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TEXT OF THE DESCRIPTION

Field of the invention

The present invention relates to an electromagnetic shielding panel and system

The present invention has been developed in particular in view of producing electromagnetic shielding systems designed to mitigate magnetic fields at civil and industrial frequencies (up to 100 kHz) .

Description of the prior art

Electric lines, transformers, electric panels, electric motors and, in general, all electrical apparatuses and systems affected by high intensity currents (for example greater than 100 A) and generally sinusoidal or, in any case, variable over time, produce magnetic fields in the surrounding space. Technical standards and laws establish maximum reference levels of the intensity of these magnetic fields considered compatible with human health or with the regular operation of devices of various types. The intensity of a magnetic field is generally defined by the value of the magnetic induction, measured in Tesla (T) or in sub-multiples (e.g. mT or μΤ) .

In some cases, the geometry of the electromagnetic emission sources or the current values do not allow compliance with the levels outlined by the standards, recommendations and laws and, therefore, magnetic field mitigation systems (shielding) are required.

The performance of a shielding system is defined by the relationship between the magnetic induction values at a point, in the absence and in the presence of shielding. This parameter is defined as the shielding factor or attenuation factor and is greater than 1. The larger the shielding factor, the greater the shield performs its function. The shielding factor is variable from point-to-point, and its valve therefore depends on the point of the space in which it is calculated. Typically, significant points assumed are those characterized by the maximum value of the magnetic field within the area to be protected or those close to positions occupied by persons or workers.

The shields can be of the open or closed type. Closed-type shields are usually used in the case of shielding of components, while in the case of shielding of electrical infrastructures, for economic reasons and technical feasibility, open shields are usually used on one or more walls of the premises containing the source or the area to be protected.

Regarding passive shields, they are divided into two categories: ferromagnetic shields and conductive shields .

Ferromagnetic shields are made of plates of ferromagnetic material (ferrous-based materials), which intercept the magnetic field to be shielded, reducing its intensity into the surrounding region. Since the magnetic field values are generally in the order of μΤ and mT, ferromagnetic shields require the use of materials characterized by a high magnetic permeability in low magnetic fields, known as the initial magnetic permeability. With particular reference to the open- type shields, ferromagnetic shields are characterized by a high shielding factor near the shield, but by a rapid decline in the shielding factor upon gradually moving away from the shield due to the natural reclosing of the magnetic field lines beyond a certain distance from the shield.

Conductive passive shields are formed of plates of conductive material, typically aluminium or copper. Their principle of operation is based on the law of electromagnetic induction: the magnetic field to be shielded creates induced currents in the shielding plates (called Foucault currents) , which generate an opposite magnetic field to the magnetic field to be shielded. Conductive shields are often used to shield the fields produced by power lines and low, medium, and high voltage components. The conductive shields are characterized by maximum shielding factors lower than those of the ferromagnetic shields. However, with conductive shields, higher shielding factor values are maintained when moving away from the shield.

In view of the fact that the ferromagnetic shields and the conductive shields have essentially complementary shielding characteristics, in the state- of-the-art, electromagnetic shielding panels are frequently used that comprise at least one ferromagnetic plate and at least one conductive plate, coupled together to form a multilayer shield. These solutions represent an excellent compromise of shield efficiency both close to and further away from the shield .

Conductive, ferromagnetic, or mixed shielding systems are generally formed by a plurality of panels of determined dimensions, arranged with respective sides alongside each other. The sides of two adjacent panels are usually fixed together by means of welding. The continuity of the conductive material between adjacent panels significantly influences the performance of the shielding system. Figure 1 shows a shielding system formed of four panels 10 arranged with their respective sides 2 facing each other, but without a reciprocal electrical connection. In this case, it is noted that the currents induced in the individual shielding panels, which are not electrically connected to each other, are reclosed on the individual panels. The shielding effect is therefore limited, as the induced currents meet a path with greater electrical impedance. The closure of the currents induced on the individual panels also generates effects at the edges on the sides of the panels that can locally cause a significant magnetic field, thus reducing the shielding effect. Likewise, ferromagnetic shields require good continuity to allow the magnetic field to pass from one panel to the adjacent ones. Simply placing the panels alongside each other introduces magnetic reluctance and a localized enlargement of the magnetic field, which can locally generate a loss in shielding efficiency.

Welding between the adjacent sides of the panels usually provides conductive continuity, but not ferromagnetic continuity. However, in practice, when installing the shielding panels, there are inevitably installation tolerances between the various panels that can generate, on large surfaces, significant interstices between the panels, even of several mm. These interstices cause an increase in the effects at the edges of the conductive and ferromagnetic shields, and make the welding operation between the conductive parts more complicated.

Object and summary of the invention

The object of the present invention is to provide an electromagnetic shielding panel and a shielding system that overcome the problems of the prior art.

According to the present invention, this object is achieved by an electromagnetic shielding panel and an electromagnetic shielding system having the characteristics forming the subject of the claims.

The shielding panel according to the present invention has a quadrangular flat panel body with two flat contiguous edges and two bent contiguous edges forming two overlapping portions, offset with respect to the plane of the panel body, each of which is configured to overlap with a flat edge of an adjacent panel .

In a shielding system formed by a plurality of panels of this type placed alongside each other, all the interstices between adjacent panels are covered by the overlapping portions. The overlapping area between the adjacent panels allows:

- a reduction in the magnetic coupling reluctance between the panels,

- compensation of the magnetic fields at the edges of the panels due to the reclosing of the currents within the conductive part of the single plate,

- restoration of the electrical continuity between adjacent panels, even in the presence of significant installation tolerances, and

facilitation of the installation of ceiling panels thanks to the fact that the overlapping portions can be used to temporarily support the panels during installation.

Brief description of the drawings

The characteristics and advantages of the present invention will become clearer in the following detailed description, given purely as a non-limiting example, wherein:

- Figure 1 is a schematic front view illustrating a shielding system according to the prior art with shielding panels not electrically connected to each other,

- Figure 2 is a plan view of a shielding panel according to the present invention,

- Figure 3 is a view of a shielding system formed by a plurality of panels according to the invention, alongside each other

- Figure 4 is a cross-section along the line IV- IV of Figure 3,

- Figure 5 is a schematic view illustrating the distribution of the magnetic flux through the overlapping area in the solution of Figure 4,

- Figure 6 illustrates the overlapping area between two adjacent panels in a first variant of the present invention,

Figure 7 illustrates the overlapping area between two adjacent panels in a second variant of the present invention,

- Figure 8 is a partial perspective view of the part indicated by the arrow VIII in Figure 7,

- Figure 9 is a schematic view showing the flow of magnetic flux in the overlapping area between two adjacent panels in the solution of Figure 7,

Figure 10 shows the overlapping area with multilayer panels of different types,

Figure 11 schematically shows the currents induced in a shielding system according to the present invention, and

- Figure 12 is a cross-section along the line XII- XII of Figure 11.

Detailed description

With reference to Figure 2, numeral 10 indicates an electromagnetic shielding panel according to the present invention. The panel 10 has a quadrangular flat panel body 12, for example, of a square shape, whose sides are indicated by A. The panel body 12 has the shape of a quadrangular flat plate with constant thickness and has two flat contiguous edges 14, 16 and two bent contiguous edges 18, 20. The flat edges 14, 16 are level with the panel body 12. The bent edges 18, 20 are formed by bending lines 18, 20, which form two strip-shaped overlapping portions 22, 24, parallel to the respective sides of the panel body 12. The overlapping portions 22, 24 are offset with respect to the plane of the panel body 12, and are configured to overlap with a flat edge 14, 16 of an adjacent panel 10.

The overlapping portions 20, 22 have respective square-shaped cuts 26, 28, the side B of which is equal to the width of the overlapping portions 22, 24. The cuts 26, 28 are adjacent to the respective flat sides 16, 14, and an additional square cut 30 with side B is located at the vertex between the bent edges 18, 20.

Figure 3 illustrates an electromagnetic shielding system 30, formed by a plurality of panels 10 alongside each other. The overlapping portions 22, 24 of each panel 10 overlap with respective flat edges 14, 16 of adjacent panels 10. In this way, the transition area between two adjacent panels is always covered by an overlapping portion 22, 24. The adjacent panels 10 are fixed together by welded sections 34, which join the outer sides of the overlapping portions 22, 24 of each panel 10 to the upper surface of the panel body 12 of an adjacent panel 10. The cuts 26, 28 allow the arrangement of the overlapping portions 22, 24 on the respective flat edges 14, 16 of adjacent panels without interference. The cut 30 between two contiguous overlapping portions 22, 24 of the same panel has the object of simplifying the bending of the overlapping portions 22 , 24.

Each panel 10 comprises at least one conductive or ferromagnetic plate. In the simplest case, each panel 10 can be formed of a single conductive or ferromagnetic plate. To improve the shielding factor, each panel 10 can be formed by at least one conductive plate overlapping with at least one ferromagnetic plate. Figure 4 shows the case in which each panel 10 has a multilayer structure consisting of a conductive plate 36 and a ferromagnetic plate 38, which are in contact with each other along respective main faces. As illustrated in Figure 4, the thickness of the panel body 12, indicated with h, is the sum of the thicknesses of the conductive plate 36 and the ferromagnetic plate 38. Each overlapping portion 22, 24 is parallel to the panel body 12 and is offset with respect to the panel body 12 by a distance equal to the thickness h of the panel body 12. In this way, the panel bodies 12 of two adjacent panels 10 are coplanar to each other and the overlapping portions 22, 24 of each panel are arranged above and in contact with the flat edges 14, 16 of the adjacent panels 10. In the example illustrated in Figure 4, the upper surface of the conductive plate 36 of a panel is in contact with the lower surface of the ferromagnetic plate 38 of the overlapping portion 24 of the adjacent panel 10. Figure 4 also illustrates the welding 34 that joins the outer edge of the overlapping portion 24 to the adjacent panel 10. The welding 34 establishes the electrical connection between the conductive plates 36 of the adjacent panels.

Figure 5 schematically shows the distribution of the magnetic flux in the junction area between two panels. The magnetic flux passes from the ferromagnetic plate 38 of a panel 10 to the ferromagnetic plate 38 of the adjacent panel through the portion of the conductive plate 36 of the panel 10 covered by the overlapping portion 24. The passage of the magnetic flux through a portion of the conductive plate 36 causes an increase in the magnetic reluctance. In order to improve the magnetic reluctance in the joining area between two adjacent panels, the solution illustrated in Figure 6 can be adopted, which provides a section 40 of the ferromagnetic plate 38 bent above the conductive plate 36 along the two flat edges 14, 16 of the panel body 12. In this way, along each flat edge 14, 16, a section 40 of the ferromagnetic plate 38 is in direct contact with the ferromagnetic plate 38 of the respective overlapping portion 22, 24. This allows a continuity of the ferromagnetic material through the junction area between two adjacent panels.

From a constructive point of view, the solution of Figure 6 is created by providing a longer plate of ferromagnetic material 38 compared to the plate of conductive material 36, and folding the portions of the ferromagnetic plate 38 protruding beyond the edges of the conductive plate 36 along the two flat edges 14, 16 of the panel body 12.

An alternative solution for obtaining the ferromagnetic continuity between adjacent panels is illustrated in Figures 7, 8 and 9. In this variant, an elongated profile 42 of ferromagnetic material, bent with a U-shaped cross section, is provided. The profile 42 of ferromagnetic material has two flat portions 44 parallel to each other and spaced apart by a distance h equal to the thickness of the panel body 12. The profiles 42 are applied along the flat edges 14, 16 of the panel body 12. In this manner, as shown in Figure 7, each profile 42 establishes a ferromagnetic continuity between the ferromagnetic plates 38 of two adjacent panels. Figure 9 illustrates the distribution of the magnetic flux in the solution of Figures 7 and 8. The solutions illustrated in Figures 6 and 7-9 allow a reduction in magnetic reluctance with respect to the solution illustrated in Figures 4 and 5.

The solution according to the present invention can be used with any panel composition. For example, Figure 10 shows the overlapping area between two adjacent panels, each of which comprises two conductive plates 36 and a ferromagnetic plate 38 sandwiched between the two conductive plates 36.

The solution according to the present invention provides compensation of the magnetic fields at the edges of the plates due to the reclosing of the currents within the conductive plates 36 of the individual panels. As illustrated in Figure 11, the currents induced in the conductive plates 36 have opposing directions along the edges of the panels and, therefore, generate local magnetic fields that are mutually compensated. This compensation causes a benefit relative to the effects at the edges. Figure 12, in fact, illustrates that in the overlapping area, the two overlapping edges are paths of currents induced in opposite directions.

The overlapping between the edges of adjacent panels in a shielding system according to the present invention allows a considerable reduction in the magnetic coupling reluctance between the panels with respect to the solutions according to the prior art in which the adjacent panels are head-to-head. The reduction in magnetic reluctance can be further improved by providing a ferromagnetic continuity between the adjacent panels as illustrated in Figures 6 and 7-9.

The welding between the conductive plates 36 of two adjacent panels allows restoration of electrical continuity between adjacent panels. The electrical continuity between the conductive plates eliminates the reclosing of the induced currents on the conductive plates 36 of the individual panels. The welding of adjacent panels can be easily carried out even in the case of high installation tolerances. Overlapping between the edges facilitates the installation of the panels and also allows greater margins on the production tolerances of the panels and on the installation tolerances.

In addition, the bent edges forming the overlapping portions facilitate installation of the ceiling panels. In fact, after having fixed a first panel to the ceiling, subsequent panels can use the protruding overlapping edges of the fixed panel as a support area.

Of course, without prejudice to the principle of the invention, the details of construction and the embodiments can be widely varied with respect to those described and illustrated, without thereby departing from the scope of the invention as defined by the claims that follow.