LONG RANGE LOW FREQUENCY ANTENNA

Abstract

A long range low frequency antenna having an elongated magnetic core; a coil surrounding the elongated magnetic core; a bobbin; where the elongated magnetic core is introduced in a cavity of the bobbin; and a housing overmolded on the bobbin in a waterproof manner. The antenna also comprises at least one damper located at one extreme of the elongated magnetic core. The at least one damper is made of an elastic and thermally-stable compound having a resin and a first filler including a natural mineral filler. Therefore, longitudinal dilatations, shrinkage, mechanical shocks, and vibrations of the elongated magnetic core are absorbed by the at least one damper, avoiding an impact over an inductance variation of the coil.

Claims

1. A long range low frequency antenna, comprising: an elongated magnetic core; a coil surrounding the elongated magnetic core; a bobbin; the elongated magnetic core introduced in a cavity of the bobbin; a housing overmolded on the bobbin in a waterproof manner; at least one damper located at one extreme of the elongated magnetic core, the at least one damper made of an elastic and thermally-stable compound comprising a resin and a first filler including a natural mineral filler, whereby longitudinal dilatations, shrinkage, mechanical shocks, and vibrations of the elongated magnetic core are absorbed by the at least one damper, avoiding an impact over an inductance variation of the coil.

2. The long range low frequency antenna of claim 1, comprising two dampers each one being located against an extreme of the elongated magnetic core.

3. The long range frequency antenna of claim 1, comprising a plurality of dampers located, continuously or discretely, against the elongated magnetic core.

4. The long range low frequency antenna of claim 1, further comprising one damper fully covering the elongated magnetic core, providing a casing.

5. The long range low frequency antenna of claim 1, wherein the natural mineral filler comprises quartz, quartzite, marble, sand and/or calcium carbonate, preferably finely divided.

6. The long range low frequency antenna of claim 1, wherein the elastic and thermally-stable compound further comprises a second filler including a given amount of aluminum hydroxide.

7. The long range low frequency antenna of claim 1, wherein the elongated magnetic core has a length comprised in a range between 200-500 mm.

8. The long range low frequency antenna of claim 1, wherein the elongated magnetic core is made of a plurality of elongated magnetic cores portions butt to butt connected.

9. The long range low frequency antenna of claim 8, wherein each butt to butt connection includes a plurality of self-adhesive ferromagnetic sheets stiffeners.

10. The long range low frequency antenna of claim 8, further comprising a plurality of elastic annular holders surrounding the elongated magnetic core portions along several different areas.

11. The long range low frequency antenna of claim 1, wherein the bobbin comprises two independent hollow parts that are configured to engage with each other via a plurality of inter-connecting features formed on an edge of each part.

12. The long range low frequency antenna of claim 1, wherein the bobbin comprises a single part with a through hole formed on at least one extreme of the bobbin to facilitate the introduction of the elongated ferrite magnetic core.

13. The long range low frequency antenna of claim 11, wherein an outer lateral wall of the bobbin is engraved with grooves or includes slots through which wires of the coil of the elongated magnetic core are positioned.

14. The long range low frequency antenna of claim 1, wherein the natural mineral filler comprises two or more different fillers of diverse granulometry.

15. The long range low frequency antenna of claim 1, wherein the proportion in the elastic and thermally-stable compound of the first filler is between 50 and 90%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0054] The previous and other advantages and features will be more fully understood from the following detailed description of embodiments, with reference to the attached figures, which must be considered in an illustrative and non-limiting manner, in which:

[0055] FIG. 1 is an exploded view of the components that constitute the proposed long range frequency antenna, according to an embodiment of the present invention.

[0056] FIG. 2 is an exploded view of the components that constitute the proposed long range frequency antenna, according to another embodiment of the present invention.

[0057] FIG. 3 is a graph showing how susceptible the inductance variation can be due to the variation of the effective permeability.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0058] With reference to FIG. 1, therein it is illustrated an embodiment of the proposed long range frequency antenna (hereinafter referred as antenna). According to this embodiment, the antenna comprises a housing 1, a bobbin 2, 3 made of two independent hollow parts (i.e. like a sandwich structure) that are configured to engage with each other via triangular-shaped inter-connecting features formed on an edge of each part 2, 3; a monolithic elongated magnetic core 5; and damping elements 4.

[0059] The elongated magnetic core 5 can be manufactured by means of a manufacturing process of a volume of pressed (>300 T) and sintered magnetic material, through the application of a progressive cutting process, thus avoiding the “banana effects” and the waste that would occur in a normal manufacturing process of this type of cores.

[0060] The elongated magnetic core 5 is particularly formed by a soft-magnetic material. The core is a parallelepiped of ferrite (typically MnZn), large in length (particularly between 200-500 mm.), but small in width and minimum in thickness to avoid the “banana effect” from the sintering process.

[0061] In an embodiment, the elongated magnetic core 5 is obtained by: obtaining a block via pressing and sintering processes; encapsulating the super-block by means of an adhesive element and a metallic support disposed in one of its sides; cutting the super-block in elongated blocks of a desired size. Cutting can be done by a slow and precise operation with a diamond blade, controlling at all times depth of cut, penetration and abrasion of the ferrite. The whole process is cooled with cooling liquid and monitored. The encapsulation of the super-block allows the cuts to be made at the same time, without losing the positioning of the remaining part once an elongated piece has been cut. Once the elongated magnetic core 5 is available, a design and final assembly process is configured, as well as the selection of materials in direct or close contact with the ferrite to ensure a minimum variation (<5%).

[0062] Referring back to FIG. 1, the elongated magnetic core 5 receives a coil 8 (see enlarged view I) wound around the same. The coil 8 is particularly made of a wire of ferromagnetic material, and is positioned along grooves or slots engraved or included in an outer lateral wall of the bobbin 2, 3. The grooves or slots permit a self-adjustable attachment of the wire of the coil 8 and facilitate that the wire do not move sideways during manufacturing or stress processes.

[0063] To assemble the different components of the antenna of FIG. 1, in an embodiment, one damping element, or damper, 4 is placed at each extreme of the elongated magnetic core 5 and one damper 4 is placed to fully cover the elongated magnetic core 5. The elongated magnetic core 5 is then introduced inside the cavity of the bobbin 2, 3, engaging the wires of the coil 8 along the cited grooves or slots. Once the bobbin 2, 3 is closed the housing 1 is overmolded on the bobbin 2, 3 in a waterproof manner.

[0064] It should be noted that in other embodiments, in this case not illustrated, the proposed antenna comprises a single damper 4 located at one extreme of the elongated magnetic core 5 only. The proposed antenna can also comprise numerous dampers 4 located against the lateral, upper and/or bottom walls of the elongated magnetic core 5. The different dampers can be positioned either continuously from each other or discreetly.

[0065] The damper/s 4 is/are made of an elastic and thermally-stable compound, particularly of a resin, for example based on siloxanes or silicones, and a natural mineral filler, for example quartz, quartzite, marble, sand, calcium carbonate, among others, particularly finely divided. The compound has a combined hardness and coefficient of expansion that minimizes or reduces to 0 the fatigue or pressure on the elongated magnetic core 5 under conditions of typical temperature variations from −40° C. to 85° C. This means that the so-called “Vilary” effect (inverse effect to Joule's magnetostriction) does not occur. Hence, by including the damper/s 4 in the proposed antenna, longitudinal dilatations, shrinkage, mechanical shocks, and vibrations of the elongated magnetic core 5 can be absorbed, thus avoiding an impact over the inductance variation of the coil 8.

[0066] The proportion of said first filler in the elastic and thermally-stable compound can vary between 50 and 90%. In some embodiments, it is planned to use different natural mineral fillers with diverse granulometries.

[0067] In some embodiments, the elastic and thermally-stable compound can further include a second filler made of a given amount of aluminum hydroxide or its derivatives. The given amount of the aluminum hydroxide can be comprised in the range of 1-5% by weight with regard to the total weight of the elastic and thermally-stable compound including the resin.

[0068] In some embodiments, the housing 1 can be overmolded by way of the HPM technique. That is, an integral overmoulding with dynamic holders of the bobbin that allows that there is no pore since in the last phase of the injection of thermostable polymer with glass fibre load, normally PA66 or PBT, the supports are removed in a dynamic way and the bobbin floats on the casting, leaving no point of support. So mechanical rigidity, impact resistance and total waterproof of the housing is granted.

[0069] With reference to FIG. 2, therein it is illustrated another embodiment of the proposed antenna. Unlike the embodiment of FIG. 1, in this case the elongated magnetic core 5 comprises a plurality of elongated magnetic cores portions 5A, 5B, 5C that are butt to butt connected. Moreover, the antenna comprises two dampers 4, one for each extreme of the elongated magnetic core 5.

[0070] Each portion 5A, 5B, 5C has a curved design (concave-convex) at its ends. This curved design provides a double functionality, on the one hand it reduces the susceptibility to impact and falls and on the other hand it provides a greater contact surface between these portions, without the need to add structural glue that would increase the risk of breakage against falls and bending.

[0071] The connection of the portions 5A, 5B, 5C includes self-adhesive ferromagnetic sheets stiffeners 6, with a thickness between 0.1 and 0.4 mm, and an initial permeability higher than 200, which have a double effect, firstly to minimize the variation of the elongated magnetic core permeability and secondly to avoid the reduction of the quality factor (Q) and the inductance. Likewise, to achieve mechanical insulation between the elongated magnetic core 5 and the bobbin 2, 3 two or more elastic annular (e.g. ring-shaped) holders/members 7 are also included, for example made of silicone rubber or of a viscoelastic material, with low hardness, that act as an absorber against external vibrations, drops and bending.

[0072] In some embodiments, in this case not illustrated, the bobbin is made of a single part and includes a through hole on at least one lateral extreme thereof to facilitate the introduction of the elongated ferrite magnetic core 5.

[0073] Unless otherwise indicated, all numbers expressing measurements, conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about”. Accordingly, unless indicated to the contrary, the numerical parameters set forth in this specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by the presently disclosed patent matter.

[0074] As used herein, the term “about”, when referring to a value or to an amount of a length, width, concentration, percentage, etc., is meant to encompass variations of in some embodiments ±10%, or in some embodiments ±5%, from the specified amount, as such variations are appropriate to perform the disclosed antenna.

[0075] The embodiments described above are to be understood as a few illustrative examples of the present invention. It will be understood by those skilled in the art that various modifications, combinations and changes may be made to the embodiments without departing from the scope of the present invention. In particular, different part solutions in the different embodiments can be combined in other configurations, where technically possible.

[0076] The scope of the present invention is defined in the following set of claims.