Tunable piezoelectric micro-mechanical resonator

• US 20030127944A1
• Filed: 12/06/2002
• Published: 07/10/2003
• Est. Priority Date: 12/06/2001
• Status: Active Grant

• Current Assignee: University Of Pittsburgh (University of Pittsburgh of The Commonwealth System of Higher Education)
• Original Assignee: University Of Pittsburgh (University of Pittsburgh of The Commonwealth System of Higher Education)
• Inventors: Clark, William W., Wang, Qing-Ming
• Granted Patent: US 6,943,484 B2
• Time in Patent Office: Days
• US Class Current: 310/316.01
• CPC Class Codes: H03H 2009/02204 operating on an additional circuit element, e.g. applying a tuning DC voltage to a passive circuit element connected to the resonator
• CPC Class Codes: H03H 2009/02251 Design
• CPC Class Codes: H03H 2009/241 Bulk-mode MEMS resonators
• CPC Class Codes: H03H 9/172 Means for mounting on a substrate, i.e. means constituting the material interface confining the waves to a volume

Abstract

One aspect of the invention relates to a composite member for a resonator having an active piezoelectric element and a passive piezoelectric element. The active piezoelectric element causes the resonator to vibrate and detects the frequency of the vibration. The passive piezoelectric element changes the frequency of the vibration. Another aspect of the invention relates to a method for controlling a resonator with composite member having a substrate carrying a composite piezoelectric element. The composite piezoelectric element includes an actuator element, a sensor element and a passive element. The method comprises inducing a resonance within the composite member with the actuator element, detecting the resonance with the sensor element, and altering the resonance by altering the electromechanical coupling of the passive element. Additional aspects and benefits of the invention are also given.

Claims

1. A composite member for a resonator, comprising:

an active piezoelectric element for causing said resonator to vibrate and for detecting a frequency of said vibration; and

a passive piezoelectric element operable to change said frequency of said vibration.

2. The composite member of claim 1 further comprising a substrate carrying said active piezoelectric element and said passive piezoelectric element.

3. The composite member of claim 1 further comprising first and second electrodes, wherein said active piezoelectric element is defined by said first electrode and a portion of said second electrode and wherein said passive piezoelectric element is defined by said first electrode and another portion of said second electrode.

4. The composite member of claim 3 wherein said active piezoelectric element further comprises:

an actuator element for causing said resonator to vibrate; and

a sensor element for detecting said frequency of said vibration.

5. The composite member of claim 4 wherein said second electrode is comprised of:

an actuator electrode, wherein said actuator electrode and said first electrode define said actuator element;

a sensor electrode wherein said sensor electrode and said first electrode define said sensor element; and

a passive electrode wherein said passive electrode and said first electrode define said passive piezoelectric element.

6. The composite member of claim 5 wherein said passive electrode is segmented and wherein said segmented passive electrode and said first electrode define a segmented passive piezoelectric element.

7. The composite member of claim 1 wherein said resonator further comprises:

an excitation circuit operable to provide a control signal to and receive a feedback signal from said active piezoelectric element; and

a tuning circuit operable to alter the electromechanical coupling of said passive piezoelectric element.

8. The composite member of claim 6 wherein said tuning circuit is operable to shunt a capacitance across said passive piezoelectric element.

9. The composite member of claim 6 wherein said tuning circuit further comprises:

a switch; and

a capacitance.

10. The composite member of claim 6 wherein said tuning circuit further comprises a varactor.

11. The composite member of claim 10 wherein said substrate is comprised of a non-piezoelectric material.

12. The composite member of claim 1 wherein said resonator is one of a clamped-unclamped cantilevered beam piezoelectric resonator, clamped-clamped cantilevered beam piezoelectric resonator, an axial rod piezoelectric resonator, a shear layer piezoelectric resonator, and a diaphragm piezoelectric resonator.

13. The composite member of claim 1 wherein said active piezoelectric element and said passive piezoelectric element are comprised of at least one of lead zirconate titanate, zinc oxide, lithium niobate, lithium tantalate, quartz, aluminum nitride, and polyvinylidine diflouride.

14. A piezoelectric resonator, comprising:

a substrate;

a first electrode carried by said substrate;

a composite piezoelectric element carried by said first electrode, said composite piezoelectric element further comprising;

an actuator element;

a sensor element; and

a passive element;

a second electrode carried by said composite piezoelectric element;

an excitation circuit operable to supply a control signal to said actuator element and operable to receive a feedback signal from said sensor element; and

a tuning circuit operable to alter the electromechanical coupling of said passive element.

15. The piezoelectric resonator of claim 14 wherein said substrate is comprised of a non-piezoelectric material.

16. The piezoelectric resonator of claim 14 wherein said second electrode is comprised of:

an actuator electrode wherein said actuator electrode and said first electrode define said actuator element;

a sensor electrode wherein said sensor electrode and said first electrode define said sensor element; and

a passive electrode wherein said passive electrode and said first electrode define said sensor element.

17. The piezoelectric resonator of claim 16 wherein said passive electrode is segmented further defining a plurality of virtual segments in said passive element and wherein said tuning circuit is operable to alter the electromechanical coupling of each of said plurality of virtual segments.

18. The piezoelectric resonator of claim 17 wherein said tuning circuit is operable to shunt a capacitance across each of said plurality of virtual segments.

19. The piezoelectric resonator of claim 14 wherein said tuning circuit is operable to shunt a capacitance across said passive element.

20. The piezoelectric resonator of claim 14 wherein said actuator element is comprised of at least one of lead zirconate titanate, zinc oxide, lithium niobate, lithium tantalate, quartz, aluminum nitride, and polyvinylidine diflouride.

21. The piezoelectric resonator of claim 14 wherein said sensor element is comprised of at least one of lead zirconate titanate, zinc oxide, lithium niobate, lithium tantalate, quartz, aluminum nitride, and polyvinylidine diflouride.

22. The piezoelectric resonator of claim 14 wherein said passive element is comprised of at least one of lead zirconate titanate, zinc oxide, lithium niobate, lithium tantalate, quartz, aluminum nitride, and polyvinylidine diflouride.

23. The piezoelectric resonator of claim 14 wherein said piezoelectric resonator is one of a clamped-unclamped cantilevered beam piezoelectric resonator, clamped-clamped cantilevered beam piezoelectric resonator, an axial rod piezoelectric resonator, a shear layer piezoelectric resonator, and a diaphragm piezoelectric resonator.

24. A tunable piezoelectric micro-mechanical resonator, comprising:

a composite member, said composite member being comprised of;

a piezoelectric actuator element;

a piezoelectric sensor element;

a piezoelectric passive element; and

a substrate carrying said piezoelectric actuator element, said piezoelectric sensor element, and said piezoelectric passive element;

an excitation circuit operable to induce a resonance at a frequency within said composite member and operable to receive a feedback signal from said composite member; and

a tuning circuit connected to said piezoelectric passive element and operable to vary said frequency.

25. The tunable piezoelectric micro-mechanical resonator of claim 24 wherein said frequency is defined by ω

_n={square root over (k/m)}, wherein k is the structural stiffness of said composite member and wherein m is the mass of said composite member.

26. The tunable piezoelectric micro-mechanical resonator of claim 25 wherein said tuning circuit is operable to change the structural stiffness of said composite member.

27. The tunable piezoelectric micro-mechanical resonator of claim 25 wherein said tuning circuit is operable to alter said mechanical frequency ω

_n by altering the electromechanical coupling of said piezoelectric passive element.

28. The tunable piezoelectric micro-mechanical resonator of claim 24 wherein said tuning circuit includes a variable capacitor.

29. The tunable piezoelectric micro-mechanical resonator of claim 24 wherein said tuning circuit includes a switch and a capacitor.

30. The tunable piezoelectric micro-mechanical resonator of claim 24 wherein said piezoelectric passive element includes a plurality of segments, each of said plurality of segments being individually controllable by said tuning circuit.

31. The tunable piezoelectric micro-mechanical resonator of claim 24 wherein said excitation circuit further comprises a feedback loop operable to supply a signal to said piezoelectric actuator element and operable to receive a signal from said piezoelectric sensor element.

32. The tunable piezoelectric micro-mechanical resonator of claim 24 wherein said piezoelectric actuator element and said piezoelectric sensor element are combined.

33. The tunable piezoelectric micro-mechanical resonator of claim 24 wherein said actuator element is defined by an actuator electrode and a first electrode, wherein said sensor element is defined by a sensor electrode and said first electrode, and wherein said passive element is defined by a passive electrode and said first electrode.

34. The tunable piezoelectric micro-mechanical resonator of claim 24 wherein said actuator element is defined by an actuator electrode and a first electrode, wherein said sensor element is defined by a sensor electrode and a second electrode, and wherein said passive element is defined by a passive electrode and a third electrode.

35. The tunable piezoelectric micro-mechanical resonator of claim 24 wherein said actuator, sensor, and passive elements are comprised of at least one of lead zirconate titanate, zinc oxide, lithium niobate, lithium tantalate, quartz, aluminum nitride, and polyvinylidine diflouride.

36. The tunable piezoelectric micro-mechanical resonator of claim 24 wherein said piezoelectric resonator is one of a clamped-unclamped cantilevered beam piezoelectric resonator, clamped-clamped cantilevered beam piezoelectric resonator, an axial rod piezoelectric resonator, a shear layer piezoelectric resonator, and a diaphragm piezoelectric resonator.

37. A method for controlling a resonator having composite member, said composite member having a substrate carrying a composite piezoelectric element, wherein said composite piezoelectric element includes an actuator element, a sensor element and a passive element, the method comprising:

inducing a resonance within said composite member with said actuator element;

detecting said resonance with said sensor element; and

altering said resonance by altering the electromechanical coupling of said passive element.

38. The method of claim 37 wherein said altering said resonance by altering the electromechanical coupling comprises shunting a capacitance across said passive element.

39. The method of claim 37 wherein said altering said resonance by altering the electromechanical coupling comprises adjusting the stiffiess of said composite member.

40. The method of claim 37 wherein said altering said resonance by altering the electromechanical coupling comprises tuning the resonance of said composite member.

41. The method of claim 37 wherein said altering said resonance by altering the electromechanical coupling comprises hopping from a first resonance to a second resonance.

42. A method for tuning a resonator operating at one of a plurality of frequency modes, said resonator being comprised of a composite member having a substrate carrying a piezoelectric element, said piezoelectric element including an actuator element, a sensor element and a passive element, the method comprising:

inducing a vibration at a single frequency within said composite member with said actuator element;

detecting said frequency with said sensor element; and

adjusting said frequency with said passive element.

43. The method of claim 42 wherein said adjusting said frequency further comprises altering the electromechanical coupling of said passive element.

44. The method of claim 42 wherein said adjusting said frequency further comprises shunting a capacitance across said passive element.

45. The method of claim 42 wherein said detecting said frequency further comprises measuring an electrical signal produced when said sensor element is placed under a mechanical strain.