Piezo-elements for wearable devices, including fitness trackers, smart watches and the like
Aspects of the present disclosure describe systems, methods, and structures that scavenge mechanical energy to provide electrical energy to a wearable, where the mechanical energy is scavenged by a bending-strain-based transducer that includes a non-resonant energy harvester. By employing a non-resonant energy harvester that operates in bending mode, more electrical energy can be generated that possible with prior-art energy harvesters. In some embodiments the bending-strain-based transducer also includes a sensor and/or a haptic device. Some transducers in accordance with the present disclosure comprise a piezoelectric layer comprising a low-K piezoelectric material, such as aluminum nitride, which enables generation of higher voltage and power/energy output and/or a thinner transducer. As a result, transducers in accordance with the present disclosure can be included in wearables for which large transducer thickness would be problematic, such as sole members (e.g., shoe insoles, midsoles or outsoles), garments, bras, handbags, backpacks, and the like.
1 . A wearable apparatus comprising:
(a) a bending-strain-based transducer having a longitudinal axis that defines a first direction, that includes:
(i) a first transducer element disposed on a first surface of a substrate, the first transducer element being a non-resonant energy harvester; and
(ii) a second transducer element disposed on a second surface of the substrate, the first and second surfaces being on opposite sides of the substrate, wherein the second transducer element is selected from the group consisting of a resonant energy harvester, a non-resonant energy harvester, a force sensor, a load sensor, a pressure sensor, and a haptic device;
(iii) a mechanically rigid structural support aligned with a second direction, the first transducer element having a third surface that is distal to the substrate and defines a first plane, and wherein the mechanically rigid structural support extends along the second direction to define a second plane, and further wherein the first plane is between the substrate and the second plane; wherein the mechanically rigid structural support functions as a fulcrum about which the transducer bends;
(b) a power handling circuit; and
(c) an energy storage module operatively coupled with the bending-strain-based transducer and configured to store energy generated by the non-resonant energy harvesters, and provide power to the bending-strain-based transducer and the other electronics included in the wearable apparatus;
wherein the bending-strain-based transducer has a quiescent shape that is non-planar.
2 . The wearable apparatus of claim 1 wherein the transducer has a longitudinal axis in a first direction and is configured to bend in response to a first force that is at least partially directed along a second direction that is orthogonal to the first direction, and wherein the bending strain transducer is further configured to inhibit compression of at least one of the first and second transducer elements in response to the first force.
3 . The wearable apparatus of claim 1 wherein the bending strain transducer has a transducer thickness that is less than or equal to 3 millimeters.
4 . The wearable apparatus of claim 3 wherein the bending strain transducer thickness is within the range from 10 microns to 1100 microns.
5 . A wearable apparatus comprising:
(a) a bending-strain-based transducer having a longitudinal axis that defines a first direction that includes:
(i) a first transducer element disposed on a first surface of a substrate, the first transducer element being a non-resonant energy harvester; and
(ii) a second transducer element disposed on a second surface of the substrate, the first and second surfaces being on opposite sides of the substrate, wherein the second transducer element is selected from the group consisting of a resonant energy harvester, anon-resonant energy harvester, a force sensor, a load sensor, a pressure sensor, and a haptic device;
(iii) a third transducer element disposed on the second surface, and wherein the third transducer element is a sensor or a haptic device;
(iv) a mechanically rigid structural support aligned with a second direction, the first transducer element having a third surface that is distal to the substrate and defines a first plane, and wherein the mechanically rigid structural support extends along the second direction to define a second plane, and further wherein the first plane is between the substrate and the second plane; wherein the mechanically rigid structural support functions as a fulcrum about which the transducer bends;
(b) a power handling circuit; and
(c) an energy storage module operatively coupled with the bending-strain-based transducer and configured to store energy generated by the non-resonant energy harvesters, and provide power to the bending-strain-based transducer and the other electronics included in wearable apparatus;
wherein the bending-strain-based transducer has a quiescent shape that is non-planar.
6 . The wearable apparatus of claim 1 wherein the wearable apparatus is a sole member.
7 . The wearable apparatus of claim 1 wherein the substrate comprises a material selected from the group consisting of a metal, a polyimide and a glass.
8 . The wearable apparatus of claim 1 wherein at least one of the first transducer element and second transducer element includes a piezoelectric layer comprising a low-K piezoelectric material.
9 . The wearable apparatus of claim 8 wherein the low-K piezoelectric material is selected from the group consisting of undoped aluminum nitride, doped aluminum nitride, scandium-doped aluminum nitride, undoped zinc oxide, doped zinc oxide, and polyvinylidene fluoride.
10 . The wearable apparatus of claim 1 wherein the substrate comprises steel and at least one of the first transducer element and second transducer element includes a piezoelectric layer comprising a material selected from the group of undoped aluminum nitride, doped aluminum nitride, and scandium-doped aluminum nitride.
11 . The wearable apparatus of claim 1 wherein the substrate includes at least one flange, and wherein the substrate has a first thickness and the flange has a second thickness that is greater than the first thickness.
12 . A wearable apparatus comprising a first bimorph transducer having a quiescent shape that is non-planar, wherein the first bimorph transducer includes a first transducer element disposed on a first surface of a substrate, the first transducer element being a non-resonant energy harvester, and wherein the first bimorph transducer is configured to bend in response to a first force, wherein the wearable apparatus further comprises:
(a) a mechanically rigid structural support aligned with a second direction, the first transducer element having a third surface that is distal to the substrate and defines a first plane, and wherein the mechanically rigid structural support extends along the second direction to define a second plane, and further wherein the first plane is between the substrate and the second plane; wherein the mechanically rigid structural support functions as a fulcrum about which the transducer bends;
(b) a power handling circuit; and
(c) an energy storage module operatively coupled with the first bimorph transducer and configured to store energy generated by the non-resonant energy harvesters, and provide power to the first bimorph transducer and the other electronics included in the wearable apparatus;
wherein the first bimorph transducer further includes a second transducer element disposed on a second surface of a substrate, the second transducer element being a haptic device.
13 . The wearable apparatus of claim 12 wherein the first bimorph transducer is further configured to inhibit compression of the first transducer element in response to the first force.
14 . The wearable apparatus of claim 12 wherein the substrate comprises at least one material selected from the group consisting of a metal, a polyimide, and a glass.
15 . The wearable apparatus of claim 12 wherein at least one of the first transducer element and second transducer element includes a piezoelectric layer comprising a low-K piezoelectric material selected from the group consisting of undoped aluminum nitride, doped aluminum nitride, scandium-doped aluminum nitride, undoped zinc oxide, doped zinc oxide, and polyvinylidene fluoride.
16 . The wearable apparatus of claim 12 wherein the substrate comprises steel and at least one of the first transducer element and second transducer element includes a piezoelectric layer comprising a material selected from the group of undoped aluminum nitride, doped aluminum nitride, and scandium-doped aluminum nitride.
17 . The wearable apparatus of claim 12 wherein the wearable is a shoe insole that includes:
a plurality of bimorph transducers that includes the first bimorph transducer;
a wireless communications module;
wherein the plurality of bimorph transducers is operatively coupled with each of the power-handling circuit and the energy-storage module.
18 . The wearable apparatus of claim 12 wherein the quiescent shape is a ruffled shape that includes a plurality of bending axes arranged along a first direction.
19 . The wearable apparatus of claim 12 wherein the substrate includes at least one flange, and wherein the substrate has a first thickness and the flange has a second thickness that is greater than the first thickness.