WO2019134160A1 - 一种核四极矩共振检测系统及其天线 - Google Patents

一种核四极矩共振检测系统及其天线 Download PDF

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Publication number
WO2019134160A1
WO2019134160A1 PCT/CN2018/071718 CN2018071718W WO2019134160A1 WO 2019134160 A1 WO2019134160 A1 WO 2019134160A1 CN 2018071718 W CN2018071718 W CN 2018071718W WO 2019134160 A1 WO2019134160 A1 WO 2019134160A1
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Prior art keywords
coil
antenna
pattern
signal
nuclear quadrupole
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PCT/CN2018/071718
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English (en)
French (fr)
Inventor
张通胜
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曼森伯格（深圳）科技发展有限公司
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Priority to EP18898759.8A priority Critical patent/EP3719522B1/en
Priority to PCT/CN2018/071718 priority patent/WO2019134160A1/zh
Priority to US16/959,320 priority patent/US11300644B2/en
Publication of WO2019134160A1 publication Critical patent/WO2019134160A1/zh

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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
    • G01R33/20—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
    • G01R33/34—Constructional details, e.g. resonators, specially adapted to MR
    • G01R33/341—Constructional details, e.g. resonators, specially adapted to MR comprising surface coils
    • G01R33/3415—Constructional details, e.g. resonators, specially adapted to MR comprising surface coils comprising arrays of sub-coils, i.e. phased-array coils with flexible receiver channels
    • 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
    • G01R33/34—Constructional details, e.g. resonators, specially adapted to MR
    • 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
    • G01R33/3614—RF power amplifiers
    • 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
    • G01R33/3642—Mutual coupling or decoupling of multiple coils, e.g. decoupling of a receive coil from a transmission coil, or intentional coupling of RF coils, e.g. for RF magnetic field amplification
    • 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
    • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/441—Nuclear Quadrupole Resonance [NQR] Spectroscopy and Imaging
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N24/00—Investigating or analyzing materials by the use of nuclear magnetic resonance, electron paramagnetic resonance or other spin effects
    • G01N24/08—Investigating or analyzing materials by the use of nuclear magnetic resonance, electron paramagnetic resonance or other spin effects by using nuclear magnetic resonance
    • G01N24/084—Detection of potentially hazardous samples, e.g. toxic samples, explosives, drugs, firearms, weapons

Definitions

  • the scheme belongs to the technical field of application of nuclear quadrupole resonance and geomagnetic NMR system, and particularly relates to a nuclear quadrupole resonance detection system and an antenna thereof.
  • the signal extracted by the nuclear quadrupole resonance technique objectively reflects the electric quadrupole structure exhibited by the nucleus under a specific material structure, so this technique can be used to detect and analyze elements or isotopes containing a quadrupole moment nucleus structure, such as Nitrogen 14 (N14), potassium 39, chlorine 35, and chlorine 37, thereby determining the presence of a substance containing such an element or an isotope.
  • a quadrupole moment nucleus structure such as Nitrogen 14 (N14), potassium 39, chlorine 35, and chlorine 37
  • N14 Nitrogen 14
  • quadrupole moment nucleus structure such as Nitrogen 14 (N14), potassium 39, chlorine 35, and chlorine 37
  • Quadrupole resonance technology can also be used for airport passengers or any public security check.
  • the frequency of the quadrupole resonance of common explosive-related components is about 500KHz. Up to the 5 MHz range, the quadrupole moment resonance technique does not require an external magnetic field compared to magnetic resonance technology.
  • the geomagnetic field magnetic resonance technology uses the magnetic field of the earth as the polarization field B0 required for magnetic resonance, the protons in the hydrogen atoms in the polarized water or petroleum components, and the magnetic field is excited by the antenna to detect the groundwater or cause the groundwater or Underground pollution of oil.
  • the strength of the geomagnetic field is approximately 0.5 Gauss, and its corresponding Lamar magnetic resonance frequency is approximately slightly above 2000 Hz.
  • the commonality of the above two kinds of resonance signals is that the signal amplitude is extremely small, and the operating frequency is distributed in the range of common electromagnetic interference generated by human cultural activities. For example, the interference of 40 times harmonic power frequency interference (for 50 Hz power frequency interference source) to the earth magnetic field nuclear magnetic resonance signal, and the interference of medium and short wave radio broadcasting to the quadrupole moment resonance signal. Therefore, when these resonance techniques are applied to detect explosives in an unshielded environment, environmental interference becomes a thorny problem. Therefore, developing antennas and signal processing methods that suppress such interference to improve signal-to-noise ratio has been the key to the successful application of these technologies.
  • the typical structure of an antenna that is traditionally the most common to suppress external interference is a gradient antenna composed of two coils.
  • the two coils are connected in such a way as to ensure that the direction of the generated magnetic field vector is exactly opposite on the two coil planes.
  • the distance between the two coils in the gradient antenna is small, and the received interference from the far side exhibits the same interference intensity and opposite phase on the two coils, so the two Offset by the gradient antenna.
  • the antenna can sense the gradient component, so that the output signal is amplified by the subsequent circuit.
  • the receiving antenna is often tuned to the operating frequency. Such a conventional antenna is satisfactory in most cases.
  • the signal is extremely small, interference from the interference source, even with a small gradient component, is sufficient to cause interference to the measured signal, affecting processing analysis and judgment.
  • the applied explosive is placed on one side of the gradient coil, that is, only one coil is used to emit the electromagnetic field and receive the NQR signal, and the other coil is far from the explosive, and only the interference is perceived. Since the interference occurs simultaneously on the two opposite-phase coils of the gradient antenna, they cancel each other out.
  • Such an antenna structure increases the thermal noise of the antenna system by reducing the number of coils that do not sense the phase of the signal, thereby reducing the signal-to-noise ratio.
  • Another anti-jamming antenna that differs from a gradient antenna is that three orthogonal coils are placed in the vicinity of the main transmitting/measuring coil, for example three orthogonal coils to detect interference.
  • These auxiliary antennas are independent of the main measurement antenna and are far enough away from the main antenna to participate in transmitting electromagnetic fields and receiving NQR signals. In this way, the interference information provided by the auxiliary antenna can be effectively eliminated from the main measurement channel by hardware or software processing methods, thereby suppressing interference.
  • such an antenna design has been applied to mine inspection, if the interference induced by the primary measurement antenna is not guaranteed by the interference received by the auxiliary antenna, the anti-interference ability of such an antenna will deteriorate.
  • the auxiliary antenna In practice, in order to ensure that the auxiliary antenna does not detect useful information, it must maintain a proper distance from the main measurement antenna, but it is possible to reduce the correlation between the main antenna and the auxiliary antenna after the space is obtained, so that the legacy is processed. The interference in the subsequent signal increases. Conversely, if the distance between the auxiliary coil and the main measuring coil is reduced to ensure the correlation of the interference, the auxiliary coil may also detect useful information, thereby omitting some useful information as interference and eliminating it in the process, reducing the signal-to-noise ratio. .
  • the antenna systems realized by these conventional technical solutions all have the anti-interference ability and the contradiction of improving the signal-to-noise ratio, and the high anti-interference and high signal-to-noise ratio measuring antenna is the core of the explosive detection using NQR technology.
  • the scheme proposes a new antenna structure that satisfies the requirements of high anti-interference ability while maximizing the signal-to-noise ratio.
  • the purpose of this scheme is to provide a nuclear quadrupole resonance detection system and an antenna thereof for detecting explosives by nuclear quadrupole resonance technology, and also for detecting groundwater and underground oil leakage by geomagnetic field nuclear magnetic resonance.
  • the aim is to solve the contradiction between the anti-interference ability and the high signal-to-noise ratio existing in the conventional technical solutions.
  • An antenna for detecting a nuclear quadrupole resonance comprising:
  • the first coil being formed with a first pattern
  • the second coil is formed with a second pattern
  • the gradient antenna formed by the first coil and the second coil simultaneously receives radio frequency interference from a signal of a target area and the outside;
  • first coil and the second coil are in the same plane, the winding directions of the first coil and the second coil are opposite, and the second pattern is evenly distributed around the first figure.
  • the first graphic is equal in area to the second graphic.
  • a detection system for nuclear quadrupole resonance including:
  • the first coil being formed with a first pattern
  • the second coil is formed with a second pattern
  • the gradient antenna formed by the first coil and the second coil simultaneously receives radio frequency interference from a signal of a target area and the outside;
  • first coil and the second coil are in the same plane, the winding directions of the first coil and the second coil are opposite, and the second pattern is evenly distributed around the first figure.
  • the first graphic is equal in area to the second graphic;
  • An electrical pulse sequence power amplifier the electrical pulse sequence power amplifier being coupled to the first coil and the second coil, respectively, for causing the first coil and the second coil to generate an excitation sequence pulse magnetic field;
  • a signal receiving unit configured to receive and process the radio frequency signals received by the first coil and the second coil.
  • nuclear quadrupole resonance detection system including:
  • the first coil being formed with a first pattern
  • the second coil is formed with a second pattern
  • the gradient antenna formed by the first coil and the second coil simultaneously receives radio frequency interference from a signal of a target area and the outside;
  • first coil and the second coil are in the same plane, the winding directions of the first coil and the second coil are opposite, and the second pattern is evenly distributed around the first figure.
  • the first graphic is equal in area to the second graphic;
  • the electrical pulse sequence power amplifier being coupled to the first coil for causing the first coil to generate an excitation sequence pulse magnetic field
  • a signal receiving unit configured to receive and process the radio frequency signals received by the first coil and the second coil.
  • the first coil and the second coil constitute a gradient antenna, and simultaneously receive a return radio frequency signal from the target detection area and an interference radio frequency signal from the outside, compared with the conventional 8-word antenna. Since the second coil is evenly distributed around the periphery of the first coil, the second coil can function as an enhancement signal regardless of whether the target detector is symmetrically distributed under the target detection area of the antenna, and the gradient formed by the center symmetry The antenna further ensures the correlation of the far-distance interference on the two coils of the gradient antenna, thereby achieving a more ideal cancellation interference.
  • the direction of the winding of the second coil in the gradient antenna is identical to the main coil (ie, the first coil).
  • the scheme can effectively improve the ability of the antenna to suppress radio interference in the environment when detecting the NQR or the ground magnetic resonance signal, and enhance the detection capability of the signal, thereby improving the signal-to-noise ratio of the system.
  • FIG. 1 is a schematic structural diagram of an antenna for detecting a nuclear quadrupole moment resonance according to a preferred embodiment of the present invention
  • FIG. 2 is a schematic structural diagram of a nuclear quadrupole resonance detecting system according to a first embodiment of the present invention
  • FIG. 3 is a schematic structural diagram of a nuclear quadrupole moment resonance detecting system according to an embodiment of the present invention.
  • FIG. 4 is a schematic structural diagram of another embodiment of a nuclear quadrupole resonance detecting system according to a second embodiment of the present invention.
  • FIG. 5 is a schematic diagram showing the distribution of the vertical direction component (Bz) of the excitation magnetic field generated by the antenna in the arbitrary plane in the first embodiment and the second embodiment of the present embodiment.
  • the embodiment of the present invention provides a nuclear quadrupole moment resonance detecting system.
  • the nuclear quadrupole moment resonance detecting system includes: a nuclear quadrupole moment resonance detecting antenna, an electric pulse sequence power amplifier 200, and Signal receiving unit 300.
  • the nuclear quadrupole resonance detecting antenna is a gradient antenna composed of a group of two coils arranged to cancel the received external interference signal when receiving the signal, the set of coils including the first coil Q1 and the second coil Q2 .
  • the winding directions of the first coil Q1 and the second coil Q2 are opposite, and are located in the same plane, the first coil Q1 is formed with a first pattern, and the second coil Q2 is formed with a second pattern, the first pattern and the second The graphic areas are equal, and the second graphic is evenly distributed around the first graphic.
  • first coil Q1 and the second coil Q2 are both metal (for example, copper wire) rings of a benign conductor or are wound by at least one wire; the first pattern formed by the first coil Q1 and the second coil Q2 are formed.
  • the second pattern is an axisymmetric or centrally symmetric pattern.
  • the first pattern is formed as a circular area, and the second pattern is an annular area uniformly distributed around the first pattern.
  • the first pattern formed by the first coil Q1 and the second pattern formed by the second coil Q2 are equal in area, that is, the area of the circular area is equal to the area of the annular area, specifically, the following relationship is satisfied. :
  • ⁇ R 1 2 ⁇ R 3 2 - ⁇ R 2 2 ;
  • S1 and S2 represent the areas of the first figure and the second figure, respectively, and R 1 , R 2 and R 3 respectively represent the radii of the three circles of the gradient antenna of the scheme from the inside to the outside, that is, the coils of the antenna system described above.
  • the radius is subject to the above formula.
  • the gradient antenna composed of the first coil Q1 and the second coil Q2 simultaneously receives the return radio frequency signal from the target detection area and the interference radio frequency signal from the outside, wherein, as the radio frequency interference Interference electromagnetic waves in the space, usually the interference of remote radio broadcast or power line radiation, which exhibits no gradient characteristics, that is, the distance between the first coil Q1 and the second coil Q2 from the interference source is much larger than the geometry of the coil itself, so
  • the interference from the far side can be regarded as a uniform distribution in the target detection area, and the first pattern formed by the first coil Q1 is equal to the area of the second pattern formed by the second coil Q2.
  • the induced interference also has equal amplitude on the two coils. Since the two coils of the gradient antenna are wound in opposite directions, the phase of the interference signal is just reversed, so the interference signals generated in the first coil Q1 and the second coil Q2 will mutually Offset, and the return RF signal generated by the target detector is a useful signal with a very strong gradient The characteristic does not constitute cancellation and suppression in the reverse wound first coil Q1 and the second coil Q2. On the contrary, according to the reciprocity law in electromagnetism, the measured signal from the target is superimposed and enhanced in the two coils, thereby Increased signal strength and improved signal-to-noise ratio while suppressing interference.
  • the second coil Q2 is evenly wrapped around the first coil Q1, and the maximum possible guarantee is that the first coil Q1 and the second coil Q2 receive the interference signal consistency, regardless of whether the target detector is symmetrically distributed under the antenna.
  • the area can effectively enhance signal acceptance and eliminate interference.
  • first coil Q1 and the second coil Q2 are both metal rings of a benign conductor (for example, a copper conductor) or are wound by at least one wire, and the optimized number of turns depends on the operating frequency; the first coil Q1 is formed.
  • the first pattern and the second pattern formed by the second coil Q2 are both axisymmetric or centrally symmetric.
  • the first pattern is formed as a circular area
  • the second pattern is formed as an annular area
  • the ring The first pattern and the second pattern have the same symmetry center
  • the first coil Q1 and the second coil Q2 are integrally formed as a completely symmetrical antenna structure.
  • the second coil Q2 When the antenna receives the signal, the second coil Q2 receives the return radio frequency signal from the detected object to the greatest extent, and the signals of the first coil Q1 and the second coil Q2 are superimposed together to enhance the signal strength in phase, thereby achieving The maximum signal to noise ratio of the gradient receiving antenna. Since the second coil Q2 is evenly distributed around the periphery of the first coil Q1, the second coil Q2 can function as an enhancement signal regardless of whether the target object is symmetrically distributed under the antenna target detection region.
  • the first coil Q1 and the second coil Q2 in the antenna in the nuclear quadrupole resonance technique have two states of transmission and reception.
  • the antenna is first in the transmitting state, and the emitted electromagnetic wave excites the target detection element in the object to a high-energy state, then stops transmitting, the antenna is turned into the receiving state, and the useful signal is received and amplified.
  • the antenna has two modes of transmitting and receiving. The following focuses on the nuclear quadrupole resonance detecting system in two different embodiments formed by two different transmitting modes and receiving modes, and ignores this. A central timing control unit known to engineers in the field.
  • the first coil Q1 and the second coil Q2 are connected in parallel, and the electric pulse sequence power amplifier 200 is connected between the common ends of the first coil Q1 and the second coil Q2, and
  • the signal receiving unit 300 is also connected between the common ends of the first coil Q1 and the second coil Q2 for receiving and processing the radio frequency signals received by the first coil Q1 and the second coil Q2, and thereby determining the target detection area. Whether there is a target test substance.
  • the transmitting line and the receiving line are shared, as shown by the signal transmitting/receiving unit in FIG. 2, the classical type of T network resonating at the operating frequency realizes time-division transmitting signals and receiving signals, simplifies the circuit, and is easy to operate.
  • the first coil Q1 and the second coil Q2 are connected in parallel with a capacitor C1 to form a parallel resonance, and the receiving circuit is isolated during transmission, and the power amplifier in the instrument is subjected to a certain excitation sequence (for example, commonly used measurement back)
  • the CPMG sequence of the wave signal transmits a sequence pulse to the antenna, and the antenna converts the sequence pulse into a sequence magnetic field of the radio frequency.
  • the transmitting antenna transmits the detection radio frequency signal to the target detection area, and transmits the detection radio frequency signal to the target detection area for a predetermined time, and then the excitation is measured.
  • the quadrupole moment jumps back to the low-energy state, and in the process of recovery, electromagnetic waves of the same frequency as the excitation magnetic field, that is, the NQR resonance signal, are converted into receiving.
  • the state antenna is received and then fed to the receiving circuit that has been transferred from the transmit to the receive state for amplification enhancement for subsequent processing analysis.
  • the first coil Q1 and the second coil Q2 constitute a gradient receiving antenna, and receive the RF signal generated by the interference source and the target detector.
  • the interfering radio frequency signals received by the first coil Q1 and the second coil Q2 cancel each other when the signals induced by the first coil Q1 and the second coil Q2 are superimposed, and the signal receiving unit 300 receives only the return from the target detection object after being excited.
  • the RF signal is transmitted, thereby eliminating interference.
  • the antenna can be modified in conventional ways to achieve a standard 50 ohms for easy matching of standard amplifiers.
  • FIG. 3 and FIG. 4 it is a schematic structural diagram of a nuclear quadrupole moment resonance detecting system in the second embodiment of the present invention.
  • the transmit and receive are respectively tuned to reach the resonant at the operating frequency.
  • the capacitor C2 is in series resonance with the first coil Q1, and the resonant circuit exhibits low impedance during series resonance, which is favorable for low voltage driving.
  • the electric pulse sequence power amplifier 200 is only connected to the first coil Q1 for causing the first coil Q1 to generate and emit a detection radio frequency signal to form an excitation sequence pulse magnetic field; the signal receiving unit 300 is configured to receive and process the first coil Q1 and the second The radio frequency signal received by the coil Q2 is further analyzed to determine whether the target detection area exists in the target detection area.
  • the first coil Q1 is connected in series with the second capacitor, and the second capacitor is connected in series to the signal transmission line between the electric pulse sequence power amplifier 200 and the first coil Q1, when the first coil Q1 transmits the pulse sequence signal.
  • the transmitting antenna exhibits low impedance, so the transmitting power source can adopt a relatively low voltage, for example, can be powered by a car battery, making the detecting system suitable for detecting the target object in the field.
  • the transmitting circuit when the antenna is in the receiving mode, the transmitting circuit is disconnected, the first coil Q1 and the second coil Q2 are connected in series, and then the capacitor C3 forms a parallel resonant loop, and the output signal is signaled.
  • the isolation network of the receiving unit 300 is fed to the preamplifier of the unit for amplification.
  • the transmitting mode the receiving unit is in the high-impedance isolation mode, and the parallel resonant circuit formed by the capacitor C3 and the antenna couples a part of the energy from the transmitting line and induces the emitting current in the second coil Q2, so that the second coil Q2 also participates in the emission. Excitation of the electromagnetic field.
  • the transmission line When the transmission ends, the transmission line is automatically disconnected, and does not affect the parallel resonance formed by the first coil Q1 and the second coil Q2 in series with the capacitor C3.
  • the parallel resonance exhibits high impedance, and the received object from the target area is emitted by the excitation. The resulting signal. Therefore, in this mode, the input amplifier of the signal receiving unit 300 must be high impedance.
  • the capacitor C3 is connected in series with the antenna composed of the first coil Q1 and the second coil Q2 in series, and starts receiving signals from the object at the end of the transmission. Due to the series resonance, the receiving line exhibits a low impedance, and therefore the input amplifier in the signal receiving unit 300 must be a low impedance input.
  • the transmitting antenna when the transmitting antenna is operating, the receiving amplifier is isolated from the receiving line by the isolated network, and the receiving line has no induced current generated, so it does not participate in the transmitting, and the transmitting antenna is equivalent to a simple circular transmitting antenna.
  • FIG. 5 shows the lead field, that is, the sensitivity distribution curve of the antenna of the solution.
  • the curve is based on the unitary current excitation of a vertical direction component (Bz) of the magnetic field generated by the antenna at a depth of 0.5 m. According to the law of reciprocity, the curve also reflects the spatial sensitivity distribution of the antenna.
  • the solid line in the figure is the field distribution of the first coil Q1 driven by the unit current
  • the broken line is the field distribution diagram when the first coil Q1 and the second coil Q2 constitute the gradient antenna. Obviously, this special gradient antenna structure improves the ability to receive signals.
  • the first coil Q1 acts as a transmitting coil to transmit a detecting radio frequency signal to the target detecting area.
  • the transmitting antenna is a circular structure antenna formed by the first coil Q1.
  • the simple circular antenna structure has the deepest excitation detection depth.
  • the circular structure antenna formed by the preferred embodiment in the transmission mode greatly improves the detection depth or detection range compared to the conventional gradient antenna.
  • the second pattern of the first coil Q2 is formed as a substantially annular region, and is disposed around the first pattern of the first coil Q1 such that the first pattern and the second pattern have the same
  • the symmetrical center the entirety of the first coil Q1 and the second coil Q2 is formed as a completely symmetrical antenna structure.
  • the first coil Q1 and the second coil Q2 constitute a gradient receiving antenna while receiving a radio frequency signal, wherein the interfering radio frequency signals received by the first coil Q1 and the second coil Q2 are superimposed when the signals of the two coils are superimposed The mutual offset.
  • the second coil Q2 receives the return RF signal from the detected object to the greatest extent, thereby achieving the maximum signal to noise ratio of the gradient receiving antenna. Since the second coil Q2 is evenly distributed around the periphery of the first coil Q1, the second coil Q2 can function as an enhancement signal regardless of whether the target object is symmetrically distributed under the antenna target detection region.

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  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Magnetic Resonance Imaging Apparatus (AREA)

Abstract

本方案属于核四极矩共振（Nuclear Quadrupole Resonance，NQR）以及地磁场核磁共振系统的应用技术领域，提供了一种核四极矩共振检测系统及其天线，该天线包括第一线圈Q1，所述第一线圈Q1形成第一图形；第二线圈Q2，所述第二线圈Q2形成第二图形；所述第一线圈Q1和所述第二线圈Q2构成的梯度天线，同时接收来自目标区信号和外界的射频干扰；其中，所述第一线圈和所述第二线圈位于同一平面，所述第一线圈Q1和所述第二线圈Q2的绕制方向相反，所述第二图形均匀分布于所述第一图形周围，所述第一图形与所述第二图形面积相等。本方案的方案能有效地提高天线在检测NQR或者应用于地磁共振时对环境中无线电干扰的抑制能力，并增强信号的检测能力，从而提高系统的信号噪声比。

Description

一种核四极矩共振检测系统及其天线 技术领域
本方案属于核四极矩共振以及地磁场核磁共振系统的应用技术领域，尤其涉及一种核四极矩共振检测系统及其天线。
 背景技术
核四极矩共振技术提取的信号客观地反映了在特定的物质结构下原子核呈现的电四极矩结构，因此这种技术能用来检测和分析含有四极矩原子核结构的元素或者同位素，诸如氮14 （N14），钾39，氯35 以及氯37，从而能确定含有这种元素或者同位素的物质的存在。特别是，炸药、尼古丁、药物普遍含有N14成分，而炸药是恐怖分子威胁现代社会的常用手段，对其进行可靠的检测是维护公共安全的必须程序。用四极矩共振技术就能有针对性地检查爆炸装置，例如地雷或者路边炸弹。四极矩共振技术也可以用来进行机场乘客或者任何公共场合的安检。常见与爆炸物相关的成分的四极矩共振的频率大约在500KHz 到5MHz的范围，和磁共振技术相比，四极矩共振技术不需要外加磁场。
地磁场磁共振技术是利用地球的磁场作为磁共振所需要的极化场B0，极化水或者石油成分中的氢原子中的质子，通过天线发射激励电磁场对此做磁共振来检测地下水或者造成地下污染的石油。地磁场的强度大约为0.5高斯，其对应的拉马（Lamar）磁共振频率大约为略高于2000Hz。
上述两种共振信号的共同点是信号幅度极其微小，而其工作频率又分布在人类文化活动产生的常见电磁干扰范围内。例如，40多次谐波的工频电干扰（对于50Hz的工频干扰源）对地磁场核磁共振信号的干扰，以及中、短波无线电广播对四极矩共振信号的干扰。因此，当应用这些共振技术在非屏蔽环境下检测爆炸物时，环境干扰就成为一个棘手的问题。因此，开发抑制这种干扰的天线和信号处理方法提高信噪比，一直是成功应用这些技术的关键。
由于上述两种技术有结构上和面临应用上要解决的困难的共性，下面我们集中表述围绕四极矩共振技术的发展和存在的问题。在叙述中，天线和线圈这两个词有可能依据场合会交替使用。
传统上最常见的抑制外界干扰的天线的典型结构，是由两个线圈组成的梯度天线。二线圈以这样的方式来连接，以保证产生的磁场矢量方向在二线圈平面上刚好相反。物理上，施加已知电流在空间产生的场分布，被称为导联场，导联场的分布，决定了同样的线圈在用做测量时的空间灵敏度分布，这种互易关系被称为电磁场的互易定律。因此，前述梯度天线的特征保证了能敏锐地检测位于附近的被测爆炸物产生的NQR信号，而对远距离外的来自干扰源的干扰有很好的抵抗作用。这是因为，相对于干扰源的距离，梯度天线中的两个线圈间的距离很小，接收到的远方传来的干扰在二线圈上呈显相同的干扰强度和相反的相位，因此二者经梯度天线抵消。而对于来自附近的爆炸物的信号，其具有较强的梯度特性，因此天线能感应到该梯度分量，从而输出信号供后续电路放大处理。实践上为了提高信噪比，接收天线往往调谐在工作频率上。这样的常规天线，在大多数情况下是能够满意工作的。但是，在NQR系统中，由于信号极其微小，来自干扰源的干扰，即便是有微小的梯度分量，也足以对被测信号造成干扰，影响处理分析和判断。
和上述梯度天线类似，只是在应用上让被测爆炸物居于梯度线圈的一边也就是仅仅一个线圈来发射电磁场并接收NQR信号，另一个线圈离爆炸物较远，只感知干扰。因为干扰同时出现在梯度天线的两个相位相反的线圈上，从而互相抵消。这样的天线结构，由于多出来一个不感知信号的相位相反的线圈，因此增加了天线系统的热噪声，从而降低了信噪比。
和梯度天线不同的另一种抗干扰天线，是在主发射/测量线圈附近，放置数个辅助天线，例如三个正交的线圈，来检测干扰的三个正交分离。这些辅助天线独立于主测量天线，距离主天线足够远，不参与发射电磁场和接收NQR信号。这样，辅助天线所提供的干扰信息，可以经过硬件或者软件处理方法来有效的从主测量通道中消除，从而抑制干扰。尽管这样的天线设计，已经应用于地雷检查，但是，如果主测量天线感应的干扰与辅助天线收到的干扰相关性不能保证，则这种天线的抗干扰能力将会恶化。实践上，为了保证辅助天线不检测到有用信息，必须和主测量天线保持合适的距离，但这又有可能降低干扰在主天线与辅助天线各自空间所获得后的相关性，从而使遗留在处理后的信号中的干扰增加。相反，如果减小辅助线圈和主测量线圈的距离以保证干扰的相关性，辅助线圈就有可能也检测到有用信息，从而将一部分有用信息误为干扰而在处理中消除掉，降低信噪比。因此，这些传统的技术方案实现的天线系统都存在着抗干扰能力和提高信噪比的矛盾，而高抗干扰、高信噪比的测量天线是应用NQR技术于爆炸物探测的核心。对此，本方案提出了一种新的天线结构，满足高抗干扰能力要求，同时使信噪比最大化。
 技术问题
传统的技术方案中存在抗干扰能力和高信噪比存在矛盾的问题。
 技术解决方案
本方案的目的在于提供一种核四极矩共振检测系统及其天线，用于核四极矩共振技术检测爆炸物，也可以用于地磁场核磁共振检测地下水和地下漏油。旨在解决传统的技术方案中存在的抗干扰能力和高信噪比存在矛盾的问题。
一种核四极矩共振检测用天线，所述天线包括：
第一线圈，所述第一线圈形成有第一图形；
第二线圈，所述第二线圈形成有第二图形；
所述第一线圈和所述第二线圈构成的梯度天线，同时接收来自目标区信号和外界的射频干扰；
其中，所述第一线圈和所述第二线圈位于同一平面，所述第一线圈和所述第二线圈的绕制方向相反，所述第二图形均匀分布于所述第一图形周围，所述第一图形与所述第二图形面积相等。
此外，还提供了一种核四极矩共振的检测系统，包括：
第一线圈，所述第一线圈形成有第一图形；
第二线圈，所述第二线圈形成有第二图形；
所述第一线圈和所述第二线圈构成的梯度天线，同时接收来自目标区信号和外界的射频干扰；
其中，所述第一线圈和所述第二线圈位于同一平面，所述第一线圈和所述第二线圈的绕制方向相反，所述第二图形均匀分布于所述第一图形周围，所述第一图形与所述第二图形面积相等；
电脉冲序列功率放大器，所述电脉冲序列功率放大器分别与所述第一线圈和所述第二线圈连接，用于使所述第一线圈和所述第二线圈产生激励序列脉冲磁场；
信号接收单元，用于信号接收并处理所述第一线圈和第二线圈接收的射频信号。
此外，还提供了另一种核四极矩共振检测系统，包括：
第一线圈，所述第一线圈形成有第一图形；
第二线圈，所述第二线圈形成有第二图形；
所述第一线圈和所述第二线圈构成的梯度天线，同时接收来自目标区信号和外界的射频干扰；
其中，所述第一线圈和所述第二线圈位于同一平面，所述第一线圈和所述第二线圈的绕制方向相反，所述第二图形均匀分布于所述第一图形周围，所述第一图形与所述第二图形面积相等；
脉冲序列功率放大器，所述电脉冲序列功率放大器与所述第一线圈连接，用于使所述第一线圈产生激励序列脉冲磁场；
信号接收单元，用于信号接收并处理所述第一线圈和第二线圈接收的射频信号。
 有益效果
上述的核四极矩共振检测用天线，第一线圈和第二线圈构成梯度天线，同时接收来自目标检测区域的回传射频信号和来自外界的干扰射频信号，和传统的8字天线相比较，由于第二线圈是均匀分布在第一线圈的外围，因此，不论目标检测物是否对称分布在天线下目标检测区域，第二线圈都能起到增强信号的作用，而这种中心对称构成的梯度天线又进一步保证了远方干扰在梯度天线二线圈上的相关性，从而达到更理想的抵消干扰。而梯度天线中的第二线圈的绕组的方向与主线圈（即第一线圈）一致，物理上，这样的结构保证了该天线系统具有高的测量灵敏度。综上所述，本方案能有效地提高天线在检测NQR或者地磁共振信号时对环境中无线电干扰的抑制能力，并增强信号的检测能力，从而提高系统的信号噪声比。
 附图说明
图1为本方案较佳实施例提供的核四极矩共振检测用天线的结构示意图；
图2为本方案第一实施例提供的核四极矩共振检测系统的结构示意图；
图3为本方案第二实施例提供的一种实施方式核四极矩共振检测系统的结构示意图；
图4为本方案第二实施例提供的另一种实施方式核四极矩共振检测系统的结构示意图；
图5为本方案第一实施例和第二实施例中，天线在0.5米处的目标平面沿任意径向产生的激励磁场垂直方向分量（Bz）的分布示意图。
 本发明的实施方式
为了使本方案的目的、技术方案及优点更加清楚明白，以下结合附图及实施例，对本方案进行进一步详细说明。应当理解，此处所描述的具体实施例仅仅用以解释本方案，并不用于限定本方案。
本方案实施例提供了一种核四极矩共振检测系统，具体的，本实施例所述的核四极矩共振检测系统包括：核四极矩共振检测用天线、电脉冲序列功率放大器200和信号接收单元300。
其中，该核四极矩共振检测用天线为一组两个线圈排布组成的梯度天线，在接收信号时能消除接收到的外界干扰信号，该组线圈包括第一线圈Q1和第二线圈Q2。
具体来说，第一线圈Q1和第二线圈Q2的绕制方向相反，且位于同一平面，第一线圈Q1形成有第一图形，第二线圈Q2形成有第二图形，第一图形与第二图形面积相等，第二图形均匀分布于第一图形周围。
进一步，第一线圈Q1和第二线圈Q2均为良性导体的金属（例如铜质导线）环或由至少一根导线绕制而成；第一线圈Q1形成的第一图形和第二线圈Q2形成的第二图形为均为轴对称或中心对称图形，在优选地实施例中，第一图形形成为圆形区域，第二图形为环形区域，均匀分布于第一图形的周围，本方案实施例中所披露的第一线圈Q1形成的第一图形和第二线圈Q2形成的第二图形的面积相等，即该圆形区域的面积与该环形区域的面积相等，具体而言，满足以下的关系：
S1=S2；
即，πR 1 2=πR 3 2－πR 2 2；
其中，S1、S2分别代表第一图形和第二图形的面积，R 1、R 2和R 3分别代表所方案的梯度天线从内到外的三个圆的半径，即上述天线系统的各线圈半径受上述公式制约。
本方案实施例提供的天线在接收信号时，第一线圈Q1和第二线圈Q2构成的梯度天线，同时接收来自目标检测区域的回传射频信号和来自外界的干扰射频信号，其中，作为射频干扰的空间中的干扰电磁波，通常为远程的无线电广播或电力线辐射的干扰，其呈现无梯度特性，即第一线圈Q1和第二线圈Q2距离干扰源的距离远远大于线圈本身的几何尺寸，因此远方来的干扰在目标检测区域内可以看成是均匀的分布，而第一线圈Q1形成的第一图形与第二线圈Q2形成的第二图形的面积相等，根据法拉第电磁感应原理，感应的干扰电动势在二线圈上也具有相等的幅度，由于梯度天线的两个线圈绕制方向相反，干扰信号的相位因此刚好反相，所以在第一线圈Q1与第二线圈Q2中产生的干扰信号会相互抵消，而目标检测物产生的回传射频信号是有用的信号，具有非常强的梯度特性，在反向绕制的第一线圈Q1与第二线圈Q2中不构成抵消和抑制，相反，根据电磁学中的互易定律，来自目标物的被测信号在二线圈中叠加增强，从而在抑制干扰的同时增加了信号强度，提高信噪比。特别是，第二线圈Q2均匀环绕在第一线圈Q1的周围，最大可能的保证了第一线圈Q1和第二线圈Q2接收干扰信号的一致性，不论目标检测物是否对称分布在天线下目标检测区域，都能有效增强信号接受能力和消除干扰。
进一步，第一线圈Q1和第二线圈Q2均为良性导体（例如铜导体）的金属环或由至少一根导线绕制而成，其优化后的匝数取决于工作频率；第一线圈Q1形成的第一图形和第二线圈Q2形成的第二图形为均为轴对称或中心对称图形，在优选地实施例中，第一图形形成为圆形区域，第二图形形成为环状区域，环设于第一图形周围，以使第一图形与第二图形具有相同的对称中心，第一线圈Q1和第二线圈Q2形的整体形成为完全对称的天线结构。天线在接收信号时，第二线圈Q2最大程度的接收了来自被检测物的回传射频信号，第一线圈Q1和第二线圈Q2的信号叠加在一起在相位上是增强信号强度，从而达到了梯度接收天线的最大信噪比。而由于第二线圈Q2是均匀分布在第一线圈Q1的外围，因此，不论目标检测物是否对称分布在天线下目标检测区域，第二线圈Q2都能起到增强信号的作用。
原理上，核四极矩共振技术中的天线中的第一线圈Q1和第二线圈Q2具有发射和接收两种状态。和传统的共振技术一样，天线首先处于发射状态，发射的电磁波激励被测物中的目标检测元素到一个高能态，然后停止发射，天线转入接收状态，接收和放大有用信号。相对应的，天线的具有发射和接收两种模式，以下重点介绍由于两种不同的发射模式和接收模式下所构成的两种不同的实施例中的核四极矩共振检测系统，而忽略本领域的工程人员熟知的中心时序控制单元。
在图2所示的第一实施例中，第一线圈Q1和第二线圈Q2并联连接，电脉冲序列功率放大器200连接在第一线圈Q1和第二线圈Q2的共接端之间，同时，信号接收单元300也连接在第一线圈Q1和第二线圈Q2的共接端之间，用于信号接收并处理第一线圈Q1和第二线圈Q2接收的射频信号，并以此判断目标检测区域是否存在目标检测物。在实际应用中，发射线路和接收线路共用，如图2中信号发射/接收单元所示，经典型的谐振于工作频率的T网络实现分时发射信号和接收信号，简化电路，且便于操作。
在共用的发射线路和接收线路中，第一线圈Q1和第二线圈Q2并联有电容C1，形成并联谐振，发射时接收电路被隔离，仪器中的功率放大器按一定的激励序列（例如常用测量回波信号的CPMG序列）向天线发送序列脉冲，天线将序列脉冲转换为射频的序列磁场，发射天线向目标检测区域发射检测射频信号，向目标检测区域发射预定时间的检测射频信号后，激励被测物中的四极矩到一个高能态，处于高能态的四极矩会跳跃恢复到低能态，在这个恢复的过程中辐射出和激励磁场同频率的电磁波，即NQR共振信号，被转换为接收状态的天线所接收，然后馈送到已从发射转入接收状态的接收电路放大增强，供后续处理分析判断。天线进入接收模式后，第一线圈Q1和第二线圈Q2构成梯度接收天线，同时接收干扰源和目标检测物产生的射频信号。第一线圈Q1和第二线圈Q2接收的干扰射频信号会在第一线圈Q1和第二线圈Q2感应的信号叠加时相互抵消，信号接收单元300只接收到来自目标检测物受激发后产生的回传射频信号，从而消除了干扰。在实际应用中，天线可以用常规方法改变其阻抗以达到标准的50欧姆，方便匹配标准放大器。
如图3和图４所示，为本方案第二实施例中核四极矩共振检测系统的结构示意图。在这个实施中，发射和接收是分别调谐达到谐振在工作频率的。其中在发射线路，电容C2与第一线圈Q1串联谐振，串联谐振时谐振回路呈现低阻抗，有利于低电压驱动。电脉冲序列功率放大器200只与第一线圈Q1连接，用于使第一线圈Q1产生并发射检测射频信号，形成激励序列脉冲磁场；信号接收单元300用于接收并处理第一线圈Q1和第二线圈Q2接收的射频信号，并进一步分析判断目标检测区域是否存在目标检测物。具体地，第一线圈Q1串接有第二电容，且第二电容串接于电脉冲序列功率放大器200和第一线圈Q1之间的信号发射线路上，在第一线圈Q1发射脉冲序列信号时，发射天线呈现低阻抗，因此发射电源可以采用相对较低的电压，例如可以采用汽车电池供电，使该检测系统适合于在野外的目标检测物的探测工作。
在本实施例中的接收天线回路中，有两种实现方式，一种是并联谐振，如图3 所示，另一种实现是串联谐振，如图4所示。以下详细论述这两种实现方式。
在图3所示的核四极矩共振检测系统中，天线在接收模式时，发射电路断开，第一线圈Q1和第二线圈Q2串联，再与电容C3构成并联谐振回路，输出信号经信号接收单元300的隔离网络馈送到该单元的前置放大器进行放大。在发射模式下，接收单元处于高阻抗隔离模式，电容C3和天线构成的并联谐振回路，会从发射线路耦合一部分能量，在第二线圈Q2中感应发射电流，于是，第二线圈Q2也参与发射激励电磁场。当发射结束后，发射线路自动断开，不影响第一线圈Q1和第二线圈Q2串联后与电容C3形成的并联谐振，该并联谐振呈现高阻抗，接收来自目标区的被测物因发射激励产生的信号。因此，在这种模式下，信号接收单元300的输入放大器必须是高阻抗。
在图4所示的串联谐振接收线路中，电容C3与第一线圈Q1和第二线圈Q2串联构成的天线组成串联谐振，在发射结束时开始接受来自被测物的信号。由于串联谐振，接收线路呈现低阻抗，因此，信号接收单元300中的输入放大器必须是低阻抗输入。在这种工作模式下，当发射天线工作时，接收放大器被隔离网络与接收线路隔离，接收线路没有感应电流产生，因此不参与发射，发射天线相当于一个简单的圆形发射天线。
图5所示为所述方案天线的导联场亦即灵敏度分布曲线。该曲线是基于单位电流激励一匝天线在0.5米深处产生的磁场的垂直方向分量（Bz）沿平面径向分布。根据互易定律，该曲线也反映了天线的空间灵敏度分布。其中，图中的实线是第一线圈Q1在单位电流驱动下的场分布，而虚线是第一线圈Q1和第二线圈Q2构成梯度天线时的场分布图。显然，这种特殊的梯度天线结构，提高了接收信号的能力。
在本方案第二实施例中，即图3和图4所示的核四极矩共振检测系统，在发射模式时，第一线圈Q1作为发射线圈向目标检测区域发射检测射频信号，此时，发射天线为第一线圈Q1形成的圆形结构天线，在天线的几何尺寸给定时，简单的圆形天线结构具有最深的激励检测深度。本优选实施例在发射模式时所形成的圆形结构天线相较于传统的梯度天线而言，很大程度上提升了检测深度或检测范围。相对应的，本优选实施例中，第一线圈Q2的第二图形形成为大致的环状区域，环设于第一线圈Q1的第一图形周围，以使第一图形与第二图形具有相同的对称中心，第一线圈Q1和第二线圈Q2形的整体形成为完全对称的天线结构。在接收模式时，第一线圈Q1和第二线圈Q2构成梯度接收天线，同时接收射频信号，其中，第一线圈Q1和第二线圈Q2接收的干扰射频信号会在二线圈的信号叠加在一起时的相互抵消。而第二线圈Q2最大程度的接收了来自被检测物的回传射频信号，从而达到了梯度接收天线的最大信噪比。而由于第二线圈Q2是均匀分布在第一线圈Q1的外围，因此，不论目标检测物是否对称分布在天线下目标检测区域，第二线圈Q2都能起到增强信号的作用。
以上所述仅为本方案的较佳实施例而已，并不用以限制本方案，凡在本方案的精神和原则之内所作的任何修改、等同替换和改进等，均应包含在本方案的保护范围之内。

Claims (12)

  1. 一种核四极矩共振检测用天线，其特征在于，所述天线包括：
    第一线圈，所述第一线圈形成有第一图形；
    第二线圈，所述第二线圈形成有第二图形；
    所述第一线圈和所述第二线圈构成的梯度天线，同时接收来自目标区信号和外界的射频干扰；
    其中，所述第一线圈和所述第二线圈位于同一平面，所述第一线圈和所述第二线圈的绕制方向相反，所述第二图形均匀分布于所述第一图形周围，所述第一图形与所述第二图形面积相等。
  2. 如权利要求1所述的核四极矩共振检测用天线，其特征在于，所述第一图形形成为圆形。
  3. 如权利要求1所述的核四极矩共振检测用天线，其特征在于，所述第二图形形状为环状区域，环绕于所述第一图形周围。
  4. 如权利要求1所述的核四极矩共振检测用天线，其特征在于，所述第一线圈为金属环或由至少一根导线绕制而成的单匝或多匝天线。
  5. 如权利要求1所述的核四极矩共振检测用天线，其特征在于，所述第二线圈为金属环或由至少一根导线绕制而成的单匝或多匝天线。
  6. 一种核四极矩共振检测系统，其特征在于，包括：
    第一线圈，所述第一线圈形成有第一图形；
    第二线圈，所述第二线圈形成有第二图形；
    所述第一线圈和所述第二线圈构成的梯度天线，同时接收来自目标区信号和外界的射频干扰；
    其中，所述第一线圈和所述第二线圈位于同一平面，所述第一线圈和所述第二线圈的绕制方向相反，所述第二图形均匀分布于所述第一图形周围，所述第一图形与所述第二图形面积相等；
    电脉冲序列功率放大器，所述电脉冲序列功率放大器分别与所述第一线圈和所述第二线圈连接，用于使所述第一线圈和所述第二线圈产生激励序列脉冲磁场；
    信号接收单元，用于信号接收并处理所述第一线圈和第二线圈接收的射频信号。
  7. 如权利要求6所述的核四极矩共振检测系统，其特征在于，所述第一线圈和所述第二线圈并联连接，所述电脉冲序列功率放大器和所述信号接收单元连接在所述第一线圈和所述第二线圈的共接端之间。
  8. 如权利要求6所述的核四极矩共振检测系统，其特征在于，还包括第一电容器，所述第一电容与所述第一线圈和所述第二线圈并联，与所述第一线圈和所述第二线圈共同形成并联谐振。
  9. 一种核四极矩共振检测系统，其特征在于，包括：
    第一线圈，所述第一线圈形成有第一图形；
    第二线圈，所述第二线圈形成有第二图形；
    所述第一线圈和所述第二线圈构成的梯度天线，同时接收来自目标区信号和外界的射频干扰；
    其中，所述第一线圈和所述第二线圈位于同一平面，所述第一线圈和所述第二线圈的绕制方向相反，所述第二图形均匀分布于所述第一图形周围，所述第一图形与所述第二图形面积相等；
    电脉冲序列功率放大器，所述电脉冲序列功率放大器与所述第一线圈连接，用于使所述第一线圈产生激励序列脉冲磁场；
    信号接收单元，用于信号接收并处理所述第一线圈和第二线圈接收的射频信号。
  10. 如权利要求9所述的核四极矩共振检测系统，其特征在于，所述第一线圈于所述第二线圈串联连接，所述第一线圈的第一端与所述第二线圈的第一端连接，所述第一线圈的第二端和所述第二线圈的第二端连接所述信号接收单元。
  11. 如权利要求9所述的核四极矩共振检测系统，其特征在于，还包括第二电容和第三电容，所述第二电容与所述第一线圈串联，所述第三电容与所述第一线圈和所述第二线圈并联。
  12. 如权利要求9所述的核四极矩共振检测系统，其特征在于，还包括第二电容和第三电容，所述第二电容与所述第一线圈串联，所述第三电容与所述第一线圈和所述第二线圈串联。
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