Antenna element for anti-theft devices

Abstract: An antenna element (33) for anti-theft devices (10, 11) of the type affecting a magnetic, acoustic or electromagnetic field, has two antennas (35) projecting from opposite sides of said element and forms together with said antennas a configuration similar to the letter S.

Description: The invention relates to an antenna element for anti-theft devices of the type affecting a magnetic, acoustic or electromagnetic field, which is maintained between bow-shaped antennas at the exit of a shop, to disturb the field and cause signal generation. The antenna element of the invention is defined by the characteristics of claim 1. An antenna device according to the preamble of Claim 1 is known from EP-A-0 002 595. In order to explain the invention in more detail an embodiment thereof will be described below reference being made to the accompanying drawing in which FIG. 1 is a fragmentary perspective view of a spectacle frame provided with an anti-theft device, and FIG. 2 is view of a cover from the back side thereof which is attached to the anti-theft device and is provided with the antenna element of the invention. The anti-theft device in FIG. 1 comprises a sleeve 10 open at one end thereof, which has rectangular cross-sectional shape and preferably is made of plastics, for example polycarbonate. On one broad side thereof the sleeve is provided with a cover 11 of the same material as the sleeve, said cover being attached to the sleeve by ultrasound welding. The sleeve 10 has opposing longitudinal slots 12 in the two narrow sides thereof, which are big enough to allow the bow 14 of a spectacle frame 13 to be passed through the slots. Clamping means is provided in the sleeve 10, and the body formed by sleeve 10 and cover 11 is mounted to the bow, and is demounted from the bow by using a special tool, which can be engaged with said clamping means. Inside the body there is located an element 33 (a so-called "diode") of the type affecting a magnetic, acoustic or electromagnetic field maintained between bow-shaped antennas at the exit of a shop, to disturb the field and cause signal generation. Said element is mounted inside the cover 11, and for this purpose the cover has on the backside thereof four small pins 34 between which the element 33 is located while antenneas 35 of flexible wire provided on the element are passed around other, large pins 36 on the backside of the cover. When the cover 11 is attached to the sleeve 10 the pins are positioned adjacent the outside surface of the sleeve such that the element is held in a well defined position. As will be seen from FIG. 2 the antenna element of the invention formed by element 33 and antennas 35 has a configuration similar to the letter S when mounted to cover 11.

Claims: Antenna device for antitheft-appliancies (10, 11) of the type affecting a magnetic field, comprising an antenna element (33) and two antennas (35) projecting from opposite sides of said element and forming together with the element a configuration similar to the letter S each bow of which consists of two parallel first straight portions mutually spaced transversely thereof, and a second straight portion extending between one ends of said first portions, the other ends of said first portions of each bow, located at opposite sides of the S, each being connected to said antenna element located therebetween, characterised in that each antenna (35) consists of a wire, and that means (34, 36) are provided on the backside of a cover (11) forming part of an anti-theft device (10, 11) defining the configuration of the antenna wires and retaining the antenna element (33) and the antennas on said substrate. Antenna device as in claim 1, characterised in that said means (34, 36) comprise projecting pins on said cover (11).

Inventors: HOLMGREN BERTIL, HOLMGREN, BERTIL
Applicants: MW TRADING APS
Application year: 1989
Main classification: G08B13
IPC codes: G08B13