HK1069563B - Radio frequency identification tag with thin-film battery antenna - Google Patents

Description

Radio frequency identification tag having thin film battery for antenna

Technical Field

The present invention relates to Radio Frequency Identification (RFID) tags, and more particularly, to active RFID tags that include a battery and an antenna as integral components.

Background

Objects associated with inventory, product manufacturing, sales planning, and related operations create challenges for accurately monitoring object location and flow. There is a continuing need to determine the location of these objects and to track the relevant information of these objects. A tag device may be used that is suitably configured to be associated with various objects, including goods, articles, people or animals, or virtually any object that is mobile or fixed and animate or inanimate. One such tag tracking system is an electronic identification system, such as RFID. To track an object and store and obtain information about the object, an RFID tag is attached, connected, or in some way associated with the object.

Information about the object to which the RFID tag is attached can be written and stored in the memory of the RFID tag. The RFID tag will be detected in a suitable electromagnetic field and the information stored in the tag can be read and changed if necessary. Typically, RFID tag devices are completely passive (no attached power source) resulting in a small and lightweight package. However, passive tags can only operate over a small range, limited by the size of the field used to supply power and communicate with the tag.

Active RFID tags include a power source connected to the tag to increase the detectable range. However, RFID tags become more bulky and more expensive due to the added battery. RFID tags must be thin and flexible to remain practical in many applications. Larger and stiffer tags will reduce the usefulness of the tag by limiting the application.

Disclosure of Invention

The present invention provides an active radio frequency identification tag that includes a radio frequency identification chip disposed on a substrate. A battery disposed on the substrate is connected to the radio frequency identification chip. At least a portion of the battery forms an antenna of the radio frequency identification chip.

The antenna may be a dipole antenna adapted to operate at microwave frequencies. Alternatively, the antenna may operate at other frequencies than microwave frequencies, for example 8MHz or 13.56 MHz.

The battery may be a thin film battery. The thin film battery may be a lithium ion battery.

Typically, the battery includes two electrodes separated by an electrolyte, and the antenna is formed by at least one of the electrodes.

The antenna and the battery can be co-located on the substrate so that the battery does not occupy any additional space.

A method of powering a radio frequency identification tag includes providing a radio frequency identification tag including a radio frequency identification chip and a thin film battery disposed on a substrate, a portion of the battery forming an antenna of the radio frequency identification chip. And placing the radio frequency identification tag into a radio frequency identification electromagnetic field formed by the radio frequency identification reader. The radio frequency identification electromagnetic field powers the radio frequency identification chip as long as the power available from the electromagnetic field is greater than the power available from the battery. And the battery powers the rfid chip as long as the power available from the electromagnetic field is less than the power available from the battery.

The method for supplying power also charges the battery as long as the power available from the electromagnetic field is greater than the power available from the battery.

Objects, advantages and applications of the present invention will become apparent from the following detailed description of specific embodiments thereof.

Drawings

FIG. 1 is a top plan view of a prior art microwave RFID tag technology.

FIG. 2 is a top plan view of one embodiment of the present invention.

FIG. 3 is a schematic diagram of a prior art RFID chip.

FIG. 4 is a partial top perspective view of one embodiment of the present invention.

Fig. 5 is a schematic diagram of the series connection of the present invention.

Fig. 6 is a schematic diagram of the parallel connection of the present invention.

Fig. 7 is a top plan view of an alternative embodiment of the present invention operating at a frequency other than microwave frequencies.

Figure 8 is a schematic diagram of an alternative embodiment of the present invention operating at a frequency other than microwave frequencies.

Detailed Description

Referring to fig. 1, a conventional passive microwave RFID tag 1 is used herein to illustrate the present invention. The microwave RFID tag 1 comprises a microwave RFID chip 2 and a dipole antenna 4 mounted on a non-conductive polymeric substrate 6. If the microwave RFID tag 1 is made active, a battery will be added as an additional component of the tag. However, the battery will affect the operation of the antenna 4, requiring the battery to be placed at a distance from the antenna 4, resulting in a larger tag. Conventional active tags are typically stiff or inflexible due to the mounting requirements of the battery being spaced apart from the antenna.

Referring to fig. 2, an active microwave RFID tag 10, as described further below, provides a thin film battery 8 that forms the dipole antenna 4 shown in fig. 1. Since the battery and antenna are formed as a co-located structure, the substrate 6 can be made relatively more flexible than conventional active RFID tags. Flexible RFID tags provide more applications than larger, more rigid tags. Suitable thin film batteries, such as the solid state lithium ion batteries shown in U.S. patent publication No. 2001/0032666A1 and U.S. patent No. 5,338,625, are constructed of a substrate mounted cathode and anode separated by an electrolyte. In lithium ion batteries, lithium ions reside in the crystal structure of the anode material. During discharge, lithium ions flow through the electrolyte material and are absorbed by the crystal structure of the cathode material. The battery charge reverses the ion flow. Lithium ion batteries are suitable for microbatteries and are formed onto substrates using methods consistent with semiconductor processing. The materials of the anode, cathode and electrolyte are beyond the scope of this application and for more details, the reader is referred to the aforementioned 32666 application and the 625 patent. Suitable lithium ion batteries are available from Cymbet Corporation of Elk River, Minnesota. For example, a material having a density of 74mAh/cm can be obtained²Capacity and a minimum of 3V dc battery of 0.03mm thickness, and other configurations depending on the amount of area available for the antenna/battery. Even a small area thin film battery can provide enough power to operate a scattering RFID tag for several read cycles. The particular battery selected for forming the antenna may be other than a thin film lithium ion battery. The main limitation on the cell is that, at the operating frequency, at least either the anode or the cathode or both must be sufficiently conductive,to form an antenna usable with RFID chips.

Referring to fig. 3, a conventional RFID chip 2 includes an antenna terminal 9, as is well known in the art, the antenna terminal 9 receives RF energy acquired by an antenna in the RF interrogation field of an RFID reader. The AC to DC converter 11 provides power to the RFID chip 2 directly from the RF interrogation field. The data contained in the interrogation field RF energy is demodulated by a demodulator 12 contained in the chip 2. The information contained in the response of the chip 2 to the RFID interrogation field is modulated on the chip 14 and transmitted through the matched impedance 16 to the antenna terminal 9.

Referring to fig. 4, a series connection embodiment of the present invention is explained. The battery 17 is formed of an upper electrode 18a and a lower electrode 18b, and the battery 20 is formed of an upper electrode 19a and a lower electrode 19 b. The electrolyte is located between the upper and lower electrodes, and the substrate on which all objects are formed is not shown for simplicity. A decoupling impedance 22 is required to decouple the battery function from the antenna function as fully described below.

Referring to fig. 5, further details of the series configuration of fig. 4 are shown. The RFID chip 2 is connected to dipole antenna devices 24 and 25, which are part of the upper electrode 18a and the lower electrode 19b, respectively. One of the choices of the decoupling impedance 22 is an inductor 23, the inductor 23 decoupling or separating the RF and DC components to the wire terminal 9. The decoupling impedance is not limited to an inductor and may be any discrete or distributed circuit, or active circuit, capable of separating the RF and DC components of the incident energy received at the antenna. If the RF energy received by antenna terminal 9 is higher than the amount of power available from batteries 17 and 20, the RF field will power RFID chip 2 through AC/DC converter 11, as in conventional passive RFID. The incident RF field will also charge the batteries 17 and 20 when data is transferred to and from the chip 2. If the RF energy received by antenna terminal 9 is lower than the energy supplied from batteries 17 and 20, the batteries will power chip 2 during the data transfer. The effective range of an active tag constructed in this manner will be significantly increased compared to conventional passive RFID tags. As long as the tag is in the vicinity of the RFID reader, the batteries 17 and 19 will charge and the tag will behave like a passive RFID tag, and as the tag is further from the reader, the tag will behave like an active RFID tag.

Referring to fig. 6, an alternative embodiment of the parallel connection of the present invention is illustrated. The cell 26 is formed of an upper electrode 28a and a lower electrode 28b, and the cell 27 is formed of an upper electrode 29a and a lower electrode 29 b. The antenna element 30 is part of the upper electrode 28 a. The antenna element 32 is part of the lower electrode 29 b. Inductors 33 and 34 perform a decoupling impedance function to separate the RF and DC components of antenna elements 30 and 32. Similar to that described above for fig. 5, if the RF energy received by antenna terminal 9 is higher than the amount of power available from batteries 26 and 27, the RF field will power RFID chip 2 through AC/DC converter 11. The RF field will charge the batteries 26 and 27 when data is transferred to and from the chip 2. If the RF energy received by antenna terminal 9 is lower than the energy supplied from batteries 26 and 27, the batteries will power chip 2 during the data transfer.

The present invention is described with respect to the specific embodiments shown in fig. 4-6 using microwave RFID tags. Microwave RFID tags typically operate at RF frequencies above about 1GHz, and the present invention is readily adaptable to RFID tags operating at other frequency ranges.

Referring to FIG. 7, an RFID tag 40 is illustrated that operates at a frequency other than microwave, such as the conventional RFID frequencies of about 8MHz and about 13.56 MHz. The RFID tag 40 includes an RFID chip 2, an antenna element 42, and a substrate 44. According to the present invention, the antenna element 42 also functions as a battery for the RFID chip 2.

Referring to fig. 8, the RFID chip 2, which is functionally identical to the RFID chip shown here, is used, for example, with reference to any conventional RFID chip. It should be understood that the exact RFID chip used in the present invention differs structurally from the RFID chip 2 described herein. The antenna element 42, which is constructed on a substrate 44, forms an electrode of the battery 44. A second electrode, separated from the first electrode by an electrolyte, both formed on the substrate 44, forms the complete cell 44. The particular electrodes selected for the antenna element 42 may vary from those shown. Decoupling inductor 46 is used to separate the DC power supplied by battery 44 onto RFID chip 2 from the RF data incident on antenna terminal 9. As with the other embodiments herein, the decoupling impedance 46 can be implemented in a variety of ways. As with microwave tags, the RFID chip 2 will be powered by the greater of the incident RF energy or power supplied by the battery 44. If the RF energy is high enough, such as when the tag is near an RFID reader, the battery 44 will charge while the data is being transferred.

It will be understood that variations and modifications may be made without departing from the scope of the invention. It is also to be understood that the scope of the invention is not to be construed as limited to the specific embodiments disclosed herein, but is to be construed only in accordance with the following claims, which are read in light of the disclosed documents.

Claims (11)

1. An active radio frequency identification tag comprising:

a radio frequency identification chip disposed on the substrate;

a battery connected to the radio frequency identification chip, the battery disposed on the substrate, wherein at least a portion of the battery forms an antenna of the radio frequency identification chip;

wherein the radio frequency identification electromagnetic field powers the radio frequency identification chip as long as the power available from the electromagnetic field is substantially greater than the power available from the battery, and the battery powers the radio frequency identification chip as long as the power available from the electromagnetic field is substantially less than the power available from the battery.

2. The tag of claim 1 wherein the antenna is a dipole antenna adapted to operate at microwave frequencies.

3. The tag of claim 1, wherein the antenna operates at 8MHz or 13.56 MHz.

4. The label of claim 1 in which the battery is a thin film battery.

5. The label of claim 4 in which the thin film battery is a lithium ion battery.

6. The label of claim 5 in which the battery includes two electrodes separated by an electrolyte, the antenna being formed by at least one of the electrodes.

7. The tag of claim 1 wherein said antenna and said battery are substantially co-located on a substrate.

8. The label of claim 1 in which the substrate is relatively flexible.

9. The tag of claim 1, wherein the battery is charged as long as the power available from said radio frequency identification electromagnetic field is greater than the power available from said battery.

10. A method of powering a radio frequency identification tag, comprising:

providing a radio frequency identification tag comprising a radio frequency identification chip disposed on a substrate and comprising a thin film battery, a portion of said battery forming an antenna for said radio frequency identification chip;

placing the radio frequency identification tag into a radio frequency identification electromagnetic field formed by a radio frequency identification reader, wherein the radio frequency identification electromagnetic field powers the radio frequency identification chip as long as power available from the electromagnetic field is greater than power available from the battery, and wherein the battery powers the radio frequency identification chip as long as power available from the electromagnetic field is less than power available from the battery.

11. The method of claim 10, further comprising charging a battery as long as the power available from the radio frequency identification electromagnetic field is greater than the power available from the battery.