Range discrimination in radio frequency identification electronic article surveillance systems

Abstract

An electronic article surveillance system based on radio frequency identification is provided having a first receiving antenna and a second receiving antenna. Radio frequency signals are transmitted to a radio frequency identification device that transmits a return signal received by the receiving antennas. A location of the radio frequency identification device can be determined based on a difference between a strength of the return signal when received by the first antenna and a strength of the return signal when received by the second antenna. If radio frequency signals are transmitted by the receiving antennas, the location of the radio frequency identification device can be determined by varying a strength of the radio frequency signals transmitted by each antenna and comparing a strength of the radio frequency signals transmitted by the first antenna when the radio frequency identification device is at a threshold value for receiving the signals to a strength of the radio frequency signals transmitted by the second antenna when the radio frequency identification device is at the threshold value.

Description

[0001] Cross-referencing of related patent applications

[0002] This application claims the benefit of U.S. Provisional Patent Application No. 62 / 981,206, filed February 25, 2020, which is incorporated herein by reference in its entirety. Technical Field

[0003] The subject matter of this invention relates to radio frequency identification (“RFID”) devices. More specifically, the subject matter of this invention relates to determining the location of an RFID device in an electronic article security (“EAS”) system. Background Technology

[0004] In retail stores, accurate counting of displayed and / or stored products is crucial. Additionally, having effective anti-theft systems in appropriate locations is essential. Radio frequency identification (RFID) tags and markings (collectively referred to herein as "RFID devices") have been employed to perform both of these functions.

[0005] Electronic article security systems using radio frequency identification (RFID) technology have two main reading areas 10 and 12 (e.g., Figure 1 As shown), each of the two main reading areas includes an associated RFID reader. The first reading area 10 is the store area where products are presented to consumers (which may be referred to herein as the "inventory area"), while the second reading area 12 is the store exit area (which may be referred to herein as the "detection area") where any RFID device that has not yet been properly deactivated can be detected to trigger some type of alarm indicating that someone is attempting to steal one or more items. When a customer correctly purchases an item, the cashier removes or deactivates the RFID device associated with that item. If the RFID device is not removed or deactivated, one or more RFID readers will read the device and trigger an alarm or other alert in the detection area 12.

[0006] While the aforementioned systems are common, they have certain drawbacks. A common problem when using RFID devices / systems for electronic article security is that, in some cases, the read range of an RFID device may be large enough that an RFID device in storage area 10 can be read in detection area 12, or vice versa. To mitigate this risk, a transition area 14 is often provided between storage area 10 and detection area 12 to physically separate the two read areas. However, due to the varying sensitivities of different RFID devices at their operating frequencies and / or the different effects of different items on the performance of associated RFID devices, it is necessary to make the transition area 14 relatively large. A larger transition area results in a smaller storage area, and consequently, fewer items that retailers can present to consumers for purchase. Therefore, it would be advantageous to provide RFID devices configured in a way that allows for a smaller transition area 14.

[0007] In many RFID-based electronic article detection (EIE) systems, attempts are made to determine the range between the RFID device and the EIE reader system by measuring factors such as when the RFID device begins to respond (when the reader system transmits at constant power) and the level of that response, often referred to as Received Signal Strength Indication (RSSI). However, this approach can be unreliable due to the attenuation factor K and the RFID device sensitivity T. K and T can be affected by environmental conditions such as reflections between the RFID device and the reader system, absorbing materials, and damage caused by attempted theft (where a thief might place the RFID device close to a person to attenuate the signal (known as the human model or human effect)). High T and low K can cause a distant RFID device (e.g., an RFID device in a storage area) to respond to tags in the EIE zone at a similar level, resulting in false alarms. It should be understood that when K is high, it is ideal for the RFID reader to transmit at maximum power for detection because someone might intentionally attempt to defeat the EIE system, but this also increases the probability of false alarms. Therefore, a K-independent determination method would be advantageous. Summary of the Invention

[0008] Several aspects of the subject matter of this invention can be implemented individually or together in the apparatus, systems, and methods described and claimed below. These aspects can be used alone or in combination with other aspects of the subject matter described herein, and the common description of these aspects is not intended to exclude their use alone or to claim them alone or in different combinations that may be set forth in the appended claims.

[0009] This document describes a method for determining the location of a radio frequency identification (RFID) device in an electronic article detection (EIE) system having a first reading area and a second reading area. The method includes: transmitting radio frequency signals to the RFID device at a first location and a second location, and receiving return signals from the RFID device. The method also involves calculating the difference between a first strength of the return signal at the first location and a second strength of the return signal at the second location, and determining whether the RFID device is located in the first reading area based at least in part on the difference between the first and second strengths.

[0010] This document also describes an electronic article detection (EOP) system for determining the location of a radio frequency identification (RFID) device, the RFID device being configured to transmit a return signal upon receiving a radio frequency signal. In some embodiments, the EOP system includes a first reading area and a second reading area, a first receiving antenna and a second receiving antenna, and a controller. In some embodiments, the first receiving antenna is configured to receive the return signal at a first intensity, while the second receiving antenna is configured to receive the return signal at a second intensity. The controller is configured to determine whether the RFID device is located in the first reading area based at least in part on the difference between the first intensity and the second intensity.

[0011] This document describes a method for determining the location of a radio frequency identification (RFID) device in an electronic article detection (EIE) system having a first reading area and a second reading area. In some embodiments, the method includes: transmitting a first radio frequency (RF) signal from a first location to the RFID device and converting the power of the first RF signal to a first power, the first power corresponding to a threshold value when a first return signal is received from the RFID device at the first location; transmitting a second RF signal from a second location to the RFID device and converting the power of the second RF signal to a second power, the second power corresponding to a threshold value when a second return signal is received from the RFID device at the second location; determining a difference between a first power and a second power, and then determining whether the RFID device is located in the first reading area based at least in part on the difference between the first power and the second power.

[0012] This document also describes an electronic article detection (EOP) system for determining the location of a radio frequency identification (RFID) device, the RFID device being configured to transmit a return signal upon receiving a radio frequency signal. In some embodiments, the EOP system includes a first reading area and a second reading area, a first receiving antenna and a second receiving antenna, and a controller. The first receiving antenna is configured to transmit a first radio frequency signal to the RFID device and convert the power of the first radio frequency signal to a first power, the first power corresponding to a threshold value when a first return signal from the RFID device is received by the first receiving antenna. The second receiving antenna is configured to transmit a second radio frequency signal to the RFID device and convert the power of the second radio frequency signal to a second power, the second power corresponding to a threshold value when a second return signal from the RFID device is received by the second receiving antenna. The controller is configured to determine whether the RFID device is located in the first reading area based at least in part on the difference between the first power and the second power. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of a conventional electronic article security system that uses radio frequency identification (RFID) devices;

[0014] Figure 2 This is a schematic diagram of an exemplary embodiment of an electronic article anti-theft system based on radio frequency identification according to the present disclosure;

[0015] Figure 3 This is a schematic diagram of another exemplary embodiment of the radio frequency identification-based electronic article anti-theft system according to the present disclosure;

[0016] Figure 4 This is a schematic diagram of an exemplary antenna arrangement for a door of an electronic article security system according to one aspect of this disclosure;

[0017] Figure 5 This is a schematic diagram of the electronic article security system disclosed herein used to determine the two-dimensional position of an RFID device; and

[0018] Figures 6A to 6C A method for determining the movement of a radio frequency identification device using an electronic article anti-theft system according to this disclosure is demonstrated. Detailed Implementation

[0019] Detailed embodiments of the invention have been disclosed herein as needed; however, it should be understood that the disclosed embodiments are merely examples of the invention, which can be implemented in various forms. Therefore, the specific details disclosed herein should not be construed as limiting, but merely as a basis for the claims and as a representative basis for teaching those skilled in the art to use the invention differently in virtually any suitable manner.

[0020] Figure 2 An exemplary embodiment of an electronic article detection system 16 based on radio frequency identification (RFID) according to this disclosure is shown. Figure 2 In one embodiment, the electronic article control system 16 includes a transmitting antenna 18 and two receiving antennas 20 and 22. While an antenna design with equivalent gain in the region of interest or components for compensating for measured RSSI / power values ​​may be preferred, the antennas of the electronic article control system according to this disclosure can be configured in various ways without departing from the scope of this disclosure. For example, Figure 2 The receiving antennas 20 and 22 can be configured as dipole antennas, directional antennas, transmission line antennas, or combinations thereof. Antennas configured in different ways will have different performance characteristics and therefore different advantages. For example, a dipole antenna will provide good angular coverage for an electronic article security system configured to detect the two-dimensional positioning of an RFID device. On the other hand, a directional antenna is better configured to keep the detection area focused forward toward the door of the electronic article security system. Accordingly, it should be understood that this disclosure is not limited to electronic article security systems with specially configured antennas, but the methods described herein can be practiced using various antennas configured in different ways.

[0021] exist Figure 2 In the electronic article security system 16, the transmitting antenna 18 transmits a radio frequency signal "S" (e.g., an RFID tag or mark attached to a product) to a radio frequency identification (RFID) device 24 located at a point within the electronic article security system 16. The RFID device 24 receives the radio frequency signal S from the transmitting antenna 18 and returns a return signal, which is received by a first receiving antenna 20 and a second receiving antenna 22.

[0022] Due to environmental conditions, the strength of the returned signal will decrease as the distance the returned signal travels increases. Figure 2 In the orientation, the first receiving antenna 20 is positioned closer to the RFID device 24 than the second receiving antenna 22, such that the strength of the returned signal, or RSSI, will be greater at the first receiving antenna 20 than at the second receiving antenna 22. Figure 2 In the figure, the distance between the radio frequency identification device 24 and the first receiving antenna 20 is represented by "r", and the distance between the first receiving antenna 20 and the second receiving antenna 22 is represented by "θ", such that the distance between the radio frequency identification device 24 and the second receiving antenna 22 is r+θ.

[0023] As mentioned above, measuring the strength or RSSI of the returned signal from the RFID device using a single antenna may not be particularly informative or useful. However, by comparing the strength or RSSI of the returned signal using two antennas 20 and 22 positioned at a known distance from each other, the approximate location of the RFID device in the electronic article security system 16 can be determined more reliably. As mentioned above, the strength or RSSI of the returned signal is a function of the distance the returned signal travels. When comparing the strength or RSSI of the returned signal received by the first receiving antenna 20 and the second receiving antenna 22, the common distance traveled by the returned signal when reaching the first receiving antenna 20 and the second receiving antenna 22 can be offset (its value is within the range of the first receiving antenna 20 and the second receiving antenna 22). Figure 2 (represented by "r" in the original text). Therefore, the difference between the strength or RSSI of the returned signal received by the first receiving antenna 20 and the second receiving antenna 22 will indicate the strength loss of the returned signal when it travels a known distance θ between the first receiving antenna 20 and the second receiving antenna 22.

[0024] The intensity or RSSI of the radio frequency signal follows the square law, such that the difference in intensity or RSSI of the returned signal received by the first receiving antenna 20 and the second receiving antenna 22 will indicate the distance r between the RFID device 24 and the first receiving antenna 20. Generally, when the distance r is relatively small, the difference in intensity or RSSI of the returned signal received by the first receiving antenna 20 and the second receiving antenna 22 will be relatively large, while when the distance r is relatively large, the difference will be relatively small. The exact magnitude of the difference will depend on many factors, but in the exemplary embodiment, when r = 1, the difference will be approximately 6 dB, when r = 5, the difference will be approximately 1.6 dB, and when r = 10, the difference will be approximately 0.83 dB.

[0025] Regardless of the specific difference between the returned signal strength or RSSI at the two receiving antennas 20 and 22, it will be seen that any RFID device 24 that does not show significant strength or RSSI changes can be considered to be at a significant distance from receiving antennas 20 and 22. Although the illustrative example has low accuracy at long distances (e.g., the signal strength or RSSI difference is small at r=5 and r=10), the electronic article security system 16 can be configured to not require high accuracy over relatively long ranges. For example, in one embodiment, the two receiving antennas 20 and 22 (or a single antenna with more than one reference plane in the case of receiving antennas incorporated into a transmission line antenna) are placed between the storage area 10 and the detection area 12, wherein the first receiving antenna 20 is positioned closer to the storage area 10 than the second receiving antenna 22. When the RFID device 24 is positioned closer to the storage area 10 than to the detection area 12 (i.e., closer to the first receiving antenna 20 than to the second receiving antenna 22), the difference between the strength of the returned signal or RSSI received by the first receiving antenna 20 and the second receiving antenna 22 should be positive (i.e., the returned signal should be stronger at the first receiving antenna 20 than at the second receiving antenna 22).

[0026] Therefore, in this illustrative configuration, the strength or RSSI difference of the returned signals received by the first receiving antenna 20 and the second receiving antenna 22 being positive and relatively small (i.e., less than a positive threshold, which in the exemplary embodiment is approximately between 1.6 dB and 6 dB) will be sufficient to indicate that the RFID device 24 is located somewhere in the storage area 10. The exact location of the RFID device 24 within the storage area (e.g., whether r = 5 or r = 10) may not be accurately determined, but it is just sufficient to know that the RFID device 24 is in the storage area 10 and not in the detection area 12 or the transition area 14. The exact positive threshold used to determine whether the RFID device 24 is sufficiently far from the receiving antennas 20 and 22 will depend on many factors (e.g., the positioning of the receiving antennas 20 and 22 within the electronic article detection system 16 and the size of the transition area 14), and therefore this disclosure is not limited to any particular positive threshold.

[0027] Similar to determining the location of the RFID device 24 within the storage area 10, the electronic article detection system 16 according to this disclosure can also determine when the RFID device 24 is located within the detection area 12. When the first receiving antenna 20 is positioned closer to the storage area 10 than the second receiving antenna 22, and when the RFID device 24 is positioned closer to the detection area 12 than the storage area 10, the difference between the strengths or RSSI of the returned signals received by the first receiving antenna 20 and the second receiving antenna 22 should be negative. Therefore, in this illustrative configuration, a negative and relatively small difference in the strengths or RSSI of the returned signals received by the first receiving antenna 20 and the second receiving antenna 22 (i.e., greater than or closer to zero, rather than a negative threshold) will be sufficient to indicate that the RFID device 24 is located within the detection area 12. The exact negative threshold used to determine whether the RFID device 24 is sufficiently far from the receiving antennas 20 and 22 will depend on many factors (e.g., the positioning of the receiving antennas 20 and 22 within the electronic article detection system 16 and the size of the transition area 14), and therefore this disclosure is not limited to any particular negative or positive threshold.

[0028] It should be understood that Figure 2 The configuration shown is merely exemplary, and the electronic article protection system according to this disclosure can be configured in different ways. For example, Figure 3 An electronic article detection system 26 was demonstrated, in which the radio frequency signal is transmitted via two receiving antennas 28 and 30 instead of a third transmitting antenna (e.g., ...). Figure 2 (Transmission) in China. Figure 3 The electronic article security system 26 can be described as operating in a "single static" mode, while Figure 2 The electronic article security system 16 can be described as operating in a "dual static" mode.

[0029] exist Figure 3 In this embodiment, each receiving antenna 28, 30 transmits radio frequency signals to the radio frequency identification device 24 and receives return signals. For example... Figure 2 In one embodiment, the strength or RSSI difference of the returned signals received by the first receiving antenna 28 and the second receiving antenna 30 can be used to determine the approximate location of the RFID device 24 (i.e., whether the RFID device 24 is located somewhere in the storage area 10 or somewhere in the detection area 12). However, when sending two different RF signals to... Figure 3When using the RFID device 24 in an electronic article detection system, care must be taken to ensure that the return signal from the RFID device 24 is transmitted with the same power. When the RFID device 24 receives just enough power to transmit the return signal (referred to herein as the “threshold”), the power of the return signal transmitted by the RFID device 24 when receiving radio frequency signals from the first receiving antenna 28 and the second receiving antenna 30 will be the same, which means constant power input and constant power output.

[0030] In one embodiment, each receiving antenna 28, 30 will begin by transmitting a low-intensity radio frequency (RF) signal and then increase the strength of the RF signal until a return signal is first received from the RFID device 24, which will be the RF signal strength of the receiving antenna at the threshold of the RFID device 24. Alternatively, instead of starting with low power, receiving antennas 28 and 30 that initially transmit higher-power RF signals can reach the threshold, where the RF signal is strong enough to reach the RFID device 24, and the power is reduced until no more return signals are transmitted. In fact, it should be understood that any of a number of suitable methods can be used to reach the threshold, which may include linear scanning or binary search.

[0031] Just as the strength difference between two returned signals can be used to determine the approximate location of the RFID device 24, the strength difference between the RF signal emitted by the first receiving antenna 28 at the threshold of the RFID device 24 and the RF signal emitted by the second receiving antenna 30 at the threshold of the RFID device 24 can indicate the approximate location of the RFID device 24. The RF signals emitted by the two receiving antennas 28 and 30 will have the same (or at least substantially the same) strength, or RSSI, when they reach the RFID device 24. These two RF signals will traverse the same distance r when they reach the RFID device 24, such that the longer receiving antenna (which is...) will have the greater strength. Figure 3 The additional strength required for the RFID device 24 to reach a threshold is due entirely to the loss associated with the distance θ between the receiving antennas 28 and 30, which is the second receiving antenna 30 facing upwards (but could be the first receiving antenna 28, depending on the location of the RFID device 24). This information can be used (by employing the principles described herein) to determine whether the RFID device 24 is significantly separated from the receiving antennas 28 and 30, where a positive or negative difference indicates the side of the receiving antennas 28 and 30 to which the RFID device 24 is located.

[0032] For optimal performance, it is preferable that the RFID device 24 does not change or only changes relatively little in its position during the aforementioned measurements. A bistatic system can be advantageous in this regard because it only requires sufficient power of the RF signal transmitted by the transmitting antenna 18 to elicit a response from the RFID device 24, whereas a monostatic system must adjust the transmitted power to keep a particular RFID device 24 below a threshold, which is slower. However, a monostatic system allows for a second method for determining the approximate location of the RFID device 24, which may be preferred in certain situations.

[0033] While the electronic article detection system according to this disclosure can be configured to be less accurate over longer ranges, it can be advantageous to make the electronic article detection system more accurate in monitoring the movement of the RFID device from transition zone 14 to detection zone 12 to prevent false alarms. The determination of the movement of the RFID device can be based on a comparison of the approximate position of the RFID device at a first time with the approximate position of the RFID device at a later second time. In one exemplary embodiment, the movement is based on the strength or RSSI difference between the returned signals received by the two receiving antennas (e.g., Figure 2 and Figure 3 In the embodiments) or the power difference of the radio frequency signals emitted by the two receiving antennas when the radio frequency identification device 24 reaches the threshold (e.g. Figure 3 In the embodiments described above, an electronic article security system of the type described above can be used to determine the approximate location of the RFID device 24 at a first time. The same method can be used to determine the approximate location of the same RFID device 24 at a second time, wherein the difference between the approximate location at the first time and the approximate location at the second time indicates the direction in which the RFID device 24 is moving.

[0034] Although Figure 2 and Figure 3 Electronic article control systems 16 and 26 can be used to determine the approximate location and movement of RFID device 24, but an electronic article control system with more receiving antennas will be able to determine the location and thus movement of RFID device 24 more accurately. Figure 4 An exemplary door 32 of an electronic article security system with four receiving antennas 34a-34d is shown, while Figure 5 Demonstrates the use of Figure 4 The illustrated method is an exemplary method for determining the location of the RFID device 24 in a system of the type shown. It should be understood that, without departing from the scope of this disclosure, an electronic article security system may have more than four receiving antennas, and such antennas may be located in various ways (including at different heights, such as one or more antennas associated with a ceiling or other antennas located at ground level).

[0035] Regardless of the exact number and location of the receiving antennas in the electronic article security (EIS) system, each receiving antenna has a known location within the EIS system and a known location relative to other receiving antennas. Based on the strength of the returned signal received by each receiving antenna 34, or RSSI, or (in the case of receiving antennas configured to also transmit radio frequency signals to the RFID device 24) the strength of the radio frequency signal transmitted by each receiving antenna 34 when the RFID device 24 reaches its threshold, the approximate distance r1-r4 between the RFID device 24 and each receiving antenna 34 can be determined. Figure 5 By simultaneously solving for the difference, the two-dimensional positioning of the RFID device 24 can be determined using the absolute and relative positioning of the receiving antennas 34a-34d and the distances r1-r4 between the RFID device 24 and the receiving antennas 34a-34d (i.e., by triangulation).

[0036] After determining the two-dimensional location of the RFID device 24 at the first time, the process can be repeated at a later second time to determine the two-dimensional location of the RFID device 24 at the second time. The locations of the RFID device 24 at these two times can be compared to determine the direction of movement of the RFID device through the electronic article control system. As mentioned above, this can be particularly relevant to determining when the RFID device 24 moves towards the detection area 12 through the transition zone 14, which may indicate an attempt to steal goods associated with the RFID device 24. The two-dimensional location of the RFID device 24 can be determined at several times to more accurately and specifically track the path of the RFID device 24 through the electronic article control system. It is possible that the receiving antenna 34 is able to determine the location of the RFID device 24 more accurately at close range; in this case, it may be advantageous to position the receiving antenna 34 adjacent to the detection area 12 to track the movement of the RFID device through the transition zone 14 towards the detection area 12.

[0037] Figures 6A to 6C The radio frequency identification device 24 was demonstrated. Figure 4 Door 32 is positioned from one side of the first position ( Figure 6A Move to the second position at door 32 ( Figure 6B Then move to the third position on the opposite side of door 32. Figure 6C ).exist Figures 6A to 6C In the process, the radio frequency identification device 24 is monitored by two receiving antennas 34a and 34b of the gate 32. These two receiving antennas 34a and 34b are separated by a distance θ (e.g., Figure 2 and Figure 3 (in the middle). When the distance between the RFID device 24 and the door 32 is greater than θ by more than four times (r > 4 × θ) (e.g. Figure 6A(in the middle) and when the RFID device 24 moves toward the door 32, the straight line between the first receiving antenna 34a and the RFID device 24 (in the middle) Figure 6A (represented by r1) and the straight line between the second receiving antenna 34b and the radio frequency identification device 24 (in) Figure 6A The angular difference between the two receiving antennas (denoted by r2) is small, so the vector distance can largely be considered as the distance θ between the two receiving antennas 34a and 34b. This is similar to... Figure 2 and Figure 3 The arrangement shown in the diagram involves two antennas that are either configured or assumed to be aligned with the radio frequency identification device 24.

[0038] As the range decreases (i.e., the RFID device 24 moves closer to the gate 32), the vector distance difference between the first receiving antenna 34a and the second receiving antenna 34b decreases, and therefore the range estimate (and the combined RSSI or strength of the returned signals received by the receiving antennas 34a and 34b) begins to increase. When the RFID device 24 is at the exact same distance from the first receiving antenna 34a and the second receiving antenna 34b (e.g., ...), the range estimation decreases. Figure 6B When the RFID device 24 transitions through gate 32, the estimated range (and the combined RSSI or strength of the returned signals received by receiving antennas 34a and 34b) begins to decrease again, but in the opposite direction, until the distance between the RFID device 24 and gate 32 is greater than θ by more than four times (r > 4 × θ) (as shown in the figure). Figure 6C (In the middle), at this time, the range increases, thus providing a more accurate range measurement. This transition shape is a characteristic of passing through gate 32 and can be analyzed by observing the difference in the calculated range change over time and the trend of the combined RSSI reaching its peak at the center of gate 32. Figure 6B ).

[0039] exist Figures 6A to 6C middle, Figure 4 The gate 32, with only one pair of receiving antennas 34a and 34b, is shown for tracking the movement of the RFID device 24. If multiple gates or multiple pairs of receiving antennas are provided (e.g., Figure 4 In the case of a pair of receiving antennas (e.g., in the middle), the system controller can select the most suitable pair of receiving antennas to monitor the movement of the RFID device 24. The most accurate range estimate comes from any pair of receiving antennas (e.g., Figure 4 The minimum value of the receiving antennas 34a and 34b or receiving antennas 34c and 34d in the pair indicates that the radio frequency identification device 24 is most closely aligned with the pair of receiving antennas.

[0040] It should be understood that the above embodiments illustrate some applications of the principles of the subject matter of this invention. Those skilled in the art can make numerous modifications without departing from the spirit and scope of the claimed subject matter, including those combinations of features individually disclosed or claimed herein. For these reasons, the scope of this invention is not limited to the above description, but rather as set forth in the following claims, and it should be understood that the claims may be directed to features including combinations of features individually disclosed or claimed herein.

Claims

1. A method for determining the location of a radio frequency identification (RFID) device in an electronic article security (EIS) system, the EIS system having a first reading area and a second reading area, the method comprising: Transmit radio frequency signals to the radio frequency identification device; Receive return signals from the radio frequency identification device at a first position and a second position; Calculate the difference between the first intensity of the returned signal at the first position and the second intensity of the returned signal at the second position; Whether the RFID device is located in the first reading area is determined at least in part based on the difference between the first intensity and the second intensity; The approximate two-dimensional positioning of the radio frequency identification device is determined at least in part based on the difference between the first intensity and the second intensity; Multiple radio frequency signals are sequentially transmitted to the radio frequency identification device via a transmitting antenna; The return signal is received sequentially from the radio frequency identification device via the first receiving antenna and the second receiving antenna; Calculate the approximate two-dimensional positioning of the radio frequency identification device for each radio frequency signal, and The direction of movement of the RFID device is determined at least in part based on the two-dimensional positioning of the RFID device for each RFID signal.

2. The method according to claim 1, wherein, The determination of whether the RFID device is located in the first reading area based on the difference between the first intensity and the second intensity is based on the signal loss that occurs between the first position and the second position, and is independent of the signal loss that occurs between the RFID device and either the first position or the second position that is closer to the RFID device.

3. The method according to claim 1 or 2, wherein, The second position is located further away from the first reading area than the first position, and When the difference between the first intensity and the second intensity is positive and less than a positive threshold, it is determined that the radio frequency identification device is located in the first reading area.

4. The method according to claim 1 or 2, wherein, The second position is located further away from the first reading area than the first position, and When the difference between the first intensity and the second intensity is greater than a negative threshold, it is determined that the radio frequency identification device is located in the second reading area.

5. The method according to claim 1 or 2, wherein, The radio frequency signal is transmitted from a location different from the first location and the second location.

6. The method according to claim 1 or 2, wherein, The transmission of radio frequency signals to the radio frequency identification device includes: transmitting a first radio frequency signal from the first location and transmitting a second radio frequency signal from the second location.

7. An electronic article security system for determining the location of a radio frequency identification (RFID) device, the RFID device being configured to transmit a return signal upon receiving a radio frequency signal, the electronic article security system comprising: First reading area; Second reading area; A transmitting antenna configured to sequentially transmit multiple radio frequency signals to the radio frequency identification device; A first receiving antenna, located at a first position and configured to receive the returned signal at a first intensity; A second receiving antenna, located at a second position and configured to receive the returned signal at a second intensity; The first receiving antenna and the second receiving antenna are configured to receive the return signal transmitted sequentially from the radio frequency identification device; as well as A controller configured to determine whether the RFID device is located in the first readout area based at least in part on the difference between the first intensity and the second intensity, to determine an approximate two-dimensional location of the RFID device based at least in part on the difference between the first intensity and the second intensity, to calculate the approximate two-dimensional location of the RFID device for each returned signal, and to determine the direction of movement of the RFID device based at least in part on the two-dimensional location of the RFID device for each returned signal.

8. The electronic article anti-theft system according to claim 7, wherein, The second position is located further away from the first reading area than the first position, and The controller is configured to determine that the radio frequency identification device is located in the first reading area when the difference between the first intensity and the second intensity is positive and less than a positive threshold.

9. The electronic article anti-theft system according to claim 7, wherein, The second position is located further away from the first reading area than the first position, and The controller is configured to determine that the radio frequency identification device is located in the second reading area when the difference between the first intensity and the second intensity is greater than a negative threshold.

10. The electronic article security system according to any one of claims 7 to 9, further comprising a transmitting antenna configured to transmit the radio frequency signal.

11. The electronic article security system according to any one of claims 7 to 9, wherein, The first receiving antenna is configured to transmit a first radio frequency signal, and The second receiving antenna is configured to transmit a second radio frequency signal.

12. The electronic article security system according to any one of claims 7 to 9, wherein, At least one of the first receiving antenna and the second receiving antenna includes a dipole antenna.

13. The electronic article security system according to any one of claims 7 to 9, wherein, At least one of the first receiving antenna and the second receiving antenna includes a directional antenna.

14. The electronic article security system according to any one of claims 7 to 9, wherein, At least one of the first receiving antenna and the second receiving antenna includes a transmission line antenna.

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