EP1331733B1 - LC-type filter module and helical filter comprising at least two such modules - Google Patents

Description

The present invention as defined in independent claim 1 relates to the field of passive electrical components or circuits, more particularly the filters formed from the combination of capacitors and inductances, and relates to a filter module composed of such components and a helical filter, in particular a bandpass, comprising at least two such modules.

In some applications, in particular in connection with nuclear magnetic resonance (NMR), it is necessary to have components adapted to high frequencies that can withstand high power. It is of course advantageous if such components are optionally easily adjustable, easy to manufacture and low cost, and report a good aging resistance.

Thus, in terms of capacities, it has been proposed a variable or adjustable capacity structure essentially comprising, on the one hand, a first element of conducting material in the form of an at least partially hollow rod or bar, comprising a hole or perforation extending axially in the body of said first member to form a portion of tube and secondly a second element also of conductive material in the form of a rod that can fit into a variable depth in said axial hole, the engagement depth of the second element in the first element determining the degree of capacitive coupling between them, and thus the value of the resulting capacitance.

The document FR-A-1,439,858 give the example of such a filter.

These capabilities are used in particular for the production of high frequency filters.

Although such a capacitance construction can withstand large dynamic currents, its voltage resistance is not sufficient in certain applications, or does not guarantee sufficient security against the risk of arcing, in case of surge .

In addition, it is also advantageous, in many cases, to group together several capacitive components with one or more inductive components, both having high power terms, into compact filtering modules that are easy to manufacture and assemble together. a variable number, low cost and having very good filtering qualities.

The present invention is intended in particular to meet at least some of the needs expressed above and to overcome at least some of the aforementioned drawbacks.

For this purpose, the subject of the present invention is an LC type filter module comprising at least two capacitors and at least one inductor, characterized in that each of the capacitors is constituted by a first elongate element made of a partially embedded conductive material, on a determined depth, in a hole or a perforation formed in a second element made of a conductive material, electrically connected to the second elements of the other capacitor or possibly to the different capacitors, at least the lateral internal surfaces defining the said elements ( e) holes or perforations being covered with a dielectric material, as well as the edges of the openings of the holes or perforations and at least parts, and preferably all, of the external surfaces of the second (s) element (s) adjoining at said edges, and in that the winding of each inductor is carried by a support body of a diel material electrical, possibly contiguous to the second element (s) or the dielectric coating covering at least partially the outer face of each second element.

Another object sought by the invention is to provide a helical bandpass filter having in particular better harmonic filtering.

For this purpose, the present invention also relates to a helical filter of at least order 2 modular structure, characterized in that it is constituted by the series association of at least two filter modules of the aforementioned type, each having specific filtering characteristics adjustable by adjusting the characteristics of at least one capacitor, the individual modules being each housed in a corresponding electromagnetically isolated compartment of a Faraday cage casing.

• la figure 1 est une représentation schématique, partiellement en coupe, d'un module de filtre selon un premier mode de réalisation de l'invention ;
• la figure 2 est une vue éclatée en perspective d'un filtre hélicoïdal composé de quatre modules de filtre montés en série, selon un second mode de réalisation de l'invention ;
• la figure 3 est une vue de dessus en perspective du filtre de la figure 2 à l'état assemblé (le capot de fermeture du boîtier étant enlevé), et,
• la figure 4 est un schéma électrique équivalent du filtre représenté sur les figures 2 et 3.

The invention will be better understood, thanks to the following description, which relates to preferred embodiments, given by way of non-limiting examples, and explained with reference to the attached schematic drawings, in which:

• Figure 1 is a schematic representation, partially in section, of a filter module according to a first embodiment of the invention;
• FIG. 2 is an exploded perspective view of a helical filter composed of four filter modules connected in series, according to a second embodiment of the invention;
• FIG. 3 is a perspective top view of the filter of FIG. 2 in the assembled state (the closure cap of the housing being removed), and
• Figure 4 is an equivalent electrical diagram of the filter shown in Figures 2 and 3.

As shown in particular in FIGS. 1 and 4 of the accompanying drawings, the filter module 1 comprises at least two capacitors 2, 2 'and at least one inductor 3.

According to the invention, each of the capacitors 2, 2 'is constituted by a first elongated element 4; 4 'in a partially embedded conductive material, to a given depth, in a hole or perforation 5 formed in a second element 6 of a conductive material, electrically connected to the second elements of the other capacity or possibly common to the different capacitances 2, 2 ', at least the lateral internal surfaces defining the said holes or perforations 5 being covered with a dielectric material 7, as well as the edges 5' of the openings of the holes or perforations 5 and at least parts , and preferably all, of the external surfaces of the second element (s) 6 adjacent to said edges 5 ', and in that the winding 3' of each inductor 3 is carried by a support body 8 made of a material dielectric, possibly contiguous with the second element (s) 6 or the dielectric coating 7 at least partially covering the outer face of each second element 6 (FIGS. 1 to 3).

The aforementioned provisions make it possible in particular to obtain improved power handling, very good protection of the capacities against the risks of arcage (between the first and second elements) and, if necessary, a very compact structure.

In order to allow an adjustment of the properties of the filter module 1, at least one of the capacitors 2, 2 'is in the form of a variable capacitance, its first elongated element 4 consisting of a screw or the like with an end portion 4 ", opposite its head, devoid of threading, and being slidable, advantageously with a sliding contact, into the hole or the perforation 5 of the corresponding second element 3, another 4 'of said first unit elements 2 of said capacitors 2, 2 ', preferably non-sliding, and the one or the second element (s) 6 forming, being integral with or each carrying one of the two branch terminals 9, 9 'of said filter module 1.

A possible structure of variable capacity 2 is described in particular in the application for French Patent No. 02,00770 in the name of the plaintiff, the contents of which are incorporated herein by reference.

According to a preferred embodiment of the invention, shown in Figures 2 and 3 of the accompanying drawings, resulting in a compact construction, easy to mount and optimum resistance to shocks and arcs, the or each second (s) ) element (s) 6 is mounted entirely in the solid support body 8 of dielectric material carrying the winding 3 'of said inductor 3, the solid body 8 thus covering its or their outer surface.

Hollow tubes 10 of dielectric material and provided with a flange 10 'at one of their ends are mounted by interlocking in the holes or perforations 5 of the second element (s) 6 thus covering the internal surfaces desdit (s) holes or perforations 5, as well as the edges 5 'of their openings and possibly the outer surface portions adjacent to these.

As can be seen from the figures of the appended drawings, the different capacitances 2, 2 'may either comprise a second common element 6, in one piece (FIG. 1), or each may comprise a second element 6 that is clean and distinct from the second elements of the or other abilities (Figures 2 to 4).

Similarly, the dielectric material 7 may cover only part or all of the outer surface of the second element (s) 6 and be made in one piece, with a continuous overlap of the side walls of the holes 5, their edges 5 'at the introduction openings of the corresponding first elements 4 and external surfaces alternative to said edges, or in several parts juxtaposed, also producing a coating 7 quasi-continuous.

According to an advantageous embodiment of the invention, easy to achieve, and as shown in Figures 2 and 3 of the accompanying drawings, the second elements 6 each consist of a portion of metal tube inserted in a fitted manner, in a hole corresponding blind 8 'formed in the solid support body 8 of dielectric material, the flush edges 5' of the different portions of tubes 6 being secured, for example by welding or crimping, with a plate of connection 11 in a conductive material, coming into contact on the face of the support body 8 provided with the blind holes 8 'for receiving the second elements 6, said wafer 11 being provided with a branch terminal 9' in the form of an ear lateral prominent.

In order to provide protection against possible arcing between the first elements 4 and the wafer 11 forming part of the corresponding second element 6, a wafer 12 made of dielectric material covers the conductive connection plate 11 and has orifices 12 'provided with radial recesses. 12 "forming annular receiving seats, with cooperation of shapes, for the flanges 10 'of the hollow tubes 10 fitted into the holes or perforations 5 of the second elements 6 of the capacitors 2, 2', the plate 12 may for example consist of a cut edge of the support body 8.

The assembly cooperating flanges 10 'with the wafer 12 ensures a continuity of the dielectric coating 7 at this level, with creation of a baffle ensuring the absence of gap.

As also shown in the figures of the accompanying drawings, the filter module 1 advantageously comprises an inductor 3 (or L i, i) and two capacitors 2 (or Ci, i) and 2 '(or Ci-1, i) connected to a common electrical node 1 ', at least one 2 of said capacitors 2, 2' being variable or adjustable due to a first element 4 mounted translational in the second element 6 corresponding and the first element 4 'of the other capacity 2 ', which may be non-variable, being secured to a connection terminal 9 in the form of a lamella 13 fixed on the support body made of dielectric material 8 and on which the end of a connection line 14 is secured. .

The blade 13 can thus serve as a support for the first elongated element 4 ', the latter may also be in the form of a screw or the like.

Preferably, said solid support body 8 has a cylindrical structure and comprises a helical groove 15 extending over at least part of its external surface, for housing the winding 3 'forming the induction 3, said support body 8 consisting preferably of polytetrafluoroethylene PTFE (Figures 2 and 3).

For a good fastening and a rigid retention of the winding 3 ', the latter can be advantageously mounted in force and in a manner adjusted in at least a portion of said groove 15.

Such an arrangement makes it possible to preserve in time the physical, electrical and electromagnetic characteristics of the inductor 3, avoiding its deformation, by providing damping of the vibrations and shocks to which said inductor 3 could be exposed and by preserving it from any deformation related to temperature variations.

In order to avoid any interference of the module 1 with the surrounding medium, the constituent parts of said capacitors 2, 2 'and of said at least one inductor 3 are housed in a metal casing 16, preferably parallelepipedal, forming a Faraday cage and are maintained in the latter by attachment to two opposite side walls of the latter by means of two screws 4, 17, studs or the like, a first of said screws constituting the first elongated sliding member 4 with a variable capacity 2 and the second screw 17 solidarisant the opposite end of the dielectric support body 8 to a corresponding wall of said housing 16 and ensuring the grounding of said at least one inductor, the two connecting lines 14 of said module 1 extending through through holes 18 , of small size, preferably substantially adjusted in size to those of the connecting lines 14 which pass through them, these orif ices being formed in the walls of said housing 16.

According to another characteristic of the invention, the winding 3 'of the inductor 3, mounted on the support body 8, has a variable pitch, increasing towards the second element (s) 6 of the capacitors 2 , 2 'or edges 5' of the openings of the holes or perforations 5 of said second element (s) 6.

This measurement makes it possible to further protect the winding 3 'against the arcage and breakdown phenomena on the side of the inductance 3 exposed to the highest voltage.

The present invention also relates to a helical filter at least of order 2 with a modular structure, characterized in that it consists of the series association of at least two filter modules 1 as described above, each having specific filtering characteristics adjustable by adjusting the characteristics of at least one capacitor 2, the individual modules 1 being each housed in a corresponding closed compartment 16 'of a Faraday cage casing 16, being isolated electromagnetically from the outside and the other module or modules 1 forming the filter.

Such an embodiment makes it possible to considerably improve the filtering of the harmonics, because of the absence of magnetic coupling between modules 1 or modules 1 with the outside.

Advantageously, the electrical connection between two adjacent modules 1 is effected by means of a corresponding line 14 extending through the wall 16 "separating said two adjacent modules 1 concerned, by an orifice 18 whose size is substantially adjusted. to that of the section of said line 14.

By limiting the parasitic inductance 19 (Ci, i + 1) of the connection between modules 1 (especially due to the connection line 14), a purely capacitive coupling is thus obtained between the modules 1 (by the capacitors Ci, i + 1) for eliminating the higher harmonics in said filter.

According to a preferred embodiment of the invention, also shown in FIGS. 2, 3 and 4, the helical filter is advantageously constituted by the series association of four filter modules 1 according to any one of claims 1 to 7, the conductors of the connection connectors 20, 20 'of said filter, mounted on the housing 16, being connected to the series association of filter modules 1 at the level of the inductances 3 of the two end modules 1 of said module string 1 forming said filter .

The capacity 2 'of the first module 1 of the chain forming the filter will then be useless and may be deleted.

Of course, the invention is not limited to the embodiments described and shown in the accompanying drawings. Modifications are possible, particularly from the point of view of the constitution of the various elements or by substitution of technical equivalents, without departing from the scope of protection of the invention.

Claims (12)

1. L-C type filter module comprising at least two capacitors and at least one inductor, characterised in that each of the capacitors (2, 2') consists of a first elongated element (4; 4') made of conductive material partially fitted, over a determined depth, in a hole or perforation (5) made in a second element (6) made of conductive material, connected electrically to the second elements of the other capacitor(s) or possibly common to the various capacitors (2, 2'), at least the internal lateral surfaces defining said holes or perforations (5) being covered with a dielectric material (7), as are the edges (5') of the openings of the holes or perforations (5) and at least parts, and preferably all, of the external surfaces of the second element(s) (6) adjoining said edges (5'), and in that the coil (3') of each inductor (3) is carried by a support body (8) made of a dielectric material, possibly contiguous with the second element(s) (6) or with the dielectric coating (7) at least partially covering the external face of each second element (6).
2. Filter module according to claim 1, characterised in that at least one (2) of the capacitors (2, 2') is produced in the form of a variable capacitor, its first elongated element (4) consisting of a screw or similar with an end portion (4"), opposite its head, that has no thread and can slide, advantageously with sliding contact, into the hole or perforation (5) of the corresponding second element (3), another (4') of said first unit elements (2) of said capacitors (2, 2'), which is preferably non-sliding, and the or one of the second element(s) (6) forming, since they are each integral or load-bearing, one of the two branch terminals (9, 9') of said filter module (1).
3. Filter module according to any one of claims 1 and 2, characterised in that the or each of the second element(s) (6) is installed wholly in the solid support body (8) made of dielectric material carrying the coil (3') of said inductor (3), this solid body (8) thus covering its or their external surface, and in that hollow tubes (10) made of dielectric material and provided with a flange (10') at one of their ends are fitted into the holes or perforations (5) of the second element(s) (6), thus covering the internal surfaces of said holes or perforations (5), and the edges (5') of their openings and possibly parts of the external surface adjoining the edges.
4. Filter module according to any one of claims 1 to 3, characterised in that the second elements (6) each consist of a portion of metal tube inserted, in a close-fitting way, into a corresponding blind hole (8') in the solid support body (8) made of dielectric material, the flush edges (5') of the various portions of tubes (6) being attached, for example by welding or crimping, to a connection plate (11) made of conductive material, making contact on the face of the support body (8) provided with blind reception holes (8') for the second elements (6), said plate (11) being provided with a branch terminal (9') in the form of a prominent lateral lug.
5. Filter module according to claims 3 and 4, characterised in that a plate (12) made of dielectric material covers the conductive connection plate (11) and comprises orifices (12') provided with radial recesses (12") forming ring-shaped seats for the positive reception of the flanges (10') of the hollow tubes (10) fitted in the holes or perforations (5) of the second elements (6) of the capacitors (2, 2').
6. Filter module according to any one of claims 1 to 5, characterised in that it comprises an inductor (3 or L i,i) and two capacitors (2 or Ci, i and 2' or Ci-1, i) connected to a common electric node (1'), at least one (2) of said capacitors (2, 2') being variable or adjustable due to a first element (4) installed with translation capacity in the corresponding second element (6) and the first element (4') of the other optionally non-variable capacitor (2') being attached to a branch terminal (9) in the form of a thin strip (13) fixed on the support body made of dielectric material (8) and to which is attached the end of a connection line (14).
7. Filter module according to any one of claims 1 to 6, characterised in that said solid support body (8) has a cylindrical structure and comprises a helical groove (15) extending over at least part of its external surface, for the housing of the coil (3') forming the inductor (3), said support body (8) preferably consisting of polytetrafluoroethylene and in that said coil (3') is press-fitted in a close-fitting manner in at least one portion of said groove (15).
8. Filter module according to any one of claims 1 to 7, characterised in that the constituent parts of said capacitors (2, 2') and of said at least one inductor (3) are housed in a closed, preferably parallelepiped, metal box (16) forming a Faraday cage and are retained therein by fixing to two opposed side walls thereof by means of two screws (4, 17), bolts or similar, a first of said screws forming the first sliding elongated element (4) of a variable capacitor (2) and the second screw (17) making the opposite end of the dielectric support body (8) integral with a corresponding wall of said box (16) and earthing said at least one inductor (3), the two connection lines (14) of said module (1) extending through traversing orifices (18) made in the walls of said box (16), of small size, preferably substantially adapted in dimensions to those of the connection lines (14) which traverse them.
9. Filter module according to any one of claims 1 to 8, characterised in that the coil (3') of the inductor (3), mounted on the support body (8), has a variable pitch, increasing in the direction of the second element(s) (6) of the capacitors (2, 2') or of the edges (5') of the openings of the holes or perforations (5) of said second element(s) (6).
10. Helical filter of at least the second order with a modular structure, characterised in that it is formed by the series connection of at least two filter modules (1) according to any one of claims 1 to 9, each with specific filtering characteristics that can be adjusted by regulating the characteristics of at least one capacitor (2), each of the various modules (1) being housed in a corresponding closed compartment (16') of a box (16) forming a Faraday cage, while being electromagnetically insulated from the exterior and from the other module(s) (1) forming the filter.
11. Helical filter according to claim 10, characterised in that the electrical connection between two adjacent modules is made by means of a corresponding line (14) extending through the wall (16") separating said two adjacent modules (1) concerned through an orifice (18) of which the size is substantially adapted to that of the cross-section of said line (14).
12. Helical filter according to any one of claims 10 and 11, characterised in that it is formed by the series connection of four filter modules (1) according to any one of claims 1 to 9, the conductors of the connection connectors (20, 20') of said filter, mounted on the box (16), being connected to the series connection of filter modules (1) in the region of the inductors (3) of the two end modules (1) of said chain of modules (1) forming said filter.

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