Piezoelectric Transducers and Inertial Sensors using Piezoelectric Transducers

Abstract

Transducers comprising a frame structure made of piezoelectric material convert energy, through piezoelectric effect, between electrostatic energy associated with voltage differential between the electrodes sandwiching the frame structure and mechanical energy associated with deformation of the frame structure. Inertial sensors such as gyroscopes and accelerators, including inertial sensors comprising ring resonators, utilize said transducers both to generate oscillations of their resonators and to sense the changes in such oscillations produced, in the sensors' frame of reference, by Coriolis forces appearing due to the movement of the sensors.

1 . A piezoelectric transducer comprising:
 a structure made of piezoelectric material, the structure including:
 a set of substantially flat concentric frames having a common top surface and a common bottom surface and characterized by a direction of elongation, the top and the bottom surfaces being substantially parallel to a reference plane, and 
 bridges connecting the frames, the bridges disposed symmetrically about a plane of symmetry of the structure so as to allow the frames to deform in the reference plane; and 
   a set of at least two top electrodes, disposed on the top surface of the frames, and a set of at least two corresponding bottom electrodes, disposed on the bottom surface of the frames, the sets of top and bottom electrodes being substantially equivalent and positioned opposite to each other, each of corresponding top and bottom electrodes disposed on at least two frames along a path that is symmetric about the plane of symmetry and crosses some of the bridges,   wherein the transducer transduces energy, through piezoelectric effect, between electrostatic energy associated with voltage differential between the corresponding top and bottom electrodes and mechanical energy associated with deformation of the frames.   
     
     
         2 . A transducer according to  claim 1 , wherein the deformation of the frames is reciprocating. 
     
     
         3 . A transducer according to  claim 1 , wherein bridges crossed by the path define a plurality of sections in the structure, the plurality of sections including at least two peripheral sections and a central section. 
     
     
         4 . A transducer according to  claim 3 , wherein the central section is longer than the at least two peripheral sections. 
     
     
         5 . A transducer according to  claim 3 , wherein deformation of the central section is characterized by higher amplitude than deformations of peripheral sections. 
     
     
         6 . A transducer according to  claim 1 , wherein the plane of symmetry is perpendicular to the direction of elongation. 
     
     
         7 . A transducer according to  claim 1 , wherein the transducer is used for at least one of driving and sensing motion of a connected mass. 
     
     
         8 . A motion sensor comprising a body defining a local reference system, the body including:
 a piezoelectric transducer including:
 a set of substantially flat concentric frames having a common top surface and a common bottom surface and characterized by a direction of elongation, the top and the bottom surfaces being substantially parallel to a reference plane; 
 bridges connecting the frames, the bridges disposed symmetrically about a plane of symmetry of the transducer so as to allow the frames to deform in the reference plane, the bridges and the frames made of piezoelectric material; and 
 a set of at least two top electrodes, disposed on the top surface of the frames, and a set of at least two corresponding bottom electrodes, disposed on the bottom surface of the frames, the sets of top and bottom electrodes being substantially equivalent and positioned opposite to each other, each of corresponding top and bottom electrodes disposed on at least two frames along a path that is symmetric about the plane of symmetry and crosses some of the bridges, 
 wherein the transducer transduces energy, through piezoelectric effect, between electrostatic energy associated with voltage differential between the corresponding top and bottom electrodes and mechanical energy associated with deformation of the frames; and 
   a resonator coupled to the piezoelectric transducer, the resonator characterized by a motion that lies substantially in the reference plane.   
     
     
         9 . A sensor according to  claim 8 , wherein the transducer causes, through piezoelectric effect, the motion of the resonator. 
     
     
         10 . A sensor according to  claim 8 , wherein the transducer senses, through piezoelectric effect, the motion of the resonator. 
     
     
         11 . A sensor according to  claim 8 , wherein the transducer is configured to enable detection of changes in electric field arising, through piezoelectric effect, from changes in the motion of the resonator within the local reference system, the changes in the motion associated with rotation of the body. 
     
     
         12 . A sensor according to  claim 8 , wherein the motion of the resonator is reciprocating. 
     
     
         13 . A sensor according to  claim 8 , wherein the body is configured to be reflectionally symmetric about a symmetry axis that is normal to the reference plane. 
     
     
         14 . A sensor according to  claim 12 , wherein the reciprocating motion includes deformation of the frames perpendicularly to the direction of elongation. 
     
     
         15 . A sensor according to  claim 8 , further comprising a substrate, wherein the body is affixed to the substrate using a set of anchors for supporting the body above a surface of the substrate, at least one anchor positioned proximate to the body's center of mass. 
     
     
         16 . A sensor according to  claim 15 , wherein the body is affixed to the substrate within a recess formed in the substrate. 
     
     
         17 . A sensor according to  claim 15 , wherein the surface of the substrate is leveled and the body is affixed to the substrate above the leveled surface. 
     
     
         18 . A sensor according to  claim 15 , wherein the set of anchors is configured to allow movement of the body relative to the substrate. 
     
     
         19 . A sensor according to  claim 15 , wherein the set of anchors includes multiple anchors positioned substantially symmetrically about the body's center of mass. 
     
     
         20 . A sensor according to  claim 8 , wherein the body further comprises a hub portion. 
     
     
         21 . A sensor according to  claim 20 , wherein the resonator comprises a ring portion, the ring portion being supported by spoke structures extending substantially in radial direction from the hub portion. 
     
     
         22 . A sensor according to  claim 21 , wherein the deformation of the frames is transferred to the ring portion along the spoke structures. 
     
     
         23 . A sensor according to  claim 21 , wherein the top and the bottom driving electrodes and the top and the bottom sensing electrodes at least partially overlap with the spoke structures. 
     
     
         24 . A sensor according to  claim 21 , wherein the hub portion and the ring portion are circular. 
     
     
         25 . A sensor according to  claim 8 , wherein the sensor is an accelerometer. 
     
     
         26 . A sensor according to  claim 8 , wherein the sensor is a gyroscope. 
     
     
         27 . A method of sensing a movement of an inertial sensor having a body of piezoelectric material, the body characterized by substantially constant thickness defined by two planes and also having a set of top electrodes disposed on a top surface of the body and a corresponding set of bottom electrodes disposed on a bottom surface of the body, the sets of top and bottom electrodes being opposite to one another, the sets of top and bottom electrodes characterized by a pattern, the body defining a local reference system, the method comprising:
 applying alternating voltage differential between top driving electrodes from the top set and corresponding bottom driving electrodes from the bottom set so as to cause reciprocating motion, in the plane, of a portion of the body through piezoelectric effect, wherein such reciprocating motion changes, within the local reference system, upon the movement of the inertial sensor; and   sensing, through piezoelectric effect, said changes to the reciprocating motion based on a voltage differential arising between top sensing electrodes from the top set and corresponding bottom sensing electrodes from the bottom set.   
     
     
         28 . A method according to  claim 27 , wherein the body is configured to be reflectionally symmetric about a symmetry axis that is normal to the plane. 
     
     
         29 . A method according to  claim 27 , wherein the pattern is configured to be reflectionally symmetric about the symmetry axis. 
     
     
         30 . A method according to  claim 27 , wherein the movement of the inertial sensor is a rotation about an axis that is perpendicular to the plane. 
     
     
         31 . A method for modifying an oscillation of a resonator in an inertial sensor, the inertial sensor comprising driving piezoelectric transducers for enabling an oscillation of the resonator and sensing piezoelectric transducers for enabling a detection of a movement of the inertial sensor, the method comprising:
 disposing piezoelectric compensating elements substantially equidistantly among the driving and the sensing piezoelectric transducers, the compensating elements and the resonator forming corresponding capacitors having capacitive gaps;   during the oscillation of the resonator, measuring, with the compensating elements, changes in electrostatic charges stored in the capacitors, the changes in charges associated with changes in the capacitive gaps due to the oscillation of the resonator; and   modifying the electrostatic charges stored in the capacitors so as to modify the oscillation of the resonator.   
     
     
         32 . A method according to  claim 31 , wherein the inertial sensor is a gyroscope. 
     
     
         33 . A method according to  claim 31 , wherein the resonator is a frame. 
     
     
         34 . A method according to  claim 31 , wherein the inertial sensor further comprises a hub and the resonator is a ring connected to the hub. 
     
     
         35 . A method according to  claim 31 , wherein modifying the stored electrostatic charges includes equalizing the changes in the stored charges among the capacitors. 
     
     
         36 . A method according to  claim 31 , wherein modifying the stored electrostatic charges enables adjustment of a resonant frequency of the resonator.