Power Transmission Coil

Abstract

In the present invention, a power transmission coil comprises a shield conductor 2 that is disposed at a position where an electromagnetic field formed by a power-transmission coil (1) intersects when the power transmission coil (1) transmits power, the shield conductor 2 comprising: the power transmission coil (1) that transmits power; a loop conductor (21) that has a slit (211); and a resonance circuit (22) having a parallel-connected inductor (221) and capacitor (222) connected between both open ends of the slit (211) in the loop conductor (21).

Description

[Technical field]

[0001] The present disclosure relates to a power transmission coil, such as a power transmission coil or a power receiving coil, in a magnetic field coupling type power transmission device that uses electromagnetic induction to transmit power from a power transmission coil to a power receiving coil in a non-contact manner, that is, to transmit power. [Background technology]

[0002] Magnetic field coupling type power transmission is known in which a portable device such as a mobile phone, headset, digital camera, or digital video has a receiving coil, and power is transmitted from a transmitting coil to the receiving coil to contactlessly power or charge the portable device. In recent years, research has been conducted not only on small devices such as portable devices, but also on large devices and applications that handle large amounts of power, such as automatic transport robots and electric vehicles. When transmitting power from the transmitting coil to the receiving coil, some of the power transmitted from the transmitting coil is not received by the receiving coil and is radiated into the air, acting as an interference wave to surrounding devices, which adversely affects the surrounding devices.

[0003] Patent Document 1 discloses an antenna (corresponding to a power transmission coil) for use in a portable device that transmits power and that can suppress emitted radiation noise without significantly reducing power transmission efficiency. The antenna shown in Patent Document 1 is a composite antenna consisting of a planar coil and a loop coil, and the resonant frequency of the resonant circuit consisting of the inductance of the loop coil and the tuning capacitance is adjusted to a frequency that is more than twice the driving frequency of the planar coil. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2012-115069 A Summary of the Invention [Problem to be solved by the invention]

[0005] In the antenna shown in Patent Document 1, the inventors attempted to verify the efficiency of power transmission, and found that the impedance Z loop When the frequency is small, the power of the driving frequency of the planar coil is not necessarily received by the receiving coil with high transmission efficiency. In addition, at frequencies below the resonant frequency of the loop coil, the impedance Z loop becomes capacitive, and the magnetic flux from the planar coil and the magnetic flux radiated from the loop coil due to the current induced in the loop coil by this magnetic flux reinforce each other. In other words, in this frequency range, the loop coil cannot suppress radiated interference waves, and if the capacitance C of the capacitor is determined so that the resonant frequency of the loop coil is sufficiently higher than the drive frequency, the frequency range in which radiated interference waves can be suppressed becomes narrow.

[0006] That is, in the antenna shown in Patent Document 1, if we consider a series resonant circuit consisting of the resistance R of the loop coil, the self-inductance L, and the capacitance C of the capacitor, the impedance Z of the loop coil is loop is expressed by the following equation (1).

[0007] TIFF0007630728000001.tif12166

[0008] In equation (1), j is the imaginary unit and ω is the angular frequency. Now, if we determine the capacitance C so that the loop coil resonates at twice the fundamental frequency, then Z loop is expressed by the following equation (2). The fundamental wave referred to here is the driving wave in Patent Document 1, and refers to the fundamental wave frequency component of the high-frequency signal transmitted (or received) by the power transmitting circuit (or power receiving circuit) connected to the planar coil.

[0009] TIFF0007630728000002.tif13166

[0010] formula (2) where ω0 is the fundamental angular frequency. Since the real part does not depend on frequency, the impedance Z of the loop coil at the fundamental angular frequency ω0 is loop The imaginary part of is expressed by the following equation (3).

[0011] TIFF0007630728000003.tif13166

[0012] As is clear from equation (3), when the self-inductance L of the loop coil at the fundamental angular frequency ω0 is small, the impedance Z of the loop coil at the fundamental angular frequency ω0 loop does not become large enough, and current is easily induced in the loop coil. As a result, conductor loss occurs in the loop coil, and if the loop coil is provided on a dielectric substrate, dielectric loss occurs due to the material of the dielectric substrate, resulting in a decrease in the power transmission efficiency of the drive frequency power.

[0013] On the other hand, the impedance Z of the loop coil at the fundamental angular frequency ω0 loop In order to make the imaginary part of the above equation sufficiently large, it is also possible to determine the capacitance C of the capacitor so that the resonant frequency of the loop coil is sufficiently higher than the fundamental wave frequency. However, as is clear from the above equation (1), in the frequency band below the resonant frequency of the loop coil, the impedance Z loop The imaginary part of is a negative value, and the impedance of the loop coil Z loop is capacitive.

[0014] Loop coil impedance Z loop If the impedance is capacitive, the magnetic flux from the planar coil and the magnetic flux radiated from the loop coil due to the current induced in the loop coil by this magnetic flux will reinforce each other, and at frequencies below the resonant frequency of the loop coil, the loop coil will not be able to suppress radiated interference waves, and the frequency range in which radiated interference waves can be suppressed will be narrow. In short, suppression of radiated interference waves and making the resonant frequency of the loop coil sufficiently higher than the fundamental wave frequency cannot be achieved at the same time.

[0015] The present disclosure has been made in consideration of the above-mentioned points, and aims to obtain a power transmission coil that does not affect the power transmission efficiency of the power transmitted by the coil transmitting power, and suppresses unnecessary radiation waves due to frequencies other than the fundamental frequency of the electromagnetic field formed by the power transmission coil, that is, the fundamental frequency transmitted by a power transmission circuit connected to the power transmission coil when the power transmission coil is a power transmission coil, or the fundamental frequency received by a power receiving circuit connected to the power receiving coil when the power transmission coil is a power receiving coil. [Means for solving the problem]

[0016] The power transmission coil according to the present disclosure includes a power transmission coil for transmitting power, a loop conductor having a slit, and an inductor and a capacitor connected in parallel between both open ends of the slit of the loop conductor. and a second inductor connected in series to the parallel resonant circuit. and a shield conductor arranged at a position where an electromagnetic field formed by the power transmission coil interlinks when the power transmission coil transmits power. Effect of the Invention

[0017] According to the present disclosure, it is possible to suppress unnecessary radiation waves due to frequencies other than the fundamental frequency of the electromagnetic field formed by the power transmission coil, without affecting the power transmission efficiency of the power transmitted by the power transmission coil. [Brief description of the drawings]

[0018] [Figure 1] 1 is a configuration diagram showing a power transmission coil according to a first embodiment. [Diagram 2] 3 is an equivalent circuit diagram of a shield conductor in the power transmission coil according to the first embodiment. [Diagram 3] 4 is a diagram illustrating the phase of impedance of a shield conductor relative to the frequency of transmitted power in the power transmission coil according to the first embodiment. FIG. [Figure 4] 4 is a graph showing power transmission efficiency versus frequency of transmitted power in the power transmission coil according to the first embodiment. FIG. [Diagram 5] 5A and 5B are diagrams illustrating the suppression effect with respect to the frequency of transmitted power in the power transmission coil according to the first embodiment. [Figure 6] 4 is a diagram showing the absolute value of impedance of a shield conductor versus the frequency of transmitted power in the power transmission coil according to the first embodiment. FIG. [Figure 7] 4 is a graph showing the radiation efficiency versus frequency of transmitted power in the power transmission coil according to the first embodiment. FIG. [Figure 8] FIG. 11 is a configuration diagram showing a power transmission coil according to a second embodiment. [Figure 9] FIG. 11 is a configuration diagram showing a power transmission coil according to a third embodiment. [Figure 10] FIG. 11 is a diagram showing a configuration of a power transmission coil according to a fourth embodiment. [Figure 11] FIG. 13 is a configuration diagram showing a power transmission coil according to a fifth embodiment. [Figure 12] FIG. 13 is a diagram showing a configuration of a power transmission coil according to a sixth embodiment. [Figure 13] 13 is a diagram illustrating the phase of impedance of a shield conductor relative to the frequency of transmitted power in a power transmission coil according to a sixth embodiment. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Embodiment 1 A power transmission coil according to a first embodiment will be described with reference to FIGS. 1 to 7. FIG. The power transmission coil according to the first embodiment is a power transmission coil or a power receiving coil in a magnetic field coupling power transmission device that uses electromagnetic induction to transmit power from a power transmission coil to a power receiving coil in a non-contact manner, that is, transmits power. In this disclosure, the power transmitting coil and the power receiving coil are collectively referred to as a power transmission coil, and the power transmission coil refers to either the power transmitting coil or the power receiving coil.

[0020] When transmitting power from the power transmitting coil to the power receiving coil in a non-contact manner, the power receiving coil is placed opposite a position where electromagnetic induction occurs with the power transmitting coil, that is, a position where the electromagnetic fields generated by the power transmitting coil interlink. At the fundamental frequency of the high-frequency signal transmitted to the transmitting coil by the transmitting circuit connected to the transmitting coil, the transmitting coil and the receiving coil are in a resonant relationship, so the receiving coil efficiently receives power at the fundamental frequency, but for unwanted waves at frequencies other than the fundamental frequency, the coupling between the transmitting coil and the receiving coil is small, so power reception is suppressed.

[0021] The explanation of the present disclosure will show an example in which the power transmission coil is applied to a power transmission coil, but even if the power transmission coil is applied to a power receiving coil, the configuration will be similar to that of the power transmission coil, based on the same concept. In addition, the power transmission coil of the power transmission coil and the power receiving coil of the power receiving coil are collectively referred to as power transmission coils, and in the case of a power transmission coil, the power transmission coil refers to the power transmission coil, and in the case of a power receiving coil, the power transmission coil refers to the power receiving coil.

[0022] When the power transmission coil is a power transmission coil, the fundamental frequency of the electromagnetic field formed by the power transmission coil is the fundamental frequency of the electromagnetic field formed by the power transmission coil, and is the fundamental frequency of the high-frequency signal transmitted by the power transmission circuit connected to the power transmission coil. When the power transmission coil is a receiving coil, the fundamental frequency of the electromagnetic field formed by the power transmission coil is the fundamental frequency of the electromagnetic field formed in the receiving coil by receiving power through electromagnetic induction with the power transmission coil, and is the fundamental frequency of the high-frequency signal received by the receiving circuit connected to the receiving coil. To avoid complicating the explanation, hereinafter, the explanation will be given as a power transmission coil.

[0023] As shown in FIG. 1, the power transmission coil includes a power transmission coil 1 and a shield conductor 2. When the present disclosure is applied to a power receiving coil, the power receiving coil includes a power receiving coil and a shield conductor. A high-frequency signal having mainly fundamental frequency components transmitted from a power transmission circuit 3 is input to the power transmission coil 1. Based on the high-frequency signal input from the power transmission circuit 3, the power transmission coil 1 forms an electromagnetic field around the power transmission coil 1, and the formed electromagnetic field links with the power receiving coil (not shown) placed in the opposing position, forming an electromagnetic field in the power receiving coil and transmitting power to the power receiving coil by electromagnetic induction.

[0024] The power receiving coil that receives the power transmitted from the power transmitting coil 1 supplies the power to a load (not shown) such as a rechargeable battery connected thereto via a power receiving circuit (not shown). A capacitor for impedance matching is connected between the power transmission coil 1 and the power transmission circuit 3. This impedance matching capacitor is omitted from the illustration as it is included in the power transmission circuit 3. The power transmission coil 1 is a coil having a planar pattern wound a plurality of times on the surface of a dielectric substrate (not shown).

[0025] The shield conductor 2 is disposed on the outside of the power transmission coil 1 . The shield conductor 2 may be disposed inside the power transmission coil 1, or may be disposed above or below the power transmission coil 1. The shield conductor 2 includes a loop conductor 21 and a resonant circuit 22 having an inductor 221 and a capacitor 222 connected in parallel.

[0026] In the shield conductor 2, the resonant circuit 22 places the loop conductor 21 in an essentially electrically open state for the fundamental frequency of the electromagnetic field formed by the power transmission coil 1, and a current of opposite phase to the high-frequency current flowing in the power transmission coil 1 is induced in the loop conductor 21 for unwanted waves of frequencies other than the fundamental frequency, in this example, unwanted waves of frequencies more than twice the fundamental frequency. When a current is induced in the loop conductor 21 , a magnetic field is generated around the loop conductor 21 by the induced current. In addition, even for frequencies less than the fundamental frequency, a current is induced in the loop conductor 21 as an unwanted wave, and a magnetic field is formed around the loop conductor 21 by the induced current.

[0027] The magnetic field formed by the high-frequency current of the harmonic frequency flowing through the power transmission coil 1 and the magnetic field formed by the high-frequency current of the opposite phase induced in the loop conductor 21 are substantially in opposite phase and cancel each other out. In other words, the shield conductor 2 has the characteristic that a current is unlikely to be induced in the loop conductor 21 at the fundamental frequency of the electromagnetic field formed by the power transmission coil 1, but a current is induced in the loop conductor 21 at frequencies other than the fundamental frequency, particularly the frequencies of unwanted waves whose radiated interference waves are to be suppressed.

[0028] As a result, the shielding conductor 2 does not affect the fundamental frequency of the high-frequency signal transmitted by the power transmission circuit 3 connected to the power transmission coil 1, i.e., the fundamental frequency of the transmitted power, and weakens the electromagnetic field formed around the power transmission coil 1 for unwanted wave frequencies. In short, a decrease in power transmission efficiency is avoided for the fundamental frequency of the transmitted power, and radiation noise caused by currents of unwanted wave frequencies flowing through the power transmission coil 1 is suppressed by radiation from high-frequency currents of the opposite phase induced in the loop conductor 21. In this disclosure, power transmission efficiency is defined as the ratio of the power supplied to the power transmitting coil 1 to the power received and output by the power receiving coil.

[0029] The loop conductor 21 is disposed at a position where it is linked with an electromagnetic field formed by the power transmission coil 1 when the power transmission coil 1 transmits electric power. The loop conductor 21 is a conductor having a loop-shaped planar pattern wound once around the outer periphery of the power transmission coil 1 on the surface of the dielectric substrate. The loop conductor 21 is a parasitic conductor having a slit 211 formed at the end of the loop.

[0030] The loop conductor 21 is disposed outside the power transmission coil 1. The loop conductor 21 only needs to be located close enough to the power transmission coil 1 so that a sufficient current is induced in the loop conductor 21 by linkage with the electromagnetic field formed by the power transmission coil 1, and may be located inside the power transmission coil 1, or above or below the power transmission coil 1. The loop conductor 21 does not need to be on the same plane as the power transmission coil 1. The thickness of the loop conductor 21 is greater than the thickness of the power transmission coil 1. In other words, the line width of the loop conductor 21 is greater than the line width of the power transmission coil 1.

[0031] The inductor 221 and the capacitor 222 connected in parallel form a parallel resonant circuit 22 . The parallel resonant circuit 22 is connected between both open ends of the slit 211 of the loop conductor 21 . That is, one terminal of inductor 221 is electrically connected to one open end of slit 211, and the other terminal is electrically connected to the other open end. Similarly, one terminal of capacitor 222 is electrically connected to one open end of slit 211, and the other terminal is electrically connected to the other open end. Inductor 221 and capacitor 222 are formed on the surface of a dielectric substrate by commonly known methods.

[0032] The parallel resonant circuit 22 increases the impedance of the shielding conductor 2 at the fundamental frequency of the electromagnetic field formed by the power transmission coil 1 to reduce the induced current, and reduces the impedance of the shielding conductor 2 at frequencies other than the fundamental frequency, i.e., the frequencies of radiated interference waves, which are unwanted waves that we wish to suppress, to make it easier for a current to be induced. The resonant frequency of the parallel resonant circuit 22 is the fundamental frequency of the electromagnetic field formed by the power transmission coil 1 . In this example, the frequency of the spurious wave to be suppressed is set to a frequency that is at least twice the fundamental wave frequency f0, although it is not limited to being twice the frequency.

[0033] Moreover, the inductance L of the inductor 221 and the capacitance C of the capacitor 222 that configure the parallel resonant circuit 22 are values ​​that satisfy ω0C=1 / ω0L. ω0 is the fundamental frequency of the electromagnetic field formed by the power transmitting coil 1, and is the angular frequency at the fundamental frequency of the high-frequency signal transmitted by the power transmitting circuit 3 connected to the power transmitting coil 1. This point will be explained in more detail below.

[0034] An equivalent circuit diagram of the shield conductor 2 is shown in FIG. In Figure 2, R L is the resistance of the impedance of the loop conductor 21, L L indicates the inductance of the impedance of the loop conductor 21, L indicates the inductance of the inductor 221, and C indicates the capacitance of the capacitor 222. The impedance Z of the shield conductor 2 is expressed by the following equation (4).

[0035] TIFF0007630728000004.tif12166

[0036] The condition for increasing the impedance Z of the shield conductor 2 and reducing the induced current at the fundamental frequency f0 (angular frequency is ω0) of the electromagnetic field formed by the power transmission coil 1 is equal to the condition for a parallel resonant circuit consisting of the inductance L of the inductor 221 and the capacitance C of the capacitor 222 to resonate, which is when the inductance L and the capacitance C satisfy the following equation (5).

[0037] TIFF0007630728000005.tif10166

[0038] When equation (5) is satisfied, the third term in equation (4) becomes infinite, and the shield conductor 2 is electrically open, that is, it is equivalent to the loop conductor 21 being open in the parallel resonant circuit 22. Therefore, no current is induced in the loop conductor 21 at the fundamental frequency f0 of the electromagnetic field formed by the power transmission coil 1, which has an angular frequency ω0. As a result, power of the fundamental frequency f0 transmitted from the power transmitting coil 1 to the power receiving coil is not affected by the shield conductor 2 and is received by the power receiving coil, so power transmission efficiency does not decrease.

[0039] Next, a method for determining the inductance L of inductor 221 and the capacitance C of capacitor 222 will be described. As described above, the resonant frequency at which the parallel resonant circuit consisting of the inductor 221 and the capacitor 222 resonates must match the fundamental frequency f0 of the electromagnetic field formed by the power transmission coil 1. Therefore, the inductance L and the capacitance C have a degree of freedom within a range that satisfies the following equation (6).

[0040] TIFF0007630728000006.tif12166

[0041] On the other hand, the effect of weakening the electromagnetic field by the shield conductor 2 can be obtained only when the impedance Z of the shield conductor 2 is inductive. The phase of the impedance Z of the shield conductor 2 constituting the equivalent circuit shown in FIG. 2 changes as shown in FIG. In Figure 3, the horizontal axis indicates the transmission frequency of the power supplied to the power transmission coil 1, and the vertical axis indicates the phase of the impedance Z of the shield conductor 2. Frequency F1 is the fundamental frequency f0 of the electromagnetic field formed by the power transmission coil 1, and frequency F2 is the frequency at which the imaginary part of the impedance Z of the shield conductor 2 shown in the above equation (4) becomes 0, that is, the resonant frequency of the shield conductor 2. As is clear from FIG. 3, the effect of weakening the electromagnetic field by the shield conductor 2 is obtained for frequencies less than the fundamental wave frequency f0 (F1) and frequencies equal to or greater than the resonant frequency F2 of the shield conductor 2.

[0042] Therefore, the condition for making the impedance Z of the shield conductor 2 inductive in order to suppress radiated interference waves of frequencies equal to or higher than the resonant frequency F2 of the shield conductor 2 is expressed by the following equation (7), where the resonant frequency F2 of the shield conductor 2 is f0×B.

[0043] TIFF0007630728000007.tif11166

[0044] In equation (7), L is the inductance of the inductor 221, L L is the inductance of the impedance of the loop conductor 21. The radiated interference emitted from the power transmitting coil is considered to be mainly harmonics generated at frequencies that are multiples of the fundamental frequency f0. In this example, when the frequency of the spurious wave to be suppressed is set to a frequency equal to or greater than twice the fundamental wave frequency f0, B in equation (7) is set to 2 as shown in the following equation (8).

[0045] TIFF0007630728000008.tif13166

[0046] Then, the inductance L and the capacitance C are determined based on equations (6) and (8). As a result, the shield conductor 2 does not affect the fundamental frequency f0 of the electromagnetic field formed by the power transmission coil 1, i.e., the fundamental frequency f0 of the transmitted power, but can suppress harmonics, i.e., unwanted waves, which have frequencies more than twice the fundamental frequency f0.

[0047] The effect of the shield conductor 2 was verified by the results of a numerical simulation obtained by the finite element method. In the simulation, the transmitting coil includes a transmitting coil 1, a loop conductor 21, and a shield conductor 2 including a resonant circuit 22 having an inductor 221 and a capacitor 222 connected in parallel. The receiving coil had the same components, physical size, and component values ​​as the transmitting coil. The transmitting coil and the receiving coil were placed facing each other with a gap of 5 mm between them.

[0048] In the power transmission coil, the power transmission coil 1 had a horizontal and vertical size of 40 mm x 20 mm, four turns, a line width of the power transmission coil 1 of 0.5 mm, and a distance between adjacent lines of 1.5 mm. The loop conductor 21 had a horizontal×vertical size of 51.5 mm×31.5 mm, one winding, and a line width of 5 mm.

[0049] The fundamental frequency f0 of the electromagnetic field formed by the power transmission coil 1, i.e., the fundamental frequency f0 of the high-frequency signal transmitted by the power transmission circuit 3 connected to the power transmission coil 1, is 13.56 MHz, and the capacitance C of the capacitor 222 is set to 3,200 pF in order to increase, i.e., maximize, the amount of suppression of unwanted waves at a frequency twice the fundamental frequency f0. Moreover, the inductance L of the inductor 221 is set to 43 nH, which resonates with the capacitor 222 at the fundamental frequency f0 (13.56 MHz). It is assumed that materials other than the power transmission coil 1 and the loop conductor 21 are lossless.

[0050] The receiving coil is exactly the same as the transmitting coil. Also, the power transmission efficiency is defined as the ratio of the power supplied from the input port to the power transmitting coil 1 to the power received by the power receiving coil and output to the output port. It is assumed that the input port and the output port are impedance-matched with the power transmitting coil 1 and the power receiving coil, respectively, at the fundamental frequency f0.

[0051] Under the above preconditions, the power transmission efficiency for the fundamental frequency of the power transmitted from the power transmitting coil to the power receiving coil was verified. The results of the verification are shown in Figure 4. In FIG. 4, the horizontal axis indicates the transmission frequency of the power transmitted from the transmitting coil to the receiving coil, the vertical axis indicates the power transmission efficiency, and curve A indicates the verification result when the power transmission coil according to embodiment 1 is used (hereinafter referred to as this example).

[0052] For comparison, comparative example 1 was tested in which there was no shield conductor 2, i.e., a power transmitting coil consisting only of a power transmitting coil and a power receiving coil consisting only of a power receiving coil, and comparative example 2 was tested in which a power transmitting coil with a ring-shaped loop conductor as the shield conductor and a power receiving coil with a ring-shaped loop conductor as the shield conductor were used. Both Comparative Example 1 and Comparative Example 2 are exactly the same as this example except for the differences. In FIG. 4, the verification results of Comparative Example 1 are shown as curve B, and the verification results of Comparative Example 2 are shown as curve C.

[0053] As is clear from FIG. 4, the power transmission efficiency for the fundamental frequency f0 (13.56 MHz) in this example and comparative example 1 is equal, 86.5%. That is, the present example obtained the same results as Comparative Example 1, which did not have a shielding conductor 2. It can be seen that the shielding conductor 2 in this example had no effect whatsoever on the transmission of power at the fundamental frequency f0, and there was no decrease in power transmission efficiency. On the other hand, the power transmission efficiency at the fundamental frequency f0 of Comparative Example 2 is 70.6% relative to the fundamental frequency f0, which is a deterioration of 15.9 percentage points compared to this example and Comparative Example 1. The shield conductor consisting of a circular loop conductor causes a decrease in power transmission efficiency.

[0054] As is clear from the above, since the parallel resonant circuit 22 having the inductor 221 and the capacitor 222 in the shield conductor 2 resonates at the fundamental frequency f0, no current is induced in the loop conductor 21, and a decrease in power transmission efficiency is avoided.

[0055] FIG. 5 shows the results of a verification of the suppression effect of the shield conductor 2 against unwanted waves of frequencies other than the fundamental wave frequency f0. FIG. 5 shows the difference in magnetic field strength between this example at a point 200 mm away from the center of the power transmission coil and that of Comparative Example 1 at a point 200 mm away from the center of the power transmission coil as the suppression effect. In FIG. 5, the horizontal axis indicates the transmission frequency of the power transmitted from the power transmitting coil to the power receiving coil, the vertical axis indicates the suppression effect, and curve A1 is the verification result of this example.

[0056] Curve A2 shows the verification result of the shield conductor 2 (Example 2) in which the line width of the loop conductor 21 is 1 mm, the capacitance C of the capacitor 222 is 1,000 pF to increase, i.e., maximize, the amount of suppression of unwanted waves at a frequency twice the fundamental frequency f0, and the inductance L of the inductor 221 is 138 nH which resonates with the capacitor 222 at the fundamental frequency f0.

[0057] As is clear from FIG. 5, there is no difference in magnetic field strength between this example and comparative example 1 for the fundamental frequency f0 (the second marker from the left in FIG. 5). In this example, the difference in magnetic field strength from comparative example 1, that is, the suppression effect, is maximum (approximately 30 dB) for the frequency of 27.12 MHz, which is twice the fundamental frequency f0, and a suppression effect of 10 dB to 15 dB is obtained even for frequencies exceeding twice the fundamental frequency f0.

[0058] Furthermore, there is no difference in magnetic field strength between Example 2 and Comparative Example 1 for the fundamental frequency f0, and the suppression effect of Example 2 is maximum (approximately 25 dB) for a frequency of 27.12 MHz that is twice the fundamental frequency f0, and a suppression effect of 5 dB to 10 dB is obtained for frequencies exceeding twice the fundamental frequency f0. In addition, in both this example and this example 2, there is no difference in magnetic field strength from Comparative Example 1, similar to the fundamental wave frequency f0, even when the power transmission frequency is 20 MHz (the third marker from the left in FIG. 5).

[0059] As is clear from the above, the parallel resonant circuit 22 having the inductor 221 and the capacitor 222 in the shield conductor 2 resonates at the fundamental frequency f0 of the electromagnetic field formed by the power transmission coil 1, so that no current is induced in the loop conductor 21 at the fundamental frequency f0, thereby avoiding a decrease in power transmission efficiency, and the impedance of the shield conductor 2 is small for frequencies more than twice the fundamental frequency f0, so that a current is induced in the loop conductor 21, and external radiation of unnecessary waves at more than twice the frequency is suppressed.

[0060] Furthermore, for frequency F1, i.e., frequencies equal to or greater than the fundamental frequency f0, and frequency F2, i.e., frequencies less than twice the fundamental frequency f0, the electromagnetic field is not weakened by the shield conductor 2, as is clear from FIG. 3, and the shield conductor 2 prevents a decrease in power transmission efficiency, as is clear from FIG. 4. On the other hand, for frequencies less than F1 and equal to or greater than F2, as is clear from FIG. 3, the electromagnetic field is weakened by the shield conductor 2, suppressing radiated interference waves.

[0061] Therefore, for frequencies of the electromagnetic field formed by the power transmission coil 1 that are equal to or greater than frequency F1 and less than frequency F2, the electromagnetic field is not weakened by the shield conductor 2, and a decrease in power transmission efficiency can be avoided. Therefore, the power transmission coil of embodiment 1 is effective for frequencies of the fundamental wave frequency of the electromagnetic field formed by the power transmission coil 1 that are equal to or greater than frequency F1 and less than frequency F2. This means that it is sufficient that the resonant frequency of the parallel resonant circuit 22 is lower than the fundamental frequency of the electromagnetic field formed by the power transmission coil 1. That is, the resonant frequency of the parallel resonant circuit 22 is not limited to the fundamental frequency of the electromagnetic field formed by the power transmission coil 1, but may be a frequency lower than the fundamental frequency of the electromagnetic field formed by the power transmission coil 1.

[0062] By making the width of the loop conductor 21 wider than that of the power transmission coil 1 and making the line width wider, for example from 1 mm to 5 mm, the inductance of the loop conductor 21 becomes smaller, so that the current induced in the loop conductor 21 becomes larger, and a greater magnetic field suppression effect is obtained for frequencies exceeding twice the fundamental frequency f0 of the electromagnetic field formed by the power transmission coil 1. In addition, since it is sufficient to reduce the inductance of the loop conductor 21, it is not limited to increasing the line width, but the thickness of the line can also be increased; in short, the thickness of the loop conductor 21 should be made thicker than the thickness of the power transmission coil 1.

[0063] When loop conductor 21 is formed on a dielectric substrate, a method for increasing the wire thickness of loop conductor 21 is to provide it on both the front and back surfaces of the dielectric substrate, and connect the conductor layer formed on the front surface to the conductor layer formed on the back surface with a through hole, thereby increasing the effective thickness of loop conductor 21. By increasing the thickness of the loop conductor 21 in this manner, the increase in the circuit area required for the power transmission coil is minimized, while the effect of suppressing unwanted waves with frequencies more than twice the fundamental frequency f0 of the electromagnetic field formed by the power transmission coil 1 is obtained.

[0064] In addition, the inductance L L By reducing this, the impedance of the shield conductor 2 can be reduced, and a current is not induced in the loop conductor 21 for the fundamental frequency f0 of the electromagnetic field formed by the power transmission coil 1, thereby avoiding a decrease in power transmission efficiency. A current is induced in the loop conductor 21 for a frequency more than twice the fundamental frequency f0, thereby suppressing external radiation of unnecessary waves of more than twice the frequency. That is, the impedance Z of the shield conductor 2 is expressed by the above formula (4), and the inductance L of the loop conductor 21 is expressed by the above formula (4). L When the imaginary part of the above equation (4) becomes infinite at the fundamental frequency f0, the absolute value of the impedance of the above equation (4) becomes small at frequencies other than the fundamental frequency f0.

[0065] The inductance L of the inductor 221 and the capacitance C of the capacitor 222 that constitute the parallel resonant circuit 22 are expressed as follows: the absolute value |Z| of the impedance of the shield conductor 2 calculated by the above formula (4) is infinite at the fundamental frequency f0 of the electromagnetic field formed by the power transmission coil 1, and the resistance R of the impedance of the loop conductor 21 at a frequency twice the fundamental frequency f0. L The inductance L of the loop conductor 21 is set to a value such that L and the absolute value of the impedance of the shield conductor 2, |Z|, are shown in FIG.

[0066] 6, the horizontal axis indicates the value normalized by the fundamental frequency f0 of the electromagnetic field formed by the power transmitting coil, and the vertical axis indicates the absolute value |Z| of the impedance of the shield conductor 2. In FIG. 6, the curve A3 indicates the inductance L L The curve A1 shows the absolute value |Z| of the impedance of the normalized shield conductor 2 when the inductance L of the loop conductor 21 is set to 10 nH. L The absolute value |Z| of the impedance of the normalized shield conductor 2 when the impedance is set to 100 nH is shown.

[0067] As shown by curves A3 and A4 in FIG. 6, the absolute value |Z| of the impedance of the shield conductor 2 is infinite at the fundamental frequency f0, and the resistance R L The inductance L of the loop conductor 21 is set to a value such that L By making it smaller, for example from 100 nH to 10 nH, the absolute value |Z| of the impedance of the shield conductor 2 can be significantly reduced up to the fundamental frequency f0, for frequencies from above the fundamental frequency f0 to less than twice the fundamental frequency f0, and for frequencies above twice the fundamental frequency f0. As a result, the inductance L of the loop conductor 21 L By making it smaller, the current induced in the loop conductor 21 for frequencies other than the fundamental frequency f0 can be increased, and the effect of suppressing the magnetic field in the unnecessary waves of frequencies other than the fundamental frequency f0 can be increased.

[0068] Fig. 7 shows the verification results of the radiation efficiency of the transmitting coil. The radiation efficiency is the ratio of the total power radiated far away to the total power supplied from the input port to the power transmitting coil 1. In FIG. 7, the horizontal axis represents the transmission frequency of the power transmitted from the power transmitting coil to the power receiving coil, and the vertical axis represents the radiation efficiency.

[0069] As is clear from FIG. 7, the radiation efficiency of this example is lower than that of Comparative Example 2 by 11.9 dB at a frequency of 230 MHz. That is, in this example, not only is the magnetic field in the vicinity of the power transmission coil 1 suppressed, but radiation to distant locations is also suppressed by 10 dB or more. As can be seen from the above simulation results, the power transmission coil in accordance with embodiment 1 can suppress radiated interference waves to the surroundings while maintaining power transmission efficiency.

[0070] In this example, as shown in FIG. 4, the power transmission efficiency is improved to 65% when the frequency of the power transmitted from the power transmitting coil 1 to the power receiving coil is 20 MHz. That is, in this example, the power transmission efficiency is improved by the parallel resonant circuit 22 having an inductor 221 and a capacitor 222 in the shield conductor 2 resonating with the two frequencies of 13.56 MHz and 20 MHz of the power transmitted from the transmitting coil 1 to the receiving coil.

[0071] The frequency at which the first power transmission efficiency peaks is the resonant frequency of the parallel resonant circuit, which in this example is the fundamental frequency f0 of the electromagnetic field formed by the power transmission coil 1, and the frequency at which the second power transmission efficiency peaks can be adjusted by setting the inductance L of the inductor 221 and the capacitance C of the capacitor 222. In short, the power transmission device to which this example is applied can efficiently transmit power at two frequencies: the fundamental frequency f0 of the electromagnetic field formed by the power transmission coil 1, that is, the fundamental frequency f0 of the transmitted power, and another frequency.

[0072] For example, by applying the present example, i.e., the transmitting coil, which has good power transmission efficiency in the two ISM bands of 6.78 MHz and 13.56 MHz, a power transmission device can be obtained that can simultaneously transmit power with a fundamental frequency of 6.78 MHz and power with a fundamental frequency of 13.56 MHz, or a wireless power transmission device that can switch between power with a fundamental frequency of 6.78 MHz and power with a fundamental frequency of 13.56 MHz.

[0073] In this case, one of the frequencies 6.78 MHz and 13.56 MHz is the first fundamental frequency, and the other frequency of 6.78 MHz and 13.56 MHz is the second fundamental frequency, both of which are fundamental frequencies, and the resonant frequency in the parallel resonant circuit 22 having the inductor 221 and the capacitor 222 is set to one of the fundamental frequencies.

[0074] Furthermore, by bringing the frequencies at which the two peaks of high power transmission efficiency occur close to each other, the peak of power transmission efficiency can be substantially made to cover a wide frequency band with respect to the frequency of the power transmitted from the power transmitting coil. In this case, it is possible to improve robustness against manufacturing errors in the power transmission coil, changes in the transmission / reception interval, and other environmental changes.

[0075] As described above, the power transmission coil of embodiment 1 comprises a loop conductor 21 having a slit 211, and a resonant circuit 22 connected between both open ends of the slit 211 of the loop conductor 21 and having an inductor 221 and a capacitor 222 connected in parallel, and is equipped with a shield conductor 2 arranged at a position where the electromagnetic field formed by the power transmission coil 1 intersects when power is transmitted from the power transmission coil 1 to the power receiving coil. Therefore, the power transmission efficiency of the power transmitted from the power transmission coil 1 to the power receiving coil is not affected, and unnecessary radiation waves of frequencies other than the fundamental frequency of the power to be transmitted are suppressed.

[0076] In the power transmission coil according to the first embodiment, the resonant frequency of parallel resonant circuit 22 is set to the fundamental frequency of power transmitted from power transmission coil 1. In addition, the inductance L of inductor 221 and the capacitance C of capacitor 222 that configure parallel resonant circuit 22 are set to values ​​that satisfy ω0C=1 / ω0L.

[0077] With this configuration, a current is not induced in the loop conductor 21 due to the fundamental frequency of the electromagnetic field formed by the power transmission coil, and a decrease in power transmission efficiency can be avoided. Furthermore, the capacitance C of capacitor 222 is set to a value that suppresses unwanted waves having a frequency that is twice the fundamental frequency of the electromagnetic field formed by the power transmission coil, thereby obtaining a suppression effect against unwanted waves having a frequency that is more than twice the fundamental frequency of the electromagnetic field formed by the power transmission coil.

[0078] In other words, since the parallel resonant circuit 22 resonates at the fundamental frequency of the electromagnetic field formed by the power transmission coil 1, no current is induced in the loop conductor 21 at the fundamental frequency of the transmitted power, thereby avoiding a decrease in power transmission efficiency, and the impedance of the shield conductor 2 is small for frequencies more than twice the fundamental frequency, so that a current is induced in the loop conductor, thereby suppressing external radiation of unnecessary waves at frequencies more than twice the fundamental frequency.

[0079] Furthermore, in the power transmission coil according to embodiment 1, by setting the resonant frequency of the parallel resonant circuit 22 to the fundamental frequency of the electromagnetic field formed by the power transmission coil 1, a second peak in the power transmission efficiency can be set at power having a frequency less than twice the fundamental frequency, and a second fundamental frequency can be obtained in addition to the fundamental frequency, making it possible to transmit at the two frequencies simultaneously or by switching between them. Furthermore, by bringing the first peak of the power transmission efficiency for the fundamental frequency of the electromagnetic field formed by the power transmission coil 1 and the second peak of the power transmission efficiency for a frequency different from the fundamental frequency close to each other, the frequency band of the transmitted power can be substantially broadened.

[0080] When the power transmission coil is the power transmission coil 1, the resonant frequency of the parallel resonant circuit 22 is the fundamental frequency of the electromagnetic field formed by the power transmission coil 1, and is the fundamental frequency of the high-frequency signal transmitted by the power transmission circuit 3 connected to the power transmission coil. However, when the power transmission coil is the power receiving coil, the resonant frequency of the parallel resonant circuit 22 is the fundamental frequency of the electromagnetic field formed in the power receiving coil by receiving power through electromagnetic induction, and is the fundamental frequency of the high-frequency signal received by the power receiving circuit connected to the power receiving coil. In any case, the resonant frequency of the parallel resonant circuit 22 is the fundamental frequency of the high-frequency signal transmitted by the power transmitting circuit 3 connected to the power transmitting coil 1 . In short, the resonant frequency of the parallel resonant circuit 22 is the fundamental frequency of the electromagnetic field formed by the power transmission coil.

[0081] Embodiment 2 Second embodiment A power transmission coil according to the present invention will be described with reference to FIG. The power transmission coil of embodiment 2 differs from the power transmission coil of embodiment 1 in that a second shield conductor 2A is provided, the frequency characteristics of which are different from those of the shield conductor 2, but is otherwise the same. In FIG. 8, the same reference numerals as those in FIG. 1 denote the same or corresponding parts.

[0082] The second shield conductor 2A is disposed outside the first shield conductor 2. The second shield conductor 2A may be disposed inside the first shield conductor 2, or may be disposed above or below it. The second shield conductor 2A includes a loop conductor 21A having a slit 211A, and a parallel resonant circuit 22A connected between both open ends of the slit 211A of the loop conductor 21A and having an inductor 221A and a capacitor 222A connected in parallel.

[0083] The second shield conductor 2A is disposed at a position where it is linked with the electromagnetic field formed by the power transmission coil 1 when the power transmission coil 1 transmits electric power. The loop conductor 21A is a conductor having a loop-shaped planar pattern wound once around the outer periphery of the first shield conductor 2 on the surface of the dielectric substrate. The loop conductor 21A is a parasitic conductor having a slit 211A formed at the end of the loop.

[0084] The impedance of the second shield conductor 2A is set to a value different from that of the first shield conductor 2, and the resonant frequency of the parallel resonant circuit 22A is set to a frequency different from that of the parallel resonant circuit 22. That is, even when the frequency of the power transmitted from the power transmitting coil 1 to the power receiving coil matches the resonant frequency of the parallel resonant circuit 22A in the second shield conductor 2A, the power transmission efficiency is improved.

[0085] As a result, in addition to the fundamental frequency of the electromagnetic field formed by the power transmission coil 1, whose power transmission efficiency is improved by the first shield conductor 2, it becomes possible to transmit power also at frequencies whose power transmission efficiency is improved by the second shield conductor 2A. As explained in the first embodiment, the resonant frequency of the parallel resonant circuit 22 is the fundamental frequency of the electromagnetic field formed by the power transmission coil, and is the fundamental frequency of the high-frequency signal transmitted by the power transmission circuit 3 connected to the power transmission coil 1. The resonant frequency of the parallel resonant circuit 22A is less than twice the fundamental frequency of the electromagnetic field formed by the power transmitting coil.

[0086] The resonant frequency of the parallel resonant circuit 22A is a third frequency different from the fundamental frequency of the electromagnetic field formed by the power transmission coil 1, at which the power transmission efficiency has a peak due to the first shield conductor 2, and the second frequency at which the power transmission efficiency has a second peak. By providing the second shield conductor 2A, it is possible to provide a peak in the power transmission efficiency also at the third frequency of the power transmitted from the power transmitting coil to the power receiving coil.

[0087] As a result, for power transmitted from the transmitting coil 1 to the receiving coil, for power with a frequency less than twice the fundamental frequency of the electromagnetic field formed by the transmitting coil 1, the first shield conductor 2 makes it possible to set a fundamental frequency at which the power transmission efficiency has a first peak and a second frequency at which the power transmission efficiency has a second peak, and the second shield conductor 2A makes it possible to set a third frequency at which the power transmission efficiency has a third peak.

[0088] Therefore, the power transmission coil in accordance with the second embodiment can transmit power at three frequencies simultaneously or by switching between them. Furthermore, by setting the fundamental frequency of the electromagnetic field formed by the power transmission coil 1 to be close to the second frequency and the third frequency, the frequency band of the power transmitted from the power transmission coil can be made wider.

[0089] Furthermore, by arranging multiple shield conductors whose parallel resonant circuits are different from each other, such as a third shield conductor, a fourth shield conductor, ... whose parallel resonant circuits have a different resonant frequency from the first shield conductor 2 and the second shield conductor 2A, and which have multiple frequencies that each show a different peak in power transmission efficiency at frequencies less than twice the fundamental frequency of the electromagnetic field formed by the power transmission coil 1, it is possible to further widen the frequency band of the power transmitted from the power transmission coil 1 to the power receiving coil.

[0090] As described above, the power transmission coil according to the second embodiment has the same effects as the power transmission coil according to the first embodiment, and in addition, it is possible to further increase the bandwidth of the frequency of the transmitted power.

[0091] Embodiment 3 A power transmission coil according to a third embodiment will be described with reference to FIG. The power transmission coil of embodiment 3 differs from the power transmission coil of embodiment 1 in that the parallel-connected inductor 221 and capacitor 222 that constitute resonant circuit 22 in shield conductor 2 are replaced by variable inductor 223 and variable capacitor 224, respectively, and that the power transmission coil of embodiment 3 is provided with a control unit 4 that controls variable inductor 223 and variable capacitor 224, and an operating status monitoring unit 5 that monitors the operating status, but is otherwise the same. In FIG. 9, the same reference numerals as those in FIG. 1 denote the same or corresponding parts.

[0092] In the power transmission coil of embodiment 3, the inductance of variable inductor 223 and the capacitance of variable capacitor 224 are controlled by the control unit 4, which is a controller, in accordance with the operating states of the transmitting coil and the receiving coil, while satisfying the condition of equation (5) above.

[0093] That is, in the operating state of the transmitting coil and the receiving coil, (a) the frequency component of the unwanted waves radiated from the transmitting coil 1 changes depending on the transmission power level from the transmitting circuit 3, (b) the frequency component of the unwanted waves transmitted by the transmitting circuit 3 changes due to a change in the value of the load connected to the receiving coil, and (c) even if the level of the unwanted waves transmitted from the transmitting circuit 3 is constant, a change in the load connected to the receiving coil may change the coupling between the transmitting coil and the receiving coil, causing a change in the level of interference waves radiated to the surroundings.

[0094] In the power transmission coil of embodiment 3, the operation status monitoring unit 5 monitors changes in the frequency components of unwanted waves in the operating states of the transmitting coil and the receiving coil, and the control unit 4 receives a status monitoring signal from the operation status monitoring unit 5 and outputs control signals to the variable inductor 223 and the variable capacitor 224, respectively, to change the inductance of the variable inductor 223 and the capacitance of the variable capacitor 224.

[0095] The operation status monitoring unit 5 monitors the operation status of the power transmitting coil and the power receiving coil, and outputs a status monitoring signal to the control unit 4. The operation status monitoring unit 5 is an antenna that detects the intensity of the electromagnetic field due to the electromagnetic waves radiated from the power transmission coil 1, and outputs a status monitoring signal indicating the detected electromagnetic field intensity. The operating status monitoring unit 5 is not limited to an antenna consisting of a coil with a conductor wound around it, but may be anything that can detect electromagnetic waves emitted from the power transmission coil 1. Furthermore, when focusing on unwanted waves that can become radiated interference waves in the microwave band, a dipole or monopole antenna is preferable.

[0096] The control unit 4 receives a status monitoring signal indicating the electromagnetic field strength from the operation status monitoring unit 5, identifies the frequency that needs to be suppressed from the electromagnetic field strength indicated by the status monitoring signal, and outputs a control signal to each of the variable inductor 223 and the variable capacitor 224 to set the inductance of the variable inductor 223 and the capacitance of the variable capacitor 224 to suppress unwanted waves at the identified frequency.

[0097] That is, in order to change the frequency at which the suppression effect shown in FIG. 5 is maximized based on the state monitoring signal from the operation state monitoring unit 5, to a frequency that requires suppression based on the electromagnetic field intensity indicated by the state monitoring signal, the control unit 4 outputs control signals to the variable inductor 223 and the variable capacitor 224, respectively, to change the frequency at which the suppression effect is maximized based on the state monitoring signal from the operation state monitoring unit 5. As a result, it is possible to obtain the maximum radiated interference suppression effect in each operating state while suppressing deterioration of power transmission efficiency at the fundamental frequency of the electromagnetic field formed by the power transmission coil 1, which is the fundamental frequency of the high-frequency signal transmitted by the power transmission circuit 3 connected to the power transmission coil 1.

[0098] Although the status monitoring signal from the operation status monitoring unit 5 is output directly to the control unit 4, the status monitoring signal from the operation status monitoring unit 5 may be received by a receiver that performs analog-to-digital conversion (AD conversion) and is placed near the operation status monitoring unit 5, and the status monitoring signal consisting of a digital signal may be transmitted to the control unit 4. In this case, even if the antenna serving as the operation status monitoring unit 5 is located away from the power transmission coil 1 and the electromagnetic field strength due to unwanted waves is very small, there is no attenuation of the high-frequency signal due to the wiring connecting the antenna and the control unit 4, and the control unit 4 can receive the status monitoring signal detected by the antenna 5 with high accuracy.

[0099] Furthermore, the operational state monitoring unit 5 is configured with one antenna, but it may be provided with a plurality of detection antennas. In an environment where there is a metal shield around the power transmission coil, the electromagnetic field strength may vary significantly depending on the location. However, if the operation status monitoring unit 5 is configured with multiple antennas, by arranging each of the multiple antennas in different locations, the frequencies that require suppression can be detected from measurements taken at various locations, and the control unit 4 can accurately identify the frequencies that require suppression.

[0100] Furthermore, each of the multiple antennas may be an antenna with a high Q value, that is, a narrowband antenna, suitable for each frequency of interest. Since the narrowband antenna has improved sensitivity, it can detect frequencies that require suppression with high sensitivity, and the control unit 4 can specify the frequencies that require suppression with high accuracy.

[0101] Furthermore, the antenna serving as the operation state monitoring unit 5 may be an antenna shared with a plurality of power transmission coils 1 arranged in close proximity to each other. That is, a status monitoring signal indicating the electromagnetic field strength detected by the shared antenna is received by a control unit 4 corresponding to each of the multiple power transmission coils 1, and the frequency that needs to be suppressed is identified from the electromagnetic field strength indicated by the status monitoring signal received by the control unit 4. A control voltage, which is a control signal that sets the inductance of variable inductor 223 and the capacitance of variable capacitor 224 to suppress unwanted waves at the identified frequency, is output to each of variable inductors 223 and variable capacitors 224 corresponding to each of the multiple power transmission coils 1.

[0102] In addition, as the antenna that is the operating status monitoring unit 5, an antenna in a wireless system installed in close proximity to the power transmission coil of embodiment 3 may be used. For example, when a power transmission coil is placed inside a room, an antenna in an entrance / exit management system that uses RFID (Radio Frequency Identification) placed at the entrance to the room may be used.

[0103] That is, the control unit 4 receives a signal received by an antenna in the access control system as a status monitoring signal, and identifies a frequency that needs to be suppressed from the signal received by the antenna. For example, when an interference wave intended for the access control system is received by an antenna in the access control system, the control unit 4 identifies the frequency of the interference wave received by the antenna as a status monitoring signal to be suppressed from the electromagnetic field intensity received by the antenna in the access control system. The control unit 4 outputs a control voltage, which is a control signal that sets the inductance of the variable inductor 223 and the capacitance of the variable capacitor 224 to suppress the spurious waves at the specified frequency, to the variable inductor 223 and the variable capacitor 224, respectively.

[0104] Furthermore, since the frequencies used in the access control system are specified, the control unit 4 may identify frequencies other than the frequencies used in the access control system that are included in the signal received by the antenna as frequencies of interference for the access control system, rather than identifying the frequencies of interference for the access control system based on the electromagnetic field strength of the signal received by the antenna. In a wireless system installed in close proximity, "closeness" refers to the distance that can be reached by electromagnetic waves, particularly unwanted waves, radiated from power transmission coil 1 in the power transmission coil according to embodiment 3.

[0105] In addition, in the power transmission coil of embodiment 3, the fundamental frequency of the electromagnetic field formed by the transmission coil 1 is not changed, and the inductance of the variable inductor 223 and the capacitance of the variable capacitor 224 are changed when the frequency components of unwanted waves change in the operating state of the transmission coil and the receiving coil. However, it is also possible to change the inductance of the variable inductor 223 and the capacitance of the variable capacitor 224 when the fundamental frequency of the electromagnetic field formed by the transmission coil 1 in the operating state of the transmission coil and the receiving coil, that is, the fundamental frequency of the high-frequency signal transmitted by the transmission circuit 3 connected to the transmission coil 1, is dynamically changed.

[0106] In this case, the operating status monitoring unit 5 monitors the fundamental frequency of the high-frequency signal transmitted by the power transmission circuit 3, in other words, the fundamental frequency input to the power transmission coil 1, and outputs a status monitoring signal to the control unit 4 according to the fundamental frequency. The control unit 4 does not change the frequency to be suppressed, but controls the inductance of the variable inductor 223 and the capacitance of the variable capacitor 224 to satisfy the condition of the above equation (5) in accordance with the angular frequency ω0 of the fundamental wave frequency f0 of the high-frequency signal transmitted by the power transmission circuit 3, based on the status monitoring signal from the operation status monitoring unit 5.

[0107] When the fundamental frequency of the electromagnetic field formed by the power transmission coil 1 is dynamically changed, the inductance of the variable inductor 223 and the capacitance of the variable capacitor 224 are changed to follow the dynamically changed fundamental frequency and satisfy the condition of the above equation (5), thereby suppressing deterioration of the power transmission efficiency for the power of the changed fundamental frequency.

[0108] As described above, the power transmission coil according to the third embodiment has the same effects as the power transmission coil according to the first embodiment. Furthermore, since the parallel-connected inductor and capacitor that make up the resonant circuit are variable inductor 223 and variable capacitor 224, the inductance of variable inductor 223 and the capacitance of variable capacitor 224 can be changed according to the operating state of the power transmission coil, thereby obtaining a high suppression effect against unwanted waves, or suppressing deterioration of power transmission efficiency for the fundamental frequency of the power transmitted from the transmitting coil 1 to the receiving coil.

[0109] For example, when the frequency components of unwanted waves change in the operating state of the transmitting coil and the receiving coil, the inductance of variable inductor 223 and the capacitance of variable capacitor 224 are changed, so that it is possible to obtain the maximum suppression effect against radiated interference waves in each operating state while suppressing deterioration of the power transmission efficiency at the fundamental frequency of the electromagnetic field formed by the transmitting coil 1, i.e., the fundamental frequency of the transmitted power. In addition, when the fundamental frequency of the electromagnetic field formed by the power transmission coil 1 in the operating state of the power transmission coil and the power receiving coil, i.e., the fundamental frequency of the transmitted power, is changed, the inductance of the variable inductor 223 and the capacitance of the variable capacitor 224 are changed, so that deterioration of the power transmission efficiency for power of the changed fundamental frequency can be suppressed.

[0110] Embodiment 4 A power transmission coil according to a fourth embodiment will be described with reference to FIG. The power transmission coil of embodiment 4 differs from the power transmission coil of embodiment 3 in that, whereas the control unit 4 identifies the frequency that needs to be suppressed in response to the state monitoring signal from the operation state monitoring unit 5, and outputs to each of the variable inductor 223 and the variable capacitor 224 a control signal that changes the inductance of variable inductor 223 and the capacitance of variable capacitor 224 uniquely for the identified frequency, the control unit 4 dynamically changes the inductance of variable inductor 223 and the capacitance of variable capacitor 224 within a range that satisfies the condition of equation (5) above in response to the state monitoring signal from the operation state monitoring unit 5, sets the inductance of variable inductor 223 and the capacitance of variable capacitor 224, and is provided with a memory unit 6, and is otherwise the same. In FIG. 10, the same reference numerals as those in FIG. 9 indicate the same or corresponding parts.

[0111] The control unit 4 receives a status monitoring signal indicating the electromagnetic field intensity from the antenna, which is the operating status monitoring unit 5, and if the electromagnetic field intensity indicated by the status monitoring signal exceeds a set threshold, dynamically changes the inductance of the variable inductor 223 and the capacitance of the variable capacitor 224 within a range that satisfies the condition of the above equation (5) until the electromagnetic field intensity indicated by the status monitoring signal from the operating status monitoring unit 5 becomes equal to or below the set threshold.

[0112] That is, even while changing the inductance of variable inductor 223 and the capacitance of variable capacitor 224, control unit 4 monitors the status monitoring signal indicating the electromagnetic field strength from operation status monitoring unit 5, and outputs control signals to variable inductor 223 and variable capacitor 224 to change the inductance of variable inductor 223 and the capacitance of variable capacitor 224 until the electromagnetic field strength indicated by the status monitoring signal from operation status monitoring unit 5 falls below a set threshold value.

[0113] When the electromagnetic field strength indicated by the status monitoring signal from the operation status monitoring unit 5 falls below a set threshold, the control unit 4 stops changing the inductance of the variable inductor 223 and the capacitance of the variable capacitor 224, and stores the set values ​​at that time in the memory unit together with information on the electromagnetic field strength indicated by the status monitoring signal from the operation status monitoring unit 5.

[0114] As described above, the power transmission coil according to the fourth embodiment has the same effects as the power transmission coil according to the third embodiment. Furthermore, the control unit 4 constantly monitors the electromagnetic field strength indicated by the status monitoring signal from the antenna, which is the operating status monitoring unit 5, and sets the inductance of the variable inductor 223 and the capacitance of the variable capacitor 224 to set values ​​when the electromagnetic field strength falls below a threshold value, thereby making it possible to appropriately control the suppression effect against unwanted waves.

[0115] Embodiment 5. A power transmission coil according to the fifth embodiment will be described with reference to FIG. The power transmission coil of embodiment 5 differs from the power transmission coil of embodiment 1 in that two slits are provided in the loop conductor, and a parallel resonant circuit consisting of an inductor and a capacitor connected in parallel between both open ends of the slit is disposed in each slit, but in all other respects it is the same. In FIG. 11, the same reference numerals as those in FIG. 1 denote the same or corresponding parts.

[0116] The loop conductor 210 has two slits 211 and 212 . The loop conductor 210 is composed of two identically shaped conductors 210A and 210B. The two conductors 210A and 210B are arranged to form a rectangle, and the open end of the conductor 210A and the open end of the conductor 210B face each other to form slits 211 and 212. The loop conductor 210 formed by two conductors 210A and 210B is the same as the loop conductor 21 in the first embodiment except that a slit 212 is further formed at a position opposite to the slit 211.

[0117] Furthermore, a parallel resonant circuit 22 constituted by an inductor 221 and a capacitor 222 connected in parallel is electrically connected between both open ends of the first slit 211 of the loop conductor 210, similar to the parallel resonant circuit 22 in the first embodiment. Similarly, a second parallel resonant circuit 23 formed of an inductor 231 and a capacitor 232 connected in parallel is electrically connected between both open ends of the second slit 212 of the loop conductor 210 .

[0118] Therefore, the shield conductor 2 includes a loop conductor 210, a first parallel resonant circuit 22 having an inductor 221 and a capacitor 222 connected in parallel, and a second parallel resonant circuit 23 having an inductor 231 and a capacitor 232 connected in parallel.

[0119] The impedance Z of the shield conductor 2 is expressed by the above equation (4) and is set to the same value as the impedance Z of the shield conductor 2 in embodiment 1, and the characteristics of the shield conductor 2 are set to the same as the characteristics of the shield conductor 2 in embodiment 1. Therefore, inductance L1 of inductor 221 and inductance L2 of inductor 231 have the same value, which is half the inductance L of inductor 221 in embodiment 1, and capacitance C1 of capacitor 222 and capacitance C2 of capacitor 232 have the same value, which is twice the capacitance C of capacitor 222 in embodiment 1.

[0120] The number of slits formed in the shield conductor 2 is not limited to two, but may be three or more, and each slit is connected to a resonant circuit having an inductor and a capacitor connected in parallel. When the number of slits is n and the number of resonant circuits is n, the inductance of the inductor of each resonant circuit is the same value, which is 1 / n of the inductance L of inductor 221 in embodiment 1, and the capacitance of the capacitor of each resonant circuit is the same value, which is n times the capacitance C of capacitor 222 in embodiment 1.

[0121] As described above, the power transmission coil according to the fifth embodiment has the same effects as the power transmission coil according to the first embodiment. Furthermore, the number of slits formed in the shield conductor 2 is multiple (n), and the number of resonant circuits connected to each slit is multiple (n), so that the shield conductor 2 can be made compact and can be easily mounted on a dielectric substrate.

[0122] For example, when the fundamental frequency of the electromagnetic field formed by the power transmission coil 1 is several MHz to several tens of MHz, an inductance of several hundred nH may sometimes be required to resonate a single resonant circuit having an inductor and capacitor connected in parallel at the fundamental frequency. Inductors with a large inductance of several hundred nH are generally large.

[0123] In contrast, the power transmission coil according to the fifth embodiment resonates a plurality of resonant circuits at the fundamental frequency, so that the inductance of each inductor can be 1 / n, making each inductor smaller and improving mountability. Another effect is that by providing n resonant circuits, the induced electromotive force induced in the shield conductor 2 is divided by each resonant circuit, so the voltage applied to one resonant circuit becomes 1 / n. This reduces the withstand voltage required for the capacitors constituting each resonant circuit, allowing smaller components to be selected and improving mountability.

[0124] Embodiment 6 A power transmission coil according to a sixth embodiment will be described with reference to FIGS. The power transmission coil of embodiment 6 differs from the power transmission coil of embodiment 1 in that while the resonant circuit 22 electrically connected to the slit 211 in the loop conductor 21 is a parallel resonant circuit made up of an inductor 221 and a capacitor 222 connected in parallel, the resonant circuit 22 is a circuit having a second inductor 225 further connected in series to the parallel resonant circuit made up of an inductor 221 and a capacitor 222 connected in parallel, but is otherwise the same. In FIG. 12, the same reference numerals as those in FIG. 1 denote the same or corresponding parts.

[0125] The shield conductor 2 includes a loop conductor 21, a parallel resonant circuit formed by an inductor 221 and a capacitor 222 connected in parallel, and a resonant circuit 22 having a second inductor 225 further connected in series to the parallel resonant circuit. One end of the parallel resonant circuit is electrically connected to one open end of the slit 211 of the loop conductor 21 , and the other end of the parallel resonant circuit is electrically connected to one end of the second inductor 225 . The other end of the second inductor 225 is electrically connected to the other open end of the slit 211 .

[0126] The impedance Z of the shield conductor 2 is expressed by the following equation (9). In formula (9), R L is the resistance of the impedance of the loop conductor 21, L L is the inductance of the impedance of the loop conductor 21, L is the inductance of the inductor 221, C is the capacitance of the capacitor 222, and L S is the second inductor 225 of Indicates inductance.

[0127] TIFF0007630728000009.tif14166

[0128] Comparing equation (9) with equation (4) expressing the impedance Z of the shield conductor 2 in embodiment 1, the impedance Z of the shield conductor 2 in embodiment 6 is calculated as follows: S This is equivalent to being larger by one digit.

[0129] That is, the inductance L of the loop conductor 21 L In order to increase the resistance, for example, the width of the loop conductor 21 can be narrowed or the number of turns can be increased. L accompanied by an increase in Resistance component R of the loop conductor 21 L An increase in the gain reduces the amount of suppression of unwanted waves. In contrast, in the sixth embodiment, the resistance component R L The inductance of the loop conductor 21 can be increased without increasing the inductance. In other words, the inductance of the loop conductor 21 is (L L +L S ) can be regarded as such.

[0130] The phase of the impedance Z of the shield conductor 2 and the assumed inductance (L L +L S ) will be explained with reference to FIG. In Figure 13, the horizontal axis shows the value normalized by the fundamental frequency f0 of the power transmitted from the transmitting coil to the receiving coil, and the vertical axis shows the phase of the impedance Z of the shield conductor 2. A standard value f / f0 of 1 is the fundamental frequency f0 of the electromagnetic field formed by the transmitting coil 1, that is, the fundamental frequency f0 of the transmitted power, and a standard value f / f0 of 2 is twice the frequency of the fundamental frequency f0, which is the frequency at which the imaginary part of the impedance Z of the shield conductor 2 shown in the above equation (4) becomes 0, that is, the resonant frequency of the shield conductor 2. Curve A5 is the assumed inductance (L L +L S ) is 10 nH, and curve A6 is the assumed inductance (LL +L S ) is 100nH.

[0131] As is clear from FIG. 13, the assumed inductance (L L +L S ) (100 nH), the phase change of the impedance Z of the shield conductor 2 is steep at the resonance frequency (f / f0=2) of the shield conductor 2. Deemed inductance (L L +L S ) is 100 nH, the phase of the impedance Z of the shield conductor 2 is approximately ±90° even at frequencies close to the resonant frequency of the shield conductor 2. The most ideal condition for the mutual weakening effect between the magnetic field formed by the current flowing through the power transmission coil 1 and the magnetic field formed by the current flowing through the loop conductor 21 is a phase difference of +90°. That is, from the viewpoint of the phase of the impedance Z of the shield conductor 2, the deemed inductance (L L +L S The larger the gain, the greater the effect of suppressing unwanted waves.

[0132] In the first embodiment, as described with reference to FIG. 6, the inductance L L For example, by reducing the impedance |Z| of the shield conductor 2 from 100 nH (curve A4) to 10 nH (curve A3), the absolute value of the impedance |Z| of the shield conductor 2 can be significantly reduced for frequencies below the fundamental frequency f0, for frequencies from above the fundamental frequency f0 to below twice the fundamental frequency f0, and for frequencies above twice the fundamental frequency f0, and the effect of suppressing the magnetic field of unwanted waves at frequencies other than the fundamental frequency f0 can be increased.

[0133] That is, in order to increase the suppression effect of the magnetic field in the unnecessary waves of frequencies other than the fundamental frequency f0, the inductance L of the loop conductor 21 is set to 1 / 100, from the viewpoint of the phase of the impedance Z of the shield conductor 2. LFrom the viewpoint of the impedance Z of the shield conductor 2, the inductance L of the loop conductor 21 should be increased. L It is often better to make it smaller, so there is a trade-off.

[0134] In the power transmission coil according to the sixth embodiment, resonant circuit 22 is configured as a circuit having second inductor 225 further connected in series to a parallel resonant circuit formed of inductor 221 and capacitor 222 connected in parallel. This reduces the inductance L of second inductor 225. S By adjusting the assumed inductance (L L +L S ) can be adjusted, and the effect of suppressing the magnetic field in the spurious waves of frequencies other than the fundamental frequency f0 can be appropriately obtained from the viewpoints of both the phase of the impedance Z of the shield conductor 2 and the impedance Z of the shield conductor 2 itself.

[0135] Furthermore, the inductance L of the second inductor 225 S By changing the inductance (L L +L S ) can be changed, making design easier.

[0136] As described above, the power transmission coil according to the sixth embodiment has the same effects as the power transmission coil according to the first embodiment. Furthermore, the inductance L of the second inductor 225 S By adjusting the above, a more appropriate suppression effect can be obtained for the magnetic field suppression effect of unnecessary waves of frequencies other than the fundamental wave frequency of the electromagnetic field formed by the power transmission coil 1.

[0137] In the power transmission coil according to embodiment 2, similarly to embodiment 6, the resonant circuits of both the first shield conductor 2 and the second shield conductor 2A may be a parallel resonant circuit consisting of an inductor and a capacitor connected in parallel, and a circuit having a second inductor further connected in series to the parallel resonant circuit. Furthermore, in each of the power transmission coil according to embodiment 3 and the power transmission coil according to embodiment 4, as in embodiment 6, the resonant circuit may be a parallel resonant circuit consisting of a variable inductor and a variable capacitor connected in parallel, and a circuit having a second inductor further connected in series to the parallel resonant circuit.

[0138] Furthermore, in the power transmission coil according to embodiment 5, similarly to embodiment 6, each of the resonant circuits connected to each of the multiple slits in the loop conductor may be a parallel resonant circuit consisting of an inductor and a capacitor connected in parallel, and a circuit having a second inductor further connected in series to the parallel resonant circuit.

[0139] The present disclosure is not limited to the power transmission coils shown in embodiments 1 to 6, and the arrangement and shape of the components that are changed by engineers in the relevant technical field using their ordinary technical knowledge without deviating from the perspective of the technical ideas shown in embodiments 1 to 6 are within the scope of the present disclosure. For example, the shapes of the power transmission coil 1 and the loop conductor 21 changed by engineers in the relevant technical field using their ordinary technical knowledge without deviating from the standpoint of the technical ideas shown in embodiments 1 to 6 are within the scope of the present disclosure.

[0140] In addition to the power transmission coils shown in embodiments 1 to 6, a matching circuit connected between the power transmission coil 1 and the power transmission circuit 3 may be used to adjust impedance matching from the standpoint of power transmission efficiency. Furthermore, the power transmission coils described in the first to sixth embodiments may be applied to a power transmission coil that transmits power at a plurality of frequencies by combining a plurality of power transmission circuits 3 with the power transmission coil 1.

[0141] The power transmission coils described in the first to sixth embodiments may be formed on a dielectric substrate, and may be formed together with the power transmission circuit 3 on the same dielectric substrate. By forming the power transmission coils shown in embodiments 1 to 6 on a dielectric substrate, the cost of the power transmission coil can be reduced and the manufacturing accuracy of the dimensions of the transmission coil and loop conductor can be improved. In turn, by forming the transmitting coil and transmitting circuit as the power transmission coil, or the receiving coil and receiving circuit as the power transmission coil, each on the same dielectric substrate, it is possible to reduce costs and improve accuracy.

[0142] It should be noted that the embodiments may be freely combined, any of the components in each embodiment may be modified, or any of the components in each embodiment may be omitted. [Industrial Applicability]

[0143] The power transmission coil according to the present disclosure can be applied to a transmitting coil or a receiving coil in a magnetic field coupling type power transmission device for a portable device such as a mobile phone, a headset, a digital camera, or a digital video, or a wireless sensor, or to a transmitting coil or a receiving coil in a magnetic field coupling type power transmission device for large-scale applications that handle large amounts of power, such as factory equipment including an automatic transport robot, or an electric vehicle. [Explanation of symbols]

[0144] 1 power transmission coil, 2 shield conductor, 21, 210 loop conductor, 211, 212 slit, 22, 23 resonant circuit, 221, 223, 231 inductor, 222, 224, 232 capacitor, 3 power transmission circuit, 4 control unit, 5 operation state monitoring unit, 6 storage unit.

Claims

1. a power transmission coil for transmitting power; a loop conductor having a slit, and a resonant circuit connected between both open ends of the slit of the loop conductor, the resonant circuit having a parallel resonant circuit of an inductor and a capacitor connected in parallel, and a second inductor connected in series to the parallel resonant circuit, the shield conductor being disposed at a position where an electromagnetic field formed by the power transmission coil intersects when the power transmission coil transmits power; A power transmission coil comprising:

2. A power transmission coil for transmitting power; a loop conductor having a slit, and a shield conductor connected between both open ends of the slit of the loop conductor and including a resonant circuit having an inductor and a capacitor connected in parallel, the shield conductor being disposed at a position where an electromagnetic field formed by the power transmission coil intersects when the power transmission coil transmits power; a loop conductor having a slit, and a second shield conductor connected between both open ends of the slit of the loop conductor and including a resonant circuit having an inductor and a capacitor, the frequency characteristics of the impedance in the shield conductor being different from those in the shield conductor, and the second shield conductor being disposed at a position where an electromagnetic field formed by the power transmission coil when the power transmission coil transmits power intersects with the frequency characteristics of the impedance in the shield conductor; A power transmission coil comprising:

3. A power transmission coil for transmitting power; a loop conductor having a slit, and a resonant circuit connected between both open ends of the slit of the loop conductor and having a variable inductor and a variable capacitor connected in parallel, the shield conductor being disposed at a position where an electromagnetic field formed by the power transmission coil intersects when the power transmission coil transmits power; a control unit that outputs a control signal for changing the inductance of the variable inductor and a control signal for changing the capacitance of the variable capacitor to the variable inductor and the variable capacitor, respectively; A power transmission coil comprising:

4. A power transmission coil described in any one of claims 1 to 3, wherein the resonant frequency of the resonant circuit in the shielded conductor is the fundamental frequency of the electromagnetic field formed by the power transmission coil.

5. The inductor and the capacitor connected in parallel in the resonant circuit in the shield conductor have an angular frequency at the fundamental frequency of the electromagnetic field formed by the power transmission coil of ω ０ , where L is the inductance of the inductor connected in parallel, and C is the capacitance of the capacitor connected in parallel, then ω ０ C=1 / ω ０ 4. The power transmission coil according to claim 1, wherein L is satisfied.

6. A power transmission coil as described in any one of claims 1 to 3, wherein in the parallel-connected inductor and capacitor in the resonant circuit in the shielded conductor, the capacitance of the capacitor is set to a value that suppresses unwanted waves of a frequency twice the fundamental frequency of the electromagnetic field formed by the power transmission coil, and the inductance of the inductor is set to a value that resonates at the fundamental frequency of the electromagnetic field formed by the capacitor and the power transmission coil.

7. A power transmission coil as described in any one of claims 1 to 3, wherein the inductance of the inductor and the capacitance of the capacitor connected in parallel in the resonant circuit in the shielded conductor are set so that the absolute value of the impedance of the shielded conductor is infinite at the fundamental frequency of the electromagnetic field formed by the power transmission coil, and is set to a value that becomes the resistance of the impedance of the loop conductor at a frequency twice the fundamental frequency.

8. In the parallel-connected inductor and capacitor in the resonant circuit, the inductance L of the inductor and the capacitance C of the capacitor are expressed as f ０ 2. The power transmission coil of claim 1, wherein L is set to a value that satisfies L L = 1 / 2π√(LC) and L < 3 × (LL + Ls). However, f ０ is the fundamental frequency of the electromagnetic field formed by the power transmission coil, L Ｌ is the inductance of the loop conductor, and Ls is the inductance of the second inductor.

9. In the parallel-connected inductor and capacitor in the resonant circuit in the shield conductor, the inductance L of the inductor and the capacitance C of the capacitor are f ０ = 1 / 2π√(LC) and L < 3 × L Ｌ 4. The power transmission coil according to claim 2, wherein the resistance is set to a value that satisfies the following: However, f ０ is the fundamental frequency of the electromagnetic field formed by the power transmission coil, L Ｌ is the inductance of the loop conductor.

10. A power transmission coil as described in any one of claims 1 to 3, wherein the impedance of the shield conductor becomes inductive at a frequency of unwanted waves relative to the fundamental frequency of the electromagnetic field formed by the power transmission coil, and a current of opposite phase to the current due to the unwanted waves flowing in the power transmission coil is induced in the loop conductor.

11. A power transmission coil described in any one of claims 1 to 3, wherein the inductance of the inductor in the resonant circuit in the shielded conductor is less than three times the inductance of the loop conductor.

12. 5. The power transmission coil according to claim 4, wherein the power transmission coil is a power transmission coil, and the fundamental frequency of the electromagnetic field formed by the power transmission coil is the fundamental frequency of the electromagnetic field formed by the power transmission coil and is the fundamental frequency of a high-frequency signal transmitted by a power transmission circuit connected to the power transmission coil.

13. 5. The power transmission coil according to claim 4, wherein the power transmission coil is a power receiving coil, and the fundamental frequency of the electromagnetic field formed by the power transmission coil is the fundamental frequency of the electromagnetic field formed in the power receiving coil by receiving power through electromagnetic induction, and is the fundamental frequency of a high-frequency signal received by a power receiving circuit connected to the power receiving coil.

14. 4. The power transmission coil according to claim 2, wherein the resonant circuit is a parallel resonant circuit formed by the inductor and capacitor connected in parallel.

15. The power transmission coil according to claim 1 , wherein a thickness of the loop conductor is greater than a thickness of the power transmission coil.

16. 4. A power transmission coil as claimed in claim 1, wherein the loop conductor has a plurality of slits, and each of the plurality of slits is connected to a resonant circuit having an inductor and a capacitor connected in parallel between both open ends of the slit.

17. an operation status monitoring unit that monitors an operation status of the power transmission coil and outputs a status monitoring signal to the control unit; A control signal from the control unit is generated based on a status monitoring signal from the operation status monitoring unit.

4. A power transmission coil according to claim 3.

18. the operation state monitoring unit is an antenna that detects an electromagnetic field intensity due to electromagnetic waves radiated from the power transmission coil, the status monitoring signal output by the operation status monitoring unit is a status monitoring signal indicating an electromagnetic field intensity from the antenna, the control unit identifies a frequency that needs to be suppressed from an electromagnetic field intensity indicated by a status monitoring signal from the operation status monitoring unit; The control signal generated by the control unit is a signal for setting the inductance of the variable inductor and the capacitance of the variable capacitor to suppress unwanted waves at the specified frequency.

20. A power transfer coil as claimed in claim 17.

19. the operation state monitoring unit is an antenna that detects an electromagnetic field intensity due to electromagnetic waves radiated from the power transmission coil, the status monitoring signal output by the operation status monitoring unit is a status monitoring signal indicating an electromagnetic field intensity from the antenna, the control signal generated by the control unit is a signal for setting an inductance of the variable inductor and a capacitance of the variable capacitor for suppressing spurious waves, a storage unit that stores a set value of the inductance of the variable inductor and a set value of the capacitance of the variable capacitor set by the control unit together with information on the electromagnetic field intensity indicated by a state monitoring signal from the operation state monitoring unit; 20. A power transfer coil as claimed in claim 17.

20. the operation state monitoring unit monitors a frequency input to the power transmission coil, the state monitoring signal from the operation state monitoring unit indicates a frequency input to the power transmission coil, The control signal generated by the control unit is a signal for setting the inductance of the variable inductor and the capacitance of the variable capacitor according to a frequency indicated by a state monitoring signal from the operation state monitoring unit.

20. A power transfer coil as claimed in claim 17.

21. The control unit receives a signal received by an antenna of a wireless system installed nearby, and identifies a frequency that needs to be suppressed from the received signal; The control signal generated by the control unit is a signal for setting the inductance of the variable inductor and the capacitance of the variable capacitor to suppress unwanted waves at the specified frequency.

4. A power transmission coil according to claim 3.

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