Flexible, piezoelectric, miniaturized vibration sensor for machine integration
A vibration sensor based on piezoelectric thin films, or smart cuts of piezoelectric materials, integrated into a functional, metallic housing that transmits vibration deformations applied to the housing correctly into the sensor in a frequency range that is typically—but not limited to—1 Hz to 20 kHz. The sensor comprises a low-stiffness layer, for instance a PCB layer, providing a controllable contact force between sensor structure machine parts, and transforming the relative movements into a mechanical stress acting onto the piezoelectric layer.
1 . A vibration sensor comprising:
a layered composite comprising
at least one substrate layer,
at least one piezoelectric layer comprising
a piezoelectric thin film or at least one cut thin layer of piezoelectric materials, and
an electrode structure, and
at least one low-stiffness layer of a stiffness less than or equal to 10 GPa,
wherein the vibration sensor is configured to be integrated into a functional, metallic housing and to receive vibration deformations from the functional, metallic housing in a frequency range,
wherein the at least one low-stiffness layer is configured to transform the vibration deformations into a mechanical stress that the vibration sensor converts to electrical energy,
wherein the mechanical stress comprises any one of: thickness changes, lateral strain changes, and shear strain changes.
2 . The vibration sensor of claim 1 , wherein the housing and connecting wires are configured to shield against parasitic electromagnetic signals.
3 . The vibration sensor of claim 1 , wherein the frequency range is 10 Hz to 20 kHz.
4 . The vibration sensor of claim 1 , wherein the frequency range is 100 Hz to 20 kHz.
5 . The vibration sensor of claim 1 , wherein the electrode structure comprises parallel electrodes including one electrode on an upper side of the at least one piezoelectric layer and one electrode at a bottom side of the at least one piezoelectric layer, and upon receiving the vibration deformations, charges or the voltage is gathered at the parallel electrodes.
6 . The vibration sensor of claim 5 , wherein the vibration sensor has a seismic mass configured to transform acceleration into a bending motion of a cantilever.
7 . The vibration sensor of claim 1 , wherein the at least one piezoelectric layer is bonded or deposited onto a metal sheet with a thickness of 10 to 500 μm, and
wherein the metal sheet is made of one of aluminum, steel, nickel, bronze, brass, and silicon.
8 . The vibration sensor of claim 1 , wherein the at least one piezoelectric layer comprises at least one of an AIN-ScN alloy film, a AIN film with dopants, PZT, LiNbO3, and oriented piezoelectric crystals joined to a metal sheet by metal or atomic layer bonding, the crystals being one of LiNbO3, and a crystalline, piezoelectric material.
9 . The vibration sensor of claim 1 , wherein the at least one substrate layer is a low stiffness layer comprising a polymer layer or a fiber reinforced polymer layer of a PCB substrate.
10 . The vibration sensor of claim 1 , wherein the at least one substrate layer comprises a polished metal sheet conditioned for thin film deposition.
11 . The vibration sensor of claim 1 , wherein the at least one low-stiffness layer contains polymers.
12 . The vibration sensor of claim 1 , wherein the vibration sensor has the form of a plate and is configured to be sandwiched between two parallel faces of the housing.
13 . The vibration sensor of claim 12 , wherein the electrode structure comprises two parallel plate electrodes, the at least one low-stiffness layer being configured to transform distance changes between the two parallel faces of the housing into a stress uniformly acting onto the composite layer.
14 . The vibration sensor of claim 12 , wherein the electrode structure is disposed on the at least one piezoelectric layer and comprises interdigitated electrodes on a side opposite to the substrate layer, the piezoelectric layer comprising an insulating layer on the other side providing electrical insulation from the substrate, the at least one low-stiffness layer being disposed between the electrode surfaces and one of the parallel faces, the substrate layer being fixed to the opposed parallel face, the low-stiffness layer being configured to transform shear deformation into a shear stress acting onto the piezoelectric layer with its interdigitated electrodes.
15 . The vibration sensor of claim 1 , wherein the at least one piezoelectric layer is a bender forming a bridge within two fixation sites within the housing, the electrode structure comprising two electrodes disposed on both sides of the piezoelectric layer.
16 . The vibration sensor of claim 1 , wherein the piezoelectric layer thickness to the substrate layer thickness ratio is less than 1:10.
17 . The vibration sensor of claim 1 , wherein the vibration sensor is configured to harvest vibrational energy.
18 . The vibration sensor of claim 1 , wherein the electrode structure is disposed on the at least one piezoelectric layer and comprises a plurality of interdigitated electrodes,
the at least one piezoelectric layer is disposed on an insulating substrate, and the electrodes are only on one side of the insulating substrate.
19 . The vibration sensor of claim 1 , further comprising a beam configured to connect two sites of the housing and configured to be deformed when the two sites of the housing move against each other,
wherein the electrode structure comprises parallel top and bottom electrodes, and
wherein the at least one piezoelectric layer is attached to the beam and generates charges and voltage between the parallel top and bottom electrodes.