Acoustic transducer

Abstract

An acoustic transducer comprises a coil (3) configured to have an electric current flow through it and at least one magnet (4) electromagnetically connected to the coil (3). The coil (3) comprises a support (5) and a coil body (6) anchored to the support (5) and having a plate-like shape defined by a printed circuit board (PCB), with the magnet (4) facing at least one outer face (11a) of the printed circuit board (PCB), placed at a predefined distance from it with the possibility to oscillate.

Description

[0001] ACOUSTIC TRANSDUCER

[0002] This invention relates to an acoustic transducer.

[0003] This invention therefore has applications in the multimedia and infotainment fields, in particular in manufacturing acoustic transducers (e.g. loudspeakers) for automotive applications.

[0004] Acoustic transducers for automotive applications, typically used for sound diffusion in vehicle audio systems, consist of electromagnetic actuators made up of wound coils connected to magnets that, depending on the current flowing in the winding, move at a predetermined frequency, generating a controlled vibration of a membrane or panel capable of diffusing sound waves.

[0005] Currently, for some applications, an extreme reduction in actuator size is required, as space is limited or available power is reduced.

[0006] For this reason, the prior art has for some time now included solutions that seek to reduce the number or size of transducer components, which has led to significant improvements in performance but, at the same time, to just as many critical issues in design or production.

[0007] For example, in certain known embodiments, it is necessary to wind micrometer-thick thin wires in coils of several dozen spirals in millimetresized housings, sometimes subjecting the transducer to significant thermal stress (T>200°C).

[0008] This aspect, in particular, makes the use of thin wires “cemented” by means of a resin layer, which at high temperatures reaches values close to its melting point and reduces its mechanical retention capacity, particularly critical.

[0009] This led the Applicant to consider alternative ways of maintaining the current high standards of performance, while at the same time overcoming the current relative technical disadvantages.

[0010] In accordance with this, the aim of this invention is, therefore, to provide an acoustic transducer with small dimensions, which is easy to assemble and at the same time maintains a high degree of operational reliability.

[0011] More specifically, it is the purpose of this invention to provide an acoustic transducer and a coil for said acoustic transducer that are easy to assemble and manufacture.

[0012] These purposes are achieved with an acoustic transducer having the characteristics of one or more of the following claims.

[0013] In particular, these purposes are achieved with an acoustic transducer, comprising a coil and at least one magnet.

[0014] A containment body defining a housing volume for the coil and magnet is preferably provided.

[0015] The coil (preferably located in the containment body) is configured to have an electric current flow through it.

[0016] Said at least one magnet (preferably located in the containment body) is electromagnetically connected to said coil.

[0017] The coil preferably comprises a support and a coil body anchored to the support.

[0018] According to one aspect of the invention, the coil body has a plate-like shape defined by a printed circuit board.

[0019] A conductive winding and a pair of connectors electrically connected to the conductive winding are preferably printed on the printed circuit board.

[0020] The magnet preferably faces at least one outer face of the printed circuit board, placed at a predefined distance from it with the possibility to oscillate.

[0021] Advantageously, the presence of a coil made on a printed circuit board makes the manufacture and assembly of the transducer much simpler, facilitating its automation and increasing its reliability.

[0022] In addition, the presence of a printed coil, preferably lithographically or silk-screen printed on a board, more preferably using multilayer technology, minimises the issues associated with the high temperatures reached by the transducer during use, thus keeping its functionality and performance intact under all conditions of use. These and other features, together with their relative advantages, will be clearer from the following exemplary, and therefore non-limiting, description of a preferred, and therefore not exclusive, embodiment of a coil for an acoustic transducer and an acoustic transducer as illustrated in the attached figures, wherein:

[0023] - Figure 1 schematically shows an exploded view of some parts of an acoustic transducer according to this invention;

[0024] - Figure 2 shows a rear schematic view of an acoustic transducer according to this invention;

[0025] - Figure 3 schematically shows a side view of some parts of the acoustic transducer in Figure 2;

[0026] - Figure 4 shows an exploded view of the components in Figure 3;

[0027] - Figure 5 shows a schematic view of a detail of the acoustic transducer in Figure 1 .

[0028] With reference to the attached figures, reference number 1 indicates an acoustic transducer according to this invention.

[0029] The acoustic transducer 1 is thus an actuator configured to transform an electrical signal into a mechanical oscillation that can generate a vibration useful for spreading sound waves.

[0030] Therefore, the acoustic transducer 1 is preferably configured to operate in a frequency range of 20Hz to 20kHz.

[0031] The acoustic transducer 1 comprises a coil 3 and at least one magnet 4. The coil 3 and magnet 4 are preferably housed in a containment body 2.

[0032] The containment body 2 defines a housing volume within which other transducer components are preferably housed.

[0033] In the preferred embodiment, the containment body 2 has one or more anchoring portions 2a, preferably defined by flanges, for coupling with a panel or membrane (not shown).

[0034] The coil 3 is placed in the containment body 2, preferably anchored to it.

[0035] This coil 3 is an element configured to have an electric current flow through it and, consequently, generate a magnetic field of varying intensity with the current.

[0036] It should be noted that the acoustic transducer 1 is preferably of the “oscillating magnet” type, but in certain embodiments it could be converted into an “oscillating coil” transducer, i.e. with the magnet anchored to the containment body 2 and the oscillating coil to generate the sound wave.

[0037] According to one aspect of the invention, said coil 3 comprises a support 5 and a coil body 6.

[0038] The support 5 is preferably anchored to the containment body 2 and configured to support the coil body 6.

[0039] The coil body 6 is therefore anchored to the support 5 and has a plate-like shape defined by a printed circuit board PCB.

[0040] In other words, the coil body 6 is defined by a printed circuit board PCB anchored to the support 5.

[0041] The printed circuit board PCB preferably has a slab- or plate-like extension in which two outer faces 11a are parallel to each other and connected by a perimeter edge 11 b (preferably square).

[0042] The printed circuit board PCB is preferably made of a composite material based on glass fibres arranged orthogonally between two layers in an epoxy resin matrix. More preferably, the printed circuit board PCB is made of vetronite. The type of vetronite can be FR4 or FR5 with a glass transition temperature of more than 200°C. In the preferred embodiment, this perimeter edge has a thickness, evaluated orthogonally to said outer faces, of less than 2 mm, preferably less than or equal to 1 mm.

[0043] In other words, the coil body 6 is preferably less than 2 mm thick, more preferably less than or equal to 1 mm, calculated as the distance between said outer faces.

[0044] This printed circuit board PCB has at least one conductive winding 7 and one pair of connectors 8 electrically connected to the conductive winding 7 on its faces.

[0045] In the preferred embodiment, the conductive winding 7 is printed on the printed circuit board PCB using lithographic or screen-printing methods. It should be noted that the printed circuit board PCB is preferably a multilayer one.

[0046] More preferably, therefore, the printed circuit board PCB comprises at least one base substrate CL, at least two conductive layers TL overlapping with opposite faces of the base substrate CL and at least two overlapping protective layers SM, each, on a respective conductive layer TL.

[0047] The conductive layers TL define the conductive winding 7 and are preferably made of copper.

[0048] In the embodiment shown schematically in Figure 1 , there are multiple layers, with prepreg PPL or substrate CL layers sandwiched between two successive conductive layers TL.

[0049] The outermost conductive layers TL are each covered with a protective layer SM (or solder mask), which is appropriately absent or removed at the connectors 8.

[0050] These outermost conductive layers TL together with the protective layer SM define the outer faces 11 a of the printed circuit board PCB.

[0051] Each conductive layer TL preferably comprises a conductive track 10 continuously extending along a spiral-shaped path between one radially outer spiral 9a, with a maximum length, and one radially inner spiral 9a, with a minimum length.

[0052] This spiral-shaped path preferably has an oblong, essentially oval shape, preferably with straight sections joined by curved sections.

[0053] Advantageously, this makes it possible to produce coil-shaped windings that maintain the mutual position between the spirals even under extreme conditions of use.

[0054] The conductive layers TL preferably have more than 35, more preferably more than 40, total number of spirals.

[0055] In the preferred embodiment, moreover, each conductive track TL has an electrical resistance of between 2 and 6 Q, preferably around 4 Q.

[0056] In this regard, each conductive track TL is preferably wider than it is thick (i.e. distance from the respective base substrate CL or prepreg). In the preferred embodiment, each conductive track TL has a cross-section (i.e. orthogonal to the printed circuit board PCB faces) with a maximum width of more than 0.2 mm, preferably about 0.3 mm, and a thickness of more than 0.05 mm, preferably about 0.08 mm.

[0057] The base substrate CL and prepreg layers (if included) are preferably less than 0.1 mm thick.

[0058] It should be noted that, in the preferred embodiment, the conductive tracks TL have a cross-section with an essentially trapezoidal geometry, with the larger base resting on the respective base layer CL or prepreg and the smaller base spaced apart from it.

[0059] In addition, the distance between two adjacent spirals is preferably less than 0.2 mm.

[0060] In addition, the support 5 of the coil 3 preferably comprises a fork-shaped body 12 shaped to mechanically and electrically connect to both outer faces 11 a of the printed circuit board PCB.

[0061] Therefore, the fork-shaped body 12 preferably comprises two arms 12a parallel to each other and spaced apart by a slot 12b to house the printed circuit board PCB.

[0062] The fork-shaped body 12 preferably lies on a plane orthogonal to said outer faces 11a of the printed circuit board PCB.

[0063] Each arm 12a has a first connector electrically and mechanically coupled to a connector 8 on the printed circuit board.

[0064] In the preferred embodiment, the connection between the fork-shaped body 12 and the printed circuit board PCB is made by soldering, preferably tin alloy soldering: commonly tin-lead, tin-silver, tin-copper or tin-silver- copper.

[0065] In the preferred embodiment, the fork-shaped body 12 is soldered to the printed circuit board PCB at the connector 8 and a second mechanical connection plate 14; preferably, each outer face 11 a of the printed circuit board PCB has a connector 8 and a second plate 14.

[0066] Moreover, an additional connector 13 for connection to a current source (not shown) is, preferably, also connected with each arm 12a.

[0067] In the preferred embodiment, the support 5 is also produced with an additional printed circuit board PCB1 shaped to engage with the printed circuit board PCB orthogonally to it. This additional printed circuit board PCB1 preferably defines the fork-shaped body 12.

[0068] The magnet 4 is, in turn, preferably located in the containment body 2 and is electromagnetically connected to said coil 3.

[0069] The magnet 4 preferably faces at least one outer face 11 a of the printed circuit board PCB, placed at a predefined distance from it with the possibility to oscillate.

[0070] The magnet 4 preferably has a parallelepiped shape and faces the respective outer face 11 a of the printed circuit board PCB with the possibility of oscillating by about 1 mm.

[0071] In the embodiment illustrated in the attached figures, the acoustic transducer 1 comprises two magnets 4 arranged on opposite sides of the printed circuit board PCB and each spaced apart by a respective outer face 11 a.

[0072] Alternatively, it may comprise a magnet and a core of ferro-magnetic material to convey the magnetic flux orthogonally to the coil 6.

[0073] The invention achieves the intended objects and attains important advantages.

[0074] In fact, thanks to the use of a printed circuit board PCB to make the coil, it is possible to overcome the critical issues of the prior art related to assembly difficulties and stability at high temperatures.

Claims

CLAIMS1. Acoustic transducer, comprising:- a coil (3) configured to have an electric current flow through it;- at least one magnet (4) electromagnetically connected to said coil (3); characterised in that said coil (3) comprises:- a support (5);- a coil body (6) anchored to the support (5) and having a plate-like shape defined by a printed circuit board (PCB) on which the following are printed:- a conductive winding (7);- a pair of connectors (8) electrically connected to the conductive winding (7), wherein the magnet (4) faces at least one outer face (11 a) of the printed circuit board (PCB), placed at a predefined distance from it with the possibility to oscillate.

2. The acoustic transducer according to claim 1 , wherein the printed circuit board (PCB) comprises:- a least one base substrate (CL);- at least two conductive layers (TL) overlapping with opposite faces of the base substrate (CL);- at least two protective layers (SM) each overlapping a respective conductive layer (TL).

3. The acoustic transducer according to claim 2, wherein each conductive layer (TL) comprises a conductive track (10) continuously extending along a spiral-shaped path between one radially outer loop (9a), with a maximum length, and one radially inner loop (9b), with a minimum length.

4. The acoustic transducer according to claim 2 or 3, wherein saidconductive layers have more than 35 loops, preferably more than 40.

5. The acoustic transducer according to claim 3 or 4, wherein said conductive track (TL) has an electrical resistance between 2 and 6 Q, preferably approximately 4 Q.

6. The acoustic transducer according to any previous claim, wherein said coil body (6) has a thickness, measured orthogonally to said outer face (11 a), of less than 2 mm, preferably less than 1 mm.

7. The acoustic transducer according to any previous claim, wherein the support (5) of the coil (3) comprises a fork-shaped body (12) shaped to mechanically and electrically connect to both outer faces of the printed circuit board (PCB).

8. The acoustic transducer according to claim 7, wherein the fork-shaped body (12) lies on a plane orthogonal to said outer faces (11 a).

9. The acoustic transducer according to claim 7 or 8, wherein the forkshaped body (12) is welded to the printed circuit board (PCB) and comprises a pair of conductive tracks electrically connected to said connectors (8) of the coil body (6).

10. The acoustic transducer according to any previous claim, comprising two magnets (4) arranged on opposite sides of the printed circuit board (PCB) and each spaced apart by a respective outer face (11 a).

11. The acoustic transducer according to any previous claim, comprising a core of ferromagnetic material connected to the magnet (4) so as to convey a magnetic flow on the printed circuit board (PCB).

12. The acoustic transducer according to any previous claim, comprising a containment body (2) defining a housing for said coil (3) and said at least one magnet (4).

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