Built-in chip transponder with antenna coil

Abstract: An antenna circuit to be used in conjunction with a chip transponder such that the antenna circuit serves for both the reception of interrogative signals intended for the transponder as well as for response signals that are to be transmitted by the transponder. The antenna circuit has at least one magnetic circuit of high µ material, and is formed of ceramic core means, that have been built into a depression in a thick-walled surface intended to receive the chip transponder. This thick-walled surface may be of metal. The ceramic core means comprise at least a ceramic core resonator (2) and half a ceramic core (3) that functions as an antenna with its open side facing outward. In one aspect, the ceramic core resonator and the half ceramic core antenna are coupled by means of one or more secondary coils of the closed ceramic core, which also form the coils of the half ceramic core antenna. In another aspect, the secondary coil forms a resonating circuit with at least one capacitive element in series. In yet another aspect, the ceramic core resonator and the half ceramic core antenna are formed by one and the same half ceramic core, which may be closed in part by a magnetic covering disk. In yet another aspect, the resonator may consist of a half ceramic core which is placed against the back of the half ceramic core antenna.

Description: FIELD OF THE INVENTION The invention relates to a multicoil antenna circuit to be used with a transponder, whereby the antenna circuit serves both for the reception of interrogative signals for the transponder as well as for the dissemination of response signals to be transmitted by the transponder, whereby the antenna circuit has at least one magnetic circuit of high µ material and is formed of ceramic core means provided in a depression in a thick-walled surface. BACKGROUND OF THE INVENTION In practice it is known that in order for a transponder to be embedded in or attached to an object or an animal that is to be identified, it must be equipped with an antenna circuit or antenna element of high µ material. Thus, a transponder of this type is often equipped with a small ferrite staff that serves as an antenna beacon. One disadvantage is the fact that such an antenna circuit does not have such a sharply defined field of radiation into space. Similarly, such an embodiment does not lend itself well to incorporation into a thick-walled surface. SUMMARY OF THE INVENTION It is the object of the present invention to provide an antenna circuit for a transponder that is to be incorporated into a thick-walled surface that does not protrude and is thus little prone to damage from the outside due to crushing, one that has an effective field of radiation while retaining a high quality factor and sufficient selection difference. This object is obtained with an antenna circuit of the type mentioned in the preface according to the invention such that the the ceramic core means comprise at least a ceramic core resonator and half a ceramic core that functions as an antenna and that, with its open side, faces outward, which resonator and antenna are mutually coupled one to the other within the depression, which also comprises the transponder as a chip, the radiation field of the antenna extending in a direction away from the surface. Said surface is, for example, made of metal. In this embodiment in keeping with the invention, a damage-resistant chip transponder that is built into a thick-walled surface and an antenna circuit are realized which, despite their incorporation into the metal, yield a high quality factor and adequate antenna properties. The selective distance in this case may be, for example, 20 to 30 cm. From US-A-3823403 an antenna circuit is known having a multicoil antenna element with an overall length substantially at a quarter wavelength or odd multiples thereof, which multicoil element is provided in a thick-walled electrically conducting surface as a ground plane. Said antenna element is suited for use with compact transceivers. The depression may be an airfilled cavity or may be loaded with a dielectric or ferrite. The loading may take the form of a core for the coil or the coil may be partially or completely embedded in the permeable material. BRIEF DESCRIPTION OF THE DRAWINGS The invention will be illustrated in greater detail by virtue of a few examples of various embodiments, calling attention to the drawings, in which: Figures 1 a and 1 b respectively present a transverse section view and an electrical diagram of the first embodiment in keeping with the invention; Figures 2a and 2b respectively present a transverse section view and electrical diagram of a second embodiment in keeping with the invention; Figures 3a, 3b, and 3c respectively present a transverse section view with a single turn, a transverse section view with the corresponding structure of a number of coil packets, and an electrical diagram of a third embodiment in keeping with the invention; Figures 4a and 4b respectively present a transverse view and an electrical diagram of a fourth embodiment in keeping with the invention; Figures 5a, 5b, and 5c respectively present a transverse view, a frontal view, and an electrical diagram of a fifth embodiment in keeping with the invention; and Figure 6 presents a transverse view of a chip transponder built into a thick-walled metallic surface and the antenna coil thereunto appertaining. DETAILED DESCRIPTION OF THE INVENTION The incorporation of a chip transponder into a thick-walled metallic surface and a ceramic core as an antenna entails the problem that the quality factor which, in open space, may be 80, for example, is diminished to 60, for example, as a result of being built in. Such incorporation, therefore, must occur in such a way that the radiation field has sufficient scope and selective distance. Preferably, such a selective distance should be 20 to 30 cm. This is realized in the embodiments that are illustrated in the following figures. Figure 1a shows a transverse view of an antenna circuit 1 that works in conjunction with the chip transponder, which circuit consists of a ceramic core resonator 2 and a ceramic core antenna 3. The resonator 2 is formed of a closed ceramic core that consists of two half ceramic cores 4, 5, from which a secondary coil (two windings) is connected with a half of a ceramic core that serves as an antenna. The resonator with the closed ceramic core can, despite the metallic environment, have a high Q, as a result of which the antenna which has the ceramic core can have a lower Q. As a result of the aforementioned loose connection, some energy is used for the radiation field. The quality factor on the primary side in the resonator remains sufficiently high. In Figure 1b, it is shown that the primary coil in the resonator forms a resonant circuit with a capacitative element C1 in series. The resonator is connected to the chip transponder 6. Figure 2a shows a transverse section of a second embodiment. The secondary circuit is now embodied in such a way as to resonate with a capacitive element C2. In the equivalent diagram, which is shown in Figure 2b, the frequency of the secondary antenna circuit 8 can be adjusted, for example, to the low side of the frequency band that is to be used, while the primary resonator 7 is then adjusted to its high side. In this embodiment, the coupling factor, determined by the number of coils and the resistor R, is chosen in such a way that a flat band curve is obtained for the transponder application. In Figure 3a, a transverse section of a third embodiment is shown, one with a so-called sliced-inductor packet 10. The resonator and the antenna are formed by one and the same half ceramic core. This embodiment has the best antenna properties with good scope of field and an appropriate selection distance. It is bothersome, however, to retain a good quality factor in this case. For the purpose of achieving this end, tinsel conductor, for example, may be used. At the same time, independent, flat, disk-shaped coil packets, as shown in figure 3b, may be used as coils in order to keep the capacity of the total assembly low, and, by these means, to retain a high quality factor of the resonator. The equivalent electrical diagram is shown in figure 3c. In Figure 4a, a transverse section view is presented of a fourth embodiment in which the resonator 12 that consists of having a ceramic core is placed with its open side against the antenna 13 that consists of half a ceramic core. In this embodiment, magnetic energy from the resonator is given off to the ceramic core antenna by way of the magnetic coupling. In Figure 4b, once again, the equivalent electrical diagram is indicated. In Figure 5a, a transverse section view of a further embodiment is indicated, in which the ceramic core resonator and the ceramic core antenna are formed once again by one and the same ceramic core 14. This ceramic core is, in part, shut off on the outside by means of a covering disk 15, such as Figure 5b indicates. The mechanism is such, in the meantime, that the resonator's field of distribution is used as the field of radiation due to the fact that the ceramic core has no ideal closed magnetic circuit. In Figure 5c, once again, the equivalent electrical diagram is shown. In Figure 6, a transverse section view is presented of a transponder 6 with the appropriate resonator-antenna circuit 17. The whole is encapsulated in a packaging 18 and incorporated into a thick metallic wall 16. The antenna circuit may be executed as indicated in Figures 1 to 5.

Claims: A multicoil antenna circuit (1) to be used in conjunction with a transponder (6), whereby the antenna circuit serves for both the reception of interrogative signals for the transponder as well as for dissemination of response signals that are to be transmitted by the transponder, whereby the antenna circuit has at least one magnetic circuit of high µ material and is formed of ceramic core means provided in a depression in a thick-walled surface (16), characterised in that the ceramic core means comprise at least a ceramic core resonator (2) and half a ceramic core (3) that functions as an antenna and that, with its open side, faces outward, which resonator and antenna are mutually coupled, one to the other, within the depression, which also comprises the transponder (1) as a chip (6), the radiation field of the antenna circuit extending in a direction away from the surface. An antenna circuit in accordance with claim 1, wherein the resonator consists of a closed ceramic core (4, 5), and wherein the ceramic core resonator (2) and the half ceramic core antenna (3) are coupled by means of one or more secondary coils of the closed ceramic core, which also form the coils of the half ceramic core antenna. An antenna circuit in accordance with claim 2, wherein the aforementioned secondary coil forms a resonating circuit (8) with at least one capacitive element (C2) in series. An antenna circuit in accordance with claim 3, wherein the resonant circuit (8) is adjusted, with its frequency on the low side of the frequency band and the resonator (7) on the high side of the frequency band. An antenna circuit in accordance with claim 1, wherein the ceramic core resonator and the half ceramic core antenna are formed by one and the same half ceramic core (10, 14) having one or more coils. An antenna circuit in accordance with claim 5, wherein the coils are executed as flat disk-shaped coil packets. An antenna circuit in accordance with claim 5, wherein the same half ceramic core (14) is closed in part by a magnetic covering disk (15). An antenna circuit in accordance with claim 1, wherein the resonator consists of a half of a ceramic core (12) which is placed against the back of the half ceramic core antenna (13) such that a portion of the magnetic energy from the resonator is transferred to the antenna via magnetic coupling. An antenna circuit in accordance with claim 1, wherein the thick-walled surface (16) consists of metal.

Inventors: D HONT LOEK, D'HONT, LOEK
Applicants: TEXAS INSTRUMENTS HOLLAND, TEXAS INSTRUMENTS INC, TEXAS INSTRUMENTS HOLLAND B.V., TEXAS INSTRUMENTS INCORPORATED
Application year: 1991
Main classification: H01Q7
IPC codes: H01Q7, H01Q1, G06K19, G06K7