WO2005094120A1

WO2005094120A1 - A micro speaker including a direct driven vibration plate

Info

Publication number: WO2005094120A1
Application number: PCT/KR2005/000861
Authority: WO
Inventors: Ok-Jung Yoo
Original assignee: Ok-Jung Yoo
Priority date: 2004-03-25
Filing date: 2005-03-24
Publication date: 2005-10-06
Also published as: KR100621648B1; KR20050095094A

Abstract

The invention relates to a micro speaker including a directly driven vibration plate having a built-in voice coil patterned using a flexible PCB manufacturing technique. The speaker includes an upper housing, a lower housing, a permanent magnet located between the upper and lower housings, and a vibration plate placed over the permanent magnet and including a metal pattern functioning as a voice coil. The center portion and the peripheral portion of the voice coil are connected without a seam and the portions of the voice coil in which electrical current flows in the same direction are aligned to air gaps between the permanent magnets.

Description

[DESCRIPTION]

[invention Title] A MICRO SPEAKER INCLUDING A DIRECT DRIVEN VIBRATION PLATE [Technical Field] -\\ The present invention relates, in general, to a micro speaker including a direct driven vibration plate and, more particularly, to a micro speaker, which has high efficiency due to improved construction compared to a conventional micro speaker, thus allowing the micro speaker to have an ultra slim structure.

[Background Art] Generally, as the thickness of devices, such as mobile phones, notebook computers, and video equipment, is reduced, the thickness of a sound generator, namely, a speaker, must also be reduced. Consequently, a micro speaker having a thickness of several millimeters and a thin speaker having the shape of a plate have been proposed. A conventional dynamic micro speaker includes a cylindrical or annular permanent magnet, an annular plate provided concentrically with the permanent magnet, and a yoke. The conventional micro speaker is configured such that a static magnetic field is supplied to an air gap defined by the plate and the yoke. Further, the conventional micro speaker includes a solenoid-type voice coil inserted into an air gap defined between the plate and a pole piece. The micro speaker generates a magnetic field which fluctuates over a time, when a signaling current is applied to the solenoid-type voice coil. The conventional micro speaker is operated such that the static magnetic field generated by a magnetic circuit including the permanent magnet, the plate, and the yoke interacts with the rotating magnetic field generated by the signaling current flowing in the voice coil, thus vibrating the voice coil in a vertical direction. The vertical vibration of the voice coil leads to the vibration of a vibration plate secured to an upper end of the coil. Further, due to the vibration of the voice coil, air which is present in front of the vibration plate and behind the vibration plate vibrates, thus producing sound waves. The above-mentioned conventional dynamic speaker is problematic in that the voice coil must have a specified height so as to enable a specified static magnetic force to be applied to the voice coil, and a space corresponding to the distance required for vertical vibration of the vibration plate must be provided under the voice coil. Further, the conventional micro speaker is problematic in that it is difficult to reduce the thickness of the micro speaker below a predetermined value, due to the magnetic circuit including the permanent magnet, the plate, and the yoke. In order to solve the problems of the conventional micro speaker, a thin speaker has been proposed. Specifically, a plate-type speaker is disclosed in Korean Utility Model Registration No. 0188945. According to the document, a voice coil is etched on a vibration plate, thus accomplishing the miniaturization, lightness, and thinness of the speaker. The construction of the conventional plate- type speaker will be described below with reference to FIG. 1. The conventional plate-type speaker includes a voice coil 1 on which a metal film is etched. The voice coil 1 is attached to a surface of a vibration plate 2 in the form of a ring having a predetermined thickness. A spacer 4 is interposed between the vibration plate 2 and a frame 3 in such a way as to contact the inner circumference of the frame 3, with permanent magnets 5 and 5' being installed under the spacer 4. Further, the permanent magnets 5 and 5 are attached to the upper surface of the frame 3. A plurality of air holes 6 is integrally formed on the frame 3 to be disposed inside the permanent magnet 5^r . Further, the permanent magnets 5 and 5' are spaced apart from each other by a predetermined interval. In this case, each of the permanent magnets 5 and 5' is arranged such that opposite magnetic poles are adjacent to each other. The spacer 4 contacts the inner surface of the frame 3, thus easily absorbing the vibration of the vibration plate 2, in addition to adjusting the amplitude of the vibration plate 2. The permanent magnets 5 and 5' are installed under the spacer 4 and are spaced apart from each other by a predetermined interval. Further, the permanent magnets 5 and 5' are integrally attached to an inside portion of the frame 3 on which the air holes 6 are integrally formed. The air holes 6 are disposed inside the permanent magnet 5' to emit sound which is produced during the vibration of the vibration plate 2. ^■ In the plate-type speaker, the voice coil 1 is positioned above the permanent magnets 5 and 5" . Thereby, when an electric current is supplied to the voice coil 1 on which the metal film is etched, the current flows in the voice coil 1. At this time, the magnetic field is generated in the permanent magnets 5 and 5' . Hence, according to Fleming' s left hand rule, which describes the interaction between the direction of a current flow and the direction of a magnetic field, a vertical force acts on the vibration plate 2 equipped with the voice coil 1, so that the vibration plate 2 vibrates . Further, each of the permanent magnets 5 and 5' has the shape of a ring which is integrally formed. The permanent magnet 5 is configured such that opposite magnetic poles are alternately arranged. Like the permanent magnet 5, the permanent magnet 5' installed inside the permanent magnet 5 is configured such that opposite magnetic poles are alternately arranged. Each of the permanent magnets 5 and 5' has the shape of a ring, and is provided on both sides of the voice coil 1 to increase magnetic flux, thus reproducing intermediate-pitched or high-pitched tones at high efficiency. However, the conventional plate-type speaker has the following problems . The conventional plate-type speaker is configured so that the direction of the current flow of a coil part located inside the vibration plate is opposite to that of the current flow of a coil part located outside the vibration plate, the directions of the current flow of upper and lower portions of the coil are opposite to each other, and the directions of the current flow of left and right portions of the coil are opposite to each other. Such a coil pattern causes electric current to flow in different directions. Thus, the outer permanent magnet 5 is configured such that opposite magnetic poles are alternately arranged in a circumferential direction. Further, the inner permanent magnet 5' is configured such that opposite magnetic poles are alternately arranged in a circumferential direction. The arrangement causes the whole surface of the vibration plate to vibrate in the same direction, according to the direction of electric current flowing in the coil pattern. As such, when the inner and outer magnetic permanents have different magnetic poles in the circumferential direction, the flow of the magnetic field is not concentrated on the air gap, but most of the magnetic field is dispersed. Thereby, the loss of the magnetic field is undesirably increased. In a detailed description, the conventional plate- type speaker includes a first magnetic field which is generated on the inner or outer permanent magnet, and a second magnetic field which is generated in the air gap between the inner and outer permanent magnets . In the conventional plate-type speaker, magnetic fields are symmetrically generated on upper and lower ends of the permanent magnets. In this case, the second magnetic field reacts with the current flow of the coil pattern, thus leading to vibration along a longitudinal axis. Meanwhile, the first magnetic field, generated in the same direction as the current flow or in the direction opposite to the current flow, leads to vibration along a transverse axis, so that the first magnetic field plays little role in generating sound. Further, a magnetic field generated at a position where the vibration plate is not provided is useless, so that half of the entire magnetic field is already lost. Moreover, the conventional plate-type speaker is configured such that the inner and outer permanent magnets have different magnetic poles. The conventional plate-type speaker is problematic in that the magnetic field is formed by opposite magnetic poles that are closet, so that the second magnetic field, substantially providing the driving force, is very slight, and in addition, the unnecessary first magnetic field may be increased. This problem become more serious, if the distance between the inner and outer permanent magnets is long, and different magnetic poles provided on each of the inner and outer permanent magnets are closer to each other. For these reasons, the conventional plate-type speaker is problematic in that its efficiency is very low.

[Disclosure] [Technical Problem] Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a speaker having a directly driven vibration plate on which a voice coil is patterned, which has an improved coil pattern and an improved magnetic pole structure, thus having a highly efficient plate structure. In order to accomplish the above object, the present invention provides a micro speaker, including an upper housing; a lower housing; a permanent magnet provided in a space defined by the upper and lower housings; and a vibration plate positioned above the permanent magnet, with metal patterns being formed on the vibration plate, the metal patterns serving as a voice coil, wherein the permanent magnet comprises a plurality of permanent magnetic elements that are spaced apart from each other at regular intervals, with opposite magnetic poles provided on sides of neighboring elements, and the metal patterns, formed on the vibration plate, extend from an edge to a center and subsequently extend from the center to the edge, so that the metal patterns are continuously connected without a seam, and metal patterns having a current flow in the same direction are disposed in air gaps between the permanent magnetic elements. Preferably, the micro speaker further includes a suspension provided on an inner surface of the housings, and supporting the vibration plate. Preferably, a magnetic pole is provided only on a side of each of the permanent magnetic elements. Preferably, some of the metal patterns formed on the vibration plate are positioned in the air gaps between the permanent magnetic elements, and the rest of the metal patterns are arranged above the permanent magnetic elements, the metal patterns positioned between the permanent magnetic elements being bent downwards, the metal patterns positioned above the permanent magnetic elements being bent upwards . Preferably, a central portion of the vibration plate is bent upwards or downwards .

[Description of Drawings] FIG. 1 is an exploded perspective view showing a conventional plate-type speaker; FIG. 2 is a sectional view of a micro speaker, according to the present invention; FIGS. 3a to 3c are views illustrating the construction of a directly driven vibration plate, according to this invention; FIG. 4 is a view showing the construction of a permanent magnet, according to this invention; and FIGS . 5a and 5b are views showing the operational principle of the micro speaker, according to this invention.

[Best Mode] Hereinafter, the preferred embodiment of this invention will be described in detail with reference to the accompanying drawings. FIG. 2 is a sectional view of a plate-type speaker, according to this invention. The plate-type speaker according to this invention includes upper and lower housings 12 and 11. A permanent magnet 13 is located in a space defined by the upper and lower housings 12 and 11. A directly driven vibration plate 14 is spaced apart from the permanent magnet 13 by a predetermined interval, with a voice coil being patterned on the vibration plate 14. The speaker also includes a suspension 15 to support an edge of the vibration plate 14. Further, a power supply line 16 extends integrally from the vibration plate 14. According to this invention, the voice coil is patterned on the directly driven vibration plate 14. It may be manufactured using a general FPCB (flexible printed circuit board) manufacturing technique. As shown in the drawing, the upper and lower housings 12 and 11 are sealed together, so that it is impossible to open the housings 12 and 11. A plurality of holes is formed on the upper and lower housings 12 and 11 at regular intervals, thus permitting the flow of air and the generation of sound. The permanent magnet 13 is positioned in the housings 12 and 11. The vibration plate 14 is installed above the permanent magnet 13 to be spaced apart from the permanent magnet 13 by a predetermined interval. Further, the directly driven vibration plate 14 is spaced apart from the upper housing 12 by a predetermined interval. As described above, a metal pattern serving as the voice coil is formed on the directly driven vibration plate 14. The power supply line 16 integrally extends from an end of the vibration plate. A metal pattern is also formed on the power supply line 16. Since the method of manufacturing the power supply line 16 and the vibration plate 14 is equal to the FPCB manufacturing method, the manufacturing method will not be described herein. The directly driven vibration plate 14 is supported by the suspension 15 which is provided on the inner wall of the housings, so that the vibration plate 14 may vibrate. The plate-type speaker according to this invention is characterized by the coil pattern formed on the directly driven vibration plate and by the structure and arrangement of permanent magnets. The characteristics of this invention will be described with reference to FIGS. 3a to 3c and FIG. 4. FIGS. 3a to 3c are views illustrating the construction of the directly driven vibration plate, according to this invention, in which FIG. 3a is a plan view of the vibration plate, FIG. 3b is a sectional view taken along line B-B' of FIG. 3a, and FIG. 3c is a sectional view taken along line A-A' of FIG. 3a. As described above, the directly driven vibration plate 14 of this invention is constructed so that the metal pattern is formed on a film. As shown in the drawings, the directly driven vibration plate 14 of this invention has the radial metal pattern. This will be described below in detail . The metal pattern of the directly driven vibration plate according to this invention is shaped such that the metal pattern extends from an edge to the center and subsequently extends from the center to the edge. The metal pattern is continuously formed without a seam. A metal pattern extending from the power supply line 16 is connected at a jumper portion 24 to the metal pattern serving as the voice coil. Thus, when power is supplied to the metal pattern serving as the voice coil, electric current flows in the direction from the edge to the center and subsequently in the direction from the center to the edge. Herein, a metal pattern, which is located at a position where a magnetic field exists and generates a vertical vibration according to a current flow, is referred to as a mobile pattern 23. Further, a metal pattern, which is located at a position where a magnetic field does not exist and does not affect the generation of vibration, is referred to as a fixed pattern 22. The mobile pattern 23 is placed at a position where a magnetic field generated by the permanent magnet exists, thus functioning to vibrate the directly driven vibration plate in a vertical direction. The fixed pattern 22 is placed at a position where a magnetic field does not exist, and functions to transfer an electric current to a neighboring mobile pattern without affecting the vibration. According to this invention, in order to increase the efficiency of the directly driven vibration plate, a film part on which the mobile pattern 23 is placed is downwardly bent, so that the mobile pattern 23 is near the center of the air gap between permanent magnets . Conversely, a film part on which the fixed pattern 22 is placed is bent upwards, so that the fixed pattern 22 is distant from the permanent magnet. Thus, the directly driven vibration plate is vibrated only by the mobile pattern 23 in which an electric current flows in the same direction, and the fixed pattern 22 does not affect the vibration of the vibration plate, so that the efficiency of the directly driven vibration plate is maximized. In other words, when an electric current flows from the edge to the center of the mobile pattern, the electric current flows from the center to the edge of the fixed pattern. If the magnetic field is present in the fixed pattern part, the mobile pattern part and the fixed pattern part will vibrate in opposite directions. In this case, the waveforms of the speaker are offset, so that it is impossible to reproduce low-pitched tones, and in addition, the efficiency of reproducing high- pitched tones is very low. However, this invention allows the magnetic field to act only on the mobile pattern part, and allows an electric current to always flow in the same direction, thus preventing the above-mentioned problem. In the drawings, triangular portions 21 are upwardly bent, and portions between the triangular portions 21 are downwardly bent. FIG. 3b is a sectional view taken along line B-B' of FIG. 3a, in which the metal pattern provided along line B-B' is a mobile pattern. FIG. 3c is a sectional view taken along line A-A' of FIG. 3a, in which a metal pattern provided along line A-A' is a fixed pattern. Thus, the metal pattern of FIG. 3b is downwardly bent, while the metal pattern of FIG. 3c is upwardly bent. The central portion of the vibration plate is upwardly or downwardly bent, according to the structure of the speaker. FIG. 4 shows the structure of the permanent magnet, according to this invention. In this invention, the permanent magnet is divided into a plurality of magnetic elements . The magnetic elements are arranged at regular intervals to form a circular shape. A magnetic pole of each magnetic element is provided on a side of the magnetic element. That is, as shown in FIG. 5a, the permanent magnet includes a plurality of permanent magnetic elements that are spaced apart from each other at regular intervals, with a magnetic pole provided on a side of each permanent magnetic element. The neighboring permanent magnetic elements have opposite magnetic poles . Thereby, static direct current flux has a constant rotating direction. The operation of the micro speaker according to this invention will be described with reference to FIGS. 5a and 5b. As shown in FIG. 5a, the permanent magnet is divided into a plurality of magnetic elements. The permanent magnetic elements are spaced apart from each other at regular intervals, and are arranged in a circular pattern. Alternatively, the permanent magnetic elements may be arranged in an elliptical pattern. Neighboring permanent magnetic elements have opposite magnetic poles. Thus, the magnetic force acts in a direction from the N pole of one permanent magnetic element to the S pole of another permanent magnetic element. Thereby, the direct current flux has a circular rotating direction. Since the metal pattern extends from the edge to the center and subsequently extends from the center to the edge, electric current flows from the edge to the center and subsequently flows from the center to the edge. The mobile pattern 23 is a part where vibration is substantially generated, while the fixed pattern 22 is a part where vibration does not occur. Thus, the fixed pattern 22 is positioned above an area where the magnetic field is not present, and the mobile pattern 23 is positioned in an area where the magnetic field is present. In order to increase the efficiency of the speaker, the fixed pattern 22 is bent upwards to be distant from the permanent magnet. Conversely, the mobile pattern 23 is bent downwards to be near to the permanent magnet. As shown in FG. 5b, the film part where the mobile pattern 23 is positioned is sufficiently bent so that the mobile pattern 23 is positioned in the air gap between the permanent magnetic elements. Thus, the magnetic field is at right angles with the electric current of the mobile pattern. Therefore, the mobile pattern part vibrates vertically according to the direction of flow of the electric current. Meanwhile, when the directly driven vibration plate of this invention is constructed to have a multi-layered structure, a two-way dual channel micro speaker is achieved. The two-way dual channel micro speaker is configured such that one vibration plate has an electrical channel for a speaker and an electrical channel for a receiver. Although the preferred embodiment of the present invention has been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims . [industrial Applicability] As described above, the present invention provides a micro speaker, which is constructed so that a permanent magnet is divided into several magnetic elements but a magnetic force continuously acts in one direction, and a metal pattern, which serves as a voice coil and has the current flow in the same direction, is placed in a position where a magnetic field exists, thus preventing undesired vibration, therefore preventing the efficiency of the speaker from being deteriorated. Further, this invention provides a magnetically shielded one-way thin speaker having a single channel or a magnetically shielded two-way thin speaker having dual channels .

Claims

[CLAIMS] [Claim 1] A micro speaker, comprising: a upper housing; a lower housing; a permanent magnet provided in a space defined by the upper and lower housings; and a vibration plate positioned above the permanent magnet, with metal patterns being formed on the vibration plate, the metal patterns serving as a voice coil, wherein the permanent magnet comprises a plurality of permanent magnetic elements that are spaced apart from each other at regular intervals, with opposite magnetic poles provided on sides of neighboring elements, and the metal patterns, formed on the vibration plate, extend from an edge to a center and subsequently extend from the center to the edge, so that the metal patterns are continuously connected without a seam, and metal patterns having a current flow in the same direction are disposed in air gaps between the permanent magnetic elements .

[Claim 2] The micro speaker according to claim 1, further comprising: a suspension provided on an inner surface of the housings, and supporting the vibration plate.

[Claim 3] The micro speaker according to claim 1 or 2, wherein a magnetic pole is provided only on a side of each of the permanent magnetic elements .

[Claim 4] The micro speaker according to claim 3, wherein some of the metal patterns formed on the vibration plate are positioned in the air gaps between the permanent magnetic elements, and the rest of the metal patterns are arranged above the permanent magnetic elements, the metal patterns positioned between the permanent magnetic elements being bent downwards, the metal patterns positioned above the permanent magnetic elements being bent upwards .

[Claim 5] The micro speaker according to claim 3, wherein a central portion of the vibration plate is bent upwards or downwards .

[Claim 6] The micro speaker according to claim 1, wherein the vibration plate has a multi-layered structure, thus providing a two-way dual channel .