportional to the current generated by the stimulus; and

reading the peak value of the first voltage and recording the peak value and a time stamp in a memory.

16. The method of claim 15, further comprising determining the duration and frequency of the transient acceleration.

17. A low-power sensor for monitoring exposure of an object to a stimulus, the sensor comprising:

a proof mass comprising at least first, second and third surfaces perpendicular to orthogonal x, y and z axes, respectively;

at least one first piezoelectric device operatively associated with the first surface,

at least one second piezoelectric device operatively associated with the second surface;

at least one third piezoelectric device operatively associated with the third surface;

wherein at least one of the first, second and third piezoelectric devices is operable to generate a current when the proof mass imparts a force thereon in response to the proof mass undergoing a transient acceleration when the object is subjected to a stimulus; and

first, second and third electronic circuits connected to the first, second and third piezoelectric sensors, respectively, and being at least partially controlled in response to the current generated from at least one of the first, second and third piezoelectric devices, respectively, due to the stimulus.

18. The sensor of claim 17, further comprising:

a first thrust plate provided on the first piezoelectric device;

a first low-friction surface contacting the first surface and the first thrust plate;

a second thrust plate provided on the second piezoelectric device;

a second low-friction surface contacting the second surface and the second thrust plate;

a third thrust plate provided on the third piezoelectric device; and

a third low-friction surface contacting the third surface and the third thrust plate;

wherein the first, second and third low friction surfaces are effective to reduce friction between the proof mass and the first, second and third thrust plates during the transient acceleration.

19. The sensor of claim 18, wherein:

the proof mass comprises a fourth surface opposite to the first surface, a fifth surface opposite to the second surface, and a sixth surface opposite to the third surface, the fourth, fifth and sixth surfaces being perpendicular to the x, y and z axes, respectively; and

the sensor further comprises;

at least one fourth piezoelectric device operatively associated with the fourth surface;

at least one fifth piezoelectric device operatively associated with the fifth surface;

at least one sixth piezoelectric device operatively associated with the sixth surface;

wherein at least one of the fourth, fifth and sixth piezoelectric devices is operable to generate a current when the proof mass imparts a force thereon in response to the proof mass undergoing the transient acceleration; and

fourth, fifth and sixth electronic circuits-connected to the fourth, fifth and sixth piezoelectric sensors, respectively, wherein the fourth, fifth and sixth electronic circuits are at least partially controlled in response to the current generated from at least one of the fourth, fifth and sixth piezoelectric devices, respectively, due to the stimulus.

20. The sensor of claim 19, further comprising:

a fourth thrust plate provided on the fourth piezoelectric device;

a fourth low-friction surface contacting the fourth surface and the fourth thrust plate;

a fifth thrust plate provided on the fifth piezoelectric device;

a fifth low-friction surface contacting the fifth surface and the fifth thrust plate;

a sixth thrust plate provided on the sixth piezoelectric device; and

a sixth low-friction surface contacting the sixth surface and the sixth thrust plate;

wherein the fourth, fifth and sixth low friction surfaces are effective to reduce friction between the proof mass and the fourth, fifth and sixth piezoelectric devices during the transient acceleration.

21. The sensor of claim 18, wherein:

the first, second and third surfaces of the proof mass are planar;

each of the first, second and third thrust plates comprises a planar contact surface; and

the first, second and third low-friction surfaces are surfaces of rotatable spheres in contact with the contact surfaces of the first, second and third thrust plates, respectively.

22. The sensor of claim 21, further comprising an elastomeric material including a plurality of cavities, each of the spheres is held and rotatable within a respective one of the cavities.

23. The sensor of claim 17, wherein the proof mass and first, second and third piezoelectric devices are inside of a rigid housing.

24. The sensor of claim 17, wherein the first, second and third piezoelectric devices comprise at least one lead zirconate titanate ceramic material or ferroelectric material.

25. The sensor of claim 17, wherein each of the first, second and third piezoelectric devices comprises at least two layers of piezoelectric material.

26. The sensor of claim 17, wherein the first, second and third piezoelectric devices comprise a polymeric substrate on which the first, second and third electronic circuits are provided.

27. The sensor of claim 17, wherein each of the first, second and third electronic circuits is operable to:

convert the magnitude of the current to a first voltage;

store the first voltage;

in real time, sense the current and determine whether the current exceeds a threshold current corresponding to a threshold transient acceleration;

when the current exceeds the threshold current, create a second voltage from the current produced by the stimulus, wherein the second voltage triggers an interrupt;

monitor the interrupt to determine the duration of the stimulus;

store a peak value of the first voltage proportional to the current generated by the stimulus; and

read the peak value of the first voltage and record the peak value and a time stamp in a memory.

28. The sensor of claim 27, wherein each of the first, second and third electronic circuits is further operable to determine the duration and frequency of the transient acceleration.

29. The sensor of claim 17, wherein each of the first, second and third electronic circuits includes a power supply and is operable to draw a current of less than about 20 mA from the power supply when no transient acceleration is present.

30. The sensor of claim 29, wherein each of the first, second and third electronic circuits is operable to draw a current of less than about 10 μ

A from the power supply when no transient acceleration is present.

31. The sensor of claim 17, wherein each of the first, second and third electronic circuits comprises:

an event driven circuit operable to (i) convert the magnitude of the current to a first voltage, (ii) in real time, sense the current and determine whether the current exceeds a threshold current corresponding to a threshold transient acceleration, and (iii) when the current exceeds the threshold current, create a second voltage proportional to the current, wherein the second voltage triggers an interrupt;

a peak and hold unit operable to store a peak value of the first voltage proportional to the transient acceleration; and

a microcontroller operable to (i) monitor the interrupt to determine the duration of the stimulus and (ii) read the stored peak value of the first voltage and record the peak value and a time stamp in a memory.

32. The sensor of claim 31, wherein the microcontroller is further operable to determine the duration and frequency of the transient acceleration.

33. A method of monitoring shock or vibration of an object, comprising:

arranging the sensor according to claim 17 with respect to an object;

converting the magnitude of the current to a first voltage;

storing the first voltage;

in real time, sensing the current and determining whether the current exceeds a threshold current corresponding to a threshold transient acceleration;

when the current exceeds the threshold current, creating a second voltage from the current produced by the stimulus, wherein the second voltage triggers an interrupt;

monitoring the interrupt to determine the duration of the stimulus;

storing a peak value of the first voltage proportional to the current generated by the stimulus; and

reading the peak value of the first voltage and record the peak value and a time stamp in a memory.

34. A flexible circuit comprising:

at least one piezoelectric device comprising;

a flexible substrate composed of a first dielectric material;

at least one first electrode on a surface of the substrate;

at least one first layer of a piezoelectric material on the first electrode;

a second dielectric material on the first layer of the piezoelectric material;

a second electrode on the second dielectric material;

at least one second layer of a piezoelectric material on the second electrode;

wherein the flexible substrate comprises cut lines and fold lines along which the flexible circuit can be folded to form a three-dimensional structure.

35. The flexible circuit of claim 34, comprising a plurality of the piezoelectric devices disposed on the surface of the substrate.

36. The flexible circuit of claim 34, wherein the substrate comprises at least six regions defined by the cut lines and fold lines, and each region comprises at least one piezoelectric device.

37. The flexible circuit of claim 36, further comprising a plurality of electronic circuits on the surface of the substrate and connected to the piezoelectric devices.

38. The flexible circuit of claim 34, further comprising an electronic circuit on the surface of the substrate and connected to the piezoelectric device.

39. The flexible circuit of claim 34, further comprising a thrust plate overlying at least one second layer of piezoelectric material.

40. A method of making the flexible circuit of claim 34, comprising:

fabricating the at least one piezoelectric device by;

forming at least one first electrode on a surface of a flexible substrate composed of a first dielectric material;

providing at least one first layer of a piezoelectric material on the first electrode;

providing a second dielectric material on the first layer of the piezoelectric material;

forming a second electrode on the second dielectric material; and

providing at least one second layer of a piezoelectric material on the second electrode;

wherein the flexible substrate comprises cut lines and fold lines.

41. The method of claim 40, further comprising forming a three-dimensional sensor from the flexible substrate.

42. The method of claim 40, further comprising fabricating at least one electronic circuit on the surface of the substrate such that the electronic circuit is connected to the piezoelectric device.

43. The method of claim 40, wherein the substrate comprises at least six regions defined by the cut lines and fold lines, and further comprising fabricating at least one piezoelectric device on the surface of the substrate in each region.

44. The method of claim 43, further comprising fabricating a plurality of electronic circuits on the surface of the substrate, wherein the electronic circuits are operable to control the piezoelectric devices.

45. The method of claim 40, further comprising placing a thrust plate over at least one second layer of piezoelectric material.