Variable capacitance device, antenna module, and communication apparatus

A variable capacitance device includes a fixing member, a fixed electrode having a first end side fixed by the fixing member, an actuator element having a first end side fixed by the fixing member directly or indirectly, a movable electrode provided to connect to the actuator element directly or indirectly and disposed to approximately face the fixed electrode, and a driving section deforming a second end side of the actuator element, to change a distance between the fixed electrode and the movable electrode.

CROSS REFERENCES TO RELATED APPLICATIONS

The present application claims priority to Japanese Priority Patent Application JP 2010-232754 filed in the Japan Patent Office on Oct. 15, 2010, the entire content of which is hereby incorporated by reference.

BACKGROUND

The present application relates to a variable capacitance device configured by using a predetermined actuator element, and also relates to an antenna module and a communication apparatus provided with such a variable capacitance device.

Recently, elements having various kinds of structure have been developed as a variable capacitance element in which a capacitance value may be changed (a capacitance value is variable). Such variable capacitance elements include, for example, air variable capacitors, poly variable capacitors, ceramic trimmer capacitors, varicaps, and the like (for example, see Japanese Unexamined Patent Application Publications No. 05-74655 and No. 2003-218217).

SUMMARY

However, in such a currently-available variable capacitance element (variable capacitance device), the extent of a capacitance change range is insufficient (as having, for example, approximately 5 to 15 times variable magnifications). Therefore, in recent years, a proposal of a variable capacitance element (variable capacitance device) that may realize a capacitance change range larger than before (larger variable magnification) has been desired.

In view of the foregoing, it is desirable to provide a variable capacitance device that may achieve a capacitance change range wider than before, and an antenna module as well as a communication apparatus having such a variable capacitance device.

According to an embodiment, there is provided a variable capacitance device including a fixing member, a fixed electrode having a first end side fixed by the fixing member, and an actuator element having a first end side fixed by the fixing member directly or indirectly, and a movable electrode provided to connect to the actuator element directly or indirectly, and disposed to approximately face the fixed electrode. The variable capacitance device further includes a driving section deforming a second end side of the actuator element, to change a distance between the fixed electrode and the movable electrode.

According to an embodiment, there is provided an antenna module including an antenna element, and the above-described variable capacitance in the embodiment.

According to an embodiment, there is provided a communication apparatus including the above-described antenna module in the embodiment.

In the variable capacitance device, the antenna module, and the communication apparatus according to the embodiments, a capacitive element is formed based on the fixed electrode and the movable electrode disposed to approximately face each other, and a space region (a gap) therebetween. When the second end side of the actuator element deforms to change the distance between the fixed electrode and the movable electrode, thereby causing the (electrostatic) capacitance value of this capacitive element to change, the capacitive element functions as a variable capacitance element. Here, the deformation volume of such an actuator element is a relatively large and thus, the amount of a change in the distance between the fixed electrode and the movable electrode also becomes large.

According to the variable capacitance device, the antenna module, and the communication apparatus in the embodiments, the second end side of the actuator element is caused to deform so that the distance between the fixed electrode and the movable electrode changes and thus, it is possible to increase the amount of a change in the distance between the fixed electrode and the movable electrode. Therefore, it is possible to greatly change the capacitance value of the capacitive element formed using these fixed electrode and movable electrode, and a capacitance change range wider than before (a variable magnification larger than before) may be realized.

DETAILED DESCRIPTION

Embodiments of the present application will be described below in detail with reference to the drawings.

1. Embodiment (an example in which one variable capacitance element is formed between a fixed electrode and a movable electrode in a set)

Modification 1 (an example in which two variable capacitance elements are each formed between a fixed electrode and a movable electrode in each of two sets)

Modification 2 (an example in which a capacitance value of a monitoring variable capacitance element is detected, and a deformation volume of an actuator element is controlled)

Modification 3 (an example 1 in which a displacement magnitude of a movable electrode is detected, and thereby a deformation volume of an actuator element is controlled: an example of detection using a magnet and a Hall element)

Modification 4 (an example 2 in which a displacement magnitude of a movable electrode is detected, and thereby a deformation volume of an actuator element is controlled: an example of detection using a reflection member and a photo-reflector)

Modification 5 (an example in which a piezoelectric element is used as an actuator element)

Modification 6 (an example in which a bimetallic element is used as an actuator element)

3. Application Example (an example in which a variable capacitance device is applied to an antenna module and a communication apparatus)

Embodiment

Overall Configuration of Variable Capacitance Device1

FIG. 1schematically illustrates an overall configuration (a schematic configuration) of a variable capacitance device (a variable capacitance device1) according to an embodiment, in a side view (a Z-X side view). This variable capacitance device1includes a support member11, a fixing member12, polymer actuator elements131and132, link members141and142, a connection member15, a fixed electrode16, a movable electrode17, and a driving section18.

Here, the support member11is a base member (a substrate) to support the entire variable capacitance device1and here, the support member11is disposed to extend on an XY plane. This support member11is made of, for example, a hard resin material such as a liquid crystal polymer.

The fixing member12is a member to fix one end side of each of the polymer actuator elements131and132and one end side of the fixed electrode16, and is made of, for example, a hard resin material such as a liquid crystal polymer. Although details will be described later (FIG. 4), this fixing member12includes three members that are a lower fixing member12D, a middle (central) fixing member12C, and an upper fixing member12U disposed along a forward direction of a Z axis.

Each of the polymer actuator elements131and132has the one end side directly fixed by the fixing member12, and is an actuator element to drive (deform) the movable electrode17along the Z axis via the link members141and142and the connection member15to be described later. These polymer actuator elements131and132each have a driving surface (a driving surface on the X-Y plane) orthogonal to a displacement direction (shifting direction) of the movable electrode17to be described later, and are disposed so that the respective driving surfaces face each other along the Z axis. The polymer actuator elements131and132correspond to a specific example of “the actuator element” according to the embodiment. It is to be noted that a configuration of each of the polymer actuator elements131and132will be described later in detail (FIG. 3).

The link members141and142are members to link (connect) the other ends of the polymer actuator elements131and132, respectively, with corresponding end parts of the connection member15to be described later. Specifically, the link member141links a lower end part of the connection member15with the other end of the polymer actuator element131, and the link member142links an upper end part of the connection member15with the other end of the polymer actuator element132. It is desirable that each of these connection members141and142be, for example, a flexible film such as a polyimide film or the like, and be made of a flexible material having rigidity comparable to or less than (preferably, equal to or lower than) that of each of the polymer actuator elements131and132. This provides the link members141and142with flexibility in curving in the direction opposite to a curving direction of the polymer actuator elements131and132, and thereby a cross-section at a cantilever including the polymer actuator elements131and132and the link members141and142takes the shape of a letter S. As a result, the connection member15is allowed to move in parallel with a Z-axis direction, and the movable electrode17is driven in the Z-axis direction while keeping a state of being parallel with the fixed electrode16.

The connection member15is a member to make connection between the other end side of each of the polymer actuator elements131and132and one end side of the movable electrode17to be described later (specifically, between the other end of each of the link members141and142and the one end of the movable electrode17). Here, this connection member15is disposed to extend in the Z-axis direction, and is made of, for example, a hard resin material such as a liquid crystal polymer.

The fixed electrode16is an electrode whose one end side is fixed by the fixing member12, and is flat-shaped to extend on the XY plane here. This fixed electrode16is disposed between the polymer actuator elements131and132in a pair.

The movable electrode17is an electrode whose one end side is fixed by the connection member15, and is disposed on the other end sides of the polymer actuator elements131and132, via the link members141and142and the connection member15described above. In other words, the movable electrode17is provided to indirectly connect to the polymer actuator elements131and132. Here, this movable electrode17is also flat-shaped to extend on the XY plane, and disposed between the polymer actuator elements131and132in the pair (specifically, between the polymer actuator element131and the fixed electrode16). That is to say, the movable electrode17is disposed to approximately face (preferably, opposite) the fixed electrode16along the Z-axis direction. Although details will be described later, this movable electrode17is allowed to shift in the Z-axis direction, according to a displacement (a displacement in the Z-axis direction) of the connection member15based on deformation of the polymer actuator elements131and132.

FIG. 2is a cross-sectional diagram (a Z-X cross-sectional diagram) illustrating an example of a detailed configuration of the fixed electrode16and the movable electrode17.

The fixed electrode16has a layered structure including a conductor layer161, and a pair of dielectric layers162A and162B provided on both sides of the conductor layer161. On the other hand, the movable electrode17has a single-layer structure including a conductor layer171. Each of the conductor layers161and171is made of, for example, a metallic material such as copper (Cu) or aluminum (Al). In addition, each of the dielectric layers162A and162B is made of, for example, a high dielectric material such as barium titanate, tantalum oxide, vinylidene fluoride, or phenolic resin. Based on such a cross-sectional configuration, the pair of conductor layers161and171, a space region (gap) (air space in this case) between the conductor layers161and171in the pair, and the dielectric layer162A (the dielectric layer on the movable electrode17side) form a capacitive element (a variable capacitance element) C1made of a capacitance. Here, when the distance between the fixed electrode16and the movable electrode17is assumed to be d1, the thickness of the dielectric layer162A is assumed to be d2, the area of a region where the fixed electrode16and the movable electrode17face each other (i.e., an area on the XY plane) is assumed to be S, the dielectric constant of the air space mentioned above is assumed to be ε1 (=1), and the dielectric constant of the dielectric layer162A is assumed to be ε2, a (electrostatic) capacitance value C of the capacitive element C1is expressed by the following expression (1). It is to be noted that the thickness d2is, for example, around 0.3 mm, and the dielectric constant ε2 is, for example, around 6 in a case where the vinylidene fluoride mentioned above is used.
C=(ε1×ε2×S)/(ε2×d1+ε1×d2)  (1)

The driving section18is provided to drive (deform) each of the polymer actuator elements131and132, and is, for example, configured by using an electric circuit employing a semiconductor element or the like. This driving section18has, specifically, a voltage supply section181to be described later, and supplies a driving voltage Vd to each of the polymer actuator elements131and132by using the voltage supply section181. It is to be noted that driving operation of the polymer actuator elements131and132by this driving section18will be described later in detail.

Detailed Configuration of Polymer Actuator Elements131and132

Next, with reference toFIG. 3andFIG. 4, a detailed configuration of each of the polymer actuator elements131and132will be described.FIG. 3illustrates a cross-sectional configuration (a Z-X cross-sectional configuration) of each of the polymer actuator elements131and132. Further,FIG. 4is a cross-sectional diagram (a Z-X cross-sectional diagram) illustrating a detailed configuration of a part of the polymer actuator elements131and132, the fixing member12, and fixed electrodes121A,121B,122A, and122B to be described later.

As illustrated inFIG. 3, each of the polymer actuator elements131and132has a cross-sectional structure in which a pair of electrode films52A and52B are formed on both sides of an ionic conductive polymer compound film51(hereinafter merely referred to as a polymer compound film51). In other words, each of the polymer actuator elements131and132has the pair of electrode films52A and52B, and the polymer compound film51inserted between these electrode films52A and52B. It is to be noted that a portion around the polymer actuator elements131and132and the electrode films52A and52B may be covered with an insulating protective film made of a material having high elasticity (for example, polyurethane or the like).

Further, for example, as illustrated inFIG. 4, the polymer actuator elements131and132are connected to the upper fixing member12U, the middle fixing member12C, the lower fixing member12D of the fixing member12, and the fixed electrodes121A,121B,122A, and122B. Specifically, in the polymer actuator element131, the electrode film52A is electrically connected to the fixed electrode121A on the lower fixing member12D side, and the electrode film52B is electrically connected to the fixed electrode121B on the middle fixing member12C side. On the other hand, in the polymer actuator element132, the electrode film52A is electrically connected to the fixed electrode122A on the middle fixing member12C side, and the electrode film52B is electrically connected to the fixed electrode122B on the upper fixing member12U side. As a result, the driving voltage Vd supplied from the driving section18(the voltage supply section181) described above is supplied to the polymer actuator element131via the fixed electrodes121A and121B, and also supplied to the polymer actuator element132via the fixed electrodes122A and122B.

It is desirable that each member and each electrode from the fixed electrode121A on the lower fixing member12D side to the fixed electrode122B on the upper fixing member12U side be fixed by being pressed with a constant pressure by a not-illustrated pressing member (a flat spring). This prevents the polymer actuator elements131and132from being destroyed even when a large force is exerted thereon, and allows stable electric connection even when the polymer actuator elements131and132are deformed.

The polymer compound film51described above is configured to be curved by a predetermined potential difference occurring between the electrode films52A and52B. This polymer compound film51is impregnated with an ionic substance. The “ionic substance” here refers to ions in general, which may be conveyed in the polymer compound film51, and specifically means a substance containing a simple substance of hydrogen ions or metal ions, or any of these cations and/or anions and a polar solvent, or a substance containing cations and/or anions which themselves are liquid such as imidazolium salt. For example, as the former, there is a substance in which a polar solvent is solvated in cations and/or anions, and as the latter, there is an ionic liquid.

As a material of the polymer compound film51, there is, for example, an ion exchange resin in which a fluorocarbon resin or a hydrocarbon system is a skeleton. As the ion exchange resin, it is preferable to use a cation exchange resin when a cationic substance is impregnated, and use an anion exchange resin when an anionic substance is impregnated.

As the cation exchange resin, there is, for example, a resin into which an acidic group such as a sulfonate group or a carboxyl group is introduced. Specifically, the cation exchange resin is a polyethylene having an acidic group, a polystyrene having an acidic group, a fluorocarbon resin having an acid group, or the like. Above all, a fluorocarbon resin having a sulfonate group or a carboxylic acid group is preferable as the cation exchange resin, and there is, for example, Nafion (made by E.I. du Pont de Nemours and Company).

The cationic substance impregnated in the polymer compound film51may be organic or inorganic, or may be of any kind. For example, various kinds of mode such as a simple substance of metal ions, a substance containing metal ions and water, a substance containing organic cations and water, or an ionic liquid are applicable. As the metal ion, there is, for example, light metal ion such as sodium ion (Na+), potassium ion (K+), lithium ion (Li+), or magnesium ion (Mg2+). Further, as the organic cation, there is, for example, alkylammonium ion. These cations exist as a hydrate in the polymer compound film51. Therefore, in a case where the polymer compound film51is impregnated with the cationic substance containing cations and water, it is desirable to seal the whole in order to suppress volatilization of water, in the polymer actuator elements131and132.

The ionic liquid is also called ambient temperature molten salt, and includes cations and anions having low combustion and volatility. As the ionic liquid, there is, for example, an imidazolium ring system compound, a pyridinium ring system compound, an aliphatic compound, or the like.

Above all, it is preferable that the cationic substance be the ionic liquid. This is because the volatility is low, and the polymer actuator elements131and132work well even in a high-temperature atmosphere or in a vacuum.

Each of the electrode films52A and52B facing each other across the polymer compound film51interposed therebetween includes one or more than one kind of conductive material. It is preferable that each of the electrode films52A and52B be a film in which particles of a conductive material powder are bound by an ionic conductive polymer. This is because flexibility of the electrode films52A and52B increases. A carbon powder is preferable as the conductive material powder. This is because the conductivity is high, and the specific surface area is large and thus, a larger deformation volume is achieved. As the carbon powder, Ketjen black is preferable. As the ionic conductive polymer, the same material as that of the polymer compound film51is desirable.

The electrode films52A and52B are formed as follows, for example. A coating in which a conductive material powder and a conductive polymer are dispersed in a dispersion medium is applied to both sides of the polymer compound film51, and then dried. Alternatively, a film-shaped substance including a conductive material powder and an ionic conductive polymer may be affixed to both sides of the polymer compound film51by pressure bonding.

The electrode films52A and52B may each have a multilayer structure, and in that case, it is desirable that each of the electrode films52A and52B have such a structure that a layer in which particles of a conductive material powder are bound by an ionic conductive polymer and a metal layer are laminated sequentially from the polymer compound film51side. This is because an electric potential becomes closer to a further uniform value in an in-plane direction of the electrode films52A and52B, and superior deformability is obtained. As a material of the metal layer, there is a noble metal such as gold or platinum. The thickness of the metal layer is arbitrary, but the metal layer is preferably a continuous film so that the electric potential becomes uniform in the electrode films52A and52B. As a method of forming the metal layer, there is plating, deposition, sputtering, or the like.

The size (width and length) of the polymer compound film51may be, for example, freely set according to the size or and weight of the movable electrode17, or a desirable displacement magnitude (deformation volume) of the polymer compound film51. The displacement magnitude of the polymer compound film51is set according to a desired displacement magnitude (the amount of a movement along the Z-axis direction) of the movable electrode17.

Operation and Effect of Variable Capacitance Device1

Next, the operation and effect of the variable capacitance device1of the present embodiment will be described.

1. Operation of Polymer Actuator Elements131and132

First, the operation of the polymer actuator elements131and132will be described with reference toFIGS. 5A and 5B.FIGS. 5A and 5Beach schematically illustrate the operation of the polymer actuator elements131and132, using a cross-sectional diagram.

At first, a case where a substance including cations and a polar solvent is used as the cationic substance will be described.

In this case, the cationic substance disperses approximately uniformly in the polymer compound film51and thus, the polymer actuator elements131and132in a state of no voltage application become flat without curving (FIG. 5A). Here, when a voltage applied state is established using the voltage supply section181in the driving section18illustrated inFIG. 5B(when application of the driving voltage Vd begins), the polymer actuator elements131and132each exhibit the following behavior. When, for example, the predetermined voltage Vd is applied between the electrode films52A and52B so that the electrode film52A is at a negative potential whereas the electrode film52B is at a positive potential, the cations in a state of being solvated in the polar solvent move to the electrode film52A side. At this moment, the anions hardly move in the polymer compound film51and thus, in the polymer compound film51, the electrode film52A side swells, while the electrode film52B side shrinks As a result, the polymer actuator elements131and132curve toward the electrode film52B side as a whole, as illustrated inFIG. 5B. Subsequently, when the state of no voltage application is established by eliminating the potential difference between the electrode films52A and52B (when the application of the driving voltage Vd is stopped), the cationic substance (the cations and the polar solvent) localized to the electrode film52A side in the polymer compound film51disperse, and return to the state illustrated inFIG. 5A. Further, when the predetermined driving voltage Vd is applied between the electrode films52A and52B so that the electrode film52A shifts to a positive potential and the electrode film52B shifts to a negative potential, from the state of no voltage application illustrated inFIG. 5A, the cations in the state of being solvated in the polar solvent move to the electrode film52B side. In this case, in the polymer compound film51, the electrode film52A side shrinks while the electrode film52B side swells and thus, as a whole, the polymer actuator elements131and132curve toward the electrode film52A side.

Next, a case where an ionic liquid containing liquid cations is used as the cationic substance will be described.

In this case, similarly, in the state of no voltage application, the ionic liquid is dispersed in the polymer compound film51approximately uniformly and thus, the polymer actuator elements131and132become flat as illustrated inFIG. 5A. Here, when a voltage applied state is established by the voltage supply section181(application of the driving voltage Vd begins), the polymer actuator elements131and132exhibit the following behavior. When, for example, the predetermined driving voltage Vd is applied between the electrode films52A and52B so that the electrode film52A is at a negative potential, whereas the electrode film52B is at a positive potential, the cations of the ionic liquid move to the electrode film52A side, and the anions hardly move in the polymer compound film51which is a cation-exchanger membrane. For this reason, in the polymer compound film51, the electrode film52A side swells, while the electrode film52B side shrinks As a result, the polymer actuator elements131and132as a whole curve toward the electrode film52B side, as illustrated inFIG. 5B. Subsequently, when the state of no voltage application is established by eliminating the potential difference between the electrode films52A and52B (when the application of the driving voltage Vd is stopped), the cations localized to the electrode film52A side in the polymer compound film51disperse, and return to the state illustrated inFIG. 5A. Further, when the predetermined driving voltage Vd is applied between the electrode films52A and52B so that the electrode film52A shifts to a positive potential and the electrode film52B shifts to a negative potential from the state of no voltage application illustrated inFIG. 5A, the cations of the ionic liquid move to the electrode film52B side. In this case, in the polymer compound film51, the electrode film52A side shrinks, whereas the electrode film52B side swells and thus, as a whole, the polymer actuator elements131and132curve toward the electrode film52A side.

2. Operation of Variable Capacitance Device1

Subsequently, the operation of the entire variable capacitance device1will be described with reference toFIGS. 6A and 6B.FIGS. 6A and 6Beach illustrate the operation of the variable capacitance device1, in a cross-sectional diagram (a Z-X cross-sectional diagram).FIG. 6Aillustrates a state before the operation, andFIG. 6Billustrates a state after the operation.

In this variable capacitance device1, the movable electrode17is driven via the connection member15and the like, according to deformation (a curve) of the pair of polymer actuator elements131and132described above. This makes the movable electrode17become movable (displaceable) along the Z axis as illustrated inFIGS. 6A and 6B.

Then, accompanying such displacement of the movable electrode17in the Z-axis direction, the distance d1between the fixed electrode16and the movable electrode17changes (here, the distance d1decreases with the displacement of the movable electrode17). In other words, in the driving section18of the present embodiment, the other end sides of the polymer actuator elements131and132are deformed (curved) so that the distance d1between the fixed electrode16and the movable electrode17changes. Therefore, based on the expression (1) described above, the (electrostatic) capacitance value C of the capacitive element C1also changes (here, the capacitance value C increases) in response to the change of this distance d1and therefore, this capacitive element C1functions as a variable capacitance element.

Here, in the present embodiment, the deformation volume of the actuator element (the polymer actuator elements131and132) is relatively large (for example, around 1 to 2 mm). For this reason, the amount of a change in the distance d1between the fixed electrode16and the movable electrode17is also large (for example, around 0 to 2 mm). As a result, in the variable capacitance device1of the present embodiment, the capacitance change range in the capacitive element C1is wider than the capacitance change range in an existing variable capacitance element (for example, an air variable capacitor, a poly variable capacitor, a ceramic trimmer capacitor, a varicap, or the like). In other words, in the variable capacitance device1, the variable magnification in the capacitive element C1is greater than the variable magnification in the existing variable capacitance element. Specifically, the capacitance change range in the existing variable capacitance element includes approximately 5 to 15 times variable magnifications, whereas the capacitance change range in the variable capacitance device1includes, for example, approximately 20 to 50 times variable magnifications.

FIG. 7illustrates an example of the relationship between the distance d1from the fixed electrode16to the movable electrode17and the capacitance value C in the variable capacitance device1. Specifically, in this example, the thickness d2of the dielectric layer162A is 0.3 mm, the area S of the region where the fixed electrode16and the movable electrode17face each other is 24 mm2, the dielectric constant ε1 is 1 (air space), and the dielectric constant ε2 of the dielectric layer162A is 6, in the expression (1) described above. FromFIG. 7, it is found that in this example, the distance d1and the capacitance value C are approximately inversely proportional to each other, and a wide capacitance change range including an approximately 40 times variable magnification is realized.

As described above, in the present embodiment, the other end sides of the polymer actuator elements131and132are deformed by the driving section18so that the distance d1between the fixed electrode16and the movable electrode17changes and thus, it is possible to increase the amount of a change in the distance d1between the fixed electrode16and the movable electrode17. Therefore, the capacitance value of the capacitive element C1formed using these fixed electrode16and movable electrode17may also be increased to a great extent and thus, it is possible to realize a capacitance change range wider than before (i.e., a variable magnification larger than before). In addition, such a wide capacitance change range (a large variable magnification) may be realized with a relatively small and simple structure.

Further, in the present embodiment in particular, the polymer actuator elements131and132are used as actuator elements and thus, compared with a case in which an actuator element in other method (such as a piezoelectric element or a bimetallic element to be described later) is used, the following advantage may be obtained. That is, it is possible to achieve lower power consumption while suppressing the driving voltage Vd to a low level, and production may be realized at low cost.

Furthermore, the fixed electrode16has the layered structure including the conductor layer161and the dielectric layer162A provided on the movable electrode17side of this conductor layer161and thus, the following advantage may be obtained. That is, thanks to the presence of this dielectric layer162A, it is possible to increase the capacitance value of the capacitive element Cl, and prevent an electrical short circuit (short) between the conductor layers161and171at the time of displacement of the movable electrode17. It is to be noted that such a dielectric layer162A (and the dielectric layer162B) may not be provided in the fixed electrode16in some cases.

In addition, the movable electrode17is configured to be driven via the link members141and142and thus, it is possible to make the movable electrode17move easily along the Z axis even when, for example, an operational variation (a variation in the deformation volume) occurs between the pair of polymer actuator elements131and132.

Modifications

Subsequently, modifications (modifications 1 to 6) of the embodiment will be described. It is to be noted that the same elements as those of the embodiment will be provided with the same reference characters as those of the embodiment, and the description will be omitted as appropriate.

FIGS. 8A and 8Beach schematically illustrate an overall configuration (schematic configuration) and operation of a variable capacitance device (a variable capacitance device1A) according to the modification 1, in a side view (a Z-X side view).FIG. 8Aillustrates a state before the operation, andFIG. 8Billustrates a state after the operation.

The variable capacitance device1A of the present modification is formed such that a plurality of variable capacitance elements are each formed between a fixed electrode and a movable electrode in each of plurality of sets. Specifically, the variable capacitance device1A is different from the variable capacitance device1of the embodiment described above in that two sets of fixed electrodes16A and16B and two sets of movable electrodes17A and17B are provided in place of the fixed electrode16and the movable electrode17. Otherwise, the variable capacitance device1A is configured in a manner similar to the variable capacitance device1.

Each of the fixed electrodes16A and16B is an electrode whose one end side fixed by a fixing member12, and is flat-shaped to extend on an XY plane here. These fixed electrodes16A and16B are disposed to face each other (to be approximately parallel with each other) between the pair of polymer actuator elements131and132.

Each of the movable electrodes17A and17B is an electrode whose one end side is fixed by a connection member15. The movable electrodes17A and17B are disposed on the other end sides of the polymer actuator elements131and132via ink members141and142and the connection member15, like the movable electrode17. These movable electrodes17A and17B are also flat-shaped to extend on the XY plane, and are disposed between the pair of polymer actuator elements131and132. Specifically, the movable electrode17A is disposed between the polymer actuator element131and the fixed electrode16A, and the movable electrode17B is disposed between the fixed electrodes16A and16B. In other words, the movable electrode17A is disposed to approximately face (opposite) the fixed electrode16A along a Z-axis direction, whereas the movable electrode17B is disposed to approximately face (opposite) the fixed electrode16B along the Z-axis direction. Like the movable electrode17, each of these movable electrodes17A and17B is also allowed to shift in the Z-axis direction, according to a displacement (a displacement in the Z-axis direction) of the connection member15based on deformation of the polymer actuator elements131and132, as will be described below.

Based on such a configuration, in the variable capacitance device1A, a capacitive element C1A is formed based on the fixed electrode16A and the movable electrode17A disposed to approximately face each other and a space region (a gap) therebetween (and a dielectric layer162A in the fixed electrode16A). In addition, a capacitive element C1B is formed based on the fixed electrode16B and the movable electrode17B disposed to approximately face (opposite) each other and a space region (a gap) therebetween (and a dielectric layer162A in the fixed electrode16B). In other words, in the variable capacitance device1A, two capacitive elements C1A and C1B are formed using two sets of the fixed electrodes16A and16B and the movable electrodes17A and17B.

Here, these capacitive elements C1A and C1B may be connected to each other in parallel as illustrated in, for example,FIG. 9A, or in series as illustrated in, for example,FIG. 9B. It is to be noted that in the case of parallel connection, the capacitance value of the variable capacitance device1A as a whole may be increased (here, to a twofold capacitance value).

In the variable capacitance device1A of the present modification, as illustrated inFIGS. 8A and 8B, each of the movable electrodes17A and17B is driven via the connection member15and the like, according to the deformation (curve) of the pair of polymer actuator elements131and132. This makes each of the movable electrodes17A and17B become movable (displaceable) along the Z axis. Then, accompanying such displacement of the movable electrodes17A and17B in the Z-axis direction, each of a distance d1A between the fixed electrode16A and the movable electrode17A and a distance d1B between the fixed electrode16B and the movable electrode17B changes (here, the distances d1A and d1B decrease with the displacement of the movable electrodes17A and17B). Therefore, like the embodiment described above, according to the change of each of these distances d1A and d1B, the (electrostatic) capacitance value of each of the capacitive elements C1A and C1B also changes (here, the capacitance value increases) and thus, these capacitive elements C1A and C1B each function as a variable capacitance element.

Here, in the present modification, it is also possible to increase the amount of a change in each of the distances d1A and d1B, and increase the capacitance value of each of the capacitive elements C1A and C1B to a large extent, by the operation similar to that in the embodiment described above. Therefore, in the present modification, a capacitance change range wider than before (a variable magnification larger than before) may be realized as well.

It is to be noted that for the present modification, there has been described the case where the two variable capacitance elements are formed using the two sets of the fixed electrode and the movable electrode. However, for example, three or more variable capacitance elements may be formed using three or more sets of the fixed electrode and the movable electrode, and may be combined and used. Specifically, the variable capacitance elements thus formed may be connected to each another in parallel, in series, or in a combination thereof (through parallel connection, serial connection, or connection in a combination thereof).

FIG. 10schematically illustrates an overall configuration (schematic configuration) of a variable capacitance device (a variable capacitance device1B) according to the modification 2, in a side view (a Z-X side view). In the variable capacitance device1B of the present modification, a capacitance value of a monitoring variable capacitance element (a capacitive element C2to be described later) to be described below is detected, and a deformation volume (a displacement magnitude, an amount of curve) of each of polymer actuator elements131and132is controlled using the detected capacitance value.

Specifically, the variable capacitance device1B is different from the variable capacitance device1of the above-described embodiment in that a fixed electrode16-1is provided in place of the fixed electrode16, and a driving section18B is provided in place of the driving section18. Otherwise, the variable capacitance device1B is configured in a manner similar to the variable capacitance device1.

The fixed electrode16-1includes an insulating member163, and a plurality of (here, two) sub-electrodes16C and16D electrically separated from each other on a surface facing the movable electrode17in the insulating member163. In other words, the fixed electrode16-1is configured using these two sub-electrode16C and16D. The insulating member163also functions as a member to support (fix) each of the sub-electrodes16C and16D, and is made of, for example, an insulating material such as vinylidene fluoride.

Based on such a configuration, in the variable capacitance device1B of the present modification, a capacitive element (a variable capacitance element) C1is formed by using the sub-electrode16C and the movable electrode17disposed to approximately face (opposite) each other, and a space region (a gap) therebetween (and a dielectric layer162A in the sub-electrode16C). In addition, a monitoring capacitive element (a variable capacitance element) C2is formed by using the sub-electrode16D and the movable electrode17disposed to approximately face (opposite) each other, and a space region (a gap) therebetween (and a dielectric layer162A in the sub-electrode16D). It is to be noted that in these capacitive elements C1and C2, the distance between the movable electrode17and the sub-electrode16C or the sub-electrode16D is d1in both cases.

The driving section18B has, as illustrated inFIG. 11, a capacitance-value detecting section182, a storage section183, and a subtraction section184, in addition to a voltage supply section181similar to that described above.

The capacitance-value detecting section182detects the capacitance value of the monitoring capacitive element C2described above. This capacitance-value detecting section182includes, as illustrated inFIG. 12, for example, an oscillating circuit182B producing an alternating current signal at a frequency of frequency f=f0, three inductors L1, L2, and L3electromagnetically coupled to each other, a diode (a rectifying device) D3, a resistor R3, and a capacitive element (a capacitor) C3. The inductor L1is connected between both ends of the oscillating circuit182B, and the inductor L2is connected between both ends of the monitoring capacitive element C2. Of the inductor L3, one end is connected to an anode of the diode D3, and the other end is connected to one end of the resistor R3and one end of the capacitive element C3. A cathode of the diode D3is connected to the other end of the resistor R3and the other end of the capacitive element C3. Based on such a connection configuration, a resonance circuit (an LC resonance circuit) is configured by using the inductor L2and the monitoring capacitive element C2, and a detector circuit is configured by using the inductor L3, the diode D3, the resistor R3, and the capacitive element C3.

In this capacitance-value detecting section182, specifically, the capacitance value of the monitoring capacitive element C2is detected in the following manner. First, in the LC resonance circuit described above, for example, resonant operation (LC resonant operation) having a resonance characteristic as illustrated inFIG. 13is performed. At this time, when the inductance of the inductor L2is assumed to be L, and the capacitance value of the capacitive element C2is assumed to be C2, a resonant frequency f2in this resonant operation is expressed by the following expression (2). Here, when the capacitance value in the capacitive element C2changes, the resonant frequency f2changes (shifts) therewith based on the expression (2) and therefore, a detection output (an output voltage Vout) at a frequency f0in the oscillating circuit182B changes as well. For example, as illustrated inFIG. 13, when the resonant frequency changes from f2to (f2+Δf) by accompanying the change in the capacitance value of the capacitive element C2, the value of the output voltage Vout at the frequency f0also changes (here, decreases only by −ΔV). Here, the capacitance value in the capacitive element C2and the output voltage Vout correspond to each other in a one-to-one relationship and thus, it is possible to also detect (measure) the capacitance value of the capacitive element C2by detecting this output voltage Vout. It is to be noted that the capacitance value of the capacitive element C2thus detected by the capacitance-value detecting section182is assumed to be a capacitance value C2d.
f2=1/{2π×(L×C2)1/2}  (2)

The storage section183illustrated inFIG. 11is a memory to store (hold) beforehand a capacitance value C2tthat is “a predetermined target value” in the capacitive element C2, and may be configured using any of various types of memory. The subtraction section184performs subtraction processing between the capacitance value C2theld in the storage section183and the capacitance value C2ddetected by the capacitance-value detecting section182(specifically, performs processing of subtracting the capacitance value C2dfrom the capacitance value C2t). As a result, a capacitance value (C2t−C2d) obtained by the subtraction is outputted to the voltage supply section181.

In the voltage supply section181of the present modification, the deformation volumes of the polymer actuator elements131and132are controlled using the capacitance value C2dof the monitoring capacitive element C2detected by the capacitance-value detecting section182. Specifically, using the capacitance value (C2t−C2d) supplied from the subtraction section184, the deformation volumes of the polymer actuator elements131and132are controlled so that this capacitance value C2dof the capacitive element C2approximately agrees (preferably, matches) with the predetermined target value (the capacitance value C2t). In other words, here, the deformation volumes of the polymer actuator elements131and132are controlled by adjusting the value of the driving voltage Vd so that the value of the capacitance value (C2t−C2d) approaches 0 (zero) (preferably, becomes 0).

In this way, in the variable capacitance device1B of the present modification, the deformation volumes of the polymer actuator elements131and132are controlled in the voltage supply section181, by using the capacitance value C2dof the monitoring capacitive element C2detected by the capacitance-value detecting section182. Therefore, it is possible to accurately adjust the capacitance value of the capacitive element C1actually used to a desired value, without being affected by vibration or a postural difference of the variable capacitance device1B.

It is to be noted that for the present modification, the case where the monitoring variable capacitance element is formed using two sub-electrodes has been described, but, for example, three or more variable capacitance elements may be formed using three or more sub-electrodes, and one of these variable capacitance elements may be used as the monitoring variable capacitance element.

FIG. 14Aschematically illustrates an overall configuration (schematic configuration) of a variable capacitance device (a variable capacitance device1C) according to the modification 3, in a side view (a Z-X side view). Further,FIG. 14Bschematically illustrates an overall configuration (schematic configuration) of a variable capacitance device (a variable capacitance device1D) according to the modification 4, in a side view (a Z-X side view). In these modifications 3 and 4, a displacement magnitude (the amount of travel) of a movable electrode17is detected, and a deformation volume (a displacement magnitude, a curving amount) of each of polymer actuator elements131and132is controlled by using the detected displacement magnitude.

The variable capacitance device1C of the modification 3 illustrated inFIG. 14Ais different from the variable capacitance device1of the embodiment described above in that a driving section18C is provided in place of the driving section18, and a magnet191and a Hall element192are further provided. Otherwise, the variable capacitance device1C is configured in a manner similar to the variable capacitance device1. The magnet191and the Hall element192correspond to a specific example of the “displacement-magnitude detecting section” according to the embodiment.

The magnet191is disposed on a connection member15(here, on a side surface), and is made of, for example, a magnetic material such as a compound (Nd2Fe14B) of neodymium (Nd)—iron (Fe)—boron (B). The Hall element192is disposed on a support member11at a position facing the magnet191, and detects the intensity of a magnetic field produced by the magnet191. It is to be noted that the intensity of the magnetic field may be detected using a magneto-resistive element (MR element), instead of using the Hall element192. In the driving section18C, the deformation volumes of the polymer actuator elements131and132are controlled using the intensity of the magnetic field (corresponding to a displacement magnitude of the movable electrode17, and a distance d3between the magnet191and the Hall element192) detected by the Hall element192. Specifically, the driving section18C controls the deformation volumes of the polymer actuator elements131and132by adjusting the value of a driving voltage Vd.

Meanwhile, the variable capacitance device1D of the modification4illustrated inFIG. 14Bis different from the variable capacitance device1in the embodiment described above in that a driving section18D is provided in place of the driving section18, and a reflection member193and a photo-reflector194are further provided. Otherwise, the variable capacitance device1D is configured in a manner similar to the variable capacitance device1. The reflection member193and the photo-reflector194correspond to a specific example of the “displacement-magnitude detecting section” according to the embodiment.

The reflection member193is disposed on a connection member15(here, on a side surface), and is made of, for example, a metallic material such as aluminum (Al). The photo-reflector194is disposed on a support member11at a position facing the reflection member193, and is formed by containing a Light Emitting Diode (LED) and a phototransistor in a single package. In the photo-reflector194, the quantity of light (reflected light) reflected by the reflection member193after being emitted from the LED is detected by the phototransistor. In the driving section18D, the deformation volumes of the polymer actuator elements131and132are controlled using the quantity of reflected light detected by the photo-reflector194(corresponding to a displacement magnitude of the movable electrode17, and a distance d4between the reflection member193and the photo-reflector194). Specifically, the driving section18D controls the deformation volume of each of the polymer actuator elements131and132by adjusting the value of a driving voltage Vd.

In this way, in the modifications 3 and 4, the displacement magnitude of the movable electrode17is detected, and the deformation volumes of the polymer actuator elements131and132are controlled using the detected displacement magnitude. Therefore, it is possible to reliably adjust the capacitance value C of the capacitive element C1to a desired value, without being affected by vibration and a postural difference of each of the variable capacitance devices1C and1D.

FIG. 15illustrates a schematic configuration and operation of each of piezoelectric elements231and232each serving as an actuator element applied to a variable capacitance device according to the modification 5. In the variable capacitance device of the present modification, the piezoelectric elements231and232to be described below are provided in place of the polymer actuator elements131and132of the embodiment described above.

Each of these piezoelectric elements231and232includes a conductive plate61extending on an XY plane, a pair of piezoelectric bodies62A and62B disposed on both sides of this conductive plate61, and a pair of fixing members63A and63B to fix one end side of each of the conductive plate61and the piezoelectric bodies62A and62B.

The conductive plate61is made of, for example, a material such as phosphor bronze. The piezoelectric bodies62A and62B are each made of, for example, a piezoelectric material such as lead zirconate titanate (PZT). It is to be noted that these piezoelectric bodies62A and62B are assumed to be each subjected to predetermined polarization treatment along a thickness direction thereof (a Z-axis direction), and have the same polarization directions.

In the piezoelectric elements231and232thus configured, when a predetermined driving voltage Vd is applied to each of the piezoelectric bodies62A and62B, one of the piezoelectric bodies (here, the piezoelectric body62A) stretches along the X-axis direction, while the other (here, the piezoelectric body62B) shrinks along the X-axis direction. As a result, the piezoelectric elements231and232as a whole curve (bend) along the thickness direction (the Z-axis direction), and a deformation volume d in the Z-axis direction is produced. It is to be noted that when the polarity of the driving voltage Vd is reversed, the deformation volume d in the reverse direction is obtained. In this way, each of the piezoelectric elements231and232functions as an actuator element by being supplied with the driving voltage Vd.

Therefore, in the variable capacitance device of the present modification in which these piezoelectric elements231and232are used as actuator elements, it is also possible to obtain an effect similar to that in the embodiment described, by similar operation.

FIGS. 16A and 16Beach illustrate a schematic configuration and operation of bimetallic elements331and332each serving as an actuator element applied to a variable capacitance device according to the modification 6, in a schematic diagram.FIG. 16Aillustrates a state before the operation, andFIG. 16Billustrates a state after the operation. In the variable capacitance device of the present modification, the bimetallic elements331and332to be described below are provided in place of the polymer actuator elements131and132of the embodiment described above.

Each of these the bimetallic elements331and332includes a pair of metal plates (a high-expansion metal plate72A and a low-expansion metal plate72B different from each other in coefficient of thermal expansion) extending on an XY plane, and a pair of fixing members73A and73B fixing the one end side of each of these metal plates. The high-expansion metal plate72A and the low-expansion metal plate72B form a layered structure by being adhered to each other.

Each of the high-expansion metal plate72A and the low-expansion metal plate72B is made of, for example, a material obtained by adding a metal such as manganese (Mn), chromic (Cr), or copper (Cu) to an alloy of iron (Fe) and nickel (Ni). The respective coefficients of thermal expansion are made to be different from each other by varying the respective amounts of addition.

In the bimetallic elements331and332thus configured, the high-expansion metal plate72A expands more than the low-expansion metal plate72B, in a state in which the temperature is higher than that in a flat state (the state before the operation) illustrated inFIG. 16A. As a result, the bimetallic elements331and332as a whole curve (bend) along a thickness direction (a Z-axis direction), and a deformation volume d of the Z-axis direction is produced. Therefore, each of the bimetallic elements331and332functions as an actuator element, by changing the temperature of each of the high-expansion metal plate72A and the low-expansion metal plate72B using a heating means such as a not-illustrated heater.

Therefore, in the variable capacitance device of the present modification in which these bimetallic elements331and332are used as actuator elements, it is also possible to obtain an effect similar to that in the embodiment described above by similar operation.

Application Example

Next, an application example (an example of application to an antenna module and a communication apparatus) of the variable capacitance devices according to the embodiment and the modifications 1 to 6 described above (the variable capacitance devices1,1A to1D and the like) will be described.

FIG. 17andFIG. 18are perspective diagrams each illustrating a schematic configuration of a communication apparatus (a portable telephone4) according to the application example of the variable capacitance devices of the above-described embodiment and the like. In this portable telephone4, two housings41A and41B are foldably coupled to each other through a not-illustrated hinge mechanism.

As illustrated inFIG. 17, in a surface on one side of the housing41A, various operation keys42are disposed, and a microphone43is disposed below the operation keys42. The operation keys42are intended to receive predetermined operation by a user and thereby input information. The microphone43is intended to input voice of the user during a call and the like.

As illustrated inFIG. 17, a display section44using a liquid-crystal display panel or the like is disposed in a surface on one side of the housing41B, and a speaker45is disposed at an upper end thereof. The display section44displays various kinds of information such as a radio-wave receiving status, a remaining battery, a telephone number of a party on the other end of the line, contents (telephone numbers, names, and the like of other parties) recorded as a telephone book, an outgoing call history, an incoming call history, and the like, for example. The speaker45is intended to output the voice of a party on the other end of the line during a call and the like.

As illustrated inFIG. 18, inside a surface on the other side of the housing41B, an antenna module46having any of the variable capacitance devices according to the embodiment and the like is disposed.

FIG. 19Aillustrates a main circuit configuration of the antenna module46. This antenna module46has an antenna element461, and the variable capacitance device1(or any of1A to1D and the like) including a capacitive element C1(variable capacitance element) in the above-described embodiment or the like.

In the antenna module46having such a configuration, compared with an existing antenna module, it is possible to obtain the following advantage by being configured using the variable capacitance device1(or any of1A to1D and the like) of the above-described embodiment or the like.

First, in a portable terminal (a communication apparatus) having a wireless communication function represented by a portable telephone, in recent years, progress has been made in multiband of frequency in use, or multimode of a mounted system, in order to speed up communication data and improve convenience. In particular, recently, multiband-multimode portable telephones, smartphones etc. which are allowed to use both a GSM (Global System for Mobile Communications) method and a UMTS (Universal Mobile Telephone System) method (a W-CDMA (Wideband Code Division Multiple Access) method) have become widespread. In such a portable terminal (communication apparatus), it is desirable to combine wireless communication systems employing various methods, such as Near Field Communication (NFC) represented by Bluetooth (registered trademark), WLAN (Wireless Local Area Network), FeliCa (non-contact IC card: registered trademark), in addition to GPS (Global Positioning System), one segment (one-segment partial reception service for a portable telephone and a portable terminal), and the like, for example.

Here, in an antenna module106of related art according to a comparative example illustrated inFIG. 19B, band switching among the wireless communications systems employing such multiple methods is realized as follows. That is, impedance adjustment elements the number of which is the same as the number of bands thereof (here, one fixed capacitive element C100and six fixed capacitive elements C101to C106) are prepared beforehand, and connection with those impedance adjustment elements is switched by a switching element SW, and thereby the band switching is realized. However, in such a configuration, the impedance adjustment elements (here, fixed capacitive elements) are necessitated first. In addition, the switching element SW to switch them is desired to be an element having small loss while suppressing high power and thus, it has been desired to use a relatively expensive component such as a gallium arsenide (GaAs) switch or the like. For these reasons, in the antenna module106of related art, the configuration is complicated and large, increasing the production cost.

In contrast, in the antenna module46according to the present application example illustrated inFIG. 19A, the variable capacitance device1or the like described above in the embodiment or the like is the only element desired for band switching and thus, the configuration of a transmitter-receiver circuit may be extremely simplified. Further, it is possible to change the capacitance value in the variable capacitance element C1continually and thus, a large number of bands may be selected (in theory, infinite). Furthermore, a wide capacitance value range from a small capacitance value to a large capacitance value may be covered by a single variable capacitance element and thus, a combination of wireless communications systems of multiple methods is realized with a simple configuration.

Other Modifications

The present technology has been described by using the embodiment, modifications, and application example. However, the present technology is not limited to these embodiment and the like, and may be variously modified.

For example, the connection member15and the link members141and142described above in the embodiment and the like may not be provided in some cases. Further, the embodiment and the like have been described for the case where the one end side of the actuator element is directly fixed by the fixing member12has been described, but the present technology is not limited to this case. In other words, the one end side of the actuator element may be fixed by the fixing member12indirectly (through the fixed electrode16and the like). Furthermore, the embodiment and the like have been described for the case where the movable electrode17is provided to connect to the actuator element indirectly, but the present technology is not limited to this case. In other words, the movable electrode17may be provided to connect to the actuator element directly (the movable electrode17may be formed in a part (surface or the like) of the actuator element).

Further, the embodiment and the like have been described mainly for the case where the pair of actuator elements are provided. However, the actuator elements may not be in a pair, and one actuator element or three or more actuator elements may be provided.

Furthermore, the shape of each actuator element is not limited to those in the embodiment and the like, and also, the layered structure is not limited to those described in the embodiment and the like, and may be changed as appropriate. Moreover, the shape and the material of each member in the variable capacitance device are not limited to those described in the embodiment and the like.

In addition, the variable capacitance device according to the embodiment is not limited to the application to the antenna module and the communication apparatus (portable telephone) described in the application example, and may be applied to other types of electronic apparatus and the like.