Patent Application
20080252174
The present invention generally relates to the field of energy harvesting. More particularly, the present invention relates to systems and methods for electrical energy harvesting from multiple piezoelectric sources.
Piezoelectric materials are used in many applications for actuation, sensing, and electric energy harvesting. Piezoelectricity is the ability of crystals to generate a voltage in response to applied mechanical stress. As such, a mechanical stress applied on a piezoelectric material creates an electric charge. Piezoceramics will give off an electric pulse even when the applied pressure is as small as sound pressure. This phenomenon is called the direct piezoelectric effect and is used in sensor applications such as microphones, undersea sound detecting devices, pressure transducers, and electric energy harvesting to power other electronic devices. Piezoelectric materials can also function quite opposite in the converse piezoelectric effect, in which an electric field applied to a piezoelectric material changes the shape of the material as a result of the applied electric energy. In contrast to the direct piezoelectric effect, the converse piezoelectric effect only causes an elongation/contraction of the dipoles in the material causing the entire material to elongate/contract, and does not produce electrical charges. The converse piezoelectric effect makes possible piezoelectric actuators for precision positioning with high accuracy.
Conventionally, piezoelectric materials may be connected to a circuit containing a diode bridge, a power conditioning circuit, and a capacitor bank. If a mechanical disturbance is applied to the piezoelectric material, energy is generated, conditioned and stored in the capacitor bank. However, if multiple piezoelectric materials are attached to the same circuit in an attempt to produce more electric energy, the energy loss will be very high and there will be less energy stored in the capacitors than if a single piezoelectric transducer was used. The reason for this is that the energy generated from each piezoelectric transducer is consumed by other transducers in the system—that is, the energy generated by one piezoelectric transducer causes the converse piezoelectric effect to occur at the other transducer(s)—resulting in consumption of a part or all of the generated energy. Also, further losses occur due to the destructive electric signal interference produced from each piezoelectric transducer, resulting in less energy available for storage.
For these reasons, traditional single circuits can only handle one piezoelectric generator at a time. If multiple generators are used, less power can be harvested. Also, these traditional single circuit devices are very expensive because each contains its own power conditioning and storage circuitry.
Thus, in view of the foregoing, there is a need for systems and methods that overcome the limitations and drawbacks of the prior art. In particular, there is a need for systems and methods that allow efficient energy harvesting from multiple piezoelectric sources without, or with minimal, energy loss. Embodiments of the present invention provide such solutions.
The following is a simplified summary of the invention in order to provide a basic understanding of some of the aspects of the invention. This summary is not intended to identify key or critical elements of the invention or to define the scope of the invention.
The energy harvesting systems and methods of the present invention include the use of multiple energy (e.g., piezoelectric) generators connected to the same energy harvesting circuit (i.e., power condition and storage circuitry) with minimal or no energy loss. The systems and methods using multiple energy generators connected to the same energy harvesting circuit result in improved energy harvesting capabilities, and a simplified and low cost energy harvesting system.
According to one embodiment of the present invention, a piezoelectric energy harvesting system includes individual diode bridge circuits that may be attached to the outgoing wires from each piezoelectric generator. The outgoing wires from each diode bridge may be connected to a single energy harvesting circuit with minimal or no energy loss. This allows for the use of an unlimited number of piezoelectric generators at the same time on the same, or a single, energy harvesting circuit.
According to another embodiment of the present invention, a piezoelectric energy harvesting system includes multiple subsystems each having one or more individual diode bridges that may be connected to the outgoing wires from multiple piezoelectric generators. The outgoing wires from all diode bridges may be connected to a single energy harvesting circuit. Multiple subsystems, each having multiple piezoelectric generators and a diode bridge, may be connected to the same energy harvesting circuit.
The energy generator produces energy and may include any type of generator that produces an alternating current (AC), including for example, piezoelectric generators, magnetic generators, and the like. The energy harvesting system may include the same type of generators or a combination of different types of generators.
According to another aspect of the invention, the piezoelectric energy generators may include piezoelectric ceramic fibers, such as in piezoelectric fiber composites, piezoelectric fiber composite bimorphs, piezoelectric multilayer composites, and the like.
The energy harvesting system may also include power conditioning and storage circuitry. Further, the system may include one or more sensors that may be powered by the energy generator, either directly and/or via stored power. The sensor may include a separate and independent sensor, or the piezoelectric energy generator may also act as a sensor in the system. In addition, a transmitter may be included. In addition, the energy harvesting system may be placed in an enclosure for housing the various components. The enclosure may be mounted to a device to be monitored and that may provide mechanical input to the energy generators.
According to another aspect of the present invention, the multiple power piezoelectric power harvesting system may be compatible to all types of energy harvesting/scavenging circuits. This enables the multiple piezoelectric generator, power harvesting system to efficiently and cost effectively extract electric energy from multiple piezoelectric generator sources with minimal or no energy loss.
Since multiple piezoelectric generators can be used independently without energy loss, each piezoelectric transducer can be tuned to a specific frequency, which results in a multi-frequency, multi-functional energy harvester and/or a single broadband harvester.
Additional features and advantages of the invention will be made apparent from the following detailed description of illustrative embodiments that proceeds with reference to the accompanying drawings.
The foregoing summary, as well as the following detailed description of preferred embodiments, is better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there is shown in the drawings exemplary constructions of the invention; however, the invention is not limited to the specific methods and instrumentalities disclosed. Included in the drawings are the following Figures:
The following is a description of several exemplary embodiments of systems and methods for harvesting electrical energy from ambient or waste mechanical energy using multiple energy generators (e.g., piezoelectric generators) with minimal or no energy loss. Energy harvesting is the process by which energy is captured and stored and includes the conversion of ambient energy into usable electrical energy. Energy harvesting generators are devices that convert mechanical energy into electrical energy. Piezoelectric energy harvesting converts mechanical energy to electric energy by stressing a piezoelectric material. This stress in a piezoelectric material causes a charge separation across the device, producing an electric field and consequently a voltage drop proportional to the stress applied. Systems and methods according to embodiments of the present invention include multiple energy generators (e.g., any generators that produce an alternating current (AC)) connected to a single energy harvesting circuit via individual diode bridges.
Embodiments of the present invention include the use of multiple piezoelectric generators connected to an energy harvesting circuit (e.g., power conditioning and storage circuitry) in a manner that results in minimal or no energy loss, such as, for example, energy losses caused by the converse piezoelectric effect. The systems and methods using multiple piezoelectric generators connected via individual diode bridge circuits to the same energy harvesting circuit result in a simplified and low cost system. The multiple generator, energy harvesting systems and methods may be compatible with various types of energy harvesting/scavenging circuits, which enables the energy harvesting system to extract electric energy from multiple piezoelectric generator sources with minimal or no loss.
The energy generator 22 produces energy and may include any type of generator that produces an alternating current (AC). In one preferred embodiment, the energy generator 22 is a piezoelectric generator. The energy generator 22 may include other types of AC generators, such as magnetic generators. The generator may include a piezoelectric and/or electrostrictive material of any type, shape, or size. The multiple energy generators 22 may comprise the same type of generators or a combination of different types of generators. Since multiple piezoelectric generators can be used independently with minimum or no loss, each piezoelectric transducer may be tuned to a specific frequency. This results in a multi-frequency, multi-functional energy harvester and/or a single broadband harvester.
Diode bridge 24 (also referred to and including a bridge rectifier) may include an arrangement of diodes (e.g., typically four) connected in a bridge circuit that provide the same polarity output voltage for any polarity of the input voltage. The diode bridges 24 function to convert Alternating Current (AC) input into Direct Current (DC) output. The size of the diode bridges 24 may vary depending on the particular application for which the diode bridge-circuit is being used. Typically, the size of a diode bridge-circuit increases with increasing power handling capabilities. The diode bridge may include a full or half bridge diode. Semiconductor diodes are preferred due to their low-cost and compact design.
The energy harvesting circuit 30 may include power conditioning circuitry (e.g., control and conversion circuitry) and storage circuitry (e.g., a capacitor). For example, power conditioning circuitry may account for any pulsating magnitude in the DC output using, for example, a smoothing capacitor to lessen the variation (e.g., smooth) the raw output voltage waveform from the diode bridge. Output leads 32 may be provided to extract electrical power from the energy harvesting circuit 30. Power may be extracted directly from the energy harvesting circuit and/or from the storage device of the energy harvesting circuit. The harvested electrical energy may be used to power an electrical device (see
As shown in
An empty space or clearance 42 may be provided between adjacent piezoelectric generators 22 to allow each generator to move and flex independently of adjacent generators. In addition, an empty space or clearance 52 may be provided between each generator 22 and the enclosure 40 (see
As shown in
The mechanical stress or strain of the piezoelectric generators 22 produces a voltage that may be collected and stored by the energy harvesting circuit 30. Connecting each piezoelectric generator 22 to the energy harvesting circuit 30 via a diode bridge 24, reduces and/or eliminates the converse effect and the associated energy loss, thereby, improving energy harvesting efficiency of the device.
As shown in
As shown, the energy harvesting circuit 30 of
The embodiment of
Although three subsystems 60a, 60b, 60c are shown in
The closer the ratio of piezoelectric generators to diode bridge circuits is to 1:1, the greater the energy harvesting efficiencies and the lower the energy loss caused by the converse effect. A preferred embodiment of the present invention is to have a ratio of piezoelectric generators to diode bridges as close to 1:1 as possible. A more preferred embodiment of the present invention is to have a ratio of piezoelectric generators to diode bridges of 1:1.
In addition to powering a sensor and transmitter used to monitor a device, the multiple generator, energy harvesting system may also be used to self-power one or more features of device 82.
Device 82 may include low power devices/systems and/or autonomous devices/systems. For example, the multiple generator, energy harvesting system may be used with devices/systems developed using micro-electromechanical (MEMS) technologies and Nanotechnologies. These devices and systems may be very small and require little power. Scavenging energy from ambient mechanical energy (e.g., stress, strain, vibration, shock, heat, light, motion, bending, flexing, pushing, deflection, RF, EMI and the like) continually replenishes the energy consumed by the device/system thereby extending the lifespan of equipment 82 and enabling device 82 to be functional almost indefinitely.
Device 82 may include any device having moving parts and/or that is in motion, including for example: equipment, machines, wireless devices, portable electronic devices, smart sensors, remote sensors, inaccessible or hard to access devices, embedded devices, micro-devices and micro-systems, MEMS and NANO devices, and the like. The harvested energy may be used to power the entire device 82 and/or to power a portion of the power requirements of the device.
The AC generator may be used to produce energy that may be collected to power other, independent sensors (such as, for example, chemical sensors). Also, AC generators made of a piezoelectric material may act as sensors to perform some tasks (e.g., in lieu of a separate sensor for one or more of the sensors identified in step 78 above). Exemplary applications where a piezoelectric generator may also act as a sensor include pressure and accelerometer applications. Use of the piezoelectric generator as a sensor eliminates an extra system component (i.e., a separate and independent sensor device).
The AC generators may include piezoelectric and/or electrostrictive materials. Piezoelectric materials exhibit a distinctive property known as the piezoelectric effect. Piezoelectric materials come in a variety of forms including crystals, plastics, and ceramics. Piezoelectric ceramic materials are essentially electromechanical transducers with special properties for a wide range of engineering applications. When subjected to mechanical inputs, such as stress from compression or bending, an electric field is generated across the material, creating a voltage gradient that generates a current flow. The piezoelectric ceramic material energy harvesting system of the present invention collects this electrical response and stores it for future use in powering an electrical circuit and/or device. Further, the piezoelectric ceramic materials may also act as sensors in applications such as acceleration, pressure, flex or other motion.
The multiple generator, energy harvesting system preferably includes advanced, high charge piezoelectric ceramic fibers (PZT, PLZT, or other electro-chemistries), rods, foils, composites, or other shapes (hereinafter referred to as “piezoelectric ceramic fibers”). Piezoelectric ceramic fibers produced by the Viscose Suspension Spinning Process (VSSP) are one example of advanced, high charge piezoelectric ceramic fibers. VSSP is a relatively low-cost technology that can produce superior fibers ranging from about 10 microns to about 250 microns. Methods of producing ceramic fibers using VSSP are disclosed, for example, in U.S. Pat. No. 5,827,797 and U.S. Pat. No. 6,395,080, the disclosures of which are incorporated herein by reference in their entirety.
In a preferred embodiment, the power generators 22 comprise piezoelectric ceramic fiber and/or fiber composite materials developed and manufactured by Advanced Cerametrics, Inc. of Lambertville, N.J.
The piezoelectric ceramic fibers may be formed to user defined (shaped) composites based on specific applications and devices. The piezoelectric ceramic fibers may be disposed in, attached to, and/or embedded in the device to be monitored or housed in a separate enclosure that may then be mounted to a device to be monitored (see
The piezoelectric ceramic fibers are preferably positioned and oriented so as to maximize the excitement of the fibers. In one embodiment, the piezoelectric ceramic fibers may be oriented in a parallel array with a poling direction of the fibers being in substantially the same direction. As shown in
The energy generators 22 may also include processing of multilayer piezoelectric fiber composites. Processes for producing multilayer piezoelectric fiber composites are disclosed, for example, in U.S. Pat. No. 6,620,287, the disclosure of which is incorporated herein by reference in its entirety. As shown in
As shown in
A typical single, PFC may generate voltages in the range of about 40 Vp-p from vibration. A typical single, PFCB (bimorph) may generate voltages in the range of about 400 Vp-p with some forms reaching outputs of about 4000 Vp-p. As a way of illustration, VSSP produced piezo fibers have the ability to produce about 1 J of storable energy in about a 10 second period when excited using a vibration frequency of 30 Hz.
Preferably, the piezoelectric ceramic fibers are used as long as possible for the given application. Generally, the longer the fiber, the more active materials and hence more charge that may be generated for a given mechanical energy input. Accordingly, elongate fibers are preferably positioned and oriented to maximize the length of the fibers thus providing for increased amounts of harvested charge/power.
In addition, generally, the amount of active materials and hence charges increases as the number of fibers increases. As such, more charge may be generated for a given mechanical energy input by increasing the number and concentration of the fibers. For example, in one embodiment the fibers are positioned so that adjacent fibers are in contact with one another (although spacing may be provided between adjacent fibers). Accordingly, the fibers are preferably positioned and oriented to maximize the number and concentration of the fibers thus providing for increased amounts of harvested charge/power.
The piezoelectric energy harvesting system power scavenging capacity is determined, at least in part, by the number and type of piezoelectric generators. As a general rule, the more generators, the more power that may be generated. The piezoelectric generators power capacity and output power is determined, at least in part, by the number or amount of piezo fibers, the amount of active materials, the material(s) of the piezo fiber, the size and form factor of the fibers/composite, and the mechanical forces (stress and strain) and frequencies. Functional or useful amounts of power may be measured in microwatt, milliwatt and nanowatts levels.
Advantages and benefits of the multiple piezoelectric generator, energy harvesting system include: improved energy harvesting efficiencies; reduced energy loss due to the converse piezoelectric effect; greater power generation and storage from multiple generators; reduce/eliminate dependency on external power sources; reduce/eliminate dependency on batteries; eliminate battery replacement and battery disposal; make more portable by, for example, reducing/eliminating dependency on a power cord and charging station; reduce the size (smaller) of the portable electronic device by, for example, having the fibers conform to the shape of the device; reduce the weight (lighter) of the portable electronic device (piezoelectric ceramic fiber solutions typically weigh a few grams and not several ounces as are other types of power systems); reduce the cost (cheaper) of the portable electronic device; enhance the service life of the electronic device; improve the reliability of the portable electronic device; provide a more robust design (generally the more energy encountered the more power generated) (e.g., PFC's and PMC's can withstand a hammer strike without damage); reduce the maintenance and life cycle costs of owning and operating the portable electronic device; conversion of a higher percentage (up to about 70% or more) of energy from ambient mechanical sources to electrical power using piezoelectric active fibers; improved performance over an extended life cycle; improve the overall quality of the portable electronic device; improving the operating experience for the user of the portable electronic device.
While the present invention has been described in connection with the exemplary embodiments of the various Figures, it is not limited thereto and it is to be understood that other similar embodiments may be used or modifications and additions may be made to the described embodiments for performing the same function of the present invention without deviating therefrom. Therefore, the present invention should not be limited to any single embodiment, but rather should be construed in breadth and scope in accordance with the appended claims. Also, the appended claims should be construed to include other variants and embodiments of the invention, which may be made by those skilled in the art without departing from the true spirit and scope of the present invention.
