WO2015087736A1 - 磁界検出装置 - Google Patents
磁界検出装置 Download PDFInfo
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- WO2015087736A1 WO2015087736A1 PCT/JP2014/081786 JP2014081786W WO2015087736A1 WO 2015087736 A1 WO2015087736 A1 WO 2015087736A1 JP 2014081786 W JP2014081786 W JP 2014081786W WO 2015087736 A1 WO2015087736 A1 WO 2015087736A1
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- magnetic field
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/02—Measuring direction or magnitude of magnetic fields or magnetic flux
- G01R33/06—Measuring direction or magnitude of magnetic fields or magnetic flux using galvano-magnetic devices
- G01R33/063—Magneto-impedance sensors; Nanocristallin sensors
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/02—Measuring direction or magnitude of magnetic fields or magnetic flux
- G01R33/022—Measuring gradient
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
- G01R33/32—Excitation or detection systems, e.g. using radio frequency signals
- G01R33/36—Electrical details, e.g. matching or coupling of the coil to the receiver
- G01R33/3628—Tuning/matching of the transmit/receive coil
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
Definitions
- the present invention relates to a magnetic field detection device that detects a weak magnetic field.
- a position measurement technique for measuring the position of a detection target by detecting a weak magnetic field generated by the detection target is known.
- a marker coil that generates an alternating magnetic field is attached to the inside of a capsule endoscope that is sized to be introduced into the digestive tract of a subject, and the alternating magnetic field generated by the marker coil
- Development of a position detection system that detects the position of the capsule endoscope in the subject by detecting the image with a magnetic field detection device provided outside the subject is underway.
- the signal detection sensitivity (detection signal) of the magnetic field detection device is used. (S / N ratio) of the above is required to be high.
- SQUID magnetometers using the superconducting quantum interference effect As examples of high-sensitivity magnetic field detection devices, SQUID magnetometers using the superconducting quantum interference effect, GMR magnetic field sensors using the giant magnetoresistance effect, and the like are known. In these magnetic field detection devices, self-excitation is used for high sensitivity. Generally, the circuit configuration of self-excitation is complicated.
- Patent Document 1 discloses a capacitance change detection method and a detection circuit for detecting a change in capacitance of a capacitor microphone.
- Patent Document 2 discloses a technique for reducing an actual resistance component that increases when an eddy current is generated in a detection coil of a magnetic field detection device.
- the number of windings of the magnetic field detection coil provided in the magnetic field detection device is increased or the magnetic field detection surface of the detection coil is increased. It is conceivable to increase the area of the (opening surface).
- the resistance of the detection coil is increased accordingly, and the thermal noise is increased. More specifically, the thermal noise increases in proportion to the square root of the resistance value of the detection coil.
- Patent Document 1 a parallel resonant circuit and a series resonant circuit are combined to create a steep region of impedance change in the frequency domain, and the steep region is used as an operating point, thereby improving the detection sensitivity of capacitance change. I am trying.
- Patent Document 1 does not disclose a method for reducing the resistance component of the resonance circuit.
- the resistance component is reduced by limiting the number of turns of the detection coil to a value less than a value defined by a predetermined conditional expression.
- a limit to the improvement in detection sensitivity due to an increase in the number of turns so that the range in which high sensitivity and low noise can be realized is limited.
- the present invention has been made in view of the above, and provides a magnetic field detection apparatus capable of detecting an alternating magnetic field generated from a marker coil with a high S / N ratio.
- a magnetic field detection device includes a wound coil for converting a magnetic field signal of an alternating magnetic field into a voltage signal, and a capacitor connected in parallel to the coil.
- a resonance circuit having an element connected in series to the subsequent stage of the resonance circuit, and a low-noise amplifier connected to the subsequent stage of the element, the element having an impedance of the resonance circuit at a detection frequency of the alternating magnetic field
- the imaginary part has a reactance opposite in sign, and the absolute value of the combined impedance of the resonance circuit and the element is smaller than the internal resistance of the coil.
- the self-inductance of the coil Ls, the capacitance of the capacitor when the C 1, the absolute value of the impedance of the coil may be greater than ⁇ (2Ls / C 1).
- the reactance of the element at the detection frequency is equal to the magnitude of the imaginary part of the impedance of the resonance circuit.
- the element includes at least one of a second capacitor, a wound second coil, and a resistor.
- the element is provided between the second capacitor connected in series to the resonance circuit, and between the second capacitor and the low noise amplifier. And the resistor connected in parallel.
- the element constitutes a filter that cuts an electric signal in a predetermined frequency band.
- an element having a reactance opposite in sign to the imaginary part of the impedance of the resonance circuit is connected to the resonance circuit, and the resonance circuit and the absolute value of the combined impedance of the element constitute the resonance circuit. Since it is smaller than the internal resistance of the coil, thermal noise generated in the coil can be suppressed and the noise level can be reduced even when the number of turns of the coil and the area of the opening surface are increased. Therefore, it is possible to realize a magnetic field detection device that can detect an alternating magnetic field with a high SN ratio.
- FIG. 1 is a schematic diagram showing a configuration example of a magnetic field detection apparatus according to Embodiment 1 of the present invention.
- FIG. 2 is a diagram showing an equivalent circuit of the magnetic field detection apparatus shown in FIG.
- FIG. 3 is a graph showing frequency characteristics of impedance in the magnetic field detection apparatus shown in FIG.
- FIG. 4 is a diagram showing an equivalent circuit of the magnetic field detection device according to the second embodiment of the present invention.
- FIG. 5 is a diagram illustrating an equivalent circuit of the magnetic field detection device according to the fourth modification of the second embodiment of the present invention.
- FIG. 1 is a schematic diagram showing a configuration example of a magnetic field detection apparatus according to Embodiment 1 of the present invention.
- FIG. 2 is a diagram showing an equivalent circuit of the magnetic field detection apparatus shown in FIG.
- the magnetic field detection device 1 according to the first embodiment is a device that receives an alternating magnetic field and converts a magnetic field signal into an electrical signal, and is connected in series with a resonance circuit 10 and a subsequent stage of the resonance circuit 10.
- a capacitor 20 that is a connected element and a low-noise amplifier 30 connected to a subsequent stage of the capacitor 20 are provided.
- the resonance circuit 10 includes a coil 11 that converts a received magnetic field signal into a voltage signal, and a capacitor 12 that is connected in parallel to the coil 11.
- the internal resistance of the coil 11 is R S
- the self-inductance is L S
- the capacitance of the capacitor 12 is C 1 .
- the impedance of the resonance circuit 10 is assumed to be Z 1 .
- the imaginary part Im [Z 1 ] of the impedance Z 1 of the resonance circuit 10 at the frequency of the alternating magnetic field (detection frequency f det ) to be detected by the magnetic field detection device 1 Any element such as a capacitor, a coil, and a resistor may be used as long as the elements have reactances having opposite signs.
- the capacitor 20 is used as such an element.
- the low noise amplifier 30 amplifies the voltage signal that is converted from the magnetic field signal by the coil 11 and input through the capacitor 20.
- the noise level N m of the magnetic field detection device 1 is given by the following equation (1).
- reference numeral V n is the voltage noise of the low noise amplifier 30
- reference numeral I n is the low noise amplifier 30 current noise
- the combined impedance of the capacitor 20 is shown.
- symbol k is a Boltzmann constant
- symbol T is an absolute temperature
- Re [Z in ] is a real part of the combined impedance Z in .
- the characteristics of the capacitor 12 and the capacitor 20 are set to reduce the thermal noise component.
- the combined impedance Z in may be reduced.
- the imaginary part Im [Z 1 ] of the impedance Z 1 of the resonance circuit 10 may be reduced by reactance of an element connected to the subsequent stage of the resonance circuit 10. Therefore, in the first embodiment, the capacitor 20 whose reactance sign is opposite to the sign of the imaginary part Im [Z 1 ] of the impedance Z 1 of the resonance circuit 10 is used in the subsequent stage of the resonance circuit 10.
- the reactance X 2 of the capacitor 20 is set equal to the magnitude of the imaginary part Im [Z 1 ] of the impedance Z 1 of the resonance circuit 10.
- the imaginary part Im [Z 1 ] can be canceled and the absolute value of the combined impedance Z in can be minimized. This condition is given by the following equation (4).
- the synthetic impedance Z in is given by the following equation (5).
- conditional expression (6) that can reduce the thermal noise and suppress the noise level N m to the lowest is obtained.
- R S 2 + X S 2 shown on the left side of the equation (6 ′) corresponds to the square of the absolute value of the impedance of the coil 11. Therefore, by setting the capacitance C 1 of the capacitor 12 at the detection frequency f det so as to satisfy the following expression (7), the resistance component (real part) of the combined impedance Z in is determined by the internal resistance R S of the coil 11. And the thermal noise component can be reduced.
- the noise level of the magnetic field detection device 1 can be reduced by using the capacitor 20 having a reactance opposite in sign to the imaginary part of the impedance of the resonance circuit 10. .
- the reactance of the capacitor 20 is made equal to the magnitude of the imaginary part of the impedance of the resonance circuit 10, the combined impedance of the resonance circuit 10 and the capacitor 20 can be minimized, so that the noise level is further reduced. Is possible.
- the thermal noise component can be reduced by setting the capacitance of the capacitor 12 so as to satisfy the expression (7). Therefore, even when the number of turns of the coil 11 and the area of the opening surface are increased for high sensitivity, it is possible to suppress the noise level and detect the magnetic field with a high SN ratio.
- the capacitor 20 is used as an element connected to the subsequent stage of the resonance circuit 10.
- a coil or a resistor is used.
- a vessel or the like may be applied.
- the sign of the imaginary part of the impedance of the resonance circuit 10 may be negative. In this case, a separate coil may be connected after the resonance circuit 10.
- FIG. 4 is a diagram showing an equivalent circuit of the magnetic field detection device according to the second embodiment of the present invention.
- a capacitor 41 and a resistor 42 are used instead of the capacitor 20 shown in FIG. Including element 40 is applied.
- the configuration other than the element 40 of the magnetic field detection device 2 is the same as that of the first embodiment.
- the capacitance of the capacitor 41 is C f and the resistance value of the resistor 42 is R f .
- the capacitor 41 is connected in series with the resonant circuit 10, and acts as a reactance whose sign is opposite to the imaginary part of the impedance of the resonant circuit 10, like the capacitor 20 in the first embodiment.
- an element having a reactance equal to the imaginary part of the impedance of the resonance circuit 10 is used as the capacitor 41.
- the resistor 42 is connected in parallel to the resonant circuit 10. For this reason, the combined resistance of the resonance circuit 10 and the element 40 as a whole is smaller than the resistance component of the resonance circuit 10. Therefore, the noise level N m of the signal input to the low noise amplifier 30 can be further reduced as compared with the case of the first embodiment.
- the second embodiment it is possible to selectively detect only a magnetic field having a specific frequency or higher while reducing the noise level.
- the element 40 selectively detects only a magnetic field in a low frequency band below a specific frequency (high frequency cut (low frequency pass). ) It may be used as a filter.
- FIG. 5 is a diagram illustrating an equivalent circuit of the magnetic field detection device according to the fourth modification of the second embodiment.
- the elements 40 described in the second embodiment are provided in multiple stages.
- the noise of the signal input to the low noise amplifier 30 is reduced.
- the level can be further reduced.
- a steep filter characteristic can be obtained, it is possible to detect a minute change in the signal.
- Embodiments 1 and 2 and Modifications 1 to 4 described above are merely examples for carrying out the present invention, and the present invention is not limited to these.
- the present invention can generate various inventions by appropriately combining a plurality of constituent elements disclosed in the first and second embodiments and the first to fourth modifications. It is obvious from the above description that the present invention can be variously modified according to specifications and the like, and that various other embodiments are possible within the scope of the present invention.
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- Physics & Mathematics (AREA)
- Condensed Matter Physics & Semiconductors (AREA)
- General Physics & Mathematics (AREA)
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Nanotechnology (AREA)
- Measuring Magnetic Variables (AREA)
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Abstract
Description
図1は、本発明の実施の形態1に係る磁界検出装置の一構成例を示す模式図である。また、図2は、図1に示す磁界検出装置の等価回路を示す図である。図1に示すように、実施の形態1に係る磁界検出装置1は、交番磁界を受信して磁界信号を電気信号に変換する装置であり、共振回路10と、該共振回路10の後段に直列接続された素子であるコンデンサ20と、該コンデンサ20の後段に接続された低雑音増幅器30とを備える。
Zin=Z1-jX2 …(3)
上記実施の形態1においては、共振回路10の後段に接続される素子としてコンデンサ20を用いたが、共振回路10のインピーダンスの虚部と符号が反対のリアクタンスを有する素子であれば、コイルや抵抗器等を適用しても良い。例えば、コイル11及びコンデンサ12の特性等の条件によっては、共振回路10のインピーダンスの虚部の符号が負になる場合がある。この場合には、共振回路10の後段に、別途コイルを接続すれば良い。
次に、本発明の実施の形態2について説明する。
図4は、本発明の実施の形態2に係る磁界検出装置の等価回路を示す図である。図4に示すように、実施の形態2に係る磁界検出装置2においては、共振回路10の後段に直列接続される素子として、図1に示すコンデンサ20の代わりに、コンデンサ41及び抵抗器42を含む素子40を適用している。磁界検出装置2の素子40以外の構成については、実施の形態1と同様である。以下、コンデンサ41のキャパシタンスをCfとし、抵抗器42の抵抗値をRfとする。
実施の形態2においては、キャパシタンスCf及び抵抗値Rfを適宜設定することにより、素子40を、特定の周波数以下の低周波帯域の磁界のみを選択的に検出する高域カット(低域通過)フィルタとして用いても良い。
実施の形態2において、コイル11及びコンデンサ12(図1参照)の特性等の条件により、共振回路10のインピーダンスの虚部の符号が負になる場合には、コンデンサ41の代わりにコイルを接続することによりリアクタンスの符号を反対(正)にすれば良い。
図5は、実施の形態2の変形例4に係る磁界検出装置の等価回路を示す図である。変形例4においては、実施の形態2において説明した素子40を多段に設けている。この場合、共振回路10に対して並列接続された抵抗器42が増加する分、共振回路10及び複数の素子40全体の合成抵抗成分が小さくなるため、低雑音増幅器30に入力される信号のノイズレベルをさらに低減することが可能となる。また、この場合、急峻なフィルタ特性を得ることができるため、信号の微小な変化を検出することが可能となる。
10 共振回路
11 コイル
12、20、41 コンデンサ
30 低雑音増幅器
40 素子
42 抵抗器
Claims (6)
- 交番磁界の磁界信号を電圧信号に変換する巻き線状のコイル、及び該コイルと並列接続されたコンデンサを有する共振回路と、
前記共振回路の後段に直列接続された素子と、
前記素子の後段に接続された低雑音増幅器と、
を備え、
前記素子は、前記交番磁界の検出周波数における前記共振回路のインピーダンスの虚部と符号が反対のリアクタンスを有し、
前記共振回路及び前記素子の合成インピーダンスの絶対値は、前記コイルの内部抵抗よりも小さいことを特徴とする磁界検出装置。 - 前記コイルの自己インダクタンスをLs、前記コンデンサのキャパシタンスをC1とした場合に、前記コイルのインピーダンスの絶対値は√(2Ls/C1)よりも大きいことを特徴とする請求項1に記載の磁界検出装置。
- 前記素子の前記検出周波数におけるリアクタンスは、前記共振回路のインピーダンスの虚部の大きさと等しいことを特徴とする請求項1に記載の磁界検出装置。
- 前記素子は、第2のコンデンサと、巻き線状の第2のコイルと、抵抗器との少なくともいずれかを含むことを特徴とする請求項1に記載の磁界検出装置。
- 前記素子は、前記共振回路に対して直列接続された前記第2のコンデンサと、該第2のコンデンサと前記低雑音増幅器との間に設けられ、前記共振回路に対して並列接続された前記抵抗器とを含むことを特徴とする請求項4に記載の磁界検出装置。
- 前記素子は、所定の周波数帯域の電気信号をカットするフィルタを構成することを特徴とする請求項5に記載の磁界検出装置。
Priority Applications (4)
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JP2015528482A JP5801019B1 (ja) | 2013-12-13 | 2014-12-01 | 磁界検出装置 |
EP14870524.7A EP3081951A4 (en) | 2013-12-13 | 2014-12-01 | Magnetic field detection device |
CN201480041601.5A CN105408757B (zh) | 2013-12-13 | 2014-12-01 | 磁场检测装置 |
US15/046,505 US9453891B2 (en) | 2013-12-13 | 2016-02-18 | Magnetic field detection device |
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JP2013258652 | 2013-12-13 | ||
JP2013-258652 | 2013-12-13 |
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US15/046,505 Continuation US9453891B2 (en) | 2013-12-13 | 2016-02-18 | Magnetic field detection device |
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US (1) | US9453891B2 (ja) |
EP (1) | EP3081951A4 (ja) |
JP (1) | JP5801019B1 (ja) |
CN (1) | CN105408757B (ja) |
WO (1) | WO2015087736A1 (ja) |
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WO2020114627A1 (de) * | 2018-12-07 | 2020-06-11 | Sew-Eurodrive Gmbh & Co. Kg | Anzeigemittel zum anzeigen der stärke eines wechselmagnetfelds eines primärleiters |
JP2021037034A (ja) * | 2019-09-02 | 2021-03-11 | 富士フイルム株式会社 | 内視鏡システム及びその作動方法 |
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CN105977862B (zh) * | 2016-05-18 | 2019-04-26 | 北京动力京工科技有限公司 | 一种巡线机器人 |
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Publication number | Publication date |
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EP3081951A1 (en) | 2016-10-19 |
JP5801019B1 (ja) | 2015-10-28 |
CN105408757B (zh) | 2018-01-05 |
EP3081951A4 (en) | 2017-08-23 |
CN105408757A (zh) | 2016-03-16 |
US20160161573A1 (en) | 2016-06-09 |
US9453891B2 (en) | 2016-09-27 |
JPWO2015087736A1 (ja) | 2017-03-16 |
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