JP5645100B2 - ANTENNA DEVICE AND COMMUNICATION DEVICE USING THE SAME - Google Patents

Description

  The present invention relates to an antenna used in a communication device such as a mobile phone and a mobile terminal device, and relates to an antenna device wound with a winding and a communication device equipped with the antenna device.

  Surface mount type antennas are also used as main antennas for mobile phones and the like, and as chip antennas for wireless LAN and GPS (Global Positioning System). These antennas need to be mounted in a very small space such as a mobile phone. In addition, on a substrate on which an antenna is mounted, a device that generates electromagnetic waves such as a speaker, a vibrator, and recently a small CCD camera is often housed in a metal case. At this time, due to dimensional constraints, it is often necessary to dispose the antenna near the speaker or vibrator or near the GND surface of the substrate, and the metal functional parts such as the speaker, vibrator or small CCD camera, or the substrate near the antenna. The radiation efficiency of the antenna deteriorates due to the influence of the image current having the opposite phase to the resonance current flowing in the antenna flowing in the GND plane.

  An example of an antenna using a conventional conductive wire is shown in FIG. 15 (Patent Document 1). This figure shows the chip antenna 90 transparently. A conductive wire 92 spirally wound in the longitudinal direction of the base 91 is connected to one end of the conductive wire 92 formed on the surface of the base 91. The power supply terminal 93 and a ground terminal 94 formed on at least one of the inside and the surface of the base 91 are provided. Reference numeral 95 denotes an open end, and reference numeral 96 denotes a ground pattern. The chip antenna 90 has a complicated manufacturing process because the conductive wire 92 is formed inside the base 91. Further, since the conductive wire 92 is formed inside the base 91, it is impossible to adjust the resonance frequency by changing the length of the conductive wire after manufacturing, or to match the input impedance to, for example, 50 ohms. Even if the conductor wire is spirally wound around the outer surface of the substrate, the chip antenna can be mounted on the board by the amount of the conductive wire. There was a problem with stability. In addition, if a bending force is applied to the substrate after mounting, stress is generated in the chip antenna terminal portion, and there is a problem that the substrate is affected by distortion due to a difference in thermal expansion coefficient from the substrate.

  Thus, for example, there is a chip antenna disclosed in Patent Document 2 as a solution to such complexity of manufacturing and poor mounting stability. As shown in FIG. 16, this surface-mount type chip antenna is provided with a stepped portion 120 over the entire circumference of the base 110, and a spiral conductive wire 130 is wound around the stepped portion 120. Are connected via conductive films or conductive caps 140 and 150 covering the entire peripheral surfaces of the terminal portions at both ends of the base 110.

  Further, there is an antenna disclosed in Patent Document 3 as a surface-mounted antenna that is easy to adjust the antenna gain, has mounting stability, and has a wide bandwidth and improved radiation efficiency. As shown in FIG. 14, the surface-mount type chip antenna includes a base 10 made of a dielectric or magnetic material, at least one terminal portion 21 (22) provided on the mounting surface of the base, A concave portion 30 provided on the mounting surface excluding the terminal portion and at least one conductive wire 40 wound around the base body are provided.

JP-A-11-205025 JP 2002-16419 A JP 2004-304783 A

Communication devices such as mobile phones are usually required to have a small size and a low profile. However, depending on the situation in which they are used, broadband characteristics and high efficiency are desired rather than a low profile. According to the surface-mounted antennas of FIGS. 15 and 16, although the mountability is improved, it is difficult to sufficiently suppress the mutual interference between the metal component on the mounting substrate and the antenna.
One of the means is to employ a helical antenna in which a core material is a ferrite material or a ceramic material and a conductor is spirally wound around the core material because of the relationship between required antenna characteristics and cost. In that case, if it is intended to sufficiently reduce the influence of the antiphase image current flowing on the GND surface of the metal part or the mounting board, a bridge-shaped ferrite core is used as shown in FIG. 14, for example, or it is separated from the mounting board. A structure may be considered in which a sub-board or the like is provided in the above-mentioned place and a ferrite core is installed on the sub-board.
However, when processing the ferrite core into a bridge shape, the step of the recess cannot be increased because the mechanical strength of the ferrite material itself is low. There is a possibility that cracking may occur during molding, firing, and processing, and the ferrite core may be damaged by the impact when the antenna device is dropped even after installation on the mounting substrate.
In addition, when the core is placed on a sub-board installed at a location away from the mounting board, it is difficult to fix the boards together, resulting in an increase in cost and a longer feed line to the antenna, making it difficult to form the feed line. In addition to the above, it is essential to maintain electrical connection even when the antenna device is dropped, and a simple method such as requiring secondary member installation and special design for that purpose. Difficult to do in

  Furthermore, if you try to reduce the cost by reducing the volume of the ferrite core, the length cannot be shortened to obtain the desired gain, and if the cross-sectional area of the helical winding is reduced, it will break The possibility of is further increased.

  In addition, when a ferrite or ceramic material is used as a core and the conductor is installed in a helical shape, it has been conventionally wrapped with a conductive wire such as enameled wire or directly coated on the surface of the ferrite material substrate with printed wiring Is most. When winding a conducting wire such as enameled wire, the tension of the copper wire when it is wound may cause breakage or chipping of the ferrite material base, and if the winding number is small, the winding position must be the same The characteristics of each antenna will vary in mass production. If a groove is provided in the base as in Patent Document 1, the position of the winding is determined, but it is difficult to form a groove in the ferrite material, which may cause cracking and chipping. When directly coating the surface of a ferrite or ceramic substrate with printed wiring or the like, it is necessary to coat at least four surfaces of a rectangular parallelepiped core, which is expensive. If it is a cylindrical base, it may be possible to coat the conductor helically while rotating, but manufacturing a cylindrical core also leads to high costs.

Therefore, the present invention, as an antenna using a magnetic or dielectric core, suppresses breakage of the core during manufacture and damage due to impact after installation, is easy to manufacture, and has a bandwidth in each frequency band. An object is to provide a wide antenna device having a high average gain and a communication device using the antenna device.
It is another object of the present invention to provide an antenna device that prevents a decrease in gain by ensuring isolation from a mounting substrate, and a communication device using the antenna device.

The antenna device of the present invention is provided with a rod-shaped magnetic core member made of a magnetic material or a dielectric, and standing on the surface of a mounting substrate that covers at least a part of a longitudinal side surface of the magnetic core member and includes a ground electrode. A cover member having a plurality of legs for floating and fixing a part of the board from the substrate, wherein the antenna includes a power feeding terminal formed on a leg on one end side of the cover member and the other A connecting portion formed on a leg portion on the end side; and a winding portion including a conductive wire electrically connected to the power feeding terminal and the connecting terminal , wherein the cover member is recessed between the leg portions. In the winding portion , the magnetic core member is wound with a conductive wire together with the cover member including the recess, a radiation electrode is provided on the back surface of the mounting substrate, and one end of the radiation electrode is mounted on the mounting substrate. Through the via hole formed in The antenna is connected to the connection terminal of the antenna, the other end is an open end, the radiation electrode is arranged in parallel with the axial direction of the winding portion of the antenna and folded, and a capacitance is formed by the open end and the feeding terminal. Therefore, it is characterized by resonating in two bands . As an antenna device for high frequency applications, high antenna characteristics can be obtained and construction is easy . To reduce the magnetic center member can also maintain high antenna characteristics, and also can prevent damage caused by shock and winding operations.

In the antenna device of the present invention, the cover member may have a shape that covers the periphery of the magnetic core member so that the tension of the winding portion around which the conductive wire is wound does not give an external force to the magnetic core member. preferable. It is preferable that the cover member covers the entire periphery of the magnetic core member. Further, for example, as shown in FIG. 7, the three sides of the rectangular parallelepiped magnetic core member may be covered so that the height between the pair of side surfaces is larger than the width of the magnetic core member so as not to receive the pressure received from the winding. .

In the antenna device of the present invention, it is preferable that the magnetic core member is disposed at the center of the winding portion of the antenna . The phrase “the magnetic core member is disposed at the center of the winding portion” refers to a mode in which the central axis of the winding portion geometrically passes through the volume portion of the magnetic core member. Further, the maximum width of the magnetic core member can be made smaller than 0.95D with respect to the minimum diameter D of the winding portion. By reducing the maximum width of the magnetic core member, the volume of the expensive ferrite core and ceramic core can be reduced.

In the antenna device of the present invention, a structure in which the other end of the winding portion of the antenna is connected to the radiation electrode on the mounting substrate via a connection terminal formed on the leg portion can be adopted. By increasing the effective length, the gain in the low frequency band is improved. By disposing the radiation electrode in parallel with the axial direction of the winding portion and turning it back, the antenna can be used as a dual band antenna. This is the LC resonance that consists of the self-inductance at the winding part of the antenna, the capacitance between the winding part and the ground electrode of the mounting board, and the capacitance between the winding part and the radiation electrode. A circuit is formed and the self-inductance of the radiation electrode, the capacitance between the radiation electrode and the ground electrode, the capacitance between the winding portion and the radiation electrode, and the open end of the radiation electrode An LC resonance circuit composed of a parasitic capacitance with the power feeding terminal is formed, and an antenna device that resonates in two bands can be obtained.
Further, the antenna device may be configured such that the radiation electrode is disposed on the surface of the mounting substrate opposite to the antenna mounting surface, and the antenna and the radiation electrode are at least partially overlapped in the vertical direction of the mounting substrate surface. .
If one end of the winding is connected to the radiation electrode on the back surface via a connection terminal and a via electrode of the mounting substrate, a further broadband and high gain antenna device can be obtained.

It is preferable that the power feeding terminal or the connection terminal is formed of a conductor continuous from one surface of the leg portion to the other surface via the bottom surface portion, and the areas of the conductors on both sides are different. By changing the area on both sides and directing the smaller area of the power supply terminal and the connection terminal to the ground electrode or circuit part side of the mounting substrate, the capacitance between the two is reduced, resulting in wider bandwidth and gain. Can be improved.

  The cover member is preferably an integrally molded product obtained by integrally molding a power supply terminal member. Both can be fixed by the cover member itself, and the manufacturing cost is low.

  It is preferable that the cover member has a notch for positioning the winding formed in a side surface portion of the magnetic core member. Especially when the number of turns in the winding part is 50 or less, or even 20 or less, the antenna characteristics change when the winding position changes for each turn. Therefore, an antenna with stable characteristics in mass production can be obtained by forming a notch. Can be obtained.

  The antenna preferably has a flat portion on the opposite side of the recess. It can be transferred onto the mounting substrate by using vacuum tweezers provided with a flat portion on the side (upper surface) opposite to the portion in contact with the mounting substrate.

  A second cover member disposed on the outer peripheral side of the winding portion may be provided to have the flat portion.

  It is preferable that a connection portion between the power feeding terminal and the winding portion of the connection terminal is formed on the same side surface of the cover member. The connection between the connecting portion and the winding portion, the bending of the connecting portion after the connection, and the like are easy on the equipment.

The magnetic core member can be made of a ferrite material. Since the ferrite core is more fragile than other magnetic core members, the antenna device of the present invention that can suppress the problem of chipping caused by the tension of the winding portion is very useful.

  By using these antennas as antenna devices and communication devices, mobile phones, wireless LAN devices, and GPS devices having desired antenna characteristics can be obtained.

  According to the present invention, it is possible to realize a chip antenna excellent in antenna characteristics that can be manufactured and adjusted by a simple process, has good mounting stability, and has a wide bandwidth and improved radiation efficiency. Further, it is possible to provide an antenna device that maximizes antenna characteristics by preventing noise and mutual interference around the antenna device.

It is a figure which shows one Example of the antenna of this invention. (A) is a perspective view, (b) is a perspective view in which a conductive wire and a ferrite core are arranged. It is a figure which shows the state which installed the antenna of FIG. 1 in the mounting board | substrate. It is a figure explaining the effect of the antenna of this invention, (A) is the surface mount type chip antenna of this invention, (B) is the surface mount type chip antenna of a comparative example, and is a front view at the time of mounting on a board | substrate. is there. It is the front view and back view of an antenna apparatus used for this invention. FIG. 2 is a development view of the antenna of FIG. 1. It is a perspective view (perspective view which has arrange | positioned a conductive wire and a core) for demonstrating another antenna of this invention. It is the front view and side view of the antenna of FIG. It is a perspective view for demonstrating the antenna of another form in this invention. It is a figure which shows the state which provided the cover in the antenna member of FIG. It is a perspective view for demonstrating another antenna of this invention. It is a perspective view for demonstrating another antenna of this invention. It is a figure which shows an example of the antenna apparatus of this invention. It is the figure which measured the characteristic of the antenna apparatus of this invention. It is the figure which measured the characteristic of the antenna apparatus of this invention. This is a conventional surface mount antenna. This is a conventional surface mount antenna. This is a conventional surface mount antenna.

  EXAMPLES Next, although an Example demonstrates this invention concretely, this invention is not limited by these Examples.

[Basic configuration of chip antenna]
The configuration in FIG. 1A is an antenna for a keyless entry system which is one embodiment of the present invention. FIG. 1B is a perspective view of a base (cover member) used for the antenna. In FIG. 1, an antenna 1a (hereinafter simply referred to as an antenna) includes a bridge-shaped base (cover member) 10a made of a dielectric, and one end of legs 11a and 12a that the base 10a fixes to a mounting board. A power supply terminal 13a provided on the base plate 10a, a connection terminal 14a for a radiation electrode formed on the mounting board provided on the other leg 12a, a recess 15a provided between the legs 11a and 12a, and a base 10a. And a ferrite core 18a disposed inside a continuation part 17a that connects the upper part of the leg part 11a and the leg part 12a of the base body 10a. A dielectric ceramic material may be used instead of the ferrite magnetic core.
The base 10a is integrally formed by resin molding. As the resin, LCP-E4008 dielectric material manufactured by Sumitomo Chemical Co., Ltd. was used. The dimensions were 10 mm in height, 45 mm in length, and 5 mm in thickness. The power supply terminal 13a and the connection terminal 14a are made by punching a conductive material (phosphor bronze C5191 or SUS304 material) having a thickness of 0.7 mm, and both terminals are the same. Costs are reduced by using the same terminal shape. Both terminals are installed on the surface on the opposite side from the surface on one side of the base body 10a through the contact surface with the mounting substrate. When viewed from the side, it has a substantially U-shape and is fixed so as not to be separated from the base body 10a by resin molding. If the sum of both ends of the terminal on both sides of the airframe is small, the reflection resistance becomes small and the antenna characteristics are deteriorated. It is preferable that both terminals of the power supply terminal 13a and the connection terminal 14a have different areas at the end portion on one side of the base body 10a and the end portion on the other side. Moreover, it is preferable to arrange | position so that the one where the area of both terminals is larger becomes the same side with respect to the base | substrate 10a. When the antenna 1a is installed on the mounting board, the capacitance on the small side of each terminal is directed to the ground electrode or circuit side of the mounting board, so that the capacitance is reduced and the bandwidth can be increased and the gain can be improved. . The bottoms of the legs 11a and 12a of the substrate 10a serve as contact surfaces with the mounting substrate. If the contact surface with the mounting substrate is large, the base 10a and the mounting substrate can be securely fixed. However, this area is appropriately determined depending on the space in which the antenna 1a can be disposed, the size of the ferrite core for obtaining necessary antenna characteristics, and the like. The base body preferably has a shape that substantially covers at least the entire side surface of the magnetic core member.
The ferrite core 18a has a rectangular parallelepiped shape, and all side surfaces in the major axis direction are covered with the base body 10a. The ferrite core 18a is inserted into the continuation portion 17a from the leg side of the base 10a. The hole portion in which the ferrite core 18a of the base 10a is disposed has a bottom portion whose diameter is smaller than that of the insertion port and the end portion of the ferrite core 18a. The ferrite core 18a is positioned by the end of the ferrite core 18 coming into contact with the bottom.
The conductive wire 16a has a wire size of 0.3 × 0.1 mm, and the number of windings is 7 turns. The ferrite core 18 is disposed at the center of the wound conductive wire 16a. In addition, one end of the conductive wire 16a is connected to the power supply terminal 13a, and the other end is connected to the connection terminal 14a. In addition, each terminal and the conductive wire 16a are connected by the connection part formed in the upper part of each terminal. The connecting portion and the conductive wire are electrically connected by soldering, brazing, caulking, welding, crimping, or the like. The connecting portion protrudes in a convex shape above the base body 10a and can be bent after being connected to the conductive wire 16a.

  Examples of the constituent material of other conductive wires include conductive wires made of conductive materials such as copper, silver, gold, aluminum, nickel, and alloys thereof. A predetermined element may be added to materials such as copper, silver, gold, aluminum, and nickel in order to improve weather resistance and the like. Alternatively, an alloy such as a conductive material and a non-metallic material may be used. As a constituent material, copper and its alloys are often used from the viewpoint of cost, corrosion resistance, and ease of production.

FIG. 2 is a diagram in which the antenna 1a of FIG. 1 is installed on a mounting board. The antenna 1a is disposed along the end of the mounting substrate 20a. When both ends of the antenna 1a are approximately the same size as the width of the mounting substrate, the resonance current generated in the axial direction of the coil and the image current on the substrate are in opposite directions, which causes a reduction in antenna characteristics. Therefore, in the present invention, the bridge can be used to float from the mounting substrate, and the gain can be improved by talking about the substrate, the ground electrode, and other circuit components to reduce the capacitance.
A ground electrode 21a is formed on the mounting substrate 20a by a printing method using a conductive paste. You may form by plating, solder plating, etc. Further, in order to supply power to the conductive wire 16a, a power supply line 22a is formed by printed wiring, and one end thereof is installed in the power supply terminal 11a.
3A is a view of FIG. 2 as viewed from above, and FIG. 3B is a view showing the back surface of the mounting substrate. A ground electrode 23a is formed on the back surface of the mounting substrate in the same manner as the front surface, and a radiation electrode 24a is formed on the back surface of the antenna 1a on the front surface. One end of the radiation electrode 24a is connected to the connection terminal 14a of the antenna 1a through a via hole formed in the mounting substrate. The other end of the radiation electrode 24a is an open end.
By feeding from the feed line, resonance of λ / 4 occurs between the antenna 1a and the radiation electrode 22a, and the antenna device can be used.

  FIG. 4 is a diagram seen from each surface of the base body 10a. A position surrounded by a broken line is a portion where the ferrite core is disposed. A groove 25a for positioning around the conductor 16a is formed in the base body 10a. Further, a flat portion is formed between the wound windings at the upper center of the continuation portion 17a, and the antenna 1a can be transported by being gripped by vacuum tweezers at the flat portion.

FIG. 5 is a perspective view showing another antenna 1b of the present invention. The conductive wire 16b is a ribbon-shaped plate formed into a helical shape by press molding, and is formed by molding and integrating the base 10b when resin molding is performed. In this embodiment, the conductive wire 16b, the power feeding terminal 13a, and the connection terminal 14a are formed from an integral plate. The central rectangular parallelepiped shows the place where the ferrite core is arranged.
6A is a view of the antenna 1b of FIG. 5 as viewed from the side, and FIG. 6B is a view of FIG. 6A as viewed from below.

FIG. 7 shows another antenna shape. As shown in FIG. 7C, the antenna 1c includes a resin base 10c, a ferrite core 18c, and a coil 16c. As shown in FIG. 7A, the base body 10c is formed with a recess 15c on the bottom side (the back side in the drawing), and leg portions 11c and 12c are formed at both ends thereof. The base body 10c has a box-like shape with an open top, and a step 26c is formed on the top as seen from the side surface in the longitudinal direction.
A ferrite core 18c is installed inside the base 10c, and a winding is wound around it. The depth of the inner surface into which the ferrite core of the substrate 10c is placed is preferably deeper than the ferrite core 18c. Since the tension of the winding does not give stress to the ferrite core, the ferrite core can be prevented from being broken, and the base 10a fixes the periphery of the ferrite core, and the position where the winding is wound by the recess 15c and the step 26c is positioned. Therefore, it is easy to wind the winding and at the same time individual characteristics in mass production are stabilized. In addition, the ferrite core is less likely to be damaged by external force. A resin may be poured after winding to integrate the ferrite core, winding, and base.

  After the winding, as shown in FIG. 8, the lid 27c is placed on the raised portions at both ends of the step 26c, and the lid member and the base body 10c are fixed with an adhesive. By disposing a flat lid member, the antenna 1c can be transported by vacuum tweezers. Further, as shown in FIG. 7C, the power supply terminal 13a and the connection terminal 14a are formed on the side surface of the base 10c by solder plating. The structure of the mounting base can be the same as that shown in FIG.

FIG. 9 shows a shape without the step 26c of FIG. Other configurations are the same as those in FIG.
In FIG. 10, the continuation portion 17e of the base body 10e is formed only on the bottom surface side with respect to the place where the ferrite core is disposed. Other configurations are the same as those in FIG.

  FIG. 11 is a diagram showing a state in which the antenna of FIG. 7 is assembled to the mounting substrate of the mobile phone communication device. The power supply line 22 and the connector 30a are installed on the mounting substrate 201, and the antenna is disposed therebetween. The connector 30a is connected to the connector 30b provided on the substrate 202 by assembling the mounting substrate to another substrate 202 (the case back cover of the communication device). One end of the radiation electrode 24 is connected to the connector 30b. The other end of the radiation electrode 24 is an open end. The positions of the connectors 30a and 30b are arranged in the vicinity of corners of a rectangular mounting board (mobile communication device). The radiation electrode extends from the connector 30b in the horizontal direction of the drawing, and further extends to the longer side of the portable communication device. By extending the open end from the connector 30b in the longitudinal direction of the mounting substrate (mobile communication device), the radiation electrode and the range gripped by the user of the mobile communication device overlap, and the gain of the antenna can be improved. 12 and 13 are diagrams comparing antenna characteristics when the conventional antenna device and the antenna device of the present invention are used. FIG. 12 shows the antenna gain measured in the FM radio broadcast band. The present invention has a higher gain of 10 dBi or more than the prior art. FIG. 13 shows received power obtained by observing broadcast radio waves from each transmitting station including FM radio broadcast using the antenna of the present invention and the conventional antenna. The present invention observes a larger received power.

1: Antenna 10: Base (cover member)
11, 12: Leg 13: Feeding terminal 14: Connection terminal 15: Recess 16: Conductive wire (winding part)
17: Continuation part 18: Core 20: Mounting substrate 21, 23: Ground electrode 22: Feeding line 24: Radiation electrode 25: Groove 26: Step 27: Cover

Claims (11)

A rod-shaped magnetic core member made of a magnetic material or a dielectric material;
A cover member that covers at least a part of a longitudinal side surface of the magnetic core member and is provided on a surface of a mounting substrate including a ground electrode , and has a plurality of legs for floating and fixing a part from the mounting substrate; Including an antenna with
The antenna is electrically connected to a power feeding terminal formed on a leg portion on one end side of the cover member, a connection terminal formed on a leg portion on the other end side, and the power feeding terminal and the connection terminal. The cover member has a recess formed between the leg portions, and in the winding portion , the magnetic core member is wound with a conductive wire together with the cover member including the recess. he,
A radiation electrode is provided on the back surface of the mounting substrate, one end of the radiation electrode is connected to the connection terminal of the antenna through a via hole formed in the mounting substrate, and the other end is an open end,
The radiation electrode is disposed in parallel with the axial direction of the winding portion of the antenna and folded, and a capacitor is formed by the open end and the power feeding terminal,
An antenna device characterized by resonating in two bands . 2. The antenna device according to claim 1, wherein the cover member of the antenna covers the periphery of the magnetic core member so that a tension of the winding portion around which the conductive wire is wound does not apply an external force to the magnetic core member. An antenna device characterized by having a shape. The antenna device according to claim 1 or claim 2, wherein the core member is an antenna apparatus characterized by being arranged in the center of the winding portion of the antenna. 4. The antenna device according to claim 1, wherein the power feeding terminal or the connection terminal of the antenna is a conductor that continues from one surface of the leg portion to the other surface through the bottom surface portion side. The antenna device is characterized in that the conductor areas on both sides are different. 5. The antenna device according to claim 1, wherein the cover member of the antenna is an integrally molded product obtained by integrally molding a power supply terminal member. 6. The antenna device according to claim 1, wherein the cover member of the antenna has a cutout portion for positioning the winding at a side portion of the magnetic core member. An antenna device characterized by that. The antenna device according to claim 1, wherein the antenna has a flat portion on a side opposite to the concave portion. The antenna device according to any one of claims 1 to 7, further comprising a second cover member disposed on an outer peripheral side of the winding portion of the antenna. 9. The antenna device according to claim 1, wherein a connection portion between the power feeding terminal of the antenna and the winding portion of the connection terminal is formed on the same side surface of the cover member. An antenna device characterized by that. The antenna device according to any one of claims 1 to 9, wherein the magnetic core member is made of a ferrite material. A communication device comprising the antenna device according to claim 1.

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