System and method for harvesting energy from environmental vibrations
View Patent ↗Embodiments of the present invention provide a system and a method for increasing the harvested energy from a piezoelectric element exposed to environmental vibrations via a two-prong system. In a first prong, a cantilever beam is tapered and shaped so as to increase and provide an approximately uniform strain on and along the beam, thus resulting in increased voltage. In a second prong of the system and method, a voltage compensating circuit, when used with a voltage inversion circuit of the prior art, increases the harvested power by injecting current to the piezoelectric element after each voltage inversion so as to increase the voltage level.
1. A system for harvesting energy from vibrations, the system comprising:
a vibration-producing device operable to produce vibrations;
a tapered cantilever beam associated with the vibration-producing device and configured to receive the vibrations;
a piezoelectric element coupled with the cantilever beam and operable to receive a strain from the vibrations so as to induce a voltage across the element;
a voltage inversion circuit coupled with the piezoelectric element and operable to invert the voltage so as to boost a power output; and
a voltage compensating circuit operable to further increase the power output by injecting current to the piezoelectric element after each voltage inversion performed by the voltage inversion circuit.
2. The system of claim 1 , wherein the tapered cantilever beam is tapered according to the following equation:
ⅆ
f
2
(
x
)
ⅆ
x
=
2
EF
(
l
T
-
x
)
I
(
x
)
f
2
(
x
)
+
F
2
(
l
T
-
x
)
2
f
2
2
(
x
)
K
1
E
2
I
2
(
x
)
-
1
.
where:
E is an electrical field,
F is a force applied to a center of a proof mass,
I(x) is the moment of inertia,
l T =l b +l m /2, and l b is the length of the beam and l m is the length of the proof mass,
ƒ 2 (x)=ƒ 1 (x)+t b /2, where the function ƒ 1 (x) is the distance between a surface of the cantilever beam surface and a center of the beam, and t b is the piezoelectric element's thickness, and
K
1
=
ɛ
2
(
x
)
+
2
ɛ
(
x
)
1
+
(
ⅆ
f
2
(
x
)
ⅆ
x
)
2
,
and
ɛ
(
x
)
=
M
(
x
)
f
2
(
x
)
EI
(
x
)
,
and
M
(
x
)
=
F
EI
(
x
)
(
l
h
+
l
m
2
-
x
)
.
3. The system of claim 1 , wherein the cantilever beam has a body including—
a first tapered surface,
a second tapered surface,
a fixed end configured to be associated with the vibration-producing device, and
a narrowed end opposite and narrower than the fixed end.
4. The system of claim 3 , wherein the piezoelectric element is at least one flexible strip at least partially coupled to at least one of the first and second tapered surfaces of the beam's body.
5. The system of claim 1 , wherein the piezoelectric element comprises a current source and a clamping capacitor, and the voltage inversion circuit boosts the power by injecting current to the clamping capacitor.
6. The system of claim 1 , wherein the voltage inversion circuit comprises at least one inductor, a plurality of voltage inverting switches, at least one transistor, and a load.
7. The system of claim 6 , wherein the voltage compensating circuit comprises a plurality of voltage compensating switches.
8. The system of claim 6 , wherein the voltage compensating circuit is at least a two-step circuit including—
a first step of synchronizing at least one voltage compensating switch with at least one voltage inverting switch by applying a delay to end the inversion of the voltage and establish a new voltage in the voltage inversion circuit, and
a second step of consecutively closing the plurality of voltage compensating switches to allow the injection of current to the piezoelectric element.
9. A system for harvesting energy from vibrations, the system comprising:
a vibration-producing device operable to produce vibrations;
a piezoelectric element associated with the vibration-producing device and operable to receive a strain from the vibrations so as to induce a voltage across the element;
a voltage inversion circuit coupled with the piezoelectric element and operable to invert the voltage so as to boost a power output; and
a voltage compensating circuit operable to further increase the power output by injecting current to the piezoelectric element after each voltage inversion performed by the voltage inversion circuit.
10. The system of claim 9 , further comprising a tapered cantilever beam coupled with the vibration-producing device and the piezoelectric element.
11. The system of claim 10 , wherein the tapered cantilever beam is tapered according to the following equation:
ⅆ
f
2
(
x
)
ⅆ
x
=
2
EF
(
l
T
-
x
)
I
(
x
)
f
2
(
x
)
+
F
2
(
l
T
-
x
)
2
f
2
2
(
x
)
K
1
E
2
I
2
(
x
)
-
1
.
where:
E is an electrical field,
F is a force applied to a center of a proof mass,
I(x) is the moment of inertia,
l T =l b +l m /2, and l b is the length of the beam and l m is the length of the proof mass,
ƒ 2 (x)=(x)+t b /2, where the function ƒ 1 (x) is the distance between a surface of the cantilever beam surface and a center of the beam, and t b is the piezoelectric element's thickness, and
K
1
=
ɛ
2
(
x
)
+
2
ɛ
(
x
)
1
+
(
ⅆ
f
2
(
x
)
ⅆ
x
)
2
,
and
ɛ
(
x
)
=
M
(
x
)
f
2
(
x
)
EI
(
x
)
,
and
M
(
x
)
=
F
EI
(
x
)
(
l
h
+
l
m
2
-
x
)
.
12. The system of claim 9 , wherein the voltage inversion circuit comprises at least one inductor, a plurality of voltage inverting switches, at least one transistor, and a load.
13. The system of claim 12 , wherein the voltage compensating circuit comprises a plurality of voltage compensating switches.
14. The system of claim 13 , wherein the voltage compensating circuit is at least a two-step circuit including—
a first step of synchronizing at least one voltage compensating switch with at least one voltage inverting switch by applying a delay to end the inversion of the voltage and establish a new voltage in the voltage inversion circuit, and
a second step of consecutively closing the plurality of voltage compensating switches to allow the injection of current to the piezoelectric element.