KR-102962669-B1 - Electronic article surveillance system for improving reception shaded areas

Abstract

The present invention is an anti-theft system installed at the entrance or exit of a commercial facility and generating an alarm signal by detecting an activated tag that has approached within a surveillance area, comprising: a pair of gates positioned facing each other at a certain distance apart; a base supporting the gates from below; and a transmitting antenna installed on at least one of the pair of gates and radiating electromagnetic waves of a natural frequency that react to the tag attached to an item, wherein the transmitting antenna comprises at least three loop coils spaced apart at a certain distance on the same vertical plane, and an electrical signal having a different phase can be applied to each of the plurality of loop coils.

Inventors

• 김재희

Assignees

• 한국기술교육대학교 산학협력단

Dates

Publication Date

20260507

Application Date

20240703

Claims (3)

1. In an anti-theft system installed at the entrance or exit of a commercial facility, which detects an activated tag that has approached within a surveillance area and generates an alarm signal, A pair of gates positioned facing each other at a certain distance apart; A base supporting the above gate from below; A transmitting antenna installed on at least one of the above pair of gates and radiating electromagnetic waves of a natural frequency that react to the tag attached to the article; and A transmitting unit that controls an electrical signal applied to the above-mentioned transmitting antenna; comprising, The above-mentioned transmitting antenna includes at least three loop coils spaced apart at a certain interval on the same vertical plane, and An electrical signal having a different phase is applied to each of the plurality of loop coils above, and The continuous transmitter comprises a signal generator that generates a sinusoidal signal of a specific frequency band; and a phase shifter that shifts the phase of the sinusoidal signal to apply an electrical signal of a different phase to each of the loop coils, wherein the phase difference between two adjacent loop coils among the loop coils is 2π, where n is set as the number of loop coils. An anti-theft system characterized by a signal amplifier that amplifies the magnitude of an electrical signal applied to each of the above loop coils, and adjusts the signal magnitude so that the magnitude of the electrical signal applied to the first loop coil and the nth loop coil differs by more than a certain value, taking into account the height of the gate and the detection frequency of the activation tag, such that the instantaneous shadow area of the z component appears outside the center detection area of the tag.
2. delete
3. delete

Description

Anti-theft system for improving reception shaded areas The present invention relates to an Electronic Article Surveillance (EAS) system for preventing theft of goods in commercial facilities. Electronic Article Surveillance (EAS) is a technology widely used in commercial facilities to prevent the theft of goods. EAS systems are broadly classified into three types based on differences in frequency and operating mechanism: Acoustic Magnetic (AM), Frequency Modulation (FM), and Radio Frequency (RF). The dual RF method primarily uses a frequency band of 8.2 MHz and is designed to sound an alarm when a signal corresponding to the resonant frequency is received through a resonant circuit installed inside the tag. Here, since tags attached to products can be installed in various directions and products placed in shopping bags or similar containers vary, it is difficult to predict the direction of the tag in advance while it passes through the surveillance system. Considering these various directions, to maximize the detection efficiency of the EAS system, the transmitting antenna must be able to effectively generate a magnetic field in response to polarization in all directions. Currently, the transmitting antennas used in most EAS systems are primarily composed of loop coils and are designed to maintain a specific shape for the magnetic field. For example, Figure 7 illustrates a conventional transmitting antenna structure. As shown in Figure 7 (a), two loop coils, namely an upper loop coil and a lower loop coil, are arranged vertically with partial overlap, and currents flow in opposite directions through each loop coil, resulting in a current distribution as shown in Figure 7 (b). In this case, if we examine the magnetic field distribution in the x-z plane of Figure 8 (a), we can see that only the x component exists at the midpoint, while the z component does not. Additionally, if we examine the magnetic field distribution in the x-y plane of Figure 8 (b), we can see that the x and y components change according to the direction of movement of the person. That is, when considering all x, y, and z components during the process of a person moving, the z component does not occur in the midpoint of the transmitting antenna, and this midpoint can become a non-detection area where the tag cannot be detected, or a detection error area. Meanwhile, to improve these dead zones, an antenna structure like the one shown in Fig. 9 has recently been used. However, when using the antenna structure of Fig. 9, the intermediate region where the z-component of the magnetic field is not generated moves from bottom to top as a person moves. In other words, when using this antenna structure, moving at the same height causes the person to pass through a region that includes some z-component, thereby increasing the tag recognition rate. However, this structure also does not eliminate dead zones but rather causes changes depending on the location, so it does not fundamentally resolve the dead zones. Additionally, there is a problem with the installation space increasing because the transmitting antenna must be enlarged in the y-axis direction. FIG. 1 is a drawing showing a front view of an anti-theft system according to an embodiment of the present invention. FIG. 2 is a plan view of an anti-theft system according to an embodiment of the present invention. FIG. 3 is a diagram showing the loop coil structure of a transmitting antenna according to an embodiment of the present invention. FIG. 4 is a block diagram showing the configuration of a transmitter according to an embodiment of the present invention. Figure 5 is a diagram showing examples of electrical signals applied to each of the loop coils of Figure 3. FIG. 6 is a diagram showing the distribution of the magnetic field formed within the detection zone at different time points when the electrical signal of FIG. 5 is applied. Figure 7 is a diagram showing a conventional transmitting antenna structure. Figure 8 is a diagram showing a magnetic field distribution to explain the shadow area occurring in the transmitting antenna structure of Figure 7. Figure 9 is a diagram showing another conventional transmitting antenna structure. In order to provide a detailed explanation sufficient for a person skilled in the art to easily implement the technical concept of the present invention, the most preferred embodiment of the present invention will be described with reference to the accompanying drawings. It should be noted that in assigning reference numerals to the components of each drawing, the same components are given the same reference numeral whenever possible, even if they are shown in different drawings. Furthermore, in describing the present invention, if it is determined that a detailed description of related known components or functions could obscure the essence of the present invention, such detailed description is omitted. Hereinafter, embodiments of the present invention will b