Imaging apparatus

An imaging apparatus includes a first magnetic core and a first coil wound around the first magnetic core, a second magnetic core and a second coil wound around the second magnetic core, an imaging element provided between the first coil and the second coil, and a magnetic member, wherein the magnetic member includes a first magnetic portion arranged between the first coil and one surface serving as a light-receiving surface side of the imaging element, a second magnetic portion arranged between the second coil and the other surface side opposite to the light-receiving surface side of the imaging element, and a third magnetic portion which connects the first magnetic portion and the second magnetic portion, and wherein the first magnetic portion is arranged so as to face the first magnetic core, and/or the second magnetic portion is arranged so as to face the second magnetic core.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an imaging apparatus having an imaging element.

Description of the Related Art

According to an imaging element which is mounted in an imaging apparatus such as a digital video camera, digital still camera, or the like, in recent years, an ISO sensitivity has risen and, even in a scene of a small light amount such as a night scene, imaging with a clearer image can be performed. However, in association with the realization of the high sensitivity of the imaging element, such a problem that the imaging element is influenced by weak noises which did not cause a problem in the related art and a disturbance occurs in the image is actually caused.

For example, in the digital video camera, a motor for driving a lens is arranged in front of the imaging element such as a CMOS (Complementary Metal Oxide Semiconductor) image sensor or the like. Since a coil is provided for the lens driving motor, there is a case where a magnetic field generated from the coil exerts an influence on the imaging element and a disturbance occurs in the image which is formed by the imaging element.

In the related arts, with respect to a technique for suppressing such a situation that magnetic field noises generated from the coil are superimposed into the imaging element, Japanese Patent Application Laid-Open No. 2014-060676 discloses such a construction that a ferromagnetic member made of a ferromagnetic material having a high relative permeability such as Permalloy or the like is arranged between the coil and the imaging element. According to the construction disclosed in Japanese Patent Application Laid-Open No. 2014-060676, the ferromagnetic member becomes a detour of a magnetic flux to the imaging element and an arrival amount of the magnetic flux generated from the coil which arrives at the imaging element is reduced.

However, if the ferromagnetic member is arranged between the coil and the imaging element as disclosed in Japanese Patent Application Laid-Open No. 2014-060676, the ferromagnetic member also approaches inevitably the imaging element. The ferromagnetic member serving as a detour of the magnetic flux does not perfectly shut off the magnetic flux and a leakage of the magnetic flux exists in the neighborhood. Therefore, there is such a problem that if the ferromagnetic member approaches the imaging element, an amount of magnetic field which arrives at the imaging element increases.

According to such a construction that two coils are arranged so as to sandwich an imaging element, there is a case where a ferromagnetic member arranged between one of the coils and the imaging element also attracts magnetic field noises generated from the other coil. In such a case, there is such a problem that an amount of magnetic field which arrives at the imaging element cannot be sufficiently reduced.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an imaging apparatus in which even if a coil is arranged near an imaging element, an arrival amount of a magnetic field generated from the coil which arrives at the imaging element can be reduced.

According to an aspect of the present invention, there is provided an imaging apparatus including: a first magnetic core and a first coil wound around the first magnetic core; a second magnetic core and a second coil wound around the second magnetic core; an imaging element provided between the first coil and the second coil; and a magnetic member, wherein the magnetic member includes a first magnetic portion arranged between the first coil and one surface serving as a light-receiving surface side of the imaging element, a second magnetic portion arranged between the second coil and the other surface side opposite to the light-receiving surface side of the imaging element, and a third magnetic portion which connects the first magnetic portion and the second magnetic portion, and wherein the first magnetic portion is arranged so as to face the first magnetic core, and/or the second magnetic portion is arranged so as to face the second magnetic core.

DESCRIPTION OF THE EMBODIMENTS

First Embodiment

An imaging apparatus according to the first embodiment of the present invention will be described.FIG. 1is an explanatory diagram illustrating a schematic construction of the imaging apparatus according to the present embodiment. An imaging apparatus100according to the present embodiment is a digital camera and, more specifically, for example, a digital video camera.

As illustrated inFIG. 1, the imaging apparatus100according to the present embodiment has a casing101, an optical element (lens) group300, a focus lens unit400, an imaging unit200, a cooling unit (cooling fan)500, and a magnetic member600. The magnetic member600has such a shape that a sheet-like or plate-like member has been bent.

In the casing101, a window portion102provided with, for example, a lens cover or the like which can be automatically or manually opened or closed is formed in a front wall portion which faces an object. The optical element group300, the focus lens unit400, and the imaging unit200are arranged in the casing101in order from the front side toward the rear side. In the casing101, the magnetic member600is arranged for the imaging unit200as will be described hereinafter. Further, in the casing101, the cooling fan500is arranged behind the imaging unit200.

The imaging unit200has an imaging element201and a printed circuit board202. The imaging element201is, for example, a CMOS image sensor. The imaging element201is not limited to the CMOS image sensor but may be a CCD (Charge Coupled Device) image sensor or another image sensor. A driving circuit, a power supplying circuit, an A/D converting circuit, a communication interface circuit, and the like are mounted on the printed circuit board202.

The imaging element201is provided in an IC (Integrated Circuit) package having a glass lid. The IC package in which the imaging element201has been provided is mounted on the printed circuit board202, so that the imaging unit200is formed. The imaging unit200is arranged in such a manner that a board surface of the printed circuit board202is perpendicular in the front-rear direction of the casing101. The imaging element201on the printed circuit board202is located on a focus lens401side and its light-receiving surface faces the focus lens401side.

The optical element group300has, for example, a plurality of lenses301,302, and303and includes a zoom lens. The optical element group300constructs an image forming optical system for forming an optical image of the object onto the light-receiving surface of the imaging element201together with the focus lens unit400. A part of the casing101is a lens barrel in which the plurality of lenses301,302, and303and the focus lens unit400are enclosed.

The focus lens unit400arranged at the rear stage of the optical element group300has the focus lens401, a lens holder402, and a driving unit (voice coil motor)406. The focus lens401is attached and fixed to the lens holder402so as to be located in front of the imaging element201. The voice coil motor406drives the lens holder402to which the focus lens401has been attached. Specifically speaking, the lens holder402is driven by the voice coil motor406and the focus lens401is moved in parallel with the optical axis direction, thereby enabling the focus lens401to be in-focused to the object.

The voice coil motor406is of a linear driving type and has a coil403, a permanent magnet404, and a magnetic yoke405. The coil403in the voice coil motor406is properly called a first coil403. The magnetic yoke405has such a hollow square shape that it is formed in a hollow rectangular frame shape in which the front-rear direction of the casing101is set to the longitudinal direction. The magnetic yoke405functions as a magnetic core of the coil403. The permanent magnet404is attached to the inside of the hollow portion of the magnetic yoke405and forms a DC (Direct Current) magnetic field (magnetostatic field) which is uniform in the upper-lower direction in a space of the hollow portion. The first coil403is wound around a lower longitudinal portion of the magnetic yoke405in such a manner that the first coil403can move along the lower longitudinal portion of the magnetic yoke405serving as its magnetic core in the front-rear direction. The first coil403may be wound around a bobbin through which the lower longitudinal portion of the magnetic yoke405has been inserted or may be wound around the lower longitudinal portion of the magnetic yoke405in a bobbinless manner. The lens holder402is fixed to the first coil403and the lens holder402is also moved in the front-rear direction by the movement in the front-rear direction of the first coil403.

When the voice coil motor406is driven, a drive current is supplied to the first coil403as will be described hereinafter. When the drive current is supplied to the first coil403, since the direction of the current perpendicularly crosses the uniform DC magnetic field in the space of the hollow portion of the magnetic yoke405, a current force is generated in the optical axis parallel direction which perpendicularly crosses the current and the magnetic field by the Fleming's left-hand rule. By this current force, the first coil403and the lens holder402fixed to the first coil403slide along the optical axis direction serving as a front-rear direction of the casing101. Since the lens holder402slides in this manner, the focus lens401moves in parallel along the optical axis direction, thereby enabling the lens to be in-focused to the object.

Upon imaging, light from the object enters the light-receiving surface of the imaging element201provided behind the optical element group300and the focus lens unit400through the optical element group300and the focus lens401. The light which entered the light-receiving surface of the imaging element201is photoelectrically converted by photodiodes in a number of pixel circuits formed in a matrix form in the imaging element201and signal charges are accumulated as image signals. After that, the reading operation of the image signals is sequentially executed every row from the matrix-shaped pixel circuits. In the reading operation, first, the signal charges accumulated in the pixel circuits are transferred as voltage signals to column circuits in the imaging element201. Then, the signal is amplified by a preamplifier at a predetermined gain. Further, the signal is transferred in the horizontal direction and is output to the outside of the imaging element201through a main amplifier. The image signal output to the outside is converted into a digital signal through the A/D converting circuit in the printed circuit board202. Then, the signal is transferred to another printed circuit board (not shown) by the communication interface circuit and, after that, an image is constructed by the image signal processing circuit. The constructed image is stored into a memory and is displayed onto a liquid crystal screen or the like.

The cooling fan500arranged on the rear surface side opposite to the light-receiving surface of the imaging unit200is a fan to forcedly cool a heat generating portion in the casing101. As a heat generating portion in the casing101, for example, the imaging element201and the image signal processing circuit can be mentioned. When the cooling fan500rotates, the external air is taken from an inlet (not shown) formed in the casing101. By the cooling fan500, the air taken into the casing101is fed into a space where the heat generating portion such as an imaging element201and the like has been provided, passes in the space, and after that, is ejected to the outside from an outlet (not shown) formed in the casing101. In this manner, the cooling fan500can eject the heat generated in the heat generating portion such as imaging element201, image signal processing circuit, other circuits, and the like in the casing101to the outside of the casing101. A flow of the air formed in the casing101by the cooling fan500is not limited to the foregoing flow but may be such a flow that the heat generated in the heat generating portion can be ejected to the outside of the casing101.

InFIG. 1, the fan using a brushless DC motor is illustrated as an example of the cooling fan500. The brushless DC motor used in the cooling fan500is of an outer rotor type and has a blade portion501as a rotor, a center coil503as a stator, and a magnetic core505serving as a core of the coil503. The coil503in the cooling fan500is properly called a second coil503.

The blade portion501is a rotor whose shaft along the optical axis is a rotation axis. A cylindrical concave portion into which the stator is inserted is provided at the center of the blade portion501. An annular permanent magnet504charged so as to alternately show the opposite magnetic pole in order of S pole, N pole, . . . along the circumferential direction is attached to the inner peripheral wall surface of the concave portion of the blade portion501. The magnetic core505serving as a core of the second coil503is formed in the central second coil503serving as a stator so as to have a plurality of gap portions at an outer circumference of the second coil503. The second coil503is wound around the magnetic core505so as to have a cylindrical shape in which a rotational axis along the optical axis is set to the axis direction. The gap portions of the magnetic core505are periodically arranged in the circumferential direction of the second coil503. When the direct current flows in the second coil503, the directions of the magnetic fields generated in the gap portions become directions which are alternately inverted in the circumferential direction of the second coil503. A magnetic field generated in the gap portion and a DC magnetic field (magnetostatic field) of the facing annular permanent magnet504are attracted and repel alternately, so that a rotational force of the motor is generated. The blade portion501is rotated by the rotational force generated in this manner, so that a flow of the air is formed.

The first coil403constructing the voice coil motor406and the second coil503constructing the cooling fan500are provided in the casing101of the imaging apparatus100. A drive current is supplied to the first coil403when driving the voice coil motor406. A drive current is supplied to the second coil503when driving the cooling fan500. Since the drive current is supplied to both of the first coil403and the second coil503as will be described hereinafter, they become a magnetic field generating source for generating a leakage magnetic field.

First, the drive current which is supplied to the first coil403is, actually, a pulse current having such a waveform that an AC (Alternate Current) component is superimposed to a DC (Direct Current) component modulated by, for example, a PWM (Pulse Width Modulation) system. The pulse current can be controlled at a high speed. Even in the case of the pulse current, when considering a time-dependent average value, since the direct current flows, such a point that a current force adapted to cause the first coil403to slide is formed is guaranteed by the DC component. Since the AC component of the pulse current can be changed at a high speed, the position of the first coil403can be stably controlled at a high speed. On the other hand, the AC component of the current also forms an alternating magnetic field. The alternating magnetic field not only passes in the magnetic yoke405but also causes a large amount of magnetic field noises to be generated in the periphery as a leakage magnetic field. The higher a frequency of the alternating current is, an eddy current flows in the magnetic yoke405in such a direction as to cancel the magnetic field. Thus, an effective permeability of the magnetic yoke405decreases. Therefore, it is difficult that the magnetic field is concentrated only in the magnetic yoke405, and thus a large amount of leakage magnetic field is generated in the circumference.

Actually, the drive current which is supplied to the second coil503in the cooling fan500has, for example, such a waveform that the AC component is superimposed to the DC component, and the pulse current according to a rotational speed and control of the cooling fan500is supplied. Even in the case of the pulse current, when considering a time-dependent average value, since the direct current flows, such a point that a rotational force adapted to rotate the blade portion501is formed by the DC component is guaranteed. Since the AC component of the pulse current can be changed at a high speed, the cooling fan500can be stably controlled at a high speed. On the other hand, the AC component of the current also forms an alternating magnetic field. The alternating magnetic field not only passes the magnetic core505but also causes a large amount of magnetic field noises to be generated in the periphery as a leakage magnetic field. The higher the frequency of the alternating current is, an eddy current flows in the magnetic core505in such a direction as to cancel the magnetic field. Thus, an effective permeability of the magnetic core505decreases. Therefore, it is difficult that the magnetic field is concentrated only in the magnetic core505, and thus a large amount of leakage magnetic field is generated in the circumference. Since a component which leaks from a gap portion of the magnetic core505does not act on the DC magnetic field (magnetostatic field) of the permanent magnet504, such a leakage component further leaks to the outside.

Since a drive sound of the cooling fan500is picked up by a microphone in the digital video camera, it is desirable that the drive sound is small as possible. For this purpose, such a construction that a large fan is used as a cooling fan500and the drive sound is reduced by rotating the large fan at a low speed is often used. In such a case, since a size of a DC motor to drive the large fan is also large and thus the leakage magnetic field itself also increases.

In this manner, the leakage magnetic field is generated from each of the two coils such as first coil403and second coil503arranged so as to sandwich the imaging element201. There is a case where when the leakage magnetic fields arrive at the imaging element201, a disturbance occurs in an image which is formed by the imaging element201. There is also a case where when the leakage magnetic fields arrive at the printed circuit board202on which the imaging element201has been mounted, an influence occurs on the operation of the circuit on the printed circuit board202. It is, therefore, necessary to reduce an arrival amount of the leakage magnetic field which arrives at the imaging element201and the printed circuit board202.

Therefore, in the imaging apparatus100according to the present embodiment, the magnetic member600is arranged for the imaging unit200having the imaging element201and the printed circuit board202. The magnetic member600will be further described in detail with reference toFIG. 2.FIG. 2is an explanatory diagram illustrating details of the magnetic member600in the imaging apparatus100according to the present embodiment.

As illustrated inFIG. 2, the magnetic member600includes a first magnetic portion601and a second magnetic portion602each serving as a sheet-like or plate-like portion and a third magnetic portion603which connects the first and second magnetic portions601and602. As will be described hereinafter, an opening portion6011adapted to expose a pixel area of the imaging element201is formed in the second magnetic portion602.

InFIG. 2, a diagram on the left side of an arrow illustrates a state before the magnetic member600is provided for the imaging unit200and a diagram on the right side of the arrow illustrates a state after the magnetic member600was provided for the imaging unit200. Details of a material and a relative permeability of the magnetic member600will be described hereinafter.

The first magnetic portion601is arranged between the first coil403of the voice coil motor406and the side of the light-receiving surface serving as one side of the imaging element201. The first magnetic portion601is arranged in such a manner that its sheet surface is substantially parallel with the light-receiving surface of the imaging element201and a board surface of the printed circuit board202.

The first magnetic portion601is arranged in such a manner that its outer peripheral edge portion is located on the outer side than a pixel area of the imaging element201. The opening portion6011adapted to expose the pixel area of the imaging element201is formed in the first magnetic portion601so that the light is transmitted from the focus lens401to the imaging element201.

A plane shape of the first magnetic portion601is not particularly limited but can have various kinds of shapes. For example, as illustrated inFIG. 2, the first magnetic portion601can be constructed so as to have portions arranged along edge portions of three sides of the pixel area of the imaging element201exposed in the opening portion6011. The first magnetic portion601can be constructed so as to have an annular portion arranged along edge portions of four sides of the pixel area of the imaging element201exposed in the opening portion6011.

Further, the first magnetic portion601has a surface which faces a part or all of a surface4051of the magnetic yoke405of the first coil403. The surface4051of the magnetic yoke405is a surface on the side of the first magnetic portion601in the magnetic yoke405.

The second magnetic portion602is arranged between the second coil503of the cooling fan500and a rear surface side opposite to the light-receiving surface side of the imaging element201. The second magnetic portion602is arranged in such a manner that its sheet surface is substantially parallel with the light-receiving surface of the imaging element201and the board surface of the printed circuit board202.

The second magnetic portion602is formed so as to cover the whole surface of the rear surface side opposite to the light-receiving surface of the imaging element201. That is, the second magnetic portion602has an area wider than an area of the region where the imaging element201has been projected in the optical axis direction. It is sufficient that the second magnetic portion602covers at least a part of the rear surface of the imaging element201. Even in this case, an influence of the leakage magnetic field can be reduced. In order to sufficiently reduce also an influence of the leakage magnetic field on the printed circuit board202, the second magnetic portion602may be formed so as to cover not only the rear surface of the imaging element201but also the whole surface of the rear surface of the circuit forming area in the printed circuit board202.

The second magnetic portion602has a surface which faces a part or all of a surface5051of the magnetic core505of the second coil503. The surface5051of the magnetic core505is a surface on the side of the second magnetic portion602in the magnetic core505.

The first magnetic portion601and the second magnetic portion602are connected by the third magnetic portion603arranged so as to stride over the imaging unit200. One edge portion of the third magnetic portion603is connected to an upper edge portion of the first magnetic portion601. The other edge portion of the third magnetic portion603is connected to an upper edge portion of the second magnetic portion602. It is not always necessary that the third magnetic portion603is connected to the upper edge portion of the first magnetic portion601and the upper edge portion of the second magnetic portion602but it is sufficient that the third magnetic portion603is connected to the first magnetic portion601and the second magnetic portion602.

The first magnetic portion601, second magnetic portion602, and third magnetic portion603may be integratedly formed by the same sheet-like or plate-like members made of the magnetic members of the same material. The first magnetic portion601, second magnetic portion602, and third magnetic portion603may be formed by different sheet-like or plate-like members made of the magnetic members of the same or different materials, and they may be connected.

Specifically speaking, the sheet-like or plate-like magnetic member600may be formed in such a manner that the first magnetic portion601, second magnetic portion602, and third magnetic portion603are continuous by bending the same sheet-like or plate-like member made of the magnetic member of the same material. The sheet-like or plate-like magnetic member600may be formed by overlaying several parts made of the magnetic members of the same or different materials and connecting those parts. The sheet-like or plate-like magnetic member600may be formed as a composite member by combining different magnetic materials.

In the sheet-like or plate-like magnetic member600, the member which covers the rear surface of the imaging element201is not limited to the second magnetic portion602. It is sufficient to use such a construction that any portion including the first magnetic portion601, second magnetic portion602, and third magnetic portion603of the sheet-like or plate-like magnetic member600covers the rear surface of the imaging element201.

In the imaging apparatus100according to the present embodiment, arrival amounts of the leakage magnetic field generated from the first coil403and the leakage magnetic field generated from the second coil503which arrive at the imaging element201and the printed circuit board202can be reduced by the foregoing sheet-like or plate-like magnetic member600. The action of the present embodiment will be described hereinafter with reference toFIGS. 3A and 3B.FIGS. 3A and 3Bare explanatory diagrams illustrating the leakage magnetic fields which are generated from the coils403and503in the imaging apparatus100according to the present embodiment.

FIG. 3Ais an explanatory diagram illustrating the leakage magnetic field which is generated from the first coil403in the voice coil motor406. In order to make the voice coil motor406for driving the focus lens401operative, the drive current containing the AC component flows in the first coil403as mentioned above. When the drive current flows in the first coil403, as an alternating magnetic field caused by the AC component of the drive current, a magnetic field700is generated in the magnetic yoke405and a leakage magnetic field701is generated in a peripheral space of the first coil403. Since a permeability of the first magnetic portion601arranged in front of the imaging element201is higher than that in the peripheral portion from a viewpoint of the magnetic circuit, the leakage magnetic field701generated from the coil403is attracted to the first magnetic portion601.

The leakage magnetic field701attracted to the first magnetic portion601is branched to two different magnetic transfer routes702and703. The magnetic transfer route702is a route which passes to the lower edge portion of the first magnetic portion601. The magnetic transfer route703is a route which passes from the first magnetic portion601to the second magnetic portion602through the third magnetic portion603. Since the leakage magnetic field701generated from the first coil403is bypassed to the magnetic transfer routes702and703, the magnetic field which is branched to the imaging element201and the printed circuit board202provided between them can be reduced. As a result, the arrival amount of the leakage magnetic field701generated from the first coil403which arrives at the imaging element201and the printed circuit board202can be suppressed. Each of the magnetic fields transferred to the magnetic transfer routes702and703is finally propagated along a transfer route which passes through the lower space of the imaging element201and is returned to the first coil403to finally form a closed line of magnetic force.

The second magnetic portion602faces the magnetic core505. Therefore, although not illustrated inFIG. 3A, a route which starts from the portion which faces the magnetic core505of the second magnetic portion602, passes the magnetic core505of the second coil503, and is returned to the first coil403can be also formed as a magnetic transfer route. This is because the magnetic field which is propagated along the magnetic transfer route703is space-propagated toward the surface5051of the magnetic core505which the second magnetic portion602faces. That is, it can be considered that the second magnetic portion602and the surface5051of the magnetic core505face and form a coupling magnetic circuit. Therefore, the leakage magnetic field generated from the coil403is propagated to the magnetic core505of the second coil503arranged on the side opposite to the imaging element201. Thus, the magnetic field which arrives at the imaging element201side is reduced by an amount of the magnetic field which is propagated to the magnetic core505. At a position which is sufficiently away from the imaging element201, the leakage magnetic field propagated to the magnetic core505is transferred from the magnetic core505to an external space, is transferred along a transfer route which is returned to the first coil403to finally form a closed line of magnetic force.

As mentioned above, in the present embodiment, the leakage magnetic field701generated from the first coil403in the voice coil motor406avoids the imaging element201and the printed circuit board202and is bypassed to the magnetic transfer route702formed in the first magnetic portion601. In the present embodiment, the leakage magnetic field701generated from the first coil403avoids the imaging element201and the printed circuit board202and is bypassed to the magnetic transfer route703formed in the first magnetic portion601, third magnetic portion603, and second magnetic portion602. Thus, in the present embodiment, even if the first coil403is arranged near the imaging element201, the arrival amount of the leakage magnetic field701generated from the first coil403which arrives at the imaging element201and the printed circuit board202can be reduced.

On the other hand,FIG. 3Bis an explanatory diagram illustrating the leakage magnetic field which is generated from the second coil503in the cooling fan500. In order to make the cooling fan500operative, the drive current containing the AC component flows in the second coil503as mentioned above. The AC component of the drive current which flows in the second coil503in the cooling fan500may have a frequency which is different from or is equal to that of the AC component of the current flowing in the first coil403in the voice coil motor406. When the drive current flows in the second coil503, as an alternating magnetic field caused by the AC component of the drive current, a magnetic field800occurs in the magnetic core505and a leakage magnetic field is generated in a peripheral space of the second coil503. Since a permeability of the second magnetic portion602arranged behind the imaging element201is higher than that in the peripheral portion from a viewpoint of the magnetic circuit, the leakage magnetic field generated from the second coil503is attracted to the second magnetic portion602.

The leakage magnetic field attracted to the second magnetic portion602is branched to two different magnetic transfer routes801and802. The magnetic transfer route802is a route which passes to the lower edge portion of the second magnetic portion602. The magnetic transfer route801is a route which starts from the second magnetic portion602and passes the first magnetic portion601through the third magnetic portion603. The leakage magnetic field transferred to the magnetic transfer route802is transferred along a transfer route which passes through the space on the side opposite to the imaging element201and is returned to the second coil503to form a closed line of magnetic force.

The magnetic transfer route801further starts from the first magnetic portion601and passes the magnetic yoke405of the first coil403. This is because the magnetic field which is propagated in the magnetic transfer route801is space-propagated toward the surface4051of the magnetic yoke405which the first magnetic portion601faces. That is, it can be considered that the first magnetic portion601and the surface4051of the magnetic yoke405face and form a coupling magnetic circuit. Therefore, the leakage magnetic field generated from the second coil503is propagated to the magnetic yoke405of the first coil403arranged on the side opposite to the imaging element201. Thus, the magnetic field which arrives at the imaging element201side is reduced by an amount of the magnetic field which is propagated to the magnetic yoke405. At a position which is sufficiently away from the imaging element201, the leakage magnetic field propagated to the magnetic yoke405is transferred from the magnetic yoke405to an external space, is transferred along a transfer route which is returned to the second coil503to finally form a closed line of magnetic force.

As mentioned above, in the present embodiment, the leakage magnetic field generated from the second coil503in the cooling fan500avoids the imaging element201and the printed circuit board202and is bypassed to the magnetic transfer route802formed in the second magnetic portion602. In the present embodiment, the leakage magnetic field generated from the second coil503avoids the imaging element201and the printed circuit board202and is bypassed to the magnetic transfer route801formed in the second magnetic portion602, third magnetic portion603, and first magnetic portion601. The magnetic transfer route801is further formed to the magnetic yoke405of the first coil403. Thus, in the present embodiment, even if the second coil503is arranged near the imaging element201, the arrival amount of the leakage magnetic field generated from the second coil503which arrives at the imaging element201and the printed circuit board202can be reduced.

As mentioned above, in the present embodiment, the arrival amounts of the leakage magnetic fields generated from the two coils arranged so as to sandwich the imaging element201and the printed circuit board202which arrive at the imaging element201and the printed circuit board202can be reduced.

Subsequently, in the present embodiment, such an effect that the arrival amount of the magnetic field which arrives at the imaging element201can be reduced by the layout of the sheet-like or plate-like magnetic member600will be described in detail on the basis of Examples.

Details of Example 1 will be described with reference toFIG. 2. In Example 1, the imaging element201of 7.5 mm×8.0 mm having a pixel area of 3.96 mm×5.28 mm is mounted on a ceramic lead package of 12.6 mm (in the vertical direction)×14.0 mm (in the lateral direction)×2.0 mm (thickness) by wire bonding. Such a semiconductor package is mounted, as a printed circuit board202, on a rigid flexible board having a rigid portion of about 25 mm×27 mm so as to sandwich a copper sheet for radiation of 1.0 mm (thickness).

The voice coil motor406is provided in such a manner that the surface4051(which faces the first magnetic portion601) of the magnetic yoke405having a hollow square shape is located at the position which is away from the surface of the imaging element201by 2.1 mm. Outer dimensions of the magnetic yoke405are equal to 5 mm (height) (a height of the hollow portion is equal to 3 mm), 5 mm (width), and 18.5 mm (length in the optical axis direction). A material of the magnetic yoke405is an SPCC material as a cold-rolled steel. The permanent magnet404of 5 mm (width) and 15 mm (length in the optical axis direction) is provided in the hollow portion of the magnetic yoke405. The first coil403is wound in a rectangular shape of 2.7 mm×7.0 mm (inner periphery) and 4.6 mm×8.9 mm (outer periphery) so as to have a winding width of 3.0 mm. The first coil403is arranged so that its axis is parallel with the optical axis. The pulse current of 127 kHz is supplied to the first coil403in the voice coil motor406, so that it is driven as a motor.

The cooling fan500is provided at a position of 26.5 mm from the rear surface of the printed circuit board202on which the imaging element201has been mounted. The brushless DC motor of the outer rotor type in the center portion of the cooling fan500has the magnetic core505of 17.0 mm (diameter) as a stator. The second coil503is wound in a circular shape of 5.9 mm (inner diameter) and 10.2 mm (outer diameter) so as to have a winding width of 2.0 mm. The second coil503is arranged so that its axis is parallel with the optical axis. The pulse current of 300 Hz is supplied to the second coil503in the cooling fan500, so that it is driven as a motor.

As a sheet-like or plate-like magnetic member600, a nano-crystal magnetic sheet of 18 μm (thickness) in which a relative permeability at a frequency of 30 Hz near a direct current is equal to 40,000 is used. In the sheet-like or plate-like magnetic member600, the nano-crystal magnetic sheet is bent and the first magnetic portion601, second magnetic portion602, and third magnetic portion603are integratedly formed.

The first magnetic portion601of 5 mm×10 mm is arranged between the first coil403and the imaging element201. The first magnetic portion601is located at a distance of 1.1 mm from the surface of the imaging element201and is located at a distance of 1.0 mm from the facing surface of the magnetic yoke405. The surface of about 50% of the surface4051of the magnetic yoke405faces the first magnetic portion601. A portion of the first magnetic portion601illustrated inFIG. 2extending to the lower side along the edge portions of the two right and left sides of the imaging element201has a width of 1 mm and a length of 14 mm.

The second magnetic portion602of 20 mm×20 mm is arranged between the second coil503and the imaging element201. The second magnetic portion602is located at a position which is away by 1.7 mm from the rear surface of the printed circuit board202on which the imaging element201has been mounted. The second magnetic portion602is formed so as to cover the rear surface of the imaging element201of 7.5 mm×8.0 mm.

As mentioned above, the third magnetic portion603connecting the first magnetic portion601and the second magnetic portion602is formed by the same material as that of the first magnetic portion601and the second magnetic portion602. A size of the third magnetic portion603is equal to 10.0 mm (lateral width) and 6.7 mm (length).

Comparative Example 1

Comparative Example 1 has a construction illustrated inFIGS. 4A and 4B. Comparative Example 1 differs from Example 1 with respect to a point that all of the first magnetic portion601, second magnetic portion602, and third magnetic portion603are not provided. That is, in Comparative Example 1, the sheet-like or plate-like magnetic member600is not provided. A construction other than a point that the sheet-like or plate-like magnetic member600is not provided is similar to that in Example 1.

Comparative Example 2

Comparative Example 2 has a construction illustrated inFIGS. 5A and 5B. In Comparative Example 2, although the first magnetic portion601and the second magnetic portion602are provided, it differs from Example 1 with respect to a point that the third magnetic portion603is not provided. That is, in Comparative Example 2, the first magnetic portion601and the second magnetic portion602are not connected but are independently separated. A construction other than a point that the first magnetic portion601and the second magnetic portion602are not connected is similar to that in Example 1.

With respect to each of foregoing Example 1 and Comparative Examples 1 and 2, an electromagnetic field simulation is performed by using commercially available electromagnetic field analyzing software and an arrival amount of a magnetic field which arrives at the imaging element201is obtained. In the electromagnetic field simulation, “Maxwell 3D” made by ANSYS Inc. is used as electromagnetic field analyzing software.

In the electromagnetic field simulation, a current which is supplied to the first coil403and the second coil503is a sine wave alternating current having a frequency of the current which is actually supplied to each coil. An analysis is independently performed every frequency. That is, a leakage magnetic field generated from each of the coils403and503is independently analyzed and thus an arrival amount of the magnetic field which arrives at the imaging element201from each of the coils403and503is independently obtained.

FIG. 6is a graph illustrating results in each of which an arrival amount of a magnetic field which arrives at a semiconductor portion of the imaging element201was obtained by the electromagnetic field simulation with respect to each of Example 1 and Comparative Examples 1 and 2. InFIG. 6, with respect to each of Example 1 and Comparative Examples 1 and 2, the arrival amount of the magnetic field which arrives at from the first coil403is illustrated in a bar graph on the left side, and the arrival amount of the magnetic field which arrives at from the second coil503is illustrated in a bar graph on the right side. As an arrival amount of the magnetic field, a magnetic flux density in the semiconductor portion of the imaging element201is obtained. The arrival amount of the magnetic field is shown by a ratio in the case where the arrival amount in Comparative Example 1 is assumed to be 100%.

As compared with Comparative Example 1 in which the sheet-like or plate-like magnetic member600itself is not arranged, in Comparative Example 2, the first magnetic portion601and the second magnetic portion602which are not connected to each other are arranged. In Comparative Example 2, the arrival amount of the magnetic field from the first coil403is reduced to only about 40% of that in Comparative Example 1. This is because of the following reason.

FIG. 4Aillustrates the leakage magnetic field from the first coil403in Comparative Example 1. InFIG. 4A, since the sheet-like or plate-like magnetic member600is not arranged, both of the magnetic transfer routes702and703are routes which pass the imaging element201.

On the other hand,FIG. 5Aillustrates the leakage magnetic field from the first coil403in Comparative Example 2. InFIG. 5A, since the first magnetic portion601is arranged, the magnetic transfer route702in the magnetic transfer routes702and703bypasses the imaging element201. However, since the first magnetic portion601is not connected to the second magnetic portion602, the magnetic transfer route703is a route which passes the imaging element201.

As mentioned above, in Comparative Example 2, since the magnetic transfer route702bypasses, the arrival amount of the magnetic field which arrives at the imaging element201is reduced by a certain amount. However, in Comparative Example 2, since the magnetic transfer route703is a route which passes the imaging element201, the arrival amount of the magnetic field which arrives at the imaging element201from the first coil403is reduced to only about 40% of that in Comparative Example 1.

In Comparative Example 2, the arrival amount of the magnetic field from the second coil503is reduced to only about 82% of that in Comparative Example 1. This is because of the following reason.

FIG. 4Billustrates the leakage magnetic field from the second coil503in Comparative Example 1. InFIG. 4B, since the sheet-like or plate-like magnetic member600is not arranged, both of the magnetic transfer routes801and802are routes which pass the imaging element201.

On the other hand,FIG. 5Billustrates the leakage magnetic field generated from the second coil503in Comparative Example 2. InFIG. 5B, since the second magnetic portion602is arranged, the magnetic transfer route802in the magnetic transfer routes801and802bypasses the imaging element201. However, since the second magnetic portion602is not connected to the first magnetic portion601, the magnetic transfer route801is a route which passes the imaging element201.

As mentioned above, in Comparative Example 2, since the magnetic transfer route802bypasses, the arrival amount of the magnetic field which arrives at the imaging element201is reduced by a certain amount. However, in Comparative Example 2, since the magnetic transfer route801is a route which passes the imaging element201, the arrival amount of the magnetic field which arrives at the imaging element201from the second coil503is reduced to only about 82% of that in Comparative Example 1.

On the other hand, in Example 1, the arrival amount of the magnetic field from the first coil403is reduced to about 30% of that in Comparative Example 1. This is because of the following reason.

FIG. 3Aillustrates the leakage magnetic field from the first coil403in Example 1. InFIG. 3A, since the first magnetic portion601and the second magnetic portion602mutually connected by the third magnetic portion603are arranged, both of the magnetic transfer routes702and703bypass the imaging element201. Therefore, in Example 1, the arrival amount of the magnetic field from the first coil403is reduced to about 30% of that in Comparative Example 1.

In Example 1, the arrival amount of the magnetic field from the second coil503is reduced to about 45% of that in Comparative Example 1. This is because of the following reason.

FIG. 3Billustrates the leakage magnetic field from the second coil503in Example 1. InFIG. 3B, since the first magnetic portion601and the second magnetic portion602mutually connected by the third magnetic portion603are arranged, both of the magnetic transfer routes801and802bypass the imaging element201. Therefore, in Example 1, the arrival amount of the magnetic field from the second coil503is reduced to about 45% of that in Comparative Example 1.

Particularly, it will be understood that, in Example 1, a suppressing effect to the leakage magnetic field from the second coil503in which a frequency of the supplied current is lower than that of the leakage magnetic field from the first coil403is higher than that in Comparative Example 2. According to the present embodiment, the arrival amount of the magnetic field which arrives at the imaging element201is reduced by a unique construction for realizing the bypass of the magnetic field and the coupling of the magnetic field to another device. That is, according to the unique construction of the present embodiment, first, the magnetic field is bypassed by the sheet-like or plate-like magnetic member600. Further, according to the unique construction of the present embodiment, the leakage of the magnetic field which is propagated from the sheet-like or plate-like magnetic member600serving as a detour of the magnetic field to the imaging element201side is coupled with the magnetic yoke405in the voice coil motor406serving as another device on the side opposite to the imaging element201. In this manner, according to the unique construction of the present embodiment, the arrival amount of the magnetic field which arrives at the imaging element201and, further, the printed circuit board202on which the imaging element201has been mounted is reduced. Such a result that the suppressing effect to the leakage magnetic field from the second coil503in Example is higher than that in Comparative Example 2 shows that the effect by the unique construction appears typically.

If the arrival amount of the magnetic field which arrives at the imaging element201can be reduced to, for example, the arrival amount in Example 1 as mentioned above, a disturbance of the image which occurs in the imaging element201of a high sensitivity can be sufficiently suppressed.

Subsequently, results obtained by the detailed examination with respect to the unique construction to realize the bypass of the magnetic field and the coupling of the magnetic field to another device mentioned above will be described.

First, a degree of coupling of the magnetic field is changed by changing the facing area between the first magnetic portion601and the magnetic yoke405. If the arrival amount of the magnetic field which arrives at the imaging element201decreases as the degree of coupling is larger, it can be shown that the arrival amount of the magnetic field which arrives at the imaging element201is reduced by the foregoing unique construction.

FIGS. 7A, 7B, and 7Care diagrams illustrating the case where the area ratio of the surface4051(of the magnetic yoke405of the first coil403) which faces the first magnetic portion601changes.FIG. 7Ashows the case where the surface of the area ratio 100% of the surface4051of the magnetic yoke405faces the first magnetic portion601.FIG. 7Bshows the case of foregoing Example 1 where the surface of the area ratio 50% of the surface4051of the magnetic yoke405faces the first magnetic portion601.FIG. 7Cshows the case of Example 3 where the surface of the area ratio 18% of the surface4051of the magnetic yoke405faces the first magnetic portion601. Those cases will be described in detail hereinafter.

Example 2 will be described with reference toFIG. 7Awith respect to only a point different from Example 1. In Example 2, a length in the upper direction of the first magnetic portion601is extended by an amount of 3.5 mm or more as compared with that in Example 1 so as to be higher than the upper surface of the magnetic yoke405. Therefore, in Example 2, the surface of the area ratio 100% of the surface4051of the magnetic yoke405faces the first magnetic portion601.

Example 3 will be described with reference toFIG. 7Cwith respect to only a point different from Example 1. In Example 3, a length in the upper direction of the first magnetic portion601is shortened by 1.1 mm. Therefore, in Example 3, the surface of the area ratio 18% of the surface4051of the magnetic yoke405faces the first magnetic portion601. Since the length in the upper direction of the first magnetic portion601is shortened, the third magnetic portion603is bent.

FIG. 8is a graph illustrating results in each of which an arrival amount of a magnetic field which arrives at a semiconductor portion of the imaging element201was obtained by an electromagnetic field simulation with respect to each of Examples 1 to 3. The electromagnetic field simulation was performed in a manner similar to the case illustrated inFIG. 6. InFIG. 8, the arrival amount of the magnetic field which arrives at from the second coil503is shown by a bar graph with respect to each of Examples 1 to 3. As an arrival amount of the magnetic field, a magnetic flux density in the semiconductor portion of the imaging element201is obtained. The arrival amount of the magnetic field is shown by a ratio in the case where the arrival amount in Comparative Example 1 mentioned above is assumed to be 100%.

Referring toFIG. 8, in any of Examples 1 to 3, the arrival amount of the magnetic field is smaller than that in the case of Comparative Example 2 illustrated inFIG. 6. It will be understood that as the area ratio in the case where the surface4051of the magnetic yoke405faces the first magnetic portion601increases, the arrival amount of the magnetic field which arrives at the imaging element201is further reduced. The results shown inFIG. 8can be described as follows.

FIGS. 7A, 7B, and 7Care diagrams illustrating states where the leakage magnetic field generated from the second coil503is propagated with respect to each of Examples 1 to 3. In any of those diagrams, the leakage magnetic field passes the magnetic transfer route801and is propagated to the surface4051of the magnetic yoke405of the coil403through the first magnetic portion601.

A propagation amount of the leakage magnetic field which is propagated as mentioned above is smallest in Example 3 illustrated inFIG. 7Camong Examples 1 to 3. Subsequently, a propagation amount of the leakage magnetic field increases in order of Example 1 illustrated inFIG. 7Band Example 2 illustrated inFIG. 7A. This is because the area ratio of the surface4051(of the magnetic yoke405) which faces the first magnetic portion601is smallest in Example 3 among Examples 1 to 3 and, subsequently, it increases in order of Example 1 and Example 2. As the area ratio of the surface4051(of the magnetic yoke405) which faces the first magnetic portion601increases in order of Example 3 illustrated inFIG. 7C, Example 1 illustrated inFIG. 7B, and Example 2 illustrated inFIG. 7A, the propagation amount of the leakage magnetic field to the magnetic yoke405increases.

That is, the increase in propagation amount of the magnetic field to the magnetic yoke405side corresponds to an increase in amount of the magnetic field which bypasses the imaging element201. Therefore, the effect obtained by bypassing the magnetic field increases and thus the arrival amount of the magnetic field which arrives at the imaging element201decreases. When considering it as a magnetic circuit, it means that a magnetic resistance between the first magnetic portion601serving as a magnetic transfer route and the magnetic yoke405was reduced by increasing the facing area between the magnetic members.

It has been proved that by bypassing the leakage magnetic field by the sheet-like or plate-like magnetic member600and further coupling the leakage of the magnetic field from its detour to the magnetic yoke405in another device on the side opposite to the imaging element201as mentioned above, the arrival amount of the magnetic field which arrives at the imaging element201or the like decreases.

It is desirable that the area ratio of the surface4051(of the magnetic yoke405) which faces the first magnetic portion601is equal to 10% or more. By setting the area ratio of the facing surface to 10% or more, the propagation amount of the magnetic field to the magnetic yoke405side is sufficiently increased and the arrival amount of the magnetic field to the imaging element201can be sufficiently reduced.

Subsequently, a positional relation between the first magnetic portion601and the magnetic yoke405of the coil403will be described further in detail with reference toFIG. 9.

InFIG. 9, a distance between the first magnetic portion601and the surface4051of the magnetic yoke405of the coil403is equal to a1. A distance between the first magnetic portion601and the surface of the imaging element201is equal to a2. The arrival amount of the magnetic field to the imaging element201changes in dependence on a relation between the distances a1 and a2.

A description will be made based on specific Examples. In foregoing Example 2, the distance a1 is equal to 1.0 mm and the distance a2 is equal to 1.1 mm.

In Example 4, inFIG. 9, the distance a1 is equal to 1.5 mm, the distance a2 is equal to 0.6 mm, and other points are similar to those in Example 2.

In Example 5, inFIG. 9, the distance a1 is equal to 0.5 mm, the distance a2 is equal to 1.6 mm, and other points are similar to those in Example 2.

In foregoing Examples 2, 4, and 5, the distance a2 increases in order of Example 4, Example 2, and Example 5 and the distance a1 decreases contrarily in association with it.

An arrival amount of the magnetic field which arrives at the semiconductor portion of the imaging element201was obtained by the electromagnetic field simulation with respect to each of Examples 4, 2, and 5.FIG. 10is a graph illustrating results in each of which the arrival amount of the magnetic field which arrives at the semiconductor portion of the imaging element201was obtained by the electromagnetic field simulation with respect to each of Examples 4, 2, and 5. The electromagnetic field simulation was performed in a manner similar to that shown inFIG. 6. InFIG. 10, the arrival amount of the magnetic field which arrives at from the second coil503is shown by a bar graph with respect to each of Examples 4, 2, and 5. As an arrival amount of the magnetic field, a magnetic flux density in the semiconductor portion of the imaging element201is obtained. The arrival amount of the magnetic field is shown by a ratio in the case where the arrival amount in foregoing Comparative Example 1 is assumed to be 100%.

InFIG. 10, it will be understood that as the distance a2 increases and the distance a1 decreases in order of Examples 4, 2, and 5, the arrival amount of the magnetic field which arrives at the imaging element201is reduced. The results shown inFIG. 10can be described as follows with reference toFIG. 9.

The leakage magnetic field which was generated from the second coil503and reached the first magnetic portion601by passing the magnetic transfer route801can be propagated to the two kinds of routes such as a route by which it is propagated to the magnetic yoke405of the first coil403and a route by which it is propagated to the imaging element201. The proper route to which the leakage magnetic field is propagated is determined by the distances a1 and a2. That is, when the distance a1 is smaller than the distance a2, a magnetic resistance of the route by which it is propagated to the magnetic yoke405is sufficiently small. Therefore, the propagation amount of the magnetic field to the route to the imaging element201side can be further reduced. Consequently, the arrival amount of the magnetic field which arrives at the imaging element201can be reduced.

Therefore, it is desirable that the first magnetic portion601is arranged between the magnetic yoke405and the imaging element201so that the distance a1 is smaller than the distance a2. That is, it is desirable that the first magnetic portion601is arranged near the magnetic yoke405than the imaging element201. The distances a1 and a2 can be properly set in accordance with a suppression amount of a disturbance of the image which is necessary in the actual product.

Also with respect to the second magnetic portion602, it can be constructed in a manner similar to the foregoing first magnetic portion601, and the arrival amount of the leakage magnetic field generated from the first coil403which arrives at the imaging element201can be reduced.

As illustrated inFIG. 9, the magnetic core505of the coil503has the surface5051which faces the second magnetic portion602. InFIG. 9, the surface of the area ratio 100% of the surface5051of the magnetic core505faces the second magnetic portion602. Although the area ratio of the surface5051of the magnetic core505which faces the second magnetic portion602is not limited to 100%, by increasing such an area ratio, the arrival amount of the leakage magnetic field generated from the first coil403which arrives at the imaging element201can be further reduced.

It is desirable that the area ratio of the surface5051of the magnetic core505which faces the second magnetic portion602is equal to 10% or more. By setting the area ratio of the facing surface to 10% or more, the propagation amount of the magnetic field to the magnetic core505side is sufficiently increased and thus the arrival amount of the magnetic field to the imaging element201can be sufficiently reduced.

A distance between the surface5051of the magnetic core505of the second coil503and the second magnetic portion602can be set to be smaller than a distance between the second magnetic portion602and the surface of the imaging element201. InFIG. 9, the distance between the surface5051of the magnetic core505and the second magnetic portion602is equal to b1. The distance between the second magnetic portion602and the surface of the imaging element201is equal to b2.

The second magnetic portion602can be arranged between the magnetic core505and the imaging element201so that the distance b1 is smaller than the distance b2. That is, the second magnetic portion602can be arranged near the magnetic core505than the imaging element201. If the distance b1 is smaller than the distance b2, a magnetic resistance of the route by which the magnetic field is propagated to the magnetic core505decreases. Therefore, the magnetic field propagation amount to the route to the imaging element201side can be further reduced, so that the arrival amount of the magnetic field which arrives at the imaging element201can be reduced. The distances b1 and b2 can be also properly set in accordance with a suppression amount of a disturbance of the image which is necessary in the actual product in a manner similar to the distances a1 and a2.

Also with respect to the second magnetic portion602, by constructing it as mentioned above, the leakage magnetic field701which is generated from the first coil403is propagated to the second magnetic portion602through the third magnetic portion603and is further propagated therefrom to the magnetic core505side. Therefore, such an effect that the arrival amount of the magnetic field which arrives at the imaging element201is further reduced is obtained.

Subsequently, a material which is used in the foregoing sheet-like or plate-like magnetic member600, that is, a material which is used in the first magnetic portion601, second magnetic portion602, and third magnetic portion603will be described.

As a material of the sheet-like or plate-like magnetic member600, for example, a stainless steel sheet such as SUS430, SUS630, or the like, an SPCC steel sheet (cold-rolled steel), or a galvanized sheet iron such as partial Silver Top (trademark) or the like can be used. Those materials are magnetic materials of a comparatively small relative permeability and, particularly, a relative permeability which is equal to or larger than 50 and is equal to or smaller than 1000. Those materials can be desirably used as a material of the sheet-like or plate-like magnetic member600. However, a material such as aluminum, copper, SUS304, conductive plastics, or the like having a relative permeability of almost 1, that is, a material other than the magnetic material cannot be used as a material of the sheet-like or plate-like magnetic member600.

As a material of the sheet-like or plate-like magnetic member600, a nano-crystal soft magnetic sheet such as FINEMET (registered trademark) or the like as a magnetic material of a comparatively high relative permeability can be also used. As another material, a noise suppression sheet (containing magnetic powder, magnetic filler, or magnetic film) of a high relative permeability such as permalloy, amorphous magnetic material, ferrite, electromagnetic steel, or BUSTERAID (registered trademark), or the like can be also used. In this case, a higher effect can be expected.

The relative permeability of the material constructing the sheet-like or plate-like magnetic member600will be described. The relative permeability of the magnetic material changes in dependence on a frequency of the magnetic field. The relative permeability of such a magnetic material can be measured by using a measuring system illustrated inFIG. 11.FIG. 11is an explanatory diagram illustrating the measuring system for measuring the relative permeability.

In the measuring system illustrated inFIG. 11, a tool31which can measure a plate-like measurement sample313by “methods of measurement of the magnetic properties of magnetic steel sheet and strip by means of a single sheet tester” specified in JIS C 2556 is used. The tool31includes a double yoke frame312having a lower yoke312aand an upper yoke312b, and a coil311surrounded by the double yoke frame312. An LCR meter32is connected to the coil311. An impedance analyzer can be also used in place of the LCR meter32.

In the measurement of the relative permeability, the measurement sample313formed in a plate shape is sandwiched in the double yoke frame312and is inserted into the coil311. Subsequently, by frequency-sweeping an AC signal to the coil311by the LCR meter32, frequency characteristics of an inductance value are obtained. The inductance value in a state where no sample is inserted is used as a reference and a real part μ′ of a complex relative permeability is obtained by the following equation (1) from the inductance value in the case where the measurement sample313has been inserted. A magnetic flux density which is applied to the measurement sample313is equal to 1 [μT] or less at each frequency. Therefore, an initial permeability of the material which acts in response to weak magnetic field noises is obtained.

Where, N denotes the number of turns of the coil311. μ0denotes a magnetic permeability of the vacuum and its value is equal to 4π×10−7[H/m]. A denotes a cross sectional area of the measurement sample313. L denotes a length of the measurement sample313. Leffdenotes an inductance measurement value obtained by the LCR meter32. Lwdenotes an inductance measurement value obtained in the case where the measurement sample313is not inserted.

In the measurement by “measuring methods for characteristics of materials of ferrite cores” specified in JIS C 2561, since the measurement is performed by using a ring-like measurement sample, it should be noted that, particularly, a thickness dependency of the magnetic permeability of the sheet-like or plate-like magnetic member cannot be accurately obtained.

FIG. 12illustrates results in which the relative permeabilities of various kinds of materials were measured by the foregoing measuring system shown inFIG. 11.FIG. 12is a graph illustrating the results in which the relative permeabilities were measured with respect to the various kinds of materials such as nano-crystal soft magnetic sheet, permalloy, ferrite, SPCC, SUS430, and copper.

Referring toFIG. 12, a state where in almost all of the magnetic materials, when the frequency rises, the relative permeability decreases is observed. This is because when the magnetic field of a high frequency has entered the sheet-like or plate-like magnetic member, an eddy current flows into the sheet-like or plate-like magnetic member in such a direction as to cancel the magnetic field. It is difficult that the magnetic field enters the magnetic member due to an effect of such an eddy current. Such a phenomenon corresponds to a decrease in effective relative permeability. Therefore, such a state that when the frequency rises, the relative permeability decreases is observed. A reason why the frequency at which the decrease in relative permeability starts differs every material is that a frequency band in which the eddy current is liable to flow differs in dependence on a conductivity and a thickness of the magnetic material.

Although a thickness of the sheet-like or plate-like magnetic member600is not particularly limited, even in the case of the same material of the magnetic member, by thinning the magnetic member600, the effective relative permeability can be further raised. Therefore, when the sheet-like or plate-like magnetic member600is formed, it is desirable to consider not only a kind of such a material but also its thickness.

It is desirable that the relative permeability of the sheet-like or plate-like magnetic member600is equal to 10 or more, more desirably, 50 or more within a range of 1 kHz to 10 MHz serving as a frequency of the leakage magnetic field which becomes the magnetic field noises. If the sheet-like or plate-like magnetic member600having such a relative permeability is used, a sufficient effect of propagating the magnetic field is obtained. Although an upper limit value of the relative permeability of the sheet-like or plate-like magnetic member600is not particularly limited, the relative permeability of the sheet-like or plate-like magnetic member600within a range of, for example, 200000 or less serving as a relative permeability of the material which can be industrially used can be selected.

On the basis of a graph obtained by measuring the relative permeability of the magnetic material like a graph illustrated inFIG. 12mentioned above, the effective magnetic material can be selected in accordance with the frequency of the leakage magnetic field so as to suppress the arrival to the imaging element201. Even in the case of using a material other than the material shown in FIG.12, by measuring the relative permeability by the measuring method shown here, the magnetic material suitable for suppression of the magnetic field noises can be selected.

In the present embodiment, it is not always necessary to form the sheet-like or plate-like magnetic member600by the single magnetic material, but it can be also formed as a complex member by combining different magnetic materials.

For example, in the sheet-like or plate-like magnetic member600illustrated inFIG. 2, the first magnetic portion601and the third magnetic portion603can be formed by using the nano-crystal soft magnetic sheet showing a comparatively high relative permeability. On the other hand, the second magnetic portion602can be formed by using thick SUS430 or SPCC showing a lower relative permeability as compared with those of the first magnetic portion601and the third magnetic portion603.

Consequently, the leakage magnetic field of the first coil403which is driven at a high frequency is effectively absorbed by the nano-crystal soft magnetic sheet inherently having the high relative permeability and constructing the facing first magnetic portion601. This is because although the relative permeability of the first magnetic portion601decreases due to the high frequency of the leakage magnetic field, since the inherent relative permeability is high, even if such a relative permeability decreases, it is equal to or larger than a certain effective value. The leakage magnetic field is propagated to the second magnetic portion602arranged behind the imaging element201. Therefore, even if the second magnetic portion602is made of the material of a comparatively low relative permeability, a predetermined effect of bypassing the magnetic field is obtained and thus the arrival amount of the magnetic field to the imaging element201can be reduced.

On the other hand, a frequency of the leakage magnetic field generated from the second coil503which is driven at a lower frequency than that of the first coil403is lower than that of the leakage magnetic field generated from the first coil403. Therefore, the leakage magnetic field generated from the second coil503is sufficiently effectively absorbed even by thick SUS430 or SPCC showing a comparatively low relative permeability and forming the second magnetic portion602. Thus, in a manner similar to the leakage magnetic field from the first coil403, even with respect to the leakage magnetic field of the second coil503, the bypassing effect of the magnetic field is obtained and thus the arrival amount of the magnetic field to the imaging element201can be reduced.

In the above case, as compared with the case where the nano-crystal magnetic sheet showing the high relative permeability is used as a material of all of the first magnetic portion601, second magnetic portion602, and third magnetic portion603, they can be constructed at low costs.

The printed circuit board202on which the imaging element201is mounted can be attached and fixed by a screw or the like to thick SUS430 or SPCC constructing the second magnetic portion602. By fixing the printed circuit board202to SUS430 or SPCC having a high rigidity as mentioned above, a rigidity of the imaging unit200can be also raised. Consequently, a durability of the imaging apparatus100to a shock at the time when it drops is improved and such an associated effect that the reliability of the apparatus is improved as a result is also obtained.

The material of the composite member is not limited to the foregoing combination but various kinds of materials can be properly combined.

According to the present embodiment, even in the case where the imaging element201is sandwiched by the two coils403and503, the arrival amount of the leakage magnetic field generated from each coil which arrives at the imaging element201can be reduced. Therefore, even if the imaging element201executes the reading operation to read out the image signal, an influence of the magnetic field is small and the inherent image signal can be desirably read out, so that the occurrence of a disturbance of the image can be suppressed.

Second Embodiment

An imaging apparatus according to the second embodiment of the present invention will be described. Component elements similar to those in the foregoing first embodiment are designated by the same reference numerals and their description is omitted or simplified.

A fundamental construction of the imaging apparatus according to the present embodiment is substantially similar to that of the imaging apparatus according to the first embodiment. The imaging apparatus according to the present embodiment differs from the imaging apparatus according to the first embodiment with respect to a point that an edge portion of the first magnetic portion601and an edge portion of the second magnetic portion602are bent. The second embodiment will be described hereinafter with reference toFIG. 13with respect to only a point different from the first embodiment.

As illustrated inFIG. 13, in the imaging apparatus according to the present embodiment, a lower edge portion6012(of the first magnetic portion601) to which the third magnetic portion603is not connected is bent toward the first coil403on the side opposite to the imaging element201. A lower edge portion6022(of the second magnetic portion602) to which the third magnetic portion603is not connected is bent toward the second coil503on the side opposite to the imaging element201.

In the present embodiment, the first magnetic portion601is provided at a position closer to the first coil403as a region where an intensity of the leakage magnetic field is larger because the edge portion6012of the first magnetic portion601has been bent. Therefore, the leakage magnetic field generated from the first coil403is more effectively attracted to the first magnetic portion601. Thus, the arrival amount of the magnetic field which arrives at the imaging element201can be further reduced.

Then, the leakage magnetic field which was propagated from the first magnetic portion601to the second magnetic portion602through the third magnetic portion603is propagated from its edge portion to the external space. At this time, since the edge portion6022of the second magnetic portion602has been bent toward the second coil503on the side opposite to the imaging element201, the leakage magnetic field which is emitted from the edge portion6022is propagated to the side opposite to the imaging element201. Thus, an effect of further reducing the arrival amount of the magnetic field which arrives at the imaging element201is also obtained.

A similar effect is also obtained with respect to the leakage magnetic field which is generated from the second coil503. That is, the second magnetic portion602is provided at a position closer to the second coil503as a region where an intensity of the leakage magnetic field is larger because the edge portion6022of the second magnetic portion602has been bent. Therefore, the leakage magnetic field generated from the second coil503is more effectively attracted to the second magnetic portion602. Thus, the arrival amount of the magnetic field which arrives at the imaging element201can be further reduced.

Then, the leakage magnetic field which was propagated from the second magnetic portion602to the first magnetic portion601through the third magnetic portion603is propagated from its edge portion to the external space. At this time, since the edge portion6012of the first magnetic portion601has been bent toward the first coil403on the side opposite to the imaging element201, the leakage magnetic field which is emitted from the edge portion6012is propagated to the side opposite to the imaging element201. Thus, an effect of further reducing the arrival amount of the magnetic field which arrives at the imaging element201is also obtained.

In this manner, in the present embodiment, owing to the simple construction in which the edge portion6012of the first magnetic portion601has been bent toward the first coil403, the effect of reducing the arrival amount of the leakage magnetic field from the first coil403which arrives at the imaging element201is enhanced. Owing to the simple construction in which the edge portion6022of the second magnetic portion602has been bent toward the second coil503, the effect of reducing the arrival amount of the leakage magnetic field from the second coil503which arrives at the imaging element201is enhanced.

According to the present embodiment, even in the case where the imaging element201is sandwiched by the two coils403and503, the arrival amount of the leakage magnetic field generated from each coil which arrives at the imaging element201can be further reduced. Therefore, even if the imaging element201executes the reading operation to read out the image signal, an influence of the magnetic field is further small and the inherent image signal can be further desirably read out, so that the occurrence of a disturbance of the image can be further suppressed.

Although the case where each of the edge portion6012of the first magnetic portion601and the edge portion6022of the second magnetic portion602was bent has been described above, it is not always necessary that both of the edge portions6012and6022have been bent. Any one of the edge portions6012and6022may be bent.

Third Embodiment

An imaging apparatus according to the third embodiment of the present invention will be described. Component elements similar to those in the foregoing first embodiment are designated by the same reference numerals and their description is omitted or simplified.

A fundamental construction of the imaging apparatus according to the present embodiment is substantially similar to that of the imaging apparatus according to the first embodiment. The imaging apparatus according to the present embodiment differs from the imaging apparatus according to the first embodiment with respect to a point that the imaging apparatus according to the present embodiment further includes a non-magnetic metal plate900. The third embodiment will be described hereinafter with reference toFIG. 14with respect to only a point different from the first embodiment.

As illustrated inFIG. 14, in the imaging apparatus according to the present embodiment, the non-magnetic metal plate900is provided between the second magnetic portion602and the imaging element201. The metal plate900is arranged in parallel with the second magnetic portion602.

The metal plate900has an area wider than that of a region where the imaging element201has been projected in the optical axis direction. A thickness of the metal plate900is larger than ⅛ of a skin depth at a driving frequency of the first coil403and is smaller than two times of the skin depth.

The action of the non-magnetic metal plate900will be described. A part of the leakage magnetic field which is generated from the first coil403penetrates the first magnetic portion601. Therefore, a magnetic field704slightly arrives at the imaging element201by the leakage magnetic field from the first coil403. This is because the magnetic field704is attracted to the second magnetic portion602arranged on the rear surface side of the imaging element201. The magnetic field704contains, particularly, a component perpendicular to the light-receiving surface of the imaging element201. The component (of the magnetic field704) perpendicular to the light-receiving surface penetrates the imaging element201and enters the metal plate900arranged on the rear surface side of the imaging element201. An eddy current901flows in the metal plate900in such a direction as to cancel the incident magnetic field704. The eddy current901has such an effect that not only the magnetic field in the metal plate900is cancelled but also its peripheral magnetic field, that is, the magnetic field in the region of the imaging element201is cancelled. As for such an effect that the magnetic field is cancelled as mentioned above, if the thickness of the metal plate900is larger than ⅛ of the skin depth at the driving frequency of the first coil403, that is, at the frequency of the magnetic field, such an effect is sufficiently large, and when it is equal to about two times of the skin depth, the effect is saturated.

By cancelling the magnetic field704by the metal plate900as mentioned above, the arrival amount of the magnetic field which arrives at the imaging element201can be further reduced.

Further, as a component of the leakage magnetic field from the first coil403, there is also a magnetic field component705which is attracted to the first magnetic portion601and is propagated to the second magnetic portion602through the third magnetic portion603. A leakage of the magnetic field component705which is propagated from the surface of the second magnetic portion602toward its outside exists slightly. Even to such a leakage of the magnetic field component705, since the metal plate900is arranged between the second magnetic portion602and the imaging element201, an eddy current902flows similarly in the metal plate900in such a direction as to cancel the magnetic field. Since the eddy current902flows in the metal plate900, an arrival amount of the slight magnetic field component which leaks slightly from the surface of the second magnetic portion602and arrives at the imaging element201can be also reduced.

Although a material of the metal plate900is not particularly limited, a non-magnetic metal material in which a conductivity is high and a relative permeability is almost equal to 1 can be used, that is, a non-magnetic metal material such as non-magnetic stainless steel, copper, copper-based alloy, aluminum, aluminum-based alloy, or the like can be used. Specifically speaking, as a material of the metal plate900, for example, copper whose conductivity is equal to about 5.7×107[S/m], aluminum whose conductivity is equal to about 1.3×107[S/m], or non-magnetic stainless steel whose conductivity is equal to about 1.0×107[S/m] can be mentioned. The skin depth is inversely proportional to a square root of a product of the frequency, conductivity, and relative permeability. Therefore, particularly, if such materials having a high conductivity are used as a material of the metal plate900, even when the metal plate900is thinner than a metal plate made of another material, a similar magnetic field cancelling effect is obtained. Thus, it is advantageous to realize a thin size of the apparatus.

The metal plate900can be arranged by thermally coupling with the imaging element201or the printed circuit board202on which the imaging element201has been mounted. A heat resistance of the metal plate900having a high conductivity is also low. Therefore, if the metal plate900having a high conductivity is thermally coupled with the imaging element201or the printed circuit board202and is arranged, such an additional effect that a heat radiating effect of the imaging element201is enhanced and a disturbance of the image by the heat is suppressed is also obtained. By closely arranging the metal plate900and the imaging element201or the printed circuit board202, they can be thermally coupled. By connecting the metal plate900and the imaging element201or the printed circuit board202by using a heat transfer material, they can be also thermally coupled.

In the case of arranging the metal plate900as mentioned above, in order to assure a cooling effect by the cooling fan500, a plurality of through-holes can be formed in the metal plate900and the second magnetic portion602, respectively.

In this case, as illustrated inFIG. 15, a plurality of through-holes903are formed in the metal plate900. Each through-hole903is formed from a principal plane (of the metal plate900) on the side of the imaging element201to a principal plane on the side of the cooling fan500so as to penetrate the metal plate900. The plurality of through-holes903are arranged, for example, in a square lattice shape or a staggered lattice shape.

A plurality of through-holes6021are formed in the second magnetic portion602. Each through-hole6021is formed from a principal plane (of the second magnetic portion602) on the side of the imaging element201to the principal plane on the side of the cooling fan500so as to penetrate the second magnetic portion602. The plurality of through-holes6021are arranged, for example, in a square lattice shape or a staggered lattice shape.FIG. 16illustrates a case where the plurality of through-holes6021arranged in the square lattice shape are formed in the second magnetic portion602.

As mentioned above, the plurality of through-holes903can be formed in the metal plate900and the plurality of through-holes6021can be formed in the second magnetic portion602. In this case, the air can flow in the through-holes903and6021, and the imaging element201and the printed circuit board202can be effectively cooled by a flow of the air formed by the cooling fan500.

Also in the case of the first or second embodiment in which the metal plate900is not arranged, the plurality of through-holes6021may be formed in the second magnetic portion602.

Although the case where the non-magnetic metal plate900is provided between the second magnetic portion602and the imaging element201has been described above, the non-magnetic metal plate may be provided between the first magnetic portion601and the imaging element201.

In this case, as illustrated inFIG. 17, a non-magnetic metal plate900ais provided between the first magnetic portion601and the imaging element201. The metal plate900ais arranged in parallel with the first magnetic portion601. As a material of the metal plate900a, a material similar to that of the foregoing metal plate900can be used.

An outer shape of the metal plate900ais wider than the area of the imaging element201. A thickness of the metal plate900ais larger than ⅛ of a skin depth at a driving frequency of the second coil503and is smaller than two times of the skin depth.

An opening portion in which a pixel area of the imaging element201is exposed is formed in the metal plate900a, so that light is transmitted into the pixel area of the imaging element201. Even if the metal plate900ahas the opening portion, a predetermined magnetic field cancelling effect is obtained in a manner similar to the metal plate900. In a manner similar to the case where the arrival amount of the leakage magnetic field from the first coil403which arrives at the imaging element201can be further reduced by the foregoing metal plate900, the arrival amount of the leakage magnetic field from the second coil503which arrives at the imaging element201can be further reduced by the foregoing metal plate900a.

It is not always necessary to provide both of the metal plates900and900a. Any one of the metal plates900and900acan be also provided.

According to the present embodiment, even in the case where the imaging element201is sandwiched by the two coils403and503, the arrival amount of the leakage magnetic field generated from each coil which arrives at the imaging element201can be further reduced. Therefore, even if the imaging element201executes the reading operation to read out the image signal, an influence of the magnetic field is small and the inherent image signal can be further desirably read out, so that the occurrence of a disturbance of the image can be suppressed.

Although the case where the metal plates900and900aare provided in the construction similar to that of the imaging apparatus according to the first embodiment has been described above, even in a construction similar to that of the imaging apparatus according to the second embodiment, the metal plates900and900acan be similarly provided.

Fourth Embodiment

An imaging apparatus according to the fourth embodiment of the present invention will be described. Component elements similar to those in the foregoing first embodiment are designated by the same reference numerals and their description is omitted or simplified.

In the foregoing embodiments, the case where the first coil403in the voice coil motor406and the second coil503in the cooling fan500were arranged so as to sandwich the imaging element201has been described. However, it is not always necessary that the two coils403and503are arranged for the imaging element201. Only one coil may be arranged. In the present embodiment, a case where the cooling fan500is not provided and the second coil503is not arranged for the imaging element201will be described with reference toFIG. 18.

As illustrated inFIG. 18, unlike the imaging apparatus100according to the first embodiment, in an imaging apparatus100aaccording to the present embodiment, the cooling fan500is not provided behind the imaging unit200. For example, in the case where the heat generation of the heat generating portion such as an imaging element201or the like in the casing101is small and it is not always necessary to forcedly cool the heat generating portion, such a construction that the cooling fan500is not provided as mentioned above can be realized. If the imaging apparatus100ais constructed as a digital still camera instead of a digital video camera, since an imaging time is very short, such a construction that the cooling fan500is not provided can be realized. A construction of the imaging apparatus100ais similar to that of the imaging apparatus100according to the first embodiment except for a point that the cooling fan500is not provided.

Also in the imaging apparatus100aaccording to the present embodiment, the sheet-like or plate-like magnetic member600is arranged in a manner similar to the imaging apparatus100according to the first embodiment. Therefore, also in the imaging apparatus100aaccording to the present embodiment, the arrival amount of the leakage magnetic field generated from the first coil403which arrives at the imaging element201can be reduced by the sheet-like or plate-like magnetic member600as mentioned above.

Modified Embodiments

The present invention is not limited to the foregoing embodiments but many various modifications are possible and the present invention can be also applied to other constructions within a scope without departing from an essence of the present invention.

For example, although the embodiments have been described above with respect to the case where the imaging apparatus is the digital video camera, the imaging apparatus is not limited it. Besides the digital video camera, the imaging apparatus may be a digital still camera or may have both functions of the digital video camera and the digital still camera.

Although the embodiments have been described above with respect to the case where the coils403and503were respectively arranged on the front side and the rear side of the imaging element201, the layout of the coils to the imaging element201is not limited to it. For example, also in a case where the coils403and503are respectively arranged on the upper side and the lower side of the imaging element201so as to sandwich the imaging element201, the sheet-like or plate-like magnetic member600can be arranged in a manner similar to the foregoing embodiments.

Although the embodiments have been described above with respect to the case where the first magnetic portion601faces the magnetic yoke405and the second magnetic portion602faces the magnetic core505, the present invention is not limited to such a case. It is sufficient that the first magnetic portion601faces the magnetic yoke405or the second magnetic portion602faces the magnetic core505.

Although the embodiments have been described above with respect to the case where the coil in the voice coil motor406and the coil in the DC brushless motor which is used in the cooling fan500are used as a first coil403and a second coil503which are arranged so as to sandwich the imaging element201. However, the first and second coils which are arranged so as to sandwich the imaging element201are not limited to those coils. For example, the first and second coils may be an inductor of an output filter unit of a switching power supply circuit, a coil in a DC brushless motor to drive a shutter, and the like, which are arranged near the imaging element.

This application claims the benefit of Japanese Patent Application No. 2015-131246, filed Jun. 30, 2015, which is hereby incorporated by reference herein in its entirety.