US 20070188053 A1
Embodiments of an injection molded energy harvesting device are described. In one embodiment, a piezoelectric cantilever is produced via an injection molding method to harvest vibration energy from an environment being sensed. The cantilever device consists of a piezoelectric material member, a proof mass of high density material coupled to the piezoelectric member, and a leadframe for electrical connection. The piezoelectric member is electrically attached to the leadframe with a standard connecting material. The entire assembly is then injection molded with plastic. The plastic encased piezoelectric member forms a cantilever that generates electricity in response to vibration exerted on the proof mass.
1. A device comprising:
a plurality of conductive leads;
a substrate strip coupled to one or more conductive leads of the plurality of conductive leads;
a piezoelectric material coupled to the substrate strip to form a piezo bimorph element;
a proof mass coupled to the bimorph element;
a body coupled to the piezo bimorph element and formed by an injection molding process that encases at least a portion of the piezo bimorph element and at least a portion of the one or more conductive leads.
2. The device of
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8. A system comprising:
a microsystem sensor including a sensor circuit, a transmitter circuit coupled to the sensor circuit, and an antenna coupled to the transmitter circuit; and
a power circuit coupled to the microsystem sensor, the microsystem sensor including a plastic body, a piezo bimorph strip coupled to the plastic body, and a proof mass coupled to the plastic body, the plastic body formed by an injection molding process configured to encase the plastic body and leave a portion of the piezo bimorph strip exposed.
9. The system of
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17. A method comprising:
providing a lead frame comprising paired conductive members connected to rail elements;
attaching adhesive to one or more conductive members of the lead frame;
attaching a piezoelectric element at least one conductive member of the one or more conductive members of the lead frame;
attaching a proof mass to a first portion of piezoelectric element;
forming an injection molded plastic body around a second portion of the piezoelectric element; and
cutting the rail elements of the lead frame from the plastic body to form separate piezoelectric devices.
18. The method of
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Embodiments of the invention relate generally to miniaturized electrical systems, and specifically to injection molded devices for harvesting energy.
The use of miniaturized electrical systems (microsystems) on the order of 1 cc has been proposed to provide distributed sensing capability. Microsystem sensors can be used to monitor various environmental and operational conditions and transmit signals back to a host receiver for many different applications, such as industrial monitoring, security applications, weather prediction, and so on. The design and implementation of such devices and systems requires overcoming several challenges, such as designing small and robust packaging and providing adequate transmitter power. A major consideration in designing such systems remains providing adequate electrical power, and for many microsystems, this challenge remains a significant obstacle. In general, current miniature battery technologies cannot store enough energy to power these systems for long periods of time, such as on the order of months. Another disadvantage of battery use is that many sensor applications involve harsh or limited access environments that can limit or disable battery performance and/or render battery maintenance virtually impossible.
One approach to overcome the problem of providing enough battery power for microsystems is to extract energy from the surrounding environment. This approach, which is called energy harvesting (or scavenging) eliminates the need for an external or stored power supply, thus allowing a system to be made fully autonomous, that is, one that requires no external power connections or maintenance. As long as the source of environmental energy is available, an energy harvesting microsystem can remained fully powered, virtually non-stop, while providing information to the user.
Several techniques have been proposed and developed to extract energy from the environment. The most common available sources of energy are vibration, temperature, and stress (pressure). In many environmental applications, vibration energy may be the most readily available and easiest to convert into electricity. In general, vibration energy can be converted into electrical energy using one of three techniques: electrostatic charge, magnetic fields, and piezoelectric materials. Piezoelectric generation of electricity from vibration energy typically represents the most cost-effective approach, as the electrostatic and magnetic techniques usually require more extensive design, packaging, and integration work to adapt to particular applications.
Embodiments of the present invention are illustrated by way of example and not limitation in the figures of the accompanying drawings, in which like references indicate similar elements and in which:
Embodiments of an injection molded energy harvesting device are described. In one embodiment, a piezoelectric cantilever is produced via an injection molding method to harvest vibration energy from an environment being sensed. The cantilever device consists of a piezoelectric material member, a proof mass of high density material coupled to the piezoelectric member, and a leadframe for electrical connection. The piezoelectric member is electrically attached to the leadframe with a standard connecting material. The entire assembly is then injection molded with plastic. The plastic encased piezoelectric member forms a cantilever that generates electricity in response to vibration exerted on the proof mass. Such a device can be used to provide power to sensor systems deployed in various vibration intensive environments, such as tire pressure monitoring systems, seismic systems, and the like.
In the following description, numerous specific details are introduced to provide a thorough understanding of, and enabling description for, embodiments of an injection molded energy harvesting device. One skilled in the relevant art, however, will recognize that these embodiments can be practiced without one or more of the specific details, or with other components, systems, and so on. In other instances, well-known structures or operations are not shown, or are not described in detail, to avoid obscuring aspects of the disclosed embodiments.
Microsystem sensors can be used in a variety of different environments to provide signals that represent one or more characteristics or parameters of the environment being sensed. One critical consideration in the installation of Microsystems is providing power to the sensor. Many environments in which microsystem sensors are deployed either produce or are subject to vibrations. In one embodiment, an energy harvesting device uses vibration energy present in an environment being sensed to produce electricity to power the sensor.
Automotive applications represent one field where vibration energy from motion of the vehicle in use is readily present and can be used to provide power to sensor networks in a car. In one embodiment, an energy harvesting device is used in a tire pressure sensing module that is deployed inside of an automobile, truck or other vehicle or machine tire to sense the air pressure inside of the tire and transmit the air pressure information to a control or processor module that can report low or abnormal tire pressures. The rubber carcass of a tire as it rolls along a surface produces vibrations that can be converted into electrical energy.
In one embodiment, the energy harvesting device for use with a tire pressure sensor comprises a piezoelectric bender that includes a piezoelectric bimorph structure. Piezoelectric materials are materials that convert vibration energy into electric energy. A single piece of piezoelectric material by itself is generally a unimorph structure that exhibits stress in equal and opposite directions under transverse loading. Consequently, the output voltage will be zero in the case of a sinusoidal vibration input. A bimorph structure has stress in one direction under a transverse load, and therefore outputs a non-zero voltage under the application of sinusoidal vibration. To provide adequate power output in a wide variety of different vibrating environments, a bimorph structure is generally preferred.
In an alternative embodiment, the bimorph strip can be implemented as a piezo/metal or piezo/piezo element, or a piezo stack comprising three or more elements in a sandwich array.
In one embodiment, the piezoelectric bender is constructed using plastic injection molding and leadframe construction techniques to facilitate cost-effective manufacture.
Depending upon the vibrational environment the piezoelectric device is subject to, a proof mass may need to be attached to the piezoelectric bimorph. In one embodiment, a proof mass, such as proof mass 208 in
Once the piezoelectric member is attached to the lead frame conductors, and any proof mass is attached to the piezoelectric member, the structure is partially encased plastic using an injection mold process, as shown in block 308 of
For the embodiment illustrated in
In one embodiment, the proof mass is attached to the exposed portion of piezoelectric element and is left exposed after the injection molding process 308. Alternatively, the proof mass can be also be encased within the injection molded plastic body.
Various different types of leadframes can be used in conjunction with embodiments of the piezoelectric bender. Standard lead frames, such as that shown in
An energy harvesting device utilizing a bimorph piezoelectric bender in an injection molded body can be used in various different applications that have long-term energy requirements. In one embodiment, the piezoelectric bender is used in an intelligent tire system to provide power to a circuit that comprises a pressure sensor and transmitter circuit for mounting within the wheel or rubber portion of the tire.
Although embodiments have been described in relation to a tire pressure sensor system, it should be understood that these or similar embodiments, can be utilized with respect to a wide variety of other microsystems involving sensors or devices that require and can operate at relatively low power. These include motion sensors, infrared sensors, leak detectors, lubricant monitors, and other applications that have a characteristic that can be measured and feature a vibrating environment. For example, sensors using an injection molded piezoelectric bender for electrical power can be mounted within a vehicle fuel tank to monitor fuel quantity or quality, or within an engine crankcase to monitor oil quantity and quality. Embodiments of injection molded energy harvesting device can be applied to many different industries, such as automotive or aerospace applications, industrial machinery, seismic applications, and oceanographic applications; among others.
The sensors used in conjunction with the injection molded energy harvesting device can be equipped with any suitable sensing and transmission circuitry, such as RF, microwave, or similar wireless communication means. Alternatively, some applications may be suitable for wired sensor communication.
Aspects of the injection molded energy harvesting device described herein may be implemented as functionality programmed into any of a variety of circuitry, including programmable logic devices (“PLDs”), such as field programmable gate arrays (“FPGAs”), programmable array logic (“PAL”) devices, electrically programmable logic and memory devices and standard cell-based devices, as well as application specific integrated circuits.
Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise,” “comprising,” and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in a sense of “including, but not limited to.” Words using the singular or plural number also include the plural or singular number respectively. Additionally, the words “herein,” “hereunder,” “above,” “below,” and words of similar import refer to this application as a whole and not to any particular portions of this application. When the word “or” is used in reference to a list of two or more items, that word covers all of the following interpretations of the word: any of the items in the list, all of the items in the list and any combination of the items in the list.
The above description of illustrated embodiments of the energy harvesting device for use with microsystem sensors is not intended to be exhaustive or to limit the embodiments to the precise form or instructions disclosed. While specific embodiments of, and examples for, the energy harvesting device are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the described embodiments, as those skilled in the relevant art will recognize.
The elements and acts of the various embodiments described above can be combined to provide further embodiments. These and other changes can be made to the energy harvesting device in light of the above detailed description.
In general, in the following claims, the terms used should not be construed to limit the described system to the specific embodiments disclosed in the specification and the claims, but should be construed to include all operations or processes that operate under the claims. Accordingly, the described system is not limited by the disclosure, but instead the scope of the recited method is to be determined entirely by the claims.
While certain aspects of the energy harvesting device are presented below in certain claim forms, the inventor contemplates the various aspects of the methodology in any number of claim forms. Accordingly, the inventor reserves the right to add additional claims after filing the application to pursue such additional claim forms for other aspects of the described system.