Patent Publication Number: US-2009219139-A1

Title: Power Harvesting for Actively Powered RFID Tags and Other Electronic Sensors

Description:
FIELD OF THE DISCLOSURE 
     The present disclosure relates to Radio Frequency Identification systems, and more specifically to material conveyance devices with actively powered Radio Frequency Identification tags. 
     BACKGROUND 
     To support the worlds growing consumer market, there is an unprecedented need to track the flow of products as they are manufactured in one country, transported across the world, and then consumed in another country. 
     Traditionally, manufactures, distributors, and retailers have relied on bar code labels to track their products and manage their inventories. While barcode labels have many advantages including low cost, they also have several disadvantages. For example, the product must be in a specific orientation and the reader must be in close proximity for the barcode label to be read. Moreover, printed bar codes labels are limited by the amount of data that they can store. 
     Radio Frequency Identification (RFID) provides the ability to store and retrieve significant amounts of information about a product. Moreover, the information can be retrieved at high transfer rates, at significant distances from the product, and from multiple tags simultaneously. As a result, Radio Frequency Identification tags provide a unique ability to track a product from the time it is manufactured until the time it is consumed. 
     Radio frequency identification relies on storing and retrieving data using Radio Frequency Identification (RFID) tags. RFID tags are typically attached or incorporated into products for the purpose of identifying and tracking the product (e.g., a compact disk, a book, or clothing, to name a few). RFID tags typically include an integrated circuit and an antenna. The integrated circuit stores and processes data, modulates and demodulates an RF signal, and in some instances performs other functions (e.g., monitor the products transportation environment). Meanwhile, the antenna receives signals that have been transmitted by a host device and transmits signals which are used to identify and track the RFID tag. 
     RFID tags are generally grouped into three categories: passive, active, and semi-passive, also know as battery assisted. 
     Passive tags do not have an internal power source and instead rely on inducing an electrical current in the tags antenna from the readers&#39; incoming RF signal. Passive tags have typically limited transmission distances (i.e., four inches to a few feet) depending on the tags operating frequency and the antenna design. 
     Semi-passive tags are similar to active tags in that they have their own power source, but the battery only powers the micro-chip and does not broadcast a signal. Semi-passive tags reflect back the readers RF energy, just like a passive tag. 
     Active tags require some type of power source, typically a battery, to power the micro-chip and broadcast the signal to the reader. Active tags are typically much more reliable than passive tags do to their ability to communicate with the reader for longer periods of time. Active tags also transmit at higher power levels than passive tags, which allows them to be read at much greater distances (i.e., up to 1500 feet). Given their greater reliability, greater range, and longer communications time, active tags have many advantages over passive tags. 
     However, given the time it takes to manufacture, distribute, and sell a product, an active tag may run out of battery power before the product has reached its final destination or has been sold. Accordingly, there is a need for an active RFID tag with a longer life. 
     SUMMARY 
     Techniques for actively powering a radio frequency identification tag are described herein. 
     In one implementation, a material conveyance device includes a structure for transporting material and a radio frequency identification device. The radio frequency identification device includes an energy storage device for supplying electrical energy to a radio frequency transceiver, a power generation device for supplying electrical energy to the energy storage device, and a power regulator for regulating the electrical energy generated by the power generation device. 
     In another implementation, a method for tracking material being transported by a material conveyance device may include receiving an interrogation signal and transmitting a signal in response to the interrogation signal, the signal being transmitted by the material conveyance device in response to the interrogation signal. The material conveyance device may include a power generation device for converting kinetic energy into electrical energy and a radio frequency transceiver for receiving the interrogation signal and transmitting the signal using electrical energy generated by the power generation device. 
     Other systems, methods, and/or devices according to other embodiments will be or become apparent to one with skill in the art upon review of the following drawings and detailed description. It is intended that all such additional systems, methods, and/or devices be included within this description, be within the scope of the present disclosure, and be encompassed by the accompanying claims. 
     This summary is not intended to identify the essential features of the claimed subject matter, nor is it intended to determine the scope of the claimed subject matter. 
    
    
     
       BRIEF DESCRIPTIONS OF THE DRAWINGS 
       The disclosure is made with reference to the accompanying figures. In the figures, the left most reference number identifies the figure in which the reference number first appears. The use of the same reference numbers in different figures indicates similar or identical terms. 
         FIG. 1  illustrates a radio frequency identification tag with active power generation. 
         FIG. 2  illustrates a system for tracking material being transported by a material conveyance device. 
         FIG. 3  illustrates a radio frequency identification tag which has been integrated into a wheel. 
         FIG. 4  illustrates a device for converting linear motion into electrical energy. 
         FIG. 5  illustrates a device for converting angular motion into electrical energy. 
         FIG. 6  illustrates a method for determining the location of a material conveyance device. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure relates to Radio Frequency Identification systems, and more specifically to material conveyance devices with actively powered RFID tags. 
     RFID tags are used in a variety of different applications including: passports, transportation payment systems (e.g., electronic passes), access control (e.g., smart cards), animal identification (e.g., implantable chips), and item tracking. However, supply chain management is potentially one of the most promising applications for RFID tags. Supply chain managers can use RFID tags to track products as they are being manufactured, distributed, and sold. Moreover, RFID tags can be used to quickly and efficiently perform inventories and conduct audits. 
     A RFID system is typically composed of tags and tag readers. A tag reader communicates with the tags by either selecting specific tags to communicate with, probing the surrounding area for tags, or in the case of tags with high level functionality (i.e., environmental monitoring), querying the tag regarding its environmental conditions. 
       FIG. 1  illustrates an actively powered RFID tag  100  in accordance with an embodiment. The RFID tag  100  could be attached to a product (e.g., library book, apparel, access badge, or pharmaceutical item, to name a few), a material conveyance device (e.g., cart, pallet, dolly, roll-a-way, etc.), or any other suitable device or component. 
     The RFID tag  100  may include an integrated circuit  102 , an antenna  104  for communicating with a tag reader, and a power generator  106  for powering the tag  100 . The integrated circuit  102  contains a memory device  108 , a micro-processor  110 , a power regulator  112 , an energy storage device  114 , and an RF transceiver  116  for communicating with a tag reader. 
     The antenna  104  could be in a number of configurations and sizes depending upon the specific application and frequency used to communicate with the tag reader. For example, the RFID tag  100  may employ a dipole antenna when transmitting at a high frequencies (e.g., 13.56 MHz). 
     The power generator  106  converts mechanical energy into electrical energy which maybe used to recharge the energy storage device  114  and/or power the tag  100  directly. 
     Generators, alternators and other power generating devices typically employ electromagnetic induction to convert mechanical energy into electrical energy. Normally, a rotating magnet, typically called the “rotor”, turns within a stationary set of conductors wound in the shape of a coil, typically called the “stator”. As the rotor turns relative to the stator, a magnetic field cuts across the stators conductors and generates an electrical current. The alternating current (AC) output may then be presented to a diode bridge which rectifies the AC output to a direct current (DC) output. 
     The power generator  106  could employ conventional electromagnetic induction to convert mechanical energy into electrical energy. This could include the rotational energy created by a rotating wheel (e.g., castor, truck, or other wheel like device), linear energy created by moving mass (e.g., mass suspended by spring), angular energy also created by a moving mass (e.g., mass suspended by pendulum), or any other suitable source of mechanical energy. Alternatively, the generator could employ piezoelectric materials (e.g., crystals and ceramics) to generate an electrical potential by subjecting the piezoelectric materials to mechanical stress. 
     Having discussed the antenna  104  and power generator  106 , the discussion will now shift to the integrated circuit  102 . As noted, the integrated circuit  102  contains a memory device  108 , a micro-processor  110 , a power regulator  112 , an energy storage device  114 , and an RF transceiver  116 . 
     The memory device  108  stores information regarding the RFID tag  100 , as well as the item that the RFID tag  100  is attached (e.g., product, component, assembly, or material conveyance device, to name a few). For example, the memory device  108  could store a unique identification number associated with the tag, the quantity of energy stored by the storage device  114 , the type and quantity of material being conveyed, the material&#39;s lot number, the material&#39;s expiration date, the transport environment, or any other suitable data or information. 
     The micro-processor  110  manages the communications with the reader, monitors the state of the energy storage device  114 , and reads and writes data to memory  108 . For example, if the energy level of the storage device  114  falls below a threshold value, the micro-processor  110  may warn the tag reader that it may no longer be able to communicate with the tag reader. Alternatively, if for some reason the power generator  106 , power regulator  112 , or storage device  114  were not operating properly, micro-processor  110  may warn the tag reader of an existing or impending component failure. 
     The discussion will now shift to the power regulator  112 . A generator&#39;s output voltage generally varies directly with the speed that it rotates. Since material conveyance devices are typically moved about at different speeds. A generator which is driven by the movement of the conveyance device will rotate at various speeds, and accordingly its output voltage will vary. A voltage regulator is designed to maintain a constant voltage by comparing the actual output voltage to a fixed reference voltage. If the output voltage is too low, the voltage regulator produces a higher voltage. Conversely, if the output voltage is too high, the voltage regulator produces a lower voltage. In this way, the output voltage is held at a constant voltage. Typical voltage regulators may include linear regulators, switching regulators, silicon controlled rectifiers, or a combination of these (e.g., hybrid regulator). 
     The power regulator  112  regulates the power produced by the power generator  106  to ensure that the energy storage device  114  is charged properly and not damaged. For example, if the power generator  106  produced an AC current and the energy storage device  114  was a battery, the power regulator  112  could be designed to limit the current by employing a limiting resistor and perform an AC to DC conversion by employing a diode bridge. The power regulator  112  then trickle charges the energy storage device  114  to ensure that the energy storage device  114  is not damaged during charging. 
     The energy storage device  114  could be a battery, a capacitor, or any other suitable electrical energy storage device. Ideally, the storage device  114  is rechargeable so that the RFID tags  100  operational life can be extended through recharging. 
     The RF transceiver  116  receives and transmits signals in response to the tag reader. The RF transceiver  116  may include a wake-up circuit for waking up the RFID tag  100  in response to signals from the tag reader, a receiver for receiving and decoding signals from the receiver, and a transmitter for transmitting signals to the tag reader. 
     The efficiency of a warehouse or production environment could be significantly improved if the materials in the warehouse or production environment could be easily tracked and identified. Specifically, a robust material tracking and identification system could ensure that materials are not misplaced or lost, that they arrive at the proper location on time, and that the proper amount of material is on hand. 
       FIG. 2  illustrates a system  200  for tracking the movement of material being transported by one or more material conveyance device(s). The system  100  may include one or more antenna(s)  202 , one or more tag reader(s)  204 , a host computer  206 , and one or more material conveyance device(s) with actively powered RFID tags  208 - 212 . 
     The antenna(s)  202  transmit and receive signals from the material conveyance device(s)  208 - 212 . The two illustrated antennas are connected to a single tag reader  204 , however they could be connected to a separate or independent tag reader(s)  204  depending upon the specific implementation. The antenna(s)  202  are typically positioned or installed to cover a specific region or zone where the material conveyance device(s)  208 - 212  are located or used (e.g., region of a warehouse or production line). For example, one or more antenna(s)  202  could be positioned in a warehouses entry way, walkway, pass through, or other high traffic area so that when a conveyance device(s)  208 - 212  enters or leaves the warehouse its presence is detected. 
     The tag reader  204  detects and communicates with the conveyance device(s)  208 - 212 , and determines the distances between the conveyance devices  208 - 212  and the antenna(s)  202 . For example, the tag reader  204  may transmit an interrogation signal to one or more conveyance device(s)  208 - 212  and then listen for a response. The conveyance device(s)  208 - 212  may respond with their unique identification code. The tag reader  204  may receive the unique identification code and determine the identity of the one or more conveyance device(s)  208 - 212  using lookup table or data base. The lookup table or data base could include other types of information such as: the type and quantity of material being conveyed, the conveyance devices destination, whether the conveyance device is authorized to be in the area, or other information of value. Alternatively, the material conveyance device(s)  208 - 212  and tag reader  204  may employ digital signal processing to communicate directly with one another (e.g., amount of energy stored in energy storage device, status of the power generator, power regulator, and energy storage device). In an alternate embodiment, the conveyance device(s)  208 - 212  could initiate the communication by transmitting a signal to the tag reader  204  (e.g., on a periodic basis or when it senses movement) and the tag reader  204  could respond. 
     The host computer  206  communicates with the tag reader  204  through a wired or wireless communications interface. The host computer  206  collects, organizes, and stores the data collected by the tag reader  204 . The host computer  206  could be a laptop computer, a personal computer, a server, a work station, a hand held device, or any other suitable computing device. The host computer  206  may also communicate with other computing devices over a communications network, such as a local area network (LAN), a wide area network (WAN), the internet, or any other suitable communications network. 
     The distance between the individual conveyance device(s)  208 - 212  and antenna(s)  202  can be calculated based on the time it takes for a signal to be transmitted to the conveyance device  208 - 212  and when a response is received by the tag reader  204 . For example, the tag reader  204  could interrogate each of the conveyance device(s)  208 - 212  using each of it&#39;s antennas  202 , and based on the transmission time determine the distance between each of the conveyance devices  208 - 212  and the antennas  202 . The tag reader  204  could then triangulate the various distances to calculate the position of each conveyance device  208 - 212 . 
     In an alternate embodiment, the material conveyance device(s)  208 - 212  include one or more sensors (e.g., proximity sensors, contact sensors, mass sensors, thermal sensors, to name a few) to determine if individual parts, components, or assemblies have been consumed or removed from the material conveyance device  208 - 212 . The sensed information could be stored for subsequent transmission or broadcast real-time by the material conveyance device(s)  208 - 212  to the tag reader  204 . The tag reader  204  could compile and processes the information and relay it to the host computer  206 . Alternatively, the tag reader  204  could convey the raw information to the host computer  206  and the host computer  206  could compile and process the information. The host computer  206  could then send the processed information over a LAN, a WAN, a wireless communications network, a phone line, or any other suitable communications network, to part suppliers, material schedulers, or material buyer for further action. 
       FIG. 3  illustrates an actively powered RFID tag  300  that could be used to track material as it conveyed from one location to another. The RFID tag  300  includes a wheel assembly  302 , a radio frequency identification RFID device  304  and one or more magnets  306  that are attached to a wheel  308 . The RFID tag  300  could be attached to material conveyance devices which are used to transport materials, products, or assemblies, just to name a few. 
     As the material conveyance device  208 - 212  is moved from one location to another, the wheel  308  rotates and the magnet(s)  306  sweep past the RFID device  304 . The rotating magnets  306  emit an electromagnetic field which induces an electrical current in a wire or coil residing in the RFID device  304 . The AC output maybe rectified (converted) to a DC output by a diode bridge and the DC output regulated based on the requirements of the RFID device  304 . The regulated DC output is then used to either recharge an energy storage device residing in the RFID device  304  or directly power the device. Alternatively, the magnet(s)  306  could be stationary and the RFID device  304  could rotate relative to the magnet(s) (e.g., the RFID device  304  could be coupled to wheel  308 ). 
     In addition to rotational motion, linear and angular motion could be converted into electrical energy and used to power the RFID device  304 .  FIGS. 4 and 5  illustrate electrical generators which maybe used to covert linear and angular motion/vibration into electrical energy. 
       FIG. 4  illustrates a linear motion generator  400  which includes a magnetic mass  402  (e.g., rotor), one or more stationary coils  404  (e.g. stator), and a spring  406 . Like a conventional electrical generator, the linear motion generator  400  converts the magnetic masses  402  linear motion into electrical energy by inducing an electric current in the stationary coils  404 . For example, the linear motion generator  400  could be attached to a material conveyance device  208 - 212  such that as it is moved from one location to another, the natural motion and vibration of the conveyance device  208 - 212  causes the magnetic mass  402  to undulate up and down. This in turn causes the masses  402  magnetic field to move up and down across the stationary coils  404  and generate an electrical current. 
       FIG. 5  illustrates an angular motion generator  500  which includes a magnetic mass  402 , one or more stationary coils  404 , and a tether  502  for maintaining the mass  402  in the correct angular position. Like the linear motion generator  400 , the angular motion generator  500  converts the magnetic masses  402  linear motion into electrical energy by inducing an electric current in the stationary coils  404 . In this instance, the angular motion generator  500  would also be attached to a material conveyance device  208 - 212 , and the conveyance device  208 - 212  natural motion (e.g., start moving, stop moving, and change of direction) causes the angular motion generator  500  to swing back and forth and generate an electrical current. 
     Piezoelectric materials (i.e., crystals and ceramics) have the ability to generate an electrical potential in response to mechanical stress. Specifically, when a piezoelectric material is mechanically stressed, there is a separation of electric charge across the materials crystal lattice which induces a voltage across the material. This piezoelectric effect is reversible; accordingly if a piezoelectric material is subjected to multiple stress cycles it will generate electrical energy. 
     Referring back to  FIG. 5 , in an alternate embodiment the tether  502  could be replaced with components made of a piezoelectric material. With the tether end  504  rigidly attached, any motion of the mass  402  would induced stress in the piezoelectric material (i.e., tether) which in turn generate electrical energy. 
       FIG. 6  illustrates a method for determining the location of a material conveyance device in accordance with an embodiment. 
     An actively powered RFID tag which has been attached to a material conveyance device is programmed, at block  602 . The programming could be performed by a hand held device, a personal computer, a server, or any other suitable programming device. The programmed data or information may include a unique identification code, the type and quantify of material being conveyed, the shipper and recipient of the material, the transportation route or delivery location, or any other information of value. 
     The material conveyance device is then moved to a new location, at block  604 . The new location could be a warehouse, a manufacturing area, a stock room, a material staging area, or any other suitable location. When the conveyance device enters the new location, a tag reader could transmit an interrogation signal. Alternatively, the RFID tag could periodically transmit a signal notifying the tag reader of its presence. 
     The material conveyance device receives the interrogation signal from the tag reader, at block  606 . The interrogation signal could be a query asking for the conveyance devices unique identification number or it could simply be a command for the material conveyance to respond. 
     The material conveyance device then responds to the interrogation signal, at block  608 . The response could include the conveyance devices unique identification number, the status or health of the RFID tag, the type and quantity of material being conveyed, the material conveyance devices destination, where the material conveyance devices route, or any other information of value. 
     If the material conveyance devices exact location is needed (i.e., located in a large warehouse or production facility); it can be determined by triangulating the distances between the various antennas and the conveyance device, at block  610 . 
     Although devices and methods for conveying materials have been described in language specific to certain features and/or methodological acts, it is to be understood that the disclosure is not limited to the specific features or acts described. Rather, the specific features and acts are disclosed as exemplary forms of implementing the disclosure.