Antenna device and electronic device

An antenna device includes a metal plate and an antenna coil. A main portion of the antenna coil includes an insulating substrate and a coil conductor on the substrate. The metal plate includes a first conductor opening and a second conductor opening. The second conductor opening is continuous with the first conductor opening but not continuous with an outer edge of the metal plate.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an antenna device preferably for use in a system such as a radio frequency identifier (RFID) system or a short-distance wireless communication system and to an electronic device including the antenna device.

2. Description of the Related Art

An antenna device used in a RFID card reader/writer is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2002-298095.

When a coil antenna approaches a metal plate, eddy currents usually occur in the metal plate and adversely affect the characteristics of the coil antenna. To address such an effect, a typical antenna device includes a magnetic sheet interposed between the coil antenna and the metal plate, as illustrated in Japanese Unexamined Patent Application Publication No. 2002-298095.

In the antenna device disclosed in Japanese Unexamined Patent Application Publication No. 2002-298095, the magnetic body shields the magnetic field of the coil antenna, so that eddy currents are prevented from occurring in the metal plate. Thus, the antenna device is capable of communicating with a communication counterpart antenna when the communication counterpart antenna is located on the side of the antenna device on which the coil antenna is located.

However, since the magnetic body and the metal plate shield the magnetic field of the coil antenna, the antenna device is not capable of communicating with a communication counterpart antenna when the communication counterpart antenna is located on the metal-plate side of the antenna device.

SUMMARY OF THE INVENTION

Preferred embodiments of the present invention provide an antenna device that includes a loop-shaped or spiral-shaped coil conductor and an areally spreading plane conductor disposed opposite to a coil opening of the coil conductor, the antenna device being configured to perform communication through either a side on which the coil conductor is disposed or a plane-conductor side. Preferred embodiments of the present invention also provide an electronic device including such a novel antenna device.

According to a preferred embodiment of the present invention, an antenna device includes a loop-shaped or spiral-shaped coil conductor and an areally spreading plane conductor disposed to face a coil opening of the coil conductor, wherein the plane conductor includes a first conductor opening and a second conductor opening, wherein the coil opening overlaps the first conductor opening when the coil conductor is viewed in a plan, and wherein the second conductor opening is continuous with the first conductor opening but not continuous with an outer edge of the plane conductor. This structure enables the antenna device to perform communication through either its side on which the coil conductor is disposed or its side on which the areally spreading conductor is disposed.

Preferably, the first conductor opening and the second conductor opening are provided on the same plane. This structure makes a simple plane conductor usable as a booster antenna.

Preferably, an end of the second conductor opening extends to a position at which an electric current induced in a conductor by the coil conductor takes a value that is half or about half of a maximum value or less. This structure prevents the electric current that bypasses the ends of the second conductor opening (passes a shortcut) from cancelling the magnetic field, such that the areally spreading conductor is configured to be used as a booster antenna.

Preferably, the plane conductor is a grounded conductor provided on a circuit board. This structure dispenses with special provision of an areally spreading conductor that defines and serves as a booster antenna.

Preferably, an entirety or a portion of a metal housing that houses the coil conductor defines and serves as the plane conductor. This structure dispenses with special provision of an areally spreading conductor that serves as a booster antenna.

An electronic device according to another preferred embodiment of the present invention is an electronic device including the antenna device having the above structure and the electronic device includes a communication circuit connected to the coil conductor.

According to various preferred embodiments of the present invention, an antenna device that includes a coil conductor and an areally spreading plane conductor is configured to perform communication through either a side on which the coil conductor is disposed or a side on which the areally spreading plane conductor is disposed while suppressing the effect of the plane conductor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Preferred Embodiment

FIG. 1is an exploded perspective view of an antenna device101according to a first preferred embodiment of the present invention. The antenna device101includes a metal plate2and an antenna coil3. A main portion of the antenna coil3includes an insulating substrate33and a coil conductor31provided on the substrate33. The metal plate2corresponds to a “plane conductor” according to preferred embodiments of the present invention and includes a first conductor opening21and a second conductor opening22.

InFIG. 1, a coil opening CW of the coil conductor31and the metal plate2are arranged to face each other and the antenna coil and the metal plate are located close to each other so that magnetic field coupling occurs between the antenna coil and the metal plate.

In the example illustrated inFIG. 1, the first conductor opening21is rectangular or substantially rectangular, similar to the shape of the coil conductor31and the shape of the coil opening CW. The first conductor opening21is arranged so as to be overlapped by the coil opening CW when viewed in a plan. The second conductor opening22is continuous with the first conductor opening21but is not continuous with the outer edge of the metal plate2. In other words, the first conductor opening21and the second conductor opening22are continuous with each other and are enclosed without touching the outer edge of the metal plate2. Although the first conductor opening21is preferably rectangular or substantially rectangular inFIG. 1, the first conductor opening21does not necessarily have to be rectangular or substantially rectangular. The shape of the first conductor opening21can be changed in accordance of the purpose of use such as a reduction of unneeded coupling with peripheral components or an effective use of an antenna mounted space.

FIGS. 2A, 2B, and 2Cillustrate an electric current flowing through the coil conductor31and an electric current flowing through the metal plate2. The second conductor opening22provided in the metal plate2varies in length betweenFIGS. 2A, 2B, and 2C.

In each ofFIGS. 2A, 2B, and 2C, when an electric current I0flows through the coil conductor31, the coil conductor31and the metal plate2are coupled together via an electromagnetic field, so that an electric current is induced in the metal plate2. Specifically, an electric current I1flows mainly along the edge of the first conductor opening2and this electric current is diverted into an electric current flowing along the edge of the second conductor opening (slit)22and an electric current flowing around the first conductor opening21and along the outer edge of the metal plate2. Specifically, an electric current I3flows along the edge of the second conductor opening (slit)22and an electric current I2flows around the first conductor opening21and along the outer edge of the metal plate2. InFIGS. 2A, 2B, and 2C, this electric current I2is drawn by a single line for the purpose of simplicity of illustration.

InFIGS. 2A, 2B, and 2C, the intensity of the electric currents I1, I2, and I3is represented by the thickness of the lines. As illustrated inFIG. 2A, when the second conductor opening22is short, the intensity of the electric current I3flowing along the edge of the second conductor opening22is high and, accordingly, the intensity of the electric current I2is low. When the second conductor opening22is made longer, as illustrated inFIGS. 2B and 2C, the intensity of the electric current I3flowing along the edge of the second conductor opening22decreases and, accordingly, the intensity of the electric current I2increases.

The electric current I2flows in the same direction as the direction in which the electric current I0flows through the coil conductor31. Thus, the fact that the electric current I2flows through the metal plate2means that the electromagnetic-field shielding effect of the metal plate2is reduced. When the electromagnetic field caused by the electric current I2is larger than the electromagnetic field caused by the electric current I1flowing along the edge of the first conductor opening21, the metal plate2acts as a booster antenna. Since the path of the electric current I2is extended farther than the path of the electric current I1, the electromagnetic-field radiation effect produced by the electric current I2is larger than the electromagnetic-field radiation effect produced by the electric current I1. Usually, when half of the amount of the electric current I1flows as the electric current I2, the metal plate2exerts an effect of a booster antenna. Thus, the metal plate2acts as a booster antenna when the amount of the electric current I2that flows around the first conductor opening21and along the outer edge of the metal plate2is larger than the amount of the electric current I3that flows along the edge of the second conductor opening22.

The second conductor opening22, even when it is short, reduces the electromagnetic-field shielding effect of the metal plate2. However, it is preferable that the second conductor opening22be sufficiently long so as to make the amount of the electric current I2larger than the amount of the electric current I3.

FIG. 3illustrates three positions along the edges of the first conductor opening21and the second conductor opening22provided in the metal plate2. Here, it is preferable that the second conductor opening22be configured so that, when the amount of electric current flowing at the joint points (1) and (3) of the second conductor opening22is taken as 100%, the amount of electric current flowing at or around a midpoint (2) of the path along which the electric current I3illustrated inFIGS. 2A, 2B, and 2Cflows (at or around the top end of the second conductor opening22inFIG. 3) is smaller than or equal to 50%, for example.

FIGS. 4A and 4Bare plan views of a simulation model of an antenna device.FIG. 4Ais a plan view of the entire antenna device whileFIG. 4Bis an enlarged plan view of a portion at which the coil conductor is located. The metal plate2preferably has dimensions of approximately 150 mm×150 mm, for example. The dimensions of the coil conductor31and the dimensions of the first and second conductor openings21and22preferably are as illustrated inFIG. 4B. A communication counterpart antenna has a flat coil shape preferably having dimensions of about 54 mm×about 86 mm, for example. The antenna device illustrated inFIG. 4Aand the communication counterpart antenna are disposed so as to face each other and spaced about 20 mm, for example, apart from each other on the Z axis while the center of the antenna device and the center of the communication counterpart antenna coincide with each other.

FIG. 5is a graph showing a relationship between the length of the second conductor opening22of the simulation model and the coefficient of coupling between a target antenna device and a communication counterpart antenna. The horizontal axis inFIG. 5indicates the length from the joint points of the second conductor opening22to the top end (short-cut position) of the second conductor opening22while the vertical axis inFIG. 5indicates the coefficient of coupling. As illustrated inFIG. 5, the coefficient of coupling increases as the short-cut position of the second conductor opening22rises (as the second conductor opening22is lengthened). Here, the coefficient of coupling in the case where an antenna device does not include metal plate2is approximately 2%, for example. Thus, in the case where the short-cut position of the second conductor opening22arrives at or exceeds 100 mm, the existence of the metal plate2produces a booster effect.

FIG. 6is a graph showing a relationship between the length of the second conductor opening22of the simulation model and the amount of current flow at the top end (short-cut position) of the second conductor opening22. The horizontal axis ofFIG. 6indicates the length from the joint points of the second conductor opening22to the top end of the second conductor opening22(short-cut position) and the vertical axis indicates the amount of electric current at or around the top end when the amount of electric current flowing at the joint points (positions (1) and (3) illustrated inFIG. 3) of the second conductor opening22is taken as 100%. As illustrated inFIG. 6, the amount of electric current at or around the short-cut position of the second conductor opening22decreases as the short-cut position of the second conductor opening22rises (as the second conductor opening22is lengthened). When the percentage arrives at or falls below 50% (when the short-cut position of the second conductor opening22rises up to about 100 mm or higher), the existence of the metal plate2produces a booster effect.

Second Preferred Embodiment

FIGS. 7A, 7B, and 7Care plan views of metal plates of three antenna devices according to a second preferred embodiment of the present invention. The first preferred embodiment describes an example in which a simple slit-shaped second conductor opening22protrudes from the rectangular or substantially rectangular first conductor opening21, but the shape of the second conductor opening22is not limited to a simple slit shape. As illustrated inFIG. 7A, the second conductor opening22may have a T shape in which a slit extending from the first conductor opening21bifurcates halfway. As illustrated inFIG. 7B, alternatively, the slit extending from the first conductor opening21may have a large width at the end. Still alternatively, as illustrated inFIG. 7C, the slit extending from the first conductor opening21may be widened toward the end.

In the antenna device including either one of the metal plates illustrated inFIGS. 7A, 7B, and 7C, the electric current flowing from the joint points of the second conductor opening22toward the top end is diverted into the electric current I2and the electric current I3. Since the top end of the second conductor opening22is widened in the X axis direction, the electric current I2is more easily induced. Thus, the amount of electric current at or around the short-cut position of the second conductor opening22is reduced even though the distance by which the second conductor opening22protrudes from the first conductor opening21is small, such that the coefficient of coupling between the antenna device and the communication counterpart antenna is significantly increased.

Third Preferred Embodiment

FIG. 8Ais a plan view of an antenna device according to a third preferred embodiment of the present invention.FIG. 8Bis a plan view of a metal plate2included in the antenna device. As illustrated inFIG. 8A, the coil conductor31is located along three sides of the first conductor opening21. The width (extending between left and right in the drawing) of the second conductor opening22is larger than the width of the first conductor opening21.

As illustrated inFIG. 8B, an electric current flowing along the edge of the first conductor opening21is diverted at the joint points (1) and (3) of the second conductor opening. The electric current I2flows around the first conductor opening and along the outer edge of the metal plate2and the electric current I3flows along the edge of the second conductor opening22. The distance between the joint points (1) and (3) of the second conductor opening is wide and the capacitance between the joint points (1) and (3) is small, such that a displacement current I4that is to flow between the joint points (1) and (3) is small. Consequently, the amount of the electric current I2increases, such that a booster effect is obtained.

The antenna device illustrated inFIG. 8Ais an example where the width of the second conductor opening22is larger than the width of the first conductor opening. As illustrated inFIG. 9, however, the width of the first conductor opening21and the width of the second conductor opening22may be equal or substantially equal to each other. In this case, the region enclosed by the coil conductor31in a plan view serves as the first conductor opening21and the remaining region serves as the second conductor opening22. The joint points of the second conductor opening22are the positions (1) and (3) illustrated in the drawing.

Fourth Preferred Embodiment

Each ofFIGS. 10A to 10Fis a plan view of a metal plate included in an antenna device according to a fourth preferred embodiment of the present invention. In either example, the metal plate2includes a first conductor opening21and second conductor openings22. The preferred embodiments disclosed thus far describe examples in which one second conductor opening22preferably is provided for each first conductor opening21, for example. However, as illustrated inFIGS. 10A, 10B, and 10C, multiple second conductor openings22may be provided. The metal plate2of the example illustrated inFIG. 10Aincludes two second conductor openings22A and22B. The metal plate2of the example illustrated inFIG. 10Bincludes three second conductor openings22A,22B, and22C. The metal plate2of the example illustrated inFIG. 10Cincludes four second conductor openings22A,22B,22C, and22D.

Moreover, when multiple second conductor openings are to be provided, the angle at which adjacent second conductor openings cross each other is not limited to 90 degrees or 180 degrees. For example, as illustrated inFIG. 10D, a second conductor opening22A may extend obliquely to a second conductor opening22B. As illustrated inFIG. 10E, two second conductor openings22A and22B may extend in the same direction. Here, an entirety or a portion of second conductor openings may be bent.

When multiple second conductor openings are to be provided, the openings may have different widths as in the case of second conductor openings22A and22B illustrated inFIG. 10F.

Fifth Preferred Embodiment

FIG. 11illustrates an internal structure of a housing of an electronic device301according to a fifth preferred embodiment of the present invention in a plan view in the state where a first housing91and a second housing92are detached from each other to expose the inside. The electronic device301preferably is, for example, a mobile phone terminal or a tablet personal computer (PC) and includes an antenna device101having a structure according to either one of the preferred embodiments and a module201on which an antenna coil is mounted. The module preferably is a module for high-frequency (HF) radio-frequency identification (RFID) and is configured to perform, for example, near field communication (NFC). Specifically, the antenna device is preferably for use as an HF antenna.

The first housing91contains components such as printed circuit boards71and81and a battery pack83. An antenna-coil built-in module is mounted on the printed circuit board71. Components such as an ultra-high-frequency (UHF) antenna72and a camera module76are mounted on the printed circuit board71. Components such as a UHF antenna82are mounted on the printed circuit board81. The printed circuit board71and the printed circuit board81are connected together using a coaxial cable84.

An antenna device101is located on the inner surface of the second housing92. A first conductor opening21provided in the metal plate2of the antenna device101is located so as to correspond to the camera module76. The first conductor opening21also serves as a window at the position of a camera lens. The antenna device101causes magnetic-field coupling with an antenna coil (feed coil) of the module201on which the feeding antenna coil is mounted.

The metal plate2may be integrated with a resin-made housing. The entirety or a portion of the metal housing may define and serve as a metal plate.

An antenna device may have a configuration in which a first conductor opening and a second conductor opening are provided in a grounded conductor provided in a printed circuit board and a coil conductor is disposed near the first conductor opening.

Sixth Preferred Embodiment

FIG. 12is a perspective view of a portion of a housing of an electronic device according to a sixth preferred embodiment of the present invention. This electronic device preferably is, for example, a mobile phone terminal or a tablet PC. The housing illustrated inFIG. 12is a housing that comes on the side opposite the side on which a display panel is disposed and is molded out from a metal plate. In the case of such a metal housing, for example, a camera lens window is configured to be used as the first conductor opening21. Alternatively, a through hole23for an earphone jack, a card slot, a press button, or the like may be used as the first conductor opening or the second conductor opening.

Seventh Preferred Embodiment

FIGS. 13A and 13Billustrate a configuration of an electronic device according to a seventh preferred embodiment of the present invention.FIG. 13Aillustrates an example in which an antenna device is included in a PC monitor (display) andFIG. 13Billustrates an example in which an antenna device is included in a PC keyboard.

In the example illustrated inFIG. 13A, a metal frame2F of a PC monitor (display) is used as a “plane conductor”, one corner portion21D of the metal frame2F is used as a first conductor opening, and a display portion22D is used as a second conductor opening. In other words, by disposing an antenna coil3at the corner portion21D of the metal frame, the metal frame2F is caused to act as a booster antenna.

In the example illustrated inFIG. 13B, a metal frame2F of a PC keyboard is used as a “plane conductor”, a touch pad portion21T of the metal frame2F is used as a first conductor opening, and a keyboard portion22K is used as a second conductor opening. In other words, by disposing an antenna coil3at the touch pad portion21T, the metal frame2F is caused to act as a booster antenna.

Eighth Preferred Embodiment

FIGS. 14A and 14Billustrate a configuration of an electronic device according to an eighth preferred embodiment of the present invention.

FIG. 14Ais a front view of a keyboard andFIG. 14Bis a right view of the keyboard.

The keyboard includes a keyboard portion5K and a touch pad portion5T. In this preferred embodiment, a first conductor opening21is provided at a portion of a front surface of the metal frame2F of the keyboard and a second conductor opening22is provided at a portion of a side surface of the metal frame2F. A coil conductor31of an antenna coil3is disposed around the first conductor opening21of the metal frame21.

The width of the first conductor opening21(the opening width in the Y axis direction inFIGS. 14A and 14B) is larger than the width of the second conductor opening22.

By providing the first conductor opening21and the second conductor opening22in the metal frame2F of a keyboard in this manner (by providing special-purpose conductor openings without utilizing existing conductor openings), the metal frame2F is configured to be used as a “plane conductor” and caused to act as a booster antenna.

Ninth Preferred Embodiment

FIGS. 15A and 15Billustrate a configuration of an electronic device according to a ninth preferred embodiment of the present invention.

FIG. 15Ais a front view of a keyboard andFIG. 15Bis a right view of the keyboard.

Unlike in the case illustrated inFIGS. 14A and 14B, in this preferred embodiment, the width of the first conductor opening21(the opening width in the Y axis direction inFIGS. 15A and 15B) is equal or substantially equal to the width of the second conductor opening22. The first conductor opening21has a thin shape extending inwardly from the edge of the metal frame2F. Accordingly, the range over which the coil conductor31is formed is thin. Other components are preferably the same as those illustrated in the eighth preferred embodiment.

In this manner, even in the case where the width of the first conductor opening21and the width of the second conductor opening22are equal or substantially equal to each other, the metal frame2F is configured to be utilized as a “plane conductor” and caused to act as a booster antenna.

Tenth Preferred Embodiment

FIGS. 16A and 16Billustrate a configuration of an electronic device according to a tenth preferred embodiment of the present invention.

FIG. 16Ais a front view of a keyboard andFIG. 16Bis a right view of the keyboard. In this preferred embodiment, a conductor opening of a space key (wide button)21K of a metal frame2F is utilized as a first conductor opening and a conductor opening of a touch pad portion22T is utilized as a second conductor opening. A coil conductor31of an antenna coil3is arranged around the conductor opening of the space key21K.

In this manner, the conductor opening of the touch pad portion22T preferably is utilized as a second conductor opening. As illustrated in this example, the width of the second conductor opening (the width of the touch pad portion22T in the X axis direction) preferably is larger than the width of the first conductor opening (the width of the space key21K in the X axis direction).

Other Preferred Embodiments

As illustrated in the seventh to tenth preferred embodiments of the present invention, an existing conductor opening or openings may preferably be utilized as either one or both of the first conductor opening and the second conductor opening or new conductor openings may preferably be exclusively provided for both the first conductor opening and the second conductor opening.

The examples of various preferred embodiments of the present invention have been described with regard to an HF RFID. Besides the HF range, preferred embodiments of the present invention are similarly applicable to a UHF system usable for the purposes of, such as wireless LAN.

Although the above-described examples include a spiral-shaped coil conductor, the coil conductor may appropriately have a loop shape having one turn or the coil conductor may have a multilayer structure. Moreover, besides rectangular or substantially rectangular, the coil conductor may have any shape, in a plan view, with which the coil conductor can cause electromagnetic-field coupling with the first conductor opening.