FIELD OF THE INVENTION

The present invention relates to RFID communication systems. More particularly, the present invention provides a system and method for simultaneous multi- frequency reading of RFID devices.

DESCRIPTION OF THE RELATED ART

Radio Frequency Identification (RFID) tags are generally micro-electronic devices used for identification and tracking. RFID tags are traditionally passive or active devices, receiving suitable operating power when placed in an electromagnetic field generated by a RFID reader.

As RFID technology has developed, two primary frequency bands have emerged for use in the industry. A low frequency band consisting of frequencies in the range of 100kHz - 150kHz (typically 125kHz) generally supports devices commonly known as proximity tags/cards, whereas a higher frequency of 13.56MHz generally supports smart card devices.

Current RFID readers are generally designed for specific operation at one of the above noted frequencies. However, the advantage of providing dual frequency systems, allowing operation in both the higher and lower frequencies, has been realised.

In this regard, previous systems have focused on implementing conventional design by providing two antennas using continuous copper loops tuned to the two frequencies. By offsetting the position of the two antennas to influence effective flux, previous systems have been able to achieve antenna co-existence without significantly reducing quality of the signal or the effective range of the field.

However, as the desire increases for readers to become smaller to suit modern computer applications, the effectiveness, and therefore range, of the reader's antennas are significantly reduced with standard configurations. Further, the ability to physically offset antennas to influence flux is retarded in such small configurations, making prior systems relatively ineffective.

For example, the antenna array system described in U.S. Patent 7,439,862 (assigned to Assa Abloy AB) utilises overlapping and opposing magnetic flux arrangements. By the Patentee's own admission, this configuration limits the size of the reader antenna housing to be comparable to area of a standard proximity card.

The present invention advantageously provides an alternative to existing RFID systems. The invention according to certain embodiments may advantageously be used to operate at dual frequencies in a micro-environment, without compromising the signal quality or the effective field strength.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided an antenna array for a RFID reader, including a reader antenna tuned to operate at a high carrier frequency; and a resonating circuit tuned to operate at a low carrier frequency. The resonating circuit includes at least two ferrite inductors.

According to a further aspect of the invention, there is provided an antenna array for a RFID reader, including a reader loop antenna tuned to operate at a high carrier frequency; and a non-loop resonating circuit tuned to operate at a low carrier frequency. The resonating circuit includes at least two ferrite inductors.

In accordance with yet a further aspect of the invention, there is provided a method of communicating relevant information from a first RFID device operating at a high carrier frequency and/or a second RFID device operating at a low carrier frequency, to a RFID reader. The method includes the steps of placing the first RFID device operating at a high carrier frequency and/or the second RFID device operating at a low carrier frequency into an electromagnetic field generated by the reader; and reading relevant information from the first RFID device operating at a high carrier frequency and/or relevant information from the second RFID device operating at a low carrier frequency received at the reader in response to the electromagnetic field. The RFID reader includes a reader antenna tuned to operate at a high carrier frequency; and a resonating circuit tuned to operate at a low carrier frequency. The resonating circuit includes at least two ferrite inductors.

In accordance with a further aspect of the present invention, the high carrier frequency is nominally 13.56MHz, and the low carrier frequency is nominally 125kHz. Further, the array is embedded on a printed circuit board substrate.

In accordance with another aspect of the present invention, the resonating circuit includes four ferrite inductors. Further, the ferrite inductors are placed in the corner of the resonating circuit when the resonating circuit is shaped to a rectangle or square configuration. Additionally, the reader antenna is positioned inside the resonating circuit. BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in a non-limiting manner with respect to a preferred embodiment in which:-

Figure 1 is an overview of an antenna configuration according to a preferred embodiment of the present invention; and

Figure 2 is a graphical representation showing dual resonance in accordance with a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the following discussion and in the claims, the terms "including" and "includes" are used, and are to be read, in an open-ended fashion, and should be interpreted to mean "including, but not limited to . . . ".

Additionally, in the following discussion and in the claims, the term "device" is to be given a broad meaning and generally refers to a RFID smartcard device operating at high frequency that may communicate with a number of systems. The term "device" may also encompass lower operating frequency devices such as a proximity card. Further, it is to be understood that other RFID devices that contain a contactless microprocessor such as 'smart' mobile communication devices, portable radio devices, passports, driver's licences, credit and debit cards (including, but not limited to, EMV authentication standards), MIFARE cards and DESFire devices, governmental or financial institution issued identification cards (such as Personal Identity Verification (PIV) cards) may be substituted/interchanged for/with a smartcard in accordance with preferred embodiments of the present invention.

The term "contactless", as used in the following discussion and in the claims, is to be given a broad meaning and relates to an environment where a device may communicate with a reader without physical contact between the device and the associated reader. It will be appreciated however, that such an environment may include a very small amount of physical contact, such as a brief touch of the device onto the reader, as is commonly known as a 'touch and authenticate' operation. The contactless environment of the present invention relates generally to ISO 14443, ISO 15693 and NFC (Near Field Communication). It will be appreciated by those of skill in the art that other relevant standards could be adopted, as appropriate.

Traditional RFID systems involve a RFID device and a suitable RFID reader. RFID devices are generally passive or active devices. The present invention is generally referenced with passive RFID devices. However, it will be appreciated that an active RFID device may be incorporated using the inventive concept.

RFID devices generally include an integrated circuit used to store and process information, as well as an antenna tuned to a suitable frequency to receive and transmit relevant information.

A RFID reader generally includes a signal generator controlled by a microprocessor or signal processor to transmit a radio frequency signal into the immediate vicinity. The signal is tuned to a suitable operating frequency and is transmitted via at least one antenna coupled to the reader.

It is to be appreciated that the operating frequencies of the antennas described in the present invention consist of a low frequency band including frequencies in the range of 100kHz - 150kHz (typically 125kHz), as well as a higher frequency of 13.56MHz. However, additional frequencies may also be incorporated as required or deemed appropriate.

A RFID system operates when a suitable RFID device is placed in the vicinity or range of a reader. Once detected, the reader sends an excitation signal at the relevant frequency, providing suitable power to activate and interrogate the device. The device is activated and interrogated using electromagnetic inductive coupling via the electromagnetic field generated by the signal generator of the reader.

Multiple antennas, known as an array, may be employed in the reader to operate at various frequencies. For example, in order for a reader to activate and interrogate proximity cards (generally operating at 125kHz), as well as smart cards (generally operating at 13.56MHz), two antennas tuned to these respective frequencies may be used.

However, consideration must be given to the arrangement of antenna arrays. Firstly, placing two (or more) antennas on a printed circuit board or other suitable support requires space in the reader housing. In the interest of minimising the size of the reader housing, the inclusion of an antenna array must be carefully considered.

Additionally, antennas placed in close arrangement can cause interference and diminish the quality and range of the signal received from the RFID device. It is this particular concern that the present invention ameliorates, allowing smaller antenna configurations without signal quality loss.

Turning now to Figure 1 , there is shown a preferred configuration of an antenna array in accordance with the present invention. The configuration includes a high frequency reader antenna, in addition to a low frequency resonator circuit. The high frequency, multi-layer reader antenna is positioned on a printed circuit board substrate. It contains appropriate windings and spacing to support operation at 13.56MHz. In this instance the antenna has a rectangular spiral shape. However, it will be appreciated that the high frequency antenna may be of any suitable winding shape.

The low frequency, non-loop resonating circuit preferably surrounds the high frequency antenna as shown in Figure 1. That is, the high frequency reader antenna is positioned inside the resonating circuit.

In order to create a suitable magnetic coupling for low frequency operation, an antenna with 1mH - 10mH inductance and a quality factor higher than 30 is preferably required. As will be appreciated, the design of an antenna operating at low frequency (such as 125kHz) requires numerous copper wire turns/windings to create the desired inductance. However, the windings occupy a relatively large area on a printed circuit board.

The physical antenna size may be reduced by placing a ferrite core in its centre. A ferrite core enables a low impedance path for electromagnetic waves. Additionally, the ferrite core increases the field density and thereby increases the inductance. Despite these advantages, placing a ferrite core inside an antenna designed over a printed circuit board (to control size) can be costly.

In a particularly preferred embodiment of the present invention, a distributed resonating antenna is provided with multiple ferrite inductors and placed at the edge of a printed circuit board of the reader's antenna configuration to facilitate operating at the lower frequencies, such as at 125kHz. The ferrite inductors are connected using copper wire embedded in the printed circuit board's substrate enabling a large inductance from only a single-turn antenna structure. The field power provided by this distributed resonating antenna configuration can vary from 1mW to 10mW and is reliant on the power available to the reader as well as the area of the single turn antenna structure, which can be minimised to such configurations of a small USB device (1cm by 1cm) or even smaller.

Figure 2 shows a frequency transfer function of the reader antenna and the resonating circuit of the present invention, where the separation of the preferred operating frequencies (125kHz and 13.56MHz) spans two decades.

The signal level of the reader antenna and the resonating circuit is preferably more than 70dB attenuated on the other, resulting in negligible signal interference between these two components of the reader.

It will be appreciated that the resonator configuration of the present invention may be substituted for conventional RFID antennas, achieving dual frequency operation in a micro-environment.

It is to be understood that the above embodiments have been provided only by way of exemplification of this invention, and that further modifications and improvements thereto, as would be apparent to persons skilled in the relevant art, are deemed to fall within the broad scope and ambit of the current invention described and claimed herein. ·