Resonant sensing using extensional modes of a plate
A device or system that incorporates teachings of the present disclosure may include, for example, a resonant structure having a plate, a mass and a set of electrodes. The plate can have an extensional mode at a frequency when excited. The set of electrodes can be used to measure an acceleration of the mass when the acceleration of the mass changes the frequency of the plate. Other embodiments are disclosed.
1. An apparatus, comprising:
a resonant structure comprising:
a mass;
a plate coupled to the mass, wherein the plate has a size, shape and material to support one or more lamb waves of an extensional mode at a frequency when excited; and
a plurality of electrodes coupled to the plate for delivering an excitation signal to the plate and for obtaining a measurement signal resulting from an acceleration of the mass which causes a modulation of the frequency of the extensional mode of the plate,
wherein the plate includes a piezoelectric layer disposed on a temperature compensated layer,
wherein the temperature compensated layer has first and third layers that have a stiffness that increases with increasing temperature over a temperature range with a second layer between the first and third layers, and
wherein the second layer is formed from a different material than the first and third layers.
2. The apparatus of claim 1 , wherein:
the frequency is a first frequency,
the plate has the extensional mode at the first frequency when excited along a first axis,
the plate has a second frequency when the mass is moved along a second axis by an external force,
the measurement signal obtained from the plurality of electrodes corresponds to a measure of a difference between the first frequency and the second frequency, the difference being proportional to the acceleration of the mass.
3. The apparatus of claim 1 , wherein the extensional mode of the plate is at least one of a plurality of extensional modes.
4. The apparatus of claim 1 , wherein:
the extensional mode of the plate is at least one of a first extensional mode or a higher order extensional mode, and
the plate has the extensional mode when excited by a piezoelectric effect.
5. The apparatus of claim 1 , wherein the plate comprises a piezoelectric layer disposed on a temperature compensated layer, and wherein the piezoelectric layer comprises at least one of aluminum nitride, zinc oxide lead zirconate titanate (PZT), Lithium niobate (LiNb03), Potassium niobate (KNb03), Lithium tantanate (LiTa03), Quartz, Barium strontium titanate (BaSrTi03), or Manganese niobium titanate (MnNbTi03).
6. The apparatus of claim 1 , wherein the plate is made of at least one of silicon or silicon oxide.
7. The apparatus of claim 5 , wherein the plate comprises a substrate and an electrode, and wherein the piezoelectric layer is disposed between the substrate and the electrode.
8. The apparatus of claim 5 , wherein the plate comprises a substrate and an electrode, and wherein the electrode is disposed between the substrate and the piezoelectric layer.
9. The apparatus of claim 5 , wherein the plate comprises a substrate and an electrode, and wherein the electrode is formed above or below the piezoelectric layer to actuate extensional modes of the plate.
10. The apparatus of claim 1 , wherein the acceleration of the mass is associated with at least one of a Coriolis acceleration in a gyroscope, a force in a force sensor or an acceleration in an accelerometer.
11. The apparatus of claim 1 , wherein the mass is connected to the plate by a plurality of anchors.
12. The apparatus of claim 1 , wherein the mass is a first mass, wherein the apparatus comprises a plurality of masses including the first mass, and wherein at least a portion of the plurality of masses are connected to the plate.
13. The apparatus of claim 1 , wherein the resonant structure comprises one of a substrate disposed about the plate and the mass on at least one side, the plate being connected to the mass, the plate being connected to the substrate, or the mass being connected to the substrate.
14. The apparatus of claim 1 , wherein the resonant structure comprises one of the plate being mechanically suspended from a substrate by at least one anchor, the mass being connected to the plate, or the mass being connected to the substrate by at least one anchor.
15. The apparatus of claim 1 , wherein at least the mass is connected to at least one lever arm.
16. The apparatus of claim 1 , wherein the plate has the extensional mode when excited differentially.
17. The apparatus of claim 16 , wherein a first electrode of the plurality of electrodes excites the extensional mode of the plate, and wherein at least a second electrode of the plurality of electrodes is used to differentially sense the extensional mode of the plate.
18. The apparatus of claim 1 , wherein the plate is a first plate, wherein the resonant structure comprises a second plate, wherein the first plate and the mass are connected, and wherein the second plate and the mass are connected.
19. The apparatus of claim 1 , wherein:
the plate is a first plate,
the frequency is a first frequency,
the resonant structure comprises a second plate having an extensional mode at a second frequency when excited,
the first plate and the mass are connected, the second plate and the mass being connected,
the measurement signal obtained from the plurality of electrodes provide a measure of the acceleration of the mass when the acceleration of the mass changes the first frequency of the first plate and the second frequency of the second plate, the acceleration of the mass being proportion to a difference between the first frequency of the first plate when changed and the second frequency of the second plate when changed.
20. The apparatus of claim 1 , wherein the resonant structure comprises a substrate, and wherein the plate is connected to the substrate and the mass by at least one anchor.
21. The apparatus of claim 1 , wherein the resonant structure comprises a substrate, and wherein the plate is connected to the substrate by at least one anchor.
22. The apparatus of claim 1 , wherein the mass is connected to a substrate by at least one anchor.
23. An apparatus, comprising:
a plate having first and second opposite surfaces, wherein the first surface has a piezoelectric layer without the second surface having the piezoelectric layer; and
a mass attached to the plate,
wherein the plate has a size, shape and material to support one or more lamb waves of an extensional mode at a first frequency when excited along an axis, wherein the plate has a second frequency when the mass is moved along the axis by an external force, and wherein a difference between the first frequency and the second frequency is associated with an acceleration of the mass when moved,
wherein the plate includes a temperature compensated layer,
wherein the piezoelectric layer is disposed on the temperature compensated layer,
wherein the temperature compensated layer has first and third layers that have a stiffness that increases with increasing temperature over a temperature range with a second layer between the first and third layers, and
wherein the second layer is formed from a different material than the first and third layers.
24. The apparatus of claim 23 , wherein the apparatus is integrated in a portable communication device.
25. The apparatus of claim 24 , wherein the portable communication device is a cellular phone.