JPH08222937A - Antenna for theft prevention device - Google Patents

Abstract

PURPOSE: To reduce the effect of an obstacle by arranging a metallic dummy obstacle through which magnetic flux passes to a lower side face of an antenna coil of a theft prevention antenna arranged on a floor. CONSTITUTION: An antenna coil 1 is mounted in a rubber made floor mat 2 and a cable 3 for connecting a transmitter is connected to an output terminal. A dummy obstacle 4 insulated from the coil 1 is fitted to a bottom face of the mat 2 and the mat is installed on a floor. The transmitter connecting to the cable 3 emits a radio wave upward, and when a self-alarming tab passes through its electric field, a reception circuit in the tab is active to raise an alarm. The obstacle 4 is formed by arranging iron stripes 4a, in which the width of each iron plate 4a and intervals among the iron plates 4a are equal to each other and a ratio of the area cupied by the obstacle 4 and the bottom area of the mat is nearly 50%. Furthermore, the coil 1 is adjusted to be an optimum when the obstacle 4 is added to the coil 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an antitheft antenna installed on a floor.

[0002]

2. Description of the Related Art Anti-theft devices include, for example, a method of operating a self-tapping tag using a 22 KHZ long wave band or an ultra-ultra long wave band, and a resonance circuit using a short wave band of 8.2 MHZ, for example. A method of detecting the presence of a tag having a tag is known. In the former method, a standing plate or standing frame incorporating an antenna is installed beside the passageway at the doorway, or a floor mat with an antenna is installed on the floor of the doorway, and is checked when passing through the doorway. It is like this.

[0003]

Under the floor, there are H steel, reinforcing bars, pipes, etc. running, and when the antenna is installed on these metal objects, the antenna is affected by the metal objects. Since the inductance of the coil changes, as shown in FIG. 4, the antenna characteristics change, such as the resonance point being shifted or the output level at a predetermined frequency being lowered. The change in the antenna characteristics causes a malfunction of the self-sounding tag, and the antitheft function is not sufficiently exerted. In particular, the structure under the floor cannot be judged from the appearance and cannot be adjusted in advance.

[0004]

DISCLOSURE OF THE INVENTION The present invention is an antitheft antenna in which the influence of a metal obstacle at a place of installation is reduced, and its structure is such that a magnetic flux can pass through the lower surface of an antenna coil. The dummy obstacles are arranged, and the dummy obstacles are arranged in a striped pattern, a grid pattern, or a random pattern, and the dummy obstacles may be about half the area surrounded by the loops. it can.

[0005]

If the dummy obstacles are provided and the antenna characteristics are adjusted so that the antenna characteristics are predetermined, the antenna characteristics will not change if there is no obstacle below the floor surface. There is no influence of the overlapping portion of the obstacle and the dummy obstacle, and the influence of the obstacle is reduced. If the ratio of obstacles is 50%, theoretically the probability of overlapping is one-half, so the effect is halved.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An antenna for a theft prevention device according to the present invention will be described with reference to the drawings. 1 is an antenna coil for 22KHZ that is multi-wound. This antenna coil 1 is incorporated in a rubber floor mat 2 and the output terminal part is
A cable 3 for connecting the transmitter is connected. A dummy obstacle 4 insulated from the antenna coil 1 is attached to the bottom surface of the floor mat 2, and is laid on the floor surface F at the entrance and exit, as shown in FIG. 2, from a transmitter connected by a cable. The electric output of radiates radio waves (electromagnetic waves) upward, and when the self-tapping tag passes within the electric field range, the receiving circuit in the tag works to issue an alarm.

The dummy obstacle 4 is composed of iron plates 4a, 4a.
. Are arranged in stripes, and the width of the iron plate 4a and the iron plates 4a, 4
The intervals between the a are even, and the ratio of the dummy obstacles 4 to the bottom area of the floor mat 2 is about 50%. Further, the antenna coil 1 is adjusted to be optimal for 22 KHZ with the dummy obstacle 4 attached.

In the antenna thus formed, the H steel 5 is provided under the floor of the installation place, as shown in FIGS. 3A and 3B, for example.
Assuming that the obstacle of No. 2 is running, when considering the surface D where the H steel 5 and the iron plate 4a overlap and the surface S where they do not overlap,
Since the antenna coil 1 has already taken into consideration the influence of the overlapping surface D, the influence of the overlapping surface D in the H steel 5 is not exerted, and only the non-overlapping surface S is affected and the dummy obstacle If the ratio of 4 is 50%, H
The effect of Steel 5 will be halved.

The dummy obstacles are preferably made of metal capable of passing magnetic flux, such as nickel or copper, in addition to iron. In addition to arranging the iron plates in a striped pattern, the dummy obstacles are assembled in a grid pattern as illustrated in FIG. It is also possible to employ the reinforced reinforcing bars and the wire netting 4b, or to form them in a random pattern, and the proportion of the area occupied by these metal portions is not limited to 50% and may be increased or decreased as appropriate.

In addition, the left and right patterns are changed so that the left and right can be reversed at the time of installation so that the one that is less affected by the characteristic change can be selected, or the floor mat is not integrated and is separated from the floor mat. However, the present invention is not limited to the embodiment, in which the pattern is provided and divided into a plurality of pieces so that the patterns can be rearranged or changed.

The antenna for the anti-theft device of the present invention reduces the influence of metal objects in the installed underfloor structure, so that the self-tapping tag passing over the antenna can be reliably operated and the anti-theft function can be maintained. it can.

Although the embodiment is an antenna for 22KHZ, it is selected for an apparatus adopting a frequency other than 22KHZ so as not to be affected by noise generated from an inverter type fluorescent lamp, for example. Corresponding with an antenna of different frequency.

[0013]

According to the present invention, since the influence of the obstacle under the floor is reduced by the dummy obstacle, the change in the antenna characteristic is small and the influence on the function can be substantially ignored.

[Brief description of drawings]

FIG. 1 is an explanatory view of separation of an antenna for an anti-theft device according to the present invention.

FIG. 2 is an explanatory diagram of an anti-theft device antenna.

3A and 3B are explanatory diagrams of a reduction effect.

FIG. 4 is an explanatory diagram showing changes in antenna characteristics.

FIG. 5 is an explanatory diagram of a modification example.

[Explanation of symbols]

1 ... Antenna coil, 2 ... Floor mat, 3 ... Cable, 4 ... Dummy obstacle, 4a ... Iron plate, 4b ...
Wire mesh, 5 ・ ・ H steel, D ・ ・ Overlapping surface, S ・ ・ Non-overlapping surface.

Claims (3)

[Claims] 1. An anti-theft antenna, comprising: an anti-theft antenna installed on a floor, wherein a dummy obstruction made of a metal capable of passing magnetic flux is arranged on a lower side surface of the antenna coil. 2. The anti-theft antenna according to claim 1, wherein the dummy obstacle is a striped iron plate. 3. The anti-theft antenna according to claim 1, wherein the dummy obstacle occupies approximately 50% of the area inside the loop of the antenna coil.