ELECTRONIC DEVICE

According to an embodiment, an electronic device includes a first board, a first ground layer, a first antenna, a second board, a second ground layer, a second antenna, a shield pipe and an electromagnetic wave absorber. When viewed from an axis direction of the shield pipe, an outermost edge of an internal wall at a first end is arranged inside an outermost edge of the first ground layer, the first antenna is arranged inside the outermost edge of the internal wall at the first end, an outermost edge of the internal wall at a second end is arranged inside an outermost edge of the second ground layer, and the second antenna is arranged inside the outermost edge of the internal wall at the second end.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2015-095837, filed May 8, 2015, the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to an electronic device.

BACKGROUND

In the prior art, a device is known in ultra-wideband (UWB) communications. The device has a structure in which a UWB communication chip set and an antenna are contained in a dedicated housing that maintains the chip set and the antenna in a state electromagnetically isolated from the periphery. In the device, the antenna is arranged inside the housing to perform UWB communications. This structure prevents the antenna from receiving spurious radiation from the peripheral devices, and increases the S/N ratio. In addition, disposing an electromagnetic wave absorber in the housing suppresses noise and multipath interference.

However, there is the problem that a complicated structure and difficult manufacturing are required to ensure an interface with the exterior in a state where the chip set and the antenna are contained in the housing, and electromagnetically isolate the inside of the housing.

DETAILED DESCRIPTION

Embodiments will be explained hereinafter with reference to the drawings.

According to an embodiment, an electronic device includes a first board, a first ground layer, a first antenna, a second board, a second ground layer, a second antenna, a shield pipe and an electromagnetic wave absorber. The first board has a first surface and a second surface opposed to the first surface, the first board having a first internal layer. The first ground layer formed on at least one of the first surface and the first internal layer. The first antenna arranged on at least one of the second surface and a region between the first ground layer and the second surface. The second board has a third surface and a fourth surface opposed to the third surface, the second board having a second internal layer, the fourth surface opposed to the second surface. The second ground layer formed on at least one of the third surface and the second internal layer. The second antenna arranged on at least one of the fourth surface and a region between the second ground layer and the fourth surface. The shield pipe arranged between the first board and the second board and formed of a conductor including a first end, a second end, and an internal wall, the first end opposed to the second surface, the second end opposed to the fourth surface. The electromagnetic wave absorber arranged on the internal wall. When viewed from an axis direction of the shield pipe, an outermost edge of the internal wall at the first end is arranged inside an outermost edge of the first ground layer, the first antenna is arranged inside the outermost edge of the internal wall at the first end, an outermost edge of the internal wall at the second end is arranged inside an outermost edge of the second ground layer, and the second antenna is arranged inside the outermost edge of the internal wall at the second end.

In the following explanation, constituent elements that are the same as or similar to the explained will be denoted by the same or similar reference numerals, and overlapping explanation thereof will be basically omitted.

Although the following explanation illustrates that a transmission antenna, a reception antenna, a wireless transmitting unit and a wireless receiving unit are independent of each other, the transmission antenna may have the function of the reception antenna, the reception antenna may have the function of the transmission antenna, the wireless transmitting unit may have the function of the wireless receiving unit, or the wireless receiving unit may have the function of the wireless transmitting unit. In other words, the antenna may have a transmitting/receiving function alone, or the wireless unit may perform signal processing related to transmission and reception alone.

First Embodiment

FIG. 1Aillustrates a cross-sectional portion of a side surface of an electronic device100according to a first embodiment. The electronic device100includes a first board110, a first transmission antenna111(also referred to as “first antenna”), a first wireless transmitting unit112(also referred to as “first wireless unit”), a first ground layer113, a second board120, a first reception antenna121(also referred to as “second antenna”), a first wireless receiving unit122(also referred to as “second wireless unit”), a second ground layer123, a shield pipe130, and a housing140. The first board110and the second board120are arranged to face each other. The shield pipe130is arranged between the first board110and the second board120. The housing140contains the first board110, the second board120, and the shield pipe130.

The first board110includes a first surface and a second surface opposed to the first surface. The first ground layer113is formed on at least one of the first surface of the first board110and an internal layer of the first board110. The first transmission antenna111is arranged on at least one of the second surface of the first board110and between the first ground layer113and the second surface of the first board110. For example, the first transmission antenna111is arranged in the internal layer of the first board110, in the case where a solder resist is applied onto the antenna surface. The first wireless transmitting unit112is arranged on the second surface of the first board110.FIG. 1Aillustrates the example where the first wireless transmitting unit112is arranged on the first board110, but the first wireless transmitting unit112may be arranged in an internal layer of the first board110, or may be arranged outside the first board110.

The first transmission antenna111is electrically connected with the first wireless transmitting unit112. The first wireless transmitting unit112communicates with the first wireless receiving unit122described later, and performs signal processing.

The first ground layer113is formed of a conductor. The first ground layer113is not required to be a conductor over all the surface thereof, but may have a hole or a crack. Part of the first ground layer113may be provided with a signal line or a power supply.

The second board120includes a first surface (also referred to as “third surface”) and a second surface (also referred to as “fourth surface”) opposed to the first surface. The second ground layer123is formed on at least one of the first surface of the second board120and an internal layer of the second board120. The first reception antenna121is arranged on at least one of the second surface of the second board120and a region between the second ground layer123and the second surface of the second board120. For example, the first reception antenna121is arranged in the internal layer of the second board120, in the case where a solder resist is applied onto the antenna surface. The first wireless receiving unit122is arranged on the second surface of the second board120. The first wireless receiving unit122may be arranged in an internal layer of the second board120, or may be arranged outside the second board120, in the same manner as the first wireless transmitting unit112.

The first reception antenna121is electrically connected with the first wireless receiving unit122. The first wireless receiving unit122communicates with the first wireless transmitting unit112, and performs signal processing.

The second ground layer123is formed of a conductor. The second ground layer123is not required to be a conductor over all the surface thereof, but may have a hole or a crack. Part of the second ground layer123may be provided with a signal line or a power supply.

The shield pipe130is a pipe that is formed of a conductor including a first end131, a second end132, an external wall134, and an internal wall135. The first end131is opened and opposed to the second surface of the first board110. The second end132is opened and opposed to the second surface of the second board120. Otherwise, the shield pipe130may be formed of a non-conductor (such as resin) having a metal-plated surface.

In the following explanation, these elements are collectively described as “conductor”. The conductor forming the shield pipe130may be electrically connected with at least one of the first ground layer113and the second ground layer123, to prevent reradiation from a current induced by the conductor.

The present embodiment illustrates the example where the shield pipe130is formed of a hollow circular cylinder. Otherwise, the shield pipe130may be formed of a hollow quadratic prism, a hollow circular truncated cone, or a hollow truncated pyramid.

The shield pipe130cuts off electromagnetic waves from the outside different from the electronic device100, to suppress interference with the electromagnetic waves.

The first end131is arranged to be opposed to the second surface of the first board110. For example, the length of the longest line segment connecting two different points of the edge of the internal wall135at the first end131is equal to or longer than the wavelength of the central frequency in the frequency band used for communication via the first transmission antenna111and the first reception antenna121.

A space may be provided between the first end131and the first ground layer113. The space is a distance between the conductors, and may be filled with an insulator such as a dielectric. For example, the space (that is, a distance between the first end131and the first ground layer113) is required to be smaller than the wavelength of the central frequency in the frequency band used for communication via the first transmission antenna111and the first reception antenna121.

The second end132is arranged to be opposed to the second surface of the second board120. For example, the length of the longest line segment connecting two different points of the edge of the internal wall135at the second end132is equal to or longer than the wavelength of the central frequency in the frequency band used for communication via the first transmission antenna111and the first reception antenna121.

A space may be provided between the second end132and the second ground layer123. The space is a distance between the conductors, and may be filled with an insulator such as a dielectric. For example, the space (that is, a distance between the second end132and the second ground layer123) is required to be smaller than the wavelength of the central frequency in the frequency band used for communication via the first transmission antenna111and the first reception antenna121.

Generally, because an antenna formed on the board has a size of the wavelength order, the antenna may be easily arranged inside an outermost edge of the internal wall135at the first end131or the second end132by setting the size of opening portions of the first end131and the second end132to be equal to or larger than the wavelength used for communication.

By setting the space to be shorter than the wavelength of the central frequency in the frequency band used for communication via the first transmission antenna111and the second reception antenna121, electromagnetic waves are prevented from leaking to the outside of the shield pipe, and electromagnetic waves are prevented from entering the inside of the shield pipe.

An electromagnetic wave absorber133is an object formed of a material that suppresses reflection of electromagnetic waves, and arranged on at least part of the internal wall135of the shield pipe130. For example, the electromagnetic wave absorber133is arranged on the internal wall135of the shield pipe130and in a region including a midpoint between the first end131and the second end132. The electromagnetic wave absorber133efficiently suppresses electromagnetic waves which radiated from the first transmission antenna111and reflected at the internal wall135of the shield pipe130, and suppresses multipath interference. Other arrangements of the electromagnetic wave absorber133will be described later.

The footprint of the electromagnetic wave absorber133in the shield pipe130can be reduced by enclosing electromagnetic waves radiated from the first transmission antenna111inside the shield pipe130. When the electromagnetic waves radiated from the first transmission antenna111are not enclosed inside the shield pipe130, the electromagnetic wave absorber133is required to be arranged inside the housing140widely, and the footprint of the electromagnetic wave absorber133is increased. For this reason, because the shield pipe130efficiently suppresses reflected waves with the smaller electromagnetic wave absorber133, the cost of the electromagnetic wave absorber133can be reduced.

FIG. 1Bis a diagram of the electronic device100when viewing the first board110from line A-A′ illustrated inFIG. 1A. When viewing the first board110from the axis direction of the shield pipe130, the outermost edge of the internal wall135at the first end131is arranged inside the outermost edge of the first ground layer113, and the first transmission antenna111is arranged inside the outermost edge of the internal wall135at the first end131.

The second board120side has a similar structure. When viewing the second board120from the axis direction of the shield pipe130, the outermost edge of the internal wall135at the second end132is arranged inside the outermost edge of the second ground layer123, and the first reception antenna121is arranged inside the outermost edge of the internal wall135at the second end132. In the following explanation, “when viewing the first board110(or the second board120) from the axis direction of the shield pipe130” is simply referred to as “as viewed from the cross section”, in similar drawings when viewing the first board110(or the second board120) from line A-A′.

The space surrounded by the internal wall135of the shield pipe130, the electromagnetic wave absorber133, the first ground layer113and the second ground layer123includes a first Fresnel zone formed by communication via the first transmission antenna111and the first reception antenna121. The first Fresnel zone is a space indicated by a spheroid formed of an aggregate of paths from transmission antenna to reception antenna. Each of differences in length between each of the paths and the direct path from the transmission antenna to the reception antenna is equal to or less than half of the wavelength of the frequency used for communication. When any obstacle exists in the spheroid, loss may occur due to blocking. For this reason, the space surrounded by the internal wall135of the shield pipe130, the electromagnetic wave absorber133, the first ground layer113and the second ground layer123includes the first Fresnel zone, to prevent loss caused by blocking.

As illustrated inFIG. 1A, for example, the electromagnetic wave absorber133is arranged on the internal wall135of the shield pipe130and in a region including the midpoint between the first end131and the second end132.FIG. 2andFIG. 3illustrate reflected waves in the case of adopting the arrangement.

FIG. 2illustrates the state where electromagnetic waves (thick-line arrows inFIG. 2) radiated from the first transmission antenna111are reflected once by the internal wall135of the shield pipe130and received on the first reception antenna121. Because the electromagnetic wave absorber133is arranged in a portion where the electromagnetic waves radiated from the first transmission antenna111are reflected by the internal wall135of the shield pipe130, the intensity of the electromagnetic waves when the electromagnetic waves are made incident on the first reception antenna121is suppressed.

As illustrated inFIG. 2, an angle (referred to as “radiation angle”) between the direction of the electromagnetic wave reflected once by the internal wall135of the shield pipe130and the direction perpendicular to the surface of the first board110is small. In the same manner, an angle (referred to as “incident angle”) between the direction in which the electromagnetic wave is made incident on the first reception antenna121and the direction perpendicular to the surface of the second board120is small. If the antenna directivity increases as the incident angle becomes smaller, this structure suppresses reflected waves of large power, and thus is effective for suppression of multipath interference.

FIG. 3illustrates the state where electromagnetic waves (thick-line arrows inFIG. 3) radiated from the first transmission antenna111are reflected a plurality of times by the internal wall135of the shield pipe130and received on the first reception antenna121. Because the electromagnetic wave absorber133is arranged in a portion where the electromagnetic waves are reflected for the third time to the fifth time by the internal wall135of the shield pipe130, the intensity of the reflected waves when the reflected waves are made incident on the first reception antenna121is suppressed.

The electromagnetic wave absorber133is arranged on the internal wall135of the shield pipe130and in a region including a midpoint between the first end131and the second end132. This arrangement suppresses electromagnetic waves reflected once by the internal wall135of the shield pipe130as illustrated inFIG. 2, and electromagnetic waves reflected a plurality of times by the internal wall135of the shield pipe130as illustrated inFIG. 3, and is effective for suppression of multipath interference.

FIG. 4Aillustrates an electronic device100acorresponding to a modification of the electronic device100. The electronic device100ais different from the electronic device100in the arrangement of the electromagnetic wave absorber133. The electromagnetic wave absorber133is arranged on a region of the internal wall135of the shield pipe130, and in the region covering from the first end131to the midpoint between the first end131and the second end132. The electronic device100aalso suppresses reflection of electromagnetic waves by the internal wall135of the shield pipe130, in the same manner as the electronic device100.FIG. 4Billustrates an external appearance similar to that ofFIG. 1A, and explanation thereof is omitted.

FIG. 4Cillustrates an electronic device100bcorresponding to a modification of the electronic device100. The electronic device100bis different from the electronic device100in the arrangement of the electromagnetic wave absorber133. The electromagnetic wave absorber133is arranged on the internal wall135of the shield pipe130, and covers from the first end131to the second end132. In other words, the electromagnetic wave absorber133is arranged in all the regions of the internal wall135of the shield pipe130. The electronic device100balso suppresses reflection of electromagnetic waves by the internal wall135of the shield pipe130.

The electromagnetic wave absorber133may be arranged on the internal wall135of the shield pipe130, and in a region located in an extending direction of the shield pipe130and including a region of the internal wall135of the shield pipe130that is close to the first transmission antenna111. For example, as illustrated inFIG. 4DandFIG. 4E, an electromagnetic wave absorber133ais arranged in an arc shape to extend from the first end131to the second end132.

FIG. 4Fillustrates an electronic device100dcorresponding to a modification of the electronic device100. The electronic device100dis different from the electronic device100in that the first end131and the second end132are provided with a first flange150and a second flange160to extend outward, respectively.FIG. 4Fomits illustration of the first transmission antenna111, the first wireless transmitting unit112, the first reception antenna121, and the first wireless receiving unit122.

The first flange150is used for fixing the shield pipe130to the first board110with screws151aand151b. The second flange160is used for fixing the shield pipe130to the second board120with screws161aand161b. The flanges may be fixed to one of the first board110and the second board120. The above screws are not limited to two, but may be one or three or more screws.

FIG. 4Gillustrates an electronic device100ecorresponding to a modification of the electronic device100. The electronic device100eis different from the electronic device100in that the first end131and the second end132are provided with a first flange150and a second flange160to extend inward, respectively.FIG. 4Gomits illustration of the first transmission antenna111, the first wireless transmitting unit112, the first reception antenna121, and the first wireless receiving unit122. Explanations of the flanges and the screws are omitted, because they are similar to those of the electronic device100d.

As described above, the electronic device according to the first embodiment prevents noise occurring outside from entering the shield pipe, with the first ground layer of the first board, the second ground layer of the second board, and the shield pipe. The electronic device also suppresses interference caused by reflection of electromagnetic waves radiated from the antenna arranged on the board, by disposing the electromagnetic wave absorber on the internal wall of the shield pipe. Accordingly, the electronic device enables suppression of interference of electromagnetic waves with a simple structure.

The frequency used for communication between the antennas may be, for example, a frequency of a millimeter wave band. Because the millimeter wave band has a short wavelength of several millimeters, the sizes of the antennas and the shield pipes can be reduced. In addition, the modulation method of the wireless system may be, for example, amplitude shift keying. This modulation method achieves a simple structure and low power consumption, but easily incurs interference of electromagnetic waves. However, using the electronic device according to the first embodiment suppresses interference of electromagnetic waves.

Second Embodiment

FIG. 5Aillustrates a cross-sectional portion of a side surface of an electronic device200according to a second embodiment. The electronic device200has a structure obtained by adding other electromagnetic wave absorbers to the electronic device explained in the above first embodiment. Specifically, the electronic device200has a structure in which an electromagnetic wave absorber170and an electromagnetic wave absorber180are arranged on a first board110and a second board120, respectively.

As illustrated inFIG. 5B, the electromagnetic wave absorber170is arranged on the first board110to surround the first transmission antenna111. Specifically, as viewed from the cross section, the outermost edge of the electromagnetic wave absorber170is arranged inside the internal wall135of the outermost edge at the first end131, and the electromagnetic wave absorber170is arranged in a position different from the first transmission antenna111.

The second board side also has a similar structure for the first board. The electromagnetic wave absorber180is arranged on the second board120to surround the first reception antenna121. Specifically, as viewed from the cross section, the outermost edge of the electromagnetic wave absorber180is arranged inside the internal wall135of the outermost edge at the second end132, and the electromagnetic wave absorber180is arranged in a position different from the first reception antenna121.

It suffices that the electronic device200is provided with at least one of the electromagnetic wave absorber170and the electromagnetic wave absorber180. The electromagnetic wave absorber170and the electromagnetic wave absorber180may be arranged to extend over all the regions except the antennas. The electromagnetic wave absorber170and the electromagnetic wave absorber180are not limited to the shape of surrounding the antenna, but part of them may be arranged on the board, or a plurality of them may be arranged on the board.

As described above, the electronic device according to the second embodiment suppresses reflection of electromagnetic waves by the boards, by disposing the electromagnetic wave absorbers also around the antennas. Accordingly, the electronic device further suppresses interference of electromagnetic waves due to multipath propagation.

Third Embodiment

FIG. 6Aillustrates a cross-sectional portion of a side surface of an electronic device300according to a third embodiment. The electronic device300is different from the electronic devices of the first embodiment and the second embodiment described above in the arrangement of the first wireless transmitting unit112and the first wireless receiving unit122.

As illustrated inFIG. 6B, as viewed in a direction perpendicular to the surface of the board, the first transmission antenna111and the first wireless transmitting unit112are arranged inside the outermost edge of the internal wall135at the first end131. The second board also has a similar structure, in which the first reception antenna121and the first wireless receiving unit122are arranged inside the outermost edge of the internal wall135at the second end132.

As described above, the electronic device according to the third embodiment suppresses discharge of noise generated from the wireless transmitting unit and the wireless receiving unit to the outside of the region surrounded by the first ground layer of the first board, the second ground layer of the second board, and the shield pipe. The electronic device also suppresses influence of noise from the outside of the region surrounded by the first ground layer of the first board, the second ground layer of the second board, and the shield pipe.

Fourth Embodiment

FIG. 7Aillustrates a cross-sectional portion of a side surface of an electronic device400according to a fourth embodiment. The electronic device400is different from the electronic devices of the first embodiment, the second embodiment, and the third embodiment described above, in that the electronic device400further includes a second reception antenna211(also referred to as “third antenna”), a second wireless receiving unit212(also referred to as “third wireless unit”), a second transmission antenna221(also referred to as “fourth antenna”), and a second wireless transmission unit222(also referred to as “fourth wireless unit”). For example, the second reception antenna211and the second transmission antenna221are used for communication using a frequency band that is different from the frequency band used for communication via the first transmission antenna111and the first reception antenna121described above.

The second reception antenna211is arranged on at least one of the second surface of the first board110, and a region between the first ground layer113and the second surface of the first board110. The second wireless receiving unit212is arranged on the second surface of the first board110.

The second reception antenna211is electrically connected with the second wireless receiving unit212. The second wireless receiving unit212communicates with the second wireless transmitting unit222described later, and performs signal processing.

The second transmission antenna221is arranged on at least one of the second surface of the second board220, and a region between the second ground layer123and the second surface of the second board120. The second wireless transmitting unit222is arranged on the second surface of the second board120.

The second transmission antenna221is electrically connected with the second wireless transmitting unit222. The second wireless transmitting unit222communicates with the second wireless receiving unit212, and performs signal processing.

The second reception antenna211, the second wireless receiving unit212, the second transmission antenna221, and the second wireless transmitting unit222may be arranged in the same manner as the first transmission antenna111, the first wireless transmission unit112, the first reception antenna121, and the first wireless receiving unit122in the first embodiment, respectively.

As illustrated inFIG. 7B, as viewed in a direction perpendicular to the surface of the board, the second reception antenna211and the second wireless receiving unit212are arranged inside the outermost edge of the internal wall135at the first end131. The electronic device400also has a similar structure on the second board, in which the second transmission antenna221and the second wireless transmitting unit222are arranged inside the outermost edge of the internal wall135at the second end132.

The space surrounded by the internal wall135of the shield pipe130, the electromagnetic wave absorber133, the first ground layer113and the second ground layer123includes a first Fresnel zone formed by communication via the second reception antenna211and the second transmission antenna221.

As described above, the electronic device according to the fourth embodiment further includes the second transmission antenna, the second wireless transmitting unit, the second reception antenna, and the second wireless receiving unit, and thereby suppresses interference of electromagnetic waves due to multipath propagation, while performing bidirectional communication with each other using frequency division duplex.

Fifth Embodiment

FIG. 8Aillustrates a cross-sectional portion of a side surface of an electronic device500according to a fifth embodiment. The electronic device500is different from the electronic device of the fourth embodiment described above in that the electronic device500further includes a rotary part310, shield pipe fixing portions311aand311b, and a fixed part320.FIG. 8Aomits illustration of the housing140.

A first board110is arranged on the rotary part310. A shield pipe130is fixed to the rotary part310via the shield pipe fixing portions311aand311b. The rotary part310is relatively rotatable with respect to a second board120, with a rotation axis r-r′ illustrated inFIG. 8A. The second board120is arranged on a surface of the fixed part320opposed to the rotary part310.

A gap exists between the second end132of the shield pipe130and the second board120, because the rotary part310is rotated together with the shield pipe130. In the case where the second end132of the shield pipe130contacts the second board120, it is desirable to reduce the friction. The distance between the second end132of the shield pipe130and the second ground layer123of the second board120should be smaller than the wavelength of the central frequency in the frequency band used for communication via the first transmission antenna111and the first reception antenna121.

As illustrated inFIG. 8B, the shield pipe fixing portions311aand311bfix the rotary part310and the shield pipe130. The shield pipe fixing portions are not limited to two, but may be one, or three or more.

Although the shield pipe fixing portions311aand311bfix the rotary part310and the shield pipe130inFIG. 8AandFIG. 8B, the shield pipe130may be fixed to the first board110using a flange and screws, in the same manner as the examples illustrated inFIG. 4FandFIG. 4G.

The shield pipe130may be fixed to the fixed part320, unlike the example illustrated inFIG. 8AandFIG. 8B. In such a case, the shield pipe130is not rotated together with the rotary part310.

The electronic device500has a structure in which a relative angle of the first reception antenna121with respect to the first transmission antenna111is changed by rotation of the rotary part310. In such a case, circularly polarized wave antennas are used as the first transmission antenna111and the first reception antenna121. This structure suppresses deterioration in communication due to polarized wave mismatch. The same is applicable to the second reception antenna211and the second transmission antenna221.

To form polarized wave diversity in the case of using circularly polarized wave antennas, the first transmission antenna111and the first reception antenna121should be set to have the same turning direction of the circularly polarized waves, the second reception antenna211and the second transmission antenna221should be set to have the same turning direction of the circularly polarized waves, and the first transmission antenna111and the second transmission antenna221should be set to have opposite turning directions. These settings suppress interference between communication between the first transmission antenna111and the first reception antenna121and communication between the second reception antenna211and the second transmission antenna221.

FIG. 9Aillustrates an electronic device500acorresponding to a modification of the electronic device500. The electronic device500ais different from the electronic device500in that the shield pipe130is divided into a shield pipe130aincluding a first end131, and a shield pipe130bincluding a second end132, and the electronic device500afurther includes shield pipe fixing portions321aand321b.

FIG. 9Aomits illustration of the housing140.

The rotary part310and the shield pipe130aare fixed to each other via the shield pipe fixing portions311aand311b. The fixed part320and the shield pipe130bare fixed to each other via the shield pipe fixing portions321aand321b.

AlthoughFIG. 9Aillustrates that the shield pipe fixing portions311aand311bfix the rotary part310and the shield pipe130aand the shield pipe fixing portions321aand321bfix the fixed part320and the shield pipe130b, they may be fixed using flanges and screws in the same manner as the examples illustrated inFIG. 4FandFIG. 4G.

A gap exists between the shield pipe130aand the shield pipe130b, because the rotary part310is relatively rotated together with the shield pipe130awith respect to the shield pipe130b. In the case where the shield pipe130acontacts the shield pipe130b, it is desirable to reduce the friction in contact. The distance between the shield pipe130aand the shield pipe130bshould be smaller than the wavelength of the central frequency in the frequency band used for communication via the first transmission antenna111and the first reception antenna121.

FIG. 9Billustrates an external appearance similar to that ofFIG. 8B, and explanation thereof is omitted.

FIG. 10Aillustrates an electronic device500bcorresponding to a modification of the electronic device500. The electronic device500bis different from the electronic device500in the arrangement of the electromagnetic wave absorber133.FIG. 10Aomits illustration of the housing140.

An electromagnetic wave absorber133aand an electromagnetic wave absorber133bare arranged on the internal wall135of the shield pipe130. Specifically, as illustrated inFIG. 10AandFIG. 10B, the electromagnetic wave absorber133ais arranged in a first region located in an extending direction of the shield pipe130and including a region of the internal wall135of the shield pipe130that is close to the first transmission antenna111. The electromagnetic wave absorber133bis arranged in a second region located in the extending direction of the shield pipe130and including a region of the internal wall135of the shield pipe130that is close to the second reception antenna211. In the example illustrated inFIG. 10AandFIG. 10B, each of the electromagnetic wave absorber133aand the electromagnetic wave absorber133bis formed in an arc shape to extend from the first end131to the second end132of the shield pipe130.

FIG. 11Aillustrates a state where a distance of a straight line between the first transmission antenna111and the first reception antenna121is longest.FIG. 11Aillustrates reflected waves radiated from the first transmission antenna111, reflected only once by the internal wall135of the shield pipe130, and received on the first reception antenna121. The intensity of electromagnetic waves radiated from the first transmission antenna111and reflected only once by the internal wall135of the shield pipe130is suppressed when they are made incident on the first reception antenna121, because the electromagnetic wave absorber133aand the electromagnetic wave absorber133bare arranged on portions of the internal wall135of the shield pipe130where the electromagnetic waves are reflected.

FIG. 11Billustrates a state where a distance of a straight line between the first transmission antenna111and the first reception antenna121is shortest.FIG. 11Billustrates reflected waves radiated from the first transmission antenna111, reflected only once by the internal wall135of the shield pipe130, and received on the first reception antenna121. The intensity of electromagnetic waves radiated from the first transmission antenna111and reflected only once by the internal wall135of the shield pipe130is suppressed when they are made incident on the first reception antenna121, because the electromagnetic wave absorber133aand the electromagnetic wave absorber133bare arranged on portions of the internal wall135of the shield pipe130where the electromagnetic waves are reflected.FIG. 11Bis a diagram in the case where the rotary part310ofFIG. 11Ais rotated by 180° around the rotation axis r-r′ with respect to the fixed part320.

As illustrated inFIG. 11AandFIG. 11B, in reflected waves radiated from the first transmission antenna111, reflected only once by the internal wall135of the shield pipe130, and received on the first reception antenna121, the radiation angle or the incident angle of an electromagnetic wave reflected in a region of the internal wall135of the shield pipe130close to the antenna is relatively small. When it is specifically explained with reference toFIG. 11B, the radiation angle and the incident angle of an electromagnetic wave radiated from the first transmission antenna111toward the electromagnetic wave absorber133b, reflected only once by the internal wall135of the shield pipe130, and received on the first reception antenna121is smaller than the incident angle and the radiation angle of an electromagnetic wave radiated toward the electromagnetic wave absorber133a, reflected only once by the internal wall135of the shield pipe130, and received on the first reception antenna121.

If the antenna directivity increases as the incident angle becomes smaller, this structure suppresses reflected waves of large power, and thus is effective for suppression of multipath interference.

As described above, the electronic device according to the fifth embodiment prevents noise occurring outside from entering the inside of the shield pipe, with the first ground layer of the first board, the second ground layer of the second board, and the shield pipe, also in the case where the first board is relatively rotated with respect to the second board. In addition, the electronic device also suppresses interference caused by reflection of electromagnetic waves radiated from the antenna arranged on the board, because electromagnetic wave absorbers are arranged on the internal wall of the shield pipe. Accordingly, the electronic device enables suppression of interference of electromagnetic waves with a simple structure.

In each of the above embodiments, at least part of the shield pipe may be formed of an electromagnetic wave absorber, and the other parts of the shield pipe may be formed of a conductor. Specifically, a portion of the shield pipe on which the electromagnetic wave absorber is arranged may not be formed of a conductor, but may be formed of a material that can support the electromagnetic wave absorber. The portion of the shield pipe on which the electromagnetic wave absorber is arranged may not be formed of a conductor, but may be formed of the electromagnetic wave absorber itself. In other words, the shield pipe may be formed of the electromagnetic wave absorber and a conductor that are formed as one unitary piece. Otherwise, the whole shield pipe may be formed of the electromagnetic wave absorber.

The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.