RFID antenna structure for increased range when coupled with a mobile device

An RFID tag device with an RFID antenna assembly that increases transmission range of the RFID tag device when adhesively coupled to a mobile device. The RFID tag device includes a RF interface that operates at a first RF frequency, a controller coupled to the RF interfaces, and the RFID antenna assembly. The RFID antenna assembly includes a first and a second dipole elements, each shaped as a half rectangle with an additional segment joining the respective element to a tuning element. The RFID antenna also includes a tuning element, which is a loop antenna, connecting the RF interface to the controller. A structure of the RF antennal assembly, when the RFID tag device is coupled to a mobile device, causes the mobile device to function as a reflector to increase gain of the RFID antenna assembly thereby improving transmission range.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to data tag devices and more particularly to radio frequency data tag devices used to conduct transactions.

BACKGROUND

As a result of the prevalence of mobile devices, such as smart phones, tablet devices, and others, there has been an increased interest in using such devices to automate a variety of tasks not traditionally associated with mobile devices. Another field that has gained in interest is radio frequency identification (RFID) data tag devices. RFID tag devices are used to store information, such as an identifier, that can be read at a distance by a reader. The reader transmits a signal through the air, and, upon receiving the signal, the RFID tag device responds by transmitting data to the reader. RFID tag devices are used in numerous applications, and can be passive or active, referring to how the RFID tag device is powered.

One field where RFID technology is presently used is for transactions. An RFID tag device identifier can be associated with an account, and money transferred from the account to an authorized recipient upon reading information from the RFID tag device in an authorized manner. One popular use of RFID technology for transactions is in vehicular tolls. A vehicle operator purchases a toll tag that includes an RFID tag device, having an identifier in the RFID tag device. The identifier is associated with a toll account for a toll authority. The vehicle operator places the toll tag in a vehicle, and upon passing through a toll gateway where the RFID tag device information is read, a toll fee is debited from the account associated with the toll tag. The toll tag devices are often mounted in the vehicle in a permanent or semi-permanent manner. Consequently, the RFID tag device cannot easily be moved from one vehicle to another, such as if the owner of the RFID tag device rents a vehicle. Furthermore, the user is not able to interact with the RFID tag device. In order to see account activity, the user must access account information, such as via a web site for such accounts.

Attempts to integrating an RFID tag with a mobile device presents a number of technology based problems. Specifically, the placement of an RFID tag near a ground plane, such as one represented by a mobile device, results in a significant performance degradation of the RFID tag such that the transmission distance of the RFID tag is adversely affected. In a vehicle toll situation, an effective distance of over 20 feet from the location of an RFID tag to a toll reader can be required, simply positioning a standard RFID tag on back of a mobile device makes it non-functional due to the ground plane detuning effects. Separation from a ground plane by a significant distance (at least 6 mm in some instances) minimizes the degradation effects of the ground plane on the transmittal range of the RFID tag. In instances where a direct coupling between a mobile device exterior casing and an RFID tag are desirable (i.e., placing an RFID tag as a sticker on the back of a mobile telephone or tablet), the distance of separating the RFID tag by at least 6 mm is unfeasible. Attenuation problems resulting from RFID tags being coupled to mobile devices have not been satisfactorily solved by any known prior art teachings outside the present disclosure.

DETAILED DESCRIPTION

The disclosure provides for a Radio Frequency Identification (RFID) tag device for operation in close proximity to a ground plane. The disclosed RFID tag device couples energy into a proximate mobile device rather than energy from the RFID tag device being attenuated by the ground plane of the mobile device's components. In embodiments, the proximate mobile device actually increase the RFID antenna gain of the RFID tag device's antenna, which improves radio frequency (RF) transmission range of the RFID tag device. In one embodiment, the RFID antenna structure includes a dipole structure and a tuning loop. In one contemplated embodiment, the RFID tag can include a near field communication (NFC) antenna assembly that powers the RFID tag based on captured energy emitted by a NFC transmitter of the mobile device. An embodiment having both an RFID antenna and a NFC antenna may require a balancing of distance and power, as the NFC antenna must be sufficiently close to the NFC transmitter to effectively capture energy for use by the RFID tag device while the RFID antenna must be shaped and distanced from the ground plan (of the mobile device's components) to ensure RFID tag device emitted energy interacts with the proximate mobile device for a gain′ (as opposed to the proximity of the mobile device resulting in signal attenuation).

FIG. 1Ashows a system of a mobile device102and RFID tag device104in accordance with some embodiments. The mobile device102is a small, portable computing device that includes one or more radio transceivers. Examples of mobile devices include, for example, cellular or “smart” phones, tablet computing devices, personal digital assistants, a wearable device, and so on. The RFID tag device104is an electronic device that utilizes electromagnetic fields to transfer data, for the purposes of automatically identifying and tracking an object in proximity to the RFID tag. One, non-limiting, use case for the RFID tag device104is for vehicular tolls, but other applications are contemplated. In embodiments, the RFID tag device104can include a first RF interface107to communicate with the mobile device102via radio link108and a second RF interface105to communicate with another device, such as an RFID reader over a second radio link. An RFID antenna assembly110(shown on printed circuit board103of device104), which is designed for maximizing transmission distances while in close proximity to mobile device102, is associated with the second RFID interface105. The second RF interface105allows for far-field communications (twenty to one hundred feet, for example) with the RFID reader, which facilitates use of the RFID tag device104in retail, tracking, and payment applications. PCB103includes NFC antenna109for the first RF interface107.

Embodiments are contemplated where multiple devices interact such that together they perform equivalent functionality to that indicated in the disclosure. For example, a wrist wearable computing device (such as a smart watch) can be communicatively linked (e.g., BLUETOOTH paired) to a smartphone. Together the paired devices provide the functionality of mobile device102expressed herein. In such an embodiment, the RFID tag device104can be coupled to (or integrated with) the wearable computing device. U.S. provisional 61/993,359 to which priority is claimed (specifically referencing the section labeled “Wearable Wristband for Tolling”) elaborates on such an embodiment. In embodiments where a wearable device is coupled to RFID tag device104, the wearable device's components function as the ground plane discussed herein and provide the transmission gain that results from the RFID antenna assembly110as described herein.

As shown byFIG. 1B, the RFID antenna assembly110includes two symmetrical dipole elements (112,114) extending along a periphery of a circuit board of the RFID tag device104. Each dipole element112,114joins to a tuning antenna element120. The tuning antenna element120is a loop antenna separating the two symmetrical dipole elements112,114. Each dipole element112,114can be shaped as a half rectangle with an additional segment joining the element112,114to the tuning element120. As arranged, the symmetrical dipole elements112,114can be mirror images of each from a perspective of a vertical centerline. The tuning element120can be a substantially rectangularly shaped element placed between the dipole elements112,114.

In one embodiment, a length116of a peripheral portion of each of the dipole elements112,114can be 50 mm (+/−10 percent). A length118of each dipole element112,114can be approximately 20 mm (+/−10 percent), a connecting length between each dipole element112,114and the tuning loop can be 5 mm (+/−10 percent). The tuning loop120can have a long side of approximately 32 mm (+/−10 percent) and a short side of approximately 7 mm. A space between the segment joining element112(to tuning loop120) and the segment joining element114(to the tuning loop) can be 1 to 12 mm in embodiments.

One of ordinary skill recognizes that the geometry of the RFID antenna assembly110will naturally vary based on the frequency of emissions, substrate dielectric constant, etc. and that the above embodiment and sizes correspond to a UHF (915 MHz) RFID tag device104. Adjustments of the above optimized for other transmission frequencies and device configurations are easily within the scope of the knowledge of one of ordinary skill (based on the disclosure herein) without undue experimentation.

FIG. 2shows an electric (E) field distribution of the antenna on a printed circuit board in proximity to a phone (specifically a SAMSUNG S3 phone was used to generate the test numbers expressed in the table ofFIG. 2) in accordance with some embodiments.

FIG. 3shows the RFID antenna assembly110and an additional NFC antenna on a single printed circuit board layout in accordance with some embodiments. The NFC antenna310can be a component of the first RF interface107that communicates with the mobile device102via radio link108. The NFC antenna310can be coupled to an energy collection circuit. Thus, RF transmissions (such as near-field transmission) from the mobile device102are captured by the NFC antenna310to power circuitry of the RFID tag device104. NFC antenna310can also be used to generate and receive NFC data signals to/from the mobile device thereby permitting communications over radio link108.

In this embodiment, the NFC antenna310is positioned in approximately the center of the printed circuit board, as is the tuning loop120, between the dipole elements112,114. The NFC antenna310represents a rectangular coil with rounded edges of a substantially flat plane. The NFC antenna can be positioned between the dipole elements112,114where approximately (+/−20 percent) half of the NFC antenna310is above a bottom of length118and approximately half of the antenna310is positioned above the bottom of length118. The NFC antenna310in one embodiment has a short side of approximately 20 mm (+/−10 percent), and a long side of approximately 40 mm (+/−10 percent).

FIG. 4is a schematic diagram of a RFID tag device400in accordance with some embodiments. The RFID tag device400can be substantially similar to the RFID tag device104shown inFIG. 1. Generally, the RFID tag device400includes circuitry to realize two different RF interfaces, and can include a memory associated with each interface, a controller for operating the RFID tag device, and an energy collection circuit to collect energy from the RF interfaces to power the RFID tag device400. Accordingly, the RFID tag device400includes a first RF interface401, that can be, for example, a NFC RF interface. The first interface401includes an antenna404and a first transceiver402that communicates according to a first RF protocol, such as an NFC protocol. The first RF interface401can further include a first memory406coupled to the first transceiver402, and can be used to store data received over the first RF interface401, or data that is to be transmitted over the first RF interface401, or both.

The RFID tag device400further includes a second RF interface409, such as a RFID interface, that includes antenna414and a second transceiver412to communicate according to a second RF protocol, such as, for example, an RFID communication protocol. The second RF interface409operates independently of the first RF interface401. The second RF interface409can further include a second memory410, such as an RFID memory, that can be coupled to the second transceiver412and can contain, for example, one or more substantially unique identifiers that can be used to identify the RFID tag device400, and which can be associated with a user or a user account in remotely located computing equipment (e.g. account servers).

In some embodiments it is contemplated that there is only one memory shared by each of the RF interfaces401,409. In some embodiments, the controller408can be provided with registers, cache, or other memory, that can operate as the first and second memories406,410. Furthermore, the first memory406, when implemented as a separate memory, can be a dual interface memory that can be accessed by the first transceiver402and the controller408by separate, independent memory interfaces. The controller408can move data between the memories406,410, as well as perform other operations such as formatting data when moving data between memories406,410. In some embodiments memory410is a ROM, and data received via first RF interface409is routed directly to the controller408. In some embodiments memory406is a dual interface memory that is writable, and non-volatile.

The RFID tag device400further includes an energy collection circuit416that is used to collect energy received from remote transmitters at antennas404,414. A first regulator418can be used to collect energy at the first RF interface antenna404, and a second regulator420can be used to collect energy at the second RF interface antenna414. Simple rectifiers (diodes) between antennas404,414and regulators418,420can be used to rectify alternating current (AC) signals to store charge in, for example, a capacitor422, through blocking diodes430The capacitor422can be electrically coupled to the interfaces401,409, alternatively or at the same time, and the controller408, to provide power to those components as necessary.

The RFID tag device400can further contain circuitry to facilitate optimum location of the RFID tag device400on a mobile device. For example, a light emitting diode426can be controlled by a switch transistor428that is operated by the controller408. Upon power-up or receiving an appropriate command via first RF interface401from the mobile device, the controller can switch on transistor428, allowing current to flow through LED426from node432, as limited by resistor434. During this operation the mobile device continuously transmits over the NFC RF interface so that capacitor422is continuously receiving electrical energy via regulator418. The resulting voltage evident across node432is dependent on the efficiency of the coupling between the NFC transmitter of the mobile device and the first RF interface401. As the RFID tag device is moved relative to the mobile device, the intensity of light emitted from the LED varies in correspondence with the efficiency of the NFC link, allowing the user to optimally locate the RFID tag device400on the mobile device.

Embodiments of the disclosure permit the RFID tag device104to be adhesively coupled to the mobile device102. Spacing between interior components of the mobile device102(functioning as a ground plane) and the circuit board of the RFID tag104can be less than 5 mm in embodiments, while still not having adverse attenuation effects to the range of the RFID tag device104due to the RFID antenna assembly110utilized herein.FIG. 5shows a decomposition of one embodiment of an adhesive coupled RFID device104. The device can include a top printed surface510, coupled via adhesive512to a circuit board514, coupled with adhesive516to a spacer518, coupled with adhesive520to a removable adhesive cover522, which has a removable adhesive protector420.

Surface510can provide an identifier for the RFID tag device104, which may include a unique key, bar code, or other unique identifier. This identifier can be used to uniquely identify the RFID tag, such as for activation purposes and/or for linking this identifier to a mobile device102. Once linked, a mobile device102identifier can be utilized as a unique reference in addition to (or as an alternative to) utilizing any identifier printed on surface510.

The circuit board514represents a printed board, such as shown inFIG. 1. The printed circuit board includes the RFID antenna assembly110. In some embodiments, an additional NFC antenna310can be included on the circuit board514.

Spacer518can be formed from a foam material or other insulator. Use of a compressible foam as a spacer can be beneficial in embodiments that rely on double-sided pressure sensitive adhesives to bond between layers and surfaces.

The adhesive layers512,516can be a low surface energy (LSE) adhesive designed to bond to hard to stick to surfaces, such as plastics, polypropylene, polyethylene, polystyrene, thermoplastic polyolefins, EVA, PTFE, powder coated paints and oily metal surfaces. A pressure sensitive adhesive tape can be used as an adhesive layer512,516in contemplated embodiments. For example, in one embodiment, layers516and520can utilize a double-sided 300LSE adhesive tape and layer512can be a double-sided 467 LSE adhesive tape.

In one arrangement adhesive layer520can be an adhesive vynol adhesive that provides for pressure-sensitive adhesive bonds for low and high surface energy materials. Specifically, layer520can be designed to form a strong bond with materials of an outer case of mobile device102, which include polycarbonate material, SE and HSE plastics, metals, fiberglass, and wood materials present in commercially available mobile devices.

FIG. 6shows a system view600of a mobile device602and RFID tag device614in accordance with some embodiments. In addition to radio interface(s), a mobile device602includes a graphical display and input means to allow a user of the mobile device602to interact with, and control operation of the mobile device602, as well as memory and a processor to execute program code for applications, programs, operating systems, and other software elements. The memory includes read only memory (ROM) and random access memory (RAM), and can include other types of memory such as flash memory, and can include memory expansion such as memory card slots.

The RFID tag device604contains identity information that can be used for conducting wireless transactions. Accordingly, the RFID tag device604includes at least two radio frequency (RF) interfaces. A RF interface is a wireless radio interface and includes an antenna and transceiver that operate according to a defined protocol or air interface. The air interface defines channel format, timing, modulation, and other aspect for radio communication. The RFID tag device604includes a first RF interface607to communicate with the mobile device602via radio link608, and a second RF interface605to communicate with another device, such as an RFID reader610, over radio link612. The radio links608,612indicate communication between the devices over their respective RF interfaces. The RFID tag device604can be held against, or substantially close to the mobile device602, such as by forming the RFID tag device604in the form of a card with an adhesive layer to affix the RFID tag device604onto a surface (such as a back surface) of the mobile device602as indicated by arrows606. In some embodiments the mobile device602and RFID tag device604communicate via radio link608using a near field communication (NFC) protocol, such as that specified by ISO/IEC 18000-3 which has an effective range of about 10 cm and operates at 13.56 MHz. Typically the NFC communication between the mobile device602and the RFID tag device604will be encrypted for security purposes. In addition to exchanging data over the radio link608, the mobile device602can power the RFID tag device604via radio link608. The energy of the NFC signal from the mobile device can be collected in the RFID tag device and used to power the circuitry of the RFID tag device604which responds to the mobile device over link608, as well as for RFID operations via radio link612. Radio link612between the RFID tag device and RFID reader610can be a RFID interface, such as, for example, that specified by ISO/IEC 18000-6c, ISO/IEC 18000-6b, or other known RFID interface standards. In some embodiments, the link612can be specifically configured to operate according to a vehicular toll standard for use in wireless tollway systems. In such embodiments, the RFID reader610can be a tollway reader that is positioned over a traffic lane of a toll road. The RFID reader610includes an antenna and transceiver to support communications with RFID tag devices, as is known. As the RFID tag device604passes by the reader610, a signal from the reader610causes the RFID tag device604to respond via link612with identification information to identify the RFID tag device604. Furthermore, the reader610can, in some embodiments, transmit transaction information to the RFID tag device604via link612. The transaction information can include information such as an identification of the reader610, location, a toll amount, the time, and so on. In some embodiments the reader610does not transmit transaction information to the RFID tag device604, and the RFID tag device604only indicates to the mobile device602that it has been read (i.e. that it has responded to a reader signal).

The mobile device602contains a transaction application618in some embodiments that allows the mobile device602to facilitate transactions, including processing transaction information received from the RFID tag device604or transaction information generated by the mobile device602upon receipt of an indication of a transaction by the RFID tag device604, and forwarding the transaction information to an account server622. In some embodiments the mobile device602initializes the RFID tag device604via link612before the RFID tag device interacts with the RFID reader610via link608. For example, in a vehicular toll embodiment, the mobile device602can determine that the mobile device602is approaching a known toll gateway location using location information and road map data that indicates the location of toll gateways. When the mobile device602, is within a selected distance of a toll gateway, the mobile device602can energize NFC link608to power up the RFID tag device604. As the mobile device602and RFID tag device604pass through the toll gateway, the toll transaction occurs over link612, and the RFID tag device604transmits transaction information to the mobile device602via link608. Any transaction information received at the mobile device602from the RFID tag device604can be processed by the transaction application618, which can store the transaction information as well as display the transaction information upon receipt of the transaction information, or at a later time upon user request. Once the RFID tag device604completes transmitting to the mobile device602subsequent to the transaction, the mobile device602can shut off the NFC link608to conserve battery life of the mobile device602.

In some embodiments the mobile device602, in addition to the radio interface to support radio link108, comprises another radio interface to communicate at farther distances, such as a cellular transceiver for communicating over a cellular radio telephony link616with a cellular telephony infrastructure network614. The cellular radio telephony link616is operated in accordance with a cellular data communications standard, such as, for example, the Long Term Evolution (LTE) standard, the Global System for Mobile Communications (GSM) Enhanced Data rates for GSM Evolution (EDGE), or code division multiple access (CDMA), among other known standards. The mobile device602can transmit transaction information over the cellular telephony radio link616, through a wide area network620, such as the Internet, to an account server622that maintains account information for an account623associated with the RFID tag device604. The account server622can be linked to one or more banks624to maintain funding for transactions applied to the account622associated with the RFID tag device604. The account server622can communicate with a back office server628that is associated with reader610over similar, if not the same, networks620,630. The back office server628logs transaction information and reconciles payment of funds due with the account server622. Processing the transaction information is typically performed by batch processing, although in some embodiments it is contemplated that processing can be performed on a per-transaction or per-occurrence basis. The account server622can verify transactions based on transaction information received from the mobile device602. The mobile device, in some embodiments, can use other radio interfaces such as, for example, a wireless local area network (WLAN) interface, such as that described in the Institute of Electrical and Electronic Engineers (IEEE) standard 802.11, and often referred to as “Wi-Fi.” In some embodiments the mobile device602can use the near field communication interface608to communicate with another device besides the RFID tag device604, which can include a networked device that can forward transaction information from the mobile device602to the account server622.

Accordingly, the embodiments provide the benefit of using a RFID tag device with increased gain in association with a mobile device to facilitate wireless transactions, allowing the user to take the RFID tag device with the user so that a variety of transactions can be completed in different locations, without tying the RFID tag device to one type of transaction, such as is the case with conventional RFID tag devices that are, for example, mounted in a vehicle for toll transactions.