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US-12622175-B2 - Piezoelectric sensor with embedded electrodes

US12622175B2US 12622175 B2US12622175 B2US 12622175B2US-12622175-B2

Abstract

A piezoelectric sensor, comprising at least one first electrode, at least one second electrode, and a piezoelectric material, wherein the piezoelectric material has an anisotropic electromechanical coupling and the at least one first and second electrodes are at least in part embedded in the piezoelectric material, the piezoelectric material having a first surface wherein the electrodes extend vertically within the piezoelectric material from the first surface.

Inventors

  • Barbara Stadlober
  • Martin Zirkl
  • Philipp Schaffner
  • Andreas Tschepp

Assignees

  • JOANNEUM RESEARCH FORSCHUNGSGESELLSCHAFT MBH

Dates

Publication Date
20260505
Application Date
20181010

Claims (16)

  1. 1 . A piezoelectric sensor ( 1 ), comprising: at least one first electrode ( 3 ) having transversely-disposed first and second surfaces; at least one second electrode ( 5 ) having transversely-disposed third and fourth surfaces; a piezoelectric material ( 6 ); wherein the piezoelectric material ( 6 ) has an anisotropic electromechanical coupling, and the at least one first and second electrodes ( 3 , 5 ) are at least in part embedded in the piezoelectric material ( 6 ) so that the first and second surfaces of the at least one first electrode ( 3 ) and the third and fourth surfaces of the at least one second electrode ( 5 ) are in contact with the piezoelectric material ( 6 ), the piezoelectric material ( 6 ) having a first surface ( 4 ), wherein the at least one first and second electrodes ( 3 , 5 ) extend substantially at a right angle within the piezoelectric material ( 6 ) from the first surface ( 4 ).
  2. 2 . The piezoelectric sensor ( 1 ) of claim 1 , wherein the at least one first and second electrodes ( 3 , 5 ) are laterally interdigitated first and second electrode fingers forming an intermeshing comb structure within the piezoelectric material ( 6 ) with the first and second electrode fingers being individually electrically connectable.
  3. 3 . The piezoelectric sensor ( 1 ) of claim 2 , wherein the first and second electrode fingers ( 3 , 5 ) are arranged in an angle 0<α<90 degrees in relation to one another.
  4. 4 . The piezoelectric sensor ( 1 ) of claim 1 , wherein the piezoelectric material ( 6 ) is additionally pyroelectric.
  5. 5 . The piezoelectric sensor ( 1 ) of claim 1 , wherein the sensor ( 1 ) comprises a substrate ( 2 ), wherein the piezoelectric material ( 6 ) forms a layer on the substrate ( 2 ).
  6. 6 . The piezoelectric sensor ( 1 ) of claim 1 , wherein the sensor ( 1 ) comprises a third electrode ( 11 ) spaced apart from the at least one first and second electrodes ( 3 , 5 ).
  7. 7 . The piezoelectric sensor ( 1 ) of claim 1 , wherein the sensor ( 1 ) comprises a substrate ( 2 ), wherein the piezoelectric material ( 6 ) forms a layer on the substrate ( 2 ) and wherein a third electrode ( 11 ) is arranged between the piezoelectric material ( 6 ) and the substrate ( 2 ).
  8. 8 . The piezoelectric sensor ( 1 ) of claim 6 , wherein a primary orientation of the polarization ( 7 ) of the piezoelectric material ( 6 ) between the third electrode ( 11 ) and a top-side ( 9 ) of the at least one first and second electrodes ( 3 , 5 ) is substantially parallel to a vertical extension of the at least one first and second electrodes ( 3 , 5 ) and substantially perpendicular to a plane representative of a lateral extension of the third electrode ( 11 ).
  9. 9 . A sensor array ( 12 ), comprising a plurality of sensors ( 1 ) according to claim 1 , wherein the plurality of sensors ( 1 ) are rotated in respect to one another.
  10. 10 . The sensor array ( 12 ) of claim 9 , wherein the sensor array ( 12 ) comprises a first and a second sub-array ( 13 , 14 ), each sub-array ( 13 , 14 ) comprising at least two of the plurality of sensors ( 1 ), wherein the at least two of the plurality of sensors ( 1 ) of each sub-array ( 13 , 14 ) are arranged non-parallel in respect to one another.
  11. 11 . The piezoelectric sensor ( 1 ) of claim 5 , wherein the substrate ( 2 ) is a flexible, elastic substrate ( 2 ).
  12. 12 . The piezoelectric sensor ( 1 ) of claim 11 , wherein the substrate ( 2 ) is a polymer foil.
  13. 13 . The piezoelectric sensor ( 1 ) of claim 12 , wherein the polymer foil is polyethylene terephthalate (PET).
  14. 14 . The piezoelectric sensor ( 1 ) of claim 6 , wherein the third electrode ( 11 ) is arranged at the first surface ( 4 ) of the piezoelectric material ( 6 ).
  15. 15 . The piezoelectric sensor ( 1 ) of claim 6 , wherein the third electrode ( 11 ) is arranged at a second surface opposite the first surface ( 4 ).
  16. 16 . The sensor array of claim 10 , wherein the at least two of the plurality of sensors ( 1 ) of each sub-array ( 13 , 14 ) are arranged at an angle of 45° degrees in respect to one another.

Description

CROSS-REFERENCE TO RELATED APPLICATION This Application is a National Stage Application under 35 U.S.C. § 371 of PCT Application No. PCT/EP2018/077617, filed Oct. 10, 2018, the entire contents of which are incorporated by reference herein. FIELD OF THE INVENTION The invention relates to a piezoelectric sensor. BACKGROUND Active sensors for the detection of forces are usually based on the piezoelectric effect. Active sensors are sensors that generate electrical energy during the measuring event rather than dissipating it. When a force is applied to a surface of the sensor, the mechanical stress is partly transformed into electrical energy which may be a qualitative and quantitative measure for the applied force. Piezoelectric sensors usually comprise a plurality of layers, wherein an active sensor material is embedded between a top-electrode-layer and a bottom-electrode-layer forming a vertical layer assembly. The active sensor material preferably consists of inorganic ceramics or electroactive polymers e.g. poly(vinylidenefluoride) (PVDF) and/or poly(vinylidenefluoride: trifluoroethylene)(P(VDF:TrFE)) or any combinations of them (e.g. nanocomposite materials). These polymer materials provide high mechanical flexibility and can be processed in industrial scale processing. In common active sensors, the sensor material is embodied as a sensor film. Mechanical stress applied on a surface of the sensor causes deformations of the sensor material which generates compensation charges in the electrodes. These charges can be transformed into a signal. In this common sensor layout, the amount of charges and hence the signal highly depend on the direction in which the mechanical stress is applied. The charges are the more, the more stress is applied in a direction normal to the sensor film (that means in a direction parallel to a spontaneous polarization of the sensor material). Lateral forces, tensions and torques acting in the plane of the film (parallel to a surface of the sensor film) only generate relatively low voltages and cannot be distinguished from the signals generated by forces having a normal component. Several concepts have been developed to measure lateral forces with piezoelectric sensors. For example, the sensor material forming the sensor film has been reinforced with mechanical structures in order to generate normal components of a lateral force inside the sensor material. In another example, the sensor film has been formed by electrospinning, wherein the filaments are of piezoelectric material, whereby enhanced sensitivity of the sensor film is achieved. These concepts still do not provide satisfying solutions when it comes to the detection of tangential components of forces applied on the surface of the piezoelectric sensor, shear forces or torque occurring on the surface the sensor is attached to or embedded in. The invention aims to provide a piezoelectric sensor with enhanced sensitivity to any forces contributing to lateral stress. The solution is defined in the independent claims. Further expedient embodiments are defined in the sub-claims. SUMMARY OF THE INVENTION The invention provides for a piezoelectric sensor, comprising at least one first electrode, at least one second electrode, a piezoelectric material; wherein the piezoelectric material has an anisotropic electromechanical coupling and the at least one first and second electrodes are at least in part embedded in the piezoelectric material, the piezoelectric material having a first surface, wherein the electrodes extend substantially at a right angle within the piezoelectric material from the first surface. The invention is based on the use of a piezoelectric material (PM) showing an anisotropic electromechanical coupling, wherein the anisotropy can be i) intrinsic, ii) introduced during processing or deposition or iii) by means of treatment after deposition. Electromechanical coupling in this context shall refer to the effect that stress or strain applied to the PM will cause an electrically measurable change in its polarization. The electromechanical coupling is usually highest in one direction, which will be referred to as primary orientation, than in the transverse directions. For piezoelectric or ferroelectric materials having a non-zero spontaneous polarization, the primary orientation shall be defined as the direction of the overall spontaneous polarization. Material examples are ferroelectrets, piezoelectric ceramics, fibers and polymers, ferroelectric materials, composite materials where at least one component is piezoelectric etc. Regarding case (iii), ferroelectric materials shall be explicitly mentioned as being suitable PMs, where the orientation of the ferroelectric domains can be altered by applying high external electric fields beyond the coercive field strength. The electromechanical coupling of a piezoelectric material can be described by the following linear constitutive equations (using Einstein notation): εij=sijkl