Patent Application
20120299594
The present invention relates to an antenna device for transmitting and receiving electromagnetic waves, and a magnetic resonance examination apparatus (henceforth referred to as “MRI apparatus”) using it.
In MRI apparatuses, imaging of a subject is attained by irradiating the subject stayed in a uniform static magnetic field generated by a static magnetic field magnet with electromagnetic waves to induce excitation of nuclear spins in the subject, receiving electromagnetic waves generated by the nuclear spins, i.e., magnetic resonance signals, and processing the signals. The irradiation of the electromagnetic waves and reception of the magnetic resonance signals are performed by a device for transmitting and receiving electromagnetic waves of radio frequency (RF), which is called RF antenna or RF coil.
RF coils are roughly classified into two kinds of those called surface antennas or local antennas, and those called volume coils or volume antennas. The surface antennas have a round shape or tabular shape, and show sensitivity in a region near the antennas, and they are used by being put on surface of a subject. On the other hand, the volume antennas have a cylindrical shape or a shape of two discs disposed upper and lower sides, and they show sensitivity in the whole volume in the cylinder or between the discs, and used by placing a subject in that space.
Examples of the volume antennas having a cylindrical shape include those of birdcage type (refer to, for example, Non-patent document 1), and those of TEM type (refer to, for example, Patent documents 1 and 2). In these volume antennas, about 16 to 24 conductive elements of a rod shape usually called rungs (crossbars or rungs of ladder) are disposed in parallel to the center axis of the cylinder and along the side of the cylinder.
Such volume antennas having a cylindrical shape are used in MRI apparatuses of the tunnel type. In MRI apparatuses of the tunnel type, a static magnetic field magnet is disposed in a cylindrical shape to form a tunnel, a subject laid on a bed is entered into the inside of the tunnel, and imaging is performed.
Regions in which sensitivity of local antennas can be obtained often correspond to only a part of such regions of volume antennas and are narrower than such regions of volume antennas. However, since sensitivity of local antennas is usually higher than that of volume antennas, local antennas are often used as a receiving antenna. Examples of the local antennas include, for example, one consisting of a conductive element bent in the shape of a loop (refer to, for example, Patent document 3), one consisting of a conductive element bent in the shape of figure eight (refer to, for example, Non-patent document 2), and so forth.
When it is desired to image a wide region with good sensitivity, a plurality of local antennas may be disposed to extend the region in which sensitivity can be obtained, and used as if it is a multi-channel volume antenna. In such a case, the antenna is constituted as an antenna having electric power supplying and receiving terminals in a number corresponding to the channel number of 3 or more, whereas the channel number of general volume antennas is 2.
For such tunnel type MRI apparatuses as mentioned above, it is desired to secure the inside of the tunnel into which a subject is entered as larger as possible, and thereby provide an examination environment in which even large build subjects and subjects with claustrophobia can comfortably have an MRI examination without anxiety. In general, in the tunnel type MRI apparatuses, a static magnetic field magnet, a gradient coil, and an RF coil are disposed in this order from the outside to the inside of the tunnel. Therefore, for the purpose of making the inside of the tunnel larger to secure a comfortable examination space, it is the easiest solution to make the internal diameter of the static magnetic field magnet larger. However, in order to make the internal diameter of the static magnetic field magnet larger, it is necessary to use a larger static magnetic field magnet, and this leads to marked increase of the manufacturing cost.
Moreover, in the volume antennas of cylindrical shape disclosed in the aforementioned prior art documents, the rungs of the aforementioned number are disposed with equal intervals for the circumferential direction. Therefore, if these volume antennas are used as an RF coil, the internal wall of the tunnel has a circular section. Since this shape does not necessarily correspond to the shape of human body laid on a bed as the subject, it is difficult to secure a space for the shoulder width direction, in particular, at the positions of both shoulders.
The present invention was accomplished in view of the aforementioned circumstances, and an object of the present invention is to provide a technique for securing a comfortable examination space in a tunnel type MRI apparatus without increasing the manufacturing cost of the MRI apparatus and sacrificing performance thereof.
According to the present invention, in an RF coil provided with an outer conductive element having a hollow cylindrical shape and one or more strip-shaped conductive elements disposed inside the outer conductive element along the same, the strip-shaped conductive elements are each constituted by connecting N of meandering or straight lines and disposed so that distances between the lines and the outer conductive element are uneven, and thereby an internal examination space is secured. In order to obtain uniform sensitivity in the inside of the RF coil, each strip-shaped conductive element is characterized in that the strip-shaped conductive element has electrically one turning conductive element part, one or more capacitors connected to the conductive element in series, and a feeding and receiving means connected in parallel with one of the capacitors, and resonates at a desired resonance frequency, and nodes at which electric current does not flow are formed in the strip-shaped conductive element when it resonates in a number of (M+1)×N−1, wherein M is 0 or a natural number of 1 or larger.
More specifically, there is provided an antenna device used for transmission and/or reception of a signal, which comprises a hollow cylindrical conductive element, one or more strip-shaped conductive elements, one or more capacitors disposed at one or more gaps provided in the strip-shaped conductive elements and connected with the conductive elements in series, and a connection means for connecting the antenna device with a transmission and reception means for transmitting and/or receiving the signal, which is connected in parallel with one of the capacitors, wherein each of the strip-shaped conductive elements comprises N of line members disposed at a certain distance from internal surface of the cylindrical conductive element with intervals between the line members for the circumferential direction of the cylindrical conductive element and each connected at one end to end of the adjacent line member with a conductive element so that the line members constitute one turned strip-shaped conductive element as a whole, the line members have a straight or meander shape and are disposed substantially parallel to the center axis of the cylindrical conductive element, length of the whole strip-shaped conductive element is adjusted so that the strip-shaped conductive element resonates at frequency of the signal, and sum of numbers of nodes of current distributions in N of the line members of the strip-shaped conductive element at the time of resonation thereof is (M+1)×N−1, wherein M is 0 or a natural number of 1 or larger. The line member is also called “one meander line”, and N of the meander lines constitute a “turned meander line”.
The present invention also provides a magnetic resonance examination apparatus comprising a static magnetic field generating means which generates a static magnetic field, an RF coil which is disposed in the static magnetic field generated by the static magnetic field generating means, and generates a radio frequency magnetic field in a direction perpendicular to the direction of the static magnetic field, or detects a radio frequency magnetic field in the direction perpendicular to the direction of the static magnetic field, a means for imaging internal information of a subject stayed in the static magnetic field using nuclear magnetic resonance signals generated from the subject and detected by the RF coil, and a mounting means on which the subject is mounted, wherein the aforementioned antenna device is provided as the RF coil, and the mounting means is disposed in the cylindrical conductive element of the antenna device.
According to the present invention, a comfortable examination space can be secured in a tunnel type MRI apparatus without increasing manufacturing cost of the MRI apparatus and without sacrificing performance thereof.
Hereafter, the first embodiment of the present invention will be explained. In all the drawings for explaining the embodiments of the present invention, the same numerical symbols are used for elements having the same functions, and repetitive explanations of these are omitted.
First, configuration of the MRI apparatus according to this embodiment will be explained.
The gradient magnetic field power supply 109 and the gradient coil 102 are connected with a gradient magnetic field control cable 107. Further, the RF coil 103 and the transceiver 104 are connected with a transmission and reception cable 106 for transmitting and receiving signals between the RF coil 103 and the transceiver 104. The transceiver 104 is further provided with a synthesizer, power amplifier, receiving mixer, analogue to digital converter, transmit-receive changeover switch, and so forth, although they are not shown in the drawing.
The MRI apparatus 100 may be of a horizontal magnetic field type or a vertical magnetic field type according to the direction of the static magnetic field formed by the magnet 101. In the case of the horizontal magnetic field type, the magnet 101 generally has a cylindrical bore (center space), and generates a static magnetic field along the side-to-side direction in
In the MRI apparatus 100 having the aforementioned configuration, electromagnetic waves and a gradient magnetic field are intermittently irradiated at intervals of around several milliseconds on the subject 112 stayed in the static magnetic field with the RF coil 103 and the gradient coil 102, respectively, signals emitted from the subject 112 by resonance with the electromagnetic waves are received, and signal processing is performed to obtain a magnetic resonance image. The subject 112 is, for example, a predetermined part of human body, laid on a bed 111, and placed in the inside of the RF coil 103. Further, the electromagnetic waves and the gradient magnetic field are irradiated and applied with the RF coil 103 and the gradient coil 102, respectively.
In this drawing, although a single RF coil is shown as the RF coil 103 for irradiation and reception of electromagnetic waves, the present invention is not limited to such a configuration. For example, an RF coil consisting of a plurality of coils such as a combination of an RF coil for wide range imaging and an RF coil for parts may be used as the RF coil 103.
In this embodiment, an antenna having a circular cylindrical shape or an elliptic cylindrical shape is used as the RF coil 103. Hereafter, an antenna 200 used as the RF coil 103 of this embodiment will be explained with reference to
The antenna 200 of this embodiment is provided with conductive elements 201 having a predetermined width (henceforth referred to as strip-shaped conductive elements), and a conductive element 202 having a circular cylindrical shape or an elliptic cylindrical shape and serving as a ground plane (grounding surface) (henceforth referred to as cylindrical conductive element).
The cylindrical conductive element 202 of this embodiment is formed from a conductive element such as a copper sheet, a copper mesh, or a stainless steel mesh. For example, the cylindrical conductive element 202 formed from a copper sheet is adhered to internal or external wall of a cylindrical case formed from fiber reinforced plastics (FRP) or the like (not shown).
The strip-shaped conductive elements 201 of this embodiment each are made up of a plurality of meandering line members 211. The adjacent meandering line members 211 are connected with a conductive element 301 to constitute one long turned conductive element. This meandering line member 211 is called a meander line 211. In
The meander line referred to here is a conductive element having a shape of elongated plate, string or pipe meandering in a width for the circumferential direction of the ellipse having the center at the position of the center axis C of the cylindrical conductive element 202 (direction perpendicular to the center axis C). The meander lines 211 are disposed inside the cylindrical conductive element 202, in parallel with the center axis C of the cylindrical conductive element 202, and with intervals for the circumferential direction of the cylindrical conductive element 202.
The meander lines 211 shown in
In
Specifically, an elliptic cylinder smaller than the cylindrical conductive element 202 and having a major axis/minor axis ratio different from that of the cylindrical conductive element 202 is provided in the elliptic cylinder constituted by the cylindrical conductive element 202, and the meander lines 211a, 211b, and 211c are disposed on the surface thereof.
This smaller elliptic cylinder is in the inside of the cylindrical conductive element 202, and the distance between the cylindrical conductive element 202 and the internal small elliptic cylinder can be adjusted so that, for example, the distance is slightly large for the up-and-down direction, and slightly small for the side-to-side direction as shown in
By such an adjustment, a larger space can be secured for the shoulder width direction as the space into which a human as the subject 112 is entered.
Further, this internal small elliptic cylinder may not be constituted by one integral cylinder, and as shown in
Among the distances between three of the meander lines 211a, 211b and 211c, and the cylindrical conductive element 202, the distances close to the right and left ends (211a) are narrower than those close to the center (211c). By using such a configuration, as the internal space of the antenna 200, a larger space can be secured for the side-to-side direction of a human laid in the inside, especially at the position of both shoulders, compared with the case where all the meander lines 211 are disposed at equal distances from the cylindrical conductive element 202.
As described above, in this embodiment, the meander lines 211 are disposed with a smaller distance with respect to the cylindrical conductive element at a position closer to both shoulders of a human body laid on the stomach or the back and entered into the inside of the cylindrical space as the examination space at the time of examination. Furthermore, in the case of
Moreover, since the size of the cylindrical conductive element 202 is not changed, the configurations other than that of the RF coil 103 are not affected, and marked increase of the manufacturing cost is not invited, either.
In the example shown in
On the other hand, at the portions around the points connecting three of the meander lines 211a, 211b and 211c, i.e., the conductive elements 301 shown in
That is, since one strip-shaped conductive element 201 shown in
Moreover, in the example shown in
In
In
In the middle of the meander line 211, a gap 501 is provided, and a capacitor 502 is disposed at the gap 501 so as to connect the lines on both sides of the gap in series. The capacitor 502 is connected to a feeding and receiving cable 505 at the connecting point 302 via a matching and balance circuit 504. The other end of the feeding and receiving cable 505 is connected to the transmission and reception means 503. When the antenna 200 of this embodiment is used as the RF coil 103 of the MRI apparatus 100, this feeding and receiving cable 505 corresponds to the transmission and reception cable 106 shown in
That is, the strip-shaped conductive element 201 constituted with the meander line 211 is connected to the transmission and reception means 503 via the matching and balance circuit 504 connected in parallel with the capacitor 502 at the connecting point 302, and the feeding and receiving cable 505.
Although the feeding and receiving cable 505 is drawn with one thick line in
When the strip-shaped conductive element 201 is constituted from a plurality of meander lines 211 as shown in
The principle of the operation of the antenna shown in
The strip-shaped conductive element 201 resonates at a resonance frequency, which is determined by length of the whole strip-shaped conductive element 201 and value of the capacitor 502. When an alternating current power at the resonance frequency is supplied to the strip-shaped conductive element 201 from the transmission and reception means 503, an electric current flows in the strip-shaped conductive element 201. The electric current generates a magnetic field around the conductive element, and magnitude of the magnetic field determines the sensitivity of the coil as the antenna 200 of the MRI apparatus 100. In
Width W604 of meandering of the meander line 211 shown in
A case where the electric current flowing in the strip-shaped conductive element 201 flows in one direction and does not have nodes of electric current will be explained with reference to
Current distribution observed when an electric current flows in the strip-shaped conductive element 201 will be considered. Since both ends 603 of the strip-shaped conductive element 201 are not connected to any element, magnitude of the electric current is zero at the ends.
When a certain moment is supposed, a large electric current (arrow 601) flows in the strip-shaped conductive element 201 around the center thereof, and the magnitude of the electric current becomes smaller at a position closer to the end (arrow 602). In
It is useful to know the number of the nodes as the whole in the cases of adjustment of the resonance frequency of the strip-shaped conductive element, and so forth. Therefore, the number of nodes formed in the whole strip-shaped conductive element 201 as one element is calculated by using the equation: (M+1)×N−1. In the equation, N represents number of the meander lines 211 constituting one strip-shaped conductive element 201, and M represents number of nodes of electric current existing in one meander line 211 (except for the nodes at both ends).
In the strip-shaped conductive element 201 having one line without no turn (meander line 211) (N=1), there is formed no node (M=0), and therefore the total number of nodes of the current distribution observed in the line of the strip-shaped conductive element 201 is calculated to be (0+1)×1−1=0.
In the example shown in
At a certain moment, the electric current flowing in the lower half of the strip-shaped conductive element 201 flows upward (arrow 703), and the electric current flowing in the upper half flows downward (arrow 702). At the position of the node 701, electric current does not flow, and the direction of the electric current flowing in the strip-shaped conductive element 201 is reversed there.
A position at which high sensitivity of the antenna can be obtained is a position near a portion at which an electric current flows well. In the example shown in
As for two of the configurations shown in
Number of nodes formed in the whole strip-shaped conductive element 201 shown in
Although the capacitor 502 provided at the gap 501 is indicated with the symbol of capacitor in
That is, when the length of the whole strip-shaped conductive element 201 is unduly long, and thus the resonance frequency is lower than a desired resonance frequency, the capacitor 803 can be disposed to make the resonance frequency to be higher up to the desired resonance frequency.
When electric power of the resonance frequency is supplied from the transmission and reception means 503 disposed in parallel with the capacitor 803 disposed at the gap 501, the electric current induced in the strip-shaped conductive element 201 flows as shown with arrows 802, and directions of the electric currents in three of the meander lines 211 become the same directions at a certain moment.
When the strip-shaped conductive element 201 has the configuration shown in
Number of nodes formed in the whole strip-shaped conductive element 201 as one element of the example shown in
Although
The transmission and reception means 503 explained with reference to
Value of coupling between the ports among four of the ports 302 shown in
When the antenna 200 is used as a four-channel input and output antenna, especially as such an antenna for nuclear magnetic resonance, it may be more efficient to generate a circularly polarized wave in the inside of the elliptic cylinder. For example, if the four channels are defined as channels 1, 2, 3 and 4 in the clockwise direction, and the phase of the electric power supplied to the channel 1 is defined to be 0, a clockwise circularly polarized wave can be induced by supplying electric power with phases of 90 degrees, 180 degrees, and 270 degrees to the channels 2, 3 and 4.
Degree of coupling between the feeding points 302 (ports) is represented with the transmission coefficient of the S parameters. The S parameters have the transmission coefficient and reflection coefficient indicating transmission and reflection characteristics of electromagnetic waves between feeding points, respectively, and can be measured by using a measurement apparatus such as a network analyzer.
For example, in the antenna 200 of this embodiment exemplified in
Similarly, when electric power (electric current) is supplied to the port 1, and much of it is not supplied to the strip-shaped conductive element group 201 belonging to the port 1 due to reflection, efficiency of the antenna is also degraded. The parameter indicating the amount of reflected power is the reflection coefficient S11. As described above, the volume antenna 200 of this embodiment can decrease the coupling value (transmission coefficient) by the configuration thereof, and thus can maintain the efficiency of the antenna. In addition, it is also possible to employ a configuration for also decreasing the reflection coefficient to further improve the efficiency.
In order to realize it, when imaging is performed by connecting the antenna 200 to the MRI apparatus 100, the matching and balance circuit 504 shown in
For example, the impedance Za of the antenna 200 is adjusted to the characteristic impedance Zc of the feeding cable (transmission and reception cable) 106 (for example, 50Ω) at an operating frequency (for example, 128 MHz, which is the magnetic resonance frequency of hydrogen nucleus at 3 teslas).
The reflection coefficient among the S parameters can be thereby reduced, and efficiency of the antenna is improved. Specifically, for example, in the aforementioned case, the reflection coefficient Sli of the port 1 can be made to be −15 dB or lower.
A connection scheme for connection with the transmission and reception means 503 different from that shown in
In the example shown in
The capacitor 1001 disposed between the meander line 211 and the cylindrical conductive element 202 as described above generally has an effect of effectually lengthening the length of the meander line 211, contrary to the capacitor 803 explained in
In the example shown in
However, even with the strip-shaped conductive element 201b, if a capacitor of an appropriate value is chosen as the capacitor 803 connected at the gap 501 of the meander line 211, and the feeding means 503 is connected to the capacitor 803, electric currents may be flown in the meander lines 211 in the same direction as in the example shown in
Further, the cylindrical conductive element 202 of the antenna 200 of this embodiment may be formed from a material other than sheet-shaped material. For example, it may be constituted with a metallic mesh such as copper or stainless steel mesh. Use of a metallic mesh does not degrade the function of the cylindrical conductive element 202 as a ground plane.
Further, when the cylindrical conductive element 202 is formed so that an alternate current of a low frequency of several kilohertzs or lower can flow through the whole elliptic cylinder thereof, an eddy current generated by the gradient magnetic field power supply 109 of the MRI apparatus 100 may flow. To prevent it, the cylindrical conductive element 202 may have a structure that it is constituted by consecutively arranged strips corresponding to divided portions of the side wall of the elliptic cylinder parallel to the axis of the elliptic cylinder, which are connected with capacitors having a large capacitance of several hundreds picofarads.
Further, when the antenna 200 of this embodiment is constituted with four of the strip-shaped conductive elements 201 as shown in
Moreover, in the case of such a four-channel antenna as shown in
As explained above, according to this embodiment, in an RF coil provided with a hollow outer conductive element and one or more strip-shaped conductive elements disposed along the outer conductive element in the axial direction, intervals between the meander lines constituting the strip-shaped conductive element and the outer conductive element are made uneven to secure an internal space. However, in order to obtain uniform sensitivity at the center section of the RF coil, the strip-shaped conductive elements are constituted with N of connected meander lines, and length of the strip-shaped conductive elements is adjusted so that electromagnetic waves resonate at the resonance frequency of the antenna to form nodes in a number of (M+1)×N−1, wherein M is 0 or a natural number of 1 or larger. With such a configuration, a comfortable examination space can be secured in the tunnel type MRI apparatus 100 without increasing manufacturing cost of the MRI apparatus 100 and without sacrificing performance of the MRI apparatus 100.
The second embodiment of the present invention will be explained below. The MRI apparatus of this embodiment basically has the same configuration as that of the MRI apparatus 100 of the first embodiment. However, in this embodiment, a new configuration is added to the antenna 200 of the first embodiment as the RF coil 103 to attempt further reduction of the coupling value and improvement in the efficiency. Hereafter, an antenna 200b of this embodiment will be explained with emphasizing the configuration different from that of the antenna 200 of the first embodiment.
As shown in
The conductive element 1201, two of the capacitors 1202, and the cylindrical conductive element 202 constitute a loop. Coupling between the ports 1 and 2 can be changed by flowing an electric current in this loop. The coupling between the ports can be suppressed by appropriately selecting values of the capacitors 1202.
The conductive element 1201 and two of the capacitors 1202 are disposed between each two of the adjacent strip-shaped conductive elements 201.
Therefore, according to this embodiment, the transmission coefficient can be further reduced in addition to the effect obtainable by the first embodiment, and thus an antenna showing further improved efficiency can be obtained.
The method for reducing coupling between the ports is not limited to the aforementioned method. Various kinds of methods generally used can be applied.
An example of use of the antenna 200 of the first embodiment shown in
In this example, a cylindrical conductive element 202 formed from a copper sheet or copper mesh having a thickness of several tens to several hundreds micrometers was adhered to an inner wall of a cylindrical case formed from FRP to form an elliptic cylindrical conductive element member. The formed elliptic cylindrical conductive element member had an internal diameter for the major axis of 594 mm, an internal diameter for the minor axis of 520 mm and a length of the elliptic cylinder of 1000 mm.
Strip-shaped conductive elements 201 are disposed on a surface of an elliptic cylinder disposed inside the cylindrical conductive element 202 and having diameters for the major axis and the major axis shorter than those of the cylindrical conductive element 202 by 10 mm and 50 mm, respectively. The disposed strip-shaped conductive elements 201 each had a width of 10 mm, and the meander line 211 had a length of 670 mm from one end to the other end in the axial direction of the elliptic cylinder, and the width W604 for the right-and-left direction of 38 mm. Gaps 501 were provided in the strip-shaped conductive elements 201 at positions of 120 mm and 240 mm from both ends, and capacitors 502 of 100 pF were inserted into the gaps and connected.
The strip-shaped conductive element 201 was constituted with three of the meander lines 211. There were disposed four of the strip-shaped conductive elements 201 as shown in
Further, in each strip-shaped conductive element 201, the transmission and reception cable 505 was connected in parallel with the capacitor 502 closest to the end and near the upper and lower parts of the antenna 200.
Electromagnetic field simulation was performed in the antenna 200 having the configuration explained above. First, with changing frequency of electromagnetic waves supplied via the transmission and reception cable 505, impedance Z of the antenna 200 was measured. As a result, a resonance peak of high impedance Z appeared at around 128 MHz (magnetic resonance frequency of hydrogen nucleus at 3 teslas), which was a frequency used in the 3-tesla MRI apparatus 100. Thus, it was demonstrated that the antenna 200 of the aforementioned embodiment resonated at a frequency of around 128 MHz.
Then, sensitivity profile of the antenna 200 having the configuration explained above was investigated. In this example, sensitivity of the antenna 200 at the center was determined by electromagnetic field simulation for a case of supplying electromagnetic waves of the aforementioned frequency having the same intensity, but different phases of 0, 90, 180, and 270 degrees, to four of the feeding points 302, respectively. In this simulation, a phantom simulating histological composition of a male human having a body weight of 65 kg was constituted on a computer and placed inside the antenna 200.
If the sensitivity in the section at the center perpendicular to the axis of the elliptic cylinder is represented in the unit of microtesla, which is intensity of the magnetic field generated with a total input power of 1 W, a magnetic field of about 0.19 microtesla was generated at the center of the elliptic cylinder of the antenna 200 of this embodiment. Thus, it was demonstrated by the above result that there was obtained sensitivity in a range necessary and sufficient for usual examination conducted by using a common MRI apparatus.
As described above, it was demonstrated that according to the antenna 200 of the first embodiment shown in
Therefore, according to the aforementioned embodiments, there can be provided RF coils for MRI providing comfortableness to persons who enter into the inside thereof for getting an examination, with maintaining the required performance, but without raising cost.
In addition, the antennas of the aforementioned embodiments can be applied to not only an RF coil 103 of an MRI apparatus, but also any instruments using electromagnetic waves having a frequency of from several megahertzs to several gigahertzs.
100: MRI Apparatus, 101: magnet, 102: gradient coil, 103: RF coil, 104: transceiver, 105: data processing part, 106: transmission and reception cable, 107: gradient magnetic field control cable, 108: display, 109: gradient magnetic field power supply, 111: bed, 112: subject, 200: antenna, 200b: antenna, 201: strip-shaped conductive element, 201b: strip-shaped conductive element, 202: cylindrical conductive element, 211: meander line, 211a: meander line, 211b: meander line, 211c: meander line, 301: conductive element connecting meander lines, 302: connecting point, 501: gap, 502: capacitor, 503: transmission and reception means, 504: matching and balance circuit, 505: feeding and receiving cable, 601: arrow indicating electric current, 602: arrow indicating electric current, 603: end of strip-shaped conductive element, 604: meandering width of meander line, 701: node of electric current, 702: arrow indicating electric current 703: arrow indicating electric current, 801: node of electric current, 802: arrow indicating electric current, 1001: capacitor, 1201: conductive element, 1202: capacitor
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-041274 | Feb 2010 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2011/051122 | 1/21/2011 | WO | 00 | 8/8/2012 |
